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INTERMEDIATES FOR DYESTUFFS 
 
INTERMEDIATES FOR 
 DYESTUFFS 
 
 BY 
 
 Pe AV TDSON > Boe. ALC. 
 Part-author of “ The Industrial Application of Coal Tar Products” 
 
 NEW YORK 
 D. VAN NOSTRAND COMPANY 
 EIGHT WARREN STREET 
 1926 
 
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INTRODUCTION 
 
 Wuart are the causes of the colour and the dyeing properties of a dyestuft ? This 
 is a twofold question. Colour and dyeing power are separate and distinct qualities. 
 A dyestufi may be so fixed on or in the fibres of the material to be dyed that it cannot 
 be immediately washed off. Not all coloured substances possess this property. On 
 the other hand, there are colourless substances, such as tannic acid, B-hydroxynaph- 
 thoic anilide, hydrated alumina, etc., which can be fixed, in the sense just mentioned, 
 on cotton, wool, and other textile materials. 
 
 As regards the cause of the colour in a dyestuff, the preliminary generalisation 
 can be made—though it does not carry us very far—that the known dyestuffs are 
 complex organic compounds containing— 
 
 (a) The ringed nuclei of benzene, naphthalene, anthracene, and certain related 
 ring structures, such as those of carbazole, acenaphthene, indole, etc. 
 
 (b) Connecting atoms, or chains of atoms, of carbon, oxygen, nitrogen, and 
 sulphur. 
 
 (c) Substituent groups attached to the rings, of which the most prominent are 
 the amino, hydroxyl, sulphonic acid, and nitro groups. 
 
 Compounds are, however, known which fulfil all these conditions and yet are 
 colourless. A theory proposed by O. N. Witt proceeds a stage further, and attributes 
 
 colour, or a predisposition to colour, to the presence of certain “‘ chromophoric ” 
 groups—e.g., 
 yo=0 ; So=n— a as None ae 
 
 or the more a groupings, 
 
 Y' ‘a Cat ee me Ne \/ : 
 see NSA AA AW 
 | 
 
 Another view is that proposed by H. E. Armstrong and A. G. Green, according to 
 which quinonoid arrangements in the carbon rings— 
 
 C 
 pad ts a bid Non 
 4 ee 
 
 \o% De: 
 | 
 p-Quinonoid. o-Quinonoid. 
 
 —are responsible for the colour. The two views are not mutually exclusive, but are, 
 indeed, to some extent complementary. 
 “ 
 
 17200 
 
vi INTRODUCTION 
 
 Dyeing properties—the possession of affinity for the textile fibres—are to be 
 attributed, according to the second part of Witt’s theory, to the presence in the 
 molecule (together with the chromophores) of the hydroxyl and amino (or substituted 
 amino) groups. These groups not only impart affinity for the fibre, but also intensify 
 the colour of the substance, and are hence called “‘ auxochromes.”’ 
 
 These generalisations are sufficiently in accord with experience to serve as useful 
 guides in the mazes of dyestuff chemistry, and are, in fact, the working hypotheses 
 of the dyestuff chemist. They indicate that the making of dyestufis involves the 
 following conditions : 
 
 (a) The fundamental substances—the raw materials—are the so-called ‘‘ aromatic ”’ 
 compounds, benzene, naphthalene, anthracene, and the related toluene, xylenes, 
 phenol, cresols, carbazole, acenaphthene, and so on. The sole economic source of 
 these substances at present is coal tar,* which therefore forms the starting-point for 
 the manufacture of dyestuffs. The isolation of the above-named substances from 
 coal tar is not described in this book. Except in a few cases, it will be assumed that 
 they are available in a sufficiently pure condition for subsequent operations. 
 
 (6) The Intermediates. The raw materials must be so acted on, by various 
 reagents, as to introduce into them the required chromophoric and auxochromic 
 groups, or groups which may in the final stages be convertible into chromophoric 
 and auxochromic groups. Thus, for instance, benzene is nitrated to form nitro- 
 benzene, and this reduced to aniline; naphthalene is sulphonated, and the sulphonic 
 acid converted into a naphthol; anthracene is oxidised to anthraquinone, and so on. 
 None of these products is a dyestuff, but all are capable of immediate conversion to 
 dyestufis by further operations. They form the intermediates for the dyestufis, and 
 it is with the processes used in making these intermediates that the following chapters 
 are concerned. 
 
 (c) The dyestuffs are formed in general by the condensation together of two or 
 more intermediates. These final stages are treated in detail in works on the chemistry 
 of the dyestufis, and will not be dealt with here. 
 
 In the preparation of both the intermediates and the dyestuffs, certain non-aromatic 
 substances (apart from the inorganic reagents—the acids, alkalies, etc.) are employed. 
 Thus, formaldehyde and phosgene are used for condensations with amines; methyl 
 and ethyl alcohols, chlorides and sulphates for the alkylation of amino and hydroxyl 
 groups; acetic acid and anhydride for the acetylation of amino groups; acetoacetic 
 ester and oxalacetic ester for condensation with hydrazines to form pyrazolones, and 
 so on. These non-aromatic substances are therefore also, in a sense, intermediates 
 for dyestufis, but they are, perhaps, more properly to be considered as auxiliaries 
 than as intermediates, and for the purposes of this book they will be so treated. 
 
 No definite and general line of demarcation exists between the intermediates and 
 the dyestuffs. A substance may at the same time be a dyestuff and an intermediate 
 
 * This is sufficient justification for the common name of “‘ Coal Tar Colours ” given to the artificial 
 dyestufis, though the use of this name has given rise, in the minds of the uninstructed, to the idea that 
 these dyestuffs are extracted from coal tar. 
 
 + A useful summary of the methods of making these auxiliary substances will be found in a paper by 
 J.T. Hewitt (Journ. Soc. Dy. Col. 1920, p. 6). 
 
INTRODUCTION Vil 
 
 for other dyestufis. A separate treatment of the intermediates is necessitated rather 
 by convenience due to the wide scope of the subject than by any strictly logical 
 difference between them and the dyestuffs. Such standard works on the chemistry 
 of the dyes as those of Georgievics, Bucherer, and Cain and Thorpe contain chapters 
 dealing with the intermediates, but the information given there is highly condensed 
 and summarised, and the main treatment is reserved for the dyestufis themselves. 
 The present book may be considered as, in effect, an elaboration of these summaries. 
 This elaboration has not been carried to the fullest possible extent. That would be 
 impossible in a single volume of reasonable size. The number of intermediates listed 
 in the “ Colour Index,” published by the Society of Dyers and Colourists, amounts to 
 about five hundred, and this includes only those which enter into the composition of 
 commercial dyestufis of known constitution. A selection has therefore been necessary, 
 and this has been made so as to include most of the important intermediates. 
 
 Arrangement of the Material. 
 
 The method to be adopted of arranging the matter in a book of this kind presents 
 some difficulty. The various items, large in number and disconnected in nature, 
 might be classified from the systematic chemical point of view as nitro compounds, 
 amines, phenols, sulphonic acids, and the like. But this method has the great dis- 
 advantage of separating, perhaps widely, substances which are naturally closely 
 related. The preparation, for example, of 1 : 8-aminonaphthol-3 : 6-disulphonic acid 
 (H-acid) is carried out in four stages, which involve the production in turn of a naph- 
 thalenetrisulphonic acid, a nitronaphthalenetrisulphonic acid, an aminonaphthalene- _ 
 trisulphonic acid, and finally the aminonaphtholdisulphonic acid. Under the scheme 
 here suggested, these four stages would be dealt with in widely separated parts of the 
 book. A further difficulty under this scheme is caused by the fact that many of the 
 substances contain several of the substituent groups which form the basis of classi- 
 fication. Whether, for instance, an aminophenol should be classed with the amines 
 or with the phenols is a point for whose decision there is no guiding principle. 
 
 Another possible classification is based on the nature of the operations used in 
 the formation of the intermediates from the starting materials—namely, halogenation, 
 nitration, reduction, sulphonation, alkalifusion,and soon. This method is attractive 
 to the chemist who is investigating the preparation of new substances or attempting 
 to improve on the existing methods of preparation of known substances, since, on 
 this plan, the many different modifications of a reaction, such as nitration, are pre- 
 sented together, and are readily available for comparison. The chapters on the 
 intermediates in Bucherer’s “‘ Lehrbuch der Farbenchemie” are written from this 
 point of view, and form a valuable summary of the subject. However, the method 
 suffers from the same defect as the preceding one—namely, that the different stages 
 in the preparation of many of the intermediates are necessarily dealt with in widely 
 separated parts of the book. 
 
 The classification actually adopted in the succeeding chapters of this book is one 
 which traces the formation of each intermediate, stage by stage, from the coal tar 
 
vill INTRODUCTION 
 
 product which forms its starting material. The various chapters are therefore taken 
 up with the preparation of the intermediates actually made from each coal tar product. 
 The charts at the beginnings of the chapters indicate, it is hoped with sufficient clear- 
 ness, the number and nature of the stages required for the preparation of a given 
 intermediate, and the treatment in the text follows as closely as possible the order 
 shown in the charts. Complications of order are, of course, caused by branched 
 chains in this genealogical arrangement, and changes of order are made where these 
 seem desirable for the sake of treating together closely connected subjects. The 
 plan has the advantage of showing in brief how, and by how many operations a given 
 intermediate is derived* from the raw material. It does not, however, altogether 
 escape the defect urged against the plans previously discussed, that of separating 
 closely connected subjects. Where, for example, a particular intermediate is obtain- 
 able from different sources, or by different methods from the same source, the pre- 
 paration of that intermediate will be found in several places depending on the source 
 or the method to be described. This defect is remedied by the use of cross references. 
 
 Method of Treatment. 
 
 The efficient manufacture of a substance involves the solution of complex problems, 
 some of which are of a high order of difficulty. The nature of these problems may 
 be briefly indicated here. They are concerned with the determination of data of all 
 kinds bearing on the nature of the materials and the reactions connected with the 
 preparation of the required substance. 
 
 (a) The physical constants of the pure substance must be accurately determined — 
 —viz., its crystalline form, melting-point, boiling-pomt under different pressures, 
 vapour pressure and density over a range of temperature, and so on. 
 
 (b) The chemical reactions involved in the process to be adopted are examined, 
 any possible side reactions detected, and the means of preventing or limiting these 
 worked out. 
 
 (c) A series of physico-chemical investigations may be required, dealing with the 
 various factors concerned in the process, such as velocities of reaction at different 
 temperatures, and the vapour pressure and solubility curves for the systems composed 
 of the starting materials, solvent, and reaction products. 
 
 (d) The most suitable materials for the construction of the plant required must 
 be considered. | 
 
 All the information gathered along these lines is required for the devising of a 
 manufacturing process of maximum efficiency, and a full account of each of the inter- 
 mediates dealt with in this book would require all these details. Needless to say, 
 that programme has not been carried out here. In fact, such a minutely detailed 
 study has been worked out for only a comparative few of the dyestuff intermediates, 
 and a description of each of these would require a volume to itself. Admirable models 
 of the kind of thing referred to are to be found in some of the “ Technical Records 
 
 * Incidentally, it may be remarked that the word “ derivative ’’ is used in this book in a practical 
 sense and not with its systematic chemical meaning. 
 
INTRODUCTION 1X 
 
 of Explosives Supply ” published by the late Ministry of Munitions. But all that is 
 possible in such a book as the present, which deals with the preparation of several 
 hundreds of substances, is to give a summary of the more important literature con- 
 nected with each substance, together with references to the sources of more detailed 
 information where such exist. Details of chemical plant and manufacturing technique 
 have been omitted, not because they are unimportant, but because the inclusion of 
 such matter was felt to be unnecessary. The nature of the plant required for any 
 ordinary chemical operation is familiar to the experienced works chemist, and is 
 described in books on chemical engineering. 
 
 Applications of the Intermediates. 
 
 No description of a dyestuff intermediate would be complete without some refer- 
 ence to the nature of the dyestuffs for which itis used. To give a list of the dyestuffs 
 made from each intermediate, especially if these were referred to under their trade 
 names, would be of little use. In any case, this has already been done in the ‘“‘ Colour 
 Index” previously mentioned. It was considered preferable in this book to attempt 
 to indicate in genera! terms the class or classes of dyestuffs for which each intermediate 
 is employed, and to estimate the part played by the intermediate in each class, 
 including its influence on the shade, fastness, and other dyeing properties.* These 
 notes on the applications of the intermediates are necessarily brief, since it would 
 hardly be appropriate here to enter into details of the methods of synthesis of the 
 dyestufis. But it is hoped that these notes, which, taken together, constitute a 
 treatment of the chemistry of the dyestuffs from an unusual point of view, will be 
 found useful and suggestive. 
 
 A. D. 
 November, 1925. 
 
 * Further information on the nature of the dyestuffs (and also of many other classes of products) 
 made from these intermediates can be found in ‘‘ The Industrial Applications of the Coal Tar Products,” 
 by H. M. Bunbury and A. Davidson (Ernest Benn, Ltd., 42s.). 
 
CONTENTS 
 
 INTRODUCTION . . ; : . ° 
 
 CHAPTER 
 
 I, 
 
 II, 
 
 XII. 
 XIII. 
 XIV. 
 
 XV. 
 
 XVI. 
 
 THE CHLOROBENZENES AND THEIR DERIVATIVES . . 
 
 NITROBENZENE AND ITS DERIVATIVES . . ° 
 
 . ANILINE AND ITS DERIVATIVES 
 
 . BENZENESULPHONIC ACIDS—-THE PHENOLS AND THEIR DERIVATIVES 
 
 THE NITROTOLUENES AND THEIR DERIVATIVES 
 
 . THE CHLORINATION AND SULPHONATION OF TOLUENE ° 
 
 XYLENE DERIVATIVES ° . . . ° 
 
 NAPHTHALENE DERIVATIVES—A PRELIMINARY SURVEY . : 
 
 . NITRONAPHTHALENES AND THEIR DERIVATIVES 
 
 . NAPHTHALENEMONOSULPHONIC ACIDS AND THEIR DERIVATIVES . 
 
 NAPHTHALENEDISULPHONIC ACIDS AND THEIR DERIVATIVES ° 
 DERIVATIVES OF B-NAPHTHOL 
 
 PHTHALIC ANHYDRIDE AND ITS DERIVATIVES : . 
 ANTHRACENE AND ANTHRAQUINONE DERIVATIVES . . 
 STABILISED DIAZO COMPOUNDS . . * ‘ 
 
 MISCELLANEOUS INTERMEDIATES . . ° ° 
 
 INDEX . : . . 
 
 xi 
 
 PAGE 
 
NO. 
 
 XII. 
 
 LIST OF CHARTS 
 
 CHLOROBENZENES AND THEIR DERIVATIVES 
 
 . NITROBENZENE AND ITS DERIVATIVES 
 
 . ANILINE AND ITS DERIVATIVES 
 
 . BENZENESULPHONIC ACIDS AND PHENOL DERIVATIVES . 
 
 . NITROTOLUENES AND THEIR DERIVATIVES . . 
 
 . DERIVATIVES OF TOLUENE BY CHLORINATION AND SULPHONATION . 
 
 . NITRONAPHTHALENES AND THEIR DERIVATIVES 
 
 NAPHTHALENEMONOSULPHONIC ACIDS AND THEIR DERIVATIVES 
 
 . NAPHTHALENEDISULPHONIC ACIDS AND THEIR DERIVATIVES 
 
 DERIVATIVES OF B-NAPHTHOL 
 DERIVATIVES OF PHTHALIC ANHYDRIDE 
 
 DERIVATIVES OF ANTHRACENE 
 
 xiii * 
 
 PAGE 
 
 103 
 121 
 143 
 153 
 165 
 183 
 201 
 215 
 
INTERMEDIATES FOR DYESTUFFS 
 
 CHAPTER I 
 THE CHLOROBENZENES AND THEIR DERIVATIVES 
 
 A. The Chlorobenzenes. 
 
 Tue chlorobenzenes of technical importance are : 
 
 Monochlorobenzene, O,H,Cl, a colourless liquid, b.p. 132°, D2° 1-1060. 
 
 p-Dichlorobenzene, C,H,Cl,, a colourless crystalline solid, m.p. 53°, b.p. 174°; 
 soluble in alcohol. 
 
 o-Dichlorobenzene, a liquid, b.p. 179°. 
 
 They are prepared by the action of chlorine gas on benzene, in presence of a 
 catalyst. Chlorine acts very slowly on benzene even at the boil, but the reaction is 
 accelerated by iron, iodine, aluminium, and its chloride, antimony pentachloride, ete. 
 Substitution takes place, and mixtures of monochloro- and dichlorobenzenes are 
 formed together with higher substitution products, the composition of the mixture 
 depending chiefly on the temperature, but also on the catalyst used and on the 
 presence or absence of moisture. As regards the effect of moisture, it has been found 
 that if this is rigidly excluded only addition products are formed. Thus apparently 
 water acts as a chlorine-carrier, and it has been suggested that the source of active 
 chlorine is HOCI. However, the presence of much moisture causes other complica- 
 tions, and if mono- or dichlorobenzenes are required, the chlorination must be carried 
 out in approximately dry conditions. 
 
 Among the catalysts, iron is the most important, and is the one used on the manu- 
 facturing scale, wrought-iron being preferred to cast-iron, as it acts less vigorously 
 than the latter. Aluminium also acts well, a yield of 87 per cent. of monochloro- 
 benzene having been obtained, using only 1 part of aluminium to 1,000 parts of 
 benzene (Meunier, C.#., 1920, 170, 1451). 
 
 A study of the kinetics of the chlorination of benzene in presence of iron as catalyst 
 has shown that the proportion of monochlorobenzene in the chlorination products 
 rises with the temperature, and at the boiling-poimt of benzene amounts to about 
 85 per cent. Again, the molecular proportion of benzene converted to monochloro- 
 benzene in a given time is 8-5 times the molecular proportion of monochlorobenzene 
 converted to dichlorobenzenes in the same time (Bourrion, C.#., 1920, 170, 1309). 
 
 The conditions of chlorination adopted will depend, of course, on the products 
 required. But the usual conditions employed are those yielding the maximum of 
 monochlorobenzene. Various forms of chlorination plant are described in Cain’s 
 “* Manufacture of Intermediate Products for Dyes,” pp. 7-10. The essential features 
 of the preparation are as follows : 
 
 The benzene to be chlorinated, which must be pure and dry, is stirred rapidly with 
 about 1 per cent. of its weight of wrought-iron powder in a vessel fitted with a reflux 
 
 1 
 
2 INTERMEDIATES FOR DYESTUFFS 
 
 condenser, and is heated to boiling. Dry chlorine is passed slowly through. The 
 hydrochloric acid formed is led off through vessels containing water, in which it is 
 absorbed. Chlorine is passed until the increase in weight corresponds to that required 
 for monochlorobenzene, or, say, about 35 parts for every 78 parts of benzene used. 
 The product is then fractionated, about 80 per cent. being obtained as monochloro- 
 benzene, 10 to 15 per cent. as p-dichlorobenzene, 1 to 3 per cent. as o-dichlorobenzene, 
 and about 5 per cent. as recovered benzene, 
 
 B. The Nitrochlorobenzenes. 
 
 Monochlorobenzene, on nitration in the usual way with mixed nitric and sulphuric 
 acids, yields nitrochlorobenzenes. Using one molecular equivalent of nitric acid, a 
 nearly theoretical yield of a mixture of o- and p-nitrochlorobenzenes is obtained, only 
 a minute proportion of the meta compound being formed. 
 
 o-Nitrochlorobenzene, needle-shaped crystals, m.p. 32-5°, b.p. 245-5° (753 mm.), 
 119° (8 mm.). 
 
 p-Nitrochlorobenzene, prisms or leaflets, m.p. 83°, b.p. 238-5 (753 mm.), 113° 
 (8 mm.); Dj. 1-52. 
 
 The following table, given by Holleman (Proc. K. Akad. Wetensch., Amsterdam, 
 1904, 7, 266), shows the solidifying points of mixtures of the two substances, and 
 serves as a guide in their separation : 
 
 Per Cent. of Para. ers Aisi Per Cent. of Para. Tae 
 0 32-09 35-43 18-43 
 1-05 31-06 37-53 21-90 
 4-60 29-92 39-96 26-10 
 6-54 29-00 41-67 28-50 
 8-88 27-89 45-86 33°98 
 12-61 26:10 48-94 37-65 
 16-26 24:19 60-18 50-10 
 19-22 22-65 64-66 54-32 
 22-91 20-75 68-54. 57-83 
 26-89 18-30 70-02 59-22 
 30-26 16-29 71-93 60-80 
 32-39 15-35 75-48 63-97 
 32-71 14-94 81-93 69-10 
 32-90 14-85 86-70 72-77 
 33-07 14-77 90-30 75-40. 
 33-10 14-65 95-57 79-13 
 34:09 16-73 100-00 82-15 
 34-94 17-47 
 
 From the table it is seen that the eutectic point is 14-65°, corresponding to a composi- 
 tion of 33-1 per cent. of para, and 66-9 per cent. of ortho compound. In Holleman’s 
 experiments the product of nitration had a solidifying pomt of about 59°, which 
 corresponds to a mixture of 70 per cent. para and 30 per cent. ortho compound. 
 From such a mixture on cooling to about 16°—~+.e., a little above the eutectic point— 
 most of the para compound crystallises out and can be separated from the still liquid 
 
‘SHAILVATUUC UHHL INV SUNAZNHAOUOTHO—T LYVHO 
 
 H®OS H°OS 
 x Clea a6 
 19 HO 
 tes eee 
 2HN 20N Zon = ?ON H®OS H®os H°OS ee 
 le AU) a0 6) age 0) oo) les 
 H®OS ‘ “h “h 1D AS ‘h y 
 20N 20N fon "ON 2%ON = PHN 
 
A INTERMEDIATES FOR DYESTUFFS 
 
 portion by centrifuging. The liquid mixture, according to a patent of the Griesheim 
 Elektron (G.P. 97013), can be further separated into its components by systematic 
 fractional distillation and crystallisation. The boiling-point difference under 8 mm. 
 pressure is only 6°, but the first fraction is richer in para and the last is richer 
 in ortho compound than the eutectic mixture, so that on cooling these, pure 
 para compound crystallises out from the former and pure ortho compound from 
 the latter. By a repetition of these processes a fairly complete separation is 
 obtained. 
 
 Hither of the two nitrochlorobenzenes, on further nitration, yields 2 : 4-dinitro- 
 chlorobenzene, but this compound is usually prepared by the direct nitration of 
 chlorobenzene. 
 
 2: 4-Dinitrochlorobenzene— Cl 
 
 —forms large rhombic crystals, m.p. 51°, b.p. 315° (with slight decomposition), D™* 
 1-697. Solublein alcohol. It has an extremely irritant action on the skin and should 
 be handled with care. 
 
 The following method of preparation is given by Fierz-David (“‘ Farbenchemie,” 
 1920, p. 108): 350 gms. of mixed acid containing 50 per cent. HNOs is stirred in an iron 
 nitrating vessel and cooled to 5°. 113 gms. of chlorobenzene is dropped in slowly, 
 with rapid stirring, the temperature being maintained below 5°. After all the chloro- 
 benzene has been added, the mixture is stirred for one hour, during which the tem- 
 perature may be allowed to rise to 10°. Itis then slowly raised to 50° and maintained 
 for one hour at this temperature. Up to this point, nitration has only proceeded as 
 far as the mononitro stage. 350 gms. of concentrated sulphuric acid is then dropped 
 in very cautiously with vigorous stirring, and the mixture is finally heated for half an 
 hour at 115° to complete the dinitration. After cooling, the product is poured into 
 2 litres of water, in which the dinitrochlorobenzene solidifies to a pale yellow cake. 
 This is separated, melted under water to remove acid, and is thus obtained practically 
 pure. The yield is 200 gms., or nearly theoretical. 
 
 In large scale practice, where both mono and dinitrochlorobenzenes are made, the 
 crude mixture of o-nitrochlorobenzene with some p-compound (obtained as above 
 described after separation of as much as possible p-nitrochlorobenzene) is nitrated 
 under approximately the same conditions as apply to the nitration of nitrobenzene 
 to dinitrobenzene. This arrangement uses up the o-nitrochlorobenzene, which finds 
 relatively little application as compared with p-nitrochlorobenzene. The o-compound 
 nitrates more readily than the p-, but naturally shows some tendency to nitrate in the 
 second o-position as well as in the p- — 
 
 Cl 
 
 Cl 
 ( ae O.N/ yee 
 
 pam | (m.p. 42°) 
 as a WA 
 
CHLOROBENZENES AND THEIR DERIVATIVES 5 
 
 —whereas p-nitrochlorobenzene should give only the one product, the second nitro 
 group entering either of the two o-positions. 
 
 2:4-Dinitrochlorobenzene has proved an exceedingly useful intermediate on 
 account of the reactivity of its chlorine atom, which is caused by the presence of the 
 two nitro groups in the o- and p-positions. The chlorine is easily displaced, for 
 instance, by —OH, through the action of dilute alkali, even sodium carbonate being 
 sufficient, thus yielding 2 : 4-dinitrophenol, the intermediate for Sulphur Black T. 
 Again, the action of ammonia and primary amines produces dinitroaniline and a 
 number of very useful diphenylamine derivatives : 
 
 (NO,),.C,H3.Cl + NH,R —— > (NO,),C,H;.NH.B 
 
 The preparation of these derivatives will be dealt with later. They are generally 
 used for the production of sulphur colours. 
 
 By condensing 2 : 4-dinitrochlorobenzene with p-aminodiphenylamine derivatives, 
 yellow dyes of the nitro class are obtained. 
 
 C. Derivatives of 2 : 4-Dinitrochlorobenzene. 
 
 oe 
 
 NO, 
 
 2 : 4-Dinitrophenol— 
 
 —pale yellow crystals, m.p. 114°, easily crystallised from water, since it dissolves in 
 21 parts of boiling water, but requires 197 parts of water at 18°. Its solubility in 
 alcohol is about equal to that in water. It is easily soluble in ether, chloroform, and 
 benzene. 
 
 It is prepared by boiling 100 parts of 2 : 4-dinitrochlorobenzene with a solution 
 of 125 parts of sodium carbonate (as Na,CO,, or an equivalent of soda crystals) in 
 1,000 parts of water, until the oily drops of dinitrochlorobenzene completely disappear. 
 This may take a considerable time, but can be hastened by very rapid stirring. The 
 solution now contains the sodium salt of dinitrophenol, and on cooling and acidifying 
 the dinitrophenol separates almost pure. The yield is nearly theoretical. 
 
 2: 4-Dinitrophenol is used only as an intermediate for sulphur colours. By 
 heating it with sodium sulphide and sulphur under various conditions of concentra- 
 tion, temperature and duration of heating, black dyes of different shades and properties 
 are formed. 
 
 p-Nitro-o-aminophenol— OH 
 
 —yellow-brown leaflets from water. The crystals which contain water of crystal- 
 lisation melt at 80° to 90°. The anhydrous substance melts at 142° to 143°. 
 
6 INTERMEDIATES FOR DYESTUFEFS 
 
 This substance has been prepared by Anwers and Réhrig (Ber., 30, 995) by reduc- 
 tion of 2 : 4-dinitrophenol with ammonium sulphide in very dilute aqueous alcoholic 
 solution, the nitroaminophenol being extracted with ether. The yield obtained was 
 only 32 per cent. 
 
 An improved method of preparation is given in G.P. 289454, in which the reduction 
 is performed by means of iron filings and sulphur dioxide. A mixture of 184 gms. 
 of dinitrophenol, 1,000 c.c. of water, and 200 gms. of iron filings, is stirred and heated 
 to 80° to 90°, and at this temperature sulphur dioxide is passed in until the iron is 
 almost entirely dissolved. The brown liquid obtained is freed from the remaining 
 iron by filtration, and air is then blown through until no more substance separates. 
 The nitroaminophenol is thus obtained as a brown crystalline powder. The yield is 
 60 per cent. 
 
 p-Nitro-o-aminophenol, like other o-aminophenol derivatives, is used as a first 
 component in monoazo dyes, these having the property of dyeing chrome-mordanted 
 wool, or of being developed by afterchroming. 
 
 2: 4’-Dinitro-4’-hydroxydiphenylamine— 
 
 NO, 
 Poi EEN 
 O.N< >-NE DoH 
 
 —forms red leaflets, m.p. 190°, soluble in alkalies. 
 
 This substance is prepared by condensing dinitrochlorobenzene with p-amino- 
 phenol as follows: 202 gms. of dinitrochlorobenzene, 150 gms. of »-aminophenol 
 (about 30 per cent. excess), and 1,500 c.c. of alcohol are heated in a flask fitted with 
 reflux condenser on the water-bath till complete solution is obtained. 150 gms. of 
 crystalline sodium acetate is added, when a deep orange-red colour is produced. 
 Under the influence of the sodium acetate condensation proceeds quickly, and after 
 an hour’s further heating, is complete. On cooling, most of the product crystallises 
 out, and is filtered off and washed with alcohol. From the filtrate a further quantity 
 is obtained by distilling off about half the alcohol and cooling. This second crop 
 contains some sodium chloride, which is washed out with water. 
 
 This intermediate is probably the most important of those diphenylamine deriva- 
 tives obtained from dinitrochlorobenzene, which, as previously mentioned, serve for 
 the production of sulphur colours by heating with sodium sulphide and sulphur in 
 different solvents, such as alcohol carbon disulphide, etc. 
 
 m-Phenylenediamine-4-sulphonic acid : 
 
 NH, 
 
 NH, 
 
 ( 
 ae 
 S0,H 
 
 The acid crystallises from water in tabular crystals, which soon turn brown in 
 the air. 
 
CHLOROBENZENES AND THEIR DERIVATIVES 7 
 
 This acid is derived from 2: 4-dinitrochlorobenzene by a method due to 
 Erdmann, G.P. 65240: 
 
 Cl SO,Na S0,H 
 “NNO, NO, /\NH, 
 | -++ NagSO3 x - | 
 ss oxy a 
 
 No, No, ; 
 
 The following process, based on Erdmann’s method, somewhat modified, is described 
 by Fierz-David (“‘ Farbenchemie,’’ 1920, p. 59): 202 gms. of dinitrochlorobenzene 
 are mixed with 500 gms. of methylated spirit (not denatured with pyridine bases). 
 To this is added the equivalent of 80 gms. of SO, in the form of a concentrated solution 
 of sodium sulphite. This solution is most conveniently prepared from the com- 
 mercial 35 per cent. bisulphite solution by adding an equivalent of 40 per cent. caustic 
 soda, the end point being such that phenolphthalein is faintly reddened. The mixture 
 is now heated to boiling on the water-bath with stirring for five hours. On cooling, 
 the dinitrosulphonate separates as yellow crystals. 
 
 Instead of distilling off the alcohol as directed in the patent, the crystals are 
 filtered off, pressed, and then redissolved in water and reduced by the method used 
 in the case of m-dinitrobenzene (p. 20). The solution of m-phenylenediaminesul- 
 phonic acid so obtained is evaporated to 400 c.c. and 100 gms. of salt added. Hydro- 
 chloric acid is then added until Congo paper is just turned faint violet (not blue). 
 After standing for two days, the separated sulphonic acid is filtered off, washed with 
 a very little water, and dried. The yield is 125 gms. of the pure acid, or 66 per cent. 
 of the theoretical. 
 
 It is important to note that traces of copper or iron in the reaction mixture may 
 prevent any of the dinitrosulphonic acid from being formed. 
 
 D. Derivatives of »-Nitrochlorobenzene. 
 p-Chloroaniline— Cl 
 
 a 
 » 
 N 2 
 
 —trhombic prisms, m.p. 69-7°. The sublimed substance melts at 70° to 71°. B.p. 
 932-3°. Forms a sulphate, (Cl.C,H,.NH,)..H,SO,, which is sparingly soluble in cold 
 water. 
 
 This substance is obtained by reducing p-nitrochlorobenzene with iron filings and 
 hydrochloric acid as in the preparation of aniline from nitrobenzene. Bashioum and 
 Powers (J. Ind. Eng. Chem., 1923, 15, 408) suggest, as the best proportions in this 
 case, 15 parts of 35 per cent. hydrochloric acid, 15 parts of water, and 100 parts of 
 nitro compound, the mixture being refluxed while 100 parts of iron filings are gradually 
 added. The distillate in the condenser appears red until reduction is complete, when 
 it becomes colourless. It was found to be necessary to remove any unnitrated 
 
8 INTERMEDIATES FOR DYESTUFFS 
 
 chlorobenzene from the nitrochlorobenzene, or reduction was retarded to a remark- 
 able degree. After completion of the reduction, the acid is neutralised, and the 
 p-chloroaniline separated by steam distillation. 
 
 p-Nitroaniline— 
 
 —yellow crystals, m.p. 147°, soluble in 45 parts of water at 100°, and in 1,250 parts at 
 12°. Easily soluble in alcohol. It is not volatile in steam. 
 
 It 1s possible to replace the chlorine of p-nitrochlorobenzene almost quantitatively 
 by NH,, by heating with aqueous ammonia in an autoclave at moderately high 
 temperatures, a process which was patented by the Clayton Aniline Co. in 1902 
 (H.P. 24869°?; G.P. 148749). While such displacements of chlorine by ammonia and 
 primary amines are generally facilitated by the presence of small amounts of copper 
 compounds, as discovered by Ullmann, a copper catalyst is not necessary in this case, 
 and, in fact, contact with copper is actually deleterious to the product. The same 
 applies to iron and lead. This necessitates the use of enamelled autoclaves, which 
 are expensive and difficult to keep in good repair. In spite of these difficulties, how- 
 ever, the process seems to have become established on the manufacturing scale, 
 though it has not entirely displaced the older process in which acetanilide is nitrated 
 (p. 36). 
 
 Pure -nitrochlorobenzene is heated with excess of a concentrated aqueous 
 solution of ammonia in an enamelled autoclave at 170° for hours. The ammonia 
 used must be free from pyridine bases, otherwise brown impurities are formed, which 
 are difficult to remove. The conversion is generally practically complete, but any 
 unchanged chloro-body may be removed by steam distillation, and after cooling, the 
 p-nitroaniline is filtered off and dried. A very pure product is obtained by this 
 method. 
 
 p-Nitrochlorobenzenesulphonic acid : 
 
 Cl 
 
 ( he 
 De. 
 
 NO, 
 
 The acid forms large triclinic plates with 2H,O, sparingly soluble in water and alcohol. 
 The sodium salt crystallises with 1H,O, as needles or leaflets, and is fairly soluble in 
 water. The chloride of the acid melts at 89° to 90°, and the amide at 185° to 186°. 
 Ullmann and Jiingel (Ber., 1909, 42, 1077) give the following method of pre- 
 paration : 157-9 parts of p-nitrochlorobenzene is stirred with 200 volume-parts of 
 20 per cent. oleum at 160° for six hours. After cooling, the mixture is run into 425 
 parts ofice. A brown solution is at first formed, from which the acid erystallises out 
 on standing. It is filtered off, washed with dilute hydrochloric acid, redissolved in 
 
 SS eee 
 
CHLOROBENZENES AND THEIR DERIVATIVES 9 
 
 boiling water, steam passed through to drive outa little unchanged nitrochlorobenzene, 
 
 and on cooling the pure acid crystallises out, the crystallisation being assisted by 
 
 adding concentrated hydrochloric acid. The yield is 246 parts, or 91 per cent. 
 Fierz-David uses a larger proportion of acid (100 gms. of monohydrate with 
 
 280 gms. of 25 per cent. oleum to 100 gms. of nitrochlorobenzene) and sulphonates at 
 
 a lower temperature, 100° to 110°. After pouring the sulphonation mixture on to 
 
 300 gms. of ice and 300 gms. of water, the product is salted out with 200 gms. of salt. 
 p-Nitroaniline-o-sulphonic acid : 
 
 N 
 
 N 
 
 es 
 
 2 
 
 SO,H 
 
 ee 
 
 2 
 
 This compound is prepared by heating p-nitrochlorobenzene-o-sulphonic acid with 
 ammonia in an autoclave. If alcoholic ammonia is used, two to three hours at 120° 
 to 140° is sufficient (Fischer, Ber., 1891, 24, 3789). But the use of alcohol is un- 
 necessary. The moist press-cake of sulphonic acid obtained in the sulphonation of 
 p-nitrochlorobenzene is stirred into its own weight of 20 per cent. aqueous ammonia 
 and heated in an autoclave at 150° for eight hours. The pressure developed is six 
 atmospheres. On cooling, the ammonium salt of the nitroanilinesulphonic acid crys- 
 tallises out in large amber-coloured cubes. From 100 gms. of p-nitrochlorobenzene, 
 a yield of 100 gms. of the ammonium salt is obtained (Fierz-David, “‘ Farbenchemie,” 
 1920, p. 61). 
 
 This intermediate is used as a first component in monoazo dyes, one of which, 
 with B-naphthol as second component, is a red lake pigment. It may also be used for 
 polyazo dyes by reducing the nitro group in the first formed monoazo dye and then 
 diazotising the aminoazo compound and coupling with a third component, as in 
 Carbon Black. 
 
 1 : 2-Dichloro-4-Nitrobenzene— Cl 
 
 ‘ 
 oo 
 
 Or 
 
 oS, 
 
 Z 
 
 —long needles, as crystallised from alcohol, m.p. 43°, b.p. 256° to 260°. 
 
 The chlorination of p-nitrochlorobenzene to produce this substance is described in 
 G.P. 167297. 20 parts of p-nitrochlorobenzene are heated to 95° to 120°, 1 part of 
 anhydrous ferric chloride added, and 4-37 parts of chlorine passed into the molten 
 substance. The liquid is then poured into cold water, and the dichloronitrobenzene 
 washed with water at 50°. It is purified by crystallisation from alcohol. 
 
 As catalysts, instead of the ferric chloride, antimony pentachloride (3 parts), 
 iodine (2 parts), or phosphorus pentachloride (5 parts), may be used, though in the 
 last case chlorination must be carried out at 150°. 
 
 By heating 1: 2-dichloro-4-nitrobenzene with alcoholic ammonia at 190° for 
 
10 INTERMEDIATES FOR DYESTUFFS 
 
 forty-eight hours, o-chloro-p-nitroaniline is obtained (Rec. érav. chim., 36, 135, 
 155) : 
 NH, 
 
 Cl 
 aie 
 ——> 
 
 wee Oy 
 NO, No, 
 
 o-Chloro-p-nitroaniline crystallises in yellow needles, m.p. 107°. 
 
 It is used as a component in trisazo dyes of the type of Diamine Green B. Diazo- 
 tised o-chloro-p-nitroaniline is coupled in acid solution with H-acid, and the product 
 coupled with diazotised benzidine on one side in alkaline solution, the other side being 
 then coupled with phenol or salicylic acid. 
 
 EK. Derivatives of o-Nitrochlorobenzene. 
 
 o-Nitrochlorobenzene is readily sulphonated in the usual way by heating with 
 five times its weight of 30 per cent. oleum on the water-bath. It is, therefore, more 
 easily sulphonated than its isomer p-nitrochlorobenzene, which requires a much 
 higher temperature. The sulphonic acid is isolated as usual by liming out and con- 
 verting to the sodium salt (Fischer, Ber., 1891, 24, 3186). The derivative so formed 
 is o-Nitrochlorobenzene-p-sulphonic acid : 
 
 The free acid crystallises in needles with 1H,O. The barium salt forms yellow leaflets 
 with 1H,O, almost insoluble in alcohol. The chloride melts at 40° to 41°. The 
 amide, yellow prisms from alcohol, melts at 175° to 176°. 
 
 The labile nature of the chlorine atom in the above compound is made use of in 
 several ways, of which mention may be made first of the preparation of aniline- 
 2: 5-disulphonic acid— 
 
 ( SO,H 
 HO,8\ 
 —as indicated in the ae scheme : 
 ole SO,H 
 NO, \ NO, NH, 
 ~ + NagSOs3 _ is ~ Reduction — 
 WO.Ne ‘YO,na ‘YO,8 
 
 Details are given in G.P. 77192 (Badische). 
 (a) Nitrobenzene-2 : 5-disulphonic acid.—20 ke. of sodium o-nitrochlorobenzene-p- 
 sulphonate is dissolved in 50 litres of water, 30 kg. of crystalline sodium sulphite 
 
CHLOROBENZENES AND THEIR DERIVATIVES 11 
 
 added, and the solution boiled for one to two hours under reflux. On cooling, part of 
 the disulphonate crystallises out and most of the remainder is separated by addition 
 of salt. After filtering, the product is pressed and dried. It is not necessary to purify 
 it for the next stage, but it may be purified by crystallisation from dilute alcohol. 
 It forms needles, soluble in cold water, but insoluble in absolute alcohol. On boiling 
 the aqueous solution with caustic soda, an orange precipitate is formed. 
 
 (0) Reduction.—32 kg. of the crude nitro compound is dissolved in 200 litres of 
 water, 10 litres of 30 per cent. acetic acid added, the solution stirred on the boiling 
 water-bath, and reduced with 30 kg. of iron powder. When the reduction is finished 
 the solution is made alkaline with soda, filtered, evaporated to some extent, and 
 acidified. On cooling the product crystallises out as the acid sodium salt, forming 
 colourless short needles. 
 
 The chlorine atom may also be replaced by hydroxyl, by heating the chloronitro- 
 benzenesulphonic acid with caustic alkali (G.P. Anm. B. 15933), thus yielding o-nitro- 
 phenol-p-sulphonie acid : 
 
 OH 
 
 ee, 
 oe 
 SO,H 
 
 This is said to be the technical method of preparing this substance, but no details 
 of the process have been published. Presumably the method is similar to that by 
 which 2 : 4-dinitrophenol is formed from 2 : 4-dinitrochlorobenzene (p. 5). 
 
 On reduction, o-nitrophenol-p-sulphonic acid gives o-aminophenol-p-sulphonic 
 acid : 
 
 The reduction is stated by Post (Ann., 205, 51) to be best carried out with tin and 
 hydrochloric acid. Vigeaes 
 Another method of preparation of o-aminophenol-p-sulphonic acid 1s given 
 on p. 94. 
 o-Nitrochlorobenzene-p-sulphonic acid may also be nitrated further to produce 
 1-chloro-2 : 6-dinitrobenzene-4-sulphonic acid : 
 
 The introduction of a second nitro group into a nitrochlorobenzene is not an easy 
 matter. A relatively high temperature must be used, and the composition of the 
 nitrating acid so arranged that no free water is present before the nitration is finished. 
 
12 INTERMEDIATES FOR DYESTUFFS 
 
 The method is given in G.P. 116759 : 27-5 parts of the potassium salt of o-nitrochloro- 
 benzene-p-sulphonic acid are dissolved in 100 parts of 25 per cent. oleum, then 15 
 parts of 87 per cent. nitric acid are gradually added. The solution is then heated to 
 120° to 130° for some time. When the nitration is finished, the solution is poured 
 into water, and the crystallised product which separates is filtered off. 
 
 The substance may also be prepared directly from chlorobenzene in one operation 
 according to the scheme: 
 
 Cl Cl Cl 
 a i ON NO, 
 Bib enmity eek 
 iy Se wer 
 
 SO,H SO,H 
 
 34 parts of chlorobenzene are mixed with 72 parts of monohydrate and 30 parts of 
 25 per cent. oleum, and the mixture is stirred on the water-bath until the chlorobenzene 
 has disappeared owing to sulphonation. The solution is now cooled and 26 parts 
 of 87 per cent. nitric acid added slowly, so that the temperature does not rise above 
 40°, after which the solution is allowed to stand for two hours. In order to introduce 
 the second nitro group, 100 parts of 60 per cent. oleum and 40 parts of potassium 
 nitrate are added, and the mixture heated at 120° to 130° for two to three hours. 
 The product is then isolated as before. 
 
 The above substance can be reduced to the corresponding diamino compound 
 (G.P. 150373) 1-chloro-2 : 6-diaminobenzene-4-sulphonic acid : 
 
 Cl 
 
 A te 
 HK 
 
 S0,H 
 
 H,N 
 
 10 parts of the potassium salt of the dinitro compound are treated with 80 parts 
 of concentrated hydrochloric acid (D 1-19). The mixture is well stirred and 20 parts 
 of granulated tin gradually added. Much heat is developed, and a yellow solution is 
 formed. On cooling, a tin chloride double salt of the diamino compound separates in 
 colourless needles. These are filtered off, dissolved in a large volume of hot water, 
 and hydrogen-sulphide passed until the tin is completely precipitated. The tin 
 sulphide is filtered off, and on cooling the filtrate deposits the diamino compound as 
 colourless needles. 
 
 1-Chloro-2 : 6-diaminobenzene-4-sulphonic acid is almost insoluble in cold water, 
 and rather sparingly in hot water. The acid crystallises with 1H,O. The sodium 
 and potassium salts are readily soluble. The substance diazotises readily to give a 
 tetrazo compound. 
 
 o-Nitrochlorobenzene may also be amidated to o-nitroaniline : 
 
 NH, 
 ee 
 
 A. 
 
CHLOROBENZENES AND THEIR DERIVATIVES 13 
 
 160 gms. of o-nitrochlorobenzene and 300 gms. of aqueous ammonia (D 0-880) 
 are heated in an autoclave for four hours at 170° to 175°. The pressure at first rises to 
 48 atmospheres, but later, as amidation proceeds, falls to 30 atmospheres. After 
 cooling, the o-nitraniline is filtered off, washed with a little water, and purified by 
 recrystallising from 7 litres of boiling water. The yield is about 90 to 95 gms. 
 o-Nitraniline forms orange-red needles, m.p. 72°, moderately soluble in boiling water, 
 but sparingly in cold water. It is somewhat volatile in steam. 
 
 By another replacement of the chlorine atom in o-nitrochlorobenzene, there is 
 
 obtained o-nitroanisole : 
 OCH, 
 
 (y 
 
 This is accomplished by heating with sodium or potassium methylate. The prepara- 
 tion, using methyl alcohol and aqueous caustic potash under ordinary pressure, is 
 described by Brand (J. pr. Chem., 1903 (ii), 67, 145). While this method works well 
 with some nitrochloro compounds—e.g., with 2: 4-dinitrochlorobenzene—it is 
 apparently better to use water-free sodium methylate in this case. The preparation 
 is described by Fierz-David (“ Farbenchemie,” second edition, 1923, p. 81) as 
 follows : 
 
 Into a litre autoclave in an oil-bath put 600 c.c. of dry methyl alcohol in 
 which previously 23 gms. of sodium has been dissolved. Add 158 gms. of pure 
 o-nitrochlorobenzene and heat in the well-closed autoclave, raising the temperature 
 during the first hour to 120°, keeping at this temperature for three hours, and finally 
 for a further hour at 128°. The pressure developed is 8 to 10 atmospheres. Blow 
 the methyl] alcohol off through a good condenser (the recovered alcohol can be used 
 again without treatment). The residual crude product is washed twice with five 
 times its volume of hot water, separated from the water, and distilled 2m vacuo. It 
 boils at 141° under15mm. The yield is 136 gms. or 88 per cent. 
 
 Another method of preparation of o-nitroanisole is given on p. 85. 
 
 F. Derivatives of p-Dichlorobenzene. 
 p-Chlorophenol— OH 
 
 white crystals, m.p. 37°, b.p. 217°, D”°® 1-306. It is almost insoluble in water, but 
 easily soluble in alcohol and ether. It is insoluble in carbonate solutions. 
 G.P. 281175 describes the preparation as follows: 30 parts of p-dichlorobenzene, 
 36 parts of solid caustic soda, and 70 parts of ordinary methyl alcohol (not specially 
 dried) are heated together in an iron autoclave at 190° to 195° for forty hours. The 
 p-chlorophenol produced is purified by distillation. The yield is about 90 per cent. 
 
14 INTERMEDIATES FOR DYESTUFEFS 
 
 The function of the methyl alcohol is presumably that of solvent, but the use of 
 other solvents—e.g., benzene—gives lower yields. Using aqueous caustic soda, no 
 chlorophenol is produced. 
 
 p-Chlorophenol is used in the preparation of quinizarin (p. 208). 
 
 Nitration of p-dichlorobenzene yields one mononitro derivative: 1 : 4-dichloro- 
 
 2-nitrobenzene : + 
 ane 
 i. 
 Cl 
 
 The dichlorobenzene is nitrated with 1-5 parts of a mixture containing 2 parts of 
 nitric acid (D 1-54) to 3 parts of concentrated sulphuric acid. After mixing at the 
 ordinary temperature the reaction is finished on the water-bath (Morgan and Norman, 
 J.C.S., 1902, 81, 1382). The product is isolated in the usual way. It forms white 
 crystals, m.p. 54-5°, b.p. 266°, D”* 1-669. It is sparingly soluble in cold alcohol, 
 easily in hot alcohol and in benzene. 
 
 It can be reduced by iron and hydrochloric acid, following the method used for 
 the reduction of nitrobenzene to aniline, and thus yields 2 : 5-dichloroaniline— 
 
 NH, 
 ( : Cl 
 cL 
 
 —which forms white crystals, m.p. 50°, b.p.744”246°. 
 On sulphonating this dichloroaniline, the sulpho group enters the p-position to 
 the amino group, yielding 2 : 5-dichloroaniline-4-sulphonic acid: 
 
 The sulphonation was carried out by Noteling and Kopp (Ber., 1905, 38, 3513) by 
 adding 40 gms. of 2 : 5-dichloroaniline to 120 gms. of 18 per cent. oleum and heating 
 the solution at 170° to 180° for about two hours. When sulphonation was complete, 
 on pouring the solution on ice, the sulphonic acid separated. By using 20 to 25 per 
 cent. oleum, the sulphonation may be carried out at 120° (G.P. 222405). 
 
 This dichloroanilinesulphonic acid yields a hydrazine derivative which, condensed 
 with acetoacetic ester, forms a pyrazolone derivative. 
 
 1 : 4-Dichloro-2-nitrobenzene may also be converted by the action of ammonia 
 
 into p-chloro-o-nitroaniline : 
 NH, 
 
 ( he 
 ms 
 er 
 
CHLOROBENZENES AND THEIR DERIVATIVES 15 
 
 This forms orange-red needles, m.p. 116-5°, and resembles o-nitraniline strongly in 
 properties including smell, solubility in water and volatility in steam, 
 
 Dichloronitrobenzene is dissolved in sufficient alcohol and heated with excess of 
 aqueous ammonia in an autoclave at 190° for eight hours. The yield is quantitative 
 (Green and Rowe, J.C.S., 103, 897). 
 
 This chloronitroaniline is used in making a yellow lake pigment, Lithol Fast 
 Yellow GG, by condensing two molecular proportions of it with one of formaldehyde. 
 The resulting compound has the constitution : 
 
 ee ats anaes 
 Ck __ >NH—CH,—NHC yal 
 No, No, 
 
CHAPTER II 
 NITROBENZENE AND ITS DERIVATIVES 
 
 NITROBENZENE is one of the fundamental intermediates for dyestuffs (and for 
 other products), and its manufacture is therefore a matter of considerable importance, 
 but a detailed description of it would be beyond the scope of this book. Such a 
 description will be found in “ Aniline and its Derivatives,” by P. H. Groggins, and in 
 the Chemical Trade Journal, 1906, $8, 59. The essentials only of the ordinary 
 process will be given here. 
 
 Nitrobenzene— NO, 
 
 @ 
 
 —a colourless highly refractive liquid with a characteristic smell; m.p. 3:6°, b.p.r¢q 
 209°, b.p.1, 96°; De 1-2093. It is very slightly soluble in water, and also dissolves 
 water to a very slight extent, but mixes in all proportions with alcohol, ether, and 
 benzene. 
 
 The benzene used for its preparation should be free from the usual impurities. 
 It should boil within 0-2° (which excludes homologues), should solidify to a white 
 crystalline mass on cooling in ice, be free from carbon disulphide and thiophene, and 
 
 contain no unnitratable hydrocarbons. The nitration is carried out with a mixture 
 of nitric and sulphuric acids of the following composition : 
 
 HNO. Ss -. sim ie Pe aa .. 30 per cent. 
 H,SO, .. oe Be es se = <n 9» 
 Ha ces ne Rs se a - + oi) Eas 
 
 The mixed acid is made up from nitric and sulphuric acids of any convenient strengths 
 available. Usually 75 per cent. nitric acid and 95 per cent. sulphuric acid are 
 used, these being mixed in the ratio of 11 parts of the nitric to 17 parts of the 
 sulphuric acid. 280 parts of the above mixed acid are used for every 100 parts of 
 benzene. 
 
 The benzene is placed in an iron vessel fitted with a rapid stirrer, a thermometer, 
 and arrangements for heating and cooling. Rapid efficient stirring is necessary, since 
 benzene does not dissolve in the mixed acid, and the two liquids must be thoroughly 
 emulsified in order to obtain smooth nitration with no side reactions. The mixed 
 acid is added to the benzene at such a rate that the temperature chosen for the nitra- 
 tion is reached, but not exceeded. The temperature of nitration may be varied 
 within fairly wide limits without harm to the product, but the tendency at present is 
 to conduct the nitration at the maximum permissible temperature, and therefore at 
 the highest possible speed in order to obtain maximum production per unit of plant. 
 At 30° the nitration takes seven to eight hours, at 50° about two to three hours. An 
 upper limit of 80° is fixed by the boiling-point of benzene, but this is not approached 
 in practice because of the danger of forming dinitrobenzenes. 
 
 16 
 
 eS ee ee ae eee 
 
‘SUAILVAINGG SLI GNV UNAZNACOULIN— TT LAVHO 
 
 20N 
 SUN 
 HO 
 ®HN 
 1) ‘AQHN 19 H®os H®os 
 
 ae | N70 
 Ee y. (T2249 285 ) 
 H®OsS 0) 2On O 0 2HN = 
 
 20N 20N ®uN ZN 
 
 t 
 . 
 
 2ON 
 
18 INTERMEDIATES FOR DYESTUFEFS 
 
 When the mixed acid has all been run in, stirring is continued till the nitration 
 has reached the desired point. On the large scale this can be determined by drawing 
 off a sample from time to time, allowing it to settle, separating the upper layer of 
 nitrobenzene, and determining the percentage of nitric acid remaining in the lower 
 acid layer by means of a Lunge nitrometer. When the residual nitric acid falls to 
 1 per cent., the operation is ended. Using the quantities of benzene and mixed acid 
 given above, the result is that a small proportion of benzene remains unattacked. 
 This is desirable in order to avoid formation of dinitrobenzene. 
 
 After allowing the mixture to settle, the upper layer of nitrobenzene has a specific 
 gravity of about 1-235, which is higher than that of pure nitrobenzene, owing to some 
 dissolved acid. The lower acid layer consists of approximately 74 per cent. sulphuric 
 acid, which is sufficiently dilute to attack iron, though not very rapidly, and the 
 nitrating vessel on the large scale is, therefore, sometimes lead-lined. The acid, after 
 denitration and concentration, is used again. 
 
 The nitrobenzene after separation from the acid is washed with water, then with 
 dilute caustic soda solution, and finally again with water. The small proportion 
 of benzene remaining in it is separated by steam distillation, the passage of 
 steam being continued till the oily drops of distillate, the first of which float in 
 water, begin to sink quickly. This distillate is separated and used in a succeeding 
 nitration. 
 
 The crude nitrobenzene obtained in this way is pure enough, provided a pure 
 benzene was used in its preparation, for ordinary purposes, such as nitration to 
 dinitrobenzene, reduction to aniline, etc. But for the ‘“ Oil of Mirbane” of perfumery 
 it is distilled in vacuo. If thiophene was present in the benzene used, this is nitrated 
 to dinitrothiophene, and the presence of this substance in the nitrobenzene is shown 
 by shaking an alcoholic solution of it with alcoholic potash, when a red colouration 
 is produced. 
 
 Further nitration of nitrobenzene yields principally m-dinitrobenzene, though 
 some o- and p-dinitrobenzenes are also formed at the same time. The reaction has 
 been studied by Holleman (Ber., 1906, 39, 1715), who found that a nearly constant 
 proportion, about 91 to 93 per cent. of the meta compound was formed under varying 
 conditions, while the proportions of the ortho and para compounds varied consider- 
 ably, though their total amount remained nearly constant. 
 
 m-Dinitrobenzene— 
 
 ra 
 Ge 
 
 —colourless or faintly yellow crystals (plates), m.p. 89-7°, b.p. 279.5 302-8°, b.p. 33 188°. 
 It is soluble in benzene and toluene. 100 parts of benzene at 18-2° dissolve 39-45 
 parts of m-dinitrobenzene. (o-Dinitrobenzene melts at 116-5°, p-dinitrobenzene at 
 171° to 172°.) 
 
 It is not usual to prepare dinitrobenzene directly from benzene in one operation, 
 but instead to nitrate further the crude mononitrobenzene. This second nitration 
 
 Se AS eee ee ee ee —s 
 
NITROBENZENE AND ITS DERIVATIVES 19 
 
 requires more drastic conditions than the first—viz., a higher temperature (115°), and 
 a more concentrated mixed acid. The mixed acid used has the composition: 
 
 H,SO, .. “ - ws oy ae -- 171 per cent. 
 FEU, 3 up - = es os Sih et" ss 
 noe CAT es “a tis < Pe es as 
 
 To the crude nitrobenzene obtained from 100 parts of benzene previously heated to 
 100°, 450 parts of mixed acid of the above composition is added with good stirring, 
 the rate of addition being regulated so as to allow the temperature to rise slowly to 
 115°, and to remain at this point during the remainder of the nitration. When the 
 acid has all been added, stirring is continued until the nitration is finished, which is 
 indicated by a sample solidifying when cooled. ‘The stirrer is now stopped and the 
 reaction mixture allowed to settle. The molten dinitrobenzene forms the upper 
 layer, the lower acid layer having a specific gravity of about 1-8 and consisting of a 
 mixed acid containing 87 per cent. H,SO, and 3 to 4 per cent. HNO;. After cooling 
 to about 70°, the acid layer is run off and the dinitrobenzene run into well-stirred 
 boiling water in order to extract the acid from the product. The washing is repeated, 
 with addition of alkali to the water, till the product is completely acid-free. It is 
 then separated and dried. As obtained in this way, the dinitrobenzene melts at 
 75° to 80° and contains some o- and p-dinitrobenzenes. It should not smell of nitro- 
 benzene. Itis purified by recrystallisation from the least possible quantity of benzene 
 or toluene. 
 
 As m-dinitrobenzene is extremely poisonous, great care must be taken in 
 handling it. 
 
 Reduction of m-dinitrobenzene with an alkaline sulphide, such as sodium or 
 ammonium sulphide, leads to m-nitroaniline— 
 
 NH, 
 
 ) 
 oh 
 
 eg 
 
 —yellow needles, m.p. 114°; 100 parts of water at 24° dissolve 0-12 part of m-nitro- 
 aniline, but its solubility in boiling water is much greater. 
 
 Technically, the reduction is carried out by means of sodium sulphide or disulphide. 
 If sodium sulphide is used, 1-5 molecules are required for the reduction of one nitro 
 group, but the nature of the oxidation products of the sulphide apparently has not 
 been accurately determined. Some sulphur generally separates during the reaction 
 and probably thiosulphate is also formed. On the other hand, if the reduction is 
 performed with sodium disulphide, the reaction is simpler, and only 1 molecule of 
 the disulphide is required for the reduction of one nitro group: 
 
 > RNH, + Na,§,0, 
 
 R.NO, + NaS, + H,O 
 
 An account has been given by Cobenzl (Chem. Zeit., 1913, 37, 299) of the prepara- 
 tion of m-nitroaniline using the disulphide, which seems successful on a large scale. 
 
20 INTERMEDIATES FOR DYESTUFFS 
 
 10 kg. of m-dinitrobenzene is stirred vigorously in 400 litres of boiling water in an 
 iron vessel till it is thoroughly emulsified. A solution is made up of 15 kg. of erys- 
 talline sodium sulphide (Na,8.9H,O) and 4 kg. flowers of sulphur in 65 litres of water. 
 Only 2 kg. of sulphur are required to form the disulphide with the above quantity of 
 sodium sulphide, but the extra sulphur, while apparently not taking part in the 
 reaction, is found in practice to be necessary for complete reduction. The disulphide 
 solution is run into the dinitrobenzene-water mixture at such a rate as not to stop the 
 boiling. A further boiling of fifteen to twenty minutes completes the reduction, the 
 m-nitraniline formed all going into solution, while the excess sulphur separates. 
 The liquid is then filtered hot (the residual sulphur can be used again), and on cooling 
 the filtrate m-nitraniline crystallises out fairly pure. The crystals are centrifuged 
 and washed alkali-free with cold water. The yield of crystallised m-nitraniline is 
 about 6-6 kg. or 80 to 82 per cent. of the theoretical, provided a good quality of 
 dinitrobenzene is used. 
 
 Cobenzl’s remarks on the subject of yield in relation to quality of starting 
 material are instructive and may be taken as illustrative of a general rule. For 
 example, crude dinitrobenzene is sometimes yellow in colour and evil-smelling, due 
 to the presence of trinitrobenzene and phenols. Such a starting material was found 
 to give a 50 per cent. yield of m-nitraniline containing tarry impurities. The same 
 starting material could be purified considerably, at the expense of a 10 per cent. loss 
 in weight, by treatment with hot soda solution, which decomposed the trinitrobenzenes 
 and dissolved out the phenols, yielding a white odourless product. This purified 
 material now gave a yield of 76 to 78 per cent. of m-nitraniline. 
 
 m-Nitraniline is used as a first component in azo dyes mostly of the monoazo class. 
 
 When the reduction of m-dinitrobenzene is carried out in an acid medium—e.g., 
 in the ordinary way using iron and hydrochloric acid—both nitro groups are reduced, 
 yielding m-phenylenediamine— 
 
 —rhombic crystals, m.p. 63°, b.p. 287°, D*® 1-1389. The base is very soluble in water, 
 alcohol, and ether. It forms a dihydrochloride, which crystallises in fine needles, and 
 is very soluble in water. It may be diazotised in solution in concentrated hydro- 
 chloric acid, and then yields a tetrazo compound; but if diazotisation is attempted in 
 the ordinary dilute solution, brown azo dyes (Bismarck Brown) are formed, due to 
 coupling of the partially diazotised base with the remainder. The base quickly turns 
 brown in the air. 
 
 The process of reduction does not di ffer essentially from the usual acid iron reduc- 
 tion, which is described in detail under Aniline (p. 26). It need only be mentioned 
 that the quantities required per gram-molecule (168 gms.) of dinitrobenzene are: 
 
 14 litres of water; 
 300 gms. of fine iron; 
 20 c.c. of concentrated HCl. 
 
 ee ee eC ee ee UN ee ee 
 
NITROBENZENE AND ITS DERIVATIVES 21 
 
 Care must be taken when reduction is finished to precipitate any dissolved iron com- 
 _ pletely by boiling with sufficient soda. After filtering hot, the solution is made just 
 acid with hydrochloric acid. 
 
 The base is not usually isolated from solution, but if desired it may be obtained 
 by evaporating the solution in vacuo till it contains about 40 per cent. of the base, 
 and on cooling in ice this deposits the base in the form of prismatic crystals containing 
 4H,O. Any isomers present remain in the mother liquor. 
 
 The critical point in the preparation of m-phenylenediamine (and of other diamines 
 and aminophenols) comes at the moment when the solution is made alkaline in order 
 to rid it of iron. Oxidation is apt to be serious at this point, resulting in brown or 
 even black products, especially if the starting material were not pure. A process 
 has been patented in G.P. 269542 which avoids this difficulty, though only at the 
 expense of using a hundred times the quantity of acid required in the ordinary process. 
 The separation of the reduction product depends on the fact that the hydrochlorides 
 of diamines are almost insoluble in concentrated hydrochloric acid. As applied to 
 m-phenylenediamine, the process is as follows: 
 
 100 gms. of m-dinitrobenzene are added to 1,270 c.c. of 30 per cent. hydro- 
 -chloric acid and the mixture warmed to 40° to 50°. 247 gms. of iron in as pure 
 a form as possible (small iron nails weighing three to a gram are recommended) are 
 added gradually with good stirring. The heat of reaction raises the mixture to 
 boiling-point. The iron almost all dissolves, and on cooling, m-phenylenediamine 
 dihydrochloride separates in white crystals, which are filtered off and dried. 
 
 m-Phenylenediamine is used as an end component in azo dyes of many different 
 types. It couples very readily in weak acid solution with diazo compounds, a note- 
 worthy feature of the resulting dyes being that almost all are brown in shade, even 
 when there are two or three other components of the most varied nature. It is 
 possible to couple two molecules of diazo compound in succession with one molecule 
 of m-phenylenediamine, the resulting disazo compound having one of two formule : 
 
 NH, NH, 
 Be: ) ae a a a Astietet 
 or 
 me Ae \ NE: 
 N=N—R’ 
 
 Azo dyes containing m-phenylenediamine as end component may, therefore, be 
 developed on the fibre, without much change of shade, by coupling a convenient diazo 
 compound with them. These complex dyes are also produced in substance. 
 
 m-Phenylenediamineoxamic acid— 
 _ NH.CO.COOH 
 
 Lay 
 
 —crystallises in fine needles from water in which it is sparingly soluble even at the 
 boil. M.p. 225° (decomp.). The sodium and ammonium salts are soluble in water. 
 
22 INTERMEDIATES FOR DYESTUFFS 
 
 The mono-oxamic acids of diamines in general are formed by heating the diamines 
 with aqueous oxalic acid. According to Klusemann (Ber., 1874, 7, 1261), m-phenylene- 
 diamineoxamic acid is prepared by gradually adding a solution of m-phenylenediamine 
 to a boiling solution of oxalic acid. The oxamic acid separates as a grey precipitate 
 from the boiling solution. The oxalate of m-phenylenediamine, formed as an inter- 
 mediate stage, is much more soluble than the oxamic acid. 
 
 Ethyl-m-aminophenol— NH.C,H; 
 
 A 
 | Jon 
 
 This substance, which is more usually prepared by other methods, has been made from 
 the above oxamic acid (G.P. 76419, Badische) by the following series of reactions : 
 
 NH.CO.COOH NH.CO.COOH NH, 
 
 <a ( “Hydrolysis > ( 
 es KtBr () NHEt Hydrolysis () NHEt 
 
 N,.HSO, OH 
 gue 
 \_ JNHEt \_ ) NHEt 
 
 The sodium salt of m-phenylenediamineoxamic acid (20 kg.) is ethylated by 
 heating with 11 to 12 kg. of ethyl bromide and 20 kg. of alcohol in an autoclave at 
 120° to 150° for six to eight hours. The alcohol is then distilled off and the residue 
 extracted with cold water to remove sodium bromide, the ethylated m-phenylene- 
 diamineoxamic acid remaining undissolved. This is boiled with 3 to 4 parts of 
 water and 1 part of sulphuric acid for a considerable time, and the water then 
 mostly boiled off. The residual solution of ethyl-m-phenylenediamine sulphate is 
 cooled with ice and diazotised with one molecular proportion of sodium nitrite. 
 The solution of diazo compound is then warmed until evolution of nitrogen ceases. 
 After neutralising with carbonate, the ethylaminophenol may be extracted with 
 ether or benzene and isolated in the usual way. 
 
 Another method of preparation of ethyl-m-aminophenol is given on p. 56. 
 
 Sulphonation of Nitrobenzene. 
 
 The sulphonation of nitrobenzene yields chiefly m-nitrobenzenesulphonic acid, 
 which forms about 90 per cent. of the sulphonation product. Not more than 10 per 
 cent. of the ortho and para isomers are produced. It is of interest, however, to note 
 here that if benzenesulphonic acid is nitrated the proportions of the three isomers are 
 considerably different. 
 
 m-Nitrobenzenesulphonic acid : 
 NO, 
 
 er 
 
NITROBENZENE AND ITS DERIVATIVES 23 
 
 123 parts of nitrobenzene are dropped slowly into about 350 parts of 25 per cent. 
 oleum previously heated to 70° and well stirred. The rate of addition is so controlled 
 that the temperature rises to about 100°, and is maintained at 100° to 110° till all the 
 nitrobenzene has been added. Thereafter the temperature is kept at 110° to 115°, till 
 a test portion of the liquid dissolves almost entirely in water and does not smell of 
 nitrobenzene. More oleum is added, if required, to complete the sulphonation. The 
 solution is now cooled and poured on to 500 parts of ice, well stirred. The sulphonic 
 acids dissolve up completely to a hot solution, but a little sulphone— 
 
 NO, NO, 
 ee 
 L J-sol ) 
 
 —which is always formed, remains undissolved, and this is filtered off. To the well- 
 stirred hot filtrate, salt is slowly added till the sodium salt of m-nitrobenzenesulphonic 
 acid is as completely salted out as possible. About 200 parts of salt are required. 
 After stirring for several hours while cooling the mass is filtered and pressed so as to 
 expel acid liquors as much as possible. The press-cake contains, besides sodium 
 m-nitrobenzenesulphonate, a little of the isomeric sulphonates and some sodium 
 sulphate. 
 
 The nitrosulphonate is not usually dried or purified, but is reduced directly to 
 
 metanilic acid— 
 NH, 
 
 oe 
 eae 
 
 —long needles, soluble in water. 1 part dissolves in 68 parts of water at 15°. 
 
 The press-cake of nitrobenzenesulphonate obtained, as just described, is dissolved 
 up in the minimum quantity of boiling water, the solution stirred rapidly, and cast- 
 iron filings added gradually, while boiling is maintained till the reduction is complete. 
 This is ascertained by spotting the liquid on filter-paper, when a colourless rim should 
 be shown. About 130 parts of iron are required. The acid adhering to the press- 
 cake is sufficient for the reduction. The liquid is now neutralised with soda, and 
 boiling is continued until any dissolved iron compounds are decomposed and the iron 
 all precipitated as hydroxide. The liquid is filtered hot, the filtrate evaporated to 
 600 volatile parts, and hydrochloric acid added till the solution is acid to Congo paper. 
 On cooling, the metanilic acid crystallises out. 
 
 Owing to the comparative solubility of metanilic acid, a substantial amount 
 remains in solution, and for this reason the acid is not usually isolated, the solution 
 being used directly for the preparation of dyestufis. The yield is estimated by 
 diazotisation of a known volume of the solution with standard nitrite solution. It 
 amounts to about 90 per cent. of the theoretical. The result obtained by titration 
 with nitrite is, however, somewhat too high, since any sulphanilic and o-aminobenzene- 
 sulphonic acids present are also diazotised. It should be noted, too, that the presence 
 
24 INTERMEDIATES FOR DYESTUFFS 
 
 of these isomers may sometimes appreciably affect the shades of the dyestufis prepared 
 from the metanilic acid. 
 
 Metanilic acid is used as first component in azo dyes of the mono- and disazo 
 classes. 
 
 Sodium metanilate, when fused Sh caustic soda at high temperatures, yields 
 
 m-aminophenol— 
 NH, 
 
 Os 
 
 —white crystals, m.p. 122° to 123°, easily soluble in ether and alcohol, moderately 
 soluble in hot water (it readily forms supersaturated solutions), sparingly soluble in 
 benzene, and insoluble in ligroin. If pure it is stable in air. 
 
 The N-acetyl derivative, C,H,(OH)NHAc, melts at 148° to 149°. The hydro- 
 chloride forms prisms, m.p. 229°. 
 
 The method of preparation is described in G.P. 44792, as follows: 20 parts of 
 caustic soda are melted up with 4 parts of water, and the temperature raised to 270°. 
 10 parts of well-dried sodium metanilate are gradually added, and the temperature 
 of the melt is then maintained at 280° to 290° for one hour. The cold melt is dissolved 
 in water, the solution acidified with hydrochloric acid, and any resinous matter 
 filtered off. The filtrate is neutralised with sodium bicarbonate, which sets free 
 the aminophenol. This is then extracted with ether and isolated in the 
 usual way. 
 
 Another method of preparation of m-aminophenol, starting from resorcinol, is 
 described on p. 101. 
 
 m-Aminophenol is used mostly as a hair and fur dye, but has also been used 
 as second component in a monoazo dye. 
 
 4-Nitroaniline-3-sulphonic acid : 
 
 NH, 
 rs 
 L SO,H 
 No, 
 
 The acid crystallises in pale yellow needles, sparingly soluble in cold water, moderately 
 in hot water. 
 
 This substance is prepared by nitrating the acetyl derivative of metanilic acid 
 (Eger, Ber., 1888, 21, 2579). 
 
 Sediment metanilate is boiled with two molecular proportions of acetic anhydride, 
 and the resulting thick paste of the acetyl derivative is dissolved in five times its 
 weight of sulphuric acid. To the well-cooled solution, the calculated quantity of 
 nitric acid (D 1-385), dissolved in four times its weight of sulphuric acid, is slowly 
 added. The mixture is allowed to stand two to three hours. It is then poured on 
 ice, and the yellow nitrometanilic acid (hydrolysis has taken place), which separates 
 on standing, is filtered off. Itis recrystallised from water and dried at 120°. 
 
NITROBENZENE AND ITS DERIVATIVES 25 
 
 It is used in preparing nitro-m-phenylenediamine : 
 
 NH, 
 ot 
 on 
 
 No, 
 
 The preparation is carried out, according to G.P. 130438 (A.G.F.A.) by amidation 
 of 4-nitroaniline-3-sulphonic acid with ammonia. This is an unusual reaction in the 
 benzene series, though common in the anthraquinone series. 
 
 4-Nitroaniline-3-sulphonic acid is heated with four times its weight of 25 per cent. 
 ammonia in an autoclave at 170° to 180° for three hours. On cooling, most of the 
 nitrophenylenediamine crystallises out as yellowish-red prisms, m.p. 161°. It is 
 soluble also in alcohol and ether. 
 
 Nitro-m-phenylenediamine is used as an end component in azo dyes in conjunction 
 with benzidine and other diamines as first components, the resulting dyes being 
 bright yellow or orange in shade. 
 
 Reduction of Nitrobenzene. 
 
 Nitrobenzene (and aromatic nitro compounds generally) can be reduced by 
 stages, according to the conditions employed, to a series of different products, whose 
 relations are shown approximately in the following scheme : 
 
 ENG, Lamia Sie dS (8) peal oe 
 | 
 
 Wj 
 R.N—N.R 
 
 De 
 
 6 
 
 | 
 
 V 
 “ae =—— R.NENER 
 
 Vv 
 
 R.NH, 
 
 Whether the reduction will proceed wholly to the amino compound (in this case 
 aniline), or will stop at one of the intermediate stages, depends on at least two 
 factors—(1) the condition of the reaction medium as regards alkalinity or acidity, 
 (2) the temperature. The azoxy and azo stages are favoured by an alkaline 
 medium, the hydroxylamine stage by neutral conditions, and reduction to the 
 amino compound by acid conditions, though the acidity need only be slight, that 
 given by solutions of the salts of the heavier metals, such as iron and zinc, being 
 ‘sufficient. Of the various reduction products, the amino compounds are most 
 important from the dyestufis’ point of view, while the azo and hydrazo compounds 
 are also of importance in the present and a few other cases, because they are inter- 
 ‘mediary to the formation of benzidine and its derivatives. 
 
26 INTERMEDIATES FOR DYESTUFFS 
 
 The reduction of nitrobenzene to aniline will be dealt with first. 
 Aniline— 
 NH, 
 
 U 
 —a colourless oil turning brown in sunlight. Freezes at—6-24° C., b.p. 184-32° to 
 184-39° at 760 mm., D,? 1.0268, n‘? 1-5850. 
 The reduction of nitrobenzene to aniline is commonly carried out by means of 
 iron and hydrochloric acid or ferrous chloride. Details with regard to plant used, 
 etc., are given in “ Aniline and its Derivatives,” by P. H. Groggins, and in the 
 
 Chemical Trade Journal, 1906, 38, 59. 
 The quantity of acid required is much less than that indicated by the equation : 
 
 C.H,NO, + 3Fe + 6HCl = C,H,.NH, + 3FeCl, + 2H,0 
 
 In practice only about 3 per cent. of the hydrochloric acid indicated by the equation 
 is used, and the end product, apart from the aniline, is chiefly magnetic iron oxide, 
 Fe,O,. Several theories have been proposed to explain the mechanism of this reaction. 
 The facts appear to be that before the reduction commences ferrous chloride is formed 
 by reaction between the iron and the acid, that at the beginning of the reduction some 
 ferric hydroxide can be observed, and that at the end almost all the iron is in the form 
 of the oxide Fe,O,. The formation of the ferric hydroxide possibly takes place thus— 
 
 C,H;NO, + 2Fe + 4H,0 = C,H,.NH, + 2Fe(OH), 
 
 —this reaction being accelerated by the ferrous chloride present. How the ferric 
 hydroxide is converted to the oxide Fe,O, is not known. However, the reaction, as a 
 whole, may be considered as following the equation : 
 
 40,H,.NO, + 9Fe + 4,0 gpeaipro> 40sHsNH, + 3Fe0, 
 
 The reduction is carried out in a cast-iron vessel fitted with a stirrer and a reflux 
 condenser, arrangements being made for the gradual addition of nitrobenzene and 
 iron borings. These borings must be of cast-iron (steel being useless for this purpose), 
 and they are previously ground in a disintegrator. | 
 
 For the reduction of 100 parts of nitrobenzene the reducing vessel is first charged 
 with about 110 parts of iron borings (this being about a tenth of the total amount of 
 iron to be used), 120 parts of 30 per cent. hydrochloric acid, and 60 parts of water. 
 The mixture is stirred and heated to the boil (usually by passing in steam through the 
 stirrer, which is made hollow for the purpose). This preliminary operation is spoken 
 of as “‘ etching ”’ the iron by the acid—that 1s, the iron is supposed to be brought into 
 a more active condition suitable for initiating the reduction. A more rational view is 
 that in this operation there is formed the ferrous chloride required for catalysis 
 of the reaction between the nitrobenzene, iron and water. 
 
 The nitrobenzene is now run in, accompanied by the main quantity of iron borings 
 
NITROBENZENE AND ITS DERIVATIVES 27 
 
 in small quantities, at such a rate that the reaction proceeds steadily, as observed by 
 the rate of refluxing of the mixture of nitrobenzene, aniline, and water. As the 
 reaction is strongly exothermic, external heating is unnecessary, on the large scale at 
 any rate, and, in fact, the addition of nitrobenzene and iron may require slowing 
 off at times owing to the violence of the reaction. Too violent a reaction leads to 
 over-reduction of the nitrobenzene with production of benzene. After all the iron 
 and nitrobenzene have been added, external heating is recommenced in degree 
 sufficient to keep the mixture refluxing until the reduction is completed. This is 
 recognised by the condensate, which is at first orange, then yellow, becoming water- 
 white in colour. 
 
 The contents of the reducing vessel now are aniline, water containing some ferrous 
 chloride in solution, and iron oxide, this last being in the form of a fine black powder. 
 The separation of the aniline is most simply and easily done by steam distillation, 
 the weight of steam required being about six times the weight of the aniline. The 
 distillate separates into a lower layer of aniline, containing about 5 per cent. of water 
 in solution (together with any benzene formed in the reduction or contained in the 
 original nitrobenzene), and an upper layer consisting of a 3 per cent. solution of aniline 
 in water. The upper layer is run off, and the aniline layer is distilled under reduced 
 pressure. The first fraction contains water, benzene, and some aniline, and this is 
 returned to the steam distillation receivers for separation of the aniline. The 
 remainder of the distillate is pure aniline. 
 
 In the regular working of the above process, the aqueous layer of the steam dis- 
 tillate is used, partly to supply the water for charging the reducing vessel at the 
 beginning of the reduction, and partly, by boiling in a separate boiler, to supply the 
 steam required for the succeeding steam distillation. The quantity of aniline con- 
 tained in this water is, therefore, kept in circulation in the process, and on a normal 
 run with this arrangement the whole of the aniline produced by the reduction of the 
 charge of nitrobenzene can be isolated. The yield of aniline from 100 parts of nitro- 
 benzene is 71-5 to 72 parts or about 95 per cent. of the theoretical. 
 
 Modifications of the Ordinary Process. 
 
 Economic considerations have led to various suggested modifications of the 
 above process with regard to the separation of the aniline from the reaction mixture. 
 These modifications have in view the reduction or elimination of the cost of dealing 
 with the relatively large quantities of water required by the steam distillation. 
 
 (a) The contents of the reducing vessel may be distilled directly under reduced 
 pressure. 
 
 (6) The iron oxide may be filtered off, the aniline and water separated, and the 
 aniline distilled. 
 
 (c) Ordinary steam from the boiler plant may be used entirely for the steam dis- 
 tillation, and most of the aniline recovered from the aqueous layer by a double 
 extraction with the nitrobenzene, which is afterwards to be reduced (G.P. 282531). 
 The water containing any residual aniline is run to waste. 
 
28 INTERMEDIATES FOR DYESTUFFS 
 
 Which, if any, of the above modifications is worth adoption is a matter of com- 
 parative costs, and need not be further dealt with here. These points are fully 
 considered in “ Aniline and its Derivatives,” by P. H. Groggins, pp. 35-57. 
 
 Alternative Processes. 
 
 (a) A large number of patents have been taken out for the reduction of nitro- 
 benzene in the form of vapour by metallic catalysts. Nickel, copper, iron, cobalt, 
 platinum, silver, and gold have all been proposed, generally at temperatures of 
 over 200°.* 
 
 G.P. 282492 (Meister Lucius and Briining) is exceptional in claiming to accom- 
 plish the reduction at 120° with finely divided nickel. Steam and hydrogen are 
 passed through nitrobenzene, and the mixed vapours led through a tube containing 
 the nickel contact mass at 120°, the passage of the vapours being regulated so that 
 no nitrobenzene escapes reduction. The yield is said to be quantitative. If these 
 claims can be sustained, the process seems to be a very convenient one, with the 
 great advantage over the usual process of being continuous. 
 
 (6) The amidation of chlorobenzene by ammonia has been attempted, but without 
 success. Apparently Ullmann’s discovery of the activating effect of copper and 
 its salts on the replacement of halogen by the amino group suggested the application 
 of the method to this case. G.P. 204951 claims an 80 per cent. yield of aniline from 
 chlorobenzene by heating with ammonia and copper sulphate in an autoclave at 
 180° to 200° for twenty hours. This claim has been examined by Quick (J. Am. Chem. 
 Soc., 1920, 42, 1033), who was only able to obtain a maximum yield of 39 per cent. 
 of aniline. 
 
 The applications of aniline to the preparation of other intermediates are dealt with 
 in Chap. III. Its direct applications as a dyestuff intermediate are numerous and 
 varied. 
 
 (i.) It is used as a first component in mono-, dis-, and trisazo dyes, but never as an 
 end component, owing to difficulty in coupling and to its tendency to form diazo- 
 amino compounds which do not readily transform. 
 
 (ii.) Triphenylmethane dyes of the Pararosaniline or Magenta type are made 
 from aniline by an empirical method in which aniline and p-toluidine (to supply 
 the “methane carbon’’) are heated with an oxidising agent. Aniline is further 
 used to phenylate the amino groups in Pararosaniline, and thus form the Aniline 
 Blues. 
 
 (i1.) Many dyes of the azine class, such as Safranine, are obtained by oxidising 
 mixtures of aniline with various para-diamines. An empirical condensation of aniline 
 with aminoazobenzene yields the Indulines, dyestuffs also of the azine class. Oxida- 
 tion of aniline with nitrobenzene or nitrophenol produces the Nigrosines, and oxidation 
 of aniline hydrochloride on the fibre forms Aniline Black. 
 
 * See G.P. 139457 (F.P. 312615); E.P. 13149 and 15334 of 1914; E.P. 5692 and 6409 of 1915 (G.P. 
 282568; U.S.P. 1207802); E.P. 16936 and 22523 of 1913 (F.P. 458033; U.S.P. 1247629); G.P. 282492; 
 
 F.P. 462006; G.P. 281100; G.P. 263396; cf. also Brown and Henke, Journ. Phys. Chem., 1922, 
 26, 161. . 
 
 , eo ee a ao 
 
NITROBENZENE AND ITS DERIVATIVES 29 
 
 (iv.) Aniline is also used in making acid wool dyes of the anthraquinone series, by 
 condensing it with chloro- or hydroxy-anthraquinones. By elimination of HCl or 
 H,0, phenylaminoanthraquinones are formed, and on sulphonating these (the sulpho 
 group entering the phenyl nucleus), the acid dyes are produced. 
 
 The various products of alkaline reduction of nitrobenzene owe their technical 
 interest to the fact that they are stages in the preparation of hydrazobenzene, which, 
 by the action of aqueous acid solutions, is transformed by intramolecular change into 
 benzidine— 
 
 C,H,.NH.NH.C,H, ———> H,N.C,H,—C,H,-HN, 
 
 Benzidine— 
 
 Cee 
 HNC > NH, 
 
 —crystallises in leaflets from water, m.p. 127-5 to 128°, b.p. 249 400° to 401°. Its 
 solubility in water at 12° is 1 part in 2,447, but in boiling water 1 part in 106-5. Itis 
 easily soluble in alcohol. 
 
 Sulphate, C,,.H,.N,.H,SO,, forms small glittering scales, almost insoluble in 
 boiling water and in alcohol. 
 
 Hydrochloride, C,,H,.N,.2HCl, forms leaflets, easily soluble in water, but pre- 
 cipitated from solution by concentrated hydrochloric acid. On boiling a solution of 
 the dihydrochloride, the monohydrochloride is formed as sparingly soluble needles. 
 
 The monoacetyl derivative melts at 198°, the diacetyl at 317°. 
 
 It will be most convenient to deal with the preparation of benzidine in two 
 stages, of which the first is concerned with the formation of hydrazobenzene, and 
 the second with its transformation to benzidine. 
 
 (a) Hydrazobenzene. The older process, as described by Schultz (‘‘ Chemie des 
 Steinkohlenteers,” 1900, I., p. 93), carries out the reduction to the hydrazo com- 
 pound in one operation by means of zinc dust and alcoholic caustic soda. A mixture 
 of 100 kg. of nitrobenzene and 50 kg. of alcohol is heated under a reflux condenser 
 and to the boiling liquid 150 to 160 kg. of zine dust are added, followed by slow 
 addition over three or four hours of a mixture of 100 kg. of alcohol and 13 kg. of 
 caustic soda solution (36° Bé). Boiling is continued until a test portion is found to 
 be light grey in colour. If this point is not reached within half an hour after all 
 the caustic soda has been added, 20 kg. of water are added and boiling continued, 
 more zinc dust being added, if necessary, to complete the reduction. The alcohol 
 is then distilled off with steam. The residual mixture contains crystalline hydrazo- 
 benzene, zinc hydroxide, sodium zincate, and unchanged zinc. It is transferred to 
 a fine sieve, on which the hydrazobenzene is retained, the remaining solids passing 
 through. It is well washed with water. The hydrazobenzene may also be freed 
 from zinc, etc., by diluting the mixture and cooling to 10° to 15° by ice, followed 
 by careful addition of just sufficient cold hydrochloric acid to dissolve out the zine. 
 The moist hydrazobenzene is used directly for the transformation to benzidine. 
 
 This process works well, and may be made to give an almost quantitative yield of 
 
30 INTERMEDIATES FOR DYESTUFFS 
 
 hydrazobenzene, but it has been displaced by processes in which the comparatively 
 expensive alcohol and zinc dust are dispensed with. Nitrobenzene may be reduced 
 to hydrazobenzene by cast-iron borings and aqueous caustic soda, as described in 
 G.P. 138496 (Weiler-ter-Meer). The quantity of iron required bears no calculable 
 relation to that suggested by any theory of the reaction, since the reduction is a 
 surface effect. For this reason the iron must be ground as fine as possible. Oil and 
 grease must be removed, and the iron is also previously etched by heating with con- 
 centrated caustic soda. 
 
 According to the patent just mentioned, reduction with iron and caustic soda has 
 also the advantage of proceeding by definite stages— 
 
 > azoxybenzene > azobenzene > hydrazobenzene 
 
 Nitrobenzene 
 
 —at any one of which the reaction may be stopped, by use of the appropriate quantity 
 of iron and caustic soda, and the product extracted by stirring with a hydrocarbon 
 solvent, such as benzene, from which it is easily recovered. The reduction by stages 
 is effected as follows : 100 kg. of nitrobenzene and 750 kg. of iron borings are stirred 
 together and warmed to about 90°, when 800 ke. of 60 per cent. caustic soda is added 
 gradually and the temperature maintained at 100° to 120°. Very powerful stirring 
 apparatus is, of course, required with such a thick, heavy mixture. The course of 
 the reaction may be observed by the change of colour and by disappearance of the 
 smell of nitrobenzene, but a more exact indication may be obtained in large scale 
 working by observation of the setting-points of samples withdrawn at intervals. 
 Thus, nitrobenzene has a setting-point of 5°. As the reduction proceeds, this falls to 
 a minimum of — 13°, corresponding to a 40 per cent. conversion to the azoxy compound. 
 The setting-piont then rises to a maximum of 31°, at which point, if the smell of 
 nitrobenzene has disappeared, formation of azoxybenzene is complete. Reduction 
 may now be continued as far as the azo compound by adding 250 kg. of iron and 
 300 kg. of 60 per cent. caustic soda and stirring further at the same temperature as 
 before. The setting-point sinks again to 25°, then rises to 63°, when reduction to 
 azobenzene is finished. Addition of another 250 kg. of iron and 300 kg. of caustic 
 soda solution, with continued heating and stirring, carry the reduction on to the 
 hydrazobenzene as indicated by the setting-point which, after falling to 55°, finally 
 rises to 122° to 125°. Towards the end the temperature must either be raised to 
 130°, or a solvent added in order to prevent the mass from solidifying. This last stage 
 is the most difficult to carry through satisfactorily, partly owing to the tendency for 
 the reduction to proceed too far and form aniline (this can be minimised by lowering 
 the temperature to 80° and adding benzene as solvent for the hydrazobenzene), and 
 partly to the tendency towards formation of inseparable emulsions. The quantities 
 of iron given are, of course, only rough approximations, the actual quantities required 
 depending on the fineness of division. 
 
 Fierz-David (“ Farbenchemie,” 1920, p. 72) prefers, as a laboratory method, to 
 carry the reduction by means of iron and caustic soda only as far as azobenzene, 
 which is then isolated by extraction with benzene and evaporation of the benzene 
 solution. Reduction to hydrazobenzene is then carried out in alcohol with zine dust 
 
NITROBENZENE AND ITS DERIVATIVES 31 
 
 and 30 per cent. caustic soda at 60° or under. On filtering (and boiling out the zine 
 residues with some fresh 90 per cent. alcohol), the filtrate separates into two layers of 
 which the lower contains aqueous sodium zincate, while the upper is an alcoholic 
 solution of hydrazobenzene. This layer is separated, saturated with carbon dioxide 
 to precipitate alkali, and the filtered solution evaporated to obtain the hydrazobenzene, 
 of which a quantitative yield is obtained. 
 
 In K.P. 203059 (Murdoch and Galbraith), the use of sodium amalgam is proposed 
 for the reduction of nitro compounds to hydrazo compounds. A suitable amalgam 
 is that obtained from the cathode chamber of a Castner-Kellner cell in which brine 
 is electrolysed. The nitro compound, mixed with water containing a water-miscible 
 solvent for the nitro body, such as pyridine, is brought into effective contact with the 
 amalgam, either by allowing the solution to flow in a thin film over the amalgam or 
 by dropping the amalgam through the well-stirred solution, the spent amalgam being 
 drawn off continuously through a U-tube at the bottom of the vessel. 
 
 (6) The transformation of hydrazobenzene to benzidine has been studied by 
 Holleman and van Loon (Proc. K. Akad. Wet., Amsterdam, 1903, 6, 262), and by 
 van Loon (Rec. trav. chim., 1904, 28, 62), who find that the amount of benzidine 
 obtained is independent of the nature of the acid used, that it diminishes as the 
 temperature is raised, and that it increases at first with increasing concentration of 
 acid, but decreases above a certain acid concentration. 
 
 A small proportion of the o-p-diamino compound, diphenylme— 
 
 —is always formed, together with traces of aniline. The optimum conditions of 
 transformation yield about 85 per cent. of benzidine and 10 to 15 per cent. of di- 
 phenyline. In practice hydrochloric acid is used for the transformation, and this 
 should be free from sulphuric acid since benzidine sulphate is insoluble, and it is 
 advantageous to dissolve the benzidine completely when formed in order to free it 
 from insoluble impurities carried by the hydrazobenzene. 
 
 The moist hydrazobenzene obtained by any of the methods previously described 
 is added gradually to a quantity of 30 per cent. hydrochloric acid (1-2 molecules), 
 sufficient to ensure a definitely acid solution at the end of the reaction. During the 
 addition the temperature is kept down by addition of ice. After stirring for several 
 hours in the cold to complete the change, the mass is heated to 80° to bring all the 
 benzidine and diphenyline into solution, any insoluble matter is filtered off, and the 
 benzidine precipitated as sulphate by adding sulphuric acid or sodium sulphate or 
 bisulphate. The sulphate of diphenyline is soluble. The benzidine sulphate is 
 filtered off and washed thoroughly with water containing a little sulphuric acid. 
 Without drying, the sulphate is then stirred up with water and soda solution added 
 till alkaline, the benzidine base being then filtered off, washed and dried. Itis finally 
 _ purified by vacuum distillation. 
 
 Benzidine is used as a first component in the preparation of azo dyestufis. Its 
 
32 INTERMEDIATES FOR DYESTUFFS 
 
 tetrazo compound couples readily with amines and phenols, yielding azo compounds 
 which are substantive colours for cotton, a property which constitutes the great value 
 of benzidine as an intermediate. This property of yielding direct cotton colours 
 apparently depends, in part at least, on the fact that the amino groups are both in the 
 para position to the dipheny] linkage, since diphenyline does not possess the property. 
 
 Several substitution products of benzidine are made with a view to modifying the 
 shade or solubility of the azo colours derived from them. But it is found that in 
 some cases the affinity of the dyes for cotton is also considerably affected. Generally 
 substitution in the ortho positions to the amino groups leaves the affinity for cotton of 
 the derived dyes unchanged or even increases it somewhat. This applies to benzidine- 
 3 : 3’-disulphonic acid, 3 : 3°-dichlorobenzidine, 3 : 3’-dinitrobenzidine, o-tolidine, and 
 dianisidine (the last two, however, are not prepared from benzidine, but from the 
 corresponding nitrobenzene derivatives, and will be dealt with later). On the other 
 hand, in benzidine-2 : 2’-disulphonic acid, the affinity of the derived dyes for cotton 
 is much diminished, and in 2 : 2’-dinitrobenzidine, it has entirely disappeared. The 
 dyes derived from these meta-substituted benzidines, however, dye wool. The sub- 
 stantive property is restored if the meta- substituents form a new ring, as in benzidine 
 sulphone and in diaminocarbazole : 
 
 HNC Cae NC Cis as 
 NC »- NH, HN > NH, 
 Pe 7 oe 
 
 NH 
 Benzidine sulphone Diaminocarbazole 
 
 Benzidinesulphonic Acids. 
 
 These are prepared by the action of concentrated sulphuric acid and oleum on 
 benzidine at high temperatures, but it is rather difficult to obtain individual products. 
 Benzidine-3-sulphonic acid : 
 
 ARDS attics 
 Halas eee 
 
 The acid is very sparingly soluble even in boiling water, and almost insoluble in 
 alcohol and ether. It forms a hydrochloride. 
 
 This acid is best prepared by the bake process, as described in G.P. 44779 
 (Ber., 22, 2461). Benzidine sulphate is stirred with 14 molecular proportions of H,SO, 
 as dilute acid and the mixture evaporated to dryness. The powdered substance is 
 spread on enamelled trays and heated in an air-oven at 170° for twenty-four hours. 
 The black mass so obtained is ground up, extracted with dilute alkali, and filtered. 
 The filtrate is made just acid with acetic acid which precipitates the monosulphonic 
 acid, but leaves any disulphonic acid in solution as sodium salt. 
 
 Benzidine-3 : 3’-disulphonic acid : 
 
 eo. 
 
 re ee ee ee ee 
 
NITROBENZENE AND ITS DERIVATIVES 33 
 
 The acid forms small white leaflets without water of crystallisation. It is almost 
 insoluble in water. 
 
 One part of benzidine sulphate is heated with 2 parts of concentrated sulphuric acid 
 at 210° for thirty-six to forty-eight hours. The product is diluted with water, the 
 solution made alkaline and filtered. Any monosulphonic acid present is first preci- 
 pitated by addition of acetic acid and is filtered off. On making the filtrate mineral- 
 acid, the disulphonic acid is precipitated. The yield is given as 90 per cent. 
 (Ber., 14, 300; 22, 2463; G.P. 44779). 
 
 Benzidine sulphone— 
 
 nn 
 8 
 SO, 
 —forms fine bright yellow leaflets, almost insoluble even in boiling water and alcohol. 
 Its salts are dissociated by water. 
 
 Formation of the sulphone is favoured by use of oleum. The preparation 
 is described in G.P. 33088 (Ber., 22, 2467). Benzidine sulphate is added to 
 excess of 20 per cent. oleum and the mixture is warmed on the water-bath until 
 benzidine can no longer be detected in a test portion. The cooled solution is then 
 poured on ice, allowed to stand twelve hours, and the benzidine sulphone sulphate 
 (C,,H,oN..SO,.H,SO,+13H,0, is filtered off. Some unchanged benzidine sulphate 
 is always present. The salt is decomposed by hot dilute caustic soda solution, and 
 the precipitated sulphone is extracted with alcohol. It is then further purified by 
 conversion to the hydrochloride. 
 
 Benzidine sulphone disulphonic acid : 
 
 HO,S SO,H 
 HNC an NH 
 ot 
 80, 
 
 The acid crystallises in pale yellow prisms with $H,O. It is moderately soluble in 
 _ hot water if this is acid-free, but the addition of mineral acid renders it practically 
 insoluble. Its sodium salt crystallises in yellow needles, which are sparingly soluble 
 in cold water, but easily soluble in hot. 
 
 It may be prepared directly from benzidine without isolation of the sulphone 
 (Ber., 22, 2469; G.P. 27954). One part of benzidine is heated with 4 parts of 40 per cent. 
 oleum for some time at 100° in order to form the sulphone. The solution is then raised 
 to 150°, and kept at this temperature until a test portion on dilution and addition of 
 alkali no longer precipitates sulphone. The solution is then poured on ice, when the 
 disulphonic acid is precipitated along with some monosulphonic acid and a little 
 unchanged sulphone, while any tri- and tetrasulphonic acids remain dissolved. The 
 precipitate is filtered off, then dissolved in dilute caustic soda solution, filtered, and 
 the monosulphonic acid precipitated by making acid with acetic acid. This is filtered 
 off and the disulphonic acid is now separated by addition of hydrochloric or sulphuric 
 
 acid. The yield is 80 per cent. 
 3 
 
34 INTERMEDIATES FOR DYESTUFFS 
 
 The azo dyes from this intermediate are substantive to cotton and also dye wool. 
 The dyeings on wool are specially fast to milling. 
 
 3 : 3’-Dichlorobenzidine— 
 axe ao (Sw, 
 
 —crystallises in needles, m.p. 133°, almost insoluble in water, but soluble in alcohol, 
 benzene, and glacial acetic acid. Its hydrochloride, C,,H,)N,Cl,.HCI, crystallises 
 from alcohol in needles, and is precipitated from its aqueous solutions by strong 
 hydrochloric acid. The sulphate, nitrate, and oxalate are very sparingly soluble, 
 even in boiling water. 
 
 The preparation from benzidine is described in G.P. 94410 (Levinstein). Benzidine 
 is first converted into the diacetyl derivative by boiling with glacial acetic acid in the 
 usual way. 26-8kg. of diacetylbenzidine are dissolved in two to three times its weight 
 of 90 per cent. sulphuric acid and the solution poured into ice water, the object being 
 to obtain as fine a suspension of the substance as possible. The suspension is cooled to 
 0°, stirred and sufficient 10 per cent. bleach or hypochlorite solution to give 4 mole- 
 cular proportions of active chlorine is slowly run in. An intense green colouration 
 appears at first, but this vanishes later and towards the end the dichlorodiacety] 
 compound has completely separated as a crystalline yellow precipitate. The mass is 
 then warmed to 40° and filtered. The product is hydrolysed by boiling with four times 
 its weight of 20 per cent. hydrochloric acid under reflux for three hours, or, at any 
 rate, until a test portion dissolves completely in dilute hydrochloric acid. The solu- 
 tion is then diluted with water, and either the hydrochloride is salted out or the base 
 is set free by addition of alkali. 
 
 Dichlorobenzidine yields azo dyes of bluer shades than those obtained from benzi- 
 dine. The fastness to acids is also much improved. 
 
 2-Nitrobenzidine— 
 
 NO, 
 nx >< 
 —crystallises in long red needles, m.p. 143°. The sulphate, C,,H,,0,N,.H,SO, +3H,O 
 is sparingly soluble in cold water, but is much more soluble than benzidine 
 sulphate. 
 
 This nitrobenzidine is prepared by nitrating benzidine in solution in a large excess 
 of concentrated sulphuric acid, which protects the amino groups, and at the same time 
 directs the nitro group into the meta position to an amino group. 
 
 28-2 parts of benzidine sulphate are stirred into 300 parts of sulphuric acid and 
 the mixture warmed at 50° to 60° until a clear solution is formed. The solution is 
 cooled to 10° to 20° and 10-1 parts of potassium nitrate (nitric acid may also be used) 
 gradually added. Stirring is continued for several hours, and the solution then 
 poured into three times its weight of water. On cooling, nitrobenzidine sulphate 
 crystallises out (Tauber, Ber., 28, 796; E.P. 13475 of 1892). 
 
 As previously explained (p. 32), substitution of benzidine in the 2-positions by 
 
NITROBENZENE AND ITS DERIVATIVES 35 
 
 negative groups diminishes considerably the affinity of the derived azo dyes for 
 cotton. This is the case with 2-nitrobenzidine, but fast wool dyes can be obtained 
 from it, notably Anthracene Red, which is made by coupling diazotised nitro- 
 benzidine with salicylic acid and then with NW-acid. The nitro group has a 
 strong reddening effect on the shade, since the dye obtained from benzidine with 
 the same two second components is brown in colour, while Anthracene Red is 
 scarlet. 
 
 3 : 3’-Dinitrobenzidine, which can be made by nitrating diacetylbenzidine, is not 
 used as a dyestuff intermediate. 
 
CHAPTER III 
 ANILINE AND ITS DERIVATIVES 
 
 THE preparation of aniline has already been described (p. 26), and this chapter 
 will be concerned with the intermediates derived from it. 
 
 Acetanilide— NH.CO.CH, 
 
 —white crystals, m.p. 112°, b.p. 304°. Very sparingly soluble in cold water, but 
 rather more soluble in boiling water. 
 
 If aniline is boiled with one molecular proportion of glacial acetic acid, equilibrium 
 is reached before the aniline acetate has been completely converted to acetanilide, 
 since the water set free as the reaction proceeds dilutes the remaining acetic acid 
 sufficiently to stop acetylation. The reaction can be pushed further towards comple- 
 tion by using an excess of acetic acid, but even then is not complete. If, however, the 
 water formed is driven off, complete acetylation is obtained. Since the water cannot 
 be driven off without carrying some acetic acid with it, the usual practice is to add 
 such an excess of acetic acid (about 50 per cent. excess) that sufficient will be left, when 
 all the water is driven off, to acetylate the aniline completely. 
 
 93 parts of pure aniline and 93 parts of glacial acetic acid (98 per cent. or over) are 
 heated together in a vessel fitted with a reflux condenser. On the large scale the 
 apparatus used is made of aluminium, which withstands the action of acetic acid very 
 well, while iron and copper are too easily acted on. The temperature of the solution 
 is kept at 110° for the first ten hours, then at 120° to 130° for a further ten hours, and 
 finally at 140° to 150° for six hours. The water and excess acetic acid are then slowly 
 distilled off, while the temperature of the melt is raised until, when the last of the 
 water and acetic acid are passing over, it reaches about 240°. The melt is then run 
 off into about 930 parts of water at 50° to 60°, which is being vigorously stirred. 
 On cooling, the acetanilide is obtained mostly in granular form, the remainder having 
 crystallised from solution in the water. The acetanilide is filtered off, dried, and 
 powdered. The melting-point of the product is 110° to 111°, and the yield about 
 132 parts or 98 per cent. It can be purified by recrystallisation from a large volume 
 of boiling water, but the crude product is sufficiently pure for its chief application— 
 namely, its conversion to p-nitroaniline. 
 
 p-Nitroaniline— 
 
 —crystallises in yellow prisms, m.p. 148-3°, D 1-424. It is not volatile in steam. 
 1 part dissolves in 1,298 parts of water at 20°, and in 45 parts of water at 100°. 100 gms. 
 of alcohol dissolve 5-84 gms, at 20°. 
 
 36 
 
‘SHAILVATHUd SLI GNV ANITINV—II LYVHO 
 FHOINC _>(HO)JHOK_ > N*(®HO) AG 
 
 *(FHO)N 
 j a 
 
 £ 
 *(*HONC _>09K_>N*2HO) (HONK PHO >N*(FHO) 5 a g 
 
 Ho 
 eee abe ore 6 0 
 ASHEN §— SyZqQ)y- SHO(MH40)N "HN suo H°0s 
 H®os H®os ) 
 N 4 
 
38 INTERMEDIATES FOR DYESTUFFS 
 
 Aniline cannot be nitrated in the ordinary way, since oxidation products are largely 
 formed due to the amino group being attacked. The amino group can be protected 
 by dissolving the aniline in a large excess of concentrated sulphuric acid, but nitration 
 in this case produces about 50 per cent. of m-nitroaniline together with substantial 
 proportions of the o- and p-compounds. This method, therefore, is of little use for 
 the preparation of any of the nitroanilines, though it has been successfully used for 
 some of the nitrotoluidines (p. 118), where the predominance of one isomer is much 
 greater. 
 
 If the amino group is protected by acylation or by condensation with an aldehyde 
 to form a Schiff’s base, nitration can then be carried out in normal fashion and the 
 nitroaniline obtained from the nitration product by hydrolysing off the acyl or 
 aldehyde group. Protection of the amino group is not the only advantage of this 
 method. The nitration can be so carried out that either the para- or the ortho- 
 nitroaniline is the main product, metanitroaniline being formed only in traces. Thus, 
 if acetanilide, C,H;.NH.CO.CHs, or benzylideneaniline, C,H;N : CH.C,H;, is nitrated 
 in sulphuric acid solution at low temperatures, about 90 per cent. of the product 
 is the para compound, the remainder being mostly the ortho compound. The 
 usual method is to nitrate acetanilide. 
 
 (a) p-Nitroacetanilide. 
 
 The acetanilide, prepared as described above (132 parts), is added slowly to 530 
 parts of concentrated sulphuric acid, which is stirred in an iron vessel cooled externally. 
 The temperature of the solution is kept below 30° in order to avoid hydrolysis of the 
 acetanilide. When this is completely dissolved, the solution is cooled to 0° and 200 
 parts of mixed acid, composed of— 
 
 HNO, .. As ae Sve oa a .. 31 per cent. 
 H,S0, ee ee ee ee ee ee ee 4 99 
 fh baa Ay aie se a - om te Pe 
 
 —is added slowly, so that the temperature does not rise above 3°. By nitrating at 
 this low temperature, the proportion of o-nitroaniline formed is reduced to the 
 minimum. After the mixed acid has all been added, stirring is continued till the 
 nitration is ended. This is recognised by precipitating a test portion in water and 
 boiling the precipitate with dilute caustic soda, which hydrolyses the acetyl com- 
 pounds, thus forming aniline from any unchanged acetanilide. Several hours are 
 required to complete the nitration. When finished, the solution is poured on to a 
 well-stirred mixture of 800 parts of ice and 1,600 parts of water. The nitroacetani- 
 lides are precipitated and, after an hour, filtered off and washed well with water. 
 In order to separate the o-nitro compound from the p-, advantage is taken of the lower 
 basicity of o-nitroaniline, which results in o-nitroacetanilide being much more easily 
 hydrolysed than the p- isomer. The precipitate is stirred up with about 700 parts of 
 water, made distinctly alkaline to litmus with caustic soda, and the mixture heated to 
 boiling, when o-nitroacetanilide is quickly hydrolysed. The o-nitroaniline formed 
 
ANILINE AND ITS DERIVATIVES 39 
 
 dissolves in the alkaline water to a yellow solution. After cooling to 50°, the p-nitro- 
 acetanilide is filtered off, washed alkali-free, and dried. The yield is 160 parts or 
 about 90 per cent. 
 
 (6) p-Nitroaniline. 
 
 The p-nitroacetanilide is now boiled under a reflux condenser with 400 parts of 
 water and about 120 parts of 35 per cent. caustic soda solution until a test portion 
 dissolves to a clear solution in hydrochloric acid, showing hydrolysis to be complete. 
 This requires several hours’ boiling. It should be kept in mind that the vapours of 
 the nitroanilines are poisonous. The quantity of caustic soda taken is such that the 
 solution is only faintly alkaline at the end of the hydrolysis. The solution is now 
 cooled and the p-nitroaniline, which has separated as yellow crystals, is filtered off, 
 washed, and dried. 
 
 The yield of p-nitroaniline is about 100 parts (from 93 parts of aniline), an overall 
 yield on the aniline used of about 73 per cent. 
 
 A detailed description of this process is given by P. Muller (Chem. Zig., 1912, 24, 
 1055). 
 
 Another process for the preparation of p-nitroaniline which seems very simple and 
 convenient is that of the Bayer patent, G.P. 72173, in which benzylideneaniline is 
 nitrated : 
 
 NH, N:CH.C,H, N:CH.C,H, 
 OHC.C,H, 7 
 + Fea ——> | 
 eA Or he 
 No, 
 NH, 
 ——_> f ) + O,H,.CHO 
 \ 
 No, 
 
 The Schifi’s bases formed by condensation of aldehydes with primary amines— 
 R.NH, + OHC.R’ ———> R.N:CH.R’ + H,O 
 
 —with elimination of water, are very sensitive to dilute mineral acids, being almost 
 immediately hydrolysed by them to the original amine and aldehyde. But they are 
 stable in concentrated sulphuric acid of 80 per cent. strength or over. On nitration 
 benzylideneaniline is said to give almost exclusively the para-nitro derivative. 
 Benzylideneaniline is prepared simply by mixing equimolecular proportions of 
 benzaldehyde and aniline and warming the mixture for a short time. The water 
 formed rises to the surface and isrun off. 18-1 kg. of benzylideneaniline is run slowly 
 with stirring into 70 kg. of 95 per cent. sulphuric acid. The temperature may be 
 allowed to rise to 50°. The solution is then cooled to 5° and nitrated with a mixture 
 of 10-8 kg. of 62 per cent. nitric acid and 10-8 kg. of concentrated sulphuric acid. 
 The temperature during nitration is kept between 5° and 10°. When the nitration is 
 ended an equal volume of water is added to the mixture, and the dilution, together 
 
40 INTERMEDIATES FOR DYESTUFFS 
 
 with the heat produced by it, hydrolyses the p-nitrobenzylideneaniline to p-nitroaniline 
 and benzaldehyde. The latter is then distilled off with steam, nearly all the benzalde- 
 hyde being recovered and used again. On cooling the residual liquid and diluting 
 further with water, the p-nitroaniline separates. The separation can be completed by 
 nearly neutralising the acid. The p-nitroaniline so obtained is claimed to be pure. On 
 crystallising from alcohol, all the fractions obtained show the same melting-point of 
 148°. The yield is over 90 per cent. 
 A third process for the preparation of p-nitroaniline is described on p. 8. 
 p-Nitroaniline is used as a first component in azo dyes. In some cases, after 
 coupling diazotised p-nitroaniline with a second component, the nitro group is 
 reduced by means of sodium sulphide, which does not affect the azo group. The 
 aminoazo compound thus formed is then, either diazotised and coupled with a third 
 component, or phosgenated to give a diphenylurea derivative : 
 7R.N:N.C,H,.N,Cl 
 R.N:N.C,H,.NO, ———> B.N:N.C,H,.NHC 
 ARB.N:N.C,H,.NH 
 O 
 R.N:N.C,H,.NH 
 
 p-Nitroacetanilide can be reduced to p-aminoacetanilide : 
 
 NH.CO.CH, 
 
 NH, 
 
 It crystallises in colourless needles when pure, but these soon turn brown. M.p. 
 162° to 162-5°.  Itis sparingly soluble in cold and moderately in hot water, but easily 
 soluble in alcohol and ether. It gives stable well-crystallised salts with mineral acids. 
 
 The reduction by the ordinary method is apt to be accompanied by some hydrolysis 
 yielding a product containing some p-phenylenediamine, but this can be avoided by 
 using acetic acid instead of hydrochloric acid and taking about 2 per cent. of the 
 theoretical quantity (see Reduction of Nitrobenzene, p. 26), so that the reduction is 
 carried out under practically neutral conditions (Nietzki, Ber., 17, 343). 
 
 The nitroacetanilide (about 160 parts), prepared from 93 parts of aniline, is added 
 slowly to a boiling mixture of 250 parts of cast-iron borings, 500 parts of water, and 
 15 parts of 40 per cent. acetic acid in aniron pot. Reduction takes place quickly, and 
 the liquid spotted on filter-paper should be colourless. Boiling is continued for a few 
 minutes after all the nitro compound has been added, the volume being maintained 
 by addition of water. The iron in solution cannot be precipitated at the boil in this 
 case, for fear of hydrolysis. The solution is cooled to 70°, made alkaline with soda, 
 which precipitates most of the dissolved iron, and the remainder precipitated by 
 careful addition of ammonium sulphide solution. The mixture is filtered and the 
 filtrate concentrated to the crystallising point, when on cooling the p-aminoacetanilide 
 
 an, 
 an 
 . 
 
 * 
 R 
 “J 
 
ANILINE AND ITS DERIVATIVES 41 
 
 Separates as brown needles. It can be purified by recrystallisation from water con- 
 taining some animal charcoal. 
 
 p-Aminoacetanilide serves to some extent the same purposes as p-nitroaniline. 
 That is, its diazo compound is coupled with an amine or phenol, and on hydrolysing 
 the acetylaminoazo compound so formed, the amino group set free may be diazotised 
 and coupled with a fresh component, or may be phosgenated. 
 
 p-Phenylenediamine : 
 
 The base forms white crystals, m.p. 147°, b.p. 267°, but quickly turns brown, and 
 finally black in air. The salts are more stable. 
 
 p-Phenylenediamine may be prepared by hydrolysis of p-aminoacetanilide with 
 acids or alkalies. Naturally, acids are preferable for the purpose, as the base is so 
 easily oxidised. Again, p-nitroacetanilide may be reduced under acid conditions, so 
 that hydrolysis accompanies reduction. Finally, p-nitroaniline yields the diamine 
 on reduction. The use of this last method on a technical scale is described by Jansen 
 (Zeit. f. Farben-Industrie, 1913, 12, 197). 
 
 A mixture of 200 kg. of ground iron borings, 9 litres of 28 per cent. hydrochloric 
 acid and water, is boiled and stirred in an iron vessel, and 200 kg. of p-nitroaniline 
 slowly added. The violent reaction with frothing which takes place on each addition 
 of the nitroaniline is allowed to subside before the next addition. Water is also 
 slowly dropped in to maintain the volume. When all the nitroaniline has been added 
 the liquid is yellow in colour. Reduction is completed by adding 14 litres of 28 per 
 cent. hydrochloric acid and stirring further until a drop of the solution gives a colour- 
 less spot on filter-paper. The solution is now made faintly alkaline to phenolphthalein 
 by the addition of soda ash (about 25 kg.), and after boiling up for ten minutes is 
 allowed to settle and filtered, the iron residues being well washed, out with hot water. 
 The solution is then concentrated to the crystallising point, when on cooling the 
 diamine separates out as a hydrate. The yield is said to be 90 to 95 per cent. and the 
 product very pure. | 
 
 The practice of precipitating the dissolved iron by making alkaline and thus setting 
 free the base does not seem desirable in the case of p-phenylenediamine. The method 
 of G.P. 269542 previously described in connection with m-phenylenediamine (p. 21) 
 can be adopted in this case to obtain white crystals of the hydrochloride. 100 gms. 
 of p-nitroaniline are reduced with 730 c.c. of 30 per cent. hydrochloric acid and 150 
 gms. of iron as described in the case of m-phenylenediamine. 
 
 p-Phenylenediamine base can only be obtained in a satisfactorily pure state by 
 vacuum distillation. 
 
 Reduction of aminoazobenzene also yields p-phenylenediamine. 
 
 p-Phenylenediamine cannot be used as an intermediate for azodyes. Onattempt- 
 ing to diazotise it a mixture of oxidation products, partly of a quinonoid nature, is 
 
A2 INTERMEDIATES FOR DYESTUFFS 
 
 formed. This difficulty is overcome by forming first a monoazo compound by means 
 of either p-nitroaniline or p-aminoacetanilide and then reducing with sodium sulphide 
 or hydrolysing, when the newly-formed amino group may be diazotised and coupled 
 with a second component. The ready oxidisability of the base, however, makes it 
 specially suitable for dyeing hair and furs. It is also used for sulphide dyes. 
 
 The Alkylation of Aniline. 
 
 The alkylanilines have long occupied an important position as intermediates for 
 dyestuffs, owing to the large number of brilliant basic dyes of the triphenylmethane 
 and other classes which can be prepared from them. The tertiary amines—dimethy]l- 
 and diethylaniline, together with benzylmethyl- and benzylethylaniline—are of 
 greatest importance, but subsidiary uses have also been found for the secondary 
 amine, mono-ethylaniline. 
 
 Two general methods are in use for the alkylation of aniline. The first (and newer) 
 method uses the alkyl chloride : 
 
 C,H, NH, + R.Cl > ©,H;,.NHR + HCl 
 C,H;.NH, + 2R.Cl > (,H,NR, + 2HCl 
 (R=CH,, C,H,, C,H,-CH,) 
 
 By this method, the alkylation may be carried out at moderate temperatures (100° or 
 under) and under moderate pressures, or, in the case of benzyl chloride, at atmospheric 
 pressure. Sufficient alkali (sodium carbonate, caustic soda, or lime) is added to 
 neutralise the hydrochloric acid formed. 
 
 The second (older method) consists in heating aniline with the appropriate avout 
 in presence of a condensing agent : 
 
 C.H,NH, + BR.OH -———s CA NERO 
 C,H,NH, + 2R.0H ———> O,H,.NR, + 2H,0 
 
 Although water is eliminated in the reaction, experience shows that dehydrating 
 agents do not, as such, facilitate alkylation. For instance, aniline, ethyl alcohol, and 
 quicklime may be heated together to a high temperature without any formation of 
 ethylanilines. The best condensing agents are acids, in particular sulphuric and 
 hydrochloric acids, so that this second method is probably identical with the first, 
 alkyl chloride or sulphate being formed from the alcohol and acid, followed ny. alkyla- 
 tion of the aniline with regeneration of the acid. 
 
 Knoevenagel (J. pr. Chem., 1914, 89, 31) found that traces of iodine accelerate the 
 reaction between aniline and alcohols in a remarkable degree. The method has been 
 patented by Knoll and Co. (G.P. 250236), who claim to obtain quantitative yields of 
 dimethyl- and diethylaniline in this way. For example, 93 parts of aniline, 96 parts 
 of methyl alcohol, and 1 part of iodine, are heated in an autoclave at 230° for seven 
 hours. The water is separated, the iodine removed by alkali, and the product dis- 
 tilled ina vacuum. With ethyl alcohol, the temperature used is 235° and the time 
 
ANILINE AND ITS DERIVATIVES 43 
 
 of heating ten hours. Confirmation of these results is lacking, and the process 
 apparently is not used technically. 
 The side reactions which are liable to occur in the ordinary alkylation process are 
 of two kinds : 
 1. The formation of quaternary ammonium salts. 
 2. The formation of nuclear alkyl derivatives. 
 
 Quaternary ammonium salts, e.g.— 
 C,H, NCH, 
 CH, 
 HSO, 
 
 —are particularly apt to form when sulphuric acid is used as condensing agent. 
 They are very stable, and are not decomposed by alkalies at ordinary temperatures, 
 but merely yield the corresponding substituted ammonium hydroxide bases, e.g.— 
 
 CH, 
 O,H,.NCCH, 
 
 | cu, 
 
 OH 
 
 —which are reconverted to the ammonium salts by acids. They are also soluble in 
 water and non-volatile in steam, so that they remain behind in the alkaline liquor in 
 the usual separation of the secondary and tertiary bases. However, they may be 
 decomposed, and the tertiary bases recovered, by heating with concentrated caustic 
 alkali at about 170° to 180°. 
 
 The second side reaction—the formation of nuclear derivatives—is apparently 
 a consequence of the first. Above a certain temperature limit which, for the bases 
 of the benzene series, is about 250° to 300°, quaternary ammonium salts undergo 
 intramolecular transformation, an alkyl group being detached from the nitrogen 
 atom and entering the nucleus in the para position : 
 
 CH 
 N Zi: ’ N(CH,),-H,S0, 
 
 /\™HSO, 
 | , 250° to 800° > 
 
 » 
 
 Yi, 
 
 Since, however, alkylation can be carried to completion at 230° or under, no 
 nuclear derivatives need be obtained unless serious local overheating has occurred 
 during the process. 
 
 Methylaniline— Shae 
 
 ’) 
 —colourless oil, b.p. 195-7° (765 mm.), 95° (25 mm.); D;? 0-9921. 
 
44, INTERMEDIATES FOR DYESTUFFS 
 
 Methylaniline is formed when aniline is heated with methyl] alcohol and a little 
 sulphuric acid in an autoclave at 180° to 200°, or when aniline hydrochloride is heated 
 with methyl alcohol at the same temperature. But the resulting products contain 
 substantial proportions of unchanged aniline and dimethylaniline, whose separation 
 is troublesome. 
 
 A special method has been devised for the preparation of methylaniline depending 
 on the use of formaldehyde. This method was first applied in the Geigy patent, 
 G.P. 75854. Aniline is mixed with an equimolecular proportion of aqueous form- 
 aldehyde and caustic soda. A clear solution is formed at first, but this soon warms 
 up, becomes cloudy, and a heavy oil separates. The whole liquid is now stirred 
 rapidly and zinc dust added. While heating at 70° to 90°, a further quantity of 
 caustic soda solution is slowly added until a test portion of the liquid dissolves, apart 
 from the zine, to a clear solution in acetic acid. The methylaniline formed is separated 
 by steam distillation. The yields by this process are very poor. 
 
 The reaction between formaldehyde and aniline is somewhat complex. A Schiff 
 base, C,H;.N : CH,, is first formed, but this quickly polymerises to oily products, and 
 finally to a white solid of unknown constitution whose composition corresponds to the 
 formula (C,H;.N : CH,);. There is also the possibility of formation of methylene- 
 dianiline, CsH;.NH.CH,.NH.C,H;. The heavy oil mentioned in the Geigy patent 
 probably contains all of the above products. It is, however, only the unstable Schiff 
 base which can be reduced to methylaniline : 
 
 C,H,.N:CH, + 2H ——-> C,H,.NHCH, 
 
 If time is given for the Schiff base to polymerise, the yield of methylaniline will be 
 correspondingly reduced. 
 
 With these facts in view, a more recent patent by G. T. Morgan (E.P. 102834) 
 proposes an improved method in which the Schiff base is reduced as soon as itis formed. 
 
 A mixture of 300 parts of water and 200 parts of 34 per cent. caustic soda solution 
 (D 1-37) containing 90 parts of zinc dust in suspension is stirred thoroughly and heated 
 to 90°. To this are added separately and concurrently at equivalent rates 60 parts of 
 aniline and 66 parts of 40 per cent. formalin, so that the addition takes about two 
 hours. Stirring and heating are then continued for a further six hours, while 40 parts 
 more formalin are slowly added. Samples are taken from time to time and tested for 
 methylaniline, until the proportion of this reaches a maximum. The methylaniline 
 is then separated from the mixture by distillation in steam. It is advantageous to 
 activate the zinc by addition of a little copper sulphate or other copper salt to the 
 mixture at the beginning. 
 
 Methylaniline is not used as a dyestuff intermediate, but is converted into two 
 tertiary amines, benzylmethylaniline and ethylmethylaniline, which are used to some 
 extent for triphenylmethane colours. 
 
 Dimethylaniline— N(CHs). 
 
 ( ie 
 U 
 
ANILINE AND ITS DERIVATIVES AS 
 
 —colourless oil, b.p. 193° (760 mm.), 103° (34 mm.). D?°0-9575. It is almost 
 insoluble in water, but is miscible with most organic liquids. It is volatile in 
 steam. 
 
 This is by far the most widely used of the alkylanilines, probably because it is 
 the most easily prepared in good purity and yield. The usual method of preparation 
 is to heat aniline with methyl alcohol and a little sulphuric acid. A long account, 
 with many details of plant, is given of this process by Walter (Chem. Ztg., 1910, 84, 
 641, 667, 681, 690). 
 
 80 kg. of pure aniline, 78 kg. of methyl alcohol (free from acetone and ethyl 
 alcohol—+.e., it must not give a positive iodoform test) and 8 kg. of concentrated 
 sulphuric acid are mixed in an autoclave and heated to about 215° for nine hours. 
 The pressure reaches about 30 atmospheres when the full temperature is attained, 
 but later falls slightly. After allowing the autoclave to cool to about 100°, the outlet 
 valve is opened and the issuing gases, methyl alcohol and methy] ether, led through 
 a condenser, where the alcohol is condensed, the methyl ether, which is gaseous at 
 ordinary temperature, passing on through a long column of water. The autoclave 
 contents are then transferred to a still, made alkaline with caustic soda, and the 
 dimethylaniline distilled in steam. The separated dimethylaniline is then distilled. 
 The yield obtained is 98 kg. or 94 per cent. of the theoretical. 
 
 Somewhat greater yields may be obtained by taking account of the fact that some 
 quaternary ammonium sulphate (p. 43) is formed during methylation. This can be 
 decomposed, with regeneration of dimethylaniline and methyl alcohol, by making 
 the autoclave contents alkaline with caustic soda and heating again to 170° for 
 several hours. After cooling the procedure is the same as before. 
 
 The usual impurities of the crude product are aniline and methylaniline. Neither 
 should be present in quantity with reasonably careful working. Any aniline present 
 can be separated during distillation of the product. The presence of methylaniline 
 is shown by adding acetic anhydride to a sample, when acetylation of the methylani- 
 line takes place with rise of temperature. Pure dimethylaniline gives a slight lowering 
 of temperature on mixing with acetic anhydride. The test may be used as a rough 
 method of estimation for small proportions of methylaniline in dimethylaniline. 
 5 c.c. of the liquid are mixed with 5 c.c. of acetic anhydride at the same temperature, 
 and the rise of temperature noted. ach degree of rise is equivalent to about 0-5 per 
 cent. of methylaniline. Usually not more than about 0:5 per cent. of methylaniline 
 is present, as indicated by this test. 
 
 Methylation of aniline with methyl chloride is described by Grandmougin ( Rev. 
 Prod. Chim., 1917, 20, 68). This process has the great advantage that low-pressure 
 vessels and moderate temperatures may be used. 50 kg. of aniline is mixed with 
 75 litres of milk of lime made from 40 kg. of quicklime, and the mixture heated to 
 100° with continuous stirring. Methyl chloride is then forced in at such a rate that 
 the pressure is maintained at 5 to 6 atmospheres. 62 kg. of methyl chloride is added 
 in all, and the addition takes about two hours. Heating and stirring are continued till 
 methylation is complete, as shown by a fall in the pressure to 23 atmospheres. The 
 dimethylaniline is then distilled with steam and purified as usual. 
 
46 INTERMEDIATES FOR DYESTUFFS 
 
 Some work of an inconclusive character has been published regarding the effect of 
 dimethyl sulphate on aniline (Ullmann, Ann., 1903, 327, 104; Werner, J.C.S., 1914, 
 105, 2762; Shepard, J. Am. Chem. Soc., 1916, 38, 2507), but a satisfactory method of 
 preparing dimethylaniline by the use of this methylating agent does not seem to have 
 been worked out. Probably the tendency to form quaternary ammonium salts is 
 too great in this case. 
 
 The Ethylanilines. 
 
 Unlike the methylation of aniline, ethylation cannot be conveniently carried 
 completely to diethylaniline, nor can ethylaniline be obtained alone by any process. 
 Mixtures of the two are always obtained. They will, therefore, be described together. 
 
 Ethylaniline— 
 NHC,H,; 
 
 0 
 —colourless oil, b.p. 204°, Dj® 0-9643. 
 Diethylaniline— N(0,d,), 
 4 
 
 ¢ 
 —colourless oil, b.p. 214°, Dj? 0-9388. 
 
 Ethylation of aniline can be carried out by means of ethyl alcohol, but in this 
 case sulphuric acid cannot be used as condensing agent owing to the large amount of 
 ether formed. Hydrochloric acid is usually employed instead, aniline hydrochloride 
 (“‘ aniline salt ’’) being heated with alcohol. Unfortunately, this necessitates the use 
 of enamelled autoclaves. 
 
 If aniline hydrochloride and ethyl alcohol m equimolecular proportions are heated 
 at 180° for twelve hours, a mixture containing about 70 per cent. of ethylaniline, some 
 diethylaniline, and unchanged aniline is formed, from which on cooling the ethyl- 
 aniline mostly separates as hydrochloride. If 25 per cent. excess of alcohol over 
 the molecular proportion is used, and the temperature raised to 190° (the pressure 
 developed is 16 atmospheres), the aniline is completely ethylated. The oil obtained 
 on making alkaline and distilling in steam as usual then contains about 23 per cent. 
 diethylaniline and 77 per cent. monoethylaniline. 
 
 The acetic anhydride method for estimating the proportion of secondary amine is 
 not sufficiently accurate for use with such mixtures. It is only of use where the pro- 
 portion of secondary amine is small. But in the case of the ethylanilines an accurate 
 determination of the specific gravity of the mixture at 15° will give the required 
 information (if aniline is absent) when used in conjunction with the table given on 
 p. 47 (Fierz-David, “‘ Farbenchemie,”’ second edition, 1923, p. 110). 
 
 As there is a difference in boiling-point of 10° between mono- and diethylaniline 
 it is possible to separate them by repeated fractional distillation, using long columns. 
 But this is not usually done. Instead, the mixture is benzylated, as described later 
 
ANILINE AND ITS DERIVATIVES A7 
 
 Specific Diethyl Specific Diethyl | Specific Diethyl Specific Diethyl 
 Gravity. | (per Cent.).|| Gravity. (per Cent.).|| Gravity. | (per Cent.). Gravity. |(per Cent.). 
 
 0:9646 0 0-9610 15-0 0-9545 41-0 0-9430 85-0 
 0-9643 1 0-9595 21-2 0-9520 50°8 0°9415 90-2 
 0:9640 2°3 0-9585 25-3 0-9495 60-4 0-9400 95:6 
 0:9637 3°7 0-9570 31-2 |  0-9470 70-0 0-93875 100 
 0-9622 9-8 0-9560 | 35-2 0-9440 81-3 — — 
 
 —$_—_——» 
 
 (p. 49), and the benzylethylaniline and diethylaniline are then more easily separated. 
 The proportion of diethylaniline in the mixture can be increased by increasing the 
 alcohol used. 
 
 If hydrobromic acid is substituted for hydrochloric acid, ethylation can proceed at 
 a much lower temperature, yielding much higher proportions of tertiary amine. 
 Stadel (Ber., 1883, 16, 30; G.P. 21241), by heating aniline hydrobromide with 2-2 
 mols. of ethyl alcohol at 145° to 150°, claimed to obtain a nearly quantitative yield of 
 diethylanilme. The method, however, apparently has not been adopted on a manu- 
 facturing scale. Hydrobromic acid is, of course, much more costly than hydrochloric, 
 and in any case the benzylethylaniline produced in the ordinary process is a valuable 
 intermediate for triphenylmethane colours. 
 
 A detailed laboratory investigation of the ethylation of aniline hydrochloride by 
 ethyl alcohol, more particularly with regard to the use of catalysts, has been made by 
 Johnson, Hill, and Donleavy (J. Ind. Eng. Chem., 1920, 12, 636). They found that 
 zinc chloride, or calcium chloride, and the bromides and iodides of sodium and 
 potassium gave increased yields of ethylated aniline, and also that cupric chloride 
 specially favoured the production of diethylaniline. The effect was further increased 
 by using cupric chloride in conjunction with one of each of the other two classes of 
 catalysts. ‘The conditions giving the highest ie of diethylaniline were as follows. 
 The autoclave was charged with : 
 
 Aniline hydrochloride - ay ws es ae -. 100 gms, 
 Ethyl alcohol (99 per cent) 360 
 
 Sodium bromide .. 4,1 ; a Gees MA cg 
 Calcium chloride .. 4 Af bea <e ols a 10. ., 
 Cupric chloride .. as = is ws ws es ars 
 
 The charge was heated at 175° to 180° for eight hours, the pressure developed being 
 280 to 310 Ibs. per square inch. Under these conditions consistent yields of 
 100 to 105 gms. of diethylaniline, containing about 5 per cent. of monoethylaniline, 
 were obtained. This corresponds to a yield of 87 to 91 per cent. 
 
 As regards other ethylating agents for aniline, ethyl chloride is available in 
 quantity, and, like methyl chloride, has the advantage of requiring for use low- 
 pressure iron vessels at temperatures not above 100°. But details are lacking of the 
 results obtainable by its use. 
 
48 INTERMEDIATES FOR DYESTUFFS 
 
 Applications of the Alkylanilines. 
 
 The chief use of the alkylanilines as dyestuff intermediates depends on their 
 readiness to condense with aldehydes as follows: 
 
 es DNB, 
 R.CHO + 2C,H,.NR’, > R.CH 
 BAe aN NR’, 
 Dt bday 
 
 If benzaldehyde or its derivatives are used, the condensation products are the 
 leuco bases of triphenylmethane dyes, from which the dyes themselves are 
 obtained by oxidation. In this way from benzaldehyde itself and dimethyl- 
 and diethylanilines are obtained Malachite Green and Brilliant Green respectively. 
 Others are obtained by using sulpho-, chloro-, and hydroxy- derivatives of 
 benzaldehyde. 
 
 Formaldehyde also condenses with the alkylanilines, yielding diphenylmethane 
 derivatives (“‘ Methane Base,” etc.), which will be dealt with later. 
 
 The dialkylanilines, on treatment with nitrous acid, give p-nitroso derivatives, 
 which are used in the preparation of azine, thiazines, and oxazine colours. But 
 the dialkylanilines are used directly in making these colours. By oxidising in 
 faintly acid solution a mixture of a dialkylaniline and a p-aminodialkylaniline, 
 an indamine is formed : 
 
 RE ie Aer 
 wane Yt Chea 
 RB, : mer NR, 
 Cl 
 
 Ew ~ 
 This indamine may be further condensed with aniline or another aromatic amine 
 to form an azine dye: 
 Canes Re 
 am sa A 
 RN: \ )NBa RN Ne NBs 
 dy cee CANS <4 
 Se 
 
 7 
 
 The indamine may also be formed by condensation of a p-nitrosodialkylaniline 
 with a dialkylaniline : 
 
 PORE ae 
 
 gir 
 pil ) 4 L Jn, ee nak Lam, 
 1 
 
 1 
 
ANILINE AND ITS DERIVATIVES 49 
 
 By using a nitroso compound containing a hydroxyl group in the ortho position to 
 the nitroso group, the indamine which is first formed condenses further to an oxazine : 
 
 ane Ja A 
 ah ae wi 
 
 “No eee 
 
 Thiazines are formed by introducing the group —S.SO,H in the ortho position to the 
 amino group of p-aminodialkylanilines, which are then condensed, by oxidation with 
 dialkylanilines, to indamines, and further to the thiazines. Details of these methods 
 are to be found in works on the chemistry of dyestuffs. They are mentioned here 
 merely to indicate the various modes of application of the dialkylanilines. 
 
 A subsidiary use of dimeth’ylaniline is its application as a second component in a 
 few azo dyes, which are chiefly of use as indicators. 
 
 Benzy Imethylanili ne— 
 CH 2; H 
 N< ; : So 5 
 
 () 
 ~ 
 —pale yellow oil, b.p. 305° to 306° or 210° (60 mm.). 
 
 Benzylethylaniline— 
 NoCH2-C.H,; 
 
 Od oH, 
 0) 
 
 —pale yellow oil, b.p. 285° to 286° (710 mm.) or 185-5 to 186-5° (22 mm.). D!®° 1-034. 
 Although the two benzylalkylanilines are intermediates of importance for acid 
 colours of the triphenylmethane series, but little information has been published 
 regarding them. The preparation of the methyl compound has been described by 
 Wedekind (Ber., 1899, 32, 519) and that of the ethyl compound by Stebbins (J. Am. 
 Chem. Soc., 1885, '7, 42), in each case by heating the monoalkylaniline with benzyl 
 chloride and then fractionating the product. But good results are not obtained in 
 this way. In order to obtain approximately complete benzylation it is advisable to 
 have present sufficient aqueous alkali to neutralise the hydrochloric acid formed. 
 
 As already mentioned, the monoalkylanilines are not used as dyestuff inter- 
 mediates. Since, however, they are present in the products of alkylation of aniline, 
 and especially in the case of ethylated aniline, it is found most economical to benzylate 
 the mixtures of secondary and tertiary bases. This is carried out by determining the 
 proportion of secondary base in the mixture, adding the calculated quantity of benzyl 
 chloride, together with about 5 per cent. excess, and the necessary aqueous solution of 
 alkali (caustic soda or sodium carbonate), and heating the mixture at 100° to 125°. 
 In the case of the higher temperatures closed vessels must be used. In any case the 
 
 4 
 
50 INTERMEDIATES FOR DYESTUFFS 
 
 mixture must be very vigorously stirred. When benzylation is finished the dimethyl- 
 or diethylaniline is distilled off with steam and purified in the usual way. The re- 
 maining benzylalkylaniline, which is not volatile in steam, is then separated, washed, 
 and purified by fractional distillation under reduced pressure. The forerunnings 
 contain some benzyl alcohol (b.p. 206°) formed by partial hydrolysis of the benzyl 
 chloride. 
 
 The benzylalkylanilines react in the same way as dimethyl- and diethylaniline 
 with benzaldehyde and its derivatives to yield the leuco bases of triphenylmethane 
 dyes of slightly bluer shades than those obtained from the diethyl compound. The 
 benzyl compounds are specially well adapted for the production of acid colours for 
 wool and silk, since they are easily sulphonated at temperatures not much above the 
 ordinary. The sulphonation may either be performed on the benzyl compound itself 
 or on the leuco triphenylmethane base made from it. In either case, the sulphonic 
 acid group enters the benzyl] nucleus first, in the para position. Thus, for example, 
 benzylethylanilinesulphonic acid— 
 
 ¢ _N(C.H,).CHAC SBOE 
 —is prepared according to G.P. 50782 (A.G.F.A.) by stirring 50 kg. of benzylethyl- 
 aniline into 120 kg. of 21 per cent. oleum at 40° to 50° and keeping the solution at 
 this temperature until a sample is soluble in dilute caustic soda. The acid is then 
 separated simply by diluting the solution with 100 kg. of water, so that the tempera- 
 ture does not rise above 50°, or, keeping under the same temperature limit, by adding 
 100 kg. of 40 per cent. caustic soda. 
 
 The sulphonation can also be carried out with monohydrate at 110° to 120°. 
 
 A disulphonic acid can also be obtained, in which the second sulpho group enters 
 the other nucleus. Benzylethylanilinedisulphonic acid : 
 
 aaa IS roca 
 < mn >N(CiH;).CHAC \SO,H 
 
 10 kg. of benzylethylaniline are stirred into 20 kg. of 20 per cent. oleum, which is 
 well cooled. When solution is complete, 25 kg. of 80 per cent. oleum are added, and 
 the solution heated at 60° until disulphonation is complete, as shown by a test portion, 
 diluted with water and partly neutralised by soda, no longer giving a precipitate of 
 sulphonate salted out by sulphate. The melt is then poured into water, neutralised 
 with milk of lime, filtered from calcium sulphate, and the calcium salt converted to 
 the sodium salt by sodium carbonate. The sodium salt is then salted out (G.P. 69777, 
 Bayer). 
 
 The benzylalkylanilines can be condensed with aromatic aldehydes, in the same 
 way as the dialkylanilines, to form the leuco bases of triphenylmethane dyes. The 
 dyes obtained on oxidation are, like those formed from the dialkylanilines, basic in 
 character. As basic dyes they show no advantage over their alkyl analogues. But 
 the presence of the benzyl groups enables sulphonation of the dyestuffs to take place 
 easily, the sulpho groups entering the benzy] nuclei, and acid dyes for wool and silk are 
 
ANILINE AND ITS DERIVATIVES 51 
 
 thus obtained, which at the same time retain all the brilliance of the basic tripheny]- 
 methane dyes. The same dyes may also be formed by using the sulphonic acid 
 derivatives of the benzylalkylanilines. 
 
 p-Nitrosodimethylaniline hydrochloride : 
 
 Cl.N(CH,), 
 N(CH,).-HCl 
 Hex 
 or U) 
 NO I 
 NOH 
 
 The base forms dark green leaflets when crystallised from benzene or carbon tetra- 
 chloride. M.p. 85°. It gradually decomposes on standing, going brown. This 
 decomposition is said to be prevented by addition of a little sodium carbonate. The 
 hydrochloride forms intensely yellow needles, moderately soluble in water, but 
 sparingly soluble in dilute hydrochloric acid, and in methyl and ethyl alcohols. The 
 hydrochloride is also unstable as usually prepared, though if pure it may be kept for 
 months. 
 
 121 gms. of dimethylaniline are dissolved in 300 c.c. of concentrated hydrochloric 
 acid, and about 1,000 gms. oficeadded. Themixtureisstirred rapidly anda saturated 
 solution of 75 gms. of sodium nitrite in water (about 200 c.c. are required) is added 
 slowly from a tap-funnel whose end dips beneath the surface, until free nitrous acid 
 can be detected by the smell. The usual starch-iodide paper test cannot be used in 
 this case, because the nitroso compound itself reacts with the iodide. The tempera- 
 ture is maintained at or near 0°, if necessary by means of moreice. An intense orange 
 solution is at first formed from which the hydrochloride soon begins to crystallise out. 
 Stirring is continued for a few hours after the nitrite has been added. The hydro- 
 chloride is then filtered off, washed with a little 10 per cent. hydrochloric acid, 
 and air-dried. If a second wash with alcohol is given, the nitroso compound will 
 keep much better. It is, however, usually prepared as required on the large scale, 
 and used immediately without drying. The content of the moist substance in 
 nitroso compound is estimated by reduction of a weighed quantity in dilute acid 
 solution with zinc dust to p-aminodimethylaniline, followed by titration with 
 nitrite. 
 
 p-Nitrosodiethylaniline hydrochloride is prepared in a similar way, but its solu- 
 bility is too great to allow of the dilution used in the preceding case. The solution of 
 diethylaniline in concentrated hydrochloric acid is cooled externally by a freezing 
 mixture, while the nitrite is run in. 
 
 As already mentioned (p. 48), the p-nitrosodialkylanilines can be condensed with 
 dialkylanilines to form indamines, which can be further condensed to azine, oxazine, 
 or thiazine dyes. In such cases there is always the alternative method of using a 
 p-aminodialkylaniline, a mixture of this with a dialkylaniline being oxidised to form 
 the indamine. However, the p-aminodialkylaniline is generally most conveniently 
 obtained by reduction of the nitroso compound, and, except in special cases, there is no 
 advantage in the use of the amino compound. 
 
52 INTERMEDIATES FOR DYESTUFFS 
 
 A large number of azine and oxazine dyes are formed by condensation of these 
 p-nitroso compounds with m-diamines or substituted m-diamines, and with phenols : 
 
 to. 
 \ NER 
 
 Ny 
 
 As phenols, resorcinol, 6-naphthol, gallic acid, dialkyl-m-amino-phenols and -cresols 
 are specially well adapted for this reaction. 
 Tetramethyldiaminodiphenylmethane (Methane Base)— 
 
 (CHNC CHK N(CH), 
 —colourless lustrous leaflets, m.p. 90° to 91°. Insoluble in water, sparingly soluble 
 in cold alcohol, but much more so in hot alcohol, and in ether and benzene. It is 
 not volatile in steam, and may be distilled undecomposed. B.p. 390°. 
 This substance is made by condensation of formaldehyde with dimethylaniline. 
 The reaction apparently takes the following course : 
 
 1. (CH,),N—C » + CH,O ——-> (CH,),.N—<)—CH,OH 
 3S yaa NS ve \an.7 \ 
 2. (CH).NC CH,OH + € —N(CH,), )eNe CH N(CH), 
 
 If a considerable excess of formaldehyde is used, higher condensation products of 
 unknown constitution are formed. This was the chief fault of the early methods of 
 preparation, together with the use of organic solvents such as alcohol or acetic acid. 
 The following method is due in essentials to Cohn (Chem. Zig., 1900, 24, 564): 242 gms. 
 (2 mols.) of pure dimethylaniline are mixed with 300 gms. of 25 per cent. hydrochloric 
 acid (just enough to hold the dimethylaniline in solution) and 90 gms. of 40 per cent. 
 formaldehyde (1-1 mols.) added. The strength of the formaldehyde solution should 
 be accurately known. The mixture is then heated on the water-bath at about 85°, 
 with occasional stirring, for five hours. After cooling, the base is separated by making 
 just alkaline with ammonia or sodium carbonate solution. It is filtered off, thoroughly 
 washed with water, and dried at about 60°. The yield is practically quantitative, 
 about 255 gms. It may be purified by recrystallisation from alcohol. 
 
 Tetraethyldiaminodiphenylmethane is prepared in the same way from diethyl- 
 aniline. 
 
 Methane base is used in making Auramine by first converting the —CH,— group 
 
ANILINE AND ITS DERIVATIVES 53 
 
 into —C: 8 by heating with sulphur, and then condensing this with ammonia 
 (from ammonium chloride) to form the imino compound —C : NH. 
 Tetramethyldiaminobenzophenone (Michler’s Ketone) 
 
 (CH,),N¢ og N(CH): 
 
 —silver-glancing leaflets. ‘The melting-point was given by Michler as 179°, but later 
 work points to the figure 172° to 172:5°. Easily soluble in alcohol and ether. 
 
 The preparation is given by Michler (Ber., 1876, 9,716, 1900). Phosgene is passed 
 into 100 gms. of freshly distilled dimethylaniline at ordinary temperature in an auto- 
 clave until 41 gms. have been added. This converts about half the dimethylaniline 
 into p-dimethylaminobenzoylchloride (CH;),.N.C,H,.CO.Cl, which partly separates 
 as a crystalline mass. The autoclave is then closed and heated for five hours in 
 boiling water. After cooling, any unchanged dimethylaniline is distilled off with 
 steam, and the residue is dissolved in dilute hydrochloric acid. The solution is 
 filtered and the ketone precipitated by addition of caustic soda. The crude ketone is 
 filtered off, redissolved in dilute hydrochloric acid, and reprecipitated by caustic soda. 
 It separates as a light flocculent precipitate, which is filtered off, washed, and dried. 
 It is then recrystallised from alcohol and the crystals washed with a little cold alcohol. 
 
 Tetramethyldiaminobenzhydrol (Michler’s Hydrol)— 
 
 NcH(OH)’  SN(CH,), 
 
 Z 
 (CH,),N <>, 
 
 ace 
 | —prismatic crystals from benzene or ether. M.p. 96°. Soluble in alcohol. It forms 
 a hydrochloride, C,,H,.ON,.HCl, which is very soluble in alcohol, but is hydrolysed 
 by water. 
 
 This substance can be prepared either by oxidation of methane base or by reduc- 
 tion of Michler’s ketone. The former is the cheaper method, and is the one used 
 technically, though the product obtained is rather impure. The latter method gives 
 an almost pure product. Both methods are described by Méhlau and Heinze (Ber., 
 
 1902, 35, 359, 360). 
 
 1. Oxidation of Methane Base.—20 gms. of pure methane base are brought into 
 solution by 50 gms. of water and 5-7 gms. of HCl as concentrated hydrochloric acid 
 (2mols.). The solution is then diluted with 1,600 c.c. of water and 9-4 gms. (2 mols.) 
 of glacial acetic acid added. The whole is cooled below 0°, stirred vigorously, and 
 a thin paste of lead peroxide containing 18-8 gms. of PbO, run in as a thin stream. 
 The strength of the lead peroxide paste must be accurately determined beforehand 
 by one of the usual methods. The oxidation is quickly completed. After five minutes 
 a solution of 26 gms. of Glauber salt in 120 gms. of water is added to precipitate the 
 lead as sulphate. This is filtered off. To the filtrate, which is an intense blue-violet 
 in colour, excess of cold dilute caustic soda is added. The hydrol separates as a grey 
 flocculent precipitate, or sometimes in a soft sticky condition. In the latter case, 
 the whole is allowed to stand for some hours, when the precipitate hardens. It is 
 filtered off, washed, and dried. The yield of crude product is 20 gms. or 94-3 per cent. 
 
54 INTERMEDIATES FOR DYESTUFFS 
 
 It is, however, not pure, its melting-point being about 87°. On digesting it with 
 cold ether, about nine-tenths of it is dissolved, and on evaporating off the ether 
 fairly pure hydrol is obtained, melting at 96° to 98°. The undissolved tenth melts at 
 103° to 104°, and consists mostly of an anhydride of the hydrol. 
 
 2. Reduction of Michler’s Ketone.—26-8 gms. of the ketone is added to 1:5 litres 
 of 95 per cent. alcohol, and the solution boiled on the water-bath. 160 gms. of 3 per 
 cent. sodium amalgam is added to the solution, which is kept gently boiling. The 
 reduction takes three to four hours, the end being recognised by the mobility of the 
 residual mercury when the amalgam has been used up. The solution is then filtered, 
 and the hydrol precipitated by running the solution into water. It is filtered off 
 and washed with water. As so obtained it melts at 95° to 96°. The yield is 
 quantitative. 
 
 Michler’s ketone and hydrol make possible an extension of the synthesis of tri- 
 phenylmethane colours to cases where the aldehydes required by the other chief 
 synthetic method are not available. They can be condensed with a large variety of 
 aromatic derivatives, including bases (primary, secondary, and tertiary), phenols and 
 phenolic acids, and the corresponding naphthalene derivatives, to form triphenyl- 
 methanes and diphenylnaphthylmethanes. Condensation generally takes place in 
 the para position to the amino or hydroxyl group, though in the case of B-naphthol 
 derivatives it takes place in the «-position. 
 
 Michler’s ketone is generally employed in the form of its dichloride, formed by 
 heating the ketone with phosphorus trichloride or oxychloride, or with phosgene. 
 
 For some cases, either the ketochloride or the hydrol may be used, but in other 
 cases one of the methods gives better results than the other. No general rule can be 
 laid down as to which should be used in a given case. 
 
 Alkylated m-Aminophenols. 
 
 These intermediates, which are required for the Pyronine and Rhodamine dyes, 
 are usually prepared from the alkylanilines by sulphonation and alkali fusion of the 
 sulphonates, though other methods are available. Very little exact information has 
 been published with regard to their preparation. The sulphonation of the alkyl- 
 anilines yields mixtures of the m- and p-sulphonic acids, the m-compounds being 
 favoured by low temperature of sulphonation. No attempt is made to separate the 
 two acids. On fusion of the sulphonates with alkali, the p-sulphonates are un- 
 attacked under such conditions as give the m-phenols. 
 
 Dimethyl-m-aminophenol— 
 
 N(CHs)s 
 ae 
 
 | Jor 
 
 —crystallises from ligroin or benzene in needles, m.p. 87°, b.p. 265° to 268° (760 mm.), 
 b.p. 133° (15 mm.). Itis almost insoluble in water, but easily soluble in alcohol, ether, 
 benzene, and acetone. It dissolves in acids and alkalies, and is precipitated from 
 
 Po ~~ 
 es ee) ee 
 
 ae eee eae 
 
ANILINE AND ITS DERIVATIVES 55 
 
 alkaline solution by carbon dioxide or acetic acid, or from mineral acid solution by 
 sodium carbonate or acetate. 
 
 The preparation of this substance is given in G.P. 44792 (Soc. Chem. Ind., Basle), 
 but the same process is described in rather more detail by Méhlau and Bucherer 
 (“ Farbenchemisches Praktikum,” 1908, pp. 30, 44) as follows: Dimethylaniline 
 (100 gms.) is slowly dropped into 650 gms. of 30 per cent. oleum, which is well stirred 
 in an enamelled sulphonation pot externally cooled with salt and ice. The tempera- 
 ture is kept below 5° during the addition. The solution is warmed to 60°, and kept at 
 _ this temperature until a sample dissolves clear in excess caustic soda solution. The 
 solution is then stirred into 3 litres of water, neutralised with milk of lime, filtered from 
 gypsum, the requisite amount of potassium carbonate added to the filtrate, the hot 
 solution of potassium salt filtered from chalk and evaporated to dryness. 
 
 For the fusion, 200 gms. of caustic potash and 25 c.c. of water are melted in a 
 nickel vessel, which is heated in an anthracene bath, and is provided with a double- 
 walled copper lid also containing anthracene. The molten potash is raised to 250°, 
 and at this temperature 150 gms. of dry finely powdered potassium sulphonate, as 
 obtained above, is added all at once and well stirred in with a strong nickel spatula. 
 The melt is then continued for two hours at 270° to 280° (inside temperature). The 
 potassium dimethyl-m-aminophenolate which is formed separates as an oily layer on 
 the surface. The melt is now cooled, dissolved in 3 litres of water, acidified with 
 hydrochloric acid, and a little brown flocky precipitate filtered off. The filtrate is 
 then neutralised with potassium bicarbonate, when dimethyl-m-aminophenol pre- 
 cipitates as an oil which soon solidifies. The separation can be completed by saturat- 
 ing the solution with salt. The liquid is now extracted with benzene, the benzene 
 solution dried with potassium carbonate, and after distilling off the benzene, the 
 residue is distilled under reduced pressure. 
 
 Another method of preparation of dimethyl-m-aminophenol is described on p. 101. 
 
 Diethyl-m-aminophenol— 
 UR (CH; )s 
 
 Os 
 
 —melts at 78°, and boils at 276° to 280° (760 mm.) or 170° (15 mm.). 
 
 The method of G.P. 44792, quoted under dimethyl-m-aminophenol above, can be 
 applied in this case also. An elaborate account of the manufacture by this method is 
 given in Wolfrum’s ‘‘ Chemisches Praktikum,”’ Part IT., p. 326, from which it appears 
 that the process used differs in two points from that described under the dimethyl 
 compound. The sulphonation of diethylaniline is carried out at 125° instead of 
 60°, and caustic soda is used in place of caustic potash for the alkali fusion. The 
 following is a brief summary of the process : 
 
 The diethylaniline (240 kg.) is run in a thin stream into 240 kg. of sulphuric acid, 
 the temperature rising to about 75°. To the well-stirred sulphate so formed is added 
 gradually 700 kg. of 40 per cent. oleum. The temperature rises to 125°, and is kept 
 at this point for four hours. It is then cooled to 70°, and run into milk of lime made 
 
56 INTERMEDIATES FOR DYESTUFFS 
 
 from 800 kg. of slaked lime and about 6,000 litres of water. The lime having been 
 exactly neutralised, a solution of 120 kg. of anhydrous sodium carbonate is added so 
 as to form the sodium salt of the diethylanilinesulphonic acid. The solution is filtered 
 and the filtrate concentrated somewhat. The caustic soda (350 kg.) required for the 
 alkali fusion is now added and the solution evaporated until it reaches a temperature 
 of 160° to 170°. This gives a mixture sufficiently dry to avoid overmuch foaming in 
 the subsequent melt. 
 
 The fusion is carried out in lots of 25 kg. in special cast-iron tubes heated slowly 
 in an oven to a temperature of 300°. The finished melts are dissolved in narrow tall 
 vessels, acidified with sulphuric acid, and boiled to drive off sulphur dioxide. Sodium 
 carbonate solution is then added until the solution is only faintly acid. The amino- 
 phenol sulphate separates as an oily layer above the concentrated sodium sulphate 
 solution. The latter is run off and the oil treated with dry sodium carbonate till a 
 sample of the mixture on dilution with water shows no separation of oil. The oil so 
 treated is then stirred with water and diluted, when the aminophenol separates as a 
 flocky precipitate, which is filtered off. More aminophenol can be obtained from the 
 filtrate, and from the previously separated sodium sulphate solution after allowing the 
 sulphate to crystallise out, by extracting these solutions with ether. The crude 
 product is purified by melting it in lots of 250 kg. and stirring into each 50 kg. of 
 toluene, then allowing to crystallise. The yield is not quite definitely stated, but 
 seems to be about 200 kg. of crude product (from 240 kg. of diethylaniline) or about 
 112 kg. of crystallised product. 
 
 Diethyl-m-aminophenol may also be prepared from resorcinol by a method similar 
 to that described for dimethyl-m-aminophenol (p. 101). 
 
 Monoethyl-m-aminophenol— 
 NHC,H, 
 ae 
 
 a 
 —m.p. 62°, b.p. 176° at 12 mm. 
 
 The preparation of this derivative is described in G.P.48151 (Badische), the method 
 used being essentially the same as that described for dimethyl-m-aminophenol (p. 22). 
 
 Another method of preparation, from m-phenylenediamineoxamic acid is given 
 on p. 22. 
 
 Applications of the Alkyl-m-aminophenols. 
 
 These intermediates are used in the preparation of dyes of the Xanthene series by 
 condensing them with various substances containing a reactive —CO— group in the 
 molecule, such as phthalic anhydride, succinic anhydride, formaldehyde, and aromatic 
 aldehydes, etc. ‘Two molecules of the aminophenol take part in the condensation, 
 which occurs in the p-position to each amino group, and is followed by ring closure 
 with elimination of water : 
 
 es 
 
 “Non HO? SNP: R,N é i se Nee BN VA as 
 
 & : © ‘ Sino Ne an 
 T Pac 
 
ANILINE AND ITS DERIVATIVES 57 
 
 Using phthalic anhydride the Rhodamines are obtained. Only monoethyl- and 
 diethyl-m-aminophenols give commercially usable dyes, the product obtained with 
 the dimethyl compound being too sparingly soluble. It gives, however, a useful dye 
 by condensation with succinic anhydride. 
 
 Unsymmetrical dyes are also made, since it is possible to condense phthalic 
 anhydride with one molecular proportion of an alkylaminophenol, and then to 
 condense the product with another alkylaminophenol or a resorcinol derivative. 
 
 Sulphanilic acid : 
 
 NH, 
 ( a 
 y, 
 S0,H 
 The acid crystallises in two hydrated forms—(1) leaflets, with 2H,O; (2) needles, with 
 1H,0. The dihydrate, which is obtained by crystallisation from solutions below 19°, 
 is very efflorescent, losing all its water of crystallisation on standing in the air. The 
 monohydrate is much more stable and even in the desiccator only loses water slowly. 
 The following table gives the solubility of the acid in water : 
 
 Gms. Anhydrous Acid per 100 Gms. 
 
 Solution. Corresponding Solid Phase. 
 
 Temperature (Degrees). 
 
 0 0-44 Dihydrate. 
 7-2 0:62 ye 
 13-3 0-84 +9 
 18-9 1-09 - 
 18-9 1-14 Monohydrate. 
 25-1 1-38 = 
 31-1 1-66 e 
 37-2 2-00 + 
 44-0 2-44 *s 
 44-0 2-36 Anhydrous. 
 47-5 2-52 
 54-5 2-85 
 
 The sodium salt crystallises in leaflets with 2H,O. 
 
 While sulphanilic acid can be obtained bysulphonation of aniline with concentrated 
 sulphuric acid (such a process is described by Groggins, “‘ Aniline and its Derivatives,” 
 p. 160), it is usually made by the bake process from aniline sulphate. The former 
 method requires a large excess of sulphuric acid and gives a product contaminated 
 with isomers and disulphonic acid. The bake process requires only the theoretical 
 amount of sulphuric acid and yields the p-sulphonic acid only. There is some 
 indication that a sulphamic acid is formed as an intermediate stage : 
 
 NH,.H,S0, NH.SO,H NH, 
 ae 
 
 Ge rf 
 J} =} —(} 
 Pe el ns 
 
58 INTERMEDIATES FOR DYESTUFFS 
 
 It has been found that the best results are obtained by using the exact amount of 
 sulphuric acid required to form the sulphate of the base. An excess of either acid or 
 base causes much oxidation, giving deeply coloured products, which are only with 
 difficulty and much loss removed from the sulphanilic acid. The strength of the 
 sulphuric acid used should, therefore, be accurately known. Another source of 
 trouble is the presence of iron sulphate in the sulphuric acid. Traces of iron salts 
 promote oxidation in the bake to a remarkable extent. Oxidation cannot be entirely 
 avoided, but may be much diminished by attention to these points and by carrying 
 out the reaction at the minimum temperature, which, in the case of aniline, is about 
 190°. 
 
 104 parts of the ordinary 95 per cent. sulphuric acid (or an equivalent quantity of 
 acid of different strength) is added to 93 parts of aniline well stirred in a suitable 
 vessel, which should not be of iron. A thick pasty mass of aniline sulphate is formed, 
 and this is stirred till it is homogeneous. It is then spread thinly on trays (not of 
 iron, but lead is suitable) and placed in an oven which is heated to 190°. For main- 
 taining an even temperature, heating of the oven with superheated steam or circulating 
 oil is best. A vacuum oven is also advantageous, as the necessary removal of water 
 is thus accomplished more easily. Heating is continued till a test portion dissolves 
 clear in soda solution. This requires about eight hours at 190°. The time required 
 may be reduced to four to six hours by heating at 200° to 210°, but this is not 
 advisable. The product is grey in colour and contains a little unchanged aniline. 
 The yield is about 175 parts. 
 
 For purification it is dissolved in 500 parts of water containing 60 parts of soda 
 ash, and the aniline distilled off with steam. The solution is then filtered, acid added 
 till Congo paper is rendered blue, and on cooling the sulphanilic acid crystallises. 
 It should be well cooled and allowed to stand for a considerable time before filtering 
 off the crystals. 
 
 Sulphanilic acid is used as a first component in a large variety of monoazo, disazo, 
 and trisazo dyes. 
 
 Phenylhydrazine-p-sulphonic acid : 
 
 The acid forms lustrous colourless needles with 1H,0. It is sparingly soluble in 
 cold water, but much more so in hot water. 
 
 The usual laboratory method of preparing aromatic hydrazines is to reduce the 
 corresponding diazonium salt with stannous chloride and hydrochloric acid. For 
 manufacturing purposes, however, it has been found preferable to use Fischer’s 
 original method (Ann., 1878, 190, 69) of reducing with sulphite. In the present case 
 sulphanilic acid is diazotised and the diazonium salt treated with sodium sulphite. 
 The first reaction which takes place is not a reduction, but the formation of a diazo- 
 sulphonate : 
 
ANILINE AND ITS DERIVATIVES 59 
 SO,H.C,H,NH, + HNO; ——s> ‘igen :N 
 
 aie + Na,SO, > §0,Na.C,H,.N=N.SO;Na 
 | 
 
 The diazosulphonate is then reduced to the hydrazinesulphonate : 
 SO,Na.C,H,.N=N.SO,Na + 2H ———s 80,Na.C,H,.NH.NH.SO,Na 
 
 This reduction has sometimes been carried out by addition of zine dust and acetic 
 acid to the solution of diazosulphonate. But this is unnecessary, and is also com- 
 paratively costly. A simpler and quite effective method of reduction consists in 
 adding a sufficient excess of sulphite beyond that required to form the diazosulphonate 
 and then adding mineral acid. The nascent sulphur dioxide set free accomplishes the 
 necessary reduction. Finally, the mineral acid, at a suitable temperature, hydrolyses 
 the hydrazinesulphonate, the N-sulphonic acid group being split off as bisulphate : 
 
 SO,Na.C,H,.NH.NH.SO,Na + H.OH -———> §80O,Na.C,H,.NH.NH, + NaHSO, 
 
 The preparation is carried out as follows : 
 
 173 gms. of sulphanilic acid is dissolved in 700 c.c. of water with addition of 56 gms. 
 of soda ash. 115 gms. of concentrated sulphuric acid is then run in with stirring 
 and the mixture cooled to 12°. The precipitated sulphanilic acid is diazotised at this 
 temperature by slowly adding a solution of 70 gms. of sodium nitrite in 180 c.c. of 
 water. A slight excess of nitrous acid should be shown by starch-iodide paper. The 
 diazosulphanilic acid is even less soluble in water than sulphanilic acid. It is filtered 
 off and washed with a little ice water. 
 
 Meanwhile 690 gms. of the ordinary 38 to 40 per cent. sodium bisulphite solution is 
 carefully neutralised by addition of 35 per cent. caustic soda, using phenolphthalein 
 as indicator. This is the most convenient method of making the required solution 
 of neutral sodium sulphite. The addition of the alkaliis continued until the indicator 
 shows pink, when, by addition of a drop or two of bisulphite solution, the slight 
 alkalinity is removed. It is important that the sulphite solution should not be 
 alkaline, or tarry products are produced later. 
 
 The sulphite solution is stirred well, cooled to about 5°, and the diazosulphanilic 
 acid (which should not have been allowed to dry, as the dry substance is explosive) 
 is added, the temperature during mixing being kept about 5°. A yellow solution of 
 diazosulphonate is formed, and this reaction is completed by allowing the solution to 
 stand for an hour. The solution is then heated to boiling and concentrated hydro- 
 chloric acid added slowly until a strong mineral acid reaction shows on Congo Red 
 paper. About 800 to 850 gms. of acid arerequired. Some sulphur dioxide is evolved, 
 but most of it is, of course, used up in the reduction of the diazosulphonate to hydrazo- 
 sulphonate. The completion of this reaction is shown by the solution becoming 
 colourless. On cooling, phenylhydrazine-p-sulphonic acid crystallises out and, after 
 standing for some hours, is filtered off and washed with a little water. The yield is 
 about 165 gms. 
 
60 INTERMEDIATES FOR DYESTUFFS 
 Phenylhydrazinesulphonic acid is used in making pyrazolone derivatives. 
 
 Diphenylamine— tye 
 CALAN IC ON ncaa 
 
 —crystallises in leaflets, m.p. 54°, b.p. 301-9° (760 mm.), 179° (22 mm.). D 1-16. 
 It is insoluble in water, but soluble in methyl! and ethyl alcohol and in ligroin. 
 
 The ordinary method of preparation of diphenylamine is to heat aniline with aniline 
 hydrochloride at a high temperature, generally in an enamelled autoclave. There is 
 much variation in the conditions used by different workers on this substance. As 
 originally described by de Laire, Girard, and Chapoteaut (1866) (see Beilstein, II., 
 337), one molecule of aniline hydrochloride and 14 molecules of aniline are heated 
 at 210° to 240° for thirty to thirty-five hours. A later description by Girard and 
 de Laire (‘‘ Traité des dérivés de la houille,”’ 1873, p. 418) gives 260° as the maximum 
 temperature, and the proportion of aniline is reduced to 1 molecule. Fierz-David 
 describes essentially the same process as the former one, heating for twenty hours at 
 230° and using 1-4 molecules of aniline to 1 molecule of aniline hydrochloride. He 
 also states that the use of an enamelled autoclave (completely enamelled inside) is 
 essential, since traces of iron or copper diminish the yield by 30 to 50 per cent., with 
 formation of resinous products. Nevertheless, Fliirscheim (U.8.P., 1212928) proposes 
 to dispense with an enamelled autoclave by adding 430 parts of hydrated ferric 
 chloride and 44-5 parts of copper powder to 892 parts of aniline, and heating to 238° 
 to 240° in an ordinary iron autoclave. Finally, a so-called catalytic process is 
 described in detail by Groggins (“‘ Aniline and its Derivatives,” p. 164), in which 
 2,000 Ibs. of aniline mixed with 30 lbs. of concentrated hydrochloric acid is heated 
 in a steel autoclave at 290° for forty hours. 
 
 In every case, the conversion of aniline to diphenylamine is incomplete. The 
 autoclave contents, after the heating is finished, therefore consist chiefly of a mixture 
 of diphenylamine and aniline. From this mixture the aniline is extracted by dilute 
 hydrochloric acid. Diphenylamine can form a hydrochloride, but this is almost 
 completely dissociated by water at even moderate dilution. The autoclave contents 
 are, therefore, stirred up with about six times the weight of water at 80°, and hydro- 
 chloric acid added until the liquid shows acid to Congo Red paper. On cooling the 
 undissolved layer of diphenylamine sets to a solid cake. This is filtered off and is 
 washed again in succession with hot water, hot water containing a little hydrochloric 
 acid, and finally with hot dilute soda solution, after which it is cooled, filtered off, and 
 dried. The crude diphenylamine is purified either by fractional distillation in a 
 vacuum or by distillation with superheated steam at 300°. In the latter case it is 
 possible to distil 1 part of the base with 2 parts of steam. It collects as a colourless 
 liquid, which sets to a pale yellow solid. Allowing for the aniline recovered from the 
 wash liquors, which is usually about 30 to 35 per cent. of the aniline started with, 
 the yield of diphenylamine is about 85 to 90 per cent. of the theoretical. 
 
 An essentially different method of preparation has been devised by Contardi 
 (Giorn. Chim. Appl., 1920, 1, 11), based on the use of zine chloride as condensing 
 agent. It had been shown in some experiments by Merz and Weith that the double 
 
 a 
 a 
 ; 
 5 
 
ANILINE AND ITS DERIVATIVES 61 
 
 compound of aniline and zinc chloride, ZnCl,.2C,H;.NH,, when heated in open vessels, 
 even at high temperatures, yielded only traces of diphenylamine. Contardi, how- 
 ever, found that the double salt, ZnCl,.2(C,H;.NH,.HCl), when heated with two mole- 
 cular proportions of aniline, formed diphenylamine with evolution of ammonia, the 
 reaction proceeding according to the equations : 
 
 1. ZnCl,.2(C,H,NH,.HCl) + 2C,H,NH, = (C,H,).NH + NH,Cl + ZnCl,.2C,H,NH, 
 2. ZnCl,.2C,H;,NH, + 2NH,Cl = Zn(l,.2(C,H,;NH,.HCl) + 2NH, 
 
 As the equations indicate, the preliminary preparation of aniline hydrochloride and 
 its double salt with zinc chloride is unnecessary, all that is required being the addition 
 of zinc chloride and ammonium chloride to the heated aniline. The zinc chloride, in 
 fact, acts catalytically, but it seems to have been found necessary to use substantial 
 quantities of it, at any rate, to start the reaction. However, after the addition of a 
 small proportion of the required zinc chloride, the remainder may be substituted by 
 a mixture of zinc oxide and ammonium chloride in the proportions necessary to form 
 zinc chloride. 
 
 The actual method is as follows. 9 parts of aniline are heated to boiling in a 
 vessel (which may be of wrought or cast iron) fitted with a reflux condenser and a 
 stirrer, and 2-25 parts of recently fused zinc chloride, together with 1 part of ammo- 
 nium chloride, are added gradually. (If zinc oxide and ammonium chloride are used 
 to replace part of the zinc chloride, arrangement must be made, by keeping the con- 
 denser suitably warm, for the water formed to escape.) When the evolution of 
 ammonia has ceased, the contents of the vessel consist of a mixture in about equi- 
 molecular proportions of diphenylamine and the double salt ZnCl,.2(C,H;NH,.HCl). 
 But, without further addition of zinc chloride, the formation of diphenylamine is 
 continued by slow addition of aniline to the boiling liquid. Aniline may be added 
 up to the capacity of the vessel used. This point having been reached and the 
 ammonia having ceased coming off, the product’is fractionally distilled. The first 
 fraction consists of unchanged aniline, which may be used again. This is followed by 
 almost pure diphenylamine. Yields up to 90 per cent. have been obtained. 
 
 The residue after distillation is chiefly the double chloride, together with a little 
 diphenylamine and tarry matter. It was found that the process could then be 
 repeated by simply adding aniline again to the boiling residue, and so on, five times in 
 all before the apparatus required cleaning out. 
 
 Diphenylamine is chiefly used as a second component in monoazo dyes. As it is 
 insoluble in water and its salts with mineral acids are dissociated by water, the coupling 
 with diazo compounds is carried out in alcoholic solution. 
 
 Methyldiphenylamine— 
 
 —an oil, b.p. 291-7° to 292-2° (740-8 mm.). D%° 1-0476. 
 The methylation of diphenylamine by the usual method has been described by 
 Girard (Bull. Soc. Chim., 1875, 28, 2). 100 kg. of diphenylamine, 68 kg. of con- 
 
62 INTERMEDIATES FOR DYESTUFFS 
 
 centrated hydrochloric acid, and 24 kg. of methyl alcohol were heated for ten to 
 twelve hours in an enamelled autoclave at 200° to 250°. Methylation was not 
 complete under these conditions. After setting free the bases by addition of alkali, 
 they were separated and distilled. The distillate was shaken with two volumes of 
 concentrated hydrochloric acid, which formed the hydrochlorides of both bases. 
 Diphenylamine hydrochloride solidified and was filtered from the hydrochloride of 
 the methyl compound, which remained liquid. The methylated base could then be 
 isolated and purified in the usual way. 
 
 Methylation with dimethyl sulphate was used by Ullmann (Ann., 327, 113). 
 10 gms. of diphenylamine was warmed on the water-bath with 9-4 c.c. (1-2 mols.) 
 of dimethyl sulphate. When the reaction was over, the product was made alkaline 
 with caustic soda and distilled with steam. The yield of methyldiphenylamine was 
 8-5 gms. or about 80 per cent. It boiled sharply at 291°. | 
 
 As a tertiary amine, methyldiphenylamine is used in making a few acid triphenyl- 
 methane dyes of blue shades by condensing it with Michler’s ketone or p-dimethyl- 
 aminobenzoyl chloride and sulphonating the products. 
 
 Aminoazobenzene— 
 
 een 
 —crystallises in brownish-yellow needles, m.p. 127°. The hydrochloride forms dark 
 steel-blue crystals. 
 
 Aminoazobenzene is prepared by intramolecular transformation of diazoamino- 
 benzene under the catalytic influence of aniline hydrochloride. Diazoaminobenzene 
 is formed by the action of diazotised aniline on aniline. The preparation, therefore, 
 proceeds as follows : 
 
 1. C,H;NH, + NaNO, + 2HCI > O,H;.N=N.Cl + NaCl + 2H,0 
 
 2, C,H,N=N.Cl + H,N.C,H, 
 3. O,H,.N=N.NH.C,H, 
 
 > C,H,.N=N.NH.C,H; + HCl 
 > C,H,.N=N.C,H,.NH, 
 
 In presence of 
 OgH5.NHp. HCl 
 It is not necessary to prepare separately and to isolate the diazoaminobenzene. All 
 that is required is to add nitrite to a sufficient excess of aniline and hydrochloric acid, 
 and to warm the mixture of diazoaminobenzene, aniline hydrochloride, and aniline 
 so formed at such a temperature that the transformation will take place. What 
 constitutes a sufficient excess of aniline and hydrochloric acid ? As regards the acid, 
 it will be noted from equations (1) and (2) that the net consumption of acid in the 
 formation of diazoaminobenzene is 1 molecule per molecule of nitrite. Therefore, a 
 little more than 1 molecule of acid must be used per molecule of nitrite in order that 
 the excess may form the aniline hydrochloride required for the transformation. 
 As regards the aniline, 2 molecules are required per molecule of nitrite for diazoamino- 
 benzene. A slight excess over 2 molecules of aniline will then give the necessary 
 aniline hydrochloride. But it is advisable to use a much larger excess of aniline than 
 this, so that the free aniline may act as solvent for the diazoaminobenzene and aniline 
 
 / 
 
 Ti a ed a he ee SO eg Ee Gee ae a tree ate ny OTE sce ne A ee et i OE ee 
 
ANILINE AND ITS DERIVATIVES 63 
 
 hydrochloride, and thus enable the transformation to proceed more quickly and 
 smoothly. 
 
 Processes, based essentially on the principles just outlined, are described by Paul 
 (Zeit. angew. Ch., 1896, 9, 689), Jansen (Zert. Farb. Ind., 1913, 12, 197), Fierz-David 
 (‘‘ Farbenchemie,” 1920, p. 190), and Groggins (‘“‘ Aniline and its Derivatives,” 
 1924, p. 200). The following table, in which are shown the relative quantities of 
 materials used by the different authorities, is of interest as displaying the extent to 
 which personal idiosyncrasy enters into the settling of the details of a chemical 
 process. 
 
 Molecular Proportions of— | Yield of 
 ield 0 
 
 Process. | Aminoazobenzene 
 NaNO,. HCl. C,H,-NH. i Mipicemaes)): 
 Paul : - te yi 1 3-0 2°5 0:66 
 Jansen a - ate oe 1 1-05 7:7 — 
 Fierz-David : ie rt 1-9 4-1 0-81 
 Groggins .. 1 1-1 11-0 = 
 
 The actual process, as described by Fierz-David (loc. cit.), is as follows. To 
 250 gms. of aniline 110 c.c. of concentrated hydrochloric acid is added with good 
 stirring. The mixture is cooled externally to 32°, and at this temperature a solution 
 of 45 gms. of sodium nitrite (100 per cent.) in a little water is added during half an hour. 
 The temperature during the addition is not allowed to rise above 34°. After two 
 hours, the temperature is raised to 40°, and after another hour at this temperature it is 
 raised to 46° and kept there for three hours more. (The end of the transformation 
 may be tested by dissolving a sample in glacial acetic acid and spotting a drop of this 
 solution on filter-paper with an acetic acid solution of «-naphthylamine. If diazo- 
 aminobenzene is still present, a violet-red colouration is obtained by coupling of 
 diazobenzene acetate with a-naphthylamine). The mixture is then added to 250 c.c. 
 of water and 250 gms. of ice and concentrated hydrochloric acid stirred in till the 
 liquid is definitely acid to Congo Red paper. The excess aniline is thus dissolved out, 
 while the sparingly soluble aminoazobenzene hydrochloride remains undissolved. 
 About 200 c.c. of hydrochloric acid are required. The aminoazobenzene hydrochloride 
 is now filtered off and washed well with 10 per cent. salt solution containing also 2 per 
 cent. of hydrochloric acid. A final wash with 2 per cent. hydrochloric acid is given 
 toremove salt. The product is dried at 50°. This temperature must not be exceeded 
 because of the danger of forming dyes of the Induline class. 
 
 Aminoazobenzene is used as a first component in azo dyes, its diazo compound 
 being coupled mostly with naphthols and their sulphonic acids, thus forming disazo 
 dyes, which are generally of bright red or scarlet shades. 
 
 It is also heated with aniline hydrochloride under various conditions to form 
 mixtures of complex azine dyes known as the Indulines. 
 
64 INTERMEDIATES FOR DYESTUFFS 
 
 Aminoazobenzenesulphonic Acids. 
 
 Two sulphonic acids, a mono- and a disulphonic acid, are made and used as first 
 components in the preparation of disazo compounds, chiefly of the Biebrich Scarlet 
 type, by coupling with the naphthols and their sulphonic acids. 
 
 (a) Monosulphonic acid : 
 
 S0,.HY N= NC NE, 
 The acid crystallises in yellowish needles with 14H,O, which are very sparingly 
 soluble in water. 100 parts of water at 22° dissolve 0-0144 part of the acid. The 
 calcium salt is also sparingly soluble, but the sodium salt is moderately soluble in water. 
 
 The preparation of this acid in pure condition and good yield offers some difficulty. 
 The obvious method of coupling diazotised sulphanilic acid with aniline does not work. 
 Coupling in the desired way takes place only to the extent of 15 to 20 per cent., some 
 diazoamino compound being formed, and the rest remaining uncoupled. If, however, 
 some easily hydrolysed derivative of aniline is used, the formation of diazoamino 
 compound is prevented and yet coupling may proceed in the normal way in certain 
 cases. In G.P. 217935 (A.G.F.A.) the aniline is acylated with p-toluenesulphon- 
 chloride. The preparation then proceeds as follows. 173 parts of sulphanilic acid are 
 dissolved in water and the necessary caustic soda, and diazotised as usual with nitrite 
 and hydrochloric acid. The diazo compound is then added to a cooled solution of 
 247 parts of p-toluenesulphonanilide in about 1,800 parts of water and 160 parts of 
 caustic soda solution (40° Bé). The p-toluenesulpho derivative of aminoazobenzene- 
 sulphonic acid separates, and when coupling is finished is filtered off, washed, and 
 dried. It is then stirred with 1,000 parts of concentrated sulphuric acid, and the 
 mixture warmed at 40° until all has gone into solution, which takes about two hours. 
 The toluenesulpho group is thus hydrolysed off. On pouring the solution into ice- 
 water, the free aminoazobenzenesulphonic acid precipitates and is filtered off and 
 washed. 
 
 By sulphonating aminoazobenzene a product may be obtained, which consists 
 mostly of the same monosulphonic acid, but contains also some of the disulphonic acid, 
 and possibly isomeric monosulphonic acids. This product is good enough for certain 
 colours, though it does not give the desired shade and properties which are obtainable 
 with the pure 4-sulphonic acid. 
 
 The sulphonation is carried out by stirring aminoazobenzene hydrochloride with 
 three times its weight of 25 per cent. oleum at 25° until a sample just dissolves clear 
 in dilute soda. At this point sulphonation to the monosulphonic acid is complete, and 
 on pouring the solution into ice-water the crude sulphonic acid is precipitated and 
 may be filtered off. nae 
 
 TN : 
 
 (6) Disulphonic acid : 80.1 (7 nen Pe \ NEL 
 The acid forms violet-shimmering red needles which are somewhat soluble in water. 
 The monosodium salt is flesh-coloured and is much less soluble than the acid, but the 
 disodium salt, which is yellow, is very soluble in water. 
 
ANILINE AND ITS DERIVATIVES 65 
 
 The disulphonic acid is prepared by continuing the sulphonation process described 
 above for the monosulphonic acid. When monosulphonation is complete, the solution 
 is raised to 40° and stirred well at this temperature until a sample is found to be 
 completely soluble in a large proportion of water. The solution is then poured on to 
 six times its weight of ice, and on adding salt till a 20 per cent. solution is obtained the 
 monosodium salt is salted out. This is filtered off and washed with 15 per cent. salt 
 solution. 
 
 The disodium salt is itself used as a dyestuff, under the name Acid Yellow or Fast 
 Yellow, but the chief use of the disulphonic acid is for the production of scarlet 
 disazo dyes by coupling its diazo compound with the naphthols and their sulphonic 
 acids. Aminoazobenzenemonosulphonic acid is used in a similar way. 
 
 Phenylglycine : 
 
 ve 
 NH.CH,.COOH 
 
 The acid forms white crystals, m.p. 127°, moderately soluble in water. The sodium 
 and potassium salts are easily soluble, the calcium salt sparingly soluble, and the iron 
 and copper salts insoluble in water. 
 
 The preparation of phenylglycine has been the subject of much investigation, due 
 to its Importance as an intermediate for Indigo. The methods followed are of three 
 kinds : 
 
 1. The condensation of aniline with chloroacetic acid. 
 
 2. The formation of the nitrile of phenylglycine by means of formaldehyde and 
 cyanides, followed by hydrolysis of the nitrile. 
 
 3. The condensation of aniline with trichloroethylene, followed by hydrolysis of 
 the product. 
 
 Kach of these methods will be dealt with in turn. 
 
 1. Condensation of Aniline with Chloroacetic Acid. 
 
 This reaction does not take the simple course indicated by the equation : 
 C,H, NH, + ClLCH,COOH = O,H,.NH.CH,COOH + HCl. 
 
 If equimolecular quantities of aniline and chloroacetic acid are heated together at 
 100°, some phenylglycine is formed, but there is also much phenyliminodiacetic acid 
 C,H;.N(CH,.COOH),, some -chloroacetanilide, Cl.CH,CO.NH.C,H;, some diphenyl- 
 diketopiperazine— 
 
 CH,—CO 
 Bree NCCE 
 OBOE 
 
 and some unchanged aniline. The tendency towards formation of phenylimino- 
 
 diacetic acid may be diminished by using an excess of aniline. Using 2 molecules 
 
 of aniline per molecule of chloroacetic acid and heating the two in water, de Mouilpied 
 
 (J.C.S8., 1905, 87, 438) obtained a yield of 70 to 80 per cent. of phenylglycine, containing 
 
 a small proportion of phenyliminodiacetic acid. The use of 3 molecules of aniline 
 5 
 
 C,H,.N 
 
66 INTERMEDIATES FOR DYESTUFFS 
 
 per molecule of chloroacetic acid seems almost entirely to prevent the formation of 
 the diacetic acid derivative. 
 
 But with the use of excess of aniline another by-product appears—namely, phenyl- 
 glycineanilide, C,H;.NH.CH,.CO.NH.C,H;—formed by condensation of the first 
 formed phenylglycine with aniline. This, however, can be reconverted to phenyl- 
 glycine by hydrolysis with alkali. 
 
 The isolation of phenylglycine from the reaction mixture may be carried out by 
 addition of sufficient alkali (e.g., soda) to set free excess aniline from its hydrochloride, 
 and distilling off the aniline with steam. This leaves an aqueous solution of the 
 sodium salt of phenylglycine accompanied by sodium chloride. If this is acidified, 
 phenylglycine is precipitated, but its solubility even in cold water is such that a 
 substantial amount remains in solution and is lost. On the other hand, evaporation 
 of the solution of the sodium salt to dryness would give a product containing sodium 
 chloride which would cause trouble in the subsequent alkali fusion of the phenyl- 
 glycine. 
 
 A process has been patented by the Badische Aniline Co. (G.P. 169358), in which 
 these difficulties are overcome by converting the phenylglycine completely to the 
 anilide, a very sparingly soluble substance which may be separated without loss and 
 then hydrolysed by a molecular proportion of caustic soda, thus yielding a solution 
 containing the sodium salt of phenylglycine only. Two methods of carrying this out 
 are described. In the first, 500 kg. of aniline and 100 kg. of chloroacetic acid are 
 heated first at 100° for three hours, then at 120° in a vacuum, until no more water is 
 evolved. A solution of phenylglycineanilide and aniline hydrochloride in aniline is 
 thus obtained. Sodium carbonate is added, and the free aniline is distilled off with 
 steam. Under these conditions no hydrolysis of phenylglycineanilide takes place. 
 On cooling the residual liquid, the anilide solidifies to a crystalline cake. This is 
 separated and heated with one molecular proportion of caustic soda solution in an 
 autoclave at 140° to hydrolyse the anilide. After steam-distilling off the aniline set 
 free by hydrolysis, the remaining solution is evaporated to drynessin a vacuum. In 
 the second method, the aniline and chloroacetic acid are refluxed with 200 litres of 
 water for three hours. The water is then distilled off under reduced pressure and the 
 distillation continued, while the temperature of the melt rises to 120° to 140°, until no 
 more water comes over. The melt is now cooled, stirred with caustic soda solution, 
 which extracts the hydrochloric acid formed during the reaction, and the mixture 
 
 allowed to settle. The aniline layer containing phenylglycineanilide in solution is 
 
 separated and is hydrolysed with aqueous caustic soda (1 mol. NaOH to 1 mol. 
 phenylglycineanilide) in an autoclave at 140° as before. The aniline is then distilled 
 off with steam and the remaining solution evaporated to dryness. 
 
 Another method of overcoming the difficulty of the formation of phenylimino- 
 diacetic acid or phenylglycineanilide by further action on the first formed phenyl- 
 
 glycine consists in the removal of the phenylglycine from the sphere of reaction, as 
 
 it is formed, by conversion into an insoluble salt. For this purpose the ferrous salt 
 seems to be particularly well suited. The large excess of aniline required in other 
 
 methods may also be dispensed with. Meister Lucius and Briining have patented a 
 
 a ee, Oe a es ee 
 
 —_— 
 
 a ee ee ee ee 
 
 a eo | ne 
 
ANILINE AND ITS DERIVATIVES 67 
 
 process of this kind (G.P. 177491), in which the molecular ratio of aniline to chloro- 
 acetic acid is reduced to 1-1: 1. A solution of 1,250 ke. of ferrous chloride in water is 
 precipitated by adding caustic soda or carbonate. 300 kg. of salt are added, and the 
 mixture heated to 90° to 100°. At this temperature 472 kg. of chloroacetic acid is 
 added, followed quickly by 510 kg. of aniline. Heating is now continued under reflux 
 for one and a half hours. After cooling, the insoluble iron salt of phenylglycine is 
 filtered off, washed with cold water, and then converted into the sodium salt by stirring 
 with water and adding the required carbonate or caustic soda. Any aniline present is 
 distilled off with steam, the mixture filtered from iron oxide or carbonate, and phenyl- 
 glycine precipitated from the filtrate by careful addition of dilute acid. 
 
 Other processes are described by Chemische Fabrik von Heyden (H.P. 14049 of 
 1902), Friswell (H.P. 18149 of 1907), Chemische Fabrik Weiler-ter-Meer (G.P. 244825) 
 and Wohl and Blank (G.P. 167698). 
 
 2. Intermediate Formation of the Nitrile. 
 
 According to G.P. 135332 (Meister Lucius and Briining), aniline reacts with 
 formaldehyde and a cyanide thus— 
 
 C,H,NH, + CH,O + NaCN + H,O = C,H,.NH.CH,COONa + NH, 
 
 —and a process of preparation of phenylglycine on these lines is described in the patent. 
 But it was shown later by the Basle Chemical Works, in G.P. 145376, that the maximum 
 yield obtainable by the above method was about 60 per cent., and that much better 
 results could be obtained by previously condensing formaldehyde with two molecular 
 proportions of aniline so as to form methylenedianiline, C,H;.NH.CH,.NH.C,H;, 
 which then reacted with cyanide as follows : 
 
 (a) C,H,.NH.CH,.NH.C,H, + KCN + H,O = (,H,NH.CH,.CN + KOH + (,H,.NH,. 
 (b) C,H,.CH,.CN + KOH + H,O = (,H,.NH.CH,.COOK + NH, 
 
 Probably the low yield in the earlier process is due to the reaction taking this course 
 to a large extent. The Basle Chemical Works, therefore, proceed as follows. A 
 mixture of 186 kg. of aniline (2-1 mols.), 200 litres of alcohol, and 5 litres of 30 per 
 cent. caustic potash or soda is treated with 80 kg. of 37-9 per cent. formalin and the 
 solution heated to boiling. At the boil, 132 litres of a 49-3 per cent. solution of 
 potassium cyanide, previously warmed, is run in. A fairly vigorous reaction takes 
 place with evolution of ammonia, and after half an hour’s heating complete solution — 
 is obtained. The alcohol and aniline are now distilled off and the residual solution of 
 potassium salt of phenylglycine evaporated to dryness. Yields of over 90 per cent. 
 are obtained. 
 
 The nitrile may also be formed by interaction of a cyanide with the methyl-o- 
 sulphonate of aniline, a method introduced by Bucherer, who describes the process as 
 follows (G.P. 157909): A mixture of 75 gms. of 40 per cent. formalin and 260 gms. 
 of 40 per cent. bisulphite is warmed for a short time on the water-bath until the 
 smell of formaldehyde has disappeared. A solution of “‘ formaldehyde-bisulphite,” 
 
68 INTERMEDIATES FOR DYESTUFFS 
 
 OH.CH,.SO,Na, is thus formed. To this is added 93 gms. of aniline and the mixture 
 stirred at 90°. Soon the aniline disappears with formation of sodium methylaniline- 
 o-sulphonate, C;,H;.NH.CH,.SO;Na. A solution of 70 gms. of 95 per cent. potassium 
 cyanide (or equivalent sodium cyanide) in 200 c.c. of water is now added, and in a 
 short time the nitrile has separated completely. The whole process requires only 
 a fraction of an hour: 
 
 C,H,.NH.CH,.SO,Na + NaCN = (O,H,.NH.CH,.CN + Na,S0O, 
 
 The conversion of the nitrile to phenylglycine is not described in the patent. Pre- 
 sumably it would be best to filter off the nitrile, thus getting rid of the sulphite, before 
 hydrolysing with an equivalent of alkali. 
 
 3. Condensation of Aniline with Trichloroethylene. 
 
 The fact that trichloroethylene is easily converted into chloroacetic acid naturally 
 suggests the possibility of preparing phenylglycine by condensing trichloroethylene 
 with aniline and hydrolysing the product. Dichloroviny] ether, C,HCl,.0C,H;, which 
 is a product of partial hydrolysis of trichloroethylene, had been condensed with aniline 
 under hydrolytic conditions so as to yield phenylglycine ester, by Imbert (E.P. 13176 
 of 1907; E.P. 5013 and 5014 of 1907). But he succeeded later in carrying out the 
 condensation with trichloroethylene itself. Apparently the reaction proceeds through 
 the intermediate formation of ethylenetriphenyltriamine by elimination of hydro- 
 chloric acid from 1 molecule of trichloroethylene and 3 molecules of aniline. This 
 base had previously been made by Sabanejeff (Ann., 178, 125). The next stage of the 
 reaction is the hydrolysis of Sabanejefi’s base to phenylglycineanilide, followed by 
 a final hydrolysis to phenylglycine. 
 
 HC—NH.C,H, 
 CHCl Gi 
 Wy + 80HeNHs anor > N.C,H, <Ho-> CoH. NH.CH,.CO.NH.C,H, 
 HC—NH.C,H, 
 
 > C,H,.NH.CH,.COOH 
 
 There is no necessity, of course, to isolate the intermediate bodies. The process is 
 described in K.P. 173540 (B.D.C., Levinstein and Imbert). 
 
 132 parts of trichloroethylene, 100 parts of lime, 800 parts of water, and 280 parts 
 of aniline are heated together in an autoclave with good stirring for twenty-four hours 
 at 180°. After cooling, the excess of aniline is distilled off. The residual liquor 
 contains the calcium salt of phenylglycine and excess lime in suspension, and calcium 
 chloride, together with a little phenylglycine calcium salt in solution. When cold the 
 mixture is filtered. (The small amount of phenylglycine calcium salt in the filtrate 
 may be precipitated as ferroussalt.) The solid residue is now boiled with the necessary 
 quantity of sodium carbonate or hydroxide to convert the calcium salt to sodium salt. 
 This is filtered free of lime, and the filtrate evaporated to dryness. 
 
 It will be noticed that the proportion of 3 molecules of aniline to one of trichloro- 
 
 e ics me si oT ee gins she = gael ng 
 er eh aN PR tat an. a emg OS eC higet we |, ee 
 
 SSSI I a Ferner Ay ie a Sie a 
 
ANILINE AND ITS DERIVATIVES 69 
 
 ethylene is used in the above process, in accordance with the theory of the reaction 
 previously given. And, in fact, if less aniline is used the yield of phenylglycine is 
 much diminished when the process is carried out as above. But an improved process 
 has been devised (E.P. 188933, Wyler and B.D.C.), in which the excess of aniline is cut 
 down to about 5 per cent. This is achieved by adding the trichloroethylene gradually 
 to the mixture of aniline and milk of lime, so that from start to finish the trichloro- 
 ethylene present always finds three molecular proportions of aniline to react with. 
 
 412 parts of aniline, and milk of lime, made from 504 parts of lime and 2,000 parts 
 of water, are heated with stirring in an autoclave to 170° and, during ten hours, 555 
 parts of trichloroethylene are pumped in, the temperature being maintained at 170° 
 to 180.° The small amount of unchanged aniline is distilled off and the residual 
 calcium salt worked up as described in the previous patent. 
 
 Quinoline— an a 
 aa 
 
 —a colourless, strongly refracting liquid of characteristic smell. It freezes at — 19-5°, 
 and boils under various pressures as follows : 238° (760 mm.), 132° (40 mm.), 118-2° 
 (20 mm.), 113-3° (16 mm.), 104:8°(9 mm.). Its specific gravity compared with water 
 at 4° is 0-9211 (234°), 1-069 (50°), 1-0947 (20°), 1-1081 (0°). Itis moderately soluble in 
 water, 100 parts of cold water dissolving about 6 parts of quinoline. It is very hygro- 
 scopic and absorbs, on standing in moist air, at 10°, water corresponding to 1-5 H,0. 
 On warming this hydrate to 40° it dissociates and becomes cloudy in appearance. 
 -Quinoline is a strong base and forms a crystalline hydrochloride, m.p. 93° to 94°, 
 soluble in chloroform and alcohol in all proportions and also in warm ether and benzene. 
 The method of preparation was discovered by Skraup (Mon., 1881, 2, 141), who 
 heated aniline with glycerine, sulphuric acid, and nitrobenzene, the last serving as an 
 oxidising agent. The glycerine is converted by the sulphuric acid to acrolein, 
 CH, : CH.CHO, which Skraup supposed to condense with aniline to give the Schifi 
 base, C,H,;.N : CH.CH : CH,, this being then oxidised to quinoline : 
 
 H,C 
 (\ wee e 
 +e + 0 —H.0- HS 
 Woe ae 
 
 Later investigation showed that the reaction more Eaae takes the course : 
 
 CHO CH 
 vA ee /\ \cu, Sor isdie 
 | a aD ae ae bu, mo” br 
 
 ea Oe ar naw 
 yy 
 > 
 ery 
 
 N 
 
70 INTERMEDIATES FOR DYESTUFFS 
 
 However, the fact that there is always a considerable quantity of aniline left after the 
 reaction is over indicates that both the Schiff base and the addition product are 
 formed, and that while the latter is converted into quinoline, the former is unaffected 
 until the reaction mixture is diluted with water, when it is simply hydrolysed, like 
 other Schiff bases, to aniline and the aldehyde acrolein again. 
 
 Other oxidising agents have been used in place of nitrobenzene, giving, it is claimed, 
 better yields of quinoline. Skraup obtained 55 parts of quinoline from 50 parts of 
 aniline and 32 parts of nitrobenzene, a yield of less than 50 per cent., and this yield 
 has not been substantially improved upon by later workers with his method. But, 
 using arsenic oxide, As,O; (Kniippel, Ber., 1896, 29, 703; G.P. 87334), a yield of 67 per 
 cent. is obtained. Calcined ferric oxide (Barnett, Chem. News, 1920, 121, 205) as 
 oxidant leads to a 60 per cent. yield of quinoline. Chloropicrin, CCl,;.NO,, has also 
 been proposed (E.P. 198462). 
 
 The following description is based on Kniippel’s method. 50 parts of aniline, 
 155 parts of glycerin, 76 parts of arsenic oxide, and 145 parts of concentrated sul- 
 phuric acid are well mixed in a vessel provided with a wide-bore reflux condenser. 
 The mixture is then heated cautiously until an appearance of boiling begins to show 
 in the liquid, when external heating is stopped. The reaction proceeds very vigorously 
 of itself, once started, and external cooling may even be required to moderate it. 
 When this reaction is over, the liquid is boiled for about three hours. It is then 
 diluted with water, made alkaline with caustic soda solution, and the quinoline and 
 aniline distilled with steam. The total distillate is made strongly acid with sulphuric 
 acid, cooled to 0° to 5°, and a saturated solution of sodium nitrite added until excess 
 nitrous acid shows on starch-iodide paper. The aniline is thus diazotised, while the 
 quinoline is unaffected. The solution is heated on the water-bath until evolution of 
 nitrogen, due to conversion of benzenediazonium chloride into phenol, ceases. On 
 making alkaline again with caustic soda and steam distilling, quinoline alone distils 
 with the steam. Most of the quinoline may be separated directly from the disiillate, 
 but part is dissolved in the water and is extracted with ether or benzene. The extract 
 is dried and the solvent distilled off. The crude quinoline is then distilled under 
 reduced pressure. The fraction collected at 110° to 114° under 14 mm. pressure is 
 fairly pure quinoline. The yield obtained is about 46 parts. 
 
 Quinoline is used in the preparation of photosensitising dyes (see the Colour Index, 
 Nos. 805 to 809). 
 
 Quinaldine— Pw ge 
 
 s 
 
 ey 
 
 Vath 
 N 
 
 —a colourless oil, b.p. 246° to 247°, having a faint smell resembling that of quinoline. 
 
 This substance was first prepared by Débner and von Miller (Ber. 16, 2465) by 
 warming a mixture of 1 part of aniline, 14 parts of paraldehyde, and 2 parts of con- 
 centrated hydrochloric acid for a few hours on the water-bath. It was shown later 
 that the reaction proceeded essentially according to the equation : 
 
 C,H,.NH, + 2CH,;.CHO = C,,H,N ok 2H,O0 + H, 
 
ANILINE AND ITS DERIVATIVES 71 
 
 No hydrogen is evolved, however. It is evidently used up in reducing part of the 
 reaction mixture. The mechanism of the reaction seems to consist in the formation 
 of crotonaldehyde, CH;.CH : CH.CHO, by condensation of 2 molecules of acetalde- 
 hyde, followed by addition of the crotonaldehyde to aniline and finally ring closure 
 to quinaldine in a manner similar to that explained under quinoline : 
 
 OHC CH 
 va aD. /\ \cu, anes 
 | ie zal da.cH a bu.cH 
 Nya, CH.CHs Na axe 
 pone 
 
 It was considered by Jones and Evans (J.C.S., 1911, 99, 334) that the hydrogen was 
 used up in reducing part of the quinaldine to tetrahydroquinaldine— 
 
 CH, 
 een 
 
 wae fa 
 —which differs from quinaldine in being a secondary base and, therefore, capable of 
 being benzoylated. Recently, however, Mills, Harris, and Lambourne (J.C.S., 1921, 
 119, 1294) have shown that, in fact, quinaldine prepared by the Dobner-Miller process 
 is accompanied by little or no tetrahydroquinaldine, but that the secondary bases 
 which are formed in considerable quantity contain n-butylaniline, a substance closely 
 resembling tetrahydroquinoline in composition and character. This implies that the 
 crotonaldehyde in part condenses with aniline to form the Schiff base, crotonylidene- 
 aniline, which is reduced by the hydrogen eliminated in the main reaction to n- 
 butylaniline : 
 
 C,H;.N: CH.CH:CH.CH, + 4H -——» (,H,.NH.CH,.CH,.CH,.CH, 
 
 Some ethylaniline is formed in a similar way by reduction of ethylideneaniline pro- 
 duced from aniline and part of the acetaldehyde. 
 
 Mills, Harris, and Lambourne (Joc. cit.) describe the preparation of Are attie by 
 a modified Débner-Miller method, zinc chloride being added to the reaction mixture 
 (as originally proposed in G.P. 24317). Acetaldehyde (350 gms.), in the form of the 
 commercial 75 per cent. solution, is added slowly to a well-stirred mixture of 300 c.c. 
 of aniline and 1,200 c.c. of concentrated hydrochloric acid, cooled in ice-water. After 
 allowing the solution to stand for half an hour, 240 gms. of zinc chloride are added, 
 and the solution heated gently under reflux until a vigorous reaction begins. When 
 this has subsided, the liquid is boiled for four to six hours. Itis then poured on excess 
 of slaked lime and the mixture distilled with steam until 12 litres of distillate have 
 
72 INTERMEDIATES FOR DYESTUFFS 
 
 collected. The oil is then separated from the aqueous layer and the dissolved bases 
 extracted from the latter by a little chloroform. The crude oil (500 c.c.) is dissolved 
 in dilute sulphuric acid and a slight excess of nitrite added to the ice-cooled 
 solution. The secondary bases are thus converted into nitrosamines, which 
 separate as an oil. They are at once extracted with ether. The aqueous 
 layer is then heated on the water-bath, made alkaline with caustic soda, and 
 the tertiary bases distilled with steam. About 315 c.c. are obtained. On 
 fractionation this distils almost entirely about the boiling-point of quinaldine. 
 A small fraction, 3-5 gms., boils at a much higher temperature, 276° to 282°, and 
 consists of 6-ethylquinaldine. 
 
 The following is given as the technical method of preparation by Ullmann: 
 30 kg. of aniline salt is stirred with 40 to 50 litres of water and 24 kg. of acetaldehyde 
 run in during five to six hours, the temperature being maintained by cooling at 25°. 
 The mixture is allowed to stand at 25° for two to three days, until a sample warmed 
 with caustic soda solution no longer separates oil. (Instead, white flocks of a base, 
 CisH.)N>, separate as described in G.P. 28217.) After adding 40 kg. of zinc chloride 
 solution (50° Bé), the mass is evaporated to dusty dryness in a copper vessel. It is 
 then melted and the temperature raised to 275° for a short time. It is then trans- 
 ferred to a still, 150 litres of water, and 50 kg. of caustic soda solution (40° Bé) added 
 so as to give a strong alkaline reaction, and the quinaldine distilled in steam, while the 
 contents of the still are continuously stirred. The crude quinaldine is separated 
 from the distillate and is fractionated. The fraction distilling at 230° to 270° is taken 
 as technically pure quinaldine. The yield is 17 kg. of quinaldine from 30 kg. of 
 aniline, 
 
 Quinaldine is used in the preparation of photosensitising dyes (Colour Index, 
 Nos. 805 to 809). It is also condensed with phthalic anhydride to form Quinoline 
 Yellow. 
 
 -Isatinanilid 
 at ( ~—CO pe tabe: 
 | op | ai bet 
 Nes N.C,H,; ee fv NEC Hs 
 NH N 
 
 —crystallises from benzene in lustrous violet-black needles, m.p. 126°. From alcohol 
 it crystallises in orange-red leaflets. It dissolves easily in hot alcohol, ether, benzene, 
 and carbon disulphide. Its solution in alcohol is yellowish-brown, but in benzene or 
 carbon disulphide is cherry-red. It also dissolves easily in mineral or organic acid 
 solutions, forming salts. The mineral acid solutions on long standing, or more quickly 
 on warming, decompose with formation of isatin and aniline. 
 
 a -Isatinanilide is prepared from aniline by the method discovered by Sandmeyer 
 of which he gives an interesting account in the Zeitschrift fiir Farben- und Textil- 
 Chemie, 1903, 2, 129 (cf. also Helv. Chim. Acta., 1919, 2, 234). The method is also 
 embodied in a series of patents by Geigy and Co. (G.PP. 115169, 113978, 113980, 
 113981). 
 
 It depends on the following set of reactions, starting from thiocarbanilide, 
 
 a = : a a", Fees Fee = — > - — « ; 2 ne 
 IO rity Sie LE RR RE el ets: Fore La Pe OE ae Te EE MR BS 
 
 AR he AEF ——. 
 
 a ee ow. 
 
ANILINE AND ITS DERIVATIVES 73 
 
 which apparently reacts in this case, as also in other cases, in its tautomeric 
 form : 
 
 ( as ie e C:iN 
 Ses al eae | | 
 vad N.CpH; + Peco, \ /-NH-O=N.CH, 
 Thiocarbanilide Hydrocyancarbodiphenylimide 
 fos) 80 NE, AOSES6O 
 ee a te Stace eget oe C=N.C,H 
 + H28 | i a H2804 | pap saa 
 Ses NH—C=N.C,H, SA 
 Thio-oxamidediphenylamidine a-Isatinanilide 
 (‘* Thioamide ’’) 
 
 (i.) Thiocarbanilide.—This is prepared by boiling aniline with an equal weight of 
 carbon disulphide under reflux until evolution of hydrogen sulphide ceases. The 
 excess of carbon disulphide is then distilled off and the residue raised to a temperature 
 a little above the melting-point of thiocarbanilide, when the liquid can be poured out 
 and powdered when cold. The yield is quantitative. 
 
 The reaction, which takes about two days to complete under the above conditions, 
 can be accelerated by the addition of alcohol and caustic potash. 
 
 Thiocarbanilide melts at 154°. 
 
 (u.) Hydrocyancarbodiphenylimide.—A solution of 70 gms. of 96 to 98 per cent. 
 potassium cyanide (or 53 gms. of sodium cyanide) in 200 gms. of water is mixed with 
 300 gms. of basic lead carbonate (white lead), 200 gms. of very finely powdered thio- 
 carbanilide, and 500 gms. of 90 per cent. alcohol. The whole is stirred and slowly 
 heated to 50° to 60°, at which temperature it is kept until the reaction is finished, as 
 shown by a sample, filtered from lead sulphide, giving a filtrate which no longer 
 blackens lead carbonate on boiling. When this point is reached, which only requires 
 a short time, the mixture is heated to boiling, filtered hot, and the residue extracted 
 twice with alcohol. On cooling the united filtrates most of the product crystallises 
 out, and more can be obtained by concentrating the mother liquor. The yield is 
 about 175 gms. and the substance is obtained as pale yellow prisms, m.p. 137°. 
 
 (iii.) Thioamide.—200 gms. of finely powdered hydrocyancarbodiphenylimide 
 is stirred vigorously with 500 gms. of yellow ammonium sulphide solution. The 
 latter is made by passing 35 gms. of hydrogen sulphide into 400 gms. of 21 to 22 per 
 cent. ammonia and dissolving in the, as yet, colourless solution 25 gms. of powdered 
 sulphur. The temperature of the mixture is kept about 25° to 35°, until a sample, 
 filtered and well washed, dissolves completely in dilute hydrochloric acid. The rate 
 of addition of the hydrogen sulphide depends on the fineness of division of the hydro- 
 cyancarbodiphenylimide, and may take two days. The thioamide is then filtered off, 
 washed, and dried. It forms a lemon-yellow powder, which is pure enough for the 
 next stage. It may be purified by crystallisation from alcohol, when it is obtained 
 as lustrous golden yellow prisms, m.p. 161° to 162°. It is soluble in dilute mineral 
 acid and also, on warming, in dilute caustic soda. 
 
 (iv.) «-Isatinanilide.—The conversion of the thioamide to isatinanilide is accom- 
 plished by heating with sulphuric acid, but it is necessary to add the thioamide to the 
 
74 INTERMEDIATES FOR DYESTUFFS 
 
 previously heated acid. If the thioamide is added to cold acid and slowly heated, 
 so much decomposition occurs that only a little isatinanilide results. 
 
 To 800 gms. of concentrated sulphuric acid at 90° is added with stirring 200 gms. 
 of well-dried thioamide. Much heat is developed, and cooling arrangements must be 
 made so as to keep the temperature from rising above 95°. These temperature limits 
 are important. A vigorous evolution of sulphur dioxide takes place, and the thio- 
 amide dissolves, giving at first a dark brown-violet solution, which finally becomes 
 intense yellowish-red. When all the thioamide has been added, the temperature is 
 raised to 105° to 110°, and kept there till evolution of sulphur dioxide ceases, which 
 takes about an hour. The solution is then cooled to the ordinary temperature and 
 run into a mixture of ice and salt solution. The isatinanilide is thus precipitated as its 
 red crystalline hydrochloride, mixed with sulphur. It is filtered off, washed acid-free 
 with concentrated salt solution, stirred into water, and dilute sodium carbonate 
 solution added till faintly alkaline. The mixture of brown isatinanilide and sulphur 
 is filtered off, washed, and dried. The sulphur is extracted with carbon disulphide, 
 and the isatinanilide crystallised from benzene or alcohol. The yield is 150 gms. of 
 recrystallised substance. 
 
 a-Isatinanilide is readily converted into Indigo by the action of hydrogen sulphide 
 in acid solution, and Indigo was at one time made by this process. It was abandoned 
 because of the lower cost of the phenylglycine fusion with sodamide. Isatinanilide, 
 however, is most conveniently made by the above method, and is used as an inter- 
 mediate for a number of vat dyes. These are prepared by condensing isatinanilide 
 with various substances containing in the molecule the group —CO—CH,— or its 
 tautomeric form —C(OH)=CH—. Examples of such bodies are hydroxythio- 
 naphthene (thiomdoxyl, p. 208), «-naphthol (p. 145), «-anthrol (p.232). Thus, with 
 thiomdoxy] : 
 
 “NCO co— 6 co—< 
 (J PSce, + omc? ( | —> ( Seen 
 \ Js NH—\ , Ss a 
 Isatin— 
 —Co —CO 
 ~ Sy 
 | ee Poe or | 7 pook 
 
 —crystallises in yellowish-red prisms, m.p. 200° to 201°, sparingly soluble in cold 
 water, but easily in hot water and in boiling alcohol or benzene. It dissolves in cold 
 dilute alkali to a dark violet solution, from which it is reprecipitated by acids. Butif 
 the alkaline solution is warmed, the colour changes to pale yellow owing to hike 
 of the isatin to o-aminobenzoylformic acid : 
 
 “\_c0.COOH 
 
 S pie 
 
 This can be reconverted to isatin by warming with acids. 
 
 Co a ee eee aS ae ee 
 
 ae 1 eS) iad 
 
ANILINE AND ITS DERIVATIVES 75 
 
 Isatin was formerly prepared by oxidation of Indigo, but poor yields are obtained 
 in this way. 
 
 It is readily prepared by heating «-isatinanilide with dilute mineral acid, pref- 
 erably hydrochloric acid, when hydrolysis takes place and aniline is split off, the 
 isatin being precipitated (G.P. 113979, Geigy) : 
 
 Vaan N.C.H (\—c0 C.H..NH 
 ee ee ie ee te ae aes 
 a : aioe 
 
 The isatin is filtered off and recrystallised from hot water. 
 
 Hither of the usual processes for the manufacture of Indigo—+.e., the phenyl- 
 glycine and phenvlglycine-o-carboxylic acid processes—can be adapted to the prepara- 
 tion of isatin by adding strong oxidising agents to the melt when the formation of 
 indoxyl or indoxylic acid is complete. Weak oxidising agents, of course, convert the 
 indoxyl or indoxylic acid into Indigo: 
 
 A 0 ye aad ct 
 i CH,.COOH sf | | ag 207 | ey, 
 re Seeks AeA 
 Indoxyl 
 ( \—cooH \ co. Varies 
 | | to | SCH.COOH —=35—> | | Sco 
 \_J—NH.CH,.COOH _NH _NH 
 
 ef ws 
 Indoxylic Acid 
 
 Thus, according to G.P. 107719 (Badische), 7 parts of indoxylic acid are added to 
 a solution at 80° of 6 parts of potassium permanganate and 10 parts of caustic soda 
 in 50 parts of water. When the solution is decolourised, the manganese dioxide is 
 filtered off, the filtrate exactly neutralised, evaporated to small bulk, and excess of 
 mineral acid added, when on cooling the isatin crystallises out. 
 
 Alternatively, 8 parts of indoxy] in aqueous solution are added slowly to a boiling 
 mixture of 20 parts of manganese dioxide (regenerated), 30 parts of water, and 7 parts 
 of caustic soda solution (25° Bé). When the oxidation is completed, the isatin is 
 isolated as above. 
 
 The yields of isatin in this process are said to be much better than those from 
 Indigo itself. 
 
 Isatin is used for the preparation of vat dyes by condensation with indoxyl and 
 thioindoxyl. Unlike «-isatinanilide, however, it is the f-carbonyl group in isatin 
 which reacts : 
 
 Indirubin 
 
76 INTERMEDIATES FOR DYESTUFFS 
 
 /\_—co oH /\—co 
 | SCH, + 00¢ | aaa | i—— 
 Neate We ees We 00 am 
 
 Thioindigo Scarlet 
 
 Indirubin itself is not used as a dyestuff, but a brominated derivative constitutes 
 Ciba Heliotrope. 
 
 a-Isatin chloride— me Ep 
 @ Yo.cl 
 oN 
 
 —crystallises in brown needles, m.p. 180°, soluble in alcohol, glacial acetic acid, and 
 hot benzene. It also dissolves in ether to a blue solution. 
 
 The preparation of this substance is described by Baeyer (Ber., 12, 456). 5 parts 
 of isatin are warmed on the water-bath with 6 to 7 parts of phosphorus pentachloride 
 and 8 to 10 parts of dry benzene. On cooling the isatin chloride crystallises and is 
 filtered off and washed with ligroin. 
 
 a-Isatin chloride, like «-isatinanilide, reacts in the «-position with indoxyl and 
 thioindoxyl or their derivatives, and is used for the preparation of vat dyes of the 
 types mentioned under «-isatinanilide. | 
 
 5 : 7-Dibromoisatin— 
 
 Br et —CO 
 Sco (m.p. 248-250°) 
 | |_wH 
 neg 
 
 Br 
 
 —is prepared by slowly warming isatin with bromine in concentrated sulphuric acid 
 (G.P. 245042). 
 
 It yields a 5: 7-dibromoisatin chloride (G.P. 237199), which is used for vat dyes 
 of the types already described. 
 
CHAPTER IV 
 BENZENESULPHONIC ACIDS 
 
 The Phenols and their Derivatives. 
 
 THE benzenesulphonic acids of technical importance are the monosulphonic acid 
 and the m-disulphonic acid, since from these are obtained respectively phenol and 
 resorcinol. Benzene is easily sulphonated with ordinary concentrated sulphuric 
 acid at moderate temperatures, though the process is rather slow, because the solu- 
 bility of benzene in sulphuric acid is very small. According to Martinsen (Zeit. 
 physik. Chem., 1907, 59, 620), who studied the kinetics of the reaction, the speed of 
 sulphonation of benzene is immeasurably great at 80°, and is complete almost in the 
 same moment that the benzene goes into solution. If arrangements are made, as in 
 G.P. 71556, for thoroughly intimate mixture of the two reactants, the sulphonation 
 may be carried out at the ordinary temperature. This is done in the patented process 
 by mixing together 1 part of benzene, 6 parts of concentrated sulphuric acid, and 
 enough infusorial earth to make a shakeable paste. On allowing the mixture to stand 
 for twenty-four hours at the ordinary temperature, complete sulphonation to the 
 monosulphonic acid isobtained. The large excess of sulphuric acid required, however, 
 makes the method unsuitable for technical use. The sulphonation of benzene is 
 accelerated by the presence of sodium salts and certain other catalysts. Ambler and 
 Cotton (J. Ind. Eng. Chem., 1920, 12, 968) found that a mixture of sodium sulphate 
 and vanadium pentoxide doubled the rate of sulphonation. 
 
 As regards the formation of disulphonic acids, the decisive factor is temperature. 
 Only very small amounts of disulphonic acids are formed at temperatures below 
 _ 200°, and temperatures of 250° to 275° are required for complete disulphonation. 
 Thus, no troublesome separations are required. 
 
 Benzenesulphonic acid : S0,H 
 
 4 
 
 ee 
 The acid crystallises with 1H,O in large colourless plates, which melt at 43° to 44°. 
 The anhydrous acid melts at 65° to 66°. The sodium salt crystallises with 1H,0 
 - inleaflets. 1 part of the salt is soluble in 1-75 parts of water at 30°. 
 ; Two processes are in use on the large scale for the sulphonation of benzene to the 
 monosulphonic acid : (1) The ordinary sulphonation of benzene as liquid at or slightly 
 above its boiling-point, (2) sulphonation of benzene as vapour at a much higher 
 temperature. These will be described in turn. 
 
 1. Liquid Phase Sulphonation. 
 
 A detailed description of this process, as worked in this country during the War, is 
 given in “Synthetic Phenol and Picric Acid,” published by the Ministry of Munitions, 
 from which the following summary has been made: 
 
 77 
 
78 INTERMEDIATES FOR DYESTUFFS 
 
 (a) Sulphonation.—Benzene and sulphuric acid are mixed in the usual cast-iron 
 sulphonation vessel, the proportion of acid used varying from 212 to 275 parts per 
 100 parts of benzene, and the strength of the acid varying between 95-3 per cent. and 
 100 per cent. The temperature at which the sulphonation is carried on depends on 
 the plant in use. With sulphonators open to the atmosphere (and carrying, of course, 
 reflux condensers) the temperature limit is the boiling-point of benzene, or 80°, but 
 in some cases closed vessels are used, and the sulphonation worked at temperatures 
 up to 120°, for the sake of quicker sulphonation. At 110° the sulphonation period is 
 four to six hours, using an acid of 98 to 99 per cent. strength. In open vessels the rate 
 of reflux of the benzene serves as a guide to the progress of sulphonation. When 
 refluxing stops, the sulphonation is nearly complete, and the temperature may then 
 be raised to 110° to complete the reaction. The disappearance of the benzene is not 
 a sufficient indication of complete sulphonation, as benzene, though almost insoluble 
 in sulphuric acid, is soluble to the extent of a few per cent. in concentrated sulphuric 
 acid-benzenesulphonic acid solutions. 
 
 The proportion of sulphuric acid employed is such that when the benzene is com- 
 pletely sulphonated, the residual sulphuric acid is about 80 per cent. in strength. 
 The amount of disulphonic acids formed is under 0-5 per cent. No sulphone is 
 formed when 95 to 96 per cent. sulphuric acid is used, but in the French factories, 
 which work with 100 per cent. acid, about 2 per cent. of sulphones, chiefly diphenyl- 
 sulphone, C,H;.SO,.C,H;, is obtained. 
 
 (b) Isolation of Sodium Benzenesulphonate.—The usual liming-out method may 
 be used, after dilution of the melt with water, but to avoid forming a slimy calctum 
 sulphate which would be difficult to filter and wash, it is necessary to keep the solution 
 hot and to leave it faintly acid, when the calcium sulphate separates in a crystalline 
 condition. The sodium sulphonate is then formed by addition of the exact quantity 
 of sodium carbonate or sulphate to the filtrate and, after filtering from calcium 
 carbonate or sulphate, sodium benzenesulphonate is obtained in almost quantitative 
 yield on evaporating down the solution. The sulphonate may also be salted out by 
 addition to the undiluted melt of 1-8 times its volume of saturated brine, though 
 there is some loss of sulphonate by this method, since the salting out is not complete. 
 
 But in the complete process for the manufacture of phenol, considerable economy 
 can be introduced by using the sulphite formed in the alkali fusion of the sulphonate 
 to neutralise the acid of the sulphonation melt. This method was used at the Elles- 
 mere Port factory during the War. The sulpnonation melt is run into the aqueous 
 sulphite solution (containing some phenol) and solid sulphite added to make up the 
 necessary quantity. The temperature rises to about 100°. (Sulphur dioxide is given 
 off, and this is used to neutralise the alkaline sodium phenate solution obtained from 
 the fusion.) At the dilution used, the sodium sulphate formed separates almost 
 completely, leaving the sodium benzenesulphonate in solution of 30 per cent. strength. 
 The sodium sulphate is filtered off, the loss due to adhering sulphonate amounting 
 to about 4 to 5 percent. The filtrate is concentrated to 50 per cent. strength, and is 
 then dried, if desired, by spraying the solution into a large brick chamber through 
 which hot gases are passing. It was formerly the custom to dry the sulphonate 
 
‘SHATLVATHUC 'TONHHd GNV SCIOV OINOHdTNSUNAZNHA— AI LYVHO 
 
 20N °HN H®OS 20N 
 N70 
 PUNK N20 80N 2HNK N90) BHN ®UN 
 HO 2H2900 HO 490 HOO 
 HeOS 3 Ay 2 A S A iN 2 2 
 ON HN H®OS HN °HN 
 
 FHOHN( ) “(FHO)N | 
 HOOD 2on\_)N%0 °HN 7ON 
 
 EHOHN HO HO HO, 914250 HO HO HOO 
 
80 INTERMEDIATES FOR DYESTUFFS 
 
 thoroughly before fusion, but it has been found that this is not necessary. Quite 
 satisfactory results are obtained by running a concentrated solution of the sulphonate 
 direct to the fusion pot. In fact, rather higher yields of phenol are obtained in this 
 way, but this is more than offset by the fact that the fusion period is increased 
 by about 50 per cent. 
 
 2. Vapour Phase Sulphonation. 
 
 The sulphonation of benzene in the form of vapour has been investigated by Dr. 
 Tyrer in the United States, by Brunner, Mond and Co. in this country, and by Pro- 
 fessor Guyot in France. Detailed results of these investigations are not available, 
 but Dr. Tyrer has patented the process (U.S.P. 1210725), which is now used by the 
 Bakelite Corporation of the United States in the course of their manufacture of 
 phenol. A good account of this process is given by D. H. Killeffer (J. Ind. Eng. 
 Chem., 1924, 16, 1066), to which reference should be made for plant details. 
 
 Benzene is vaporised at 10 to 12 lbs. pressure (in order to ensure the absence of 
 liquid benzene on reaching the sulphuric acid) and the vapour led into ordinary con- 
 centrated sulphuric acid (66° Bé), which has been previously heated to 150°. The 
 temperature of the acid is then gradually raised to 170° to 180°, while the benzene 
 vapour is passed through at such a rate that some benzene escapes and condenses 
 along with the steam also escaping. At the temperature mentioned, the rate of 
 sulphonation of benzene is about ten times that obtained in liquid phase sulphonation 
 in open vessels. Moreover, since the water formed in the reaction is carried off, 
 sulphonation may be continued until almost all the sulphuric acid has been used up, 
 thus leading to considerable economy, both of acid and of alkali to neutralise it after- 
 wards. The course of the sulphonation is followed by noting the specific gravity of 
 the mixture, which falls as the reaction proceeds. It has been found convenient to 
 use up about 95 per cent. of the sulphuric acid, this point being indicated by the 
 specific gravity of the mixture attaining 39° Bé. Some diphenylsulphone (about 
 2 per cent.) is always formed in this process, besides a rather higher proportion of 
 disulphonic acids than is obtained in the ordinary sulphonation. 
 
 The reaction having been carried to the desired point, the sulphonation mixture 
 is worked up by any of the methods already described. The custom at the Bakelite 
 factory referred to is simply to neutralise the mixture with sodium carbonate solution 
 so as to produce a hot 50 per cent. solution of the sulphonate, which is then run 
 directly to the fusion pots. The small proportion of sodium sulphate present in the 
 solution apparently causes little trouble in the fusion. 
 
 Phenol— ee 
 
 g 
 —forms long colourless prismatic crystals, m.p. 43°, b.p. 183°, D’® 1-066. It is 
 
 soluble in 15 parts of water at ordinary temperature. At 84° it is miscible with water 
 in all proportions. 
 
BENZENESULPHONIC ACIDS 81 
 
 When sodium benzenesulphonate is fused with caustic soda at a sufficiently high 
 temperature, reaction occurs in accordance with the equation : 
 
 C,H,.SO,Na + 2NaOH = C,H,ONa + NaSO, + H,0 
 
 In practice the melt can be successfully carried out with 24 molecular equivalents 
 of alkali, though in some factories quantities up to 8 molecular equivalents are used. 
 Caustic potash gives no better results than soda. 
 
 The caustic soda is melted in the usual iron fusion pot and the liquid raised to 
 about 300°. While the replacement of the sulphonic acid group by hydroxy] can be 
 effected at temperatures well below 300°, a convenient fluidity of the melt must be 
 maintained, and if the minimum proportion of alkali is employed, temperatures of 
 300° and over must be used. It is important that the sulphonate should contain very 
 little sodium sulphate, as this causes a serious thickening of the melt if present in 
 quantity. The sulphonate is added gradually with constant stirring, while the 
 temperature of the melt is slowly raised until, after the last of the sulphonate has been 
 added, it reaches 340°, at which point it is maintained until the reaction is finished. 
 The determination of the end-point is an empirical matter, arrived at by ascertaining 
 the fusion period giving the best yield of phenol under the conditions employed. But 
 a rough indication is given by cessation of frothing. 
 
 Oxidation by exposure to the air during fusion causes some loss of phenol. Nearly 
 theoretical yields can be obtained by performing the fusion out of contact with air. 
 On the other hand, experiments in which air was bubbled through during fusion gave 
 yields less than the usual by 20 per cent. Sodium carbonate is the chief product of 
 oxidation, with possibly some salicylate. However, under ordinary conditions, the 
 loss by oxidation is small. 
 
 The sodium sulphite formed is practically insoluble in caustic soda and sodium 
 phenate, and therefore separates in solid form without, however, having the effect of 
 thickening the melt much. When the reaction is finished, the melt is run into such 
 a quantity of water that the sulphite remains almost entirely undissolved in the 
 _ strongly alkaline phenate solution formed, and is filtered off by means of a filter of 
 fine nickel gauze, and washed with a little water, the washings being added to the 
 filtrate. Some phenate persistently adheres to the sulphite. But this only causes 
 loss of yield on the first working of the process if, as previously described, the sulphite 
 is used in the neutralisation of the sulphonation mixture. 
 
 The phenol is now precipitated from the alkaline filtrate by acidification. The 
 acid commonly used is sulphuric acid, but in the Ellesmere Port process, as already 
 mentioned, the sulphur dioxide evolved in the neutralisation of the sulphonation 
 mixture is used. Carbon dioxide is also an economical means of acidification, but in 
 this case the conversion of sodium phenate to phenol is not complete, and a stronger 
 acid must be added to finish the conversion. The phenol (containing some water 
 in solution) separates as the upper liquid layer, and an aqueous solution of sodium 
 sulphate, or sulphite, or carbonate, and some phenol, forms the lower layer. The two 
 layers are separated. The phenol in the lower layer is either kept in circulation in 
 the process by using this aqueous solution for dilution and neutralisation of the 
 
 6 
 
82 INTERMEDIATES FOR DYESTUFFS 
 
 sulphonation melt, or the phenol may be extracted with solvent naphtha or 
 benzene. . 
 
 The phenol is now distilled under reduced pressure. The first runnings contain the 
 water present, and on standing separate into two layers, of which the aqueous layer is 
 used in the dissolving of the fusion melt, while the phenolic layer is returned to the 
 still. The distillation is controlled by testing samples for setting-point. The phenol 
 is collected when the setting-point reaches 39°. The residues contain dihydroxydi- 
 phenols, diphenylene oxide, and tarry matter. 
 
 The overall yield of phenol from benzene is at best about 90 per cent., though 
 usually under that figure. The main loss occurs through side reactions during fusion 
 of the sulphonate. 
 
 Phenol is used as a second component in azo dyes, mostly in conjunction with 
 benzidine as first component, though other diamines are also used. In the cases where 
 benzidine is used, 1 molecule of diazotised benzidine is coupled with 1 molecule of 
 phenol and with 1 molecule of another component. The resulting dyes are generally 
 too sensitive to alkalies to be useful as dyestuffs (though there are notable exceptions, 
 such as Diamine Green B, etc.), and the hydroxyl group of the phenol nucleus is 
 usually ethylated to overcome this defect. 
 
 Phenol is also used as intermediate for two triphenylmethane derivatives, Aurine 
 and Phenolphthalein, which are likewise too sensitive to alkalies and are only 
 employed as indicators. 
 
 A third general use of phenol is in the preparation of indophenols by oxidising a 
 mixture of phenol and a p-diamine or p-aminophenol : 
 
 Poo ee AR Aes 
 yeh ee 
 HOV / we HOLY YAO 
 
 These indophenols are then used in making sulphur colours. 
 p-Nitrosophenol— 
 
 O 
 aa 
 | or ) 
 Yo NOH 
 
 —crystallises in greyish-brown leaflets, which decompose at 124°. It is moderately 
 soluble in water, and easily soluble in alcohol, ether, and acetone, the solutions being 
 pale green in colour. It is sparingly soluble in glacial acetic acid. 
 
 The usual method of preparation is that described by Lange (“‘ Die Schwefel- 
 farbstoffe,” 1911, p. 133). 
 
 94 kg. of phenol is dissolved in 1,000 litres of water and 85 kg. of concentrated 
 caustic soda solution. A solution of 75 kg. of sodium nitrite in 300 litres of water and 
 1,000 kg. of ice is added. Cold dilute sulphuric acid, made from 235 kg. of concen- 
 trated sulphuric acid and 650 kg. of ice, is then added during one and a half hours, the 
 
BENZENESULPHONIC ACIDS 83 
 
 temperature being kept below 5°. The precipitated nitrosophenol is filtered off, 
 centrifuged, and air-dried. 
 
 A modified method is described in E.P. 203060 (Siderfin, Tallentyre, Shannon, and 
 Galbraith), in which nitrosation is accomplished by the gradual addition of water or 
 ice to a sulphuric acid solution of nitrosylsulphuric acid. To 256 gms. of a solution of 
 nitrosylsulphuric acid, containing the equivalent of 21-3 gms. of HNO, per 100 c.c., 
 are added successively in small quantities 60 gms. of water or ice, 70 gms. of phenol 
 liquefied with 10-5 gms. of water, and a further 120 gms. of water or ice. The tem- 
 perature of the reaction mixture is kept at about 0°. The solution may then be 
 diluted to precipitate the nitrosophenol, or it may be treated directly with carbazole 
 derivatives to prepare carbazoleindophenols, which are required for the production of 
 dyes of the Hydron Blue class. 
 
 The usefulness of p-nitrosophenol as an intermediate depends on its ability to 
 form indophenols by condensation with bases, these indophenols being then used for 
 the production of sulphur colours. The most notable example is the indophenol 
 
 formed with carbazole— 
 Cag 
 Seale) 
 a el s 
 
 —which is used in making Hydron Blue. 
 o-Nitrophenol— 
 
 —crystallises in bright canary-yellow needles, m.p. 45°, b.p. 214°. It is volatile in 
 steam. It is sparingly soluble in cold water, but dissolves in carbonate or caustic 
 alkaline solutions giving a deep red solution. 
 
 p-Nitrophenol— 
 
 —crystallises in colourless needles, m.p. 114°, and is not volatile in steam. It is 
 moderately soluble in hot water and very soluble in alcohol. 
 
 A mixture of these two nitrophenols is formed in about equal proportions when 
 phenol is nitrated with 20 per cent. nitric acid at about the ordinary temperature. 
 Sometimes an equivalent solution of sodium nitrate, to which sulphuric acid has been 
 added, isused. Ineithercase a large excess of reagent is used, about 1-8 molecules of 
 HNO, to 1 molecule of phenol. 
 
 94 gms. of phenol, liquefied by addition of a little water, is dropped slowly into a 
 well-stirred solution of 150 gms. of sodium nitrate in 400 c.c. of water and 250 c.c. of 
 concentrated sulphuric acid, the temperature being kept below 20°. After stirring 
 
84 INTERMEDIATES FOR DYESTUFFS 
 
 for a further two hours, the liquid is allowed to stand, when the mixed nitrophenols 
 separate as a dark heavy oil. The aqueous layer is decanted off and the nitrophenols 
 washed free of acid by means of water containing a littlechalk. Caustic soda must not 
 be used, as this would resinify the crude nitrophenols. The o-nitrophenol is then 
 distilled off with steam, and after allowing the distillate to stand several hours is 
 filtered off. The yield is about 40 gms. From the residue p-nitrophenol is obtained 
 by one or two extractions with boiling 2 per cent. hydrochloric acid. The filtrates 
 from the extractions on cooling deposit the para-compound in long colourless 
 needles, the yield being 40 gms. 
 
 A method by which only p-nitrophenol is obtained is described in G.P. 91314 
 (Soc. Chim. des Usines du Rhéne). If phenol is first condensed with an aromatic 
 sulphonyl chloride so as to form the phenyl ester of the sulphonic acid, on nitration 
 of this ester the nitro group first enters the phenol nucleus in the para position. Thus 
 using p-toluenesulphony] chloride as cheapest, we get : 
 
 OES Aa acorns: eae 
 HyC¢ _S0,.0¢ » > HCC 80.0 NO, 
 It is possible to hydrolyse this nitrophenyl ester to nitrophenol and sulphonic acid, 
 but the temperature required is too high. If, however, the nitration is carried further 
 so that a second nitro group enters (this time the toluene nucleus), the resulting 
 dinitro derivative— 
 
 Pek Ps Pah 
 AS 802.0% NO, 
 
 —can be hydrolysed with dilute caustic soda on the water-bath. The process is as 
 follows : 
 
 100 kg. of phenol is dissolved in 1,000 litres of water and 42 kg. of caustic 
 soda. The solution is warmed and 210 kg. of p-toluenesulphonyl chloride added — 
 gradually, and heating continued until the sulphonyl chloride has disappeared. The 
 liquid is then cooled, the ester separated, well washed, and dried. It melts at 94° 
 to 95°. 
 
 For the nitration, a finely powdered mixture of 100 kg. of the ester and 100 kg. of 
 potassium nitrate is added gradually to 1,000 kg. of concentrated sulphuric acid, which 
 is stirred and the temperature kept between 10° and 25°. When nitration is ended, 
 the dinitro compound is filtered off, washed with water, and dried. It is obtamed 
 almost pure, and melts at 115°. 
 
 Hydrolysis is carried out by heating a suspension of 100 kg. of the dinitro body in 
 a dilute aqueous solution of 30 kg. of caustic soda at about 100° until all has 
 dissolved : 
 fie Baas CH >80,Na + GED a 
 O.N ON 
 On cooling, sodium p-nitrophenate crystallises out and is filtered off, and converted 
 into the nitrophenol by acid. The yield is said to be quantitative. 
 
BENZENESULPHONIC ACIDS 85 
 
 Both o- and p-nitrophenol can be obtained by the action of caustic soda solution 
 on the corresponding o- and p-nitrochlorobenzenes (pp. 2, 4), but although this 
 is said to be the technical process of preparation, no details have been published. 
 
 Derivatives of o-Nitrophenol. 
 o-Aminophenol— OH 
 
 Be 
 
 —crystallises when pure in colourless scales, but these soon become brownish-red in 
 air. M.p. 174°. It can be sublimed. It is soluble in 59 parts of water at 0°, and 
 rather more soluble in alcohol. Its hydrochloride crystallises in needles, soluble in 
 1-25 parts of water at 0°, and in 2-36 parts of alcohol. 
 
 It may be prepared from o-nitrophenol by reduction with sodium sulphide 
 (Ullmann’s “‘ Enzyklopadie,” vol. 9, p. 47). 
 
 40 parts of crystalline sodium sulphide (Na,S.9H,O) is melted and heated to 
 125°, and at this temperature, while stirring, 10 parts of o-nitrophenol is added slowly, 
 the temperature being gradually raised to 140°. The melt is at first red, but changes 
 finally to ight brown. It is diluted with water and filtered. The filtrate should be, 
 at most, pale brown in colour. The aminophenol is precipitated by addition of sodium 
 bicarbonate. The yield is 6-1 parts or 78 per cent. 
 
 The commercial product usually contains some aminophenazoxine, formed by 
 condensation of 2 molecules of the aminophenol : 
 
 N 
 ya 4 \Z a ih 
 | | | re) 
 
 ee Sy bviee 
 
 o-Aminophenol is used as a hair and fur dye, and also by condensation with 
 2: 4-dinitrochlorobenzene yields a diphenylamine derivative used in making a 
 sulphur colour. 
 
 o-Nitroanisole— OCH; 
 
 Oe 
 
 Se 
 —a colourless oil at ordinary temperature. The solid melts at 9-4°, b.p. 273° 
 (760 mm.), 150-5° to 151° (19 mm.), D®? 1-254. 
 
 The methylation of o-nitrophenol is carried out by means of methyl chloride. 
 139 parts of nitrophenol is dissolved in 400 parts of water containing 40 parts of 
 caustic soda. 80 parts of sodium carbonate and 400 parts of methyl alcohol (90 per 
 cent. will do) are added, and the solution cooled to 10° in an autoclave fitted with a 
 stirrer. Methyl chloride is then added to the extent of 88 parts (1-75 mols.) and the 
 autoclave heated at 100° for eight hours. The pressure developed is about 60 lbs. 
 
86 INTERMEDIATES FOR DYESTUFFS 
 
 After cooling the product is poured into water, the nitroanisole separated, and after 
 washing with a little caustic soda solution to remove unchanged nitrophenol, then 
 with water, is dried and distilled. The yield is over 80 per cent. 
 
 The alcohol used can, of course, be recovered and used again. 
 
 Another method of preparation is described on p. 13. : 
 
 o-Nitroanisole can be reduced to o-anisidine by means of iron and a little hydro- 
 chloric acid, as in the preparation of aniline. 
 
 o-Anisidin 
 se el OCH, 
 
 €w@ 
 
 —a colourless oil at ordinary temperature, m.p. 2:5°, b.p. 225°, Dj? 1-0978. Its 
 acetyl derivative melts at 87° to 88°. 
 
 A modification of the ordinary method of reduction applied to o-nitroanisole is 
 described by Heumann (“ Die Anilinfarben,” IV., 1., 310). 
 
 o-Anisidine is used as a first component in azo dyes, to which it imparts unusual 
 brightness of shade, due probably to the methoxy group in the o-position. 
 
 Dianisidine— CHO OCH, 
 
 BNC ><> 
 
 —crystallises from dilute alcohol in colourless leaflets, m.p. 137° to 138°, which become 
 violet in air. It is fairly soluble in hot water, but sparingly in cold water, easily 
 soluble in alcohol, ether, benzene, chloroform, and acetone. Its hydrochloride 
 crystallises in prisms, easily soluble in water, but on boiling with water is partly 
 dissociated, giving a sparingly soluble basic salt. The sulphate, C,,H,,.0,N,.H,SO,, 
 crystallises from water in short needles. 100 parts of water at 20° dissolve 1-12 
 parts of the sulphate and at 100° 4-17 parts. The diacetyl derivative forms colourless 
 prisms, m.p. 231°. 
 
 Dianisidine is prepared by reduction of o-nitroanisole to hydrazoanisole and 
 
 transformation of this in acid solution, the process being similar to that by which © 
 
 benzidine is prepared from nitrobenzene (p. 29) : 
 OCH, CH,O CH,O OCH, 
 
 OCH, | 
 2x6, > aT > at 
 
 Very little information has been published with regard to the course of the 
 successive reactions, in particular as to the final transformation. It is known, 
 however, that there is no o-p-compound formed—that is, no diphenyline derivative, 
 as in the preparation of benzidine. The only reaction which occurs besides the 
 main one is a slight amount of fission of the hydrazoanisole with formation of 
 o-anisidine. 
 
 A description of the manufacture of dianisidine, with some plant details, has 
 been given by Jansen (Zevt. fiir Farben-Ind., 1913, 12, 247). For the plant details, 
 
 a Ce Se ee ee, «Sh. 
 
 eae Oe 
 
BENZENESULPHONIC ACIDS 87 
 
 the original paper should be consulted. The essentials of the process are as 
 follows : 
 
 30 kg. of o-nitroanisole, 40 kg. of zinc dust, and 20 ke. of alcohol are stirred and 
 warmed until reduction begins, when a mixture of 14 kg. of alcohol and 4 kg. of 30 
 per cent. caustic soda is slowly added until the mixture has become pale grey. This 
 requires about six hours. No temperature is mentioned. The mixture is then diluted 
 with about 25 litres of water, 5 kg. of hydrochloric acid diluted with some water added, 
 and finally another 340 litres of water. After allowing to settle, the mixture is 
 filtered through wool, the hydrazoanisole remaining on the filter. 
 
 The hydrazo compound -is then stirred into 173 kg. of sulphuric acid (arsenic- 
 free), which has been previously diluted with about 220 litres of water and cooled to 
 48° to 50°. After stirring for five hours, the liquid is warmed during two hours to 
 60°, stirred two hours more at this temperature, and then raised to 90°. 2 kg. of 
 zinc dust is added to decolourise the liquid, which should be yellowish, not brown. 
 The liquid is filtered at 90°, 1 kg. of thiosulphate and 1 kg. of hydrochloric acid added, 
 and then 250 kg. of hydrochloric acid, the whole being stirred for a few hours. It is 
 then allowed to stand for two days, when it becomes thick with a crystalline precipi- 
 tate, and this is filtered off through wool. The crystalline paste is stirred with 90 
 litres of hot water and heated till it dissolves, when the solution is filtered, the residue 
 being boiled out with a further quantity of water. To the total filtrate, heated to 
 boiling, 55 kg. of ammonia is added all at once, the mixture well stirred, and allowed to 
 stand for two days. The precipitated dianisidine base is filtered off, washed with 
 weak ammonia, then with very dilute caustic soda until the filtrate just reddens 
 phenolphthalein. The yield is 20 kg. of base (about 83 per cent.). 
 
 _ The crude base obtained by some such method as this cannot conveniently be 
 purified by vacuum distillation as can be done with benzidine. Too much decomposi- 
 tion occurs. A fair purification, however, can be obtained through the sulphate, 
 formed by adding Glauber salt to a solution of the hydrochloride. The precipitated 
 sulphate is washed with ice-cold water on the filter, and the base again obtained by 
 stirring the sulphate with ammonia. 
 
 Dianisidine, like benzidine and tolidine, yields a tetrazo compound, which can be 
 coupled with either two molecules of the same end component, or 1 molecule each 
 of two different end components in succession. The resulting azo dyes are direct 
 cotton colours, which are considerably bluer in shade than those derived from benzi- 
 dine or tolidine, but otherwise show much the same properties with regard to fastness 
 to light, washing, acids, etc. They areusually somewhat brighter than the correspond- 
 ing benzidine dyes. 
 
 By nitration of the acetyl derivative of o-anisidine in glacial acetic acid solution, 
 a mixture of two nitro derivatives is formed, which on hydrolysis yields the two nitro- 
 anisidines : 
 
 4-Nitro-2-anisidine— OCH, 
 
88 INTERMEDIATES FOR DYESTUFFS 
 
 —orange needles (from water), m.p. 118°. Acetyl derivative m.p. 131° to 
 132°. 
 5-Nitro-2-anisidine— OCH; 
 
 —m.p. 139° to 140°. Acetyl derivative, m.p. 153° to 154°. 
 
 The proportions of the two nitro derivatives may be varied by variation of the 
 temperature and other conditions. Thus, as described in G.P. 98637 (Mulhouse) : 
 
 (1) 20 kg. of acet-o-anisidide may be added gradually to a stirred mixture at 10° 
 of 120 kg. of nitric acid (38° Bé) and 100 kg. of glacial acetic acid. The nitration is 
 finished within a few minutes after the last of the acetyl compound has been added. 
 The nitro compounds are precipitated by addition of water, filtered off, and washed 
 with water. In this way a mixture of 66 per cent. of 5-nitro- with 33 per cent. of 
 4-nitro-anisidine is obtained. 
 
 (2) 12 kg. of acet-o-anisidide may be nitrated with 200 kg. of nitric acid (41° Bé), 
 the temperature being regulated between 25° and 40° so that no solid separates. This 
 procedure gives 75 per cent. of the 5-nitro- and 25 per cent. of the 4-nitro-anisidine. 
 
 The two nitro compounds are separated by the difference in basicity of the bases. 
 The product of nitration is hydrolysed by heating with 40 to 60 per cent. sulphuric 
 acid, the bases being precipitated with water and filtered off. They are then dissolved 
 in warm 25 per cent. sulphuric acid and, on adding water to the solution, the 5-nitro- 
 anisidine is precipitated and may be filtered off. The more strongly basic 4-nitro- 
 anisidine is then precipitated from the filtrate by neutralising with alkali. 
 
 A modified form of this method of separation is given in G.P. 228357. The 
 mixture of the two nitroacetyl compounds is hydrolysed with warm 70 per cent. 
 sulphuric acid. Sufficient water is then added to reduce the acid to 40 per cent. 
 On cooling, the sulphate of the 5-nitroanisidine crystallises out, while the filtrate on 
 neutralisation yields the 4-nitro compound. 
 
 The nitroanisidines are used like p-nitroaniline for the production of dyeings on 
 cotton by coupling their diazo compounds with f-naphthol or Naphthol AS. The 
 4-nitro compound gives orange or scarlet shades, while the 5-nitro compound gives 
 
 red or pink. 
 OH 
 € 
 Nee 
 NH. 
 
 p-Aminophenol— 
 —crystallises in leaflets, m.p. 184°. It dissolves in 90 parts of water and in 22 parts 
 of alcohol at 0°. It oxidises quickly in air. Its solution in alkali is colourless at first, 
 but rapidly becomes violet. The hydrochloride is soluble at 0° in 1-4 parts of water. 
 The sulphate is sparingly soluble in water. 
 
 Many different methods have been used or proposed for the preparation of 
 p-aminophenol, but the most widely adopted are: (1) The reduction of p-nitrosophenol 
 
BENZENESULPHONIC ACIDS 89 
 
 with sodium sulphide; (2) reduction of p-nitrophenol with tin and hydrochloric acid 
 (Paul, Zeit. angew. Chem., 1896, 9, 594), or with iron and hydrochloric acid (Paul, 
 loc. cit., 1897, 10, 172); (3) electrolytic reduction of nitrobenzene (G.P. 295841, Soc. 
 Chem. Ind., Basle). 
 
 (1) According to Cain (‘‘ Intermediate Products, etc.,” p. 118), p-nitrosophenol is 
 dissolved in 30 parts of water containing some sodium sulphide, and a concentrated 
 solution of 4 parts of crystalline sodium sulphide is added slowly until the yellow 
 colour of the alkaline solution of nitrosophenol has disappeared. After cooling, the 
 solution is made just acid with hydrochloric acid, the precipitate filtered off, extracted 
 with boiling water, and the solution filtered, when, on cooling, p-aminophenol 
 separates. 
 
 (2) The reduction of p-nitrophenol with iron and acid is carried out as follows : 
 250 parts of p-nitrophenol, 45 parts of concentrated hydrochloric acid, and 500 parts 
 of water, are stirred in an iron reduction vessel fitted with a reflux condenser, and 
 heated to 98°. About 400 parts of iron borings are added in lots of 15 to 20 parts at 
 atime. After each addition an energetic reaction takes place, and this is allowed to 
 subside before the next addition is made. The mixture is then brought to boiling- 
 point, 50 parts more iron added, and boiling continued for half an hour to finish the 
 reduction. After diluting with 2,000 parts of water, the solution is made just alkaline 
 with 25 to 30 parts of soda ash, so as to precipitate dissolved iron. On filtering and 
 cooling the filtrate, the »-aminophenol crystallises out. The yield is 140 parts or 
 71 per cent. 
 
 (3) The electrolytic reduction of nitrobenzene was first investigated by Gatter- 
 mann (Ber., 1893, 26, 1847), who found that, while p-aminophenol was the main 
 product, some aniline was also formed. Phenylhydroxylamine is supposed to be 
 formed as an intermediate stage in the production of the aminophenol : 
 
 “NHOH 
 
 NO, NH, 
 vi 
 \ \ Ya 
 
 Using the conditions described in G.P. 295841, it is claimed that the proportion 
 of aniline formed can be reduced to about 20 per cent. of the aminophenol. The 
 vessel used for the electrolysis is a lead cylinder, and thisservesasanode. Thecathode 
 is a hollow perforated copper cylinder, which is placed inside a porous cylinder 
 standing in the lead vessel. Inside the copper cylinder is a stirrer, and one or more 
 rods of lead dip into the cathode chamber. The anode chamber contains 30 per cent. 
 sulphuric acid, and the cathode chamber is charged with 25 litres of dilute sulphuric 
 acid (15° Bé) and 6 kg. of nitrobenzene. The mixture in the cathode chamber is kept 
 emulsified by rapid stirring. At 80° to 95° a current of about 3 amperes per sq. dem. 
 of cathode surface at 3 to 34 volts is passed until the nitrobenzene has disappeared. 
 
 Milk of lime is then added, and the aniline distilled off with steam. The remaining 
 solution of p-aminophenol is filtered hot from calcium sulphate and evaporated 
 to crystallising point. The yield of p-aminophenol is about 56 per cent. of the 
 
90 INTERMEDIATES FOR DYESTUFFS 
 
 theoretical. The presence of arsenic in the sulphuric acid reduces the proportion of 
 aniline formed to about 10 to 15 per cent. of the p-aminophenol. 
 
 p-Aminophenol serves chiefly as an intermediate for sulphur colours, either by 
 heating it directly with sodium polysulphides or more commonly by first condensing 
 it with 2:4-dinitrochlorobenzene to form 2: 4-dinitro-4’-hydroxydiphenylamine 
 (p. 6), which is then worked up for sulphur colours. 
 
 p-Aminophenol can be diazotised, and is used as first component in a few azo dyes. 
 
 p-Nitrophenetole— 
 C,H, 
 
 ae 
 
 NO, 
 
 —crystallises i in prisms, m.p. 58°, b.p. 283°, D*® 1-18. 
 
 This is prepared by ethylation of p-nitrophenol with ethyl chloride in the same 
 manner as o-nitroanisole is obtained from o-nitrophenol (p. 85). A yield of 90 per 
 cent. is obtained. 
 
 p-Phenetidine— es 
 
 \ 
 
 NH, 
 —a colourless oil at ordinary temperature, m.p. 2° to 4°, b.p. 254°, D'® 1-0613. The 
 hydrochloride melts at 234°, can be sublimed, and is easily soluble in water. The base 
 is only slightly volatile in steam at 100°. 
 
 p-Phenetidine is prepared usually by reduction of p-nitrophenetole with iron and 
 hydrochloric acid. An interesting variation of the usual reduction method is described 
 by Ullmann (“ Enzyklopadie,” vol. 9, p. 55). 
 
 To 100 kg. of water at about 6°, add slowly a mixture of 50 kg. of p-nitrophenetole 
 and 50 kg. of iron borings, while simultaneously 7 kg. of hydrochloric acid is 
 dropped in. At the beginning a few drops of 10 per cent. platinum chloride 
 solution are added to the reaction mixture, which soon initiates a vigorous reaction. 
 The reduction is finished in six to ten hours, as shown by a sample giving up no 
 nitrophenetole to an ether extract. The base is then set free with soda, the liquid 
 let settle for a few hours, the aqueous layer run off, and the remaining mass of 
 borings and phenetidine after mixmg with sawdust is extracted three times with 
 toluene. On fractional distillation of the extract, a yield of 80 per cent. of 
 phenetidine is obtained. 
 
 p-Phenetidine may also be prepared directly from phenol with the assistance 
 of some of the previously prepared base, as described in G.P. 48543 (Riedel). 
 The base is diazotised, couplede with phenol, the azo compound ethylated, 
 and on reduction of the product two molecular proportions of »-phenetidine are 
 formed in place of the one used to start with. The course of the reactions may he 
 indicated thus: 
 
BENZENESULPHONIC ACIDS 91 
 
 7 \w. if ie Z \nwen’ 
 Et0< DNENCL + € OH ————s HOC Nm oH 
 > EtoC DNENC OEt ee BOK NH, + HNC DOR 
 
 13-7 kg. of phenetidine, dissolved in 200 litres of water and 37-5 kg. of 20 per cent: 
 hydrochloric acid, is diazotised in the usual way with 7 kg. of sodium nitrite dissolved 
 in water. The solution of diazo compound is run into a solution of 9-5 kg. of phenol 
 and 20 kg. of sodium carbonate in 350 kg. of water. The azo compound separates in 
 quantitative yield as a brown precipitate, which may be crystallised from aqueous 
 alcohol as small brown needles, m.p. 104° to 105°, soluble in caustic alkalies, alcohol, 
 glacial acetic acid, etc. 
 
 The azo compound is ethylated by dissolving 10 kg. of it in 50 litres of alcohol 
 and 1-66 kg. of caustic soda, adding 4-6 kg. of ethyl bromide and heating under 
 pressure for ten hours at 150°. (Ethyl chloride or ethyl sodium sulphate may equally 
 well be used for the ethylation.) The alcoholis distilled off, sodium bromide extracted 
 with water, and any unchanged hydroxyazo compound with dilute caustic soda. 
 The diethoxyazobenzene obtained crystallises from alcohol in lustrous yellow leaflets, 
 m.p. 156°, which can be sublimed without decomposition. It is sparingly soluble in 
 alcohol, but easily soluble in acetone and glacial acetic acid. 
 
 For the reduction 10 kg. of the diethoxy compound is warmed with 6 kg. of tin 
 and 50 kg. of 20 per cent. hydrochloric acid. When all the diethoxy compound has 
 disappeared owing to reduction and solution of the »-phenetidine formed from it, 
 the solution is made alkaline and the phenetidine distilled in superheated steam. 
 
 The method works well and has been used on the manufacturing scale. 
 
 o-Nitro-p-phenetidine : 
 
 OC,H, 
 ( \No, 
 
 NH, 
 
 When acet-p-phenetidine (phenacetine) is nitrated with aqueous nitric acid, the 
 nitro group enters the ortho position to the amino group, but if the nitration is carried 
 out in sulphuric acid solution, the nitro group takes a position ortho to the ethoxy 
 group. This latter compound is the more valuable of the two. Its preparation is 
 given in G.P. 101778 (Meister Lucius and Briining). 
 
 A solution of 18 parts of phenacetine in 80 parts of sulphuric acid (66° Bé) is 
 nitrated at 5° with a mixture of 12 parts of nitric acid (36° Bé) and 12 parts of con- 
 centrated sulphuric acid. The nitro body is precipitated by pouring the reaction 
 mixture on to ice, and is obtained as a light yellow precipitate. It is hydrolysed by 
 dissolving in diluted sulphuric acid and heating for several hours at 80° to 90°. On 
 cooling, the sulphate of the nitrophenetidine separates as a thick crystalline mass of 
 reddish colour. It is purified by recrystallisation from hot water. The free base is 
 obtained by addition of alkali as an orange-yellow oil, which solidifies on standing. 
 It may be crystallised from dilute alcohol as yellow needles, m.p. 170°. 
 
92 INTERMEDIATES FOR DYESTUFFS 
 
 Like the nitroanisidines and other similar bodies this substance is used for dyeing 
 on cotton by coupling its diazo compound with f-naphthol. It gives orange-yellow 
 dyeings of good fastness. 
 
 Picric acid— 
 
 —-crystallises in lemon-yellow prisms, m.p. 122-5°, sparingly soluble in water. It is 
 still less soluble in water containing sulphuric acid, and is almost insoluble in 40 per 
 cent. sulphuric acid. The sodium salt is readily soluble in water. The salts with lead 
 and some other metals are rather dangerously explosive. 
 
 Picric acid may be prepared by the direct nitration of phenol (G.P. 126197, 
 Gutensohn), but the tendency of the nitric acid to oxidise phenol (to oxalic acid, etc.) 
 is so strong that this method is not usually employed. It has been found that a 
 preliminary sulphonation of the phenol protects it in large degree from oxidation and 
 in the subsequent nitration the sulphonic acid groups are displaced by nitro groups. 
 
 OH 
 ic 
 OH ivela ti OH OH 
 ( } So,H ann O.N( ‘NO, ON( NNO, 
 OH 
 x ¥ Te \ 
 Norse | Wee eos SO,H NO, 
 fr 
 SO,H 
 
 The nature and proportions of the intermediate sulphonic acids and nitrosulphonic 
 acids depend on the conditions of sulphonation and nitration. Detailed investiga- 
 tions of the intermediate stages in the formation of picric acid by the ordinary process 
 have been made by King (J.C.S., 1921, 124, 2105) and by Marqueyrol and colla- 
 borators (Bull. Soc. Chim., 1919, 25, 370; 1920, 27, 140, 195, 370, 547). 
 
 There has been much variation of practice in carrying out the preparation of 
 picric acid, especially in the degree of dilution used. Several different processes are 
 described in the “‘ Technical Records of Explosives Supply ” (No. 6, Synthetic Phenol 
 and Picric Acid), published by the Ministry of Munitions. That which allows of the 
 most exact regulation of the reactions is the process in which strong acids are used 
 throughout. It is carried out as follows: 30 lbs. of phenol is melted and run into an 
 enamelled nitrating vessel provided with stirrer and steam-jacket. 3-5 molecular 
 proportions of 94 per cent. sulphuric acid is added and the temperature raised to 
 100°. After two hours at this temperature, sulphonation equilibrium has been reached, 
 and the solution is cooled to about the ordinary temperature. 
 
 The nitrating acid which is now run in has the composition : 
 
 HSO pe. as hs i. me .. 57-5 per cent. 
 HNO, Se =f bs ws we oo OOO nae 
 H,0 ee ee oe ee ee ee 4:0 rr} 
 
BENZENESULPHONIC ACIDS 93 
 
 —and the total quantity used contains 4-5 molecular proportions of nitric acid. 
 Half of this quantity is first run in below 50° during about two hours. External 
 cooling may be necessary at this stage. A mixture of mononitro- and dinitrosulphonic 
 acids has been formed. Addition of the mixed acid is now stopped, and the tempera- 
 ture raised to 65° in order that all the nitric acid so far added may be used up. At 
 65°, the remaining half of the mixed acid is slowly added at such a rate that the heat 
 evolved raises the temperature by 1° every three minutes until 80° is reached, when 
 about three-quarters of the total acid has been added. The remainder of the acid 
 may be added more quickly, so as to produce a regular rise of temperature, and so that 
 when the last of the acid is run in the temperature has attained 115°. This tempera- 
 ture must be reached to complete the nitration, but at 115° nitration is very rapid and 
 all the nitric acid is quickly used up. The mixture is allowed to cool to 100°, and is 
 then cooled externally as quickly as possible to 25°. The picric acid formed crystallises 
 out, and the mass is filtered through asbestos. After washing the picric acid with 
 a little 75 per cent. sulphuric acid to remove adhering spent acid, the washing 
 is continued with water. The yield of picric acid is 218 per cent. of the 
 phenol used. 
 
 The spent acid contains 73 per cent. H,SO,, 0-65 per cent. HNO, 3-6 per cent. 
 HNO,, and 4:2 per cent. picric acid. 
 
 While formerly used as a dyestuff, its chief use in the dyestuff industry now is in 
 the preparation of picramic acid. 
 
 Picramic acid— OH 
 
 —crystallises in red needles, m.p. 168° to 169°. 100 parts of water at 22° dissolve 
 0-14 part, and in hot water it is readily soluble. It is dissolved both by alkalies and 
 by acids giving in aqueous caustic soda a brownish-red solution, but in hydrochloric 
 acid a colourless solution. 
 
 It is prepared from picric acid by reduction with sodium hydrogen sulphide 
 (Brand, J. pr. Chem., 1906 [2], 74, 472). It is not necessary to prepare the sodium 
 hydrogen sulphide previously; it may be formed in the reaction mixture by addition 
 of a molecular proportion of hydrochloric acid to sodium sulphide. 
 
 229 gms. of picric acid is dissolved in 2 litres of water at 50°, with addition of 
 60 gms. of sodium carbonate. 400 gms. (1-6 gm.-mols.) of sodium sulphide crystals, 
 Na,S.9H,0, dissolved in 750 c.c. of water, is run in slowly, and at the same time dilute 
 hydrochloric acid, made from 155 c.c. of 30 per cent. hydrochloric acid and 500 c.c. 
 of water, is added at about the same rate, the solution being well stirred. Stirring is 
 continued for a further half-hour, and the solution then allowed to stand for twelve 
 hours. Sodium picramate separates, and this is filtered off and washed with a little 
 saturated salt solution. It is then dissolved in 3 litres of water, filtered, and the 
 solution run into nearly boiling dilute acid, made from 120 c.c. of 30 per cent. hydro- 
 chloric acid and 700 c.c. of water. The solution is allowed to cool, when picramic acid 
 
94 INTERMEDIATES FOR DYESTUFEFS 
 
 crystallises out, and is filtered off, washed with cold water, and dried. The yield is 
 about 167 gms. or 84 per cent. 
 
 As an o-aminophenol derivative, picramic acid is used for the preparation of 
 several afterchrome or metachrome wool colours by coupling its diazo compound with 
 various phenolic compounds. 
 
 o-Aminophenol-p-sulphonic acid : 
 
 The acid crystallises in scales with 1H,O, sparingly soluble in cold water. 
 
 The preparation of this substance from o-nitrochlorobenzene-p-sulphonic acid has 
 already been mentioned (p. 11). It may also be prepared as described in G.P. 93443 
 (Soc. Chem. Ind., Basle) by sulphonating o-aminophenol. 
 
 100 parts of o-aminophenol are dissolved in 480 parts of sulphuric acid, 240 parts 
 of 24 per cent. oleum added, and the solution heated at 90° to 95° for an hour. The 
 aminophenolsulphonic acid may then be isolated in the usual way, after dilution, 
 through the calcium and the sodium salt. 
 
 o-Aminophenolsulphonic acid can be diazotised, and is used as first component in 
 a number of monoazo dyes, the second component being a m-diamine, or dihydroxy 
 compound of the benzene or naphthalene series. These dyes are distinguished by 
 the fastness to light, milling, and potting of their afterchromed shades. 
 
 2-Nitro-6-aminophenol-4-sulphonic acid : 
 
 OH 
 O,N f \NH, 
 
 = 
 SO,H 
 
 The acid crystallises in greyish-brown prisms, sparingly soluble in cold, but easily 
 in hot water, giving reddish-yellow solutions. The potassium salt is sparingly soluble 
 in cold water. 
 
 The preparation of this substance is given in G.P. 93443, quoted above, starting 
 from o-aminophenol. When the sulphonation is complete, the solution is cooled to 
 0° and nitrated directly at 0° to 3° with a mixture of 58 parts of nitric acid and 116 
 parts of sulphuric acid. After standing for two hours the solution is poured on ice 
 and the precipitate filtered off and pressed. It is purified by dissolving it in 400 parts 
 of boiling water and allowing to crystallise. 
 
 A much purer product is claimed by Hillyer and the National Aniline Co. (U.8.P. 
 1504044), who find it preferable to isolate the o-aminophenolsulphonic acid before 
 nitrating. 100 parts of pure dry o-aminophenol-p-sulphonic acid is dissolved in 
 300 parts of sulphuric acid (66° Bé). Very little heat is developed. The solution is 
 cooled to—5° and nitrated with a mixed acid composed of 29 to 30 per cent. HNO;, 
 65 per cent. H,SO,, and 5 per cent. H,O, sufficient of the mixed acid being taken to 
 
BENZENESULPHONIC ACIDS 95 
 
 contain 34 partsof HNO,;. The temperature during nitration is kept below 0°. After 
 stirring for two to three hours, the solution is poured on to 500 parts of ice. The 
 product partly separates as solid. The total yield is 80 to 90 per cent., about 65 to 
 75 per cent. being as solid and 15 to 30 per cent. in solution. The whole may be brought 
 into solution, and used directly for azo colours, by nearly neutralising with alkali. 
 
 Starting from phenol itself, the substance may be prepared, as in G.P. 121427 
 (Badische), by sulphonating to the p-sulphonic acid, nitrating to the 2: 6-dinitro 
 compound and partially reducing this : 
 
 OH OH OH OH 
 
 m 2 O.N/ \NO, ON’ SNH, 
 
 aa || > Pie ee | 
 
 Pat es Mee 
 SO3H SO3H SO3H 
 
 Phenol (10 parts) is sulphonated with 13 parts of sulphuric acid at 100° to 110°. 
 The solution is then cooled and poured into 100 parts of water. The nitration is 
 carried out by adding 40 parts of 62 per cent. nitric acid, and heating the mixture to 
 boiling till a sample on cooling deposits crystals of dinitrophenol. The solution is then 
 cooled, filtered from dinitrophenol, and the 2: 6-dinitrophenol-4-sulphonic acid 
 isolated as the yellow crystalline potassium salt by adding 10 parts of potassium 
 carbonate. After dissolving 30 parts of this salt in 300 parts of hot water, the solution 
 is cooled and 200 parts of ammonium sulphide added. Reduction takes place with a 
 slight development of heat, and is complete in two to three hours. The product is 
 isolated, either as acid by adding hydrochloric acid, or as potassium salt by acidifying 
 with acetic acid and adding potassium chloride. 
 
 2 : 6-Diaminophenol-4-sulphonic acid : 
 
 OH 
 HN NH, 
 
 SO,;H 
 
 The acid crystallises in white leaflets, soluble in water, the solutions becoming brown 
 by air oxidation. 
 
 It is prepared by reducing 2 : 6-dinitrophenol-4-sulphonic acid (above) with zinc 
 dust and hydrochloric acid (G.P. 148212, Meister Lucius and Briining). The solution 
 obtained is usually employed directly in making azo dyes, but the sodium salt can be 
 isolated by addition of sodium acetate and the necessary common salt. 
 
 This diaminophenolsulphonic acid yields a yellow tetrazo compound which, 
 coupled with two molecular porportions of f-naphthol or Schaffer acid, gives disazo 
 dyes. These are wool colours which can be afterchromed to produce fast black shades. 
 
 Salicylic acid: 
 OH 
 
 ( is 
 \ 
 
96 INTERMEDIATES FOR DYESTUFFS 
 
 The acid crystallises from water in needles, m.p. 158-5°. The following table gives 
 the solubility of the acid in water expressed as grams of acid in 1,000 gms. of solution 
 (Savarro, Atti R. Accad. Sct. Torino, 1913, 48, 455) : 
 
 0° 1-24 | BO ha cox bs, eee CAE -. 13-70 
 
 5° 1-29 Apr? 6. oa ake NO care rene Whe >: 
 10° 1:35 SGT tis y -- 489 BOP as -. 22-09 
 15° . 1-84 i, are we 608 SB ars os eee 
 20° 2-00 el a ae on Nee DO") ies -- 37°35 
 25° 2-48 BO re ee! OD eee -- 60:48 
 30° 2-98 0s a ~» 10-04 100° va wet WE 
 
 At 18-2° it dissolves in 172 parts of benzene, in 2-5 parts of 90 per cent. alcohol, in 
 2 parts of ether, and in 80 parts of chloroform. Its sodium salt is soluble in water 
 and in alcohol. 
 
 It is prepared by the action of carbon dioxide on sodium phenate. As originally 
 described in Kolbe’s patent G.P. 426, carbon dioxide was brought into contact with 
 sodium phenate at 180° to 200°. This procedure gave at most a 50 per cent. yield of 
 salicylic acid, the reaction product containing always considerable quantities of 
 phenol. The reason for this was pointed out by Schmitt, who showed that the reaction 
 under Kolbe’s conditions was in effect as follows : 
 
 2C,H,.ONa + CO, 
 
 > C,H + (,H,.0H 
 
 **\cooNa 
 
 Schmitt further proved that at much lower temperatures phenol could form, by 
 addition with carbon dioxide, a carbonate which at 120° to 145° was transformed by 
 
 intramolecular change into salicylic acid : 
 OH 
 
 € CK one 
 
 His improved process (G.P. 29939), therefore, consisted in passing carbon dioxide into 
 sodium phenate at about the ordinary temperature until phenyl sodium carbonate 
 was completely formed, and then heating this at 120° to 145° to effect the transforma- 
 tion to salicylic acid. Incidentally, it was shown that an essential condition for the 
 formation of phenyl sodium carbonate was absolute dryness of the sodium phenate, 
 which necessitated heating the latter in a high vacuum at 150° to 160°. Later it was 
 shown by Heyden (G.P. 38742) that it was not necessary to cool the dried phenate to 
 ordinary temperature in order to form phenyl sodium carbonate. The formation of 
 the carbonate could be carried out at such a temperature (120° to 145°) that its trans- 
 formation to salicylate would immediately follow, it being only necessary to avoid such 
 a temperature (above 145°) as would bring Kolbe’s reaction into play, with partial 
 formation of phenol. The preparation is, therefore, carried out as follows : 
 
 Pure phenol is used, whose setting-point is not below 39°, and which does not 
 redden on fusion. It is stirred into an equimolecular quantity of caustic soda (free 
 from carbonate) dissolved in a little water. The phenol dissolves and the solution is 
 now heated in an autoclave with powerful stirrmg gear under high vacuum so as to 
 evaporate the sodium phenate to dusty dryness, the temperature being ultimately 
 
 C,H,;ONa + CO, > C,H;.0.COONa 
 
BENZENESULPHONIC ACIDS 97 
 
 raised to about 160°. Grinding of the phenate to fine powder is facilitated by having 
 a number of heavy balls in the autoclave. 
 
 The autoclave is now cooled to 100° and carbon dioxide, free from moisture, 
 carbon monoxide, or sulphur compounds, is passed in, with constant stirring. The 
 carbon dioxide is quickly absorbed at first, with development of heat, and the tem- 
 perature must not be allowed to rise above 145°. Later, absorption slows off some- 
 what and the pressure of the carbon dioxide in the autoclave is maintained at 5 to 6 
 atmospheres until the end of the reaction, which is indicated by a simultaneous fall of 
 temperature and rise of pressure due to non-absorption of the carbon dioxide now 
 being forced in. After cooling and blowing off excess of carbon dioxide, the salicylate 
 is dissolved in the minimum quantity of water, giving a yellow solution from which it 
 is precipitated by addition of hydrochloric acid. 
 
 As thus obtained, the product contains some impurities, which, according to G.P. 
 65131 (Hofmann), can be removed by adding stannous chloride solution to the hot 
 solution of salicylate until the liquid becomes water-white. The tin is precipitated 
 as SnO(OH),. This is filtered off and the salicylic acid precipitated from the filtrate 
 by acid. 
 
 It may be further purified by distillation with superheated steam at 140°. 
 
 The yields obtained on the manufacturing scale approximate to the theoretical. 
 
 Salicylic acid is used very largely as a second component in all classes of azo dyes 
 from mono- to tetrakisazo. Two molecules of a diazo compound can be coupled 
 with 1 molecule of salicylic acid, one in the para position, and one ortho to the hydroxy] 
 group, but only one or two of the azo dyes made from it are of this nature. All the 
 monazo dyes derived from salicylic acid are yellow or orange in shade, and in most of 
 the others the shades vary between yellowand brown. Toall these dyes, but especially 
 to the mono and disazo dyes, salicylic acid imparts the property of dyeing on 
 chromemordanted wool or the capability of being afterchromed. 
 
 A few dyes of the triphenylmethane series are derived from salicylic acid by con- 
 densation with formaldehyde, Michler’s hydrol, etc. These also are chrome wool 
 colours. 
 
 In the anthraquinone series a yellow lake pigment is made by condensing salicylic 
 acid with «-aminoanthraquinone to form the anthraquinonylamide of salicylic acid. 
 
 Aminosalicylic acid : 
 
 This substance may be prepared from salicylic acid by nitration, which yields a 
 mixture of the 3- and 5-nitrosalicylic acids— 
 
 OH OH 
 a ( ae 
 Xo, 
 
98 INTERMEDIATES FOR DYESTUFFS 
 
 —followed by reduction of the 5-nitro derivative as described by Hirsch (Ber., 1900, 
 38, 3239) and Hiibner (Ann., 1879, 195, 6). But a simpler method, which avoids 
 production of isomers, is to couple a suitable diazo compound with salicylic acid and 
 reduce the azo compound formed. 
 
 As described by Fischer and Schaar-Rosenberg (Ber., 1899, 32, 81), 500 gms. of 
 aniline hydrochloride is dissolved in 600 gms. of hydrochloric acid (D 1-19) and 
 3,000 gms. of ice, the mixture showing a temperature of — 20°. This is diazotised by 
 a solution of 290 gms. of sodium nitrite in 1 litre of water. When diazotisation is 
 complete (in about fifteen minutes), the solution is run into a solution of 533 gms. of 
 salicylic acid and 2,200 gms. of soda crystals in 10 litres of water. The azo compound 
 separates as the yellow sodium salt, and this is filtered off and washed with a little 
 water. 
 
 It is now reduced either with stannous chloride, as used by the above mentioned 
 authors, or better with sodium hydrosulphite (Na,S8,0,) as recommended by Grand- 
 mougin (Ber., 1906, 39, 3930). In the latter case, the azo compound is stirred into 
 10 litres of boiling water, the mixture made alkaline with caustic soda solution, and 
 sodium hydrosulphite added till reduction is complete, as shown by the disappearance 
 of the colour of the azo compound. About 1,350 gms. of sodium hydrosulphite 
 powder arerequired. The aniline formed is distilled off with steam, leaving a solution 
 of sodium aminosalicylate, which may either be used directly for azo dyes or the 
 aminosalicylic acid may be precipitated by acidification. 
 
 Aminosalicylic acid can be diazotised, and is used as a first component in a series 
 of disazo dyes in which its diazo compound is coupled with «-naphthylamine or 
 Cleve’s acids as middle component, the last component being a naphtholsulphonic 
 acid or dihydroxynaphthalenesulphonic acid. In this way, wool colours are obtained 
 which, by afterchroming, yield very fast blacks and greens. Aminosalicylic acid is 
 also used in making chrome colours of the triphenylmethane class by condensation 
 with Michler’s hydrol and similar bodies. 
 
 Benzene-m-disulphonic acid : 
 SO,H 
 - 
 
 | SO,;H 
 
 The sodium salt crystallises with 4H,O. 
 
 Sulphonation of benzene to the disulphonic acids takes place at temperatures of 
 over 200°. The product is almost entirely the m-disulphonic acid, under ordinary 
 conditions only about 1 per cent. of the p-disulphonic acid being formed. However, 
 if heating be continued for a long time past the point of complete disulphonation, or if 
 mercury salts are present during sulphonation, some of the m-acid is transformed into 
 p-acid, an equilibrium mixture of the two acids in the proportion of 2: 1 being ulti- 
 mately attained. Since both acids yield resorcinol on fusion of their sodium salts 
 with caustic soda, the separation of the acids is not a matter of technical importance. 
 
 Manufacturing methods of preparation of benzenedisulphonic acid (and of resorcinol 
 from it) are described by Bindschedler and Busch (Mon. Scv., 1878, 1169), Schoop 
 
BENZENESULPHONIC ACIDS 99 
 
 (Zeit. Chem. Ind., 1887, 2, 1), and Miihlhauser (Dingl. Polytech. J., 1887, 268, 154). 
 As described by the last-mentioned, the preparation is as follows: 
 
 (a) Monosulphonation.—60 kg. of benzene and 300 kg. of sulphuric acid (67° Bé) 
 are well stirred and heated at 80° for ten hours, under a reflux condenser. 
 
 (6) Disulphonation.—The reaction mixture having been transferred to a larger 
 sulphonation pot, 85 kg. of dry powdered sodium sulphate are added, and the mixture 
 gradually heated during four hours to 225°, at which temperature it is maintained 
 for a further eight hours. While rising in temperature, some benzene distils off and 
 sulphur dioxide is evolved. 
 
 After cooling the solution is run into 1,500 litres of water, the hot solution neutra- 
 lised with slaked lime made from about 200 kg. of lime, and after adding 800 litres of 
 cold water to make the gypsum easier to filter, the mixture is filtered. The gypsum 
 is boiled up with another 1,500 litres of water and again filtered off. The united 
 filtrates are concentrated to about half the volume, and sufficient soda (6 to 10 kg.) 
 added to convert the calcium into the sodium salt. The calcium carbonate is filtered 
 off, and the solution of the sodium salt evaporated to dryness, and finely powdered. 
 The yield of dry sodium salt is about 200 kg., or rather under 90 per cent. 
 
 The preparation of benzenedisulphonic acid from the monosulphonic acid has 
 been studied in detail by Senseman (J. Ind. Eng. Chem., 1921, 18, 1124) with a view 
 to obtaining the highest possible yield. The best results were obtained by heating 
 the monosulphonic acid at 250° for one hour with about 150 per cent. excess of 95 
 per cent. sulphuricacid. A sodium salt or vanadium pentoxide was added as catalyst, 
 the amount used being about 0-1 per cent. of the weight of acid taken. In this way 
 yields of about 92 per cent. were obtained. 
 
 Resorcinol— 
 
 —crystallises in colourless prisms, m.p. 119°, b.p. 276-5°, or, under 16 mm. pressure, 
 178°. D5 1-2717. On standing in air, it becomes pink and then brown, due to the 
 action of ammonia. 100 parts of water at 0° dissolve 86-4 parts of resorcinol, at 
 12-5° 147-3 parts, and at 30° 228-6 parts. It is also very soluble in alcohol and ether, © 
 but sparingly soluble in cold benzene, 1 gm. dissolving in 435 gms. of benzene at 24°. 
 It is almost insoluble in chloroform and carbon disulphide. Its aqueous solution 
 gives a dark violet colour with ferric chloride. With bromine a precipitate of tri- 
 bromoresorcinol is formed. This reaction is used in its estimation (Pence, J. Ind. 
 Eng. Chem., 1911, 8, 820). 
 
 Resorcinol results in normal fashion from the fusion of the sodium salt of benzene- 
 m-disulphonic acid with caustic soda. References to methods of manufacture have 
 been given under benzenedisulphonic acid above. In the process described by 
 Miihlhauser (loc. cit.), the dry sulphonate is added gradually to twice its weight of 
 caustic soda, which has been fused with a little water and raised to a sufficiently high 
 temperature. The temperature is not specified, but is such that the sulphonate 
 
100 INTERMEDIATES FOR DYESTUFFS 
 
 dissolves quickly with a hissing noise. Heating is continued with stirring until the 
 foaming dies down and the melt becomes oily in appearance and begins to turn 
 brown. It is then poured on iron plates and allowed to solidify. The broken up 
 cakes are dissolved in about twice the weight of water and the solution made just acid 
 to litmus by addition of concentrated hydrochloric acid, sulphur dioxide being given 
 off. The resorcinol is then extracted with amyl alcohol four times, the amyl alcohol 
 distilled off with steam, and the residual aqueous solution of resorcinol evaporated to 
 dryness in an enamelled pan. The yield of crude resorcinol from 125 parts of disul- 
 phonate is 28 to 29 parts. For purification it is distilled at first under ordinary 
 pressure until some water and phenol come off, then under about 100 mm. pressure. 
 The yield of pure distilled resorcinol is 20 to 23 parts. This corresponds to about 
 42 to 48 per cent. on the disulphonate, or an overall yield of 38 to 43 per cent. calcu- 
 lated on the original benzene. 
 
 An investigation has been made by Phillips and Gibbs (J. Ind. Eng. Chem., 1920, 
 18, 857) of the best conditions for the fusion of the disulphonate to resorcinol. They 
 obtained the highest yields of resorcinol by fusing the disulphonate with 14 to 16 
 molecular proportions of caustic soda at 310° for two hours. Generally, a few per 
 cent. of disulphonate remained unchanged under these conditions. Addition of water 
 to the melt caused a considerable decrease in yield. The yields obtained were about 
 60 to 63 per cent., but this figure represents the total proportion of resorcinol formed, 
 as estimated by the bromine method, and not the resorcinol actually isolated in pure 
 condition. 
 
 Resorcinol is used as an end component in azo dyes. It couples very readily 
 with diazo compounds, and it is possible to couple 2 molecules of a diazo compound, 
 in succession, with 1 molecule of resorcinol, the resulting disazo dyes having the 
 
 constitution : 
 Ce Ste N—R 
 
 oe N—R’ 
 
 The azo dyes containing resorcinol as a component, like those containing m-phenylene- 
 diamine, are brown in shade. 
 
 Resorcinol is also condensed with phthalic anhydride to produce Fluorescein, and 
 through this the various dyes of the Kosin and Rhodamine types. 
 
 By condensation with p-nitrosodimethylaniline hydrochloride (on the erect it 
 yields an oxazine dye. 
 
 Amidation of Resorcinol. 
 
 The hydroxyl groups of resorcinol may be replaced either singly or together by 
 amino or substituted amino groups by the action of ammonia or an amine. The 
 reaction is facilitated, like the corresponding reaction with the naphthol derivatives, 
 by the use of sulphites of the amines in addition to the free amine. That is, the 
 Bucherer reaction (p. 139) applies. 
 
BENZENESULPHONIC ACIDS 101 
 
 m-Aminophenol may be prepared, according to G.P. 49060 (Leonhardt), by heating 
 10 parts of resorcinol with 6 parts of ammonium chloride and 20 parts of 10 per cent. 
 ammonia for twelve hours at 200° in an autoclave. The product is acidified with 
 hydrochloric acid, any unchanged resorcinol extracted with ether, and the aqueous 
 solution neutralised with sodium carbonate and evaporated to crystallising point. 
 The m-aminophenol thus obtained is said to be completely air-stable. 
 
 No doubt the use of ammonium sulphite would enable the reaction to proceed at 
 a lower temperature. 
 
 Dimethyl-m-aminophenol has been made, according to E.P. 18726 of 1900 
 (Badische), by heating 250 parts of resorcinol with 2,500 parts of 20 per cent. dimethyl- 
 amine sulphite solution, and 400 parts of 30 per cent. dimethylamine solution in an 
 autoclave at 125° until the resorcinol has disappeared, or nearly so. The liquid is then 
 made alkaline with caustic soda or carbonate, and the excess dimethylamine driven 
 off by steam. After acidifying the remaining solution with hydrochloric acid and 
 boiling off sulphur dioxide, on evaporating to dryness the hydrochloride of dimethy]- 
 m-aminophenol is obtained. 
 
 The other alkyl-m-aminophenols may be obtained in a similar manner. 
 
 According to E.P. 168689 (B.D.C., Green, and Brittain), the reaction can be made 
 to proceed further, at any rate in the case of the monoalkylamines, so as to form 
 symmetrical dialkyl-m-phenylenediamines. Thus, e.g., sym. Dimethyl-m-phenylene- 
 diamine— 
 
 NHCH, 
 
 ae 
 as! 
 
 —is prepared by heating 55 parts of resorcinol with 66 parts of 35 per cent. methyl- 
 amine sulphite solution and 125 parts of.25 per cent. methylamine solution in an 
 autoclave at 125° for twelve hours. The product is made alkaline, and the excess 
 of methylamine distilled off. The residue is acidified with hydrochloric acid, and any 
 unchanged resorcinol extracted with ether. On now making the aqueous solution 
 slightly alkaline with caustic soda, the dimethyl-m-phenylenediamine may be extracted 
 with ether. It is finally purified by distillation in vacuo (b.p. 170° under 10 mm.). 
 The yield is 67 per cent. 
 
 Monomethyl-m-aminophenol is formed as a by-product to the extent of about 
 5 per cent. 
 
CHAPTER V 
 THE NITROTOLUENES AND THEIR DERIVATIVES 
 
 THE nitration of toluene is carried out in the same manner as that of benzene 
 (Chap. II.). Complications arise, however, in the case of toluene owing to the greater 
 number of possible isomers, and to the fact that the methyl group may be oxidised 
 to some extent during the process, producing benzoic acids and even, in extreme 
 cases, to tetranitromethane. By-products of this kind, however, are not of serious 
 account in a carefully conducted nitration. For the manufacture of dyestuff mter- 
 mediates, only the mononitrotoluenes and the 2 : 4-dinitrotoluene are of importance. 
 
 Mononitrotoluenes. 
 
 Nitration of toluene with one molecular proportion of nitric acid yields invariably 
 a mixture of the three isomers in which the o- and p-compounds predominate. Holle- 
 man and his collaborators (Rec. trav. chim., 1909, 28, 408; 1914, 33, 1) found that, 
 using nitric acid alone (D 1-475, or 84 per cent.), the proportions of the isomers 
 obtained at different temperatures remained nearly constant, as indicated in the 
 following table : 
 
 Temperature. Per Cent. Ortho. Per Cent. Meta. Per Cent. Para. 
 O* 56-0 3-1 40-9 
 30° 56-9 3-2 39-9 
 60° 57-5 4-0 38-5 
 
 The use of mixed acid causes a noticeable change in the proportions to about 63 per 
 cent. o-, 2 per cent. m-, and 35 per cent. p-compound. But, using mixed acid, these 
 proportions again remain fairly constant over a wide range of temperature and com- 
 position of the mixed acid. 
 
 The mononitration of toluene can be carried to completion with a more dilute 
 mixed acid and at a lower temperature than that required for benzene. A mixed 
 acid of the approximate composition— 
 
 HNO, 3: . ee av a is .. 25 per cent. 
 H,SO, oe o- oe oe ee oe ee 55 99 
 ) = PLS pe ee ae se ae se - mPa |, a 
 
 —is used, 230 parts of this mixture being taken for the nitration of 100 parts of toluene. 
 The nitration is carried out at 30°. In other details, the procedure is the same as that 
 used for benzene. The yield of mixed nitrotoluenes is 140 to 142 parts from 100 parts 
 of toluene. 
 
 The separation of the isomers is accomplished by a combination of repeated 
 fractional distillation i vacuo and crystallisation, like that described for the separa- 
 tion of o- and p-nitrochlorobenzenes (p. 2). The first fraction consists mostly of 
 
 ah ik oa + £02 
 
 § 
 ‘% 
 - 
 
‘SHATLIVATHEC YHA UNV SANENTOLOULIN— A LYVHO 
 
 Sun FUN 
 
 rye eH eH5 eH 
 11 . 
 iT] 
 ®uUN 20nN "ON 2HN 2HN { N 
 ‘Age @ S-f \o*H stouH 
 sou ON “ee ee 5 
 sfoH H®OS oe Nn 2HN SH29HN CHOHN HO 
 eHD tH tuo HD fHo €HO SHIN 
 { es t Pe t pe | 
 2 ®UN 
 2 2 20N THN HN 
 ON HN oe O O eu5 ou 
 9 a) H®Os 
 
 € 
 €HO SHD fu9 €HO HO 
 c A, : | 
 20N ON 
 ( } | ( ) = 
 20N 
 
104 INTERMEDIATES FOR DYESTUFFS 
 
 the o-compound, and on cooling the residue to about 0° much of the p-compound 
 crystallises out and can be separated from the oil by the centrifuge. The whole 
 process of separation requires a special apparatus and technique which cannot be 
 described here. Finally, most of the o- and p-compounds are separated in a pure 
 state, but a residual middle fraction is obtained in which the m-compound has accu- 
 mulated until it has reached a substantial proportion. Apparently it has been found 
 possible to separate m-nitrotoluene from this residue, or to separate m-toluidine 
 from the reduced mixture, since a few dyes have appeared on the market in which 
 m-toluidine figures as an intermediate. But no information has been published on 
 this point. 
 
 Methods have been patented for the isolation of the o-compound by subjecting 
 the mixture to the action of reagents which attack only the m- and p-compounds. 
 Alkaline arsenite at 130° to 150° under pressure reduces the m- and p-compounds to 
 azoxy and amino derivatives, leaving o-nitrotoluene unchanged (G.P. 78002). The 
 Clayton Aniline Co. proposed in G.P. 92991 to heat the nitrotoluenes with the 
 sulphide residues from the Leblanc soda process, thereby converting the m- 
 and p-compounds to the amines and leaving the o-isomer unchanged. How- 
 ever, the high efficiency of modern distillation apparatus renders such processes 
 unnecessary. 
 
 o-Nitrotoluene is a liquid at ordinary temperature. It exists in two modifications, 
 the labile «-form having a melting-point, given by various observers as from — 9° to 
 - 10-56°. The stable 6-form melts at— 3-6°. The boiling-point is 220-4° (760 mm.). 
 Di? 11643. It is volatile in steam, 30 gms. of o-nitrotoluene distilling with 1 kg. of 
 steam at 100°. 
 
 p-Nitrotoluene forms colourless rhombic crystals, m.p. 54-5°, b.p. 237-7° (760 mm.), 
 D 1-23. 
 
 m-Nitrotoluene.—M.p. 16°, b.p. 230°. 
 
 2 : 4-Dinitrotoluene— 
 OH, 
 ( Nie 
 he 
 
 No, 
 
 —needle-shaped crystals (from water), m.p. 71°, D®* 1-:3108. Sparingly soluble in 
 cold alcohol and ether, easily soluble in benzene. 
 
 This product is manufactured in the same way as m-dinitrobenzene (p. 18). 
 Toluene is nitrated first to the mixture of mononitrotoluenes, using a mixed acid of 
 the same composition as that used with benzene. This acid is more concentrated 
 than is necessary, and probably to a small extent causes formation of dinitrotoluenes 
 at this stage, but this is immaterial. The spent acid having been separated, fresh 
 mixed acid of the same composition as that used for dinitrobenzene is run into the 
 mononitrotoluenes at 115°. The product is worked up as described under dinitro- 
 benzene. A detailed account of the process is given by Kayser (Zeit. Farbenind., 
 1903, 2, 16, 31). 
 
NITROTOLUENES AND THEIR DERIVATIVES 105 
 
 As by-products a little of the 2 : 6- and traces of the 2 : 3-dinitrotoluenes are formed. 
 The yield obtained from 100 parts of toluene is 175 to 180 parts of dinitrotoluene or 
 90 to 93 per cent. 
 
 A. Derivatives of o-Nitrotoluene. 
 o-Toluidine— CH, 
 
 i ae. 
 ie 
 
 —a colourless liquid at ordinary temperature, b.p. 198-1° (760 mm.), Dzo 0-9986, 
 D721-0031. It exists in two forms, one of which freezes at— 21°, the other at— 15-5°. 
 It is almost insoluble in water. It is volatile in steam, 34 gms. of o-toluidine distilling 
 with 1 ke. of steam. 
 
 The hydrochloride, C,H,N.HCl+-H,0, forms thick transparent crystals, m.p. 214-5° 
 to 215°, soluble in water and alcohol. 
 
 The sulphate, (C,H,N),.H.SO,, crystallises in needles, moderately soluble in water. 
 
 Acetyl derivative, m.p. 110°. 
 
 o-Toluidine is prepared by reduction of o-nitrotoluene in the usual way (p. 26). 
 
 It is used as a first component in a number of monazo dyes, and also, in one disazo 
 dye, Brilliant Crocein 9B, as middle component. It forms part of the mixture of 
 bases used in the preparation of Magenta. It is used in the preparation of an acid 
 Rhodamine colour by condensation with fluorescein chloride and subsequent sul- 
 phonation. o-Toluidine also takes part in the formation of several azine and thiazine 
 dyes, by oxidising mixtures of it with p-diamines or thiosulphonic acid derivatives of 
 p-diamines. A dimethylindigo is made from it by condensation with chloroacetic 
 acid and alkali fusion of the resulting o-methylphenylglycine. 
 
 o-Toluidinesulphonic acid : i 
 
 CH 
 
 a ape 
 4 
 
 ars 
 
 The acid crystallises with 1H,O in prisms, sparingly soluble in cold water, but much 
 more soluble in hot water. The sodium salt crystallises with 4H,O. 
 
 This substance is prepared by heating o-toluidine acid sulphate, C,HyN.H,SO,, at 
 200°, following the process used in preparing sulphanilic acid from aniline (p. 57). 
 
 It is used as a first component in a few monazo dyes, particularly in conjunction 
 with B-naphthol and with phenylmethylpyrazolone as second components. 
 
 Aminoazotoluene— 
 
 CH, f CH, 
 | a TE eae y 
 N=N— NH 
 
 —crystallises in dark yellow leaflets or in short red prisms with a blue reflex, m.p. 100°. 
 The base is almost insoluble in water, but is soluble in alcohol. The hydrochloride 
 forms orange yellow tables, sparingly soluble in cold water. 
 
106 INTERMEDIATES FOR DYESTUFFS 
 
 Aminoazotoluene is prepared from o-toluidine by the same procedure as that used 
 in making aminoazobenzene from aniline (p. 62). 
 
 Aminoazotoluene is sulphonated to form a yellow wool dye. It is diazotised and 
 coupled with various «- and f-naphtholsulphonic acids, thus forming red wool dyes, 
 known as Cloth Reds. By reduction of aminoazotoluene a mixture, in equimolecular 
 proportions, of p-tolylenediamine, and o-toluidine is obtained which serves for the 
 preparation of Safranine T. 
 
 Alkyl Derivatives of o-Toluidine.—o-Toluidine is not so easily alkylated as aniline, 
 presumably because of the presence of the methyl group in the o-position to the 
 amino group. Thus it is possible to alkylate so that the main products are the 
 secondary bases, and, on the other hand, alkylation to the tertiary bases is difficult. 
 The tertiary bases derived from o-toluidine are not used as dyestuff intermediates, 
 but the secondary bases have attained considerable importance, much more, in fact, 
 than the secondary bases derived from aniline. Aniline supplies the tertiary bases 
 required, while o-toluidine supplies the secondary bases. It is a matter of relative 
 ease of preparation, and therefore of relative costs. 
 
 Methyl-o-toluidine— 
 
 CH, 
 
 ( Pass 
 lr 
 
 —a colourless liquid, b.p. 207° to 208°, D*® 0-973. 
 Acetyl derivative, m.p. 55° to 56°. 
 Ethyl-o-toluidine— CH, 
 
 f ileeges 
 Noe 
 
 —a yellowish liquid, b.p. 214° to 216°, D?® 0-9534. 
 
 Acetyl derivative, b.p. 254° to 256°. 
 
 These two substances can be prepared, like the alkylanilines, by heating o-toluidine 
 with the respective alcohols and a mineral acid at a somewhat higher temperature 
 than that used for the alkylanilines. No precise details of the methods have been 
 published. Monnet, Reverdin, and Noelting (Ber., 1878, 11, 2278) heated a mixture 
 of 750 gms. of o-toluidine, 400 gms. of methyl alcohol, and 700 gms. of hydrochloric 
 acid at 200° to 220° for a day. Probably sulphuric acid could be used in. place of 
 hydrochloric with advantage. 
 
 In the preparation of ethyl-o-toluidine, according to Thomas (J.C.S., 1917, 111, 
 562), and Price (J.S.C.I., 1918, 87, 82T), sulphuric acid can be used along with ethyl 
 alcohol, although this has not been found possible in the ethylation of aniline. These 
 authors give no details of their methods of preparation, but describe methods of 
 removing unchanged o-toluidine from the secondary base. The former employs 
 oxalic ester, which forms an oxamic ester with the toluidine, but does not react with 
 the secondary base. The latter adds to the mixture sufficient 96 per cent. sulphuric 
 
NITROTOLUENES AND THEIR DERIVATIVES 107 
 
 acid to form the sulphate of o-toluidine, which is insoluble in the remaining secondary 
 base, and is removed by centrifuging and washing the sulphate with benzene or 
 alcohol. 
 
 Of the two bases, ethyl-o-toluidine is the more widely used, presumably because it 
 can be obtained in better yield than the methyl compound. They are used directly 
 in making dyes of the triphenylmethane series, by condensation with chloro- and 
 hydroxybenzaldehydes. These dyes are of various shades of blue, and are remark- 
 ably brilliant. 
 
 Indirectly, both bases are used also in preparing azine and thiazine colours, for 
 which purpose their p-nitroso derivatives are prepared. 
 
 p-Nitrosoethyl-o-toluidine : hae 
 
 ( \NHC.H, 
 ON SY 
 The base forms green leaflets (from benzene), m.p. 140°. Its hydrochloride forms 
 yellow crystals soluble in water. 
 
 When nitrous acid acts on ethyl-o-toluidine, a nitrosamine is first formed, but this 
 is transformed under the action of concentrated hydrochloric acid into the p-nitroso 
 derivative : 
 
 CH, CH, CH, 
 NHO,H, /NN(NO)C /\NHC,H, 
 — (je — AC 
 ara 
 
 The method used by Fischer and Hepp (Ber., 19, 2994), who originally prepared such 
 bodies for carrying out the transformation, was to isolate the nitrosamine by extrac- 
 tion with ether, add absolute alcohol to the ethereal solution, and saturate with gaseous 
 hydrochloric acid. It has been found, however, that in the case of ethyl-o-toluidine 
 the transformation proceeds partly in aqueous hydrochloric acid solutions of moderate 
 strength, and can be made to go almost completely if the concentration of the hydro- 
 chloric acid is maintained at the maximum. 
 
 The preparation is described in G.P. 264927 as follows: 135 parts of ethyl-o- 
 toluidine are dissolved in 400 parts of hydrochloric acid (20° Bé or 32 per cent.), the 
 solution cooled to 0°, and a concentrated solution of 73 parts of sodium nitrite run 
 in slowly, the temperature being kept about 0°. The nitrosamine separates as a 
 yellow oil. This is extracted with ether or benzene, the solution dried, and the solvent 
 evaporated off. It is then transformed by Fischer and Hepp’s method. 500 parts 
 of absolute alcohol are added to it, and the solution saturated in the cold with gaseous 
 hydrochloric acid. After standing for some hours, the yellow hydrochloride of the 
 p-nitroso compound crystallises out. 
 
 As mentioned above, this treatment with absolute alcohol may be omitted, with 
 little sacrifice in yield, by using a more concentrated hydrochloric acid and keeping the 
 water used in dissolving the nitrite to the minimum. 
 
 p-Nitrosomethyl-o-toluidine can be prepared in a similar manner. 
 
108 INTERMEDIATES FOR DYESTUFFS 
 
 These nitroso compounds are applied, like the nitroso derivatives of dimethyl- 
 and diethylaniline (p. 51) in making dyes of the azine series (the Brilliant Rhodulines, 
 etc.), and of the thiazine series (New Methylene Blue N). 
 
 o-Chlorotoluene : 
 CH, 
 
 (y 
 
 o-Toluidine can be converted, through its diazo compound, by means of the Sand- 
 meyer reaction, into o-chlorotoluene. This forms a good alternative method to the 
 more usual one (p. 127), as the yield obtained is high. The following is the procedure 
 described by Ullmann (“‘ Organisches Chemisches Praktikum,” p. 190): 50 gms. 
 of cupric chloride is dissolved in 100 c.c. of 33 per cent. hydrochloric acid and 20 c.c. 
 of water. 20 gms. of zinc foil strips are added, and the mixture heated to boiling 
 until the solution, at first dark brown, becomes pale brown, and the cuprous chloride 
 begins to separate as a crystalline film on the surface. 
 
 While the cuprous chloride solution is cooling, 130 c.c. of 33 per cent. hydrochloric 
 acid is stirred into 600 gms. of ice, the temperature of the mixture falling to — 18°. 
 To this is added 54 gms. of o-toluidine, which dissolves and then separates as hydro- 
 chloride. A solution of 35-5 gms. of sodium nitrite in 100 c.c. of water is now added 
 quickly, with vigorous stirring. The temperature does not rise above 0°, no nitrous 
 acid escapes, and starch-potassium-iodide paper should be faintly coloured blue by 
 the solution. The diazo compound is then poured moderately quickly into the now 
 almost decolourised cuprous chloride solution, keeping the temperature between 30° 
 and 40°. Nitrogen is evolved, and the chlorotoluene separates as a brown oil. When 
 the reaction is finished, the o-chlorotoluene is distilled off with steam. The distillate 
 is shaken with caustic soda to dissolve out any o-cresol present. The chlorotoluene 
 is then separated, warmed for a little with calcium chloride to dry it, and distilled. 
 The yield of crude substance is 58 gms.,and of the distilled, 53 gms., distilling between 
 152° and 160° (mostly at 156°). This corresponds to a yield of 85 per cent. 
 
 o-Tolidine— 
 
 HC CH, 
 —lustrous leaflets (from alcohol), m.p. 129°, easily soluble in alcohol and ether, 
 sparingly soluble in water. 1 part dissolves in 1,000 parts of cold water or in 300 parts 
 of boiling water. 
 
 It forms a dihydrochloride, of which 1 part dissolves in 17 parts of water at 12°, 
 and also a more sparingly soluble monohydrochloride. 
 
 The sulphate, C,,H,,.N2.H.SO,, crystallises in needles or leaflets. 100 ¢.c. of water 
 dissolve 0-12 gm. of the sulphate. 
 
 The diacetyl derivative melts at 315°. 
 
 o-Tolidine is prepared from o-nitrotoluene in the same way as benzidine from 
 nitrobenzene—1.e., by reduction of nitrotoluene to hydrazotoluene and transformation 
 
NITROTOLUENES AND THEIR DERIVATIVES 109 
 
 of this by hydrochloric acid (p. 29). The yield obtained is lower than that of 
 benzidine, being about 64 to 65 per cent., using the process described by Schultz (see 
 under Benzidine). In this case, as in the case of benzidine, the hydrazo compound 
 transforms partly to the o-p-diamino compound, and some fission also takes place 
 with formation of o-toluidine. 
 
 o-Tolidine is used in making azo dyes of the same types as those derived from 
 benzidine. The shades produced are somewhat bluer than those of the corresponding 
 benzidine dyes. 
 
 o-Tolidinedisulphonic acid : 
 
 This is prepared like the corresponding benzidinedisulphonic acid (p. 33). 
 
 It forms a disodium salt (+5H,O), which is readily soluble in hot water. 
 
 By coupling its tetrazo compound with £-naphthol a fast red wool dye, Milling 
 Scarlet 5B or Acid Anthracene Red, is obtained. 
 
 5-Nitro-2-aminotoluene— 
 
 —crystallises from water in yellow needles, m.p. 127° to 128°. It is sparingly soluble 
 in. boiling water, but easily soluble in alcohol. It forms no salts. 
 
 This substance may be prepared, like p-nitroaniline, by nitration of the acetyl deri- 
 vative of o-toluidine, but considerable quantities of the 3-nitro derivative are formed at 
 thesametime. The 5-nitro compound is almost the sole product when the p-toluene- 
 sulphony] derivative of o-toluidine is nitrated (G.P. 157859, 163516, 164130, A.G.F.A.). 
 
 26-1 kg. of the p-toluenesulphony! derivative of o-toluidine, in a finely powdered 
 condition, is stirred into a mixture of 200 litres of water and 42 kg. of nitric acid 
 (22-5° Bé). The mixture is warmed on the water-bath, and nitration proceeds with 
 alteration of the white crystals of the toluidide to yellow flocks of its 5-nitro derivative. 
 About six to eight hours are required to complete the nitration. The product is then 
 filtered off, washed, and dried. After recrystallising from alcohol it melts at 173° to 
 175°. The toluenesulphonyl group is split off by warming the product with concen- 
 trated sulphuric acid, and the 5-nitro-2-aminotoluene isolated in the usual way. 
 
 B. Derivatives of p-Nitrotoluene. 
 p-Toluidine— CH, 
 
 8 
 
 NH, 
 
 —crystallises in leaflets (from dilute alcohol), m.p. 45°, b.p. 200-4° (760 mm.), D 1-058. 
 It dissolves in 285 parts of water at 11-5°, and is easily soluble in alcohol, ether, and 
 
110 INTERMEDIATES FOR DYESTUFFS 
 
 benzene. It is volatile in steam, 33 gms. distilling with 1 kg. of steam. From the 
 steam distillate it separates as a monohydrate in leaflets, m.p. 41-5°, which effloresce 
 in air. 
 
 The hydrochloride forms leaflets or needles, m.p. 243°, soluble in water. 
 
 The sulphate, (C,H,N)..H.SO,, forms scales of which 5-06 parts dissolve in 100 
 parts of water at 22°. 
 
 The acetyl derivative crystallises from benzene in needles, m.p. 153°. 
 
 p-Toluidine is prepared by reduction of p-nitrotoluene in the usual way (p. 26). 
 
 It is used as a first component in a few monoazo dyes. In conjunction with aniline 
 it is employed in the manufacture of Magenta, the p-toluidine furnishing the ‘‘ methane 
 carbon” for the triphenylmethane molecule. Itisalso largely applied in the preparation 
 of acid wool colours of the anthraquinone series. Hydroxyanthraquinones, especially 
 those containing hydroxyl groups in «-positions, are condensed with p-toluidine so as 
 to substitute the toluidino group for hydroxyl—e.g.: 
 
 ne NH.C,H,.CH, 
 ye EN AOA 
 
 + 2CH,.C,H,.NH, > | 
 ay: \co”% Pie “C0” ‘fq 0.8,.CH, 
 
 The products so formed are then sulphonated, the sulpho groups entering the toly] 
 nuclei. -Toluidine seems to be preferred to aniline for this purpose, probably because 
 on sulphonation the sulpho groups take positions ortho to the —NH— groups, 
 whereas in the case of aniline sulphonation would occur in the para positions. 
 
 p-Nitrotoluene-o-sulphonic acid : 
 CH, 
 ( sn 
 * 
 
 NO, 
 
 The acid crystallises from water in pale yellow prisms (-++2H,O), m.p. 133-5°. From 
 dilute sulphuric acid it crystallises water-free. The anhydrous acid melts at 130°. 
 100 parts of water at 23° dissolve 67-7 parts of the acid. It is also soluble in alcohol, 
 ether, and chloroform. The sodium salt is sparingly soluble in water. | 
 
 This substance is obtained by sulphonating p-nitrotoluene with three times its 
 weight of 25 per cent. oleum. The mixture is stirred at a moderate temperature 
 (25° to 30° will suffice, but the sulphonation is quicker at water-bath temperature), 
 until a sample is soluble in water. The solution is then poured into about three times 
 its weight of saturated salt solution, when the sodium salt of p-nitrotoluenesulphonie 
 acid separates almost quantitatively. It is filtered off and pressed. The product 
 thus obtained may be used direct, or it may be purified by dissolving in hot water and 
 salting out again. 
 
 p-Nitrotoluene-o-sulphonic acid undergoes a remarkable reaction when heated 
 with caustic soda solution. Simultaneous oxidation of the methyl group and reduc- 
 tion of the nitro group take place with formation of deeply coloured stilbene deriva- 
 
NITROTOLUENES AND THEIR DERIVATIVES 111 
 
 tives. The first product is a blood-red solution, consisting chiefly of a dinitroso- 
 stilbenedisulphonic acid : 
 
 elt { ( Ree 
 sof or 
 No No 
 
 Continued action of alkali causes further condensation to form mixtures of yellow or 
 
 orange dyestuffs, whose composition depends on the concentration of the alkali, on 
 
 the temperature, and on the duration of heating. Dyestuffs of this kind are made by 
 
 such empirical methods, and form the Stilbene Yellows and Mikado Yellows of 
 
 commerce. They are direct cotton colours, and also dye wool and silk. 
 Dinitrostilbenedisulphonic acid : 
 
 HO,S(/ ( nee 
 “a NS. 
 No, No, 
 
 The acid crystallises in colourless or faintly yellow needles, soluble in water. The 
 sodium salt is only moderately soluble in cold but easily in hot water. It is scarcely 
 soluble in water containing caustic soda or sodium chloride. 
 
 This is prepared by oxidising p-nitrotoluenesulphonic acid in caustic alkaline 
 solution with sodium hypochlorite. 
 
 Dinitrodibenzyldisulphonic acid— 
 
 CH, CH, 
 Bef ) ( \s0,H 
 
 Cay, 
 
 NO,. 2. NO, 
 
 —is formed as an intermediate stage, and it is necessary, if the stilbene compound is to 
 be used in making Chrysophenine, to ensure that the dibenzyl compound is completely 
 oxidised to the stilbene. According to Green and Wahl (Ber., 30, 3078), the dibenzyl 
 compound is favoured by a comparatively low temperature of oxidation, and by 
 using a large excess of caustic soda, which precipitates the sodium salt of the dibenzyl 
 compound as itis formed. On the other hand, the conditions favouring the stilbene 
 compound are: less caustic soda, a higher temperature, and an excess of hypochlorite 
 over the calculated amount. However, the temperature to be used is limited by the 
 consideration that, as previously explained, p-nitrotoluene-o-sulphonic acid is readily 
 converted in hot caustic alkaline solution into complex yellow and orange stilbene 
 dyes. Greenand Wahl (loc. cit.) oxidise at 50°, and also recommend this temperature 
 in their English Patent, E.P. 5351 of 1897, but in their German Patent, G.P. 113514, 
 the oxidation is performed at 80°. 
 
 The process described in the paper cited is as follows: To a solution of 100 gms. 
 of sodium p-nitrotoluenesulphonate in 2 litres of warm water 200 c.c. of 30 per cent. 
 
112 INTERMEDIATES FOR DYESTUFFS 
 
 caustic soda and 500 c.c. of sodium hypochlorite solution (7 per cent. active chlorine) 
 are added. The mixture is warmed at 50° until the hypochlorite has almost dis- 
 appeared. On cooling, the sodium salt of dinitrostilbenedisulphonic acid crystal- 
 lises out. 
 
 According to G.P. 113514, 200 gms. of p-nitrotoluenesulphonate is dissolved in 
 2 litres of water at 80° and, while stirring vigorously, 100 c.c. of 30 per cent. caustic 
 soda isrunin. This is immediately followed by the addition of 234 c.c. of sodium 
 hypochlorite solution (14 per cent. active chlorine) until a slight excess of unused 
 chlorine is present. Hydrochloric acid is then added until the solution is only faintly 
 alkaline and the dinitrostilbenesulphonate is salted out. 
 
 Essentially the same process is described in G.P. 106961 (Levinstein), the only 
 difference being that the caustic soda and hypochlorite solutions are mixed before 
 adding. 
 
 The strength of the product in stilbene compound may be estimated by titration 
 in ice-cold alkaline solution with standard permanganate. The dibenzyl compound is 
 not oxidised by permanganate under these conditions. 
 
 A number of yellow direct cotton colours of the same nature as those obtained 
 from p-nitrotoluenesulphonic acid (p. 111) are derived from dinitrostilbenedisulphonic 
 acid by heating with caustic soda solutions of various strengths at different tempera- 
 tures. Deeper shades are obtained by adding a reducing agent, such as glycerol, 
 dextrose, or zinc dust. Another series of dyes is obtained by condensing various 
 primary amines, diamines, and aminophenols with dinitrostilbenedisulphonic acid in 
 boiling caustic alkaline solution. Unitary products are not obtained, and little is 
 known of their constitution. The processes used are purely empirical. For the 
 preparation of these dyes, the presence of dinitrodibenzyldisulphonic acid in the stil- 
 bene compound matters little, as it yields similar dyes. 
 
 Diaminostilbenedisulphonic acid : 
 
 CH CH 
 HO,S () Ow 
 oe a’ 
 NH, NH, 
 
 The acid forms a brownish-yellow crystallme powder, almost insoluble in water. 
 The salts are easily soluble. 
 
 This was formerly prepared (G.P. 38735, Leonhardt and Co.) by boiling sodium 
 p-nitrotoluenesulphonate with caustic soda solution until it was converted as far as 
 possible into the dinitrosostilbenedisulphonic acid or Stilbene dyes previously men- 
 tioned (p. 111), and then reducing the product directly with zinc dust. The yields 
 obtained were not good. 
 
 Green and Wahl (E.P. 5351 of 1897) reduced dinitrostilbenedisulphonic acid with 
 zinc dust, but, according to Fierz-David (‘‘ Farbenchemie,”’ 1920, p. 119), the ordinary 
 reduction method with iron can be used. 100 gms. of the crude sodium salt of dinitro- 
 stilbenedisulphonic acid is dissolved in 300 c.c. of hot water, neutralising at the same 
 time any free alkali by a little dilute hydrochloric acid. This solution is added during 
 
NITROTOLUENES AND THEIR DERIVATIVES 113 
 
 half an hour to a boiling mixture of 200 gms. of iron borings, 20 c.c. of 40 per cent. 
 acetic acid, and some water. After completion of the reduction and precipitation of 
 dissolved iron by addition of the necessary sodium carbonate, the filtered solution is 
 made strongly acid with hydrochloric acid, when diaminostilbenedisulphonic acid is 
 precipitated, and after standing for ten hours is filtered off. 
 
 Diaminostilbenedisulphonic acid yields a tetrazo compound, and is used in making 
 disazo dyes, of which that obtained by coupling with phenol and ethylating the 
 product, named Chrysophenine, is the most important. 
 
 Dehydrothiotoluidine— 
 
 arerny 
 | ) ae Qiieaeciis 
 13h RS saa oa a an 
 fin 
 
 —crystallises from alcohol in brilliantly iridescent pale yellow prisms, m.p. 194-8°, 
 b.p. 434° (766 mm.). It is almost insoluble even in boiling water, but is soluble in 
 acetic acid, and moderately soluble in benzene, ether, and hot ethyl and amy] alcohols. 
 The solutions generally show a violet-blue fluorescence. 
 
 It dissolves in concentrated hydrochloric acid to form an orange dihydrochloride. 
 On adding water to the solution a yellow monohydrochloride precipitates. 
 
 The acetyl derivative melts at 227°. 
 
 It forms a yellow soluble diazo compound which shows great stability. 
 
 Dehydrothiotoluidine should be handled with care, as it gives rise, with most 
 people, to an eczematic irritation of the skin. 
 
 Dehydrothiotoluidine forms part of the product obtained by heating p-toluidine 
 with sulphur at 180° to 270°. The reaction was first studied by A. G. Green (see the 
 article on “‘ Primuline and its Derivatives’”’ in Thorpe’s “ Dictionary of Applied 
 Chemistry ’’), who showed that, as far as the formation of dehydrothiotoluidine was 
 concerned, it occurred in accordance with the equation : 
 
 2C,H,.NH, + 48 = C,,H,.N.S a. 3H,S 
 
 However, if p-toluidine and sulphur, in the proportion of 2 molecules of the former 
 to 4 atoms of the latter, are heated until evolution of hydrogen sulphide ceases, 
 further reactions take place and bodies of similar type but higher molecular weight 
 are formed by a repetition of the first reaction with dehydrothiotoluidine itself. Thus 
 there are formed a dithio and a trithio base, which have probably the constitutions : 
 
 peeks 
 5, { <> 
 ae es 
 oan ( ey o2 NH 
 5 ( earl haan 
 H,C ge saa ee 
 
 These latter bodies constitute that part of the product which is known as 
 
 Primuline base. Besides these main products, there are found in the melt 
 8 
 
114 INTERMEDIATES FOR DYESTUFFS 
 
 small quantities of the o-thiophenol derivative of p-toluidine (I) and thio-p- 
 toluidine (II) : 
 
 CH, CH, CH, 
 () e JN 
 Ls Geral 
 NH, NH, NH, 
 
 I II 
 
 Some p-toluidine is always left unchanged. Apart from these by-products, the product 
 obtained by heating 2 molecules of p-toluidine with 4 atoms of sulphur contains about 
 50 per cent. of dehydrothiotoluidine and 40 per cent. of primuline base. The propor- 
 tion of dehydrothiotoluidine to primuline in the melt can be raised by lowering the 
 proportion of sulphur to p-toluidine, but no conditions have been found to yield 
 dehydrothiotoluidine without some accompanying primuline base. Green (loc. cit.) 
 recommends the proportion of 2 atoms of sulphur to 2 molecules of p-toluidine if 
 dehydrothiotoluidine is required. The preparation in that case would be carried 
 out as follows : 
 
 214 parts of p-toluidine and 64 parts of sulphur are heated together in a vessel 
 provided with an air condenser and some means of absorbing the hydrogen sulphide 
 evolved later. The temperature is slowly raised, and at 170° to 180° hydrogen 
 sulphide is given off. The heating is regulated so that the reaction does not become 
 too violent. When the evolution of gas slackens, the temperature is slowly raised to 
 about 210° and maintained at this point until no more hydrogen sulphide is given off. 
 The unchanged p-toluidine is then distilled off under reduced pressure, this being 
 followed by small quantities of the above-mentioned by-products. The residual 
 liquid is chiefly dehydrothiotoluidine, but contains some primuline and other impuri- 
 ties. It can be used directly by running the melt on to iron plates and powdering 
 the solid cakes when cold. If pure dehydrothiotoluidine is required, the only satis- 
 factory method of obtaining it is to continue the vacuum distillation at a sufficiently 
 high temperature to drive over the dehydrothiotoluidine itself. Recrystallisation of 
 the crude melt from solvents is useless. 
 
 G.P. 53938 (Cassella) recommends the addition of naphthalene to the melt i in 
 order to prevent the temperature from rising above 210°, but this is unnecessary if 
 the above proportions are used, since the excess of p-toluidine serves the same purpose 
 and is more easily removed from the finished melt. 
 
 Dehydrothiotoluidine is used as a first component in azo dyes, «-naphtholsulphonic 
 acids being generally used as end components. These dyes, like those obtained from 
 benzidine, are direct cotton colours. They also possess affinity for wool and silk, and 
 are therefore used in dyeing union materials. 
 
 A basic dye, Thioflavine T, is also made from dehydrothiotoluidine by methylation 
 of the base so far as to form a monoquaternary ammonium salt : 
 
 CH; Cl 
 
 an NN(CH,)>- 
 REE 
 
 Pee 
 
 a 
 - oe 
 
NITROTOLUENES AND THEIR DERIVATIVES 115 
 
 Dehydrothiotoluidinesulphonic acid : 
 
 os 
 C.C,H,(SO,H).NH 
 ae L Jos SC.C,H,(SO,H).NH, 
 
 The acid forms small yellow needles (with 1H,O) or orange leaflets (with 2H,O). It 
 is insoluble in cold and sparingly soluble in hot water. The salts are colourless, and 
 mostly moderately soluble in water, the solutions showing a violet-blue fluorescence. 
 The ammonium salt crystallises in fine white needles (+-H,0), and is sparingly soluble. 
 The acid yields a yellow sparingly soluble diazo compound, which is stable even in 
 boiling water. 
 
 The sulphonic acid just described is prepared by the sulphonation of dehydrothio- 
 toluidine with oleum containing a high percentage of free sulphur trioxide. The 
 exact position of the sulpho group is unknown. 
 
 The published descriptions of the preparation of this acid (‘‘ Primuline,”’ etc., 
 by A. G. Green, Thorpe’s ‘“ Dictionary of Applied Chemistry ’’; Jansen, Zeit. Farben- 
 md. 1913, 12, 215) deal with the sulphonation of the so-called primuline melt, 
 which is obtained by heating p-toluidine and sulphur in the proportion of 2 molecules 
 of the former to 44 atoms of the latter. The melt so obtained contains about 60 per 
 cent. of primuline base, and only 30 to 35 per cent. of dehydrothiotoluidine. It yields 
 a mixture of the sulphonic acids of both bases, from which dehydrothiotoluidine- 
 sulphonic acid is separated by means of its sparingly soluble ammonium salt. 
 
 Formerly, it was the primuline which was chiefly desired, but in recent years the 
 use of dehydrothiotoluidine and its sulphonic acid has greatly extended, while that of 
 primuline has declined. The primuline melt has, therefore, probably been modified 
 by reduction of the proportion of sulphur used so as to yield a larger percentage of 
 dehydrothiotoluidine. However, the sulphonation process is essentially the same, 
 whatever the proportions of the bases in it, and the following summary of the process 
 described by Green is applicable to any modified melt or even to the high percentage 
 crude dehydrothiotoluidine previously described. 
 
 The melt is carried out by heating a mixture of 1,000 lbs. of p-toluidine and 670 
 Ibs. of sulphur in an enamelled iron pot provided with an enamelled stirrer and an air 
 condenser. The mixture is boiled for several hours, during which hydrogen sulphide 
 is evolved and the temperature gradually rises. The evolution of hydrogen sulphide 
 begins at 170°, and is completed when the temperature reaches 270°. The melt is 
 then discharged from the pot, cooled, and powdered when solid. The yield is about 
 1,125 lbs. 
 
 400 Ibs. of the powdered melt is dissolved with rapid stirring in 1,000 lbs. of 100 per 
 cent. sulphuric acid. The temperature is allowed to rise freely during this operation, 
 and reaches about 90°. The solution is then cooled below 40°, and 800 to 900 lbs. of 
 70 per cent. oleum slowly added, the temperature being kept about 40°. About six 
 hours are required for the addition. Stirring is then continued until sulphonation 
 is complete, as shown by the sulphonic acids, precipitated from a sample by dilution 
 with water, dissolving to a perfectly clear solution in boiling dilute ammonia. It 
 
116 INTERMEDIATES FOR DYESTUFFS 
 
 is necessary to make sure that this test is complied with, otherwise difficulty arises 
 later in filtering the precipitated sulphonic acids. On the other hand, the course of 
 the sulphonation must be followed closely by means of this test so as to determine 
 exactly the point of completed sulphonation. Ifthe reaction is continued beyond this 
 point soluble disulphonic acids are formed, resulting in diminished yield, especially 
 of dehydrothiotoluidinesulphonic acid. 
 
 When sulphonation is complete, the solution is run into about 3,000 gallons of 
 cold water, and the sulphonic acids, which separate as a bulky orange-yellow precipi- 
 tate, are filtered off and washed completely free of mineral acid with cold water. 
 The paste of mixed sulphonic acids is then stirred into cold concentrated ammonia, 
 sufficient being used to give a slight excess of freeammonia. Both acids dissolve up 
 as ammonium salts, but that of the dehydrothiotoluidinesulphonic acid soon begins 
 to crystallise out, and after standing for a few days to complete the separation, is 
 filtered off and washed with a little cold water. 
 
 The filtrate, which contains the soluble ammonium salt of primuline, is treated 
 with common salt, when the primuline is salted out as a dark yellow granular preci- 
 pitate. 
 
 The yields obtained are 530 to 560 Ibs. of ammonium dehydrothiotoluidinesul- 
 phonate and 1,700 to 1,800 lbs. of primuline of standard dyeing strength from 1,000 
 Ibs. of p-toluidine. 
 
 In G.P. 281048 (Bayer) is described the preparation of a dehydrothiotoluidine- 
 sulphonic acid, which is said to be different from that mentioned above. The bake 
 process is used, and the product is, therefore, probably the o-sulphonic acid : 
 
 240 parts of dehydrothiotoluidine are intimately mixed with a solution of 147 parts 
 of 100 per cent. sulphuric acid in water, and the mixture is heated till dry. It is then 
 finely powdered and heated in vacuo at 235° to 250° in a vessel provided with a stirrer 
 and anaircondenser. Whenno more water distils over, the sulphonic acid is dissolved 
 up in hot water and the necessary alkali, the solution filtered, and on cooling the 
 sodium salt crystallises out as colourless leaflets. This sulphonic acid also yields a 
 yellow sparingly soluble diazo compound. It is said to yield azo dyes of greater 
 intensity and better light fastness than those obtained from the sulphonic acid pre- 
 pared in the ordinary way. 
 
 Dehydrothiotoluidinesulphonic acid is used as a first component in several mono- 
 azo dyes which, like those obtained from dehydrothiotoluidine base, are direct cotton 
 colours. With «- and B-naphtholsulphonic acids as second components, the dyestuffs 
 obtained give pink and scarlet shades on cotton. Dyestuffs, which are probably of 
 the azo class, are also obtained by condensing dehydrothiotoluidinesulphonic acid — 
 with dinitrostilbenedisulphonic acid in alkaline solution. 
 
 By coupling diazotised dehydrothiotoluidinesulphonic acid with a molecular 
 proportion of the acid itself, a diazoamino compound is obtained, known as Thiazole 
 
NITROTOLUENES AND THEIR DERIVATIVES 117 
 
 Yellow, which gives very intense but very fugitive shades on cotton. On the other 
 hand, by oxidising dehydrothiotoluidinesulphonic acid with sodium hypochlorite an 
 exceedingly fast yellow dyestuff is obtained. 
 
 Primuline is often used in place of dehydrothiotoluidinesulphonic acid, and yields 
 dyes of almost identical shades and similar properties. 
 
 3-Nitro-4-aminotoluene (m-nitro-p-toluidine) : 
 
 CH, 
 
 Os 
 
 The base forms red prisms, m.p. 117° to 118°, soluble in alcohol. Its acetyl derivative 
 crystallises in lemon-yellow needles, m.p. 94° to 95°. 
 
 This substance is prepared by nitration of the acetyl derivative of »-toluidine, 
 either in sulphuric acid solution, as in the preparation of p-nitroaniline, or in solution 
 in glacial acetic acid (Ehrlich, Ber., 15, 2009). The nitro-p-acetotoluidine so produced 
 is then hydrolysed by boiling with concentrated hydrochloric acid or with caustic 
 alkali. 
 
 This nitrotoluidine, by coupling its diazo compound with f-naphthol, forms a 
 bright red lake pigment of excellent quality as regards fastness to water, lime, and - 
 heat. It is also used in conjunction with Naphthol AS for producing red dyeings 
 on cotton. 
 
 C. Derivatives of 2 : 4-Dinitrotoluene. 
 
 m-Tolylenediamine— 
 CH, 
 
 Se 
 
 NH, 
 
 —crystallises in prisms or needles (from water), m.p. 99°, b.p. 283° to 285°. It is 
 easily soluble in boiling water, but much less so in cold water. The diacetyl derivative 
 melts at 224°. 
 
 It is prepared from 2: 4-dinitrotoluene in the same way as m-phenylenediamme 
 from m-dinitrobenzene. 
 
 m-Tolylenediamine resembles m-phenylenediamine closely in properties and in 
 chemical behaviour. Bythe action of nitrous acid it gives a Bismarck Brown of redder 
 shade than that formed from m-phenylenediamine. It is used as an end component 
 in various mono-, dis-, and trisazo dyes. 
 
 Acridine dyes are formed from it by condensation with formaldehyde and benz- 
 aldehyde. 
 
 It is also used in the preparation of several sulphur colours by heating it with 
 sodium polysulphides under various conditions. 
 
118 INTERMEDIATES FOR DYESTUFFS 
 
 m-Tolylenediaminesulphonic acid : 
 CH; 
 
 ts 
 HOS.) 
 NH, 
 The acid crystallises in small prisms, sparingly soluble in water. The sodium salt 
 crystallises with 4H,O, and is soluble in water. 
 
 It is prepared by adding m-tolylenediamine sulphate gradually to the calculated 
 quantity of oleum and heating the solution for about three hours on the water-bath. 
 When the sulphonation is finished, the solution is poured on ice, and the sulphate of 
 the sulphonic acid separates. This is converted to the hydrochloride, and used direct 
 for azo dyes (Biickel, Zeit. Farbenind., 1904, 3, 137). 
 
 4-Nitro-2-aminotoluene— 
 CH; 
 ( \NH, 
 U 
 
 NO, 
 
 —crystallises from alcohol as large orange-yellow prisms with blue reflex, m.p. 107°, 
 b.p. 310°. It dissolves in 100 parts of boiling water. 
 
 This compound can be prepared, either by reducing 2: 4-dinitrotoluene or by 
 nitrating o-toluidine by Noelting and Collin’s method, in which the base is nitrated 
 in a large excess of concentrated sulphuric acid. 
 
 The former method seems preferable as giving a product free from isomers. 
 Reduction with ammonium sulphide or sodium disulphide does not give good results 
 in this case, but, according to G.P. 289454 (Pomeranz), reduction with iron and 
 sulphur dioxide, which is equivalent generally to reduction with alkaline sulphides, 
 is specially suitable. 
 
 A mixture of 182 gms. of 2 : 4-dinitrotoluene, 200 gms. of iron borings, and 1 litre 
 of water, is warmed to 80° to 90°, and excess of sulphur dioxide passed in. The iron 
 dissolves except for a small residue, which is filtered off, and on cooling the nitro- 
 toluidine crystallises out. The yield obtained is 110 gms. or about 80 per cent. 
 
 On nitrating o-toluidine dissolved in a large excess of sulphuric acid the product 
 contains 75 per cent. of 4-nitro-2-aminotoluene, about 20 per cent. of 6-nitro compound 
 (m.p. 91-5°) and 3 to 4 per cent. of the 5-nitro compound (m.p. 130°). The large 
 scale preparation of the 4-nitro compound by this method is described by Jansen 
 (Zeit. Farbenind., 1913, 12, 181). 
 
 192 kg. of o-toluidine is added very slowly, with good stirring and cooling arrange- 
 ments, to 840 kg. of 98 per cent. sulphuric acid, the temperature being allowed to rise 
 to 30° to 35°. White lumps of the sulphate form on the surface of the acid, but these 
 tedissolve. The solution is then cooled to 10° and a mixture of 125 kg. of 90 per cent. 
 nitric acid and 300 kg. of 98 per cent. sulphuric acid is dropped in through a funnel, 
 whose end dips beneath the surface of the solution. During the addition the tempera- 
 ture is kept at 10°, except towards the end, when it is allowed to rise to 12°. When 
 
 Oe ee pert 
 
NITROTOLUENES AND THEIR DERIVATIVES 119 
 
 the nitration is finished, the solution is run into 4,500 litres of a solution containing 
 1,200 kg. of salt. The sulphate of 4-nitro-2-aminotoluene separates as a pale yellow 
 crystalline mass, while the 6-nitro compound remains in solution. After twenty-four 
 hours’ stirring, the precipitated sulphate is filtered and washed with small quantities 
 of saturated salt solution. The yield obtained is 190 kg., reckoned as base. 
 
 The diazo compound of 4-nitro-2-aminotoluene is coupled with f-naphthol to 
 form an orange lake pigment. It is also used with B-naphthol and Naphthol AS to 
 produce orange and scarlet dyeings on cotton by a similar method to that used for 
 Para Red. 
 
CHAPTER VI 
 
 THE CHLORINATION AND SULPHONATION 
 OF TOLUENE 
 
 THE action of chlorine or chlorinating agents on toluene proceeds in two ways, 
 according to conditions—viz., by substitution either in the nucleus or in the side chain. 
 A third possibility—the formation of addition products—has apparently not been 
 observed. At the boil, or in the cold in sunlight, side chain chlorination takes place, 
 if catalysts are absent. In the presence of catalysts such as iodine and many metallic 
 chlorides, nuclear chlorination occurs. 
 
 A comprehensive review of the literature on the chlorination of toluene is given by 
 Cohen and Dakin (J.C.S., 1901, 79, 1111), who also give the results of further investiga- 
 tions in later papers (J.C.S., 1905, 87, 1034; 1910, 97, 1623). 
 
 Benzyl chloride— OH.O 
 
 A 
 
 —a colourless liquid having a characteristic aromatic odour. The vapour is irritating 
 totheeyes. B.p. 179°. D;21-104. Itis insoluble in water, but is slowly hydrolysed 
 by boiling with water, milan benzyl alcohol, C,H,;.CH,OH. 
 
 The usual method of preparation of this substance is to pass dry chlorine into dry 
 boiling toluene, to which about 2 per cent. of phosphorus trichloride or pentachloride 
 has been added to accelerate the reaction, until the theoretical increase in weight is 
 obtained. Iron vessels cannot be used, since iron induces nuclear chlorination, lead 
 vessels being undesirable, though not absolutely prohibitive, for a similar reason.* 
 Hnamelled or tile-lined vessels have been used. In Germany, glass vessels heated in 
 calcium chloride baths are sometimes employed. The reaction is also sometimes 
 further accelerated by use of the light from a quartz-mercury lamp. Provision, of 
 course, has to be made for absorbing the hydrochloric acid evolved. 
 
 When the chlorination has reached the desired stage, the product is washed with 
 very dilute alkali and then fractionated. It contains, besides benzyl chloride, some 
 unchanged toluene and the higher chlorination products, benzal chloride and benzo- 
 trichloride. 
 
 A continuous manufacturing process is described by Marckwald in G.P. 142939 
 (E.P. 17695 of 1902). 
 
 The use of nascent chlorine, by passing sulphur dioxide into a mixture of ieee 
 and bleaching powder, was suggested by Conant (U.S.P. 1233986). A similar idea, 
 carried out in an aqueous medium, is the subject of a patent by Levinstein and Bader 
 (H.P. 134250). Toluene (3 mols.) is emulsified, by rapid stirring, with a sodium 
 hypochlorite solution containing 1 molecule of active chlorine. The mixture is cooled 
 to — 5° and dilute sulphuric acid (4 mol.) or other acid added gradually during 
 
 * Wahl, Normand, and Vermeylen (C.r., 1922, 174, 946), found that chlorination of toluene in 
 presence of lead chloride gave a mixture consisting mainly of o- and p-chlorotoluenes. 
 
 120 
 
‘NOILVNOHdINS GNV NOILVNINOTHO AT ANANTIOL JO SHALLVATYAG— IA LYVHO 
 
 0) 
 
 OHO 
 
 m Oh = 
 
 OHO OHD 
 
 t t 
 J” wos() 
 
 "h OHO 
 
 b 
 
 al } 
 
 19 
 VJ 19 al) 
 OHO 
 a 
 
 <r 
 \e) 
 
 DO 8D 8O 
 = 
 
 8 
 O 
 a 
 O 
 ea 
 O 
 O 
 a 
 a 
 Oo 
 
122 INTERMEDIATES FOR DYESTUFFS 
 
 six hours. The mixture is then allowed to settle, and the chlorinated toluene layer 
 separated. On fractionation it gives unchanged toluene, benzyl chloride, and a 
 small residue of benzal chloride, ete. The yield of benzyl chloride is 60 to 70 per cent. 
 calculated on the active chlorine used. 
 
 Benzyl chloride is used in benzylating amines, especially the secondary alkyl- 
 anilines. 
 
 Benzal chloride— Ong 
 
 & 
 
 Pe 
 
 —a strongly refracting liquid, b.p. 206°, D** 1-2557. 
 
 Benzotrichloride— 
 Col. 
 van 
 
 m 
 
 —a strongly refracting liquid, b.p. 213° to 214°, D* 1-380. 
 
 These two substances are usually prepared together in varying proportions by 
 passing chlorine into toluene, as described in the case of benzyl chloride. They cannot 
 be separated by fractional distillation, but their respective products of hydrolysis, 
 benzaldehyde, and benzoic acid, are easily separated. The passage of the chlorine is, 
 therefore, continued until the desired proportions of benzal chloride and benzotri- 
 chloride are formed, as indicated by the increase in weight, or, more conveniently, by 
 the specific gravity of the liquid. The mixture, after removal of any unchanged 
 toluene and benzyl chloride by fractional distillation, is then hydrolysed to benzalde- 
 hyde and benzoic acid, as described later. 
 
 Complete chlorination to benzotrichloride is not usually attempted, partly because 
 the last of the chlorine is only slowly taken up, and partly because the tendency 
 towards nuclear chlorination greatly increases at this stage. 
 
 Benzaldehyde— 
 CHO 
 
 : 
 
 —a colourless highly refracting liquid of characteristic aromatic odour, b.p. 179-1° 
 (751 mm.),62°(10mm.). Itfreezes at— 13-5°. D*? 1-0504. It dissolves in 300 parts 
 of water. 
 Benzaldehyde is prepared either by hydrolysis of benzal chloride or by direct 
 oxidation of toluene. The hydrolysis of benzal chloride, which was formerly carried 
 out by heating with milk of lime in autoclaves, is now accomplished, at ordinary 
 pressure and at water-bath temperature, by water with the addition of a little iron 
 powder as catalyst. This improvement was introduced by Schultze (G.P. 82927, 
 85493). The ordinary crude mixtures of benzal chloride and _ benzotrichloride 
 are used, any benzyl chloride being previously removed by fractionation. The 
 
THE CHLORINATION OF TOLUENE 123 
 
 benzotrichloride undergoes a similar hydrolysis, with formation of benzoic 
 acid. 
 
 In a lead-lined (or copper) vessel, 60 kg. of the crude benzal and benzotrichlorides 
 is warmed to 25° to 30°, 20 gms. of iron powder added and, after fifteen to thirty 
 minutes, 10 to 15 kg. of water. The mixture is warmed gradually to 90° to 95°, and 
 the reaction, once started, proceeds vigorously. The hydrochloric acid evolved is 
 absorbed in water. When the evolution of gas has ceased, the mixture is made 
 alkaline with milk of lime made from 9 to 10 kg. of quicklime and the benzaldehyde 
 distilled off with steam. The residual aqueous liquor is filtered, and the filtrate 
 acidified, when benzoic acid is precipitated. 
 
 The benzaldehyde obtained from the steam distillate contains as impurities chloro- 
 toluenes, benzyl alcohol, etc. It is purified through its bisulphite compound. The 
 crude product is agitated with four to five times its weight of ordinary 35 per cent. 
 bisulphite solution until the benzaldehyde is dissolved. After allowing to settle, the 
 bisulphite compound is separated from the undissolved oily impurities. The solution 
 is then made alkaline with soda and distilled with steam. The separated and dried 
 benzaldehyde is finally purified by distillation. 
 
 Benzaldehyde is also prepared, as mentioned above, by direct oxidation of toluene. 
 Manganese dioxide, in conjunction with sulphuric acid, has been found to be the best 
 oxidising agent for this purpose, and the process is described in G.P. 101221 (Sociésé 
 Chimique des Usines du Rhone). 300 kg. of toluene and 700 kg. of 65 per cent. 
 sulphuric acid are thoroughly mixed by rapid stirring, and 90 kg. of finely divided 
 manganese dioxide (the regenerated oxide should be used) is gradually added, while 
 the temperature is kept at 40°. When the reaction is ended, the benzaldehyde and 
 unchanged toluene are distilled with steam, and the benzaldehyde separated from the 
 toluene and purified by the bisulphite method. The yield of benzaldehyde is 50 kg. 
 and 250 kg. of toluene is recovered. A little dibenzyl, C;H;.CH,.CH».C,H;, is always 
 formed asa by-product. The essential feature of the method is that, in order to avoid 
 further oxidation to benzoic acid, a large fraction of the toluene is left unoxidised. 
 According to a later patent by the same firm (G.P. 107722), however, the whole of the 
 toluene may be oxidised to aldehyde without fear of this further oxidation. 
 
 An improvement in the purification process was introduced by the Griesheim- 
 Elektron firm in G.P. 154499. The crude aldehyde is mixed with water and sulphur 
 dioxide passed in at the ordinary temperature. A soluble compound of the aldehyde 
 with sulphur dioxide is formed. After separating the solution from the undissolved 
 matter, it is heated to 100°, when the compound decomposes, sulphur dioxide being 
 evolved, and the benzaldehyde is separated from the water. 
 
 Benzaldehyde is used chiefly in the production of dyes of the triphenylmethane 
 series by condensing it with two molecular proportions of a tertiary base derived from 
 aniline, such as dimethylaniline, benzylethylaniline, etc., and oxidising the con- 
 densation product. The resulting dyes are basic and dye textiles in various shades 
 of green. 
 
 Basic dyes of the acridine series are also made from benzaldehyde by condensing 
 it with meta-diamines, such as m-tolylenediamine. 
 
124 INTERMEDIATES FOR DYESTUFFS 
 
 m-Nitrobenzaldehyde— 
 
 —pale yellow crystals, m.p. 58°, b.p. 164° (23 mm.). 
 
 This substance forms the main product when benzaldehyde is nitrated in the 
 ordinary way with mixed acid (Friedlander and Henriques, Ber., 1881, 14, 2802). At 
 low temperatures, about 5°, o-nitrobenzaldehyde is practically the only other 
 product, but at temperatures above the ordinary the p-isomer is also formed to 
 some extent. 
 
 The nitration is described in detail in U.S.P. 1509412. Mixed acid having the 
 composition— 
 
 HNO, oe ay a bs ny .. 28-30 per cent. 
 H,SO, * a Ae Ve ee .. 63-66 si 
 H,O oa mo oe e's Ks -- 4-7 ma 
 
 —isused. 74 litres of this acid is cooled below 15°, and 3 kg. of benzaldehyde added 
 at such a rate that the temperature can be kept between 5° and 15°. About six hours 
 are required for the addition. The mixture is stirred for an hour longer to complete 
 the nitration. It is then poured into 18 kg. of ice and 43 kg. of water, stirred, and 
 allowed to settle. The dilute acid layer is run off, and the oily mixture of aldehydes 
 washed first with warm water and then with warm dilute soda solution until acid-free. 
 The temperature of the washing liquors should be about 40° in order to keep the alde- 
 hydes liquid. The oil is then cooled to 10° and stirred until it has crystallised as far 
 as possible. The crystals of m-nitrobenzaldehyde are separated from the remaining 
 oil by centrifuging. This gives a fairly pure product. 
 
 The residual oil contains o-nitrobenzaldehyde (which forms about 20 per cent. of 
 the total product) mixed with a little m-compound and some dinitrobenzaldehydes. 
 
 m-Aminobenzaldehyde : 
 
 This is prepared by reduction of the bisulphite compound of m-nitrobenzaldehyde, 
 since the nitrobenzaldehyde is not itself easily reduced. The reduction may be 
 carried out by iron or zinc and acid, as in G.P. 62950 (Meister Lucius and 
 Briining), but better results are obtained by the process described in G.P. 66241 
 by the same firm. 
 
 680 kg. of ferrous sulphate crystals are dissolved in 2,000 litres of water and 250 ke. 
 of precipitated chalk added. The mixture is boiled and vigorously stirred while a 
 solution of 60 kg. of m-nitrobenzaldehyde in 120 kg. of 30 per cent. bisulphite and 
 500 litres of water is run in slowly. The reduction is immediate. Much frothing 
 takes place owing to the carbon dioxide evolved. The mixture is filtered hot, and the 
 filtrate, acidified with hydrochloric acid, is boiled to expel sulphur dioxide. The 
 
THE CHLORINATION OF TOLUENE 125 
 
 resultimg solution of m-aminobenzaldehyde hydrochloride is used direct, chiefly for 
 the preparation of m-hydroxybenzaldehyde. 
 
 m-Hydroxybenzaldehyde— 
 CHO 
 
 oe 
 
 ree 
 
 —m.p. 107°, b.p. 240°, or 160° to 161° (20 mm.). 
 This substance is prepared by diazotising m-aminobenzaldehyde and boiling the 
 solution of diazo compound. No details of the method have been published. 
 m-Hydroxybenzaldehyde is used in making Cyanol FF, a triphenylmethane dye, 
 by condensing the aldehyde with ethyl-o-toluidine and sulphonating the product, 
 when two sulpho groups enter the aldehyde nucleus. 
 
 Benzoic acid— 
 COOH 
 
 H 
 
 —lustrous needles or leaflets, m.p. 121-4°, b.p. 249°, Di? 1-2659. It sublimes readily, 
 and is volatile in steam. 100 parts of water at 10° dissolve 2 parts, and at 75° 22 parts 
 of benzoic acid. It is also soluble in alcohol, ether, and chloroform. The sodium 
 salt crystallises with 1H,0. 
 
 Benzoic acid is prepared either from benzotrichloride or directly from toluene by 
 oxidation. The former process is the cheaper of the two, but yields a product con- 
 taining chlorobenzoic acids and other chloro derivatives, while the latter gives a 
 chlorine-free benzoic acid. 
 
 As explained in connection with the preparation of benzotrichloride, the chlorina- 
 tion of toluene is not carried so far as to convert the toluene completely to the tri- 
 chloride owing to the increasing extent of nuclear chlorination towards the end. If 
 benzoic acid is required as the chief product, chlorination is continued until the specific 
 gravity of the liquid reaches 1-34 to 1-37 (S.G. of benzotrichloride : 1-39), and the 
 resulting mixture of benzal chloride and benzotrichloride is hydrolysed by the process 
 of G.P. 85493, as described under Benzaldehyde (p. 123). Benzoic acid in this case 
 is the main product, with benzaldehyde as by-product. 
 
 Toluene can be oxidised to benzoic acid by manganese dioxide and sulphuric 
 acid, but for good yields stronger oxidising agents arerequired. A process of oxidation 
 with chromic acid is described in G.P. 261775 (Buckau). A solution containing 
 130 gms. of chromic acid and 300 to 400 gms. of sulphuric acid per litre is heated 
 to 85° to 100°, and toluene vapour passed through. Benzoic acid is formed, and is 
 dissolved up by the toluene layer, which accumulates on the surface of the chromic 
 acid solution, thus being removed from further attack by the oxidant. The toluene- 
 benzoic acid solution is separated from the acid layer and the benzoic acid isolated. 
 The chromic sulphate is reoxidised electrolytically and used again. The yield of 
 benzoic acid is 70 to 90 per cent. of the toluene consumed. 
 
126 INTERMEDIATES FOR DYESTUFFS 
 
 Benzoic acid is used in the preparation of a few chrome wool colours belonging to 
 different chemical classes. It condenses with pyrogallol yielding a trihydroxybenzo- 
 phenone, which constitutes the commercial dye Alizarine Yellow A. Condensed with 
 gallic acid it forms a trihydroxyanthraquinone, a chrome brown (Anthracene Brown) 
 of excellent fastness qualities : 
 
 Oe 
 oe eae 
 EAS AL i \/\¢9?\/F 
 
 It also reacts with Michler’s hydrol to form a triphenylmethane dye, Chrome Green, 
 the condensation taking place in the meta position to the carboxyl group. 
 
 Benzoic acid is also used as a catalyst in the phenylation of Rosaniline to produce 
 the Aniline Blues, its exact function being unexplained. 
 
 Benzoyl chloride, C,H;.CO.CI, a colourless liquid, b.p. 198°, D?P 1-2122, may be 
 prepared from benzoic acid by the action of phosphorus pentachloride, but some 
 cheaper reagent is generally used. 
 
 G.P. 146690 proposes to use sodium chlorsulphonate, which is prepared by heating 
 chlorsulphonic acid with the calculated quantity of sodium chloride at 150° until evolu- 
 tion of hydrochloric acid ceases. 170 parts of sodium chlorsulphonate and 150 parts of 
 sodium benzoate (anhydrous) are heated together until the benzoyl chloride formed 
 distils off : 
 
 C,H;.COONa + Cl.SO,Na 
 
 > O,H,.CO.cCl + Na,SO, 
 
 Thionyl chloride and sulphuryl chloride have also been used. 
 Benzoyl chloride is chiefly used in benzoylating aminoanthraquinones to produce 
 vat dyes of the Algol series. The benzoyl derivatives are found to possess good 
 
 affinity for cotton, a property which is almost entirely lacking in the free amino 
 compounds. 
 
 The Chlorotoluenes. 
 
 The conditions favouring the substitution of chlorine in the nucleus of toluene 
 are (1) low temperatures (ordinary temperature is suitable), and (2) the presence of 
 catalysts. Iodine, as catalyst in this case, seems not merely to favour nuclear chlorina- 
 tion, but actually to hinder side-chain chlorination even at the boiling-point. Ferric 
 chloride and molybdenum chloride are also useful as catalysts in this reaction. When 
 toluene is chlorinated under these conditions, a mixture of o- and p-chlorotoluenes is 
 formed, together with some dichloro derivatives. On fractionating the product a 
 mixture of the two monochlorotoluenes can be isolated, but they cannot be separated 
 from one another by distillation owing to the closeness of their boiling-points. A 
 method of separation is described below. Of the two, only the o-compound has 
 found much application in the dyestuff industry. 
 
 o-Chlorotoluene— CH, 
 
 ( qe 
 
 el 
 
THE CHLORINATION OF TOLUENE 127 
 
 —a colourless oil, b.p. 159°, Dj? 10877. It freezes at —34°. (p-Chlorotoluene’ 
 liquid, b.p. 162°, Dj? 1-0749. Freezes at 7-4°.) 
 
 The two monochlorotoluenes may be separated, according to E.P. 159837 (Wahl), 
 by a process which depends on the fact that o-chlorotoluene is more readily sulphonated 
 than the y-compound, and that the conditions of sulphonation as regards tem- 
 perature and acid concentration can be so arranged that only o-chlorotoluene is 
 sulphonated. s 
 
 The mixture of chlorotoluenes (40 parts) is heated with 75 parts of 93 per cent. 
 sulphuric acid at 114° to 115° for two and a half hours. In this way nearly all the 
 o-compound is sulphonated and the p-compound, together with the small residue of 
 unsulphonated o-compound, remains as an oil which is separated from the acid layer 
 on cooling. The solution of o-chlorotoluenesulphonic acid is then heated to 180° and 
 superheated steam passed through. The sulphonic acid is hydrolysed, o-chloro- 
 toluene distils with the steam and is separated from the distillate. 
 
 A better process, and one which avoids the formation of p-chlorotoluene, is that 
 described in G.P. 294638 (Badische). Toluene-p-sulphonic acid is chlorinated, the 
 chlorine entering the o-position only, and o-chlorotoluene is then easily obtained by 
 hydrolysis of the sulphonic acid. The toluene-p-sulphonic acid is most conveniently 
 obtained from its chloride (p. 130). The direct chlorination of toluene-p-sulphonyl 
 chloride, however, is useless, as the chlorine partly expels the —SO,CI group. 
 
 300 parts of molten toluene-p-sulphonyl chloride is run slowly into 300 parts of 
 sulphuric acid (60° Bé) at 95°. A vigorous evolution of hydrochloric acid takes place, 
 and the liquid is further heated at 100° for two hours in order to expel the hydro- 
 chloric acid completely. The solution is cooled to 20° and 3 parts of sublimed ferric 
 chloride added. Chlorine is then led in until the specific gravity of the solution, 
 originally 49-5° Bé, rises to 53-5° Bé, when'the formation of o-chlorotoluene-p-sul- 
 phonic acid is complete. This is now hydrolysed directly with superheated steam, as 
 described above, and the separated o-chlorotoluene purified by distillation. 
 
 If toluene-p-sulphony] chloride is not available, toluene may be sulphonated under 
 the conditions specified by Hollemann (Ber., 1911, 44, 2508), so as to form the 
 maximum proportion of the p-sulphonic acid. This idea is used in G.P. 287932 
 (Meister Lucius and Briining), an alternative method of chlorination being also 
 described. 
 
 Toluene (460 parts) is sulphonated by heating with 2,300 parts of 84 per cent. 
 sulphuric acid at 100° to 105° for seven hours. The proportion of p-sulphonic acid 
 formed is about 85 per cent. The solution is poured into 2,600 parts of ice, and after 
 adding 600 parts of common salt and 900 parts of concentrated hydrochloric acid, 
 chlorination is carried out by slowly adding during eight hours a solution of 250 
 parts of sodium chlorate, the temperature being kept at 55°. The sodium salt of 
 o-chlorotoluene-p-sulphonic acid crystallises out and, after cooling and stirring for 
 several hours, is filtered off. An 80 per cent. yield of pure sodium-o-chlorotoluene- 
 p-sulphonate is thus obtained. The filtrate contains p-chlorotoluene-o-sulphonate. 
 The o-chlorotoluene-p-sulphonate is then hydrolysed, as already described, to form 
 o-chlorotoluene. 
 
128 INTERMEDIATES FOR DYESTUFFS 
 
 Another method of preparation of o-chlorotoluene—from o-toluidine—is described 
 on p. 108. 
 
 -Chl ldeh CHO 
 o-Chlorobenzaldehyde— & i 
 
 v, 
 
 —a colourless liquid, b.p. 208° (748 mm.). It freezes at 11°. 
 
 This is prepared from o-chlorotoluene by first subjecting it to side-chain chlorina- 
 tion, so as to form o-chlorobenzalchloride, and then hydrolysing the latter compound. 
 The method is described by Erdmann (Ann., 1893, 272, 151). 
 
 The o-chlorotoluene used must be. completely dry. 750 gms. of it, to which 23 gms. 
 of phosphorus pentachloride is added, is heated in a flask, with reflux condenser, 
 immersed in an oil-bath at 150° to 180°, preferably in good daylight. A strong stream 
 of dry chlorine is passed through in minute bubbles until the increase in weight amounts 
 to about 380 to 400 gms. The product may then be fractionated, the fraction dis- 
 tilling at 226° to 236° being chiefly o-chlorobenzalchloride. This fractionation, 
 however, is unnecessary. 
 
 1,100 gms. of the crude chlorobenzalchloride (containing, of course, also chloro- 
 benzylchloride and chlorbenzotrichloride) is added to a mixture of 2,200 gms. of con- 
 centrated sulphuric acid and 2,200 gms. of 10 per cent. oleum at ordinary temperature. 
 The chlorobenzalchloride and the trichloride are hydrolysed to aldehyde and carbo- 
 xylic acid respectively, and these dissolve in the sulphuric acid. The chlorobenzyl 
 chloride and any unchanged chlorotoluene are unaffected and form an oily layer on the 
 surface of the acid. As the hydrochloric acid is evolved, the temperature of the 
 solution falls and after about an hour reaches its minimum, the stream of hydro- 
 chloric acid now weakening considerably. After a further hour’s stirring, the solution 
 has again reached atmospheric temperature, and at the end of six hours’ more stirring 
 the reaction is finished. The mixture is allowed to settle, and the upper oily layer 
 removed. The acid solution is then poured on ice and the oily chlorobenzaldehyde 
 separated. Itis washed with dilute sodium carbonate solution, and with water, dried 
 with calcium chloride, and distilled. The yield obtained from 750 gms. of o-chloro- 
 toluene is about 170 gms. of the aldehyde. 
 
 (o-Chlorobenzoic acid may be obtained from the dilute acid solution and from the 
 aldehyde wash liquors. It crystallises in large needles, m.p. 140°. 1 part dissolves 
 in 881 parts of water at 0°.) 
 
 o-Chlorobenzaldehyde is used in making greenish-blue pie aN dyes by 
 condensation with dialkylanilines or with ethyl-o-toluidine. 
 
 2: 5-Dichlorobenzaldehyde— CHO 
 
 4\ a 
 
 ue 
 —colourless crystals, m.p. 57° to 58°. 
 
 A method of preparing this substance directly from benzaldehyde is described by 
 Gnehm and Banziger (Ann., 1897, 296, 62; U.S.P. 315932). 
 
THE CHLORINATION OF TOLUENE 129 
 
 A solution, of 10 gms. of iodine in 60 gms. of benzaldehyde is dropped slowly into 
 540 gms. of antimony pentachloride, stirrmg the while, the temperature being kept 
 under 60°. When all the benzaldehyde has been added, the mixture is heated at 
 104° to 105° until no more visible gas is evolved. This takes several hours. The 
 escaping vapours are condensed to recover the iodine. The product is now stirred 
 into 300 gms. of concentrated hydrochloric acid diluted with 600 gms. of water. The 
 oil is separated from antimony chloride solution, and, to remove adhering antimony 
 chloride, is warmed with a very little caustic soda solution and filtered from the 
 precipitated antimony oxide. The alkaline solution is removed, and the oil shaken 
 and heated with 180 gms. of 33 per cent. sodium bisulphite solution diluted with an 
 equal weight of water. The hot solution of bisulphite compound of the aldehyde is 
 separated from undissolved oil, and on cooling sets to a snow-white crystalline mass 
 of the bisulphite compound. This is filtered off and boiled under reflux for some time 
 with 135 gms. of hydrochloric acid. The aldehyde separates as an almost colourless 
 oil, which is removed, dried, and distilled. More of the aldehyde may be obtained by 
 repeated extraction of the residual oil with more bisulphite solution. Distillation of 
 the aldehyde yields a first fraction, up to 231°, containing o- and m-monochloro- 
 benzaldehydes, this beg followed by the main quantity at 231° to 238°, consisting 
 of 2: 5-dichlorobenzaldehyde, and a small third fraction above 238°, containing 
 3: 4-dichlorobenzaldehyde. 
 
 2: 5-Dichlorobenzaldehyde may also be prepared from 2: 5-dichlorotoluene by 
 the method of G.P. 32238 (Badische), which is similar to that by which o-chloro- 
 benzaldehyde is made from o-chlorotoluene. 
 
 The 2: 5-dichlorotoluene required can be obtained by the process described in 
 H.P. 169025 (B.D.C., Green, and Clibbens). 680 gms. of toluene-p-sulphonic acid is 
 neutralised with caustic soda and dissolved in sufficient water to make about 11 litres 
 of solution. Chlorine is passed in until 10 c.c. of the liquid has acquired acidity 
 equivalent to 5-5 c.c. of N/1 alkali. A mixture of the sodium salts of 2 : 5-dichloro- 
 and 2:5: 6-trichlorosulphonic acids is formed, from which, under the conditions 
 stated, nearly all the 2:5: 6-trichlorosulphonate separates in crystalline form. 
 On filtering, and evaporating the filtrate, the 2: 5-dichlorosulphonate is obtained 
 practically pure. The dichlorosulphonic acid is then hydrolysed im the usual way 
 (p. 127) to obtain 2 : 5-dichlorotoluene. 
 
 2:5-Dichlorobenzaldehyde is used, like monochlorobenzaldehyde, in making 
 greenish-blue triphenylmethane dyes. These are faster to washing than the corre- 
 sponding colours from the monochloro compound. 
 
 Benzaldehyde-o-sulphonic acid : 
 CHO 
 
 f bas 
 ned 
 The acid hasnotbeencrystallised. Thesodiumand bariumsaltscrystalliseinlong prisms. 
 
 This substance is most conveniently prepared from o-chlorobenzaldehyde by the 
 action of neutral sodium sulphite, as described in G.P. 88952 (Geigy). 
 
130 INTERMEDIATES FOR DYESTUFFS 
 
 A neutral solution of sodium sulphite is prepared by diluting 50 litres of 40 per 
 cent. bisulphite with 150 litres of water and neutralising with caustic soda, using 
 phenolphthalein as indicator. To this is added 20 kg. of o-chlorobenzaldehyde, and 
 the mixture is heated in an autoclave at 170° to 180° for eight hours. The pressure 
 developed is about 8 atmospheres. The solution is now treated with 13 kg. of sulphuric 
 
 acid and boiled to expel sulphur dioxide and traces of unchanged chlorobenzaldehyde. 
 
 The sulphonic acid is then isolated either by neutralising with carbonate, evaporating 
 to dryness, and extracting the sodium salt with alcohol, or by forming the barium salt 
 in the ordinary way and evaporating its solution to the crystallising point. The 
 barium salt is rather sparingly soluble. 
 
 Benzaldehyde-o-sulphonic acid is used in making a few triphenylmethane dyes by 
 condensation; for example, with benzylethylaniline or with cresotic acid. 
 
 The Sulphonation of Toluene. 
 
 Toluene is sulphonated at moderate temperatures by concentrated sulphuric acid 
 yielding a mixture of o-, m-, and p-monosulphonic acids in which the p-acid greatly 
 preponderates, while the m-acid is present in very small proportion. The subject 
 has been studied in detail by Hollemann and Caland (Ber., 1911, 44, 2504). They found 
 that a rise in the temperature of sulphonation favoured the p-acid at the expense of the 
 o-acid, whereas an increased proportion of acid favoured the o-acid at low tempera- 
 tures. Variation of the concentration of the sulphuric acid from 96 to 100 per cent. 
 had no influence on the proportions of the isomers. 
 
 The sulphonation of toluene so as to produce the highest proportion of p-sulphonic 
 acid has been described on p. 127. The p-sulphonic acid can be separated from its 
 isomers by adding to the sulphonation mixture so much water that, on removal of the 
 toluene-p-sulphonic acid, a sulphuric acid of 66 per cent. strength is left, the p-acid 
 being very sparingly soluble in acid of that strength (G.P. 57391), and crystallises out 
 with 1H,O. On heating the filtrate to 170° and passing superheated steam at 200°, the 
 remaining o- and m-acids are hydrolysed, and the toluene so formed is recovered. 
 The process is described in greater detail by Inglis (J. Soc. Chem. Ind., 1918, 87, 288T). 
 
 The manufacture of saccharin, for which toluene-o-sulphonic acid is required, led 
 to the development of a procedure by which the maximum proportion of the o-acid 
 could be obtained. It was found that the greatest proportion of o-compound was 
 obtained when toluene was acted on by a large excess of chlorsulphonic acid at low 
 temperatures. A mixture of the sulphonyl chlorides is formed in the proportion of 
 40 per cent. of the o- to 60 per cent. of the p-compound. Excess of chlorsulphonic 
 acid (about 4 molecules to 1 molecule of toluene) is required in order to avoid formation 
 of toluenesulphonic acid by a secondary reaction, thus : 
 
 (a) C,H, + OLSO,H ———> O,H,.80,01 + H,0 
 (b) C,H,.SO,Cl + H,O ———> C,H,.S0,H + HCl 
 
 The procedure, as described by Gilliard, Monnet, and Cartier (G.P. 98030), is as 
 follows: Into 400 kg. of chlorsulphonic acid, stirring at 0°, is run slowly 100 kg. of 
 
THE SULPHONATION OF TOLUENE 131 
 
 toluene, the temperature being kept under 5°. The mixture is stirred for twelve 
 hours more, keeping within the same temperature limits of 0° to5°. It is then poured 
 on ice, when the mixture of sulphony! chlorides separates in liquid condition. The 
 acid layer*is removed by decantation, and the chlorides washed with water. The 
 mixture is then cooled to — 20°, and after twelve hours at this temperature most of the 
 p-sulphonyl chloride has crystallised out, and this is separated by filtration or by 
 centrifuging. The remaining liquid, amounting to about 60 per cent. of the original 
 total, is composed of 70 per cent. o-compound, and 30 per cent. p-compound. A 
 further separation is described in G.P. 95338 (Majert and Ebers). The liquid is 
 distilled under reduced pressure until about 30 to 40 per cent. has passed over. This 
 fraction is almost pure o-sulphonyl chloride. The residue is then frozen again at 
 — 20°, when more of the p-sulphony! chloride crystallises out and is filtered off. The 
 treatment is repeated with the mother liquor. 
 
 The toluene-p-sulphonyl chloride thus obtained as a by-product of saccharine 
 manufacture has become a useful reagent in several ways in the preparation of dyestuff 
 intermediates. By acting on it with methyl and ethyl alcohols, toluene-p-sulphonic 
 methyl and ethyl esters are obtained, which are used as alkylating agents. Again, 
 by stirring the sulphonyl chloride with concentrated aqueous ammonia, toluene-p- 
 sulphonamide is formed, which Ullmann has shown can be used effectively in con- 
 verting chloroanthraquinones into the corresponding aminoanthraquinones (p. 222). 
 
CHAPTER VII 
 XYLENE DERIVATIVES 
 
 THE xylene derivatives are obtained from commercial “ pure xylene,” a mixture 
 of the three xylenes which boils between 138° and 142°. It contains usually about 
 60 per cent. of m-xylene, and quantities of o- and p-xylenes, each varying between 
 10 and 25 per cent. A little ethylbenzene is also present. 
 
 Nitroxylenes.—The xylenes are not usually separated. The mixture is nitrated by 
 the same process as that used for nitrobenzene (p. 16), though the temperature should 
 be kept lower (about 20°) during nitration in order to avoid oxidation of the methyl 
 groups. A mixture of five mononitroxylenes is thus obtained, whose properties are 
 given in the following table : 
 
 = eee See ee ne ee 
 
 Constitution. Meliing-Point. Botling-Point. Specific Gravity. 
 CH; | CH; | NOs 
 3-Nitro-o-xylene 1 2 3 7° to 9° 245° to 246° (760 mm.) | 1-147 at 15°» 
 4-Nitro-o-xylene .. 1 2 “ 30° 258° (748 mm.) 1-139 ,, 30° 
 2-Nitro-m-xylene 1 3 2 Liquid 225° (744 mm.) 1112, 15° 
 4-Nitro-m-xylene 1 3 + 20° 244° (760 mm.) 1-135 ,, 15° 
 2-Nitro-p-xylene 1 4 2 Liquid 239° (739 mm.) 1-132 ,,, 15° 
 
 The sixth possible nitroxylene, 5-nitro-m-xylene, is not formed in this way. 
 Xylidines.—The nitroxylenes are not separated, but are reduced directly to the 
 
 xylidines by iron and hydrochloric acid, as in the preparation of aniline from nitro- 
 
 benzene (p. 26). The five xylidines so formed have the following properties : 
 
 Specific Gravity Melting-Point| Melting-Point of 
 
 Melting-Point. Boiling-Point. at 15°, of HCl Salt. | Acetyl Derivative. 
 o-3-Xylidine. . AT Liquid 223° 0-991 254° 134° 
 o-4-Xylidine. . we 49° 226° 1-0755 256° 99° 
 m-2-Xylidine ie Liquid 216° 0-980 — 176-5° 
 m-4-Xylidine sp Liquid 212° 0-9184 235° 129° 
 p-Xylidine .. ne 15°5° 215° 0-980 228° 139-5° 
 
 The mixed xylidines are used to some extent for monoazo dyes, in which the diazo 
 compounds are coupled with B-naphthol and its sulphonic acids as second components. 
 
 Separation of the Xylidines. 
 
 The chief constituents of the xylidine mixture are m-4-xylidine (usually referred 
 to simply as m-xylidine), which forms about half of the mixture, and p-xylidine, 
 which is present to the extent of 10 to 20 per cent. These two xylidines are separated 
 from the mixture by one of the following methods. 
 
 m-Xylidine : CH, 
 
 A 
 ce 
 
 NH, 
 1382 
 
XYLENE DERIVATIVES 133 
 
 This is best separated by the method described in G.P. 39947 (Limpach). 121 parts 
 of the xylidine mixture and 30 parts of glacial acetic acid are mixed and allowed to 
 stand for a day or two. m-Xylidine acetate alone crystallises out. The crystals 
 are separated by centrifuging. 
 
 p-Xylidine : CH, 
 
 Bie 
 
 CH, 
 
 A crude p-xylidine is obtained from the mother liquor remaining after the separation 
 of m-xylidine acetate, by adding to it 1 molecular proportion of hydrochloric acid. 
 p-Xylidine hydrochloride crystallises out, and after a few days is separated by centri- 
 fuging. The crude base is recovered from its salt in the usual way. 
 
 From this crude base pure p-xylidine can be obtained by the method of G.P. 
 71969 (Bayer). 121 parts of the crude base are mixed with 106 parts of benzaldehyde. 
 The mixture heats up to about 60° and water separates, owing to the formation of the 
 benzylidene derivatives of the bases : 
 
 C,H,(CH;),NH, + C,H,.CHO > C,H,(CH;),N:CH.C,H, + H,0 
 
 To some extent, however, the reaction takes another course, pp’-diaminodi-p-xylyl- 
 phenylmethane being formed : 
 
 The water is separated either by long standing of the mixture in tall narrow vessels 
 or by slow evaporation. The oil sets to a crystalline mass on cooling, the crystallisa- 
 tion being complete in twenty-four hours. The crystals are separated by centrifuging 
 and pressing from the residual oil, and are washed with alcohol. The pure benzylidene 
 compound of p-xylidine is thus obtained as pale yellow crystals, m.p. 102° to 103°. 
 It is decomposed by heating with dilute mineral acid, and the liberated benzaldehyde 
 is distilled off with steam. The remaining solution is then made alkaline with caustic 
 soda or milk of lime, and the p-xylidine distilled in steam. 
 
 The diaminodixylylphenylmethane remains in the alkaline liquid, as it is not 
 volatile in steam. 
 
 Applications of the Xylidines. 
 
 m-Xylidine is used as a first component in azo dyes, in which its diazo compound 
 is coupled with f-naphthol or the naphtholsulphonic acids. 
 p-Xylidine, on the other hand, is chiefly used as a middle component in dis- and 
 
134 INTERMEDIATES FOR DYESTUFFS 
 
 trisazo dyes. It couples readily with diazo compounds, and the free amino group in 
 the resulting aminoazo compound can then be diazotised and coupled with a third 
 component. 
 
 m-Xylidine-o-sulphonic acid : CH, 
 
 Pe 
 a 
 
 NH, 
 
 This acid may be prepared by the procedure described in E.P. 175019 (B.D.C., 
 Baddiley, Payman, and Wignall). Sulphonation with chlorsulphonic acid in an 
 organic solvent is found to introduce a sulphonic acid group in the o-position to the 
 amino group. 
 
 121 gms. of m-xylidine is dissolved in 500 gms. of tetrachlorethane, and to the 
 stirred solution 122 gms. of chlorsulphonic acid is slowly added, the temperature being 
 allowed to rise to 80°. The solution is then gradually heated to the boiling-point, and 
 is boiled under reflux until the evolution of hydrochloric acid ceases. After cooling, 
 the m-xylidinesulphonic acid is extracted with aqueous alkali, and the free acid preci- 
 pitated by acidifying with hydrochloric acid. 
 
 m-Xylidine-o-sulphonic acid is used as first component in an azo dye, Normal 
 Yellow 3GL, of which a pyrazolone derivative is second component. 
 
 Dehydrothio-m-xylidine— 
 
 —crystallises from alcohol in prisms, m.p. 107°, b.p. 282° to 284° (13to 14mm.). Itis 
 insoluble in water, very soluble in hot alcohol, and sparingly soluble in cold alcohol. 
 The acetyl derivative melts at 227°. 
 
 This is prepared, like dehydrothiotoluidine, by heating m-xylidine (6 parts) with 
 sulphur (1 part) at 180° to 200° until evolution of hydrogen sulphide ceases. The 
 excess of xylidine is distilled off. The residue contains, besides dehydrothio-m- 
 xylidine, an isomeric body named isodehydrothio-m-xylidine : 
 
 ( eye P 
 AE ING OUP, eee a ° 
 acl Js vererttl 2 (m.p. 121°) 
 
 The two are separated by extracting the mixture with 30 per cent. hydrochloric acid, 
 in which the zsobase is insoluble. 
 
 Dehydrothio-m-xylidine is used, like dehydrothiotoluidine, as first component in 
 several monoazo dyes, the second components being «- and f-naphtholsulphonic acids. 
 
 Oc =, eee 
 
CHAPTER VIII 
 
 NAPHTHALENE DERIVATIVES: A PRELIMINARY 
 SURVEY 
 
 In the preparation of dyestuff intermediates from naphthalene, the general aim, 
 as with intermediates from other sources, is to introduce the auxochrome groups, 
 amino and hydroxyl, accompanied by sulphonic acid groups to confer solubility on 
 the products or to occupy certain positions in the molecule in order to exclude the 
 formation of undesired isomers during the preparation of dyestuffs from the inter- 
 mediates. Up tothe present, therefore, the naphthalene derivatives which have been 
 made have been of the nature of naphthylamines, naphthols, aminonaphthols, and 
 their sulphonic acids, with the addition of a few naphtholcarboxylic acids. These 
 substances have been used almost exclusively as intermediates for azo dyes, for 
 which they are peculiarly suited, and on their usefulness for this purpose depends the 
 great preponderance of azo dyes as compared with other classes. About 600 of the 
 1,200 dyestufis mentioned in the Colour Index belong to the azo class. 
 
 The methods used for the preparation of these intermediates involve the operations 
 of (1) sulphonation, (2) nitration, (3) hydrolysis with alkalies, and (4) replacement of 
 the amino group by hydroxyl, or of hydroxyl by amino, by the aid of sulphites, this 
 last being known as the Bucherer reaction. It is somewhat remarkable that, up to the 
 present, chlorination has played no part in the preparation of these compounds, 
 although a number of chloro derivatives have been made, and it is known that the 
 chlorine atom in such compounds can be replaced by hydroxyl under the action of 
 alkalies. 
 
 I. Sulphonation of Naphthalene. 
 
 The fundamental work on the sulphonation of naphthalene was carried out by 
 Armstrong and Wynne (whose results are mentioned, with little detail, in the Proceed- 
 ings of the Chemical Society, 1885 to 1895), and by Merz, Ebert, and collaborators. 
 Valuable additions to our knowledge in this field have also been made later by Euwes 
 (1909), Witt (1915), and recently by Fierz-David in a number of papers in Helvetica 
 Chimica Acta (1920 to 1923). 
 
 Considering the number of isomers theoretically possible in the case of the poly- 
 sulphonic acids, it is fortunate that actually the number of isomers formed is much 
 limited according to the rule, established by Armstrong and Wynne, that a second 
 sulpho group never enters the ortho, para, or peri position to the first. It has also 
 been established that when two sulpho groups are introduced, they enter different 
 nuclei in the naphthalene molecule. 
 
 (2) Monosulphonic Acids.—Naphthalene is sulphonated rather easily by con- 
 centrated sulphuric acid to a mixture of the «- and f-sulphonic acids. The proportion 
 of each isomer formed depends on the temperature of sulphonation, but under no 
 conditions is either isomer obtained as the sole product. The addition of mercury 
 salts to the reaction mixture has no appreciable influence on the proportions of the 
 isomers. Low temperatures favour the formation of the «-acid, while high tempera- 
 
 135 
 
136 INTERMEDIATES FOR DYESTUFFS 
 
 tures favour the f-acid. At temperatures under 40°, the sulphonation product 
 contains about 96 per cent. of the «-acid and 4 per cent. of the B-acid. At 160° to 
 165°, the proportions are 85 per cent. of the B-acid and 15 per cent. of thea-acid. This 
 is the highest porportion of the f-acid so far obtainable. 
 
 (6) Disulphonic Acids.—In conformity with the rules given above, only four 
 disulphonic acids are formed by the direct sulphonation of naphthalene or naphthalene- 
 monosulphonic acids. These are the 1:5-,1:6-, 2: 7-, and 2: 6-disulphonic acids :* 
 
 SO,H SO,H 
 he (= aa 
 BING AS hai ranted Set HOD ae 
 i 5-acid. 1:6-acid. 2: 7-acid. 2: 6-acid. 
 
 An elaborate investigation of the disulphonation of naphthalene made by Fierz-David 
 and Hasler (Helv. Chim. Acta, 1923, 6, 1133) has led to the following conclusions : 
 Under 40°, almost constant proportions of the 1: 5- and 1 : 6-acids, about 70 per cent. 
 of the 1:5- and 25 per cent. of the 1:6-, are formed, together with traces of the 
 2:7-acid. As the temperature of sulphonation is raised, the proportion of 1: 5-acid 
 diminishes, owing to replacement by 1 : 6- and 2 : 7-acids, and at 130° to 135° the 1 : 5- 
 acid is not present in the mixture. At 140°, the 2:6-acid begins to appear, and 
 increases in proportion as the temperature rises, until at 180° a maximum proportion 
 of about 30 per cent. is reached, the other components being the 1 : 6- and 2 : 7-acids. 
 
 At 165°, the mixture contains about 25 per cent. of the 2 : 6-acid, 65 per cent. of the 
 
 2: 7-acid, and 10 per cent. of the 1 : 6-acid. 
 (c) Trisulphonic Acids.—Only three trisulphonic acids are possible by the 
 Armstrong-Wynne rule—namely, the 1:3:5-, 1:3:6- and 1:3: 7-acids: 
 
 S S Ss 
 lah es ere 
 ANA Beste Ce 
 1:3: 5-acid. 1:3: 6-acid. 1:3: 7-acid. 
 
 Of these, the 1:3: 5- and 1:3: 6-acids only are of importance for the preparation 
 of dyestuff intermediates, the 1 : 3: 6-acid being by far the more important as inter- 
 mediate for H-acid. The 1:3: 5-acid can obviously only be formed from the 1 : 5- 
 disulphonic acid. The 1:3: 6-acid is formed both from the 1 : 6- and from the 2 : 7- 
 disulphonic acid, and is the only possible trisulphonic acid from either : 
 
 S 
 Oe 
 
 S 
 BO Ente Nites 
 Pept, ee A I 
 Og 
 
 * The 1: 7-acid is also possible under the rule, but apparently is not formed. 
 
 ee 
 
NAPHTHALENE DERIVATIVES 137 
 
 It is of interest also that the 1 : 3 : 6-acid cannot be sulphonated further. Only one 
 tetrasulphonic acid, the 1:3:5:7-acid, has been definitely proved to be formed, 
 and this is formed from either the 1 : 3: 5- or the 1 : 3: 7-trisulphonic acid. 
 
 The following scheme, given by Fierz-David (J. Soc. Chem. Ind., 1923, 42, 4217), 
 shows in graphic form the relations between the various sulphonic acids : 
 
 40°C. 160°C 
 (Y) 
 Oe) 
 * 4 + ae 
 40°C. 160 aA 
 ) 
 0) 
 WD 
 65-70% 30-35% 7S5- oo STI a wae 25% 
 SS : 
 
 COs 
 
 S S 
 
 oe 95% 100% 
 
 nee 
 
 IL. Nitration of Naphthalene and Its Sulphonic Acids. 
 
 Naphthalene, when nitrated, gives almost exclusively the «-nitro derivative, only 
 traces of the B-nitro derivative being formed. On further nitration, the 1: 5- and 
 1; 8-dinitro derivatives are obtained in the proportion of 1 to 2. The tri- and 
 tetranitro derivatives have not been used for dyestuff intermediates. On reduction, 
 the nitro compounds yield the amines, but only «-naphthylamine is of importance 
 as a dyestuff intermediate, the 1 : 5- and 1 : 8-diamines not being used. As f-nitro- 
 naphthalene is not formed by direct nitration of naphthalene, 6-naphthylamine is 
 prepared by another method. 
 
 When the naphthalenesulphonic acids are nitrated, the nitro group again enters an 
 “-position, but not quite so exclusively as in the case of naphthalene itself. Small 
 proportions of f-nitro derivatives are formed, the more the higher the temperature 
 of nitration. Fierz-David has found that, using the calculated quantity of nitric 
 acid for mononitration, an appreciable proportion of sulphonic acid, 4 to 14 per cent., 
 always escapes nitration, and if excess of nitric acid is used, dinitro compounds are 
 
138 INTERMEDIATES FOR DYESTUFFS 
 
 formed. This is one of the main causes of the comparatively low yields obtained of 
 the ultimate naphthylaminesulphonic acids prepared in this way. 
 
 Naphthalene-«-sulphonic acid, on nitration, yields 60 to 70 per cent. of the 1 : 8- 
 and 30 to 40 per cent. of the 1 : 5-nitrosulphonic acids. If, on the contrary, «-nitro- 
 naphthalene is sulphonated, an 80 per cent. yield of the 1 : 5-nitrosulphonic acid may 
 be obtained, along with some 1 : 6- and 1 : 7-nitrosulphonic acids. 
 
 Nitration of naphthalene-f-sulphonic acid gives 40 to 50 per cent. of the 1:6-, 
 and about 40 per cent. of the 1 : 7-nitrosulphonic acids, along with a little of the 1 : 3- 
 acid. 
 
 The products of nitration of the di- and trisulphonic acids are as follows : 
 
 C0 — CO: Ua 
 
 60 to 70 per cent. ee 30 per cent. 
 
 S O,.N 8 
 are WA LA 
 | spaacomeere a L) | “+ | | + Unknown products 
 aSre SA/ Nee 
 43 per cent. 15 per cent. 
 TN Oe s/\7 Ns 
 F— (1) 
 ny o6 
 NO, 
 CS) (Ys 
 _—_———> 
 cl le) 
 NO, 
 Ss ON NS 
 [ Wi ) ( _ ) + a little O,N/ iy a 
 a 
 ae Nee Jee 
 S Ss S 
 S O.N 
 oe DNS 
 mn 
 i) Js Us 
 Ss 
 oe PVN 
 —_> 
 Us Js 
 NO, 
 
 In ordinary practice the nitronaphthalenesulphonic acids are not isolated, but are 
 reduced directly to the desired naphthylaminesulphonic acids. 
 
 * SO,H is here abbreviated to S for convenience. | 
 
NAPHTHALENE DERIVATIVES 139 
 
 III. Hydrolysis of Naphthalene Derivatives. 
 
 Alkali fusion of the naphthalenesulphonic acids takes the normal course, and «- 
 and f-naphthols are prepared in this way from the monosulphonic acids. In the case of 
 a-naphthol, however, another method is available for its preparation, since «-naphthyl- 
 aminesulphate is hydrolysed by water at 200° to «-naphthol, and a pure product 
 free from f-naphthol is obtained by this method. The disulphonic acids yield the 
 dihydroxynaphthalenes by alkali fusion, but of these only the 1 : 5-compound is of 
 importance. By heating the di- and trisulphonic acids with concentrated solutions of 
 alkali at temperatures of 200° and over in autoclaves, one sulpho group may be 
 replaced, yielding naphtholsulphonic acids. In this way 2-naphthol-7-sulphonic acid 
 (F-acid) is prepared from the 2: 7-disulphonic acid. But all the other f-naphthol- 
 sulphonic acids are prepared by the sulphonation of B-naphthol, and most of the 
 a-naphtholsulphonic acids are prepared from the corresponding naphthylamine- 
 sulphonic acids by heating their diazonium sulphates or otherwise. 
 
 Heating with concentrated aqueous alkali in autoclaves is used in the case of 
 naphthylaminesulphonic acids to replace one sulpho group by hydroxyl, thus yielding 
 aminonaphtholsulphonic acids. In this way 1: 8-aminonaphthol-3 : 6-disulphonic 
 acid (H-acid) is prepared from 1-naphthylamine-3 : 6 : 8-trisulphonic acid, as are also 
 1 ; 8-aminonaphthol-4 : 6-disulphonic acid (K-acid), 1 : 8-aminonaphthol-4-sulphonie 
 acid (S-acid), 1 : 8-aminonaphthol-2 : 4-disulphonic acid (2S-acid), 2-amino-5-naphthol- 
 7-sulphonic acid (J-acid), 2-amino-8-naphthol-6-sulphonic acid (Gamma acid), and a 
 few others, from the corresponding naphthylaminesulphonic acids. 
 
 In such cases, however, the reaction can proceed further to replace the amino group 
 also by hydroxyl. Thus H-acid and S-acid may be further hydrolysed to 1: 8- 
 dihydroxy-3 : 6-disulphonic acid (Chromotrope Acid) and 1: 8-dihydroxynaphthalene- 
 4-sulphonic acid (Dioxy-S-acid) respectively. 
 
 IV. The Bucherer Reaction. 
 
 It has been mentioned that the amino group in naphthylamine derivatives can 
 often be replaced by hydroxyl through the action of water or alkalies at high tempera- 
 tures. H.T. Bucherer (J. pr. Chem., 1904, [2], 69, 88) discovered that this replacement 
 was much facilitated by the use of sulphites, and that, in addition, the reverse 
 replacement of hydroxyl by the amino group, which can be accomplished sometimes 
 by heating at high temperatures with ammonia, can be carried out more easily in 
 presence of sulphite. The action of the sulphite is not catalytic in the ordinary sense. 
 It must be used in molecular quantities, sometimes in large excess, and intermediate 
 compounds are formed (these have been isolated in many cases), which Bucherer 
 regards as the sulphurous esters of the naphthols, whether the starting material is a 
 naphthol or a naphthylamine derivative : 
 
 R.OH R.NH, 
 
 a ae 
 
 AN yp 
 R.0.SO,Na 
 
140 INTERMEDIATES FOR DYESTUFFS 
 
 This view of their constitution has been controverted by Voroschéov (J.C.S. Abstr., 
 1916, 1., 293), and Friedlander (Ber., 1921, 54, 620-624), who regard them as bisulphite 
 compounds of the ketonic forms of the naphthols : 
 
 ‘ HO 0.SO,Na 
 SZ 
 
 OH C 
 A\/\ i / CH, 
 | ewer “-F NaHiS03 > } 
 eed AN 
 
 The former obtains support for his view from the analysis of the isolated intermediates 
 in some cases, 
 
 The important consideration, however, in connection with the naphthalene deriva- 
 tives in question, is the properties of these intermediates. They are fairly stable in 
 neutral or acid solution, though some are partially hydrolysed to naphthol and 
 bisulphite, but they are very sensitive to caustic alkalies and even to carbonates, 
 being quickly and completely hydrolysed to naphthol and sulphite, even at compara- 
 tively low temperatures. By ammonia, on the other hand, they are easily converted 
 into naphthylamine. On Bucherer’s view, therefore, the reactions may be summarised 
 as follows : 
 
 R.on: —t_bisuphite. 2 .0.80,.Ne — tee 
 -Palkali <p bisulphite 
 
 The method has proved exceedingly useful and economical. {-Naphthylamine, 
 for example, which had previously been made by heating B-naphthol with ammonia 
 solution at 200° for a day, under very high pressure, could now, by Bucherer’s method, 
 using ammonium sulphite and ammonia, be formed by heating at 150° for eight hours 
 at 6 atmospheres pressure, and obtained in better yield and purer condition. An 
 example of the reverse change is the preparation of 1-naphthol-4-sulphonic acid 
 from |-naphthylamine-4-sulphonic acid (naphthionic acid) by heating with sodium 
 bisulphite followed by hydrolysis with alkali. | 
 
 The reaction is not quite generally applicable. Sulphonic acids of «-naphthol 
 containing sulpho groups in the ortho or meta position to the hydroxyl, and 6-naph- 
 tholsulphonic acids in which there is a sulpho group in the 4- or meta position, do not 
 give the reaction. They do not even form the intermediate sulphurous esters. 
 
 ane, eee 
 2 Da a ie 
 
CHAPTER IX 
 NITRONAPHTHALENES AND THEIR DERIVATIVES 
 | Naphthalene— Pio lips 
 
 ey 
 
 —a white crystalline solid, m.p. 80-1°, b.p. 218°. The specific gravity compared with 
 water at 0° is as follows : 1-1517 at 15°, 1-1508 at 18°, 0-9778 at 79-2°, 0-9628 at 100°. 
 
 It sublimes readily, and is volatile in steam and in alcohol vapour. It is insoluble 
 in cold water, but hot water dissolves traces of it. It is soluble in alcohol, ether, 
 acetic acid, benzene and its homologues, and very soluble in phenols. At 15°, 
 100 parts of alcohol dissolve 5-29 parts of naphthalene, but at the boiling-point of 
 alcohol the two are miscible in all proportions. At 15-5, 100 parts of benzene, 
 toluene, or xylene dissolve 45-8, 32-0, and 31-5 parts respectively of naphthalene. 
 Molten naphthalene dissolves sulphur, metallic sulphides, and Indigo. 
 
 The commercial naphthalene used for the manufacture of dyestuff intermediates 
 is required to reach a high standard of purity. It should be white, and should leave 
 no residue on volatilisation. The setting-point (this is determined in preference to 
 the melting-point) should be 79-6° to 79-8°. Heated with concentrated sulphuric 
 acid it should dissolve to a clear solution, almost colourless, at the most slightly pink 
 at water-bath temperature, or light brown at 180°. The solution on dilution and 
 making alkaline with caustic soda should give no smell of pyridine bases, and on 
 addition of bromine water and hydrochloric acid to the filtered alkaline extract should 
 
 give no clouding due to bromophenols. 
 NO, - 
 \ 
 
 a-Nitronaphthalene— 
 
 —crystallises in yellow needles, m.p. 61°, b.p. 304°, D* 1-331. 100 parts of alcohol 
 (87-5 per cent.) at 15° dissolve 2-8 parts. It dissolves to a blood-red solution in 
 sulphuric acid. 
 
 The nitration of naphthalene may be carried out at moderate temperatures with 
 fairly dilute mixed acid. In fact, in the preparation of the mononitro compound, 
 the maximum dilution is used in order to avoid formation of dinitro derivatives. 
 The manufacture of «-nitronaphthalene, as described by Witt (Chem. Ind., 1887, 10, 
 216), gives a product of satisfactory purity in almost quantitative yield. 
 
 1,000 parts of mixed acid of the approximate composition— 
 
 HNO, 4 ois Pus ae es .. 12-5 per cent. 
 H,SO, ee oe ee oe ee ee 58-0 99 
 H,O ee ee ee ee oe oe -» 29°5 99 
 
 —is stirred and heated to 45°. 250 parts of very finely powdered naphthalene is 
 added gradually through a sieve in order to avoid formation of clumps. The tem- 
 | 141 
 
142 INTERMEDIATES FOR DYESTUFFS 
 
 perature is then maintained at 45° to 50° until the nitration is finished, which takes 
 about a day. The nitro compound separates, as semisolid clumps on the surface of 
 the acid. The spent acid is run off, and the nitro compound well washed with boiling 
 water to remove acid. It is finally granulated by running the molten substance into 
 vigorously stirred cold water. The product so obtained contains about 95 per cent. 
 of a-nitronaphthalene, together with a little dinitro compound, unchanged naph- 
 thalene and traces of the f-nitro compound. It is pure enough for its sole usual 
 application—namely, reduction to «-naphthylamine. But it may be purified by 
 melting it up with about a tenth of its weight of cumene or solvent naphtha and 
 allowing to crystallise. 
 
 The spent acid has the composition : 1 per cent. HNO , 65 per cent. H,SO,, 34 per 
 cent. H,O, and, of course, can be used for a fresh charge by making up to the required 
 strength with 60 per cent. nitric acid and ordinary concentrated sulphuric acid. 
 
 a«-Naphthylamine— 
 NH, 
 
 ve 
 
 —crystallises in colourless scales or flat needles, m.p. 50°, b.p. 300-8°, D5? 1-171. Itis 
 almost insoluble in water, 100 c.c. of water at ordinary temperature dissolving 
 0-167 gm. It is easily soluble in alcohol and ether. 
 
 Its salts are rather sparingly soluble in water, especially the sulphate, 
 (C,)H,NH,),.H,SO,-+-2H,0O, which crystallises in white scales, sparingly soluble in 
 cold water and alcohol, but easily in hot water. The hydrochloride, C,,H,NH,.HCl, 
 forms long needles, soluble in alcohol, but 100 parts of water at 20° dissolve 3-77 parts. 
 
 Its acetyl derivative, C,)H,.NH.CO.CHs, forms needles, m.p. 159°. 
 
 The usual method of preparation is by reduction of the nitro compound with iron 
 borings and a little hydrochloric acid, as in the preparation of aniline. In this case, 
 however, the reduction mixture is not boiled. The reaction is so vigorous, and the 
 tendency towards elimination of the amino group during reduction is so great, that the 
 reduction is usually carried out at about 50°. Even then, there is always some 
 naphthalene formed. 
 
 Continuing the description of the process given by Witt (see under «-Nitronaph- 
 thalene), 800 parts of iron borings, 40 parts of concentrated hydrochloric acid, and 
 400 parts of water are stirred in an iron vessel (no reflux) and heated to 50°. 600 parts 
 of the air-dried crude nitronaphthalene are added gradually, the temperature being 
 maintained about 50°. A fairly vigorous reaction occurs. About six or eight hours 
 are required to complete the reduction. A sample should be almost entirely soluble 
 in dilute hydrochloric acid. The mixture is now made alkaline with milk of lime 
 made from 50 parts of lime, or with soda. The separation of the «-naphthylamine from 
 the sludge of iron oxide, iron, etc., in an economical manner, has always been a 
 difficult problem to which no absolutely satisfactory solution seems to have been 
 found. Distillation of the base in superheated steam is apparently the best method, 
 
 but the high temperature required causes further side reactions, particularly reduction 
 
 ~~ F. Were 
 
 a 
 ; 
 ; 
 y 
 i 
 4 
 ; 
 
SHAILVATYAC YAHL CNV SANDIVHLHAVNOULIN—ILA LYVHO 
 
 H®OS H®OS H*OS 
 S*OH 
 S*OH 
 HO SHN PHN 
 
 t 
 Semae3 OD 
 
 Pe 
 
144 INTERMEDIATES FOR DYESTUFFS 
 
 to naphthalene. The contents of the reduction vessel having been transferred to 
 a suitable still and heated to about 200°, superheated steam at 250° is passed through, 
 the mixture being stirred continuously. Each part of steam carries over } to 1 part 
 of naphthylamine. Some iron powder and oxide is also carried over, and the product 
 collects as a black oil or solid, (The residue in the still contams pyrophoric iron.) 
 This is separated from the water and distilled in a vacuum, when the base is obtained 
 as a water-white oil, which crystallises on cooling. The yield of «-naphthylamine is 
 about 110 parts, or an overall yield of about 77 per cent. on the naphthalene used. 
 The chief source of loss is the steam distillation. The commercial product always 
 contains a little naphthalene, as shown by the fact that a small proportion of it is 
 insoluble in dilute hydrochloric acid. The naphthalene present can be estimated 
 by distilling the acid solution with steam and extracting the aqueous distillate with 
 ether. The base itself is estimated by titration with nitrite, checked by coupling the 
 diazo compound with Schaffer salt. 
 
 a-Naphthylamine is used as a first component in a number of important monoazo 
 dyes. It can also serve as a middle component, since it couples readily, in the p- 
 position to the amino group, with diazo compounds, and the resulting aminoazo dyes 
 can be diazotised and coupled with a third component. Dyes of very deep blue or 
 black shades are produced in this way, as for instance the Coomassie Navy Blues and 
 Victoria Black. 
 
 A few basic dyes of the azine and oxazine series are made from a-naphthylamine by 
 condensing it with p-nitrosoalkylanilines or with nitroso derivatives of the dialkyl-m- 
 aminophenols. 
 
 Secondary Bases from «-Naphthylamine. 
 
 These are made partly for use as end components in azo dyes, but more especially 
 for the preparation of naphthalene analogues of the triphenylmethane colours. Like 
 the alkylanilmes, they condense with Michler’s ketone or hydrol in the para position 
 to the amino group, yielding blue basic dyes, such as Victoria Blues B and R. 
 
 Ethyl-«-naphthylamine— NHC,H, 
 LONE 
 
 he 
 
 —a colourless oil which quickly turns blue in air. B.p. 77, 325° to 330°, b.p. o, 191°. 
 This substance is made by ethylating a-naphthylamine with ethyl alcohol and 
 
 hydrochloric acid, as in the preparation of ethylaniline (p. 46), or with ethyl chloride. 
 Phenyl-«-naphthylamine— NH.C,H, 
 
 Ore 
 
 S. 
 
 —crystallises in prisms, m.p. 62°, b.p. o52 325°, b.p. 15 226°. It is soluble in alcohol, 
 ether, and benzene, the solutions showing blue fluorescence. It is a comparatively 
 weak base, and is insoluble in dilute acids. 
 
NITRONAPHTHALENES AND DERIVATIVES = 145 
 
 For its preparation, «-naphthylamine and aniline are heated together, and Knoeve- 
 nagel’s method of accelerating the reaction with iodine (J. pr. Chem. [2], 89, 20) gives 
 the best results. The method is described in G.P. 241853 (Knoll and Co.). Equi- 
 molecular quantities of «-naphthylamine and aniline are heated with about 1 per cent. 
 of iodine (calculated on the aniline) for six hours at 230°, and then for two hours at 
 250°. The product is washed with dilute hydrochloric acid, then with water, dried 
 and distilled ina vacuum. The yield is given as 85 per cent. 
 
 -Tolyl-«-naphthylamine— 
 p-Tolyl-«x-naphthylamine hea 
 
 cule 
 
 —crystallises in prisms, m.p. 78°, b.p.,, 236°. It is soluble in ether and alcohol, and 
 is best crystallised from alcohol. The solutions show blue fluorescence. 
 
 It is prepared, by a method similar to that used for phenyl-«-naphthylamine, by 
 heating a-naphthylamine with p-toluidine and iodine. A somewhat higher tem- 
 perature, 260° to 270°, is used and the condensation is not quite so complete, the yield 
 obtained being about 70 per cent. 
 
 «-Naphthol— OH 
 
 (L) 
 
 we ) 
 —crystallises in lustrous needles, m.p. 94°, b.p. 278° to 280°, D* 1-224. It is only 
 slightly soluble in water, but dissolves in alcohol, ether, and benzene, and also in 
 solutions of caustic alkalies. It is volatile in steam. 
 
 a-Naphthol is prepared by hydrolysis of salts of x-naphthylamine at high tempera- 
 tures, as described in G.P. 74879 (Meister Lucius and Briining). The sulphate is 
 usually employed: 
 
 (C,,H,-NH,),H,SO, + 2H,0 > 2C,H,.OH + (NH,).S0, 
 
 Fierz-David (“ Farbenchemie,”’ 1920, p. 127) gives the process in detail. 143 gms. 
 of w-naphthylamine is melted in 1 litre of hot water in a lead-lined or enamelled 
 autoclave provided with a stirrer. 110 gms. of concentrated sulphuric acid is added in 
 a thin stream, with stirring. The mixture is then heated at 200° for eight hours, the 
 pressure developed being 14 atmospheres. After cooling, the naphthol is separated 
 from the aqueous solution of ammonium sulphate, and purified by melting up with a 
 little water. After solidifying again, it is separated from the water and dried. A very 
 pure product is obtained, the yield being 94 to 95 per cent. 
 
 a-Naphthol may also be prepared, and more cheaply, from naphthalene-«-sulphonic 
 acid (p. 152), but the product obtained in this way always contains 6-naphthol, and if 
 a pure «-naphthol is required the above process is preferable. 
 
 A nitro dye, Martius Yellow, is made by nitrating «naphthol. Again, by sul- 
 phonating «naphthol to its 2:4:7-trisulphonic acid and nitrating this, which 
 
 10 
 
146 INTERMEDIATES FOR DYESTUFFS 
 
 displaces the sulpho groups in the 2- and 4-positions by nitro groups, Naphthol Yellow 
 S is obtained. 
 
 a-Naphthol is also used as second component in a number of monoazo dyes. 
 
 It condenses with p-nitrosodimethylaniline to form an indophenol, a rather 
 unstable vat dye similar to Indigo in shade. 
 
 Naphthionic acid : 
 
 wt 
 
 UW 
 
 SO;H 
 
 The acid crystallises in small lustrous needles with }H,O, and is very sparingly soluble 
 in water. It dissolves in 3,225 parts of water at 20°, and in 438-5 parts at 100°. 
 
 The sodium salt crystallises in large prisms with 4H,O, and is readily soluble in 
 water, as are also the calcium and barium salts. The solutions, when dilute, show 
 blue fluorescence. 
 
 The acid is hydrolysed by steam at 180° to «-naphthylamine. 
 
 While naphthionic acid may be prepared by sulphonating «-naphthylamine in 
 the usual way by heating it with three times its weight of 94 per cent. sulphuric acid at 
 130°, the ordinary method is to bake a«-naphthylamine sulphate at 170° to 180°. 
 The remarks made with regard to this process in connection with sulphaniliec acid 
 apply in this case also. That is, the proportion of sulphuric acid used should be 
 exactly that required to form the sulphate, and iron salts should be excluded. The 
 best results seem to be obtained by the process described by Schultz (“‘ Chemie des 
 Steinkohlenteers,”’ third edition, p. 202). 
 
 50 kg. of «-naphthylamine is melted and at 60° 36-5 kg. of 94 per cent. sulphuric 
 acid stirred in. The mass becomes pasty. It is slowly heated, with continuous 
 stirring, to 170° to 180°, when it becomes fluid and homogeneous. Itis now vigorously 
 stirred and 24 kg. of powdered crystalline oxalic acid added, the effect of which is to 
 “blow up ” the mass and make it porous. It is spread evenly on lead plates and 
 heated in an oven (preferably a vacuum oven) at 170° to 180°, with careful temperature 
 regulation, for eight hours. The product contains, besides naphthionic acid, about 
 3 to 7 per cent. of e-naphthylamine-5-sulphonic acid (Laurent’s acid), and usually also 
 some a-naphthylamine. It is powdered, boiled up with water, and neutralised with 
 milk of lime. The mixture is filtered hot, the residue being well washed out with 
 boiling water, and the naphthionic acid is precipitated from the filtrate by addition of 
 hydrochloric acid. It is filtered off, washed with cold water, and dried. The yield 
 of crude acid is 64 kg. or about 80 per cent. 
 
 It is purified by dissolving in the minimum quantity of hot water and soda, 
 extracting any o-naphthylamime present with solvent naphtha, and allowing the 
 sodium naphthionate to crystallise out. The more soluble sodium salt of Laurent’s 
 acid remains in solution. : 
 
 Naphthionic acid is used as an intermediate for azo dyes. It may function both 
 as a first component and as anend component. In the former case, coupled with the 
 
NITRONAPHTHALENES AND DERIVATIVES 147 
 
 naphthols and their sulphonic acids, it yields the Fast Reds, a series of monoazo dyes 
 
 for wool characterised by good fastness to light. In the latter case, it is coupled with 
 
 diazotised diamines of the benzidine type to produce the Congo Reds and Benzo- 
 
 purpurins, direct cotton colours of bright shades, but very sensitive to acids. 
 a-Naphthol-4-sulphonic acid (N W-acid): 
 
 OH 
 a 
 SO;H 
 The acid crystallises in transparent plates, soluble in water. With ferric chloride its 
 solution gives a blue colouration, changing to red on warming. The sodium salt is 
 also soluble in water, but can be salted out from concentrated solutions. It is soluble 
 in 90 per cent. alcohol. The other salts are easily soluble in water. 
 This acid was originally obtained from naphthionic acid by Neville and Winther 
 (J.C.S., 1880, 37, 632). The naphthionic acid is first diazotised, and the sparingly 
 
 soluble diazo compound as a thin paste with water is run into a boiling 4 per cent. 
 solution of sulphuric acid : 
 OH 
 ON 
 
 NH, N:N 
 af os. ON 
 me = 
 aN 
 S0,H So, S0,H 
 With this strength of sulphuric acid solution, coupling always takes place to some 
 extent between the, as yet, unchanged diazo compound and the naphthol sulphonic 
 acid formed, yielding a red azo dyestuff. This could be prevented by using a stronger 
 acid solution, but in that case another side reaction is favoured—namely, elimination 
 of the sulphonic acid group by hydrolysis. The method is not now used. 
 
 NW-acid has also been made by heating sodium naphthionate with 50 per cent. 
 caustic soda solution in an autoclave at 240° to 260° (G.P. 46307). But poor yields 
 are obtained by this process. The reaction has been investigated by Fierz-David 
 (Helv. Chim. Acta, 1920, 3, 318), who found that, besides NW-acid, a large proportion 
 of a-naphthol and traces of 1 : 4-dihydroxynaphthalene were formed. The maximum 
 yield of NW-acid obtained was 54 per cent. 
 
 The best method of converting naphthionic acid to NW-acid is that discovered by 
 Lepetit in 1896 and patented later by Bayer and Co. in G.P. 109102. The naphthionic 
 acid is acted on by sodium bisulphite, which quantitatively replaces the amino group 
 by hydroxyl. This reaction was independently discovered by Bucherer, who extended 
 its application to similar compounds and also to the reverse process of the amidation 
 of hydroxyl compounds. It is generally known as the Bucherer reaction, and has 
 proved exceedingly useful in the preparation of many amines and phenols of the naph- 
 thalene and benzene series (see p. 139 for further details of this reaction). 
 
 The preparation is carried out as follows : 32 kg. of sodium naphthionate is heated 
 
148 INTERMEDIATES FOR DYESTUFFS 
 
 under reflux with 20 litres of water and 75 kg. of sodium bisulphite (40° Bé—+.e., 40 
 per cent.) for twenty-four hours. The liquid is then acidified with hydrochloric acid. 
 This precipitates any unchanged naphthionic acid, which is filtered off. The excess 
 of bisulphite is also decomposed, sulphur dioxide being evolved. The intermediate 
 sulphite derivative of the naphtholsulphonic acid is only slowly hydrolysed by acid, 
 but is quickly attacked by alkali. The liquid is now made alkaline with caustic soda 
 and boiled for a short time to hydrolyse the sulphite derivative and to expel ammonia. 
 On making acid again, the naphtholsulphonic acid is set free and the sulphite formed 
 in the hydrolysis is decomposed, more sulphur dioxide being evolved. The solution 
 of NW-acid so obtained may be used direct for the preparation of dyestuffs, or the 
 sodium salt may be salted out in the usual way. 
 
 NW-acid is used as an end component for azo dyes. Coupling with diazo com- 
 pounds takes place (in alkaline solution) in the ortho position to the hydroxyl! group. 
 It is used particularly in conjunction with diazotised aminoazobenzene and amino- 
 azotoluene to produce the Cloth Reds, and with diazotised diamines of the benzidine 
 series for direct cotton colours of blue shades. 
 
 1: 5- and 1 : 8-Dinitronaphthalenes : 
 
 NO, O.N NO, 
 PP We AES Pa ef 
 ky eS 
 
 O.N 
 
 1 : 5-Dinitronaphthalene crystallises in yellow needles from glacial acetic acid, 
 m.p. 216°. Insoluble in water, scarcely soluble in concentrated sulphuric acid and 
 cold nitric acid, as also in most organic solvents. In benzene it is sparingly soluble 
 in the cold, but easily soluble when hot. In the ordinary technical pyridine 1 part 
 dissolves in 125 parts cold, and in 10 parts hot. 
 
 1 : 8-Dinitronaphthalene crystallises in yellow rhombic tables, m.p. 172°. It is 
 in general more soluble than the 1:5-compound. Concentrated sulphuric acid 
 dissolves it. 1 part is soluble in 10 parts of cold pyridine bases and in 1-5 parts of 
 hot pyridine. 
 
 A mixture of these two dinitronaphthalenes is formed, when naphthalene or a-nitro- 
 naphthalene is nitrated with the necessary quantity of nitric acid as mixed acid. It 
 has been found best to proceed from «-nitronaphthalene. The nitration is described 
 by Friedlander (Ber., 1899, 32, 3531) as follows: 
 
 a-Nitronaphthalene is dissolved in four to five times its weight of concentrated 
 sulphuric acid and nitrated at 0° with the calculated quantity of nitric acid as a mixture 
 of 1 part of nitric acid (D 1-4) with 2 parts of sulphuric acid. A red solution is at 
 first formed, but, owing to separation of the nitro compounds, this soon becomes white 
 and thick. When the nitration is finished, the mixed dinitro compounds are isolated 
 as usual by dilution with water, filtration, and washing. The mixture is used in the 
 preparation of Naphthazarin and a few sulphur colours. 
 
 For certain dyes, however, the individual dinitro compounds are required, and 
 several different methods have been used for their separation, methods which depend 
 
NITRONAPHTHALENES AND DERIVATIVES 149 
 
 on their difference in solubility. For example, the dry mixture is boiled with acetone, 
 which dissolves out the 1 : 8-compound, and the extractions are continued until the 
 melting-point of the residue rises to 212°. Another and quicker method is to dissolve 
 the whole mixture in six times its weight of boiling pyridine bases. On cooling, the 
 1: 5-compound mostly crystallises out, and by concentrating the mother liquor to 
 a third of its volume most of the remainder is obtained. 
 
 The nitration may also be so carried out, by using more sulphuric acid than given 
 above, as to give a good separation of the two substances (G.P. 117368). 100 parts 
 of «-nitronaphthalene is dissolved in 600 parts of concentrated sulphuric acid and 
 nitrated as before with a mixture of 51 parts of nitric acid (D 1-4) and 260 parts of 
 sulphuric acid. When the nitration is finished, the reaction mixture is heated to 
 80° to 90° until the dinitro compounds have gone into solution. On cooling, almost 
 all the 1: 5-compound separates, while the 1: 8- remains in solution and may be 
 isolated, after filtration, in the usual way. 
 
 Another method of separation depends on a remarkable reaction undergone by 
 1 : 8-dinitronaphthalene when heated with neutral sulphite, the 1 : 5-compound being 
 unattacked (G.P. 215338, 221383, Meister Lucius and Briining). When boiled with 
 excess of sodium bisulphite, both dinitronaphthalenes yield sulphonic acid derivatives 
 of the corresponding diamines. But if heated at 80° to 90° with neutral sulphite, the 
 1 : 8-compound is attacked and free alkaliis developed. This, if allowed to accumu- 
 late, would decompose the dinitronaphthalenes, forming deeply coloured soluble 
 compounds. But if the alkali is neutralised as formed, or if arrangement is made 
 for its setting free ammonia in the solution, the reaction proceeds smoothly, the 
 1 : 8-compound only being affected, with formation of 1-naphthylsulphamino-4 : 7- 
 disulphonic acid, a substance which is easily hydrolysed to 1-naphthylamine-4 : 7- 
 disulphonic acid (Dahl’s acid ITI, see p. 150) : 
 
 O.N NO, NH.SO,H NH, 
 eae H0,8/ Y ele 
 BA SO,H x S0,H 
 
 200 kg. of a 60 per cent. paste of the mixed dinitronaphthalenes is heated for five 
 to six hours at 80° to 90° with a solution of sodium ammonium sulphite made from 
 740 kg. of 40 per cent. bisulphite and 140 kg. of 25 per cent.ammonia, The unchanged 
 1 ; 5-compound is filtered off. On cooling the 1-naphthylsulphamino-4 : 7-disulphonic 
 acid crystallises out as needles. It is hydrolysed by stirring with concentrated 
 hydrochloric acid for several hours, and the 1-naphthylamine-4 : 7-disulphonic acid 
 purified by recrystallising from hot water. 
 
 1-Naphthylamine-4 : 6- and 4 : 7-disulphonic acids (Dahl’s acids, II and III): 
 
 (II) NH, (IIT) NH, 
 
150 INTERMEDIATES FOR DYESTUFFS 
 
 1-Naphthylamine-4 : 6-disulphonic acid crystallises in needles from hot water, in 
 which it is very soluble, though much less so in cold water. Solutions of the acid and 
 its salts show blue fluorescence. The salts are soluble in water. The calcium salt 
 crystallises in needles with 5H,O and is soluble in 85 per cent. alcohol, but insoluble 
 in 96 per cent. alcohol. 
 
 1-Naphthylamine-4 : 7-disulphonic acid crystallises in needles from water, in which 
 it is only sparingly soluble. 100 parts of water at 20° dissolve 0-7 part of the acid, 
 and at 100° 5 parts. The sodium and potassium salts are readily soluble in water, the 
 acid sodium salt much less soluble, and the barium and calcium salts sparingly soluble. 
 The calcium salt is insoluble in 85 per cent. alcohol. Solutions of the acid and its 
 salts show blue fluorescence. 
 
 A mixture of the two acids, in the proportion of 30 per cent. of II to 70 per cent. 
 of III, is formed when naphthionic acid is sulphonated at 30° with three and a half 
 times its weight of 25 per cent. oleum (G.P. 41957, Dahl and Co.). About three days 
 are required to complete the sulphonation. The acids are then converted into calcium 
 salts in the usual way and evaporated to dryness. The finely powdered mixture is 
 extracted with ten times its weight of 85 per cent. alcohol, which dissolves out the 
 4:6-salt. The separated calcium salts are then converted into sodium salts. 
 
 1-Naphthylamine-4 : 7-disulphonic acid may also be obtained alone from 1 : 8- 
 dinitronaphthalene (p. 149). 
 
 The two acids are used, generally in mixture, as first components in a few black 
 disazo dyes, in which they are coupled with «-naphthylamine as middle component. 
 They are also used in one dye, Apollo Red, or Archil Substitute, as end components. 
 
CHAPTER X 
 
 NAPHTHALENEMONOSULPHONIC ACIDS AND 
 THEIR DERIVATIVES 
 
 THE monosulphonation of naphthalene has been studied by Merz and Weith 
 (Ber., 1870, 8, 195), Kuwes (Rec. trav. chim., 1909, 28, 298), and by Fierz-David and 
 Weissenbach (Helv. Chim. Acta, 1920, 3, 312). Their results show that in general a 
 mixture of the «- and 6-sulphonic acids is formed, in which the proportions of the two 
 acids vary with the temperature of sulphonation, the proportion of «-acid being high 
 at temperatures under 80° and decreasing with rise of temperature to a minimum of 
 15 per cent. at 160°. Euwes has also shown that either acid can be transformed into 
 the other by heating in sulphuric acid, so that at a definite temperature a mixture in 
 definite proportions of the two acids is obtained. Some idea of the composition of 
 such equilibrium mixtures may be obtained from the following table given by Euwes 
 from the results of heating naphthalene and 100 per cent. sulphuric acid in equi- 
 molecular ratio at various temperatures for eight hours : 
 
 Percentages in Product of— 
 
 Naphthalene Recovered 
 Temperature. ieee sco pray Seater ema eae: Ree NOT 
 
 4 i a) a-Acid. p-Acid. ‘i 
 
 80° 27-0 96-4 3-6 and 
 100° 20-0 83-2 16-8 — 
 129° 10-0 44-4 55-6 1-0 
 138-5° 8-6 28-4 71-6 — 
 150° 6-4 18:3 81-7 3-2 
 
 At temperatures under 40°, even with a large excess of sulphuric acid, some naph- 
 thalene escapes sulphonation. 
 
 It is stated in G.P. 50411 (Chemische Fabrik Griinau, Landshoff, and Meyer) 
 that naphthalene, sulphonated with 93 per cent. sulphuric acid at 40°, gives the a-acid 
 as the sole product. This has been disproved by Fierz-David and Weissenbach, who 
 showed that under all conditions a mixture of «- and f-acids is obtained. Even when 
 sulphonation is carried out below 0°, about 2 per cent. of the sulphonation product is 
 B-acid. | 
 
 Naphthalene-«-sulphonic acid : S0.H 
 
 3 
 
 an 
 The acid crystallises with 2H,0, m.p. 90°. It is soluble in water and alcohol, but is 
 sparingly soluble in slightly diluted sulphuric acid. It is rather easily hydrolysed on 
 heating with dilute sulphuric acid at 160°. 
 The sodium salt crystallises with 1H,0. 
 
 The potassium salt (-+-4H,0) dissolves in 13 parts of water at 11°. 
 151 
 
152 INTERMEDIATES FOR DYESTUFFS 
 
 The calcium salt (--2H,O) dissolves in 16-5 parts of water at 11°, and dissolves 
 calcium sulphate easily. 
 
 The barium salt (+H,O) dissolves in 87 parts of water at 11°. 
 
 The aniline salt crystallises in white leaflets, m.p. 183°. 
 
 The chloride melts at 68°. 
 
 The preparation of the pure acid is described by Fierz-David and Weissenbach 
 (loc. cit.), but the conditions used are not such as would normally be employed. 
 
 If the sodium salt is to be isolated for subsequent fusion to «-naphthol or for other 
 purposes, the following method is suitable (Ullmann, “‘ Enzyklopadie,”’ vol. 8, p. 319): 
 
 150 to 200 parts of 93 per cent. sulphuric acid is warmed to 40° and 100 parts of 
 finely powdered naphthalene stirred in. Stirring is continued until the naphthalene 
 has completely dissolved. The sulphonic acid separates in liquid form, and either 
 care must be taken that no solid sulphonic acid from a previous operation is present 
 (in which case the mass would suddenly go solid and stirring would be impossible), 
 or the mixture is impregnated with a little solid sulphonic acid at the start, when 
 crystallisation takes place gradually and a stirrable crystalline product is obtained. 
 The mixture is now diluted with water, unchanged naphthalene filtered off, converted 
 by milk of lime into the calcium salt, and this into the sodium salt in the usual way, 
 the solution of the sodium salt being evaporated to dryness. 
 
 The chief use to which the «-sulphonic acid is put is its nitration to a mixture of 
 the 1: 8- and 1 : 5-nitronaphthalenesulphonic acids, and for this purpose the acid 
 need not be isolated. Moreover, a sufficiently large excess of stronger sulphuric acid 
 is used to obtain complete sulphonation, and to assist in the subsequent nitration. In 
 this case, then, the sulphonation is carried out as follows (Fierz-David, ‘‘ Farben- 
 chemie,”’ 1920, p. 36): 
 
 128 gms. of finely powdered naphthalene is rapidly stirred into 260 gms. of mono- 
 hydrate at 0°. As soon as the naphthalene is all added, the mixture is impregnated 
 as before with a little solid «-sulphonic acid in order to prevent sudden solidification 
 to a hard mass. Sulphonation begins at once with evolution of heat, and the 
 temperature rises to about 35°. If the naphthalene is not completely sulphonated at 
 this temperature, the mixture is heated further, to 60° at the highest, until all the 
 naphthalene is sulphonated. The mixture so obtained is then nitrated, as described 
 later (p. 154). 
 
 a-Naphthol is obtained by fusion of naphthalene-«-sulphonic acid with caustic 
 soda at 270° to 320°, the method used being the same as that described under f- 
 naphthol. : 
 
 The a«-naphthol obtained from the sulphonate, however, always contains some 
 B-naphthol, and the method of preparation from «-naphthylamine (p. 145) is generally 
 preferred, 
 
 1-Naphthylamine-8-sulphonic acid (Peri-acid)— 
 
 HO,S NH, 
 
 Be 
 
 eae ae 
 
‘SHAILVAIMAC YIAHL ANV Sdl0V OINOHdTNSONOWANATVHLHdIVN—IIA LYVHO 
 
 H*Os 
 “HN OH 
 Peet H®*os H®OS 
 ma late 
 HN-S2%0 “e HO OH 
 
 08 OS Oe 
 
 ZHN S®OH = (IFIOLYOyUGHN. SoH SUN 
 
154 INTERMEDIATES FOR DYESTUFFS 
 
 —and 1-Naphthylamine-5-sulphonic acid (Laurent’s acid) : 
 
 Peri-acid crystallises in needles with 1H,0, very sparingly soluble in water. 
 1 part of the acid dissolves in 4,000 parts of water at 21° and in 238 parts at 100°. 
 
 The sodium and potassium salts are sparingly soluble in water. 100 parts of water 
 at 24° dissolve 1-13 parts, and at 100° 2-67 parts of the sodium salt. 
 
 Laurent’s acid forms microscopic needles with 1H,O. 1 part of the acid dissolves 
 in 950 parts of water at 15°, but in hot water the acid is moderately soluble. 
 
 The salts are soluble in water. Their solutions show a greenish fluorescence. 
 Addition of bromine water produces an intense violet colouration, changing quickly 
 to red-violet, and finally disappearing. 
 
 These two acids are obtained together by reducing the mixture of the correspond- 
 ing nitrosulphonic acids which is formed when naphthalene-«-sulphonic acid is nitrated. 
 
 128 gms. of naphthalene is sulphonated, as described on p. 152. When sulphona- 
 tion is finished, the mixture is cooled to 10° to 15° and 103 gms. of 60 per cent. nitric 
 acid slowly added over two and a half hours, the temperature beng maintained at 
 10° to 15°. The thick crystallime mass of sulphonic acid dissolves up as the nitro- 
 sulphonic acids form. The solution is then stirred for a further twelve hours to 
 complete nitration, and poured into 2 litres of water. A solution is thus obtained 
 containing 1 : 8- and | : 5-nitronaphthalenesulphonic acids in the ratio 2: 1, together 
 with less than 5 per cent. of the nitrosulphonic acids (1 : 6- and 1: 7-) formed from 
 the B-naphthalenesulphonic acid present in the sulphonation mixture. 
 
 The nitro-acids are now reduced by adding the solution with vigorous stirring to 
 260 gms. of iron turnings, the addition being made at such a rate that the solution in 
 the reduction vessel remains neutral to Congo paper. Much heat is developed, and 
 the temperature rises to about 80°. The solution becomes violet in colour owing to 
 formation of intermediate hydroxylamine compounds. After the solution of nitro- 
 acids has all been added, the mixture is heated to boiling until the violet colour changes 
 to greenish, which indicates completed reduction. The 1:5- and 1 : 8-aminoacids 
 may now conveniently be separated as their sparingly soluble ferrous salts. For this 
 purpose 40 gms. of iron powder is added cautiously to the still boiling solution, when 
 the ferrous salts separate as grey-white crystals. After cooling, sulphuric acid is 
 added till the mixture is definitely mineral acid, which decomposes the ferrous salts, 
 precipitating the free amino-acids. These are filtered off, well washed to remove 
 ferrous sulphate, and then dissolved in sufficient water, together with 40 gms. of 
 magnesite. The solution is filtered and, on adding salt till a 10 per cent. salt solution 
 is formed, the 1 : 8-salt separates, and after some time is filtered off. On acidifying 
 the filtrate the 1 : 5-acid is precipitated. 
 
 The yield is about 100 gms. of 100 per cent. 1 : 8-acid and 40 gms. of 100 per cent. 
 1:5-acid. The acids are estimated by titration with standard nitrite solution. 
 
NAPHTHALENEMONOSULPHONIC ACIDS 155 
 
 The above method of reduction of the nitro-acids is not generally applicable to 
 the nitronaphthalenesulphonic acids, as often the reduction under these conditions 
 will not proceed beyond the hydroxylamine stage. This is the case with the 1: 6- 
 and ] : 7-nitro-acids present as impurities in the above case, and the method, therefore, 
 serves very well for removal of the reduction products of these acids from the final 
 product, since the hydroxylamino-acids are soluble and are, therefore, washed away 
 with the ferrous sulphate. 
 
 Another reduction process, which is generally applicable, is carried out by first 
 neutralising the diluted solution of nitrosulphonic acids with chalk (or partly with 
 magnesite, so as to form the magnesium salts), filtering off calcium sulphate, making 
 the filtrate faintly acid again, and running the solution into a boiling mixture of water 
 and iron borings previously etched by a little acetic acid. The process is more fully 
 described on p. 163. The 1 : 6-and 1 : 7-nitro-acids in this case are completely reduced 
 to the amino-acids (Cleve’s acids), which then appear as impurities, especially in the 
 Laurent’s acid. 
 
 Peri-acid is worthless as a dyestuff intermediate, either when used as a first or as 
 an end component in azo dyes. Buta number of useful derivatives are obtained from 
 it, and these will be described later. 
 
 Laurent’s acid, on the other hand, is employed, both as first and as end component, 
 in several commercial dyestuffs. When used as end component, coupling takes place 
 in the ortho position to the amino group. 
 
 1-Phenylnaphthylamine-8-sulphonic acid (Phenylperi-acid) : 
 
 HO,S NH.C.H, 
 WU 
 The acid crystallises in leaflets, sparingly soluble in water. The sodium salt is easily 
 soluble. 
 
 Several patents (G.P. 70349, 118655, 170630) describe the preparation of this 
 substance by heating Peri-acid with aniline in an autoclave at 140° to 170° under 
 various conditions. But the use of an autoclave is unnecessary. 
 
 Peri-acid is heated and stirred with three times its weight of aniline. Any water 
 present is first distilled off under reduced pressure. Heating is then continued 
 under ordinary pressure at 160° to 170° for twenty-four hours. The excess of 
 aniline is then distilled off and the aniline salt of Phenylperi-acid, which 
 remains, is converted into the sodium salt by addition of the necessary quantity of 
 caustic soda solution. The aniline set free is distilled off in steam, and the residual 
 solution of the sodium salt of Phenylperi-acid used directly for the preparation of 
 dyestuffs. 7 
 
 p-Tolylperi-acid is prepared similarly, using p-toluidine in place of aniline. 
 
 Phenyl- and tolylperi-acids are used particularly for the preparation of navy blue 
 and black disazo dyes in which they play the part of end components, «-naphthyl- 
 amine being the middle component in most cases. 
 
156 INTERMEDIATES FOR DYESTUFFS 
 
 Naphthasultone— 0,S—-O 
 PAW AL 
 
 a 
 
 —crystallises from alcohol in prisms, m.p. 154°, almost insoluble mm water. 
 
 This substance is formed in almost quantitative yield when Peri-acid is diazotised 
 in the usual way with nitrite and dilute sulphuric acid and the suspension of the 
 sparingly soluble diazo compound in the dilute acid is boiled. 
 
 It is an anhydride of «-naphthol-8-sulphonic acid, and may be converted into this 
 acid by heating with alcoholic ammonia at 130°, adding lead acetate, and decomposing 
 the lead salt with hydrogen sulphide. This, however, is not usually carried out. 
 Instead it is sulphonated and converted into 1-naphthol-4 : 8-disulphonic acid : 
 
 HO,S OH 
 ue 
 SO,H 
 
 The sulphonation is carried out simply by heating the sultone with two to three times 
 
 its weight of sulphuric acid at 80° to 90° until the product is soluble in water (G.P. 
 
 40571, Schéllkopf Aniline and Chemical Co.). This intermediate is used for azo dyes. 
 «-Naphthylamine-4 : 8-disulphonic acid : 
 
 HO,S NH, 
 [ Say 
 ye 
 SO,H 
 
 Not much information is available regarding this acid. The monosodium salt crystal- 
 lises in scales, sparingly soluble in cold water. The disodium salt is easily soluble. 
 
 This acid is prepared by sulphonating Peri-acid with three times its weight of 
 10 per cent. oleum, the two being mixed in the cold, and the sulphonation finished at 
 100° (G.P. 40571, Schollkopf). The neutral sodium salt is obtained in the ordinary 
 way by neutralising the diluted melt with lime and addition of soda to the filtered 
 solution of the calcium salt. 
 
 o-Naphthylamine- 4: 8-disulphonic acid is not used as a dyestuff intermediate 
 itself, but gives rise to several important intermediates. 
 
 1 : 8-Aminonaphthol-4-sulphonic acid (S-acid) : 
 
 HO NH, 
 Fe wais. © 
 SO,H 
 
 The acid crystallises in needles, almost insoluble in water. The alkali salts are easily 
 soluble, and their solutions show bluish-green fluorescence. 
 
NAPHTHALENEMONOSULPHONIC ACIDS 157 
 
 S-acid is prepared by fusion of 1-naphthylamine-4: 8-disulphonic acid with 
 caustic soda (or, according to Fierz-David, preferably with caustic potash) at 200° in 
 open pans (G.P. 63074, Badische; G.P. 75317, Bayer). 
 
 According to the later patent the sodium salt of the naphthylaminedisulphonic 
 acid is heated with 4 to 5 parts of caustic potash and 1 part of water at 200° until the 
 melt becomes mobile and a sample dissolved in water shows the characteristic fluores- 
 cence. The melt is then dissolved in twice its weight of water and made just acid with 
 hydrochloric acid, when the S-acid separates. 
 
 The use of S-acid as an intermediate for azo dyes is dealt with in connection with 
 other 1 : 8-aminonaphthol-sulphonic acids on p. 172. 
 
 1 : 8-Dihydroxynaphthalene-4-sulphonic acid (Dioxy-S-acid) : 
 
 HO OH 
 Ne saan 
 
 SO,H 
 The acid and its salts are soluble in water. 
 
 This acid is obtained if the fusion of 1-naphthylamine-4 : 8-disulphonic acid is 
 carried out at a higher temperature (250°) than that used for S-acid (G.P. 71836, 
 Bayer), or it may be obtained from S-acid by fusion with caustic soda at 220° to 250° 
 (G.P. 80315, Bayer). 
 
 But these acids are so readily oxidised in alkaline solution at high temperatures, 
 that the following preparation at a much lower temperature, an application, of the 
 Bucherer reaction, is probably preferable (G.P. 109102, Bayer). 
 
 23-9 kg. of S-acid are stirred with 60 litres of water in an enamelled pan and exactly 
 neutralised with caustic soda. 128 kg. of bisulphite solution (40° Bé—+.e., 38 to 40 
 per cent.) are added and the solution heated at 90° until a sample on acidifying gives 
 only a slight precipitate of unchanged S-acid. The solution is then acidified, 
 unchanged S-acid filtered off, made alkaline with caustic soda, and boiled till all the 
 ammonia is expelled. It is then acidified with hydrochloric acid and again boiled to 
 expel sulphur dioxide. The neutralised solution can then be used direct, or the 
 substance may be salted out. 
 
 Dioxy-S-acid is used as an end component in azo dyes, and in consequence of its 
 hydroxyl groups imparts to them the property of forming chromium lakes by after- 
 chroming, with consequent increase of intensity and fastness. 
 
 1: 8-Naphthasultam-2 : 4-disulphonic acid : 
 
 0,S——NH 
 /\/\ 80.8 
 
 U y 
 S0,H 
 
 This acid forms a disodium salt which crystallises in fine needles with 2H,0, soluble 
 in water without fluorescence. A trisodium salt is also formed, which crystallises in 
 yellow leaflets soluble in water with green fluorescence, similar to that of fluorescein. 
 
158 INTERMEDIATES FOR DYESTUFFS 
 
 The l-naphthylamine-2 : 4: 8-trisulphonic acid, of which this substance is the 
 anhydride, is unknown. 
 
 The sultam-disulphonic acid is prepared by adding 300 parts of the acid sodium 
 salt of 1-naphthylamine-4 : 8-disulphonic acid gradually to 600 parts of 40 per cent. 
 oleum. The solution is then warmed to 80° to 90°, at which it soon sets to a solid 
 white mass. Heating is continued until a sample, diluted with water, no longer 
 diazotises or couples with diazotised aniline (after reducing the acidity of the test 
 solution with sodium acetate). The mixture is then diluted with ice-water and the 
 acid converted through the calcium salt into the sodium salt in the usual way, the 
 solution of sodium salt being evaporated to dryness, in preparation for the fusion with 
 alkali, by which it is converted into the aminonaphtholsulphonic acid (see later). 
 
 The sodium salt may be prepared in pure crystalline form by adding alcohol 
 to a hot concentrated solution of it and cooling, when the salt separates almost 
 completely in lustrous large yellow leaflets. 
 
 Naphthasultamdisulphonic acid is not used as a dyestuff intermediate, but is 
 fused with alkali to produce 1 : 8-aminonaphthol-2 : 4-disulphonic acid (2S-acid): 
 
 The acid is readily soluble in water. The acid sodium salt crystallises in fine needles, 
 easily soluble in water, but precipitated from solution by addition of hydrochloric acid. 
 Dilute solutions of the alkali salts show a beautiful green fluorescence. 2S-acid gives 
 a reddish-yellow soluble diazo compound which can be salted out of solution. 
 
 The preparation, as also that of the previously described naphthasultamdisulphonic 
 acid, is given in G.P. 80668 (Bayer; cf. also Dressel and Kothe, Ber., 1894, 27, 2139). 
 
 1 part of the sodium salt of the naphthasultamdisulphonic acid is fused with 24 
 parts of caustic potash or soda, to which 0-2 part of water has been added, in an open 
 panat170°. (Thereaction may also be carried out, using more water, in an autoclave.) 
 As soonasa sample of the melt, dissolved in water and coupled with a diazo compound, 
 shows no increase in dye formation, the whole melt is dissolved in water and the 
 solution acidified with hydrochloric acid. The acid sodium salt of 2S-acid separates 
 in colourless needles. It may be purified by recrystallisation from water. 
 
 The use of 2S-acid as an intermediate for azo dyes is considered later (p. 172) in 
 connection with other 1 : 8-aminonaphtholsulphonic acids. 
 
 1-Amino-5-naphthol— 
 
 NH, 
 SON 
 
 Bhs 
 
 Bail 
 HO 
 
 —may be prepared from 1-naphthylamine-5-sulphonic acid (Laurent’s acid) by 
 heating the Laurent’s acid with 5 molecular proportions of caustic soda as 30 per 
 
NAPHTHALENEMONOSULPHONIC ACIDS 159 
 
 cent. solution in an autoclave (rotary or stirred) at 250° for three hours. As by- 
 products 1: 5-dihydroxynaphthalene and a-naphthylamine are also formed. The 
 melt is worked up by filtering off the sodium salt of any unchanged Laurent’s acid 
 (this being insoluble in the caustic soda solution). The naphthylamine is then extracted 
 with ether. On saturating the alkaline solution with carbon dioxide, the amino- 
 naphthol is precipitated in 52 per cent. yield (Fierz-David, Helv. Chim. Acta, 1920, 
 3, 318). 
 
 1 : 5-Dihydroxynaphthalene : OH 
 
 Inyaroxynap aiene a6 
 
 a6 
 ea 
 HO 
 
 Laurent’s acid may also be used as a source of this important intermediate (Fierz- 
 David, loc. cit.). The preparation is carried out, as given above, for 1 : 5-amino- 
 naphthol, except that the reaction mixture is heated at 290° for three hours. The 
 higher temperature favours production of the dihydroxy compound at the expense of 
 the aminonaphthol. After removing unchanged Laurent’s acid, o-naphthylamine and 
 aminonaphthol as given above, on making the solution acid with hydrochloric acid, 
 1; 5-dihydroxynaphthalene is precipitated. The yield under these conditions is 
 60 per cent, 
 
 Another method of preparation is given on p. 178. 
 
 Naphthalene-f-sulphonic acid : 
 
 | ( me \\s0,H 
 
 WY 
 
 The anhydrous acid melts at 90-5° to 91°, and is easily soluble in benzene and toluene. 
 It forms a trihydrate, crystallising in leaflets, m.p. 83°, very soluble in water. The 
 trihydrate loses water in the desiccator, giving a monohydrate, m.p. 124°. The 
 chloride melts at 79°, the amide at 212°. 
 
 The sodium salt (anhydrous) dissolves in 17 parts of water at 25°, the calcium salt 
 (also anhydrous) in 76 parts of water at 10°, the barium salt (+H,O) in 290 parts of 
 water at 10°. 
 
 The aniline salt forms white needles, m.p. 269°, soluble in alcohol. 
 
 The sulphonation of naphthalene to the f-acid has been studied by Witt (Ber., 
 1915, 48, 743), who gives much exact information regarding it. His method of pre- 
 paring the substance is convenient and quick, therefore suitable for laboratory 
 purposes. 250 gms. of naphthalene is melted and heated to 160°. 400 gms. of 
 sulphuric acid (93-7 per cent.) is stirred in, the temperature being maintained about 
 160°. This requires about fifteen minutes. Sulphonation is very rapid, and after a 
 further five minutes is complete. After standing for a short time, the solution is 
 poured into 300 c.c. of water. On cooling, nearly all the f-acid crystallises out as 
 trihydrate, being salted out by the a-acid present. (As already mentioned, sulphona- 
 tion of naphthalene at 160° gives a mixture of 85 per cent. of B-acid with 15 per cent. 
 ofa-acid.) The f-acid may be purified (from a little sulphone) by dissolving 600 gms. 
 
160 INTERMEDIATES FOR DYESTUFFS 
 
 of it in 300 c.c. of water at 70°, adding 100 c.c. of concentrated hydrochloric acid, 
 and allowing to cool. It crystallises from this solution as trihydrate. 
 
 It is possible, however, to sulphonate naphthalene completely with a much smaller 
 excess of acid than that used by Witt, and on the large scale, especially where the 
 6-sulphonic acid is to be converted into f-naphthol (its principal use), a weight of 
 sulphuric acid equal to that of the naphthalene is found to suffice, and to give most 
 economical working. 
 
 A detailed description of the manufacture of B-naphthol is given by R. N. Shreve 
 (Colour Trade Journal, 1924, 14, 43), of which the following are the essential features: 
 
 (a2) Naphthalene f-sulphonic Acid.— Naphthalene (3,350 lbs.) is heated till melted, 
 and at 90° to 100° C. sulphuric acid (3,350 lbs. of 93 per cent.) is run in while stirring. 
 The temperature is allowed to rise to 160°, and is kept there until all the acid has been 
 added. Heating is then continued at 160° to 165° for several hours until the sulphona- 
 tion is finished. During this time the water produced by the reaction, together with 
 some naphthalene, distils off and passes through condensers surrounded by water at 
 90°, to prevent blocking by solid naphthalene. 
 
 The next stage of the process consists in the removal of the «-sulphonic acid by 
 taking advantage of its comparative ease of hydrolysis in diluted acid at 160°. Sul- 
 phonation being complete, dry steam is blown into the solution, which is kept at 160°, 
 when the a-sulphonic acid is hydrolysed to naphthalene and sulphuric acid, the 
 naphthalene distilling off through the condensers. About 18 per cent. of the naph- 
 thalene used is recovered in this operation and in the distillate during sulphonation. 
 Dry steam must be used or foaming takes place. About seven hours’ passage of 
 steam is required to reduce the «-sulphonic acid content to 0-15 to 0-20 per cent. 
 
 The sulphonation mixture is now run into 13,400 lbs. of water with vigorous 
 stirring, and a solution of 4,750 lbs. of salt in 9,350 lbs. of water added, which salts 
 out the sodium salt of the f-sulphonic acid fairly completely after stirring for ten 
 hours and allowing to cool to 25° to 30°. 
 
 In this connection some figures are given by W. T. Cooke (J. Soc. Chem. Ind., 1921, 
 40, 56T, 239T), showing the influence of sodium chloride and sodium sulphate on the 
 solubility of sodium f-naphthalenesulphonate. He shows that the solubility of the 
 f-salt is reduced practically to zero when the concentration of NaCl or Na,SO, reaches 
 about 10 gms. in 100 gms. of solution, especially at lower temperatures (about 30°). 
 The concentration of NaCl--Na,SO, obtained, using the above quantities, is about 
 12 to 14 parts per 100 parts of solution. | 
 
 The §-salt is now filtered off and pressed, by which means the water content of the 
 press-cake is reduced to about 30 per cent. This is sufficiently low for the subsequent 
 fusion. 
 
 (6) Fusion to £-Naphthol.—1,975 lbs. of caustic soda (95 per cent.) and 400 lbs. 
 of water are melted together in the fusion pot, and heated, whilst stirring, to 305°. 
 B-salt, in the form of the ground press-cake containing 30 per cent. of water, is then 
 added until the temperature falls to 295°, when the addition is stopped until the tem- 
 perature again rises to 305°, then more sulphonate is added, and so on, until the full 
 charge of 6,540 lbs. of moist B-salt has been added. The melt is then kept at 300° for 
 
NAPHTHALENEMONOSULPHONIC ACIDS 161 
 
 six hours. The finished melt is run into 2,500 gallons of water, using for this purpose 
 the weak B-naphthol washings from a previous operation. The hot solution is filtered 
 at 80° and dilute sulphuric acid added to the filtrate till it is no longer alkaline to 
 phenolphthalein. £-Naphthol separates in part as solid, and the whole is liquefied 
 by heating to 95°, when, on allowing to settle, the B-naphthol forms the upper layer. 
 The sulphite liquor beneath is run off and cooled, when about 10 per cent. of the p- 
 naphthol separates and isremoved. The liquid f-naphthol is washed with boiling hot 
 water until the wash water shows a specific gravity of 1. The naphthol is then dried at 
 115°, and distilled ina vacuum. Under a pressure of 50 mm. it distils at 185° to 190°. 
 
 The yield of sulphonate from naphthalene is 86 per cent., and of pure f-naphthol 
 from sulphonate 74 per cent. The overall yield of pure naphthol from naphthalene 
 is, therefore, about 64 per cent. 
 
 There is a considerable residue in the vacuum still, which forms when cold a black 
 shiny brittle mass known as naphthol pitch and used as insulating material in electric 
 cables. It probably contains £8’-dinaphthol or 6f’-dinaphthylene oxide. 
 
 f-Naphthol— 
 tee 4 \oH 
 
 ag 
 
 RANE 
 
 —crystallises in lustrous scales, m.p. 122°, b.p. 285° to 286°, D4 1-217. It is almost 
 insoluble in cold water, but dissolves in 75 parts of boiling water. It is soluble in 
 most organic solvents, and in solutions of caustic alkalies, but not carbonates. It 
 sublimes easily. It is only slightly volatile in steam at 100°, but may be distilled in 
 superheated steam. 
 
 The commercial product usually shows a very high degree of purity (over 99 per 
 cent.). It is estimated by titration with standard iodine solution (31, used per 
 molecule of naphthol), or with diazotised p-nitraniline, the naphthol being dissolved 
 in the least possible caustic soda and carbonate added as required. 
 
 B-naphthol is used, as a dyestuff intermediate, for azo dyes, chiefly of the monoazo 
 class. Coupling with diazo compounds takes place in the «-position ortho to the 
 hydroxyl group : 
 
 HO 
 
 “S/N OH R.N:NC Cone 
 
 R.N:N.Cl + | | Bical __ 
 Se IS lg 
 
 Its chief use is for the production of Para Red dyeings on the fibre by coupling with 
 
 diazotised p-nitraniline. The monoazo dyestuffs, of which Para Red is a type, in 
 
 which nitro-, chloro-, nitrochloroanilines and similar bases containing negative 
 substituent groups figure as first components, are remarkably insoluble bodies, being 
 
 insoluble in caustic alkalies, notwithstanding the presence of the hydroxyl group. 
 
 They are specially useful, on this account and also because of their brightness of shade, 
 
 as lake pigments. 
 B-Naphthol is also used as an end component in a considerable number of dis- and 
 
 trisazo dyes. 
 11 
 
162 INTERMEDIATES FOR DYESTUFFS 
 
 An oxazine dye, Meldola’s Blue, is made from f-naphthol by condensation with 
 p-nitrosodimethylaniline. 
 1-Naphthylamine-6-and 7-sulphonic acids (Cleve’s acids): 
 
 NH NH, 
 
 CO ale 
 Shea aks 
 
 1-Naphthylamine-6-sulphonic acid crystallises in cubes from hot water, or in 
 leaflets if crystallisation is slow. 1 part dissolves in 1,000 parts of water at 16°. 
 The sodium salt forms two crystalline hydrates with H,O and 41H,0 respectively. 
 It is easily soluble in water, but is readily salted out. The calcium salt is easily, but 
 the barium salt sparingly, soluble in water. The aqueous solutions give with ferric 
 chloride a cornflower blue colouration. 
 
 1-Naphthylamine-7-sulphonic acid crystallises in needles or flat prisms with 1H,0. 
 1 part dissolves in 220 parts of water at 25°. The sodium salt (needles, +3H 0) i is 
 easily soluble in water, but, unlike the 1: 6-acid, is not readily salted out. The 
 calcium salt is easily, but the barium salt sparingly, soluble in water. With ferric 
 chloride a blue colouration is obtained, which changes to red with acetic acid. 
 
 When naphthalene- f-sulphonic acid is nitrated, a mixture of about equal quantities 
 of 1: 6- and 1: 7-nitronaphthalenesulphonic acids is formed, together with a little 
 of the 1: 3-acid. On reduction these yield the two Cleve’s acids. 
 
 The usual practice in such preparations is to start from naphthalene and to carry 
 out the whole preparation—sulphonation, nitration, and reduction—without isolation 
 of the intermediate products, as already described in the case of Peri-acid and Laurent’s 
 acid (p. 154). A process on these lines is described by Fierz-David (“‘ Farbenchemie,” 
 1920, p.30). But although such a method is suitable in the case of Peri- and Laurent’s 
 acids, prepared from the «-sulphonic acid containing only 4 to 5 per cent. of the 
 B-sulphonic acid, in the present case the proportion of isomers seems too great. When 
 naphthalene is sulphonated so as to produce the maximum proportion of f-acid, the 
 product contains at least 15 per cent. of the a-acid, which on nitration and reduction 
 yield the 1: 5- and 1: 8-amimo acids (Peri- and Laurent’s acids), which are similar in 
 properties to the Cleve’s acids and not readily separated fromthem. For the prepara- 
 tion of fairly pure Cleve’s acids, it is advisable, either to isolate the B-sulphonic acid 
 (as sodium salt, see the manufacture of 6-naphthol, p. 160), or, without isolating, to 
 hydrolyse the «-sulphonic acid in the mixture with steam at 160°, and then, after 
 cooling, to add the excess of sulphuric acid required to assist in the nitration. The 
 disadvantage of isolating the f-sulphonate is the large excess of sulphuric acid required 
 to redissolve it. Ina Cassella patent (G.P. 67017) describing the preparation of these 
 acids, the £-sulphonate is dissolved in five times its weight of sulphuric acid at 30° 
 (a higher temperature must not be used, or f-acid is partly transformed to a-acid). 
 On the other hand, if naphthalene has been sulphonated with about an equal weight 
 of 93 per cent. sulphuric acid and the «-acid has been removed by hydrolysis, on 
 cooling to the low temperature necessary for the nitration, the melt sets to a solid 
 
NAPHTHALENEMONOSULPHONIC ACIDS 163 
 
 mass. This difficulty is overcome by adding, at the lowest possible temperature 
 before solidification takes place, such a quantity of 85 per cent. sulphuric acid as will 
 result in a stirrable mixture. The additional quantity of sulphuric acid required for 
 this purpose is about twice that used for the sulphonation. Nitration may be com- 
 menced at about 55°, in order to assist in liquefying the mixture, but is continued at 
 10°to 15°. Nitration at higher temperatures leads to formation of B-nitro derivatives. 
 The calculated quantity of 60 per cent. nitric acid is used. After the nitric acid has 
 been added the mixture is allowed to stand several hours to complete nitration. The 
 solution is then poured into water. 
 
 The reduction of the nitrosulphonic acids cannot be carried out in this case in the 
 strongly acid solution, as shown by Fierz-David and Weissenbach (Helv. Chim. Acta, 
 1920, 8, 305), since in acid solution reduction proceeds only to the hydroxylamine 
 stage. Reduction of a nearly neutral solution of the calcium or, preferably, the 
 magnesium salts with iron borings gives fairly satisfactory results. The process, 
 then, is as follows: 
 
 Sufficient magnesite is added to the solution to form the magnesium salts of the 
 nitrosulphonic acids, and neutralisation is completed with chalk or limestone. Calcium 
 sulphate is filtered off, well washed, and the united filtrates, acidified slightly with 
 dilute sulphuric acid, added gradually to a boiling mixture of water and cast-iron 
 borings previously etched with a little acetic acid. For each 128 parts of naphthalene 
 used, about 300 parts of iron, 500 parts of water, and 20 parts of 40 per cent. acetic acid 
 are required for the reduction. When the reduction mixture has become colourless, it 
 is made faintly alkaline to litmus by addition of magnesite, and filtered. From the 
 filtrate, the sodium salt of the 1 : 7-naphthylaminesulphonic acid can be salted out by 
 adding sufficient salt to give a 6 per cent. solution. After stirring for about a day, 
 the | : 7-salt is filtered off, and the 1 : 6-acid precipitated from the filtrate by acidifying 
 with hydrochloric or sulphuric acid. 
 
 The yields obtained from 128 parts of naphthalene are about 70 parts of the 1 : 7- 
 acid and 80 parts of | : 6-acid, as estimated by titration with standard nitrite solution. 
 
 For most purposes, the two acids are not separated, as they yield dyes of the same 
 shade and dyeing strength. 
 
 The Cleve acids are used, like «-naphthylamine, as middle or end components in 
 various dis- and trisazo dyes, which are navy blue or black inshade. The 6-sulphonic 
 acid is specially used for a few trisazo dyes, of which Benzo Fast Blue FR is typical, 
 this dye being composed as follows : 
 
 > J-acid. 
 
 > Cleve’s acid 
 
 Aniline > Cleve’s acid 
 
CHAPTER XI 
 
 NAPHTHALENEDISULPHONIC ACIDS AND THEIR 
 DERIVATIVES 
 
 THE formation of the four disulphonic acids, 1 : 5-, 1: 6-, 2: 7-, and 2: 6-, from 
 naphthalene has already been discussed (p. 136). It was indicated that low tempera- 
 ture sulphonation yielded a mixture of the 1 : 5- and 1 : 6-acids, while at temperatures 
 above 140° the product was chiefly a mixture of 2: 7- and 2: 6-acids. 
 
 While uses have not been found for the 2 : 6-acid, the other three form the sources 
 of naphthylamine-, naphthol-, and aminonaphtholsulphonic acids. For this purpose 
 the disulphonic acids are treated in three different ways : 
 
 (i.) By further sulphonation to trisulphonic acids, nitration of these, and reduction, 
 they produce naphthylaminetrisulphonic acids, and these may further be fused with 
 alkali to form aminonaphtholsulphonic acids. 
 
 (ii.) By direct nitration and reduction they yield naphthylaminedisulphonic acids, 
 and from these, by replacement of the amino group, naphtholdisulphonic acids. 
 
 (ii.) By alkali fusion of salts of the disulphonic acids naphtholmonosulphonic 
 acids and dihydroxynaphthalenes are obtained. 
 
 Only for the third of these processes—+.e., for the alkali fusion, need the disulphonic 
 acids be isolated. They are generally made by sulphonation of naphthalene, or some- 
 times of the monosulphonic acids, and further sulphonated or nitrated without isolation. 
 
 Naphthalene-1 : 5-disulphonic acid : 
 
 SO,H 
 ie 
 rei 
 HO, 
 
 The acid crystallises in lustrous scales, with 4H,O, very soluble in water. The 
 anhydrous acid melts at 240° to 245° with decomposition. The disodium salt (scales, 
 +2H,0) dissolves in 9 parts of water at 18°. The barium salt is described by 
 Armstrong and Wynne as crystallising with 4H,O and as easily soluble in water, but 
 Fierz-David and Hasler (Helv. Chim. Acta, 1923, 6, 1133) state that it crystallises with 
 1H,0, and is almost insoluble. However, the inconsistency may be only apparent, 
 since Fierz-David formed the barium salt from boiling solutions, in which the tetra- 
 hydrate is probably not the stable form. : 
 
 The 1 : 5-acid can be prepared with no simultaneous formation of isomers, accord- 
 ing to Armstrong and Wynne (Proc. Chem. Soc., 1886, 2, 231), by sulphonating naph- 
 thalene with chlorsulphonic acid. Naphthalene is dissolved in carbon disulphide, and 
 a slight excess over two molecular proportions of chlorsulphonic acid added. When 
 sulphonation is finished, the carbon disulphide is distilled off. A little of the «-mono- 
 sulphonic acid is present in the product. This may be removed by neutralising the 
 solution of the product with lead carbonate, and isolating the lead salts. These are 
 dried, powdered finely, and extracted with hot alcohol, which removes the lead 
 
 164 
 
‘SUAILVAIYUC YAHL ANV SCIOV OINOHdTOSIGUNATVHLHdIVN—XI LAVHO 
 
 GOR: 
 
 HO OH 
 
 { i) { H&os H®o f 
 CaO H®os SoH H®os S*oH 
 : PUN S*OH 
 HN fon SoH t PUN re PHN S®OH Z0N S*®OH 
 : | : | ¢0) me lee 
 H ag: OH HOS S®OH H®os H*0S 
 HO S*OH 
 2 Z 
 
 we 
 
 HOS ON S®OH S*OH 
 ar | hae 
 
 WD 
 
166 INTERMEDIATES FOR DYESTUFFS 
 
 a-sulphonate. The undissolved residue is the disulphonate, from which the acid may 
 be obtained in the usual way. 
 
 When formed by sulphonation of naphthalene with oleum, it is always accom- 
 panied by the 1 : 6-acid, and its separation from this isomer is best accomplished, 
 according to Fierz-David and Hasler (loc. cit.), through the insoluble barium salt. 
 The preparation is described as follows: 
 
 128 gms. of finely powdered naphthalene is added during a quarter of an hour with 
 stirring to 300 gms. of 100 per cent. sulphuric acid. As the mass begins to thicken, 
 300 gms. of 64 per cent. oleum is dropped in, the temperature being allowed to rise to 
 30°. The quantity of free SO, added is 20 per cent. in excess of that required to unite 
 with the water formed by the sulphonation. This excess is found to be required for 
 complete disulphonation. If less is used, it is found that the 6-sulphonic acid present 
 is left unchanged. On the other hand, if much more is used, trisulphonic acids are 
 formed. When all the oleum has been added, the solution is stirred (in a closed vessel) 
 for at least eight hours at 40°. A snow-white milky mass is formed. This is poured 
 into 3 litres of water, and 52:5 gms. of 100 per cent. sodium carbonate added. The 
 solution is heated to boiling, and neutralised with barium carbonate. After filtering 
 hot, it is evaporated down to 14 litres. Hydrochloric acid is then added till the 
 solution is just acid to Congo paper, and to the boiling solution barium chloride 
 solution is added in small portions until no further precipitate forms. As the barium 
 salt of the 1 : 5-acid precipitates at once as a white sandy precipitate, the end point 
 is easily observed. While still warm the precipitate is filtered off and washed with 
 cold water. A yield of 70 to 72 per cent. is obtained—.e., 274 to 282 gms. of barium 
 salt, C,)>H,(SO;).Ba-+-H,O. The mother liquor contains the soluble barium salt of 
 the 1 : 6-acid, together with a little 2 : 7-salt. 
 
 The 1 : 5-acid may be obtained from the salt by stirring it with water and adding 
 the calculated quantity of dilute sulphuric acid. After warming for half an hour on 
 the water-bath, the barium sulphate is filtered off and the filtrate evaporated to 
 crystallising point. 
 
 Various other methods of sulphonation and separation of the 1:5-acid are 
 described vaguely in the patents (G.P. 45776, G.P. Anm. H. 2619 of 1889). 
 
 Naphthalene-1 : 6-disulphonic acid : 
 
 The free acid crystallises with 4H,O, and is soluble in water. The disodium salt 
 crystallises with 7H,O, 1 part of the salt (calculated as anhydrous) dissolving in 
 3 parts of water at 18° to 20°. The barium salt (+34H,0) dissolves in 16 parts of 
 water at 18° to 20°. 
 
 This acid can be obtained free from isomers by sulphonating the B-monosulphonic 
 acid with chlorsulphonic acid (Armstrong and Wynne, Proc. Chem. Soc., 1886, 2, 231). 
 The potassium salt of naphthalene-f-sulphonic acid is mixed with three molecular 
 proportions of chlorsulphonic acid, the excess being used in order to obtain a liquid 
 
NAPHTHALENEDISULPHONIC ACIDS 167 
 
 product. The sulphonation is rapid and is completed by heating on the water-bath 
 for afew minutes. A little sulphochloride is formed. Water is now cautiously added, 
 and the potassium acid sulphate which separates after a time is filtered off, and the 
 filtrate evaporated to dryness. 
 
 Fierz-David and Hasler find that the 1 : 6-acid is best obtained by starting from 
 the f-sulphonic acid or by sulphonating naphthalene first at 165°, then at 40°. 
 
 128 gms. of naphthalene is heated to 165° and, while stirring, 200 gms. of 100 per 
 cent. sulphuric acid dropped in. After stirring for half an hour at 165°, the solution 
 is cooled to 30°. Then, keeping the temperature below 35°, 275 gms. of 66 per cent. 
 oleum is slowly added during an hour. The solution is stirred for nine hours more at 
 40°. The quantity of sulphone formed is at most about 0-5 per cent. The solution 
 is now poured into 2 litres of cold water, heated to boiling, and neutralised with barium 
 carbonate. The insoluble barium salt of the 1 : 5-acid precipitates with the barium 
 sulphate. After filtering and washing the residue well, the barium is precipitated from 
 the filtrate by sodium carbonate (about 106 gms.). The barium carbonate having 
 been filtered off, the solution is concentrated to about 500c.c. On cooling, the sodium 
 salt of the 1 : 6-acid crystallises, and after some hours is filtered off, pressed, and dried. 
 The yield is 140 gms. or about 40 per cent. 
 
 If B-sulphonate is used to start with, yields of 55 to 60 per cent. of the 1: 6-salt 
 can, be obtained. 
 
 Other methods of preparing the 1 : 6-acid are described in G.P. Anm. B. 9514 of 
 1889 and G.P. 45229. 
 
 Naphthalene-2 : 7-disulphonic acid : 
 
 HO,S/ \/“ SO, 
 
 o 
 eal 
 
 The acid crystallises in long deliquescent needles. The disodium salt (+6H,O) and 
 the calcium salt (+6H,0) are easily soluble in water, the barium salt (+-2H,0) less 
 soluble. 
 
 As already mentioned, this acid, together with the 2: 6-acid, is formed when 
 naphthalene or its B-sulphonic acid is disulphonated at high temperatures. Above 
 130°, as shown by Fierz-David, no | : 5-acid is present in the sulphonation product, 
 but along with the 2: 7- and 2: 6-acids there is always a substantial proportion of 
 1: 6-acid. At 160°, when the proportion of 2: 7-acid is probably a maximum, the 
 composition of the mixture is roughly 65 per cent. of 2: 7-acid, 10 per cent. of 1 : 6- 
 acid, and 25 per cent. of 2: 6-acid. The proportion of 2: 6-acid can be fairly well 
 determined owing to its forming an insoluble barium salt, but the proportions of the 
 2: 7- and 1: 6-acids are not definitely ascertained, as a good method of separation is 
 lacking. The 2: 6-acid can also be separated from the other two by means of its 
 sparingly soluble calcium and lead salts. The calcium salt of the 2: 6-acid loses 
 water of crystallisation at 100°, being converted into the almost insoluble anhydrous 
 salt. 
 
 The 2: 7-acid may, therefore, be prepared almost free from 2: 6-acid but still 
 
168 INTERMEDIATES FOR DYESTUFFS 
 
 containing some 1: 6-acid by the method of Ebert and Merz (Ber., 1876, 9, 592). 
 Naphthalene is sulphonated with five times its weight of sulphuric acid at 160° for 
 five hours. The product is poured into water and converted into calcium salts. 
 Ebert and Merz evaporated the solution of calcium salts to dryness and heated at 
 200° to 230° until dehydrated, when on extraction with water, the 2 : 6-salt remained 
 undissolved. But evaporation to dryness is not necessary. The solution of calcium 
 salts from 200 kg. of naphthalene and 1,000 kg. of sulphuric acid, after evaporating 
 to a volume of 3 cubic metres, may be treated with 900 kg. of common salt, and the 
 solution boiled, when the calcium salt of the 2: 6-acid separates and is filtered off. 
 On cooling the filtrate to 15°, most of the 2: 7-salt will have separated, the 1 : 6-salt 
 remaining in solution. The 2: 7-salt is filtered off and converted into sodium salt as 
 usual (G.P. 48053). 
 
 Fierz-David and Hasler (Helv. Chim. Acta, 1923, 6, 1133), studying the proportions 
 of the different disulphonic acids formed at high temperatures, proceeded as follows: 
 
 128 gms. of naphthalene was heated to 165°, and while stirring, 200 gms. of 100 per 
 cent. sulphuric acid dropped in during fifteen minutes. Then, at 160°, 400 gms. 
 more ‘‘ monohydrate ”’ was added, and the solution heated for various periods. The 
 sulphonation having proceeded for the prescribed period, the mixture was then worked 
 up in a manner similar to that described under naphthalene-1 : 5-disulphonic acid. 
 The 2: 6-acid was precipitated as insoluble barium salt (it had been previously 
 ascertained that the 1: 5-acid, which also forms an insoluble barium salt, is not 
 present in the sulphonation product under the above conditions), and any mono- 
 sulphonic acid separated and estimated. The results were as follows: 
 
 Period of Heating at Monosulphonic Acid Total Disulphonic : . . . 
 
 160°. in Product. Acids, «| _-2#6-Dioulphonic Acid. 
 Hours. Per Cent. Per Cent. Per Cent. 
 
 1 87 9 
 
 2 6 94 10 
 
 5 — 100 19 
 
 8 — 100 22 
 
 11 — 100 24 
 
 The filtrate from the 2 : 6-salt was always a mixture of the 2: 7- and 1 : 6-salts. 
 1 : 8-Aminonaphthol-3 : 6-disulphonic acid (H-acid) : 
 
 The acid forms colourless crystals, sparingly soluble in cold water. The acid sodium 
 salt (needles, +-14H,O) and the acid barium salt (needles, +4H,O) are both sparingly 
 soluble in water. With ferric chloride a brownish-red colouration is obtained. The 
 acid gives a yellow soluble diazo compound. 
 
 The preparation of H-acid from naphthalene involves, as shown by the chat’ on 
 
NAPHTHALENEDISULPHONIC ACIDS 169 
 
 p. 165, the operations of (1) sulphonation to naphthalene-1: 3: 6-trisulphonic acid, 
 (2) nitration of the trisulphonic acid, (3) reduction of the nitro compound, and 
 (4) alkali fusion of the naphthylaminetrisulphonic acid. 
 
 Sulphonation.—The main problem lies in the production of the 1 : 3 : 6-trisulphonic 
 acid free from isomers as far as possible. Two of the four disulphonic acids, the 
 1:6- and the 2: 7-acids, are known to yield the 1:3: 6-trisulphonic acid as sole 
 product on further sulphonation : 
 
 ings cre 
 
 sya YW 
 1:6 Ne as, 
 NL 
 S 
 0) 
 a 
 1:3:6 
 
 Of the other two disulphonic acids, the 1 : 5-acid yields the 1:3: 5-trisulphonic acid, 
 and the 2 : 6 (=3 : 7)-acid yields the 1 : 3 : 7-trisulphonic acid on further sulphonation. 
 If, therefore, naphthalene could be so sulphonated as to form either the 1 : 6- or the 
 2: 7-disulphonic acid, or both, in absence of the 1: 5- or the 2: 6-acids, further sul- 
 phonation should give the desired 1 : 3 : 6- trisulphonic acid alone. 
 
 According to the results obtained by Fierz-David, it is possible to form such a 
 mixture of 1:6- and 2:7-disulphonic acids. On sulphonating naphthalene with 
 sulphuric acid containing just enough free sulphur trioxide for disulphonation, there 
 is formed at temperatures below 40° a mixture of 1: 5- and 1: 6-acids. On heating 
 this mixture to 130° to 135° the 1 : 5-acid gradually disappears, its place beg taken 
 by 2: 7-acid, and if sufficient time is allowed there is obtained within the temperature 
 limits mentioned a mixture of 2:7- and 1: 6-acids. The 2: 6-acid does not begin 
 to form until about 140°. Ifthese results are correct, then the conditions are indicated 
 for the preparation of the 1 : 3 : 6-trisulphonic acid unmixed with isomers, or con- 
 taining only a small proportion of them. 
 
 In an early patent by Giirke and Rudolph, naphthalene-1: 3: 6-trisulphonic acid 
 is prepared, either by adding naphthalene to eight times its weight of 24 per cent. 
 oleum and heating for several hours at 180°, or by adding 1 part of naphthalene to 
 6 parts of 40 per cent. oleum under 80°, and then heating on the water-bath until the 
 SO, has disappeared. By either method considerable quantities of the isomers must 
 be formed. 
 
 A process involving three stages is described by Fierz-David (“ Farbenchemie,”’ 
 1920, p. 15), and also in the Industrial Chemist, 1925, 1, 141. Naphthalene is sul- 
 phonated first at high temperature to the B-monosulphonic acid, the product is then 
 cooled, and sulphonated further at about the ordinary temperature so as to form the 
 
170 INTERMEDIATES FOR DYESTUFFS 
 
 1 : 6-disulphonic acid as far as possible. By a final period of heating at 160° to 165°, 
 the 1 : 3: 6-trisulphonic acid is formed to the extent of about 60 per cent. 
 
 The most satisfactory method seems to be that given by Fierz-David (“ Farben- 
 chemie,” second edition, 1923, p. 20). 
 
 128 gms. of naphthalene is heated to 165°, and 260 gms. of monohydrate slowly 
 added with good stirring. About ten minutes are required for the addition, after 
 which the temperature is lowered to 125°, at which point it is kept for three and a half 
 to four hours. 420 gms. of 60 per cent. oleum is now added, the temperature being 
 allowed to rise during the addition to 140°. Thereafter the temperature is raised to 
 170° and kept there for six hours. The solution is then cooled to 15°. 
 
 Nitration.— Without isolation, the trisulphonic acid is now nitrated by slowly 
 adding the calculated quantity of nitric acid (103 gms. of 60 per cent. nitric acid), 
 the temperature being maintained at 15° by external cooling. Ten hours’ further 
 stirring is given to complete the nitration. 
 
 Reduction.—For the reduction of the nitrotrisulphonic acid so formed, either 
 (1) iron may be added to the diluted strongly acid solution, or (2) the diluted solution 
 may be neutralised with chalk or lime and the calcium salt converted into sodium salt, 
 which is then reduced in faintly acid solution with iron. The former method involves 
 less labour than the latter, but gives a lower yield of the amino compound. Both 
 processes will be described. 
 
 (1) The nitration mixture is poured into a mixture of 1,500 gms. of ice and 1,500 
 gms. of water, the temperature of the resulting solution being below 0°. The whole 
 of the iron required for the reduction—180 gms. of iron borings—is added at once, 
 and, with continuous stirring, the reduction proceeds with rise of temperature ulti- 
 mately to about 50°. The iron salt of the 1-naphthylamine-3 : 6 : 8-trisulphonic acid 
 (Koch acid) may separate to some extent. When the reduction is finished (after 
 about eight hours), the solution is warmed to 70°, decanted or filtered from unused 
 iron and sludge, and salt added in quantity sufficient to give a 20 per cent. solution, 
 which salts out the Koch acid. After allowing ten hours for the salting out to be 
 completed, the precipitate is filtered off and washed with 500 c.c. of 15 per cent. salt 
 solution. It is then redissolved in a litre of hot water, neutralised with 50 gms. of 
 chalk, filtered from calcium sulphate and iron oxide, and the Koch acid reprecipitated 
 as acid sodium salt by addition of 150 gms. of salt and 40 gms. of concentrated 
 sulphuric acid. It is then filtered off and pressed. The yield of Koch acid is about 
 320 gms., as moist press-cake, which, as estimated on a sample by titration with 
 nitrite, corresponds to about 34 gms. of nitrite or an overall yield from the naphthalene 
 of about 50 per cent. ; 
 
 (2) The nitration mixture is poured into 14 litres of water. The solution heats up 
 to 70° to 80° and nitrous fumes are evolved. 225 gms. (3 mols.) of anhydrous sodium 
 sulphate (or the corresponding quantity of Glauber salt) is added so as to form the 
 sodium salt of the nitrotrisulphonic acid during the subsequent neutralisation. About 
 650 gms. of limestone or chalk is then added until the solution is neutralised. There 
 is a change of colour from pale to strong yellow at the neutral point. The mixture 
 is filtered and the residue well washed with cold water. The filtrate is made just acid 
 
NAPHTHALENEDISULPHONIC ACIDS 171 
 
 to Congo paper with dilute sulphuric acid and dropped slowly into a boiling well- 
 stirred mixture of 150 gms. of iron borings (grey cast-iron), } litre of water, and 
 10 c.c. of 40 per cent. acetic acid. The reduction takes about an hour. A drop of 
 the solution on filter-paper should be colourless. Any iron in solution is then preci- 
 pitated by adding soda ash until the solution is alkaline to litmus (about 5 gms. 
 required). It is then filtered and evaporated to $ litre. On adding 100 gms. of salt 
 and enough sulphuric acid to make the solution acid to Congo paper, the acid sodium 
 salt of Koch acid is salted out, and is filtered off and pressed. The yield obtained is 
 about 350 gms. of press-cake, corresponding to 35 gms. of nitrite, or 53 per cent. yield 
 on the naphthalene used. 
 
 Fusion with Alkali—tIn Bayer’s original patent (G.P. 69722) it is proposed to 
 convert 1-naphthylamine-3 : 6: 8-trisulphonic acid into 1: 8-aminonaphthol-3 : 6- 
 disulphonic acid, either by fusion with twice its weight of caustic soda (containing 
 a little water) in an open vessel at 180° to 190°, or by heating in an autoclave with 
 30 to 40 per cent. caustic soda solution at 210°. | 
 
 It has been found that open fusion with alkali is not suitable for substances so 
 easily oxidised as the aminonaphthol-sulphonic acids. The second method of heating 
 with concentrated alkali is, therefore, the one now generally used. In the case of 
 H-acid, however, the temperature of 210° is unnecessarily high, about 180° to 190° 
 being sufficient. Again the strength of the caustic soda solution used is of great 
 importance. Too dilute a solution will readily replace the amino group as well as the 
 8-sulpho group by hydroxyl. This takes place even with strong caustic soda if the 
 melt is carried on for too long a period. A caustic soda solution of about 35 to 38 
 per cent. strength gives the most satisfactory results, and the time required will depend 
 on the scale of working. 
 
 Continuing the description of the process given by Fierz-David, a stirring autoclave 
 is charged with a quantity of damp press-cake of Koch acid, corresponding to 28 gms. 
 of nitrite (about 280 gms. of press-cake), 130 gms. of caustic soda, and 130 gms. of 
 water, or such a quantity of water as, with the water in the press-cake, will give a 
 caustic soda solution of about 35 per cent. The mixture is then heated with stirring 
 at 178° to 180° for eight hours, the pressure developed being about 7 atmospheres. 
 On opening the autoclave a little ammonia escapes, as it 1s impossible to avoid re- 
 placement of the amino group to a slight extent. The product is dissolved in a litre 
 of water, and 50 per cent. sulphuric acid added till the solution 1s strongly acid to 
 Congo paper. The H-acid is precipitated as acid sodium salt, and after a few hours 
 is filtered off, washed with 10 per cent. salt solution containing a little acid, pressed, 
 and dried. 
 
 The product is analysed in two ways—(1) by titration with standard nitrite solution 
 in acid solution which determines the proportion of NH, group present by diazotisa- 
 tion, (2) by titration with standard diazobenzene in alkaline solution which determines 
 the proportion of OH group present by coupling of the diazobenzene in the ortho 
 position to the OH group. The results are conveniently expressed as the weight of 
 product containing 16 gms. of NH, and 17 gms. of OH respectively. Ona sample of 
 pure H-acid, the two results would, of course, be equal, since each is the molecular 
 
172 INTERMEDIATES FOR DYESTUFFS 
 
 weight in grams of H-acid. Ona good specimen of H-acid, the results should agree 
 within 0-5 per cent. 
 
 H-acid is used in various capacities in a large number of azo dyes of all classes. 
 
 (a) It can be diazotised, and is applied as a first component in several mono- and 
 disazo dyes, in which it is coupled with amines in acid solution. It is not coupled 
 with phenols, because in the alkaline solutions required for such couplings the diazo- 
 tised H-acid tends to couple with itself (7.e., in the o-position to the hydroxyl group). 
 
 (b) It is used as a middle component in polyazo dyes. A diazo compound is 
 coupled in alkaline solution with H-acid. The amino group of the H-acid half of the 
 molecule in the resulting monoazo dye can then be diazotised and coupled with a 
 third component. 
 
 (c) H-acid also serves as a middle component in another sense. A diazo compound 
 may be coupled with H-acid in acid solution, when coupling takes place in the o-posi- 
 tion to the amino group. A second diazo compound can then be coupled in alkaline 
 solution with the product, in which case the coupling occurs ortho to the hydroxyl 
 group. The typical case of this kind is Naphthol Blue Black : 
 
 GF Gerareh Poe , ; a ae 
 & -_N=N | | N= N— DNOs 
 HOS. A /S0.H 
 
 (d) Allied to this use of H-acid is its use in the preparation of certain black and 
 green direct cotton dyes. Thus, Direct Deep Black EW or Chlorazol Black E extra 
 is made by coupling the tetrazo compound of benzidine in acid solution with one mole- 
 cular proportion of H-acid. Diazotised aniline is then coupled with the product in 
 alkaline solution, coupling taking place in the o-position to the hydroxyl group. 
 Finally, the resulting compound is coupled with one molecular proportion of 
 m-phenylenediamine : 
 
 Diamine Green B, on the other hand, is prepared by first coupling diazotised 
 p-nitraniline with H-acid in acid solution, then coupling the tetrazo compound of 
 benzidine with the product (1 molecule) in alkaline solution, and finally coupling 
 with phenol : 
 
 HO NH, 
 
 Da NGS, Bok RET as die Ne, ct lr db 
 S-N=N ae ; N=N—C___ NO, 
 
 IY ¢ >= N—< AS): 
 
NAPHTHALENEDISULPHONIC ACIDS 173 
 
 (e) Disazo dyes of bright blue shades are made by coupling the tetrazo compounds 
 of diamines of the benzidine series with two molecular proportions of H-acid in 
 alkaline solution. These are direct cotton colours. 
 
 Several other aminonaphthol sulphonic acids resemble H-acid in having the 
 amino and hydroxyl groups in the pert position to one another. Most of these are 
 described elsewhere,—e.g., S-acid (p. 156), 2S-acid (p. 158), K-acid (p. 174). These 
 1 : 8-aminonaphtholsulphonic acids are used, though not so widely as H-acid, for dyes 
 of the same types as those described above, especially for those described in paragraphs 
 (c), (d), and (e). 2S-acid, however, owing to the presence of the sulpho group in the 
 2-position, is incapable of forming dyes of the (c) and (d) types. 
 
 1-Naphthol-3 : 6 : 8-trisulphonic acid (Oxy-Koch acid) : 
 
 HO,S OH 
 
 MS ) 
 ed | SO,H 
 
 Began 
 
 This acid is prepared from 1-naphthylamine-3 : 6 : 8-trisulphonic acid (Koch acid) 
 by diazotisation in a solution strongly acid with sulphuric acid, followed by boiling 
 of the solution of diazo compound until nitrogen is no longer evolved. Naphtha- 
 sultonedisulphonic acid— 
 
 —is thus formed, but on neutralisation of the solution with lime the calcium salt of 
 the naphtholtrisulphonic acid is obtained, and this is then converted into the sodium 
 salt as usual (G.P. 56058). 
 
 According to G.P. 71495, Koch acid may be hydrolysed, so as to replace the amino 
 group by hydroxyl, by heating the acid sodium salt with water in an autoclave at 
 180° to 250°. 
 
 The acid is used as an intermediate for azo dyes. 
 
 1 : 8-Dihydroxynaphthalene-3 : 6-disulphonic acid (Chromotrope acid) : 
 
 HO OH 
 Paes 
 HOS, sk /S0H 
 
 The acid crystallises in needles or leaflets with 2H,O, and is easily soluble in water. 
 The disodium salt is easily soluble in water, but can be salted out. The disodium 
 salt is acid to carbonate and a neutral trisodium salt can be formed, as also a tetra- 
 sodium salt, which is alkaline in reaction. The alkaline solutions show a violet-blue 
 fluorescence. : 
 Chromotrope acid can be prepared, either from H-acid or from 1-naphthol-3 : 6 : 8- 
 trisulphonic acid, by the action of alkali. According to G.P. 68721 (Bayer), it is 
 made from H-acid by dissolving 15 kg. of the sodium salt in 150 kg. of 5 per cent. 
 
174 INTERMEDIATES FOR DYESTUFFS 
 
 caustic soda solution and heating in an autoclave at 265° for eight hours. The pressure 
 developed is 22-5 atmospheres. After boiling to expel ammonia, the solution is 
 acidified to precipitate the acid sodium salt of chromotrope acid. 
 
 The preparation from 1-naphthol-3: 6: 8-trisulphonic acid is described in 
 G.P. 67563 (Meister Lucius and Briining). 13-5 parts of 60 per cent. caustic soda 
 solution is heated at 100° and 17-9 parts of a paste containing 6-65 parts of the sodium 
 salt of the naphtholtrisulphonic acid (or of the sultone, see above) is added, the 
 mixture being then heated at 170° to 220° until foaming ceases. The melt is dissolved 
 in water and acidified to precipitate the acid sodium salt of chromotrope acid. 
 
 Chromotrope acid is capable of coupling with 2 molecules of a diazo compound 
 one in each position ortho to a hydroxyl group. Itis usually, however, coupled with 
 only 1 molecule of diazotised amine, the resulting dyes, the “‘ chromotropes ” of 
 Meister Lucius and Briining, having the property of dyeing wool from an acid bath, 
 generally in bluish-red shades, which can be afterchromed with bichromate to blue- 
 black or black dyeings of considerable fastness. These dyestuffs also give very level 
 dyeings, a property of importance in dyeing wool. 
 
 1 : 8-Aminonaphthol-4 : 6-disulphonic acid (K-acid) : 
 
 HO NH, 
 Wl, ee 
 
 wos ) : 
 
 O,H 
 
 This substance is prepared from naphthalene-1 : 5-disulphonic acid by the same 
 sequence of operations as is used in preparing H-acid from the 1 : 6- and 2: 7-disul- 
 phonic acids (see Chart, p. 165). In this case, however, it is probably best to 
 start, not from naphthalene, but from the isolated 1 : 5-disulphonate. 
 
 In order to form the 1:3: 5-trisulphonic acid from the 1: 5-disulphonic acid, 
 low temperature sulphonation is required since, although only one trisulphonic acid 
 can be formed, the 1 : 5-disulphonic acid in solution in sulphuric acid undergoes trans- 
 formation to its isomers the 1: 6- and 2: 7-acids. The process patented by Kalle 
 and Co. (G.P. 93700, 99164) is as follows: 10 parts of sodium naphthalene-1 : 5- 
 disulphonate is stirred into 40 parts of monohydrate and, at 40°, 9 parts of 70 per cent. 
 oleum dropped in. The mixture is then heated to 80° to 90° until a sample, diluted 
 with water, gives no precipitate on adding salt. 
 
 Nitration of the 1:3:5(=4:6: 8)-trisulphonic acid to 1-nitronaphthalene- 
 4:6: 8-trisulphonic acid and reduction of this to 1-naphthylamine-4 : 6 : 8-tri- 
 sulphonic acid are carried out, as described under H-acid. Lither the acid or the 
 neutral process of reduction may be used. The l-naphthylamine-4 : 6 : 8-trisulphonic 
 acid is obtained finally as the acid sodium salt, which is readily salted out. In alkaline 
 solution it shows a green fluorescence. 
 
 For the conversion of the naphthylaminetrisulphonic acid to aminonaphthol- 
 disulphonic acid, the acid sodium salt obtained from 10 parts of 1 : 5-disulphonate 
 is heated with 20 parts of 75 per cent. caustic soda solution at 140° to 200°, the amino- 
 
NAPHTHALENEDISULPHONIC ACIDS 175 
 
 naphtholdisulphonic acid being finally precipitated as acid sodium salt by acidifying 
 with hydrochloric acid. 
 
 The Bayer process (G.P. 78604, 80741; G.P. Anm. F. 7004, 7006, 7059, K. 11104) 
 differs in several points from that of Kalle and Co. For the sulphonation, 100 parts 
 of sodium naphthalene-1 : 5-disulphonate is stirred into 300 parts of 20 per cent. 
 oleum, the temperature rising to 60° to 80°. The mixture is then heated slowly to 
 130°. According to the patent, the disulphonate does not dissolve until about this 
 temperature, but then suddenly dissolves, and is converted into trisulphonic acid. 
 
 The nitration is carried out as usual, but reduction is performed by the neutral 
 process. For the alkali fusion 75 per cent. caustic soda is used, as in the Kalle process, 
 but the melt is performed in an autoclave at 170° to 175°, this being probably about 
 the best temperature. (The 140° to 200° of the Kalle patent seems to be the ordinary 
 calculated vagueness of such documents.) 
 
 As a component of azo dyes, K-acid is used similarly to the other 1 : 8-amino- 
 naphtholsulphonic acids (p. 172). 
 
 1-Naphthylamine-3 : 6-disulphonic acid (Freund’s acid) : 
 
 NH, 
 ean 
 veOw 
 The acid is easily soluble in water andalcohol. The acid sodium salt (needles, +3H,0) 
 and the calcium salt (scales) are soluble in water. 
 
 This acid is prepared by nitration of naphthalene-2: 7-disulphonic acid and 
 reduction of the nitro-acid. The isolated 2: 7-acid is not usually employed for the 
 purpose, since it is not readily separated from its isomers. Instead, naphthalene 1s 
 sulphonated so as to produce the maximum proportion of the 2: 7-acid, which is 
 obtained by sulphonation at 160° to 165°. The mixture of disulphonic acids so 
 formed contains 65 to 70 per cent. of 2: 7-acid, 20-25 per cent. of 2: 6-acid, and a 
 little 1:6-acid. The preparation is described by Fierz-David (“ Farbenchemie,” 
 second edition, 1923, p. 26). 
 
 128 gms. of naphthalene is heated and stirred at 165°, while 400 gms. of mono- 
 hydrate is added during fifteen minutes. The solution is then heated for an hour at 
 165° to complete the disulphonation. After cooling to 15°, nitration is carried out as 
 usual with 103 gms. of 60 per cent. nitric acid, the temperature being kept below 30°. 
 The subsequent procedure is similar to that described under H-acid (p. 170), using 
 the “ neutral’ method of reduction. But 200 gms. of iron powder are used for the 
 reduction, and this is etched with 20 c.c. of concentrated hydrochloric acid instead of 
 acetic acid. The solution of sodium salts of the nitro-acids is acidified with 10 c.c. 
 of hydrochloric acid before adding to the iron for reduction. 
 
 When reduction is complete and any dissolved iron precipitated by sodium 
 carbonate and filtered off, the filtrate is evaporated to 800 c.c. and, while boiling, 
 100 gms. of potassium chloride added, followed by 100 c.c. of hydrochloric acid. On 
 cooling, the acid potassium salt of Freund’s acid separates. After twelve hours, this 
 
176 INTERMEDIATES FOR DYESTUFFS 
 
 is filtered off, washed with 200 c.c. of saturated salt solution, and well pressed. The 
 yield is about 270 gms. of dry salt, corresponding to 35 gms. of nitrite, or slightly over 
 50 per cent. The product may be purified by dissolving in four times its weight of 
 boiling water and allowing to crystallise. The acid sodium salt, which is also sparingly 
 soluble in cold water, is not so suitable for the separation, as it precipitates in a form 
 which is difficult to filter. 
 
 The preparation of Freund’s acid by a similar method is also given in G.P. 27346 
 (Freund). 
 
 Another method of preparation depends on the fact that the 8-sulphonic acid 
 group in 1-naphthylamine-3 : 6: 8-trisulphonic acid (Koch acid, p. 170) is easily 
 eliminated by reduction (G.P. 233934, Kalle and Co.) : 
 
 HO,S NH, NH, 
 ry ee 
 —___—__ > I 
 | 
 
 HOS. He // 30a HOS. ok /SOsH 
 
 9-5 kg. of the acid sodium salt of Koch acid, containing 90 per cent. of diazotisable 
 acid, is boiled with 7-5 kg. of caustic soda solution, 3 kg. of zine dust, and 90 litres of 
 water for seven hours under reflux. On neutralising with hydrochloric acid and 
 filtering from zinc oxide, acidification of the filtrate precipitates the acid sodium salt 
 of 1-naphthylamine-3 : 6-disulphonic acid. 
 
 Freund’s acid is used as first component in a few disazo dyes in conjunction with 
 a-naphthylamine or Cleve’s acids as middle components. | 
 
 1-Naphthol-3 : 6-disulphonic acid : is 
 
 O 
 Peo 
 moe 
 
 SAN 
 
 The acid is easily soluble in water. Its alkaline solutions show a pale green fluores- 
 cence. The acid sodium salt is readily soluble in water, but can be salted out. 
 Freund’s acid can be converted into the naphthol-disulphonic acid, either by 
 running a solution of the diazo compound into boiling dilute sulphuric acid (G.P. 27346, 
 Freund), or by heating the acid with three times its weight of water at 180° (G.P. Anm. 
 C. 4375, Cassella). Both methods are similar to those by which N W-acid is obtained 
 from naphthionic acid (p. 147). ) 
 a-Naphthol-3 : 6-disulphonic acid is also prepared by alkali fusion of naphthalene- 
 1:3: 6-trisulphonic acid. 
 It is used as end component in a number of azo dyes, chiefly of the monoazo class. 
 2-Naphthol-7-sulphonie acid (F-acid)— 
 
 HO,S/ i ‘oH 
 
 or 
 
 NL 
 
 —crystallises in needles from water containing hydrochloric acid, and melts at 89°. 
 It is easily soluble in water and alcohol. Solutions of the salts show a blue fluores- 
 
NAPHTHALENEDISULPHONIC ACIDS 177 
 
 cence, The sodium salt (needles, +-24H,0) is soluble in 12 parts of water at 15°, and 
 can. be salted out. 
 
 F-acid is prepared by alkali fusion of naphthalene-2 : 7-disulphonic acid. Accord- 
 ing to G.P. 42112 (Cassella), 100 kg. of sodium naphthalene-2 : 7-disulphonate and 
 400 kg. of 50 per cent. caustic soda solution are heated together in an autoclave at 
 225°, until an acidified sample extracted with ether shows traces of the dihydroxy 
 compound inthe ether. About ten hours’ heating is sufficient. The melt is then dis- 
 solved in 1,000 litres of water, acidified with hydrochloric acid, boiled to expel sulphur 
 dioxide, and the solution cooled, when the sodium salt of F-acid crystallises out. 
 
 It is possible also to use the mixed sodium salts of naphthalene-2 : 6- and 2: 7- 
 disulphonic acids, as obtained from the high temperature disulphonation of naph- 
 thalene (p. 167). Thus, according to G.P. 45221 (Cassella), 130 kg. of the mixed salts 
 are heated with 35 kg. of caustic soda, 180 litres of water and 40 kg. of common salt 
 in an autoclave at 240° to 270° for sixteen hours. A mixture of the salts of 2-naphthol- 
 6-sulphonic acid (Schaffer acid) and F-acid is thus formed, and the mixed sodium 
 salts may be isolated as above. After amidation, as described under 2-naphthylamine- 
 7-sulphonic acid, the mixture is used for azo dyes. 
 
 The two acids, however, can be separated. The alkaline melt from the autoclave 
 contains the two disodium salts of the acids [C,)H,(ONa).SO,Na], and that of Schiffer 
 acid mostly separates from the melt along with the sodium sulphite. It is filtered off, 
 and the monosodium salt of F-acid obtained from the filtrate by acidifying. Or the 
 whole melt may be dissolved in 500 litres of water, acidified with hydrochloric acid 
 and boiled to expel sulphur dioxide. The boiling solution is then saturated with 
 salt, which throws out the Schiffer salt, and after filtering hot, the filtrate, on cooling, 
 gives crystals of the F-salt. 
 
 While formerly used for azo dyes, this use seems now to be restricted to its addition 
 in small proportion to B-naphthol in order to obtain a modified shade of Para Red. 
 F-acid is mostly converted into the corresponding naphthylaminesulphonic acid 
 (also called F-acid, or the two are sometimes distinguished by the names Oxy-F- and 
 Amido-F-acid). 
 
 2-Naphthylamine-7-sulphonic acid (Amido-F-acid): 
 
 ae af ae 
 + Vi 
 
 The acid crystallises in needles or prisms with 1H,0 from lukewarm water, but this 
 monohydrate loses water at 100° (on boiling with water), forming the anhydrous acid as 
 a sparingly soluble sandy powder, soluble in 350 parts of boiling water. The sodium 
 salt crystallises with 4H,O and dissolves in 70 parts of cold water, but is easily soluble 
 in hot water and in 96 per cent. alcohol. The barium salt is sparingly soluble. 
 _ Solutions of the salts show a red-violet fluorescence. 
 This acid is best prepared by Bucherer’s method—that is, by heating the sodium 
 salt of F-acid with ammonium sulphite and ammonia in an autoclave at about 150° 
 (Bucherer, J. pr. Chem., 70, 357). 
 12 
 
178 INTERMEDIATES FOR DYESTUFFS 
 
 The amidation of F-acid with ammonia alone at 250° is described in G.P. 43740 
 (Cassella). 
 
 Amido-F-acid is used as an end component in azo dyes, usually in conjunction 
 with tolidine as first component. 
 
 1 : 5-Dihydroxynaphthalene— ek 
 
 oh 
 
 NSS 
 HO 
 
 —crystallises in colourless leaflets from water, and sublimes in long needles, m.p. 
 258° to 260°. It is sparingly soluble in water, easily soluble in alcohol, but 
 almost insoluble in benzene. It is stable in air, but in alkaline solution oxidises 
 quickly. 
 
 Its preparation from naphthalene-1 : 5-disulphonic acid is described by Ewer and 
 Pick (G.P. 41934). 
 
 100 kg. of sodium naphthalene-1 : 5-disulphonate is stirred with 300 to 400 kg. of 
 caustic soda at 220° to 260° in an open cast-iron pan, or in an autoclave at the same 
 temperature, enough water being added to give a thick paste. (Presumably the latter 
 method is preferable in view of the sensitivity of alkaline solutions of the dihydroxy 
 compound to air.) 1-Naphthol-5-sulphonic acid, as sodium salt, is formed as an 
 intermediate stage in the reaction. Tests are carried out on the melt as follows : 
 5 gms. of the melt is dissolved in 200 gms. of water, and the solution filtered and cooled. 
 To 100 c.c. of the solution sodium bicarbonate is added till a slight cloudiness appears : 
 about 7 gms. of bicarbonate being required. A solution of diazotised benzidine is 
 then added until a drop on filter-paper spotted on the colourless rim with sodium 
 naphthionate solution shows a pale brown colouration. The remaining 100 c.c. of 
 solution is then added, followed by 10 gms. of bicarbonate. If the melt is completed, 
 the whole of the azo dye formed in the test separates in gee flocks. The solution 
 should not be violet. 
 
 The melt is now run into the calculated quantity of dilute hydrochloric or sul- 
 phuric acid. On cooling, the dihydroxynaphthalene separates in nearly white dense 
 flocks. 
 
 Another method of preparation, from Laurent’s acid, is given on p. 159. 
 
 This intermediate gives, by coupling with diazotised o-aminophenol-p-sulphonic 
 acid, an azo dye which can be afterchromed on wool to a black of exceptionally good 
 shade and fastness, named Diamond Black PV. | 
 
 Naphthylaminedisulphonic Acids derived from Naphthalene-1 :5 and 1 : 6- 
 Disulphonic Acids. 
 
 When the mixture of 1 : 5- and 1 : 6-disulphonic acids, obtained by the sulphona- 
 tion of naphthalene, as described on pp. 166 and 167, is nitrated, each disulphonic 
 acid yields both an «- and a f-nitrodisulphonic acid as follows : 
 
NAPHTHALENEDISULPHONIC ACIDS 179 
 NO, S 
 
 00 = WO + Ce 
 io ie Coe 
 
 On reduction, the nitro-acids give a mixture of the corresponding naphthylaminedi- 
 sulphonic acids from which the 1 : 3: 8- and 1 : 4: 8-naphthylaminedisulphonic acids 
 may each be separated. As to the separation of the 2: 4: 8- and 2:4: 7-naphthyl- 
 aminedisulphonic acids, little information has been published, though the former 1s 
 known to be used as first component in azo dyes. The proportions of the 1:3: 8- 
 and 1:4: 8-acids obtainable may be varied by alteration of the temperature of 
 sulphonation of the naphthalene so as to vary the proportions of 1: 5- and 1: 6- 
 disulphonic acids in the mixture, and details of the method of separation must be 
 altered to suit the varying proportions. 
 
 A method of separation of the two «-naphthylaminedisulphonic acids is described 
 by Paul (Zeit. angew. Chem., 1896, 9, 559). The preliminary sulphonation is carried 
 out by adding 280 kg. of oleum slowly during four to five hours to 100 kg. of molten 
 naphthalene at 80°. The finished sulphonation mixture is then cooled to 30° and 
 100 kg. of 60 per cent. nitric acid (2.e., 20 per cent. excess) is added during eighteen 
 hours, while the temperature is maintained at 20° to 30°. The nitration mixture is now 
 run into milk of lime made from 170 kg. of lime and 1,000 kg. of water. The mixture 
 is boiled and filtered from gypsum. The calcium salts of the nitro-acids are converted 
 into sodium salts, and the solution of these evaporated to a volume of 1,500 litres. 
 
 The reduction is effected in an unusual way. The solution of sodium salts is 
 boiled and, while stirring, 200 kg. of iron borings added. 100 kg. of sulphuric acid 
 (66° Bé) is then run in slowly over two and a half hours, and boiling continued for a 
 further two to three hours, with addition of more iron if necessary to complete the 
 reduction. After neutralising the solution with slaked lime and converting the solu- 
 tion of calcium salts into sodium salts, the liquid is evaporated till it reaches 28° Bé, 
 and then allowed to stand for eight days. The sodium salt of 1-naphthylamine- 
 4: 8-disulphonic acid crystallises out. It may be purified by dissolving in about 
 four times its weight of hot water, cooling to 40°, filtering from any sparingly soluble 
 sodium salt of Peri acid (from any «sulphonic acid in the original sulphonation 
 mixture), and acidifying with hydrochloric acid, when the acid sodium salt precipitates. 
 
 The filtrate from the 1 : 4 : 8-acid is diluted with 1,000 litres of water, and 600 kg. 
 of salt and 480 kg. of hydrochloric acid added. It then shows 28° Bé. After standing 
 for some time, the acid sodium salt of 1l-naphthylamine-3 : 8-disulphonic acid 
 separates. Itis recrystallised with the aid of salt. 
 
 The yield of each acid is about 20 per cent. 
 
 The final filtrate contains 2-naphthylamine-4 : 7- and 4 : 8-disulphonie acids. 
 
180 INTERMEDIATES FOR DYESTUFFS 
 
 Another method of separation of the 1:4:8- and1:3:8-acids is given in 
 Hi. P. 161859 (South Metropolitan Gas Co.). It depends on the difference in solubility 
 of the barium salts of the acids. A suitably concentrated solution of the neutral 
 sodium salts of the mixed acids is boiled with enough barium chloride to convert all 
 the acids present to barium salts. The barium salt of the 1 : 4 : 8-acid is precipitated, 
 and is filtered off from the hot liquid and washed. The filtrate and washings are 
 acidified with hydrochloric acid, which precipitates the acid barium salts of the 
 1:3:8-acid. This is filtered off from the still hot liquor in order to keep in solution 
 the salts of the 2:4: 7- and 2:4: 8-acids. 
 
 1-Naphthylamine-4 : 8-disulphonic acid has already been described (p. 156) in 
 connection with another method of preparation. 
 
 1-Naphthylamine-3 : 8-disulphonic acid— 
 
 —crystallises in scales with 1H,0, very soluble in hot water. Its acid sodium salt 
 (needles, +6H,O) is soluble in 30 parts of cold water. Its disodium salt (needles, 
 +6H,O) is very soluble in water. It gives a colourless sparingly soluble diazo 
 compound, 
 
 This acid is not used as an azo component, but is converted into the corresponding 
 naphtholdisulphonic acid. 
 
 1-Naphthol-3 : 8-disulphonic acid (¢-acid) : 
 
 The disodium salt (prisms, +-6H,0) is soluble in 5-5 parts of cold water. 
 
 1-Naphthylamine-3 : 8-disulphonic acid may be converted into e-acid in two ways : 
 
 (a) 36 kg. of the acid sodium salt of the naphthylaminedisulphonic acid is dissolved 
 in 500 litres of cold water with the aid of 4 to 5 kg. of caustic soda. The solution is 
 acidified with 20 kg. of concentrated sulphuric acid, and then diazotised with 7 kg. of 
 sodium nitrite dissolved in 75 litres of water. The sparingly soluble diazo compound 
 mostly separates. The mixture is now boiled until evolution of nitrogen ceases. On 
 cooling, the sodium salt of the sultonesulphonic acid crystallises in long colourless 
 needles (+3H,0) : 
 
 HO,S NH, O,S—-N, ar ge OH 
 HNO, > -(0 Alkali > 
 SVAN SO,H eat Jeon SO,H Uk Pro. 
 
 The sultone is easily converted into the sodium salt of the naphtholdisulphonie acid 
 by warming with the necessary quantity of caustic soda solution (G.P. 52724, Ewer 
 and Pick). 
 
NAPHTHALENEDISULPHONIC ACIDS 181 
 
 A variation of this method (G.P. 45776, A.G.F.A.) is to filter off the diazo com- 
 pound, then to stir with water containing a little sulphuric acid, and boil as before. 
 Instead of isolating the sultone, the hot solution is neutralised with lime (this also 
 hydrolyses the sultone), filtered from calcium sulphate, converted into sodium salt 
 in the usual way, and evaporating the solution to crystallismg point, when, on 
 cooling, long colourless prisms of the disodium salt of e-acid separate. 
 
 (0) The amino group may also be replaced by hydroxyl by a method analogous 
 to that by which a-naphthylamine is converted into «-naphthol. 
 
 The acid sodium salt of 1-naphthylamine-3 : 8-disulphonic acid is heated with four 
 times its weight of water in an autoclave at 180° for five to eight hours. The e-acid 
 is isolated by salting out or by evaporation (G.P. 71494, Meister Lucius and Briining). 
 
 e-Acid is used as an end component in mono-, dis-, and trisazo dyes. 
 
CHAPTER XII 
 DERIVATIVES OF B-NAPHTHOL 
 
 In contrast with o-naphthol, B-naphthol is not only itself an important dyestuff 
 intermediate, but gives rise to a considerable number of useful intermediates, which are 
 mostly derived by sulphonation. These intermediates are almost entirely used as 
 end components in azo dyes. The reason for the extensive use of B-naphthol and its 
 sulphonic acids as compared with a-naphthol lies in the fact that coupling with 
 B-naphthol takes place in the «-position, giving azo compounds of the general formula 
 I, whereas with «-naphthol it takes place in the 4-position (formula IJ) : 
 
 N=N.R 
 | OH 
 ee oy 
 PN ee \ 
 N=N.R 
 I Il 
 
 It is found that the p-hydroxyazo compounds (II) are useless as dyestuffs because 
 of their lack of fastness and intensity, and also their sensitivity to alkalies. The 
 o-hydroxyazo dyes, on the other hand, show great intensity and brightness of 
 shade, little or no sensitivity to alkalies, and a fair degree of fastness. Only those 
 «-naphtholsulphonic acids in which the presence of a sulphonic acid group in the 
 4-position (or the 3- or 5-positions), as in NW-acid, Freund’s acid, etc., forces the 
 coupling to take place in the 2-position, yield azo dyes of practical value. 
 
 Sulphonation of /-Naphthol. 
 
 f-Naphthol is very easily attacked by sulphuric acid even in the cold. At tem- 
 peratures below 15° there seems to be first formed a sulphuric ester (I) which, however, 
 if actually formed, rapidly transforms to the 1-sulphonic acid (II), and this in turn 
 to the 8-sulphonic acid (III): 
 SO;H HO,S 
 
 “\“\ on “N/N0.80,.0H fe rr /NoH 
 | | + Hods04 > | ) > 
 LAS Rona Aor 
 
 I I 
 
 At slightly higher temperatures the 8-sulphonic acid (Crocein acid) transforms to the 
 6-sulphonic acid (Schaffer acid), which is the most stable of the monosulphonic acids 
 obtained by direct sulphonation of f-naphthol, and persists without further trans- 
 formation until disulphonation occurs. The transformation of the 8- to the 6-sul- 
 phonic acid is not quite complete at any temperature, but mixtures of the two acids in 
 equilibrium at definite temperatures are obtained. The proportion of the 8-sulphonic 
 acid diminishes as the temperature rises. 
 
 Using sufficient sulphuric acid for disulphonation, two disulphonic acids are 
 
 182 
 
"IOHLHAVN-9 JO SHAILVAINAG—X LUVHO 
 
 OH 
 S*OH 
 $1499"°HN StOH = SH®9O"HN 
 e 
 OH 
 S*OH 
 ZN S*OH ZHN 
 OH 
 
 Htos S*OH 
 S*OH HEOS S*OH S®°OH ‘Ud HNOO 
 HO ston SUN PUN PUN ®HN HO 
 
184 INTERMEDIATES FOR DYESTUFFS 
 
 formed—namely, f-naphthol-6 : 8-disulphonic acid (G-acid) and $-naphthol-3 : 6- 
 disulphonic acid (R-acid): 
 
 HO,S 
 Gen Gei 
 HOR Wa ) HOS. Fan /S0so 
 G-acid R-acid 
 
 G-acid preponderates at temperatures below 50°, but diminishes in proportion as the 
 temperature of sulphonation rises. Further sulphonation produces {-naphthol- 
 3:6: 8-trisulphonic acid. 
 
 2-Naphthol-1-sulphonic acid : SO,H 
 
 ( ne Mis 
 
 Rye 
 The sodium salt crystallises from diluted alcohol in leaflets which are easily soluble 
 in water. The acid is unstable and readily hydrolyses back to £-naphthol. 
 
 This acid is formed as described in G.P. 74688 (Tobias) by adding 1 part of 
 B-naphthol to 2 to 24 parts of sulphuric acid (90 to 92 per cent.). The temperature 
 is allowed to rise to 40°, and kept there for ten minutes. The mass solidifies. After 
 diluting with water, the sodium salt may be obtained by salting out, or through the 
 calcium salt in the usual way. 
 
 But, as obtained in this way, it is contaminated with the 8- and 6-sulphonic acids. 
 Probably the best method of obtaining the 1-sulphonic acid free from isomers is to 
 use Armstrong’s method of sulphonation with chlorsulphonic acid. -Naphthol is 
 dissolved in carbon disulphide and the calculated quantity of chlorsulphonic acid 
 added. When sulphonation is finished, the solvent is evaporated off. 
 
 It has been proposed to use this acid in place of 6-naphthol for developed colours 
 (Calico Printers’ Association and Fourneaux, G.P. 204702). It would give colours 
 identical with those obtained from f-naphthol, since coupling with diazo compounds 
 takes place in the 1-position, the sulpho group being eliminated. It would have the 
 advantage of solubility in water. 
 
 It is mainly used, however, for the production of the corresponding naphthylamine- 
 sulphonic acid. 
 
 2-Naphthylamine-1-sulphonic acid (Tobias acid): 
 
 - §0,H 
 
 Cla 
 
 Noe 
 The acid crystallises in needles, sparingly soluble in cold water, but more soluble in 
 hot water. The sodium salt is easily soluble in water, but can be salted out. The 
 
 diazo compound is yellow and sparingly soluble in water. 
 Amidation of the naphtholsulphonic acid by ammonia alone or by ammonium — 
 
— 
 
 DERIVATIVES OF 6-NAPHTHOL 185 
 
 chloride and ammonia at temperatures over 200° does not give good results. Some 
 6-naphthylamine is formed owing to the instability of the acid. 
 
 This can be avoided by using the Bucherer reaction (J. pr. Chem., 1904 [2], 70, 
 357). The sodium salt of the naphtholsulphonic acid is heated with 40 per cent. 
 ammonium sulphite and 20 per cent. ammonia at about 150°, the Tobias acid being 
 isolated by acidifying the product. 
 
 Tobias acid is particularly well suited for the preparation of lake pigments—for 
 example, Lithol Red, which is obtained by coupling diazotised Tobias acid with 
 f-naphthol. 
 
 2-Naphthol-8-sulphonic acid (Crocein acid): 
 
 HO,S 
 
 ( nA Je 
 iy BS 
 
 The acid is soluble in water. On boiling the aqueous solution, the acid is hydrolysed 
 to f-naphthol and sulphuric acid. The monosodium salt crystallises in leaflets, 
 easily soluble in water, sparingly in alcohol. The disodium salt forms needles con- 
 taining 2C,H,O when crystallised from alcohol. 
 
 2-Naphthol-6-sulphonie acid (Schiffer acid): 
 
 ( ‘e OH 
 HOS. aN 
 The acid crystallises in leaflets, m.p. 125°, soluble in water and alcohol. The sodium 
 salt (leaflets, --2H,O) dissolves in 58 parts of water at 14° and in 3:3 parts at 80°. 
 It is insoluble in alcohol. The calcium salt (leaflets, +- 5H,0) dissolves in 30 parts of 
 water at 18°, and is soluble in alcohol. 
 
 These two acids are conveniently described together since, as already mentioned, 
 they are in general formed together, although, according to G.P. 33857, by sulphonat- 
 ing 1 part of B-naphthol with 2 parts of sulphuric acid at 20°, which requires about 
 seven days, very little Schaffer acid is formed. 
 
 The sulphonation is usually carried out at 50° to 60°, as described in G.P. 18027, 
 20397 (Bayer). Dry and finely powdered 8-naphthol is stirred quickly into twice its 
 weight of concentrated sulphuric acid. Heat is developed, but the temperature is 
 not allowed to rise above 60°. Stirring at 50° to 60° is continued until sulphonation is 
 finished. The solution is then poured into twice its weight of water. 
 
 The salts of the two acids may now be separated to some extent, either by neutralis- 
 ing the solution with soda ash, or by adding two-thirds of the calculated quantity of 
 caustic soda. In either case about four-fifths of the Schiffer salt separates, the 
 Crocein salt remaining in solution with the rest of the Schaffer salt. A better separa- 
 tion can be obtained by neutralising the solution with lime, converting the calcium 
 salts into sodium salts and evaporating the solution of sodium salts to dryness. On 
 extracting the dry salts with 3 to 4 parts of 90 per cent. alcohol at the boil, the Crocein 
 salt dissolves, and is filtered hot from the undissolved Schiffer salt. 
 
186 INTERMEDIATES FOR DYESTUFFS 
 
 The Schaffer salt in these ways can be obtained fairly pure—at any rate, after a 
 recrystallisation or salting out from water. But the Crocein salt is always obtained 
 mixed with some Schaffer salt. However, by taking advantage of the difference in 
 the rates of coupling of the two salts with diazo compounds, it is possible to remove 
 the remaining Schaffer salt. Crocein salt, probably owing to the presence of the 
 sulpho group in the 8-position, couples with diazo compounds much more slowly 
 than Schaffer salt, and in a mixture of the two it is possible to obtain coupling 
 with the whole of the Schaffer salt before any reaction takes place with the 
 Crocein, salt. Moreover, the azo dyes formed with the Schaffer salt are more readily 
 salted out. 
 
 An aliquot part of the solution of Crocein salt and Schaffer salt, left after removal 
 of the main quantity of Schaffer salt, is diluted with water, acidified with a few drops 
 of acetic acid, and titrated with 4, p-nitrobenzenediazonium chloride solution (con- 
 taining sufficient sodium acetate to render it neutral to Congo paper). With practice, 
 the point at which coupling of the diazo compound with the Schaffer salt is complete 
 may readily be found, the red monoazo dye formed being salted out by the addition 
 of half-saturated salt solution. The main quantity of the solution of Crocein and 
 Schaffer salts is then treated with the calculated quantity of a diazo compound to 
 couple with the Schaffer salt, the dye salted out, and the remaining solution of Crocein 
 salt used direct for making azo dyes. 
 
 Preparation of Schaffer Acid in Conjunction with R-Acid. 
 
 It is possible to sulphonate B-naphthol so as to produce a mixture of Schaffer acid 
 and R-acid. The method is described by Fierz-David (‘“‘ Farbenchemie,” 1920, 
 p. 42). Into 200 gms. of 100 per cent. sulphuric acid 142 gms. of pure finely powdered 
 f-naphthol is stirred. The temperature rises rapidly to about 80°, and stirring is 
 continued for a quarter of an hour till the mass becomes homogeneous. The tempera- 
 ture is then raised to 100° to 110°, and is kept at this pomt until a test portion no 
 longer shows separation of f-naphthol on pouring into water. This requires about 
 three hours’ heating. The solution is then poured into 1 litre of water and neutralised 
 with about 200 gms. of chalk. Without filtering, the calcium salts are converted into 
 sodium salts by adding a warm solution of sodium sulphate until a filtered sample 
 gives no precipitate with sodium sulphate. The mixture is then filtered and the 
 residual calcium sulphate well washed. The solution of sodium salts is evaporated to 
 i litre, and sufficient salt added to form a 20 per cent. solution. The solution is then 
 cooled and stirred for a day, when the Schaffer salt separates completely. It is filtered 
 off and washed with a little salt solution. It contains a very small proportion of 
 R-salt, as shown by a slight fluorescence of its aqueous solution. The yield is 160 
 gms. of 100 per cent. Schaffer salt. 
 
 On, acidifying the filtrate with concentrated sulphuric acid and allowing to stand 
 for a long time, the acid sodium salt of R-acid separates. About 80 gms. of R-salt 
 are obtained. 
 
 Schaffer acid is used as an end component chiefly in monoazo dyes for wool of 
 
DERIVATIVES OF B-NAPHTHOL 187 
 
 red and bordeaux shades. A nitroso derivative is also made whose iron salt is used 
 for fast green shades on wool. 
 Crocein acid is used like Schiffer acid, but gives yellower shades of red. 
 2-Naphthylamine-6-sulphonic acid (Bronner acid): 
 
 FNS es NH, 
 ou 
 
 The acid crystallises in leaflets (+-1H,0), soluble in 2,500 parts of cold or 260 parts of 
 boiling water. Solutions of the acid or its salts show a blue fluorescence. The salts 
 are mostly sparingly soluble. The sodium salt (leaflets, -+-2H,O) dissolves in about 
 40 parts of cold water. The calcium and barium salts are much less soluble. 
 
 Bronner acid is prepared by the amidation of Schiffer acid, using Bucherer’s 
 method. Schiffer salt (50 parts) is heated with 75 per cent. ammonium sulphite 
 solution (8 parts) and 20 per cent. ammonia (74.parts) at 200° for six hours. On 
 acidifying the product, Bronner acid is precipitated. 
 
 Brénner acid is used chiefly as a first component in azo dyes, giving, for example, 
 a scarlet by coupling its diazo compound with f-naphthol. 
 
 2-Naphthol-3 : 6-disulphonic acid (R-acid): 
 
 Les, age 
 
 Host ne Prot 
 
 The acid forms silky deliquescent needles, very soluble in water and alcohol. The 
 sodium salt crystallises in aggregates of minute needles, soluble in cold water, but 
 sparingly soluble in alcohol and in brine. The barium salt crystallises in needles 
 (+6H,0), soluble in 12 parts of boiling water, but insoluble in alcohol. Solutions of 
 
 the salts show a bluish-green fluorescence. 
 2-Naphthol-6 : 8-disulphonic acid (G-acid): 
 
 f ar a 
 HOS\ 
 
 Very little information has been published regarding this acid or its salts. The 
 potassium salt is said to be soluble in 2-5 parts of boiling water. The sodium salt 
 is soluble in 80 per cent. alcohol. Apart from the potassium salt, the salts of G-acid. 
 are much more soluble in water than those of R-acid. 
 
 These two acids are formed together when -naphthol is sulphonated with sufficient 
 sulphuric acid (3 to 4 parts, according to the strength of the acid) to form disulphonic 
 acid. G-acid preponderates at low temperatures, while R-acid is the main product 
 at temperatures of 100° and upwards. 
 
 In the original patent describing their preparation (G.P. 3229, Meister Lucius 
 and Briining), 10 kg. of B-naphthol and 30 kg. of concentrated sulphuric acid are 
 
188 INTERMEDIATES FOR DYESTUFFS 
 
 heated together for twelve hours at 100° to 110°. The sulphonic acids are converted 
 to their sodium salts, which are dried and digested with 3 to 4 parts of 75 to 85 per 
 cent. alcohol. G-salt dissolves, while R-salt remains undissolved. 
 
 Apart from the expense of this method of separation, it was found to be unsatis- 
 factory, since R-salt dissolves to some extent and the G-salt obtained is, therefore, 
 impure. A later patent, G.P. 33916 (Beyer and Kegel) describes a simpler process 
 which was adopted generally on the manufacturing scale. The sulphonation mixture, 
 prepared by heating f-naphthol with four times its weight of concentrated sulphuric 
 acid at 125° to 150° for five to six hours, was poured into hot water, the solution 
 neutralised with soda and saturated with common salt. On cooling, most of the 
 R-salt separated. ) 
 
 This method yields a fairly pure R-salt, but the G-salt remaining in the filtrate is 
 accompanied by substantial quantities of R-salt and possibly also Schaffer salt. These 
 latter compounds, however, can be removed by the method used for removing Schafier 
 salt from Crocein salt (p. 186), since G-salt, owing to the presence of the sulpho group 
 in the 8-position, like Crocein salt, only couples very slowly with diazo compounds, 
 whereas R-salt couples readily and quickly, and the azo dyes formed are easily salted 
 out. 
 
 The relative importance of R- and G-acids has changed since the above patents 
 were published, G-acid having become increasingly important as a source of the much- 
 used Gamma-acid (see Chart X., p. 183). Sulphonation is, therefore, carried out at as 
 low a temperature as possible in order to obtain the maximum proportion of G-acid. 
 Such a process is described by Fierz-David (““ Farbenchemie,”’ 1920, p. 44), the separa- 
 tion of the two acids depending on the sparing solubility of the acid potassium salt 
 of G-acid. 
 
 142 oms. of finely powdered f-naphthol is added slowly to 420 gms. of 100 per cent. 
 sulphuric acid, which is well stirred. The temperature is kept between 30° and 35°. 
 Stirring is continued until a sample on dilution with a little water no longer gives a 
 precipitate. If this point is not reached in two days, a little more monohydrate is — 
 added, or, very cautiously, some 15 per cent. oleum. The solution is now poured into 
 1 litre of water and neutralised with chalk or milk of lime, the calcium sulphate being 
 then filtered off. The potassium salts are then formed by adding to the filtrate, 
 either potassium carbonate (about 150 gms.) or the cheaper commercial 90 per cent. 
 potassium sulphate, until the calcium is completely precipitated as carbonate or 
 sulphate, which is filtered off. The solution of potassium salts is evaporated to 
 400 c.c., and sufficient hydrochloric acid (about 100 gms.) added to make it strongly 
 mineral acid. On cooling, the acid potassium salt of G-acid separates in fairly pure 
 condition and, after standing for a day, is filtered off, washed with a little 10 per cent. 
 potassium chloride solution, and well pressed. The mother liquor, containing the 
 R-salt, is either salted out with 150 gms. of salt or is used directly for azo dyes. 
 
 The yields obtained are 160 gms. of G-salt (as acid potassium salt, M.W. 341), and 
 145 gms. of R-salt (M.W. 341). 
 
 A different method of separation is proposed in E.P. 210120 (C. L. Masters, 
 Southern Dyestuffs Co., U.S.A.), and is claimed to give very pure G- and R-salts. 
 
 \ 
 
DERIVATIVES OF B-NAPHTHOL 189 
 
 It depends on the facts that the dipotassium salt of G-acid is very sparingly soluble in 
 a concentrated solution of the dipotassium salt of R-acid, and that on boiling the 
 dipotassium salt of R-acid with excess of calcium hydroxide, an almost insoluble 
 basic calcium potassium salt is precipitated. 
 
 B-Naphthol (1,152 Ibs.) is sulphonated with 34 to 4 parts of sulphuric acid (66° Bé) 
 for forty-eight to sixty hours at about 60°. The finished sulphonation melt is run 
 into sufficient water to make a 20 per cent. sulphuric acid solution, 1,392 lbs. of 
 potassium sulphate added, and the solution boiled for a short time. Sufficient milk 
 of lime (made from about 2,300 Ibs. of quicklime) is then added to neutralise the acid, 
 and the calcium sulphate filtered off. The filtrate, which contains the potasstum 
 salts of the sulphonic acids, is concentrated to the point of incipient crystallisation, 
 filtered to remove a little calcium sulphate and allowed to cool. The G-salt, which 
 crystallises out, is filtered off, washed free of R-salt by means of a little saturated 
 potassium sulphate solution, and dried. 
 
 The filtrate is boiled up for a short time with milk of lime, made from about 170 lbs. 
 of quicklime. The basic calcium potassium salt of R-acid which precipitates is 
 filtered off, washed free of soluble impurities, and suspended in 3,500 lbs. of water. 
 Sulphuric acid is added to precipitate the calcium as sulphate, which is filtered off. 
 The R-salt is then salted out from the filtrate by adding 525 Ibs. of common salt. 
 
 R-acid is used as an end component in a large number of mono-, dis-, and trisazo 
 dyes. The mono- and disazo dyes are generally red in shade. 
 
 G-acid is also used as an end component in the same classes of azo dyes as those 
 for which R-acid is used, though to a much smaller extent. The shades produced are 
 yellower than those produced from R-acid, a difference expressed in the naming of the 
 acids (G@=gelb, R=rot). G-acid is further applied in the preparation of a diphenyl- 
 naphthylmethane colour (Wool Green 8) by condensing it with Michler’s hydrol. 
 
 2-Naphthylamine-3 : 6-disulphonic acid (Amido-R-acid)— 
 
 : Ore Bn 
 
 post Je SO,H 
 
 —and 2-Naphthylamine-6 : 8-disulphonic acid (Amido-G-acid)— 
 
 Oe, 
 ~ 
 eee 
 ae 
 —can be prepared by heating R-acid and G-acid respectively with ammonia and 
 ammonium sulphite (Bucherer reaction). 
 
 Amido-R-acid is applied both as a first and as an end component in azo dyes, 
 but chiefly in the latter capacity, since diazo compounds couple readily with it in 
 the 1-position. 
 
 Amido-G-acid, on the other hand, is useless as an end component, owing to the 
 presence of the sulpho group in the 8-position, which practically inhibits coupling with 
 
190 INTERMEDIATES FOR DYESTUFFS 
 
 diazo compounds. It is, however, used as a first component in polyazo dyes. Its 
 largest application is to the preparation of Gamma-acid, which is described on p. 194. 
 
 f-Naphthylamine— a Gis , 
 
 ea 
 
 —crystallises from water in lustrous leaflets, m.p. 112°, b.p. 294°. It has no smell. 
 It is sparingly soluble in cold, but easily in hot water, and in alcohol and ether. It 
 is moderately volatile in steam. | 
 
 Its hydrochloride, C,,H,.NH,.HCl, forms leaflets, easily soluble in water and 
 alcohol. Its sulphate, (C,,H,NH,),.H,SO,, is sparingly soluble in water. Its acetyl 
 compound melts at 134° to 136°. . 
 
 6-Naphthylamine is prepared by Bucherer’s method (J. pr. Chem. [2], 69, 88; 
 G.P. 117471) from f-naphthol by heating 100 parts of the naphthol with 150 parts 
 of 40 per cent. ammonium sulphite solution and 100 parts of 20 per cent. ammonia in 
 an, autoclave with stirrer at 150° for eight hours. The pressure developed is about 
 6 atmospheres. On cooling, the 6-naphthylamine separates as a solid cake, which 
 is broken up, filtered, and washed with water. The crude product contains some 
 unchanged f-naphthol and some £6’-dinaphthylamine : 
 
 ry 
 KY ort babs 
 
 It is purified by dissolving in water and the necessary hydrochloric acid (free from 
 sulphuric acid), filtermg from undissolved f-naphthol, and precipitating as sulphate 
 by adding a concentrated solution of sodium sulphate. After standing for some time 
 to complete the precipitation, the sulphate is filtered off, washed with cold water, and 
 dried. The base may be isolated by stirring the sulphate with water, and a slight 
 excess of sodium carbonate, but the sulphate is generally used directly for the pre- 
 paration of B-naphthylaminesulphonic acids, etc. A further purification, especially 
 from dinaphthylamine (b.p. 471°), can be carried out by vacuum distillation of the 
 base. The yield is about 85 per cent. 
 
 With a view to lessening the cost of production of f-naphthylamine, it has been 
 proposed by Campbell (J. Soc. Dy. Col., 1922, 38, 114), and by Galbraith, ete. 
 (E.P. 184284), to use instead of pure f-naphthol the crude melt obtained by the 
 fusion. of naphthalene-f-sulphonic acid with caustic soda (p. 160). This, of course, 
 contains sodium sulphite formed in the fusion, and it is only necessary to add an 
 ammonium salt in order to obtain the mixture of f6-naphthol, ammonium sulphite, 
 and ammonia required for the amidation. The process, as described in the above 
 patent, is carried out as follows: An autoclave is charged with 4,800 gms. of the 
 crude naphthol melt, 2,953 gms. of ammonium chloride, 2,617 c.c. of aqueous ammonia 
 (D 0-880), and 9,280 c.c. of water. It is then heated at 170° for fourteen hours, the 
 maximum pressure being 180 lbs. After cooling, the excess of ammonia is blown off 
 and the f-naphthylamine isolated, as already described. Any unchanged f-naphthol 
 
 ’ ad ee <a p A 
 ise ROSY nig a a , ee ae : 
 lk eet ti a ee en Nh, Peo ye Danley ah, Wn 
 
DERIVATIVES OF B-NAPHTHOL 191 
 
 is removed by two extractions with caustic soda solution. The base is then distilled 
 under reduced pressure, and a 79-7 per cent. yield of 6-naphthylamine obtained. 
 
 £-Naphthylamine is used as an end component in a few azo dyes. It is also used 
 in naphthylating Rosaniline, thus producing blue dyes analogous to the Aniline Blues, 
 A vat dye, Indanthrene Red BN, is made by condensing f-naphthylamine with 
 1-chloroanthraquinone-2-carboxylic acid, the condensation taking place between the 
 amino group of the £-naphthylamine and the chlorine atom. The formation of the 
 dyestuff is further explained on p. 212. The main use for f-naphthylamine consists 
 in its sulphonation to the 6 : 8- and 5 : 7-disulphonic acids from which Gamma- and 
 J-acids are prepared. This is dealt with in the following pages. 
 
 Sulphonation of B-Naphthylamine. 
 
 While f-naphthylaminesulphonic acids can, in several cases, be prepared by 
 amidation of the corresponding 6-naphtholsulphonic acids—e.g., Bronner acid (p. 187), 
 amido-F-acid (p. 177), Amido-R-acid (p. 189), Amido-G-acid (p. 189), the sulphona- 
 tion of f-naphthylamine provides an equally convenient method of preparing some 
 of these acids, and in addition makes possible the preparation of certain sulphonic 
 acids, which cannot be obtained through the sulphonation of B-naphthol. Thus, 
 while 2-naphthylamine-6 : 8-disulphonic acid (Amido-G-acid) can be prepared by 
 either method, 2-naphthylamine-5 : 7-disulphonic acid can only be obtained by the 
 sulphonation of f-naphthylamine. It is principally with the object of preparing 
 these two disulphonic acids that the sulphonation of f-naphthylamine is carried out 
 on the manufacturing scale, though 2-naphthylamine-1 : 5-disulphonic acid and the 
 3:6: 8-trisulphonic acid are also made in this way and used to some extent. The 
 6:8- and 5:7-disulphonic acids are required for the preparation of Gamma-acid 
 (2-amino-8-naphthol-6-sulphonic acid) and J-acid (2-amino-5-naphthol-7 -sulphonic 
 acid) respectively, two widely used intermediates for azo dyes. The sulphonation of 
 £-naphthylamine will, therefore, be considered from the point of view of the prepara- 
 tion of these two disulphonic acids. 
 
 £-Naphthylamine is sulphonated by three to four times its weight of 94 to 100 per 
 cent. sulphuric acid to a mixture of monosulphonic acids, whose composition varies 
 with the temperature of sulphonation (Green and Vakil, J.C.S., 1918, 118, 35). At 
 temperatures under 100°, a mixture of the 5- and 8-sulphonic acids (about 60 per cent. 
 of the 5- and 40 per cent. of the 8-acid) with traces of the 6- and 7-sulphonic acids 18 
 formed. At temperatures of 150° and upwards about equal proportions of the 6- and 
 7-sulphonic acids are obtained. The 8-sulphonic acid slowly transforms to the 5-acid 
 on long heating in sulphuric acid solution. The monosulphonic acids are almost 
 insoluble in water, but their sodium salts are readily soluble. The 8-acid may be 
 separated from the others by the insolubility of its sodium salt in 90 to 95 per cent. 
 alcohol, the sodium salts of the others being soluble (G.P. 29084, Dahl and Co.). 
 
 Disulphonation is obtained by the use of a large excess of oleum. The published 
 information on this point is chiefly due to Fierz-David (“ Farbenchemie,” 1920, 
 pp. 45-51; second edition, 1923, p. 43; Helv. Chim. Acta, 1923, 6, 1146), who has 
 
192 INTERMEDIATES FOR DYESTUFFS 
 
 shown that disulphonation can be carried to completion at about 55°, when a mixture 
 of the 6: 8- and the 5 : 7-disulphonic acids, together with some | : 5-disulphonic acid 
 isformed. These may be separated under certain definite conditions by the difference 
 in solubility of the acids in dilute sulphuric acid, the 6 : 8-disulphonic acid being the 
 least soluble and the 1 : 5-acid the most soluble. An improved method of separation 
 is obtained by using a larger excess of sulphuric anhydride and sulphonating finally 
 at 85°, when the 5:7- and 1: 5-disulphonic acids are converted into the 1:5: 7- 
 trisulphonic acid, while the 6 : 8-disulphonic acid remains unaffected. The 6: 8- 
 disulphonic acid is then readily separated from the much more soluble trisulphonic 
 acid. The latter, on heating its dilute sulphuric acid solution to the boil, loses the 
 l-sulphonic acid group by hydrolysis, yielding the 5:7-disulphonic acid. The 
 relations between the various sulphonic acids are indicated by the following scheme : 
 
 S 
 ae NH, 
 ree 
 
 avai 
 | ) a a ik a \NH, 
 y } Aas er 
 _ en S gf DE NH, 80 y De: 
 S a 
 a (i NH a iY Sa 
 
 Ne ba 
 
 (S = SO,H) 
 
 2-Naphthylamine-6 : 8-disulphonie acid (Amido-G-acid): 
 HO,S 
 
 Oe. 
 HOG 
 
 art 
 The acid crystallises with 4H,O in small fine needles. Solutions of its salts show a 
 strong blue fluorescence. 
 2-Naphthylamine-5 : 7-disulphonic acid : 
 
 HO,S/ \” \NH, 
 
 we 
 
 xy 
 
 The acid crystallises with 5H,O in lustrous leaflets from water and in long needles from 
 
 hydrochloric acid solutions. Solutions of its salts, if pure, show a green fluorescence, 
 
 but this is easily masked by the blue fluorescence of any 6 : 8-disulphonic acid present. 
 (2-Naphthylamine-1 : 5-disulphonic acid, when pure, shows a red fluorescence.) 
 
DERIVATIVES OF B-NAPHTHOL 193 
 
 The following table gives the solubilities of the acids and their salts expressed as 
 grams of substance in 100 grams of solution at 20° : 
 
 2:5: 7-Acid. | 2:6:8-Acid. 
 H,A + 5H,O ie »- 23-0 | H,A + 4H,O 9-2 
 Na,A + 6H,O ot ark aa Na,A + 3H,O 59-0 
 NaHA + 4H,O a) eee cae NaHA + 4H,0 7:5 
 K,A + 2H,0 “fi :. 684 K,A + 2H,0 51-6 
 KHA + 4H,0 fe Nee Mes KHA + 2H,0 2°5 
 MgA + 8H,O Gf See acl MgA + 8H,O 8-7 
 CaA + 4H,O ae .. 40-2 CaA + 3H,O 29-1 
 BaA + 3H,O oe Pepe 28 | | BaA + 3H,O 12-0 
 
 These two acids are best prepared by direct sulphonation of f-naphthylamine, as 
 described by Fierz-David (loc. cit.). The naphthylamine may either be sulphonated 
 to the disulphonic acids, when a mixture of the 6: 8- and 5: 7-acids, together with 
 some 1: 5-acid, results, these being then separated by their differences in solubility, 
 or sulphonation may be carried further, when the 5: 7- and 1: 5-disulphonic acids 
 are converted into the 1:5: 7-trisulphonic acid, while the 6: 8-disulphonic acid is 
 unaffected. The latter method of so-called exhaustive sulphonation is preferable for 
 the reasons already explained (p. 192). It is carried out as follows: 
 
 Finely powdered f-naphthylamine sulphate (192 gms.=1 gm. mol.) is stirred 
 during ten minutes into 800 gms. of 15 per cent. oleum, the temperature being kept 
 below 50° in order to keep down the proportion of 8-monosulphonic acid formed as 
 faras possible. Stirring is continued at about 50° until monosulphonation is complete, 
 as shown by a test portion dissolving to a clear solution in dilute soda. This usually 
 takes about fifteen minutes. The solution is now cooled to 40° and 350 gms. of 66 per 
 cent. oleum added within fifteen minutes. The temperature is then maintained at 
 55° for a day, by which time disulphonation should be complete. On the following 
 day, the temperature is raised to 85° slowly and kept at this point for eight hours to 
 form the 1:5: 7-trisulphonic acid. The solution is then cooled to 50° and poured 
 with good stirring into a mixture of 800 gms. of ice-water and 1,100 gms. of ice. 
 When all is added, the temperature of the solution should be about 60°. On cooling, 
 and allowing to stand for six hours at 20°, the 6 : 8-disulphonic acid separates com- 
 pletely and is filtered off and pressed. 
 
 The filtrate is then boiled for four hours (b.p. 125°), the volume being kept up, 
 when the 1:5: 7-trisulphonic acid loses its l-sulpho group by hydrolysis and, on 
 cooling and allowing to stand for two days at 0°, the 5 : 7-disulphonic acid separates. 
 It is filtered off and pressed. 
 
 The final filtrate contains about 22 gms. of sulphonic acids per litre, which are not 
 recovered. 
 
 For purification, the press-cake of the 6 : 8-acid is dissolved in about 700 c.c. of 
 boiling water and 70 gms. of salt added to the solution, which then sets to a solid 
 mass of the acid sodium salt of the 6: 8-acid. After standing for twelve hours, this 
 is filtered off, pressed, and dried. The press-cake of the 5: 7-acid is dissolved in 
 five times its weight of water and precipitated as acid sodium salt with half its weight 
 
 of salt. 
 13 
 
194 INTERMEDIATES FOR DYESTUFFS 
 
 The yield of 6: 8-acid obtained corresponds to 30 gms. of nitrite, and that of 
 5 : T-acid to 26 gms. of nitrite, or a combined yield of 81 per cent. 
 
 Another method of preparing 2-naphthylamine-6 : 8-disulphonic acid is described 
 on p. 189, where its application as an intermediate for azo dyes is also given. 
 2-Naphthylamine-5 : 7-disulphonic acid is not used as a dyestuff intermediate, but 
 serves for the preparation of J-acid (p. 195). 
 
 2-Amino-8-naphthol-6-sulphonic acid (Gamma-acid): 
 
 HO 
 Gaye 
 Pe Liege 
 
 The acid forms very sparingly soluble needles. The alkali and alkaline earth salts 
 are readily soluble. The lead salt forms sparingly soluble needles. 
 
 This acid is readily prepared from the sodium salt of 2-naphthylamine-6 : 8- 
 disulphonic acid by heating it with concentrated caustic soda at high temperatures, 
 usually in an autoclave (Cassella and Co., G.P. Anm. C 3063; E.P. 16699 of 1889). 
 _ The disulphonate, which should be fairly free from salt, is heated with twice its weight 
 of 50 per cent. caustic soda solution at 190° to 195° for six hours in a stirring autoclave. 
 After cooling, the melt is diluted with water, and the solution acidified with mineral 
 acid, when the Gamma-acid is precipitated. 
 
 The strength and purity of Gamma-acid, as with other aminonaphtholsulphonic 
 acids (see H-acid, p. 171) are estimated by (1) coupling a weighed quantity in alkaline 
 solution with a standard solution of a diazo compound, and (2) titrating a second 
 sample in weak acid solution with standard nitrite solution. The two results should 
 agree closely. | 
 
 Gamma-acid can be coupled with diazo compounds in two ways: (1) i in alkaline 
 solution, when coupling takes place in the o-position to the hydroxyl group; (2) in 
 weak acid solution, when coupling takes place in the o-position to the amino group 
 (the 1-position). It is, therefore, capable of forming two different azo dyes with the 
 
 same first component : 
 eh N—R 
 
 R—N= (Y bi Gee 
 HO,8 Ve HO,S\ A 
 
 Examples of both kinds are made, generally in conjunction with diamines of the benzi- 
 dine series as first components. But those of the first class (I) are the more valuable, 
 because in them the amino group of the Gamma-acid part of the molecule can be 
 diazotised and coupled with a new end component. This last diazotisation and 
 coupling are usually carried out on the fibre, the original dye being said to be “ devel- 
 oped.” In this way a number of valuable blacks and browns are produced on cotton, 
 using various developers such as m-phenylenediamine, f-naphthol, ete. 
 
DERIVATIVES OF £8-NAPHTHOL 195 
 2-Phenylamino-8-naphthol-6-sulphonic acid (Phenylgamma-acid) : 
 
 HO 
 /S\/NNH.OH, 
 
 | ) 
 
 The acid is practically insoluble in water, but its salts are mostly soluble. 
 
 This substance is obtained from Gamma-acid by an application of the Bucherer 
 reaction. According to Fierz-David (‘‘ Farbenchemie,” 1920, p. 127), 224 gms. of 
 100 per cent. Gamma-acid is heated with 200 gms. of aniline, 750 gms. of sodium 
 bisulphite solution (25 per cent. SO,), and 750 c.c. of water under reflux for twenty- 
 four hours. The solution is then made distinctly alkaline with sodium carbonate, 
 excess aniline distilled off with steam, and the residual solution acidified with hydro- 
 chloric acid, when phenylgamma-acid is precipitated. The yield is about 270 gms. 
 of 90 per cent. acid or a yield of 90 per cent. 
 
 The hydroxyl group is unaffected in this reaction, owing to the presence of a 
 sulpho group in the m-position, in accordance with the rule elucidated by Bucherer 
 (p. 140). 
 
 Phenylgamma-acid is used as an end component in several complex azo dyes, the 
 coupling being effected in alkaline solution. 
 
 2-Amino-5-naphthol-7-sulphonic acid (J-acid): 
 
 HOS oe 
 a ‘\ 
 
 The acid forms a pale grey crystalline powder, sparingly soluble in cold water, rather 
 more soluble in hot water. The salts are soluble, and their solutions show a blue 
 fluorescence. 
 
 It is prepared from 2-naphthylamine-5 : 7-disulphonic acid by a method similar to 
 that used for Gamma-acid (G.P. 75469, Badische). 
 
 Phenyl-J-acid— 
 ne, I as 
 eat 
 
 HO 
 
 —is prepared from J-acid by the same method as that used for preparing Phenyl- 
 gamma-acid from Gamma-acid. 
 
 J-acid resembles Gamma-acid (p. 194) in forming two sets of dyes, according to 
 whether it is coupled with diazo compounds in alkaline or in acid solution. It is, 
 therefore, used like Gamma-acid for the preparation of developing colours. 
 
 J-acid also possesses the remarkable property of conferring on polyazo dyes, of 
 which it is an end component, the ability to dye cotton without the aid of a mordant. 
 Phenyl-J-acid also possesses this property, and both intermediates are used as end 
 
196 INTERMEDIATES FOR DYESTUFFS 
 
 components in several trisazo dyes which, though not containing benzidine derivatives, 
 or other diamines as first components, are direct cotton colours. 
 2-Hydroxy-3-naphthoic acid (8-Oxynaphthoic acid): 
 
 /\/ oH 
 Goes 
 
 The acid crystallises in leaflets, m.p. 216°. It is almost insoluble in cold water, but is 
 sparingly soluble in hot water, moderately in benzene and chloroform, and easily 
 soluble in alcohol and ether. Its sodium salt is soluble in water. 
 
 This substance is prepared by the action of carbon dioxide on dry sodium f-naph- 
 tholate in the same manner as salicylic acid is prepared from sodium phenate (p. 96). 
 Presumably sodium f-naphtholcarbonate is first formed. The temperature required 
 for its conversion to the 3-naphthoic acid is much higher than that required for salicylic 
 acid, being 200° to 250° (G.P. 50341, Heyden). If the naphtholcarbonate is heated 
 at 130°, 2-hydroxy-l-naphthoic acid is formed (m.p. 156° to 157°), a very unstable 
 substance which readily loses carbon dioxide and reverts to 6-naphthol. 
 
 According to U.S.P. 1450990 (Shorey), the yield and quality of the oxynaphthoic 
 acid are much improved by working at the upper temperature limit, 250°, since 
 B-naphthol is formed from the naphtholate to some extent, and the presence of this is 
 deleterious by hindering contact of carbon dioxide with the sodium compound, and by > 
 promoting the formation of more f-naphthol. By working at 250°, however, any 
 B-naphthol formed is at once vaporised, and can be removed from the autoclave, 
 condensed, and returned to it later. A pressure of 50 lbs. per sq. in. is maintained in 
 the autoclave. 
 
 A method of purifying the technical product 1 is described by Strohbach (Ber., 
 1901, 34, 4142). 
 
 B-Oxynaphthoic acid is used as an end component in a few monoazo colours, which 
 are applied as lake pigments. Its main use, however, is for the preparation of its 
 anilide and similar derivatives, of which a description follows. 
 
 2-Hydroxy-3-naphthoic anilide (Naphthol AS)— 
 
 nee 
 
 se ahh 
 
 —colourless leaflets, m.p. 243° to 442°, soluble in hot glacial acetic acid and nitro- 
 benzene, sparingly soluble in alcohol. 
 
 This is prepared by condensation of aniline with 2-hydroxy-3-naphthoic acid in an 
 indifferent solvent, using phosphorus trichloride, phosphorus oxychloride, thionyl 
 chloride, etc., as condensing agents. The following method is given by G.P. 293897 
 (Griesheim-Elektron). 
 
 A suspension of 188 parts of 2-hydroxy-3-naphthoic acid in toluene is stirred with 
 93 parts of aniline and 60 parts of phosphorus trichloride slowly dropped in. The 
 mixture is then boiled under reflux until free amine is no longer present. After 
 
DERIVATIVES OF B-NAPHTHOL 197 
 
 making faintly alkaline with sodium carbonate, the toluene is distilled off with steam 
 and the residual naphthoic anilide filtered off, washed, and dried. It is obtained as a 
 colourless powder. 
 
 Substantially the same method is described in G.P. 294799 (Meister Lucius and 
 Briining), where the yield of anilide is given as 91 per cent. 
 
 Other arylamides of 6-oxynaphthoic acid are made in a similar manner—e.g., 
 the m-nitroanilide (Naphthol AS-BS), the «-naphthalide (Naphthol AS-BO), and the 
 p-anisidide (Naphthol AS-RL). 
 
 Naphthol AS and the other members of this series are used in producing insoluble 
 azo colours on cotton in much the same way as f-naphthol is used. But they have 
 the advantage that they possess definite affinity for cotton, so that after steeping the 
 cotton in an alkaline solution of Naphthol AS, etc., it need only be squeezed before 
 passing on to the solution of diazotised base. The dyeings produced are also fuller, 
 more level and brighter than those obtained with B-naphthol. 
 
 «-Nitroso- 8-naphthol— NG 
 ( ae j OH 
 er 
 
 —a light yellow powder, or brownish-yellow crystals, m.p. 112°, almost insoluble in 
 water, but soluble in organic solvents. It is best crystallised from hot ligroin (D 0-71 
 to 0-72). 
 
 This substance is prepared by dissolving f-naphthol in water and the necessary 
 amount of caustic soda so as to make approximately a 10 per cent. solution, adding a 
 slight excess of sodium nitrite, cooling to 0°, and dropping into the well-stirred solution 
 dilute sulphuric acid until the solution is permanently acid to Congo paper, the 
 temperature being kept about 0°. The nitrosonaphthol separates at once. It is 
 filtered off, washed acid-free with cold water, and air-dried. The yield is almost 
 quantitative. The light yellow powder obtained soon darkens in colour, and the 
 substance should be freshly prepared as required. 
 
 It is used to some extent as a dyestuff, but is chiefly applied to the preparation of 
 1-amino-2-naphthol-4-sulphonic acid. 
 
 1-Amino-2-naphthol-4-sulphonic acid: 
 
 NH, 
 
 (Y 
 
 ale 
 ae: 
 
 The acid crystallises in needles (+1H,O), almost insoluble in cold water, and sparingly 
 soluble in hot water. Its sodium salt is soluble in water, and the solution quickly 
 becomes brown in the air, owing to oxidation. 
 
 The preparation of this substance by the action of sodium bisulphite on nitroso-f- 
 naphthol is described by Boéniger (Ber., 1897, 27, 23). The nitroso-f-naphthol first 
 combines with bisulphite to form a soluble naphtholhydroxylaminesulphonate. On 
 
198 INTERMEDIATES FOR DYESTUFFS 
 
 addition, of acid to the solution, reduction and intramolecular transformation take 
 place, with formation of the aminonaphtholsulphonic acid : 
 
 a 
 NO A Kiso NH, 
 VASP eS (Ne SO 
 OO" > (= (0) 
 Sah 
 
 ae 
 
 A 6 to 7 per cent. paste of 1 part of nitroso-f-naphthol is rubbed with 3 to 4 parts 
 of cold 40 per cent. bisulphite solution. The nitroso compound quickly dissolves, 
 except for a little resinous matter, which is removed by filtration. The solution is 
 then warmed to 30° to 40° and 3 to 4 parts of hydrochloric acid (21° Bé) added. The 
 solution should then be strongly mineral acid. On allowing it to stand the amino- 
 naphtholsulphonic acid separates out, and is filtered off, washed, and dried. 
 
 1-Amino-2-naphthol-4-sulphonic acid is used as a first component in a number of 
 monoazo dyes, which are, therefore, ortho-hydroxyazo compounds, and as such are 
 specially suited for development on the fibre (wool) by afterchroming to produce fast 
 black and blue-black dyeings. The diazotisation of 1-amino-2-naphthol-4-sulphonic 
 acid requires special conditions, in particular the presence of a copper salt, since if 
 diazotisation is carried out in the usual way internal condensation takes place with — 
 formation of a diazo-oxide, which does not couple with amines or phenols. 
 
CHAPTER XIII 
 PHTHALIC ANHYDRIDE AND ITS DERIVATIVES 
 Phthalic anhydride— _co 
 
 a 
 jes eae 
 
 NY 
 
 —crystallises in long white needles, m.p. 131°, b.p. 284:5°, D, 1-527. It sublimes 
 readily. Itis sparingly soluble in water (by which it is slowly converted into phthalic 
 acid), but is moderately soluble in alcohol, benzene, toluene, etc. 
 
 Phthalic acid forms rhombic crystals, melting at about 200°, and at the same time 
 losing water, and being converted into the anhydride. 
 
 Phthalic anhydride is prepared by the oxidation of naphthalene, either (1) with 
 sulphuric acid in presence of mercury as catalyst, or (2) with air, using certain metallic 
 oxides, such as vanadium pentoxide, as catalysts. 
 
 (1) Oxidation with Sulphuric Acid.—This process, depending on the use of mercury 
 as catalyst, was discovered by E. Sapper, and was patented in 1896 by the Badische 
 Anilin- und Soda-Fabrik (G.P. 91202, E.P. 18221 of 1896). A fairly detailed descrip- 
 tion of the process has been given by Dr. H. Levinstein (J. Soc. Dyers, 1901, 17, 139). 
 
 The oxidation is carried out in a shallow covered iron pan fitted with a stirrer 
 which just scrapes the bottom, and a wide outlet pipe leading to a condenser. In 
 this pan the mercury catalyst is first prepared by heating 4 kg. of mercury with 120 kg. 
 of 100 per cent. sulphuric acid until all the sulphuric acid has distilled over. A pre- 
 viously prepared solution of 350 kg. of naphthalene in 3,675 kg. of sulphuric acid 
 (66° Bé) and 1,050 kg. of 23 per cent. oleum is then run into the oxidation pan in 
 portions of 22 litres and heated at 290° to 295°, so that each portion distils over in 
 thirteen to seventeen minutes, Oxidation of the naphthalene takes place in accord- 
 ance with the equation : 
 
 ais 
 C,,H, 4- 9SO, = C,H, O + 980, + 2CO, +. 2H,O 
 re 
 
 Charring also occurs to some extent, with a resulting increase in the proportion of 
 carbon dioxide in the evolved gases. The carbon dioxide content of the gases is 
 determined at intervals, and, when it reaches 0-6 to 0-8 per cent., the addition of 
 naphthalene solution is interrupted. The accumulated carbon is oxidised off as far 
 as possible by distilling a quantity of 66° Bé sulphuric acid from the pan, which is 
 then ready for further additions of the naphthalene solution. When the carbon 
 dioxide content reaches 1 per cent., the quantity of accumulated carbon in the pan 
 is such that it is necessary to stop the process and clean out the pan. 
 
 In the condenser phthalic anhydride and diluted sulphuric acid collect, the sulphur 
 dioxide being passed on to the sulphuric acid plant (contact process), where it is 
 reoxidised to sulphur trioxide and used again. The phthalic anhydride is separated 
 from the diluted sulphuric acid by decanting and centrifuging, and is washed free of 
 
 acid. It is then dried and sublimed. 
 199 
 
200 INTERMEDIATES FOR DYESTUFFS 
 
 (2) Oxidation with Air.—The oxidation of naphthalene in the vapour phase by 
 air in presence of catalysts has been developed into a manufacturing process in 
 U.S.A. by Gibbs and others (original patents : U.S.P. 1285117; E.P. 119518). Manu- 
 facturing details have not been published, but an account of the laboratory experi- 
 mental work is given by Conover and Gibbs (J. Ind. Eng. Chem., 1922, 14, 120) and 
 much of the physical data required for the process is given in a series of papers in the 
 same journal by Monroe (1919, 11, 1116, 1119; 1920, 12, 969). 
 
 In these experiments, hot air was passed through boiling naphthalene, and the 
 mixture of naphthalene vapour and air passed through a tube containing the catalyst 
 heated to a suitable temperature. The vapours leaving the catalyst were condensed, 
 and the product worked up for phthalic anhydride. The substances found to be 
 most active as catalysts were oxides of certain metals of the fifth and sixth periodic 
 groups, particularly vanadium pentoxide and molybdenum trioxide. 
 
 In attempting to use oxygen alone, it was found that if the temperature rose above 
 300° with vanadium pentoxide as catalyst or 350° with molybdenum trioxide, ignition 
 of the naphthalene vapour, sometimes with violent explosions, was apt to occur. On 
 the other hand, if the temperature was kept at a safe point below these limits, only a 
 slight amount of oxidation took place. Using air, however, the temperature could 
 be raised to 500° without danger of ignition, and oxidation to phthalic anhydride was 
 a maximum at about 450°. 
 
 Some typical results obtained, using vanadium pentoxide as catalyst, are given 
 in the following table : 
 
 Naphthalene— 
 is ee | Anhydride Produced Anhydride in Yield of Anhydride 
 Piece Nip ese} Tost per Hour Product on C,H, Attacked 
 (per Cent.).| (per Cent.). | (per Cent.). (Gina.): | (per. Cenh}e (par Vea 
 61-9 14:5 23-6 1-24 86-9 83-5 
 54:8 19-0 26-2 0-99 80-6 78-5 
 55:6 21-7 22-7 1-15 76-0 81-8 
 
 The oxidation product contained, besides phthalic anhydride, some unchanged 
 naphthalene, a little benzoic acid (about 1 per cent.), minute traces of naphthols, some 
 brown matter, and substances of sharp irritating odour, these last being apparently 
 naphthaquinones. The phthalic anhydride was isolated by fractional sublimation. 
 Moisture and naphthalene pass over at lower temperatures than phthalic anhydride, 
 and could be separated quite sharply. The phthalic anhydride could then be sublimed 
 away from the brown matter, etc., which was less volatile. Another method of 
 purification consisted in dissolving the product in carbon tetrachloride, adding a 
 decolourising charcoal, filtering and cooling in successive stages, when the phthalic 
 anhydride crystallised out, leaving the naphthalene in solution. 
 
 Further investigations of the oxidation of naphthalene vapour by air in presence 
 of vanadium oxide have been made by Weiss, Downs, and Burns (J. Ind. Eng. Chem., 
 1923, 15, 965), and by T. Kusama (Nippon Kwagaku Kwai Shi, 1923, 44, 605). 
 
‘ACINGAHNV OIIVHLHd AO SHAILVATHAC—IX LYVHO 
 
 0 ZHN HOOO'*HO'S 
 ‘ i HOOD 
 
 t t pied he 
 
 ort ye ele) 
 ae cee e3 0” ne ° Ae 
 fHO le) me (oe) 
 
202 INTERMEDIATES FOR DYESTUFFS 
 
 The chief use of phthalic anhydride was formerly for the preparation of Indigo 
 through anthranilic acid and phenylglycine-o-carboxylic acid, of which particulars are 
 given later in thischapter. Itis apparently still used for this purpose, but the alterna- 
 tive preparation of Indigo from aniline through phenylglycine (p. 65) has diminished 
 the importance of phthalic anhydride in this connection. At the same time, increasing 
 application has been found for it as a source of anthraquinone and its derivatives. 
 Several examples of this are given at the end of this chapter. 
 
 As a direct intermediate for dyestuffs, it is used in the preparation of 
 phenolphthalein, of the Fluorescein dyes (Eosine, Rose Bengal, etc.), and of the 
 Rhodamines. 
 
 Dichlorophthalic anhydrides : 
 
 Cl Cl | 
 —co a’ S—co ci” S—co 
 No No So 
 —co”% SEL Bal py ea cil I-co~ 
 a A NEY 
 3: 6-Dichloro- 3: 4-Dichloro- 4:5-Dichloro- 
 
 (M.p. 191°, b.p. 339°) (M.p. 120° to 121°, b.p. 329°) (M.p. 185° to 187°, b.p. 313°) 
 
 A mixture of these three substances is formed when chlorine is passed through a 
 solution of phthalic anhydride in oleum, iodine being present. The preparation is 
 described by Villiger (Ber., 1909, 42, 3529). 
 
 A solution of 600 gms. of phthalic anhydride and 2 gms. of iodine in 3,240 gms. of 
 23 per cent. oleum is vigorously stirred and a slow stream of chlorine passed, while the 
 temperature is gradually raised from 40° to 60°. The rate of passage of the chlorine 
 is so regulated that only traces of chlorine or sulphur trioxide escape. When the 
 increase in weight of the solution amounts to 580 gms., which requires about forty 
 hours, the chlorsulphonic acid formed is distilled off up to 250°. The residual solution, 
 on cooling, sets to a mass of crystals. Knough ice is carefully added to precipitate 
 the mixed anhydrides, which are then filtered off. The mixture obtained is composed 
 of about 50 per cent. of the 3: 6-, 30 to 35 per cent. of the 3 : 4- and 15 to 20 per cent. 
 of the 4:5-dichloro compound. For the manufacture of dyestuffs they are not 
 separated, as they give closely similar products. 
 
 It is possible, however, to separate 3 : 6-dichlorophthalic acid from the other two 
 compounds, owing to the insolubility of the zinc salts of the latter. The paste of 
 mixed chloro compounds obtained, as described above, is stirred into 4 litres of hot 
 water, which hydrolyses the anhydrides to the acids. The sulphuric acid present is 
 precipitated by adding barium chloride, and after filtering off the barium sulphate the 
 filtrate is exactly neutralised with sodium carbonate. The solution is then boiled out, 
 and a concentrated solution of zinc chloride added. After heating for an hour, the 
 precipitated zinc salts are filtered off. A solution of calcium chloride is then added 
 to the boiling filtrate until no further precipitate of calcium 3 : 6-dichlorophthalate is 
 formed. This is filtered off, converted into the acid by hydrochloric acid, and isolated 
 by extraction with ether. The acid is then converted into anhydride by heating it 
 just below its melting-point. 
 
PHTHALIC ANHYDRIDE AND DERIVATIVES — 203 
 
 The 3: 4- and 4: 5-dichlorophthalic acids are more difficult to separate from one 
 another. 
 
 Using a similar method of preparation, but working with 50 per cent. oleum at 
 60° to 70°, Pratt and Perkins (J. Am. Chem. Soc., 1918, 40, 216) obtained from 1,500 
 gms. of phthalic anhydride a calcium precipitate of 974 gms. and a zinc precipitate 
 of 1,746 gms. The yields of the anhydrides, however, were much lower than would 
 correspond with these figures. 
 
 Tetrachlorophthalic anhydride— 
 
 Cl 
 aay 
 Cl 00. 
 cal Ico” 
 or 
 C4 
 
 —crystallises in prisms or needles, m.p. 255° to 257°. It is insoluble in cold water, 
 and sparingly soluble in ether. The corresponding acid crystallises with $H,0, and 
 is converted into the anhydride on heating at 109°. 
 
 The preparation is carried out by the method of Juvalta (G.P. 50177). Ina cast- 
 iron pan 10 kg. of phthalic anhydride, 30 kg. of 50 to 60 per cent. oleum and 0-5 kg. 
 of iodine are mixed and chlorine is passed in at 50° to 60°. The chloro compound 
 mostly separates as it is formed, causing the mass to become thick. The temperature 
 is gradually raised to 200°, and when at this temperature all the iodine has been 
 converted into iodine chloride, the reaction is over. Most of the chlorsulphonic acid 
 is then distilled off, and enough ice is added to the residue to reduce the temperature to 
 below 50°. The tetrachlorophthalic anhydride is filtered off, washed, and dried. 
 
 Dichloro- and tetrachlorophthalic anhydrides are used in the preparation of Kosin 
 dyes (Rose Bengal, Phloxine, etc.), which are bluer in shade and more brilliant than 
 those prepared from the unchlorinated phthalic anhydride. 
 
 Phthalimide— 
 
 S20 
 
 ‘NH 
 ‘i si 
 | co 
 
 —m.p. 234°. It sublimes readily. 
 
 This is prepared from phthalic anhydride by heating with ammonia or ammo- 
 nium carbonate. The former method is described by Levinstein (J. Soc. Dyers, 
 1901, 17, 139). 
 
 In a cast-iron pan 650 parts of phthalic anhydride are melted and, while ammonia 
 is slowly passed through, gradually raised to 140° during four hours. During the 
 next seven to eight hours the temperature is raised to 170°. It is then raised to 240°. 
 About 70 to 75 parts of ammonia are required, and the process lasts about eighteen 
 hours in all. The molten phthalimide is then run off, and when cool is ground to a 
 fine powder. The yield is 635 parts. 
 
 A convenient laboratory method is to heat 50 gms. of phthalic anhydride with 
 60 gms. of ammonium carbonate to 225° in a flask immersed in an oil-bath. At 100° 
 water and carbon dioxide escape, and the mass melts. Towards the end it again 
 
204 INTERMEDIATES FOR DYESTUFFS 
 
 solidifies. It is then dissolved in boiling water, the solution filtered, and, on cooling, 
 phthalimide crystallises out (Mohlau and Bucherer, “‘ Farbenchemisches Praktikum,” 
 p- 289). 
 
 Phthalimide is used for the preparation of anthranilic acid. 
 
 Anthranilic acid: 
 ( yi 
 \ NH, 
 
 The acid crystallises in colourless leaflets, m.p. 144:6°. 100 parts of water at 13-8° 
 dissolve 0:35 part. 100 parts of 90 per cent. alcohol at 9-6° dissolve 10-7 parts. 
 Solutions of the acid and its salts show a blue fluorescence. 
 
 This substance is usually prepared by the action of sodium hydroxide and sodium 
 hypochlorite on phthalimide (Hofmann transformation) : 
 
 CO COONa 
 OHA |. NE + 3Na0H + NaOCl = CHK + Na,CO, + NaCl + H,0 
 
 2 
 
 The preparation is described in G.P. 55988 (Badische): 1 part of finely powdered 
 phthalimide is covered with a cold solution of 2 parts of caustic soda in 7 parts of 
 water, and allowed to stand for an hour, during which the phthalimide is hydrolysed 
 to sodium phthalamate : 
 
 /oO-NEs 
 
 PMN Goons 
 
 The solution is then stirred and 10 parts of hypochlorite solution, containing 5-06 per 
 cent. NaOCl, is run in. The temperature rises to 50° to 60°. The solution is then 
 warmed for a few minutes to 80°, at which temperature the transformation is quickly 
 completed. After cooling, the solution is nearly neutralised with hydrochloric or 
 dilute sulphuric acid. It is then acidified with acetic acid, when most of the anthra- 
 nilic acid precipitates and is filtered off. The remainder can be precipitated from the 
 filtrate as the insoluble copper salt by adding copper sulphate solution. 
 
 The industrial application of this method is described by Levinstein (J. Soc. Dyers, 
 1901, 17, 139) thus: 500 parts of phthalimide are dissolved in a cold solution of 
 144 parts of chlorine in 640 parts of caustic soda solution (40° Bé) and 440 parts of 
 water. The solution is filtered and, while stirring, is saturated with sulphur dioxide. 
 On adding 600 parts of hydrochloric acid, anthranilic acid separates. 
 
 Anthranilic acid can also be prepared in good yield (80 to 85 per cent.) by oxidation 
 of acet-o-toluidide with permanganate (G.PP. 119462, 94629). re 
 
 Besides its application as a stage in the production of Indigo from phthalic 
 anhydride, anthranilic acid is used as a first component in several monoazo colours, 
 which are chiefly used as lake pigments. It is also condensed with chloroanthra- 
 quinones to produce o0-carboxyphenylaminoanthraquinones, which are further 
 condensed to anthraquinoneacridone derivatives (Indanthrene Violet RN and Red 
 Violet 2RN). 
 
PHTHALIC ANHYDRIDE AND DERIVATIVES 205 
 
 Phenylglycine-o-carboxylic acid : 
 \cooH 
 \ sce, c008 
 
 The acid forms a sandy powder, melting at 207° with decomposition. Itis moderately 
 soluble in hot water, alcohol, ether, and glacial acetic acid, but almost insoluble in 
 benzene. 
 
 This substance can be prepared by the action of anthranilic acid on chloroacetic 
 acid.) In Heumann’s patent (G.P. 56273), the two acids are heated together, with or 
 without water, at about 100° for one to two hours. Under these conditions, however, 
 some decomposition of the phenylglycine-o-carboxylic acid occurs. G.P. 127178, 
 therefore, recommends the use of the sodium salts of the acids, these being heated in 
 
 solution at a temperature of not over 40°, in order to avoid formation of anthranilo- 
 diacetic acid : 
 COOH 
 
 oH 
 NH(CH,.COOH), 
 
 An acid sodium salt of phenylglycine-o-carboxylic acid is formed, which is insoluble in 
 the cold mixture, and is filtered off. By this method the reaction takes several days 
 to complete. 
 
 Haller (J. Ind. Eng. Chem., 1922, 14, 1040) finds that the formation of anthranilo- 
 diacetic acid can be avoided by using excess of anthranilic acid (2 molecules of 
 anthranilic acid to one of chloroacetic acid), and carries out the preparation as 
 follows : 
 
 25 gms. of anthranilic acid is stirred with 150 c.c. of water, containing 22-4 gms. 
 of sodium carbonate (2-33 mols.) and 8-6 gms. of chloroacetic acid dissolved in 50 c.c. 
 of wateradded. The mixture is heated and stirred at 90° for one hour. After cooling, 
 the solution is acidified with hydrochloric acid, and allowed to stand for twenty-four 
 hours. The phenylglycine-o-carboxylic acid which separates is filtered off and 
 washed with water. Unchanged anthranilic acid is recovered from the mother 
 liquor by dissolving 70 gms. of sodium acetate in it and allowing the solution to stand 
 overnight. The yield of phenylglycine-o-carboxylic acid is 68-6 per cent. or, allowing 
 for the anthranilic acid recovered, 83-3 per cent. 
 
 Another method of preparation of phenylglycine-o-carboxylic acid, developed by 
 H. T. Bucherer and the Badische Anilin- und Soda-Fabrik, depends on the following 
 series of reactions : 
 
 NH, //NE.CH, 805Na 
 
 (1) CHC | +  HO.CH,S0,Na_ ——> CHC + H,0 
 COONa Formaldehydebisulphite COONa 
 
 //NH.CH,S0,Na /NH.CH,.ON 
 
 (2) CoH + NaCN ——> OH, + Na,SO, 
 COONa - \ cOONa 
 NH.CH,.ON me ees og NH O00Na 
 
 3) C,H + a + ——> < + 
 
 Be Sandie : * *\cooNa : 
 
206 INTERMEDIATES FOR DYESTUFFS 
 
 The method is described by Mohlau and Bucherer (“ Farbenchemisches Prak- 
 tikum,” p. 289) : 
 
 7-5 c.c. of 40 per cent. formaldehyde solution (0-1 mol.) and 20 c.c. of sodium 
 bisulphite solution (38° Bé, 0-1 mol.) are mixed and heated for about a quarter of an 
 hour until the smell of formaldehyde has disappeared. ‘To the neutral solution of 
 sodium hydroxymethylsulphonate so formed, a concentrated solution of 15-9 gms. 
 (0-1 mol.) of sodium anthranilate is added and the mixture heated on the water-bath 
 until the solution no longer contains diazotisable matter. About half to three-quarters 
 of an hour is required for this reaction. A solution of 7 gms. of potassium cyanide in 
 25 c.c. of water is now added and heating continued at 70° to 80° for a further quarter 
 of an hour to form the nitrile, which can then be precipitated by acidifying with 
 acetic acid. 
 
 The nitrile can be formed from anthranilic acid in one operation without the use 
 of bisulphite as follows: Anthranilic acid (14 gms.=0-1 mol.) is suspended in 50 c.c. 
 of benzene, and 7 gms. of potassium cyanide, powdered as finely as possible, is added. 
 7-5 c.c. of 40 per cent. formaldehyde is then added with shaking. Much heat is 
 developed, and the potassium salt of the nitrile is formed in the aqueous layer. 
 
 The upper benzene layer is then separated, and the syrupy aqueous solution of 
 the nitrile treated with 20 c.c. of 40 per cent. caustic soda solution. The mixture is 
 heated cautiously till hydrolysis sets in with vigorous evolution of ammonia. When 
 this slackens, the solution is further boiled until the ammonia is completely driven off, 
 the volume of the solution being maintained by addition of water. The cooled pale 
 blue solution is carefully neutralised with concentrated hydrochloric acid, using 
 phenolphthalein as indicator. It is then acidified with 15 c.c. glacial acetic acid, and 
 after allowing to stand for some time, the phenylglycine-o-carboxylic acid is filtered 
 off, washed, and dried. 
 
 Phenylglycine-o-carboxylic acid is used for the manufacture of Indigo. 
 
 Thiosalicylic acid— 
 Ae nee 
 
 L su 
 
 —pale yellow crystals, m.p. 164° to 165°. 
 This is prepared by the action of sodium disulphide on diazotised anthranilic acid 
 and reduction of the dithiosalicylic acid so formed (G.P. 205450, Kalle and Co.) : 
 
 :( \cooH fe - ( COOH HOGG 
 + a, 
 _N:N.Cl "a —N:N—S—S—N:N—( ) 
 \cooH HOOC/ / \cooH 
 AR Pomel oh ( [| g g u Reduction Lat 
 
 137 kg. of anthranilic acid are stirred with 500 litres of water and 240 kg. of con- 
 centrated hydrochloric acid, ice is added, and diazotisation carried out in the usual 
 way by running in a strong solution of 69 kg. of sodium nitrite. The diazo solution is 
 
PHTHALIC ANHYDRIDE AND DERIVATIVES — 207 
 
 let flow into a well-stirred solution of 33-6 kg. of sulphur and 260 kg. of sodium sulphide 
 in 260 litres of water, to which has been added 120 kg. of caustic soda solution (40° Bé) 
 and 300 kg. of ice. The temperature during addition of the diazo solution is not to 
 exceed 5°. Nitrogen is evolved and the temperature of the mixture rises to 15° to 25°, 
 dithiosalicylic acid being formed. After several hours the solution is acidified with 
 hydrochloric acid, the precipitated dithiosalicylic acid filtered off, and washed with 
 1,000 litres of water. It is then dissolved by boiling it with water and 60 kg. of soda 
 ash, filtered from sulphur, and the filtrate boiled with 60 to 100 kg. of iron powder 
 (or the equivalent in zinc dust) until a sample, treated with caustic soda and filtered, 
 on acidifying no longer smells of hydrogen sulphide, but gives a precipitate easily and 
 completely soluble in cold alcohol. The mixture is then treated with 120 kg. of caustic 
 soda solution (40° Bé), again boiled up, filtered from iron, etc., and the filtrate acidified 
 with hydrochloric acid, when thiosalicylic acid is precipitated as a colourless or pale 
 yellow precipitate. After cooling, this is filtered off and washed. 
 
 Thiosalicylic acid is used in the preparation of phenylthioglycol-o-carboxylic acid. 
 
 Phenylthioglycol-o-carboxylic acid— 
 
 ( Nee 
 '$.CH,.COOH 
 
 eS gs 
 —white crystals, m.p. 213°. 
 
 This is prepared by the action of chloroacetic acid on thiosalicylic acid, the reaction 
 proceeding smoothly with no such side reactions as occur in making the analogous 
 phenylglycine-o-carboxylic acid. 
 
 A solution of 15-4 kg. of thiosalicylic acid in water and 24 kg. of caustic soda 
 solution (40° Bé) is treated with a solution of 9-5 kg. of chloroacetic acid in water and 
 the necessary sodium carbonate. The mixture is gently warmed. On addition of 
 acid, phenylthioglycol-o-carboxylic acid separates as white crystals, which are filtered 
 off, washed, pressed, and dried (G.P. 192075, Kalle and Co.). 
 
 It is used in preparing 2-hydroxythionaphthen and its carboxylic acid. 
 
 2-Hydroxythionaphthen-1-carboxylic acid— 
 
 /\c(OH 
 | j 'Sc.coon 
 os 
 
 —m.p. 213°. Sparingly soluble in cold water, more soluble in alcohol. 
 2-Hydroxythionaphthen (Thioindoxy])— 
 
 /“~ (0H) 
 ' \ 
 | aoe cH 
 oa 
 —m.p. 71°. 
 
 These two substances are readily prepared by alkali fusion of phenylthioglycol-o- 
 carboxylic acid, internal condensation taking place with formation of the sodium 
 salt of the hydroxythionaphthencarboxylic acid. This sodium salt is fairly stable, 
 
208 INTERMEDIATES FOR DYESTUFFS 
 
 but on acidification the acid formed readily loses carbon dioxide to form hydroxythio- 
 naphthen : 
 
 OH 
 bee 
 \_ /S—CHs COOH 
 
 20 kg. of phenylthioglycol-o-carboxylic acid is stirred with a little water and added 
 at about 100° to a mixture of 100 kg. of caustic soda and 20 litres of water. The tem- 
 perature is then raised to 170° to 180° and kept at this point for an hour. The cooled 
 melt is dissolved in water and made slightly acid, avoiding rise of temperature. The 
 precipitated hydroxythionaphthencarboxylic acid is filtered off and pressed. 
 
 To obtain hydroxythionaphthen, the acidified solution is heated until evolution of 
 carbon dioxide ceases. On cooling, hydroxythionaphthen crystallises out and is 
 filtered off (G.P. 192075, Kalle and Co.). 
 
 Hydroxythionaphthen and its carboxylic acid are used in the preparation of 
 Thioindigo Red. 
 
 “™ C(O \ .C(OH 
 —> | ) Sc.coon eds ( | ox 
 Scena SO ra 
 
 Anthraquinone Derivatives from Phthalic Anhydride. 
 
 Phthalic anhydride can be condensed with various benzene derivatives to form 
 anthraquinone derivatives either (1) directly, under the influence of a condensing ~ 
 agent, such as sulphuric acid or boric acid, or (2) by an application of the Friedel- 
 Crafts reaction, using aluminium chloride, a benzoylbenzoic acid derivative is first 
 formed, and this, when acted on by dehydrating agents, condenses internally to form 
 an anthraquinone derivative. Quinizarin (1: 4-dihydroxyanthraquinone) is best 
 prepared by the first method, while anthraquinone itself and 6-methylanthraquinone 
 
 are obtained by the second method. 
 OH 
 Gans 
 
 Quinizarin— 
 \\00/ YG 
 
 —yellowish-red leaflets or red needles, m.p. 198°, almost insoluble in water, but 
 soluble in caustic alkalies to an intense blue-violet solution. It is soluble in benzene 
 and ether, the solution in the latter showing a greenish-yellow fluorescence. 
 
 The method of preparation is described in G.P. 255031 (Bayer), p-chlorophenol 
 being condensed with phthalic anhydride in sulphuric acid solution, in presence of 
 boric acid. The chlorine atom is replaced by hydroxyl during the condensation. 
 The action of the boric acid is not understood, but it is quite essential since, without it, 
 the yield of quinizarin is only 4 to 5 per cent. 
 
 To 400 parts of 96 per cent. sulphuric acid are added 80 parts of phthalic anhydride, 
 20 parts of boric acid, and 23 parts of p-chlorophenol. The mixture is heated at 150° 
 for three hours, and is then raised to 180° to 200°, at which temperature it is kept 
 
PHTHALIC ANHYDRIDE AND DERIVATIVES 209 
 
 until the quinizarin formation is complete, as shown by the solution no longer deepen- 
 ing in colour. After cooling, the solution is poured into 20 parts of water, filtered, 
 and the residue boiled up with a large proportion of water. The quinizarin is then 
 filtered off and dried. The yield is 70 to 80 per cent. 
 
 Another method of preparing quinizarin is described on p. 231. 
 
 Quinizarin is used for the production of acid wool colours by condensation with 
 p-toluidine and sulphonation of the products, when the sulpho groups enter the tolyl 
 nuclei. Only one of the hydroxyl groups of quinizarin can be replaced conveniently 
 by direct action of p-toluidine on quinizarin, and the sulphonated product constitutes 
 Alizarin Irisol. Thereplacement of both hydroxy] groups by tolylamino is more easily 
 accomplished if lewcoquinizarin (prepared by reduction of quinizarin with sodium 
 hydrosulphite and caustic soda) is used, and the product oxidised. The resulting 
 dyestuff is Alizarin Cyanine Green. 
 
 Anthraquinone : es 
 cl 18 
 (For properties, etc., see p. 216.) 
 
 The synthesis of anthraquinone from phthalic anhydride and benzene has been 
 described by Heller (Zezt. angew. Chem., 1906, 19, 669; Ber., 1908, 41, 3631). 
 
 A mixture of 1 kg. of phthalic anhydride, 3-5 kg. of benzene, and 1:8 kg. of alu- 
 minium chloride, is stirred in a lead-lined pan fitted with a reflux condenser, and is 
 slowly warmed. At 30°, hydrochloric acid begins to come off, and the mass becomes 
 _ thicker as the temperature rises, until eventually the stirrer is stopped. Heating is 
 continued at 70° until evolution of hydrochloric acid ceases. The mass is then 
 cooled, diluted with 3 to 4 parts of water, and the unchanged benzene distilled off with 
 steam. ‘The residue is made alkaline by gradual addition of caustic soda, and the 
 liquid boiled for several hours to decompose the aluminium compounds into alumina, 
 and to form the sodium salt of benzoyl-o-benzoic acid : 
 
 ae," we 
 Joon l 
 
 After filtering, the solution is acidified, which precipitates the benzoylbenzoic acid. 
 The yield is 95 to 97 per cent. 
 
 This is then converted into anthraquinone by heating with 5 to 6 parts of sulphuric 
 acid at 150° for an hour, the yield on this stage being quantitative. 
 
 f-Methylanthraquinone— 
 | ( Sue Ose 
 yee 
 
 —pale yellow needles, m.p. 177°, soluble in acetic acid and benzene, but sparingly 
 
 soluble in ether. 
 14 
 
210 INTERMEDIATES FOR DYESTUFFS 
 
 The method of preparation here is similar to that used for anthraquinone, but, as 
 described by Heller (loc. cié.), differs in a few details. 
 
 Finely powdered phthalic anhydride (50 gms.) is dissolved in 200 gms. of dry 
 toluene by heating. After cooling the solution, 75 gms. of aluminium chloride is 
 gradually added, and the mixture stirred for five hours at the ordinary temperature. 
 When evolution of hydrochloric acid has ceased, the mixture is warmed for an hour on 
 the water-bath. It is then cooled, ice added, and the excess of toluene distilled off with 
 steam. The residual liquid contains a semi-solid cake of crude toluyl-o-benzoic acid : 
 
 ( bass ( bi 
 SOAET ON 
 
 The aqueous liquid is poured off and the solid dissolved as far as possible in sodium 
 carbonate. The filtered solution is acidified with hydrochloric acid and, after stand- 
 ing, the precipitated toluyl-o-benzoic acid is filtered offand dried. The yieldis 75 gms. 
 It is dissolved in 730 gms. of 20 per cent. oleum, and the solution warmed for one and a 
 half hours on the water-bath. It is then poured on ice, and the filtered methylan- 
 thraquinone purified by boiling with dilute soda. 
 
 B-Methylanthraquinone is used chiefly for the preparation of 2 : 2’-dimethyl-1 : 1’- 
 dianthraquinonyl, which readily undergoes internal condensation to pyranthrone, an 
 
 orange vat dyestuff of valuable properties. For the preparation of the dimethyldian- — 
 
 thraquinonyl two methods have been described—(1) by nitration of B-methylanthra- 
 quinone to the «-nitro derivative, reduction of this to the amino compound, diazotisa- 
 tion of the latter and treatment of the diazo compound with copper Rae : 
 
 co. No 
 Cor — CO 0 
 ——_—>> SMA OR 
 \A\¢9% v Nor NBOM SWZ NG ae 
 Cae Ne Ce 
 eran a 
 NY ONG \ Neo 
 ~~ e 
 \7\c07 
 
 (2) by chlorination of £-methylanthraquinone to 1-chloro-2-methylanthraquinone 
 and condensation of 2 molecules of this by copper powder in a high-boiling solvent : 
 
 OC — COO" — Ga 
 
 > = a8 
 
 \7\c07 6 WONG ZN?” \co% 
 Be an, 
 
PHTHALIC ANHYDRIDE AND DERIVATIVES 211 
 
 The intermediate amino- and chloro-derivatives are prepared as follows : 
 
 1-Amino-2-methylanthraquinone.—Red crystals, m.p. 202°, insoluble in water, 
 but soluble in alcohol, ether, benzene, and glacial acetic acid. 
 
 (a) Nitration: This is described by Romer and Link (Ber., 1883, 16, 695). Toa 
 cooled solution of 2 parts of B-methylanthraquinone in six to seven times its weight of 
 sulphuric acid, 1 part of potassium nitrate (or the equivalent of sodium nitrate) is 
 gradually added. The nitro compound separates as a greenish-yellow crystalline 
 mass which, after twenty-four hours, is poured into water and the yellow precipitate 
 filtered off. It is washed, and boiled with alcohol until the extract is pale yellow. 
 It may be purified by crystallisation from glacial acetic acid, and is obtained as yellow 
 _ erystals, m.p. 269° to 270°, sparingly soluble in alcohol and benzene, but soluble in 
 xylene, nitrobenzene, and aniline. 
 
 (0) Reduction: This was effected by Romer and Link with stannous hydroxide, 
 but sodium sulphide, the usual reducing agent for nitro compounds of the anthra- 
 quinone series, is preferable (G.P. 131873, Badische; Scholl and Holdermann, Ber., 
 1907, 40, 1696). 
 
 The nitro compound (1 part) is boiled with 34 parts of crystallised sodium sulphide 
 and 20 parts of water for an hour. The amino compound is obtained fairly pure in 
 this way, but is purified if necessary by crystallisation from glacial acetic acid. 
 
 I-Chloro-2-methylanthraquinone,—Pale yellow crystals, m.p. 176°, sparingly 
 soluble in cold alcohol, but moderately soluble in boiling alcohol, and easily soluble 
 in benzene and toluene. 
 
 B-Methylanthraquinone in weak oleum solution can be chlorinated with chlorine 
 gas (H.P. 207840, Thomas and Scottish Dyes). It is, of course, advantageous in this 
 case to start with toluyl-o-benzoic acid (p. 210), and effect the condensation to methyl- 
 anthraquinone and chlorination of the latter in one operation. 
 
 39 parts of toluyl-o-benzoic acid is heated with 350 parts of 5 per cent. oleum in 
 the usual way to form £-methylanthraquinone (p. 210). This condensation being 
 complete, 0-35 part of iodine is added, and dry chlorine is passed through the solution 
 at 50° to 60° until the required increase in weight is attained, allowing for the solu- 
 bility of chlorine in oleum. A more efficient control of the reaction is obtained by 
 drawing samples from time to time, and taking the melting-point of the isolated 
 product. When the melting-point falls below 150°, the chlorine is slowed off and the 
 percentage of chlorine in the subsequent samples determined. When the chlorine 
 content reaches 13:8 to 14-0 per cent., the passage of chlorine is stopped. The 
 melting-point of the sample at this stage is usually 140° to 149°. By pouring the 
 _ Solution into ice, the chloromethylanthraquinone is precipitated, and can be isolated 
 in the usual way. 
 
 Another method of chlorinating 8-methylanthraquinone, by sulphury] chloride in 
 presence of iodine as catalyst, is described in G.P. 269249 (A.G.F.A.). 
 
 A mixture of 3 parts of 6-methylanthraquinone, 5 parts of nitrobenzene, 0-2 part 
 of iodine, and 3 to 4 parts of sulphuryl chloride is heated on the water-bath under 
 reflux. Sulphur dioxide and hydrochloric acid are evolved, and the reaction is 
 complete in eight to ten hours. After distilling off any unchanged sulphury] chloride, 
 
212 INTERMEDIATES FOR DYESTUFFS 
 
 on cooling the chloromethylanthraquinone separates in star-shaped needles, which 
 are filtered off. A further quantity can be obtained from the mother liquor by dilution 
 with alcohol. 
 
 1-Chloroanthraquinone-2-carboxylic acid: 
 
 Cl 
 CO 
 Ge te COOH 
 : N Re 
 
 The preparation of this substance is described in the above-mentioned patent of 
 Thomas and Scottish Dyes. 
 
 Instead of isolating the chloromethylanthraquinone, the solution is cooled, and 
 350 parts of sulphuric acid added. Water is then slowly added until the acid strength 
 is about 80 per cent. This precipitates some chloromethylanthraquinone. Finely 
 powdered manganese dioxide (95 parts) is now added, and the mixture heated to 
 110°, at which point it is kept for some hours. When oxidation is complete, the 
 solution isrun into water. Ifany unchanged manganese dioxideis left, this is removed 
 by adding bisulphite solution and boiling up. The solution is then cooled and the 
 carboxylic acid filtered off. It can be purified by solution in dilute alkali and reprecipi- 
 tation with acid. The yield obtained (from 35 parts of toluyl-o-benzoic acid) is — 
 30 to 32 parts. 
 
 1-Chloroanthraquinone-2-carboxylic acid is used in preparing a red vat dye, 
 Indanthrene Red BN, by condensing it with f-naphthylamine, and further con- 
 densing the product to an acridone derivative : 
 
 OG ec Ug 
 
 : SoA : ane WX ee 
 / (OY eee (YOY 88 ee. 
 aa ee 
 Gans Wage \ Nee 
 
CHAPTER XIV 
 ANTHRACENE AND ANTHRAQUINONE DERIVATIVES 
 
 Anthracene— 
 Lad se 
 
 Gas 
 
 et SCE 
 
 —crystallises in white tables, showing a blue-violet fluorescence ;m.p. 218°, b.p. 340°; 
 insoluble in water, sparingly soluble in alcohol: solubility at 15-5° in benzene 1-04 per 
 cent., in acetone 0-55 per cent., in light pyridine 0-85 percent. Solutions of anthracene, 
 on standing in sunlight, deposit a polymeride, para-anthracene, (C,,H,,)., which melts 
 at 244°, passing at the same time back into anthracene. 
 
 Anthracene is obtained from the solid which separates on allowing the fraction of 
 coal tar distilling between 270° and 400° to stand for several days. This solid is 
 separated from the residual oil by the centrifuge and by hot pressing. It then contains 
 40 to 45 per cent. of anthracene associated mainly with carbazole and phenanthrene. 
 Various processes are used, or have been proposed, for its purification. The most 
 convenient seems to be that which depends on successive treatments with pyridine 
 bases, since the solubility of carbazole at the ordinary temperature in that solvent is 
 about 12 per cent., and that of phenanthrene about 25 percent. Thecrudeanthracene 
 is heated up with a few times its weight of pyridine bases to about 100°, when the 
 whole dissolves, and, on cooling, almost all the anthracene crystallises out. It is 
 separated by the centrifuge, and the pyridine treatment repeated. In regular opera- 
 tion of this process, fresh pyridine is used for the second treatment, while for the first 
 treatment the mother liquor from the second treatment is used. In this way a 
 product containing about 90 per cent. of anthracene is obtained. This is further 
 purified to a slight extent by subliming with steam at 200°, and this operation also has 
 the advantage of converting the anthracene into a finely divided form well adapted 
 for subsequent conversion to anthraquinone. 
 
 Special attention has been given in recent years to processes in which purification 
 of the anthracene is combined with separation of pure carbazole. Thus Kinzlberger 
 and Co. (H.P. 144648 and 144656) heat crude anthracene with coal-tar naphtha and 
 80 per cent. caustic potash for several hours at 120°. The naphtha solution of 
 anthracene, etc., is drawn off from the solid potassium carbazole compound, and the 
 anthracene crystallises out on cooling. Again, A. Kagan (E.P. 172864) first partly 
 purifies the crude anthracene by crystallisation from hot cresols, followed by washing 
 with petrol ether. The anthracene is then recrystallised from pyridine, carbazole being 
 obtained from the mother liquor by distilling off the pyridine and recrystallising the 
 residue from toluene, followed by sublimation. Crude anthracene of 46 per cent. 
 strength treated in this way is said to give an 89 per cent. anthracene and a carbazole 
 of 96 to 98 per cent. purity. 
 
 Anthracene is used almost entirely for the preparation of anthraquinone, but a vat 
 dye of subsidiary importance, Indanthrene Olive G, is also made from it. 
 
 213 
 
214 INTERMEDIATES FOR DYESTUFFS 
 
 Substitution Products of Anthracene. 
 
 Very little information has been published regarding the substitution products of 
 anthracene, such as the anthracene sulphonic acids and chloroanthracenes. But these 
 have evidently been studied technically to some extent with a view to their use in the 
 preparation of the corresponding anthraquinone derivatives, in order to evade certain 
 difficulties in the direct preparation of the latter from anthraquinone. It is of interest, 
 therefore, to note such few and vague details as are available. 
 
 Chloroanthracenes.—When chlorine is passed into a solution or suspension of 
 anthracene in a neutral organic solvent at ordinary temperature, meso-dichloro- 
 
 anthracene— 
 a 
 Ge as 1G 
 
 —-is formed, and is isolated as yellow needles, melting at 209°, and easily soluble in 
 benzene, but sparingly in alcohol and ether. The same compound is obtained by 
 warming a suspension of anthracene in carbon disulphide with sulphur chloride 
 (S,Cl,) until the evolution of hydrochloric acid ceases (Lippman and Pollak, Ber., 
 34, 2786). 
 
 With chlorine at higher temperatures various mixtures of addition and substitution 
 products are obtained. 
 
 Anthracene Sulphonic Acids.—Anthracene is easily sulphonated by ordinary 
 concentrated sulphuric acid to mixtures of mono- and disulphonic acids, which are 
 not easily separated. But, by using sulphuric acid of 67 per cent. strength (53° Bé), 
 according to G.P. 72226, the B-monosulphonic acid is obtained : 
 
 BEBE 
 \4\cH7™ 
 
 100 kg. of anthracene is stirred with 200 kg. of 67 per cent. sulphuric acid at 
 120° to 135° till a test shows almost complete disappearance of the anthracene. The 
 solution is then diluted with 1,000 litres of water, neutralised with soda, and left to 
 crystallise, when the sodium salt of the 6-sulphonic acid separates in greenish iridescent 
 masses. It may be purified by recrystallisation from hot water. 
 
 Another method of sulphonation, leading to a mixture of the a-and f-monosul- 
 phonic acids is described in G.P. 251695 (Bayer): 300 parts of anthracene are 
 dissolved in 600 parts of glacial acetic acid. To the well-cooled solution 200 parts of 
 chlorsulphonic acid are added slowly. When this has all been added, the mixture 
 is quickly heated to 95°, and kept at this temperature for five hours. A clear, light 
 olive solution is obtained. This is poured into 5,000 parts of water, and the sulphonic 
 acids salted out and filtered off. The product is dissolved as far as possible in 
 
 4,500 parts of boiling water, cooled to 40°, and filtered. The filtrate contains the ; 
 
“ANHOVAHINV AO SHALLVAISEHC—IITX LUVHO 
 
 $4% 0 
 
 g rego) 
 oe ioe Ae 
 
 HtoS H*OsS S°OH 
 
 “0 
 Metties-ctho — ofp oe : 
 
216 INTERMEDIATES FOR DYESTUFFS 
 
 a-sulphonate, which can be salted out with 120 parts of salt. From the residue the 
 
 less soluble £-sulphonate can be boiled out with a large volume of water. The yield is 
 
 given as 50 per cent. of the «-sulphonate, and 30 per cent. of the 6-sulphonate. 
 meso-Dichloroanthracenesulphonic Acids: 
 
 (a) The 6-monosulphonic acid— 
 
 S036) 
 
 —is described in G.P. 260562 (Badische) as a yellow powder, somewhat soluble in 
 water, the solutions having a blue fluorescence. It is obtained when dichloro- 
 anthracene (1 part) is stirred into chloroform (100 parts) and chlorsulphonic acid 
 added slowly at 30°, the solution being afterwards kept at 40° for four hours. The 
 same sulphonic acid is said to be produced when oleum is used in place of chlorsul- 
 phonic acid. 
 
 This meso-dichloroanthracene-f-sulphonic acid is used to prepare £-aminoanthra- 
 quinone as follows (G.P. 288996) : 100 parts of a 50 per cent. paste of the acid are 
 heated with 60 parts of copper oxide and 600 parts of 25 per cent. ammonia solution 
 in a stirred autoclave for twenty-four hours at 200°. The crude 6-aminoanthra- 
 quinone is filtered off and the copper, etc., removed by extraction with dilute nitric 
 acid or by recrystallisation of the product from nitrobenzene or other suitable solvent. 
 A particularly pure S-aminoanthraquinone is said to be obtained in this.way. Other 
 oxidising agents, such as manganese dioxide, may be used in place of copper oxide. 
 
 (6) meso-Dichloroanthracene-2:6 and 2:7-disulphonic acids are apparently 
 obtained by sulphonating meso-dichloroanthracene, but no information is available 
 as to how this is carried out. 
 
 The 2: 7-acid yields 2: 7-dichloroanthraquinone when acted on by sodium 
 chlorate and hydrochloric acid (G.P. 228876). 60 kg. of the sodium salt of dichloro- 
 anthracene-2 : 7-disulphonic acid are dissolved in 1,000 litres of water, and 100 ke. 
 of hydrochloric acid (20° Bé) are added, followed by a solution of 50 to 100 kg. of 
 sodium chlorate in 750 litres of water. The solution is heated for twenty-four hours 
 at about 100°. The 2: 7-dichloroanthraquinone precipitates in pure condition. 
 
 bes 
 
 NNO 
 
 —very pale yellow needles, m.p. 284-6°, b.p. 382°. It is insoluble in water, and 
 sparingly soluble in most organic solvents. Glacial acetic acid and nitrobenzene 
 dissolve it fairly well when hot, and it can be conveniently crystallised from these 
 
 solvents. It also dissolves readily in concentrated sulphuric acid, which does not 
 sulphonate it even when hot; the anthraquinone is precipitated unchanged on dilution. 
 
 Anthraquinone— 
 
 ,) 
 + 
 3 
 7 : 
 A 
 b 
 B 
 ee 
 i o 
 
ANTHRACENE AND ANTHRAQUINONE 217 
 
 A characteristic reaction is the formation of a red solution, of the sodium derivative 
 of oxanthranol— 
 
 (OH) 
 C,H 0,H 
 ee ; 
 —on reduction with hydrosulphite and alkali. 
 
 I. Preparation from Anthracene. 
 
 Anthracene can be oxidised to anthraquinone in various ways, of which the best 
 established and the one used industrially is oxidation with chromic acid. Formerly a 
 very crude anthracene was used as starting material, but the tendency now is to 
 employ as pure an anthracene as possible, certainly one of over 90 per cent. strength, 
 obtained in some such manner as that described above. 
 
 (a) Oxidation with Chromic Acid.—The anthracene is oxidised according to the 
 equation : 
 
 CuHiy + NaCr,0, + 4H,SO, = CyH,O, + NaSO, + Cr,(SO,); + 5H,0 
 
 Any phenanthrene present is oxidised to phenanthraquinone. Other impurities 
 mostly oxidise to carbon dioxide and water. The quantity of dichromate required 
 will naturally depend on the proportion of impurities present. 
 
 150 parts of purified sublimed anthracene are stirred into 3,000 parts of water in 
 a lead-lined vessel. 300 parts of sodium dichromate are added, and the solution 
 heated to 80°. 900 parts of 50 per cent. sulphuric acid are then slowly run in over ten 
 to twelve hours, the temperature at the same time being raised to the bouling-point. 
 Some frothing occurs owing to evolution of carbon dioxide, and if the anthracene 
 used is very impure, it may be necessary to work at greater dilution and to add the 
 acid more slowly. After the acid has all been added, the mixture is boiled for some 
 time to complete the oxidation. The progress of the oxidation is tested by filtering 
 and washing a sample and then subliming the solid. Unchanged anthracene appears 
 in the sublimate as silvery leaflets, while anthraquinone forms sharp needles. The 
 solution is also tested from time to time for the presence of chromic acid. 
 
 When oxidation is complete, the reaction mixture is filtered, well washed with 
 water, and dried. (On the manufacturing scale the filtrate is either worked up for 
 chromic sulphate, which is sold to the tanners, or the chromic salt is reoxidised to 
 dichromate. This recovery of the chromium compounds is an important economic 
 feature of the process.) The crude anthraquinone is now partly purified by heating it 
 with two and a half times its weight of 80 per cent. sulphuric acid at 120° for a few 
 hours, which sulphonates any unchanged anthracene and some other impurities which 
 may be present. The solution is then poured into water and the precipitated anthra- 
 quinone filtered off, washed, and dried. A final purification 1s obtained by subliming 
 the product with superheated steam at 240° to 260°. The yield obtained is 106 parts 
 of anthraquinone from 100 parts of anthracene or about 90 per cent. The loss is 
 chiefly due to unoxidised anthracene. For the purpose of estimating the yield, the 
 
218 INTERMEDIATES FOR DYESTUFFS 
 
 anthracene content of the starting material is determined by the Luck method 
 (Lunge, ‘“‘ Technical Methods of Analysis,’ Vol. II., p. 805). 
 
 (b) Oxidation with Nitrogen Oxides.—A number of patents have been taken out 
 for the use of oxides of nitrogen or of nitric acid in the oxidation of anthracene 
 [G.P. 215335, 234289 (H.P. 16312, 1909), 254710, 256623, 268049 (E.P. 11472, 1910)]. 
 
 (c) Use of Oxygen and a Catalyst or Oxygen Carrier.—The Chemische Fabrik 
 Worms Akt. Gesell., ina series of recent patents (H.P. 156215, 156538, 156540, 169145), 
 describe the oxidation of anthracene by oxygen containing a little nitrogen peroxide. 
 For example, in the first patent, 100 kg. of anthracene are mixed with 500 to 1,000 kg. 
 of acetic acid and a small proportion of fuming nitric acid. The mixture is heated to 
 80° to 90° and oxygen is forced in under pressure. Absorption is rapid and oxidation 
 is complete in three to five hours. According to E.P. 156540, the acetic acid solvent 
 may be diluted considerably with other (inactive) solvents, such as water, nitrobenzene, 
 or dichlorobenzene. If acetic acid diluted with 20 per cent. of water is used, the 
 yield of anthraquinone is 95 to 98 per cent. with a purity of 92 to 95 per cent. How- 
 ever, a purer product is obtained if water is excluded, and the water formed in the 
 oxidation is taken up by a suitable agent, such as acetic anhydride, and if also sodium 
 nitrite is substituted for the fuming nitric acid (K.P. 156538). In this case, a 95 per 
 cent. yield of anthraquinone of 99 to 100 per cent. purity is claimed. 
 
 Other catalytic methods are described in G.P. 292681 and U.S.P. 1285117 
 (E.P. 119518, 1917). 
 
 IJ. Synthetic Method. 
 This is described on p. 209. 
 
 Sulphonation of Anthraquinone. 
 
 The great majority of the useful derivatives of anthraquinone are obtained, as 
 the chart on p. 215 indicates, through the sulphonic acids, and the sulphonation of 
 anthraquinone is, therefore, the most important fundamental operation in the prepara- 
 tion of the anthraquinone intermediates. In contrast with anthracene, which is 
 easily sulphonated at comparatively low temperatures by weak sulphuric acids, 
 anthraquinone is unattacked by 96 per cent. sulphuric acid even at 100°, though 
 sulphonation begins at 200°. Oleum of 20 per cent. SO; content and upwards is 
 required for the sulphonation of anthraquinone at more convenient temperatures. 
 When the sulphonation is carried out in the ordinary manner, f-sulphonic acids only 
 are formed—namely, the 2-monosulphonic acid and the 2: 6- and 2: 7-disulphonic 
 acids. For long these were the only anthraquinonesulphonic acids known until the 
 discovery, made simultaneously in 1903 by Iljinskij and Schmidt, that sulphonation 
 in presence of a little mercury salt yielded «-sulphonic acids—that is, the 1-mono- 
 sulphonic acid and the 1 : 5- and 1 : 8-disulphonic acids (but not the 1 : 4-acid). This 
 discovery was of the greatest importance for the development of dyestuffs of the 
 anthraquinone series, since the «-derivatives are, in general, more reactive and more 
 deeply coloured than the #-derivatives. The f-sulphonic acids will be dealt with 
 first. | 
 
ANTHRACENE AND ANTHRAQUINONE 219 
 Anthraquinone- f-sulphonic acid : 
 yet 30 ” wt \s0,H 
 SZ NGO eg) 
 
 The acid forms white leaflets, soluble in water and in alcohol, but insoluble in ether. 
 The sodium salt, C,,H,O,.80,Na,H,O, forms silvery leaflets (it is commonly known 
 as “ silver salt ”), sparingly soluble in cold water, and insoluble in caustic soda solution 
 and in alcohol. 
 
 It has not been found possible to conduct the sulphonation of anthraquinone in 
 such a way that only monosulphonic acid is produced. If the anthraquinone is 
 completely sulphonated, substantial quantities of disulphonic acids are formed. In 
 order to avoid this formation of disulphonic acids as far as possible, the sulphonation 
 is stopped when about 75 to 80 per cent. of the anthraquinone has been attacked. 
 This is achieved by arranging the quantity and strength of the oleum used, so that 
 when most of the anthraquinone has been sulphonated, the oleum will have been 
 _ reduced to monohydrate strength and sulphonation will stop. 
 
 208 parts of finely divided anthraquinone are stirred into 320 parts of 25 per cent. 
 oleum or a quantity of stronger oleum containing an equal amount of free SO;. The 
 temperature is raised slowly, over several hours, to 140°, and kept at this point for 
 eight hours. The melt is then cooled, poured into 6,000 parts of water, and the 
 unchanged anthraquinone (about 50 to 80 parts) filtered off. The f-sulphonic acid 
 may now be separated by neutralising the filtrate with chalk, filtering off the calcium 
 sulphate, converting the calcium sulphonate into sodium salt by careful addition of 
 soda, filtering from calcium carbonate, and evaporating to the crystallising point, 
 when the sodium salt separates on long standing as silvery crystals. 
 
 But, according to Crossley (J. Am. Chem. Soc., 1915, 37, 2178), in this method 
 much of the calcium salt remains adhering to the calcium sulphate and is lost. He 
 obtains better yields by neutralising the acid solution with caustic soda and con- 
 centrating. The manufacturing method is to neutralise about three-eighths of the 
 acid by soda ash, when part of the sodium salt separates, and is filtered off. The 
 filtrate is then evaporated under reduced pressure until it reaches a specific gravity 
 of 1-18 (measured hot). It is allowed to stand, when the main portion of the sodium 
 salt crystallises out. This is filtered off and washed with salt solution. The yield 
 of sodium salt is 140 to 200 parts, depending on the extent to which the anthra- 
 quinone is sulphonated. 
 
 The necessity for leaving some of the anthraquinone unsulphonated is, of course, 
 a weakness and a source of troublein the above process. The anthraquinone recovered 
 is in a slimy condition difficult to filter and to wash free of sulphonic acids. A recent 
 American patent, U.S.P. 1474507, suggests a method ot overcoming this difficulty. 
 When sulphonation has proceeded as far as required, sufficient concentrated sulphuric 
 acid is added to the hot melt to make the ratio of H,SQ, to dissolved (unsulphonated) 
 anthraquinone about 3:1, keeping the temperature about 100° to 110°. The 
 solubility of anthraquinone in 100 per cent. H,SO, at this temperature is about 35 per 
 
220 INTERMEDIATES FOR DYESTUFFS 
 
 cent., while in 85 per cent. H,SO, the solubility is 1-3 per cent. Water is, therefore, 
 added slowly during two hours, keeping the temperature about 110°, until the 
 strength of the sulphuric acid has fallen to 75 per cent., and stirring is continued at 
 this temperature until separation of the anthraquinone is complete. Under these 
 conditions it separates in a crystalline form which, after drowning the charge in water, 
 is easily filtered and washed acid-free. 
 
 The mother liquors contain about 2 per cent. of disulphonic acids—namely, the 
 2: 6- and 2 : 7-acids. 
 
 Anthraquinone-2-sulphonic acid is used in preparing alizarin, f-aminoanthra- 
 quinone, and f-chloroanthraquinone. 
 
 Anthraquinone-2 : 6- and 2: 7-disulphonie acids: 
 
 vA eC \s0,H HO,S/ ap Se ee 
 
 | | 
 nosh ) Realy, a See Ry ie 
 
 (The 2 : 6-acid is sometimes referred to as the «-disulphonic acid, and the 2 : 7- 
 as the f-disulphonic acid, these names being survivals from the time when the con- 
 stitutions of these acids were unknown.) 
 
 The 2: 6-acid forms small yellow crystals, the 2 : 7-acid beautiful yellow plates. 
 Both acids are soluble in water and alcohol, but insoluble in ether and benzene. 
 Generally the salts of the 2 : 6-acid are sparingly soluble and not easily crystallised, 
 while those of the 2: 7-acid are easily soluble and crystallise well. The sodium salt 
 of the 2 : 6-acid crystallises with 7H,O, that of the 2 : 7-acid with 4H,O. 
 
 The sulphonation is usually carried out by heating 100 parts of anthraquinone 
 with 200 to 300 parts of 45 to 50 per cent. oleum at 160° to 170° till a test portion 
 dissolves clear in water, and then continuing the heating for an hour longer in order 
 to convert any monosulphonic acid present into disulphonic acid. These conditions 
 favour the formation of the 2: 6-acid. If a lower temperature is used, more of the 
 2:7 acid is obtained. 
 
 The melt is now poured into water and the solution neutralised by caustic soda. 
 On concentrating the solution a point is reached at which, on cooling, almost all the 
 sodium salt of the 2 : 6-acid separates as a bluish-grey crystalline precipitate, while 
 the 2 : 7-salt and sodium sulphate remain in solution. The latter can be precipitated 
 by alcohol, filtered off, and the 2 : 7-salt obtained by evaporating the filtrate to dry- 
 ness (Crossley, J. Am. Chem. Soc., 1915, 87, 2178). 
 
 The 2: 6-acid is used for making Flavopurpurin, and the 2 : 7-acid for Anthra- 
 purpurin. The corresponding diamino compounds are also made from the acids. 
 
 2-Aminoanthraquinone— at 
 Cee. 
 NN 
 
 —orange-red needles, m.p. 302°. Insoluble in water; soluble in chlorobenzene and 
 nitrobenzene, from which solvents it crystallises well. Its salts with the mineral 
 
ANTHRACENE AND ANTHRAQUINONE 221 
 
 acids are dissociated by water. It dissolves in concentrated sulphuric acid to a yellow 
 solution. Acetyl derivative, yellow, m.p. 262°. 
 
 2-Aminoanthraquinone is prepared by the action of ammonia at a high temperature 
 on anthraquinone-2-sulphonic acid or, rather, its sodium salt, the reaction proceeding 
 according to the equation : 
 
 C,,H,0,,80,Na + 2NH, = C,H,O,NH, + Na(NH,)SO, 
 
 The yields obtained, however, by the use of ammonia alone are usually about 50 per 
 cent. This is ascribed to the reducing action of the sulphite produced on the yet 
 unchanged sulphonate, and various improvements have been proposed which are based 
 on this theory of the course of the reaction. 
 
 (1) In G.P. 256515 (Badische), an oxidising agent is added. 250 parts of a 50 per 
 cent. paste of sodium anthraquinone-f-sulphonate are stirred with 156 parts of 80 per 
 cent. manganese dioxide and 130 parts of water in an autoclave. 580 parts of 25 per 
 cent. ammonia are added, and the mixture is heated at 200° for twenty-four hours. 
 The f-aminoanthraquinone formed is freed from manganese dioxide by treatment 
 with sulphurous acid or sodium bisulphite. The melting-point of the product is 
 given as about 300°, and the yield nearly quantitative. 
 
 Sodium dichromate may be used as oxidising agent in place of manganese 
 dioxide. 
 
 (2) The addition of a salt of a metal which forms an insoluble sulphite is proposed 
 in G.P. 267212 (Meister Lucius and Briining). Barium chloride or the barium salt 
 of the f-sulphonic acid is preferred, the preparation being carried out as follows : 
 4-12 ke. of finely powdered sodium anthraquinone-f-sulphonate are added to a solution 
 of 2-36 kg. of crystalline barium chloride in 3-1 times its weight of water. 20-5 litres 
 of aqueous 25 per cent. ammonia are then added, and the mixture heated for forty- 
 eight hours at 170° to 177°, the pressure developed being 21 to 22 atmospheres. 
 After cooling, the f-aminoanthraquinone is filtered off, and is purified by successive 
 extractions with boiling water, dilute acid, and dilute soda. It is finally crystallised 
 from chlorobenzene. The yield is 2-19 kg. or 73-7 per cent. 
 
 Whether the improved yield obtained by the use of barium chloride is dependent 
 on the formation of insoluble barium sulphite during the reaction is rendered doubtful 
 by some results given in a recent patent (G.P. 347683) of the firm of Geigy. It was 
 found that, although calcium sulphite is insoluble, no improvement in yield was 
 obtained by using calcium chloride. At the same time, however, it was observed that 
 calcium chloride in conjunction with certain other inorganic salts, in particular 
 ammonium chloride, sodium chloride, or magnesium chloride, did give an improved 
 yield of B-aminoanthraquinone, and that, in fact, the use of calcium chloride along 
 with magnesium chloride resulted in a better yield than could be obtained with 
 barium chloride—namely, 80 per cent. 
 
 8-aminoanthraquinone can also be prepared from B-chloroanthraquinone (p. 222), 
 and from meso-dichloroanthracenesulphonic acid (p. 216). 
 
 The chief uses of f-aminoanthraquinone are in the preparation of Indanthrene 
 Blue and Flavanthrene. 
 
222 INTERMEDIATES FOR DYESTUFEFS 
 
 2-Chloroanthraquinone— 
 oroan qu On * és 
 &, \co7% \ 
 
 —very pale yellow crystals, m.p. 210°. Insoluble in water. 
 
 Its preparation is described in G.P. 205195 as follows: 20 kg. of sodium anthra- 
 quinone-f-sulphonate are dissolved in 600 litres of water and 60 litres of hydrochloric 
 acid (20° Bé) at 100°. A solution of 20 kg. of sodium chlorate in 200 litres of water is 
 slowly added, keeping the temperature at 100°, until no further separation of B-chloro- 
 anthraquinone takes place. The chloro compound is filtered off and washed. 
 
 $-Chloroanthraquinone is used for condensations with «-aminoanthraquinones to 
 produce «f-dianthrimides and trianthrimides, which possess better dyeing properties 
 than the corresponding ««-dianthrimides. It hasalso been proposed to make Alizarin 
 from f-chloroanthraquinone by fusion with caustic alkali and an oxidising agent. 
 Lastly, B-aminoanthraquinone may be prepared from it. 
 
 f-Aminoanthraquinone from f-Chloroanthraquinone.—According to G.P. 295624 
 (Badische), the preparation is carried out by heating together 250 parts of 8-chloro- 
 anthraquinone, 4,000 parts of 20 per cent. ammonia, and 8 parts of crystalline 
 copper sulphate in a stirring autoclave at 200° for twenty-six hours. The f-amino 
 compound separates in a pure condition, and is simply filtered off and washed. 
 The yield is nearly quantitative. In absence of the copper salt, the amidation of 
 the chloro body is not complete. 
 
 Anthraquinone-«-sulphonic acid : 
 
 ee: 
 
 The acid forms colourless leaflets, m.p. 214°, soluble in water. The potassium salt 
 forms straw-yellow leaflets, and is sparingly soluble even in hot water. The calcium 
 
 salt crystallises in needles, and is moderately soluble in hot water. The barium, 
 - strontium, and lead salts are almost insoluble in boiling water. The aniline salt 
 forms pale yellow needles, m.p. 291°. The sulphochloride, C,,H,0,.SO,Cl, crystallises 
 from nitrobenzene or toluene in golden yellow prisms, m.p. 218°. 
 
 As already mentioned, anthraquinone can be sulphonated almost exclusively in the 
 a-position if the sulphonation is carried out in presence of a trace of mercury salt 
 (Iljinskij, Ber., 1903, 86, 4194; E.P. 10242 [1903]. R. E. Schmidt, Ber., 1904, 37, 
 66; G.P. 149801, E.P. 13803 of 1903). The following process is founded on that of 
 Schmidt, with modifications due to Fierz-David (‘‘ Farbenchemie,” second edition, 
 1923, p. 179). 
 
 208 gms. of anthraquinone are added with stirring to 300 gms. of 18 per cent. 
 oleum, and immediately followed by 5 gms. of finely powdered yellow mercuric oxide. 
 (It is necessary that the mercuric oxide should be finely divided because the mercuric 
 sulphate formed from it is surprisingly insoluble in sulphuric acid, and a thorough 
 
 distribution of the mercury salt must be obtained so that it may be given every chance 
 
ANTHRACENE AND ANTHRAQUINONE 223 
 
 to exert its directing effect, or the subsequent sulphonation will take place in the 
 B-position.) The mixture is now stirred for an hour at 50°, then a further hour at 120°. 
 Then 50 gms. of 60 per cent. oleum is added drop by drop within a quarter of an hour, 
 the temperature being maintained at 120° for another one and a half hours. These 
 quantities and conditions are such that part of the anthraquinones left unsulphonated, 
 in order to avoid as far as possible the formation of disulphonic acids. The melt is 
 now poured into a mixture of 2,000 c.c. of water and 1,000 gms. ofice. The unattacked 
 anthraquinone separates, and is filtered off (about 55 gms.). To the filtrate is added 
 70 gms. of potassium chloride, after which the potassium salt separates gradually. 
 It is obtained in good crystalline form by stirring the solution for several hours at 60°. 
 It is then filtered off, washed with a little water, and dried. The yield is 170 gms. of 
 potassium salt, or 70 per cent., calculated on the sulphonated anthraquinone. 
 
 The mother liquor contains a few grams more of the «-sulphonate, together with 
 some 1:5- and 1: 8-disulphonates and very little of the 6-sulphonate if the sul- 
 phonation has been properly carried out. 
 
 Anthraquinone-1 : 5- and 1 : 8-disulphonic acids: 
 
 ae a 
 HOX \co% \Z% , SIAC a 
 
 The conditions for the preparation of these acids are similar to those for the 
 a-sulphonic acid, but stronger oleum and a higher temperature are used. 
 
 100 parts of anthraquinone are intimately mixed with 1 part of mercurous 
 sulphate (or yellow mercuric oxide), and the mixture stirred into 200 parts of 44 per 
 cent. oleum. ‘The solution is slowly heated. At about 130° to 140° a reaction begins 
 with evolution of heat. The temperature is so regulated as not to rise above 150° to 
 160°, and is maintained at this point until a test portion of the liquid is found to be 
 completely soluble in water. Heating is continued further until the free SO, has 
 disappeared. Meanwhile, the 1: 5-disulphonic acid has begun to crystallise out. 
 The melt is now cooled to 50° and 75 parts of sulphuric acid (60° Bé or 78 per cent.) 
 added, which completes the separation of the 1: 5-acid. This is filtered off through 
 asbestos, and is purified by dissolving it in hot water and salting out as the potassium 
 salt by means of potassium chloride. The acid filtrate from the 1 : 5-acid is run into 
 water, and to the hot solution sufficient potassium chloride solution is added to form 
 the potassium 1 : 8-disulphonate. On cooling, this separates as pale yellow needles 
 (G.P. 157123, E.P. 13808 of 1903; ef. also E.P. 10242 of 1903). 
 
 The chart at the beginning of this chapter indicates sufficiently the number and 
 variety of the derivatives obtained from the «-sulphonic acids. Those obtained from 
 the «-monosulphonic acid will be dealt with first. 
 
 «-Aminoanthraquinone— NH, 
 a) 
 
 ERVIN. 
 
224 INTERMEDIATES FOR DYESTUFFS 
 
 —dark red prisms with metallic reflex, most conveniently crystallised from xylene. 
 The melting-point of the pure substance is variously stated as 241° (Fierz-David), 
 243° (Ullmann), and 252° (Beisler and Jones, J. Am. Chem. Soc., 1922, 44, 2299). The 
 last-named figure is probably correct. 
 
 In G.P. 273810 (Meister Lucius and Briining), the preparation of «-aminoanthra- 
 quinone is described, following a method similar to that used for the S-compound. 
 300 parts of potassium anthraquinone-«-sulphonate are stirred into 2,700 parts of 
 25 per cent. ammonia and 300 parts of water, 225 parts of crystalline barium chloride 
 
 are added, and the mixture is heated in an autoclave at 180° to 186° for twenty hours. 
 
 The «-aminoanthraquinone is filtered off and washed with alkali to remove certain 
 by-products. It is then boiled with dilute hydrochloric acid to decompose the 
 barium sulphite, filtered, washed, and dried. The yield of «-aminoanthraquinone is 
 90 per cent. 
 
 A more recent patent, E.P. 169667 (1921, S.C.J., Basle), proposes to use an 
 aromatic nitro compound as oxidising agent to deal with the sulphite produced. 
 165 parts of potassium anthraquinone-«-suphonate, 500 parts of 24 per cent. ammonia, 
 and 60 parts of sodium nitrobenzene-m-sulphonate are heated together at 160° to 165° 
 for twelve hours. Pure crystalline «-aminoanthraquinone separates in 80 per cent. 
 yield. Metanilic acid is recovered from the filtrate. 
 
 Other methods available for the preparation of «-aminoanthraquinone are (1) the 
 reduction of «-nitroanthraquinone (p. 235), and (2) the amidation of «-chloroanthra- 
 quinone (p. 229). 
 
 While «-aminoanthraquinone is used in the production of a few vat dyes of the 
 dianthrimide and trianthrimide types obtained by condensation with chloroanthra- 
 quinones, it also serves as the starting material for a number of other intermediates, 
 as indicated in the chart. 
 
 «-Acetylaminoanthraquinone can be prepared in the usual way by warming the 
 amino compound with acetic anhydride. Another method is described in G.P. 211958. 
 10 parts of «-aminoanthraquinone are dissolved in 100 parts of 23 per cent. 
 oleum. 10 parts of acetic anhydride are then added, and the solution stirred at 
 30° to 40° until a test portion diluted with water no longer gives a red but 
 instead a yellow precipitate. The solution is then poured into ice and water with 
 good stirring, so as to avoid local heating, and the precipitate filtered off and 
 washed acid-free. 
 
 a-Benzoylaminoanthraquinone, which forms glistening, greenish-yellow, felted 
 needles, m.p. 255° to 256°, is prepared by heating «-aminoanthraquinone with an equal 
 weight of benzoyl chloride in ten times the weight of nitrobenzene at 180° to 190° 
 until the evolution of hydrochloric acid ceases. On cooling, the benzoyl compound 
 crystallises out, and is filtered off and washed free of nitrobenzene with alcohol. 
 
 1 : 4-Diaminoanthraquinone— 
 
 NH, 
 Pe aun ne 
 
 N00 SG, 
 
ANTHRACENE AND ANTHRAQUINONE 225 
 
 —violet needles, m.p. 268°. Very soluble in benzene and nitrobenzene, less so in 
 alcohol, and sparingly in methyl alcohol. It is most conveniently crystallised from 
 alcohol. It is more strongly basic than the monoaminoanthraquinones, and dissolves 
 to an almost colourless solution in hydrochloric acid. Its solution in sulphuric acid 
 is yellow, but on adding boric acid to this solution and warming the colour changes 
 to crimson. The diacetyl derivative forms reddish-yellow needles, m.p. 271°. 
 
 The preparation of this compound from a-acetylaminoanthraquinone has been 
 described by Romer (Ber., 15, 1790), and the method patented in G.P.’s 125391 and 
 135561 (Bayer). 10 kg. of a-acetylaminoanthraquinone are dissolved in 100 kg. of 
 sulphuric acid (66° Bé), keeping the temperature during solution below 15° to prevent 
 hydrolysis. 12-5 litres of mixed acid containing 20 per cent. of HNO, are then 
 added slowly, the temperature being maintained at 15°. The nitration proceeds 
 quickly, and is finished in about an hour. While the external cooling is continued, 
 60 kg. of ice is added, which causes separation of the nitro body in a crystalline form. 
 This is filtered off and washed with cold water. It is then purified by crystallisation 
 irom ten times its weight of glacial acetic acid or pyridine. Pure l1-acetylamino-4- 
 nitroanthraquinone forms golden yellow crystals insoluble in water, dilute acids, or 
 alkalies, slightly soluble in alcohol, ether, and ligroin, and easily soluble in aniline. 
 It crystallises particularly well from epichlorhydrin in long reddish-yellow needles, 
 melting at 256° to 258°. 
 
 The purified nitro body is now hydrolysed by heating it with five times its weight 
 of 80 per cent. sulphuric acid at 90° to 100° for half to one hour. Or the nitration 
 solution may be heated directly, without isolating the acetylaminonitroanthraquinone, 
 though this, of course, gives a less pure aminonitro compound. After cooling, the 
 solution is run into water and the precipitate filtered off and washed acid-free. 
 1-Amino-4-nitro-anthraquinone is a red powder, insoluble in water and sparingly 
 soluble in alcohol. It may be crystallised from epichlorhydrin as beautiful red 
 needles, melting at 290° to 295°. 
 
 The reduction of the aminonitro compound is carried out by stirring 10 kg. of the 
 
 finely powdered substance into 400 litres of water, adding a solution of 20 kg. of 70 per 
 cent. sodium sulphide in 20 kg. of 23 per cent. caustic soda and warming at water-bath 
 temperature. A green solution of the hydroxylamine derivative is formed at first, 
 but this soon changes to the diamine, which separates as a brown crystalline precipi- 
 tate. When reduction is complete, the diamine is filtered off, washed with water, 
 and purified by dissolving it in dilute hydrochloric acid and reprecipitating. It may 
 be crystallised from aniline as large dark violet bronzy crystals, which contain aniline 
 of crystallisation. 
 _ The amino group of the a-aminoanthraquinone may alternatively be protected 
 during nitration by acylation with oxalic acid, as described by Noelting and Wort- 
 mann (Ber., 89, 643). This is a method which has not been much used in the prepara- 
 tion of dyestuff intermediates, or, indeed, in any department of synthetic chemistry, 
 but is certainly worthy of consideration as a technical method. 
 
 Noelting and Wortmann prepared the oxamic acid of «-aminoanthraquinone, 
 C,,H,O,.NH.CO.COOH, by heating the amino compound with five times its weight 
 
 15 
 
226 INTERMEDIATES FOR DYESTUFFS 
 
 of crystalline oxalic acid for two days at 150° to 160°. The melt was then boiled out 
 with water, filtered, washed with alcohol and ether, and dried for half an hour at 
 120°. The melting-point of the oxamic acid is 226°. It was nitrated by suspending 
 it in concentrated sulphuric acid and adding mixed acid (containing 25 per cent. of 
 HNOQ;) at 5°. The nitro body separated as a yellow precipitate, which was filtered 
 off through asbestos. It was hydrolysed by soda to the aminonitro compound, which, 
 after crystallisation from nitrobenzene, melted at 296°, and was, therefore, purer than 
 that obtained by Romer (m.p. 290° to 295°). The reduction was carried out as before 
 by sodium sulphide. 
 
 1 ; 4-Diaminoanthraquinone is used in the preparation of Algol Red 5G (which is 
 simply the dibenzoyl derivative) and of Helindone Brown AN. 
 
 Halogen Derivatives of «-Aminoanthraquinone. 
 
 The chlorination of the free base with chlorine apparently, to judge by the 
 literature, yields mixtures of various chloro derivatives, including N-chloro as well as 
 nuclear substituted compounds, from which nothing definite can be isolated. It is 
 otherwise with the bromination of «-aminoanthraquinone, which yields, according to 
 the conditions employed, either the 2-bromo or the 2 : 4-dibromo derivative in fairly 
 satisfactory yield. However, the 4-chloro derivative may also be obtained, as shown 
 in G.P. 199758, if the amino group is first acylated. | 
 
 1-Amino-2-bromoanthraquinone— 
 
 oe 
 \A\c9/\4 
 
 —orange crystals from glacial acetic acid, m.p. 180° to 181°. Its solution in con- 
 centrated sulphuric acid is yellow, and in 40 per cent. oleum bluish-violet. 
 
 The preparation of this substance is described in G.P. 160169. 20 parts of «- 
 aminoanthraquinone is obtained in a finely divided condition by solution in sulphuric 
 acid and reprecipitation with water. It is then stirred into 500 parts of glacial acetic 
 acid and slowly heated to the boil, while a solution of 15 parts of bromine in 100 parts 
 of glacial acetic acid is gradually added. When bromination is complete, the solution 
 is cooled, and the bromamino compound filtered off. It is recrystallised from glacial 
 acetic acid. 
 
 1-Amino-2-bromoanthraquinone can be methylated as follows bie P. 288825) 
 to produce 1-methylamino-2-bromoanthraquinone : 
 
 NH.CH, 
 Pee 
 
 | sf a, 
 awn ae 
 
 1 part of 1-amino-2-bromoanthraquinone, 4 parts of 96 per cent. sulphuric acid, 
 and 4 parts of dimethyl sulphate are heated at 185°, until a test portion dissolved in 
 
ANTHRACENE AND ANTHRAQUINONE 227 
 
 40 per cent. oleum no longer gives the violet solution of the aminobromo compound, 
 but instead a brownish-yellow. The solution is then cooled, 12 parts of water are 
 stirred in with external cooling, and the precipitated sulphate filtered off and washed 
 acid-free. 
 1-Methylamino-2-bromoanthraquinone forms red crystals, m.p. 170° to 172°. 
 1-Amino-2 : 4-dibromoanthraquinone : 
 
 NH, 
 LANG wens a Hs 
 
 le 
 
 Bote \co”% ae 
 
 Fiery red felted needles, m.p. 226°, sparingly soluble in alcohol, ether, benzene, and 
 glacial acetic acid, but easily soluble in hot nitrobenzene and pyridine. 
 
 A method of preparing this derivative by the action of bromine vapour on dry 
 a-aminoanthraquinone spread in thin layers in a closed vessel, is described in 
 G.P. 115048. But, according to Ullmann and Eiser (Ber., 1916, 49, 2165), the method 
 is unsatisfactory. They prepare the substance as follows: 44-6 gms. of o-amino- 
 anthraquinone are dissolved in 75 c.c. of nitrobenzene by heating to 150° to 160° in a 
 flask fitted with a reflux condenser. A mixture of 75 gms. of bromine and 25 c.c. of 
 nitrobenzene is slowly dropped in, with frequent shaking. The solution is then heated 
 for three hours more at 160°, after which it is allowed to cool. The dibromo compound 
 which crystallises out is filtered off and washed with alcohol. The yield is 61 gms. or 
 80 per cent., the product so obtained melting at 222°. By steam-distilling the nitro- 
 benzene from the mother liquor, 12 gms. of a less pure product, melting at 199°, is 
 recovered. 
 
 The bromine atom in the 4-position in this substance readily reacts with aromatic 
 amines to produce mono-substituted 1: 4-diamines, which are blue in colour, and 
 which, on sulphonation, yield blue acid colours for wool. Alizarine Sky Blue is an 
 example. 
 
 This 4-bromo atom is also labile in other ways. For instance, it is replaced by 
 hydroxyl on heating the substance with sulphuric acid, thus producing 1-amino- 
 2-bromo-4-hydroxyanthraquinone : 
 
 NH, 
 fated = 
 
 \A\c0/\G 
 
 According to G.P. 203083 (E.P. 28104, 1907 ), 10 parts of 1-amino-2 : 4-dibromoanthra- 
 quinone are warmed to 100° to 110° with 100 parts of monohydrate till a test portion 
 dissolved in pyridine no longer gives a bluish-red solution. The melt is then poured 
 into water, the precipitate filtered off, washed till neutral, and dried. It melts at 243° 
 with decomposition, and gives a yellow solution in sulphuric acid, or if boric acid is 
 added, a bluish-red solution. 
 
 It is used in the preparation of a dihydroxy-indanthrene, Algol Blue 3G. 
 
228 INTERMEDIATES FOR DYESTUFFS 
 
 1-Amino-4-chloroanthraquinone— 
 Cae 
 SNC oe 
 —tred needles, m.p. 179° to 180°. Moderately soluble in hot xylene, amyl alcohol, 
 and glacial acetic acid; soluble in nitrobenzene. 
 
 As mentioned above, this substance cannot be prepared by direct chlorination of 
 o-aminoanthraquinone, but if the amino group is first acylated, chlorination of the 
 acyl derivatives in suspension or solution in various solvents, such as water, acetic 
 acid, carbon tetrachloride, etc., yields the 4-chloro derivative (G.P. 199758). 
 
 10 parts of 1-acetylaminoanthraquinone are stirred with 80 to 100 parts of glacial 
 acetic acid. 10 parts of crystalline sodium acetate are added, and the whole heated 
 at 80° on the water-bath, while chlorine is passed through in excess. The solution is 
 cooled, filtered, and the product washed with water and dried. 1-Acetylamino-4- 
 chloroanthraquinone is thus obtained as yellow crystals, which, after recrystallisation 
 from glacial acetic acid, melt at 203° to 204°. 
 
 The acetyl compound is easily hydrolysed by heating with 80 per cent. sulphuric 
 acid for an hour at 90° to 100°, and thus yields 1-amino-4-chloroanthraquinone. 
 
 1-Methylaminoanthraquinone— co. NHCH 
 Gere 
 MOMS OS 
 
 —yellowish-red needles, m.p. 167°. 
 
 This is prepared like «-aminoanthraquinone by amidation of the «-sulphonic acid, 
 using, instead of ammonia, methylamine, as described in G.P. 175024 (Bayer). But, 
 as in the case of the amino compound, improved yields are obtained if provision is 
 made for dealing with the sulphite produced in the reaction. In G.P. 256515 
 (Badische), an oxidising agent, potassium bromate, is added : 
 
 100 parts of potassium anthraquinone-«-sulphonate, 600 parts of 6 per cent. 
 aqueous methylamine solution, and 13 parts of potassium bromate, are heated and 
 
 stirred in an autoclave at 150° for five or six hours. The methylaminoanthraquinone — 
 
 separates in a pure crystalline condition, and merely requires filtering off and washing 
 with water. 
 
 The bromination of 1-methylaminoanthraquinone under special conditions, as 
 described in G.P. 164791, leads to eee 
 
 oo 
 
 10 parts of 1-methylaminoanthraquinone are dissolved in 100 parts of warm 
 pyridine, and the solution heated on the water-bath, while 6 to 8 parts of bromine are 
 
ANTHRACENE AND ANTHRAQUINONE 229 
 
 gradually added. Heating is continued for one to two hours. On cooling, reddish- 
 brown needles of the bromo compound separate and are filtered off and washed free 
 of pyridine. The substance melts at 194°. Its solution in warm 40 per cent. oleum is 
 deep blue. ! 
 «-Chloroanthraquinone— Cl 
 PS ONES 
 
 Bele 
 
 —yellow needles, m.p. 162°. Easily soluble in hot benzene, glacial acetic acid, and 
 amyl alcohol. Crystallises well from alcohol. Its solution in sulphuric acid is 
 yellowish-brown. 
 
 a-Chloroanthraquinone is prepared from anthraquinone-«-sulphonic acid by 
 replacement of the sulpho group by chlorine. Several methods of carrying out this 
 replacement have been used, including the use of chlorine gas (G.P. 205195) and 
 thionyl chloride (G.P. 267544), but the best method is that involving the use of nascent 
 chlorine developed from sodium chlorate and hydrochloric acid, as already described 
 in the case of f-chloroanthraquinone. The application of this method to the pre- 
 paration of «-chloroanthraquinone is thus described by Ullmann and Ochsner (Ann., 
 388, 2): 
 
 In a 3-litre flask fitted with a reflux condenser and a rapid stirrer, 40 gms. of 
 potassium anthraquinone-«-sulphonate, 170 c.c. of concentrated hydrochloric acid and 
 1,200 c.c. of water are heated to boiling, and into the boiling liquid a solution of 
 40 gms. of sodium chlorate in 200 c.c. of water is dropped through the condenser 
 during three hours. The «-chloroanthraquinone separates immediately as a yellow 
 precipitate, and no chlorine escapes. To complete the reaction the solution is boiled 
 for an hour after the chlorate has all been added. The chloro compound is then 
 filtered off, washed with hot water, and dried. The yield is 28-4 gms. or 95 per cent. 
 of pure «-chloroanthraquinone. 
 
 An earlier method of preparation (G.P. 131538, Bayer) from «-aminoanthraquinone 
 by diazotisation and application of the Sandmeyer reaction does not give good 
 results. 
 
 «-Chloroanthraquinone is used for condensations with aminoanthraquinones to 
 produce dianthrimides and trianthrimides. 
 
 a-Chloroanthraquinone may be converted into «-aminoanthraquinone by con- 
 densation with p-toluenesulphonamide, followed by hydrolysis of the toluene- 
 sulphoylaminoanthraquinone : 
 
 CyuH,0,Cl + H,N.SO,.C,H,.CH, > (C4 H,0,.NH.S0,.C,Hy.CH, 
 ——_> (,,H,0..NH, + SO,H.C,H,.CH; 
 
 The process is thus described by Ullmann and Fodor (Ann., 880, 319): 
 
 5 gms. of «-chloroanthraquinone, 5 gms. of p-toluenesulphonamide, 4 gms. of 
 potassium carbonate, 0-2 gm. of copper acetate, and 0-1 gm. of copper powder are 
 stirred with 50 c.c. of nitrobenzene and heated at 180° to 200° for three hours. The 
 
230 INTERMEDIATES FOR DYESTUFFS 
 
 solution is finally brownish-yellow in colour. The nitrobenzene is now distilled off 
 with steam, and the residual aqueous suspension filtered. The solid obtained melts at 
 218°. Itisrecrystallised from glacial acetic acid, and thus yields 6-5 gms. of «-toluene- 
 sulphonylaminoanthraquinone as yellow needles, m.p. 228-5°. It is only slightly 
 soluble in alcohol, moderately (1 in 25) in boiling glacial acetic acid and in toluene and 
 xylene, and very soluble in pyridine and nitrobenzene. 
 
 The hydrolysis is carried out by dissolving the substance in ten times its weight of 
 concentrated sulphuric acid. An orange-coloured solution is formed, but on slightly 
 warming this changes to yellow, due to hydrolysis. The «-aminoanthraquinone is 
 precipitated by pouring the solution into ice water, and is obtained quite pure (m.p. 
 243°). The overall yield is about 83 per cent. 
 
 This process has the great advantage over the usual one that it avoids the use of 
 an autoclave, but it is undoubtedly more expensive. 
 
 o-Hydroxyanthraquinone (Erithroxyanthraquinone)— 
 
 OH 
 PA 
 
 Go 
 AY NODS 
 
 —orange needles, m.p. 193°. In powder form bright yellow. Sublimes easily. 
 Slightly volatile in steam. Soluble in caustic soda solution, but not in ammonia or 
 carbonate. Moderately soluble in alcohol, more so in benzene and ether. 
 
 This substance cannot be prepared by the usual alkali fusion of the corresponding 
 a-sulphonic acid, since under the ordinary conditions of fusion the anthraquinone 
 nucleus in this case is ruptured, and varying proportions of m-hydroxybenzoic and 
 sulphobenzoic acids are formed. The replacement of the sulpho group by hydroxyl 
 in the anthraquinone series, in fact, requires much less drastic conditions than those 
 employed in the benzene or naphthalene series. In the present case, heating at 
 moderate temperatures with very dilute caustic soda or milk of lime (G.P. 172642) or 
 carbonates (G.P. 197649) will effect the replacement. 
 
 25 kg. of potassium anthraquinone-«-sulphonate are heated with 18 kg. of lime 
 and 400 litres of water in a stirring autoclave for three to four hours at 190°. After 
 cooling to about 100°, the reaction mixture is acidified with hydrochloric acid, when 
 the «-hydroxyanthraquinone separates as a yellow precipitate in very pure condition. 
 The yield is said to be quantitative (G.P. 172642). 
 
 A method of preparation from «-aminoanthraquinone through the diazo compound 
 is described in G.P. 97688, but this does not work well, and is unnecessarily circuitous. 
 
 a-Methoxyanthraquinone : 
 if ie tad he 
 
 As 
 
 The preparation of this substance directly from the «-sulphonic acid by boiling 
 with methyl alcohol and caustic soda is described in G.P. 156762 (Bayer), but the 
 
ANTHRACENE AND ANTHRAQUINONE 231 
 
 yield obtained is too small to make the method practicable. It can be prepared, 
 however, by methylation of «-hydroxyanthraquinone under the special conditions 
 given in G.P. 243649 (Meister Lucius and Briining). 
 
 100 gms. of the dry sodium salt of «-hydroxyanthraquinone are stirred into 
 200 gms. of the methyl ester of p-toluenesulphonic acid heated at 180°. The melt 
 soon thickens, due to the separation of the methoxy compound as a pale yellow 
 substance. After cooling, the mass is rubbed up with alcohol, filtered, the residue 
 washed with water, and then with a little alcohol, and dried. The yield is said to be 
 nearly theoretical. 
 
 a-Hydroxy- and «-methoxyanthraquinone, when nitrated, yield in each case 
 chiefly the 4-nitro derivative. The nitro compounds, on reduction with sodium 
 sulphide, give the corresponding amino compounds, whose benzoyl derivatives con- 
 stitute the dyestuffs Algol Pink R (1-benzoylamino-4-hydroxyanthraquinone) and 
 Algol Scarlet G (1-benzoylamino-4-methoxyanthraquinone). 
 
 Quinizarin : 
 
 none 
 w \co”% Nia 
 (For properties and another method of preparation, see p. 208.) 
 
 The preparation of quinizarin from anthraquinone or 1-hydroxyanthraquinone has 
 been described in a series of patents by Bayer and Co. (G.P. 81960, 81245, 161954, 
 162792). The methods used, which are due to R. E. Schmidt, consist in subjecting 
 the anthraquinone or its derivative to the oxidising action of sulphuric acid, assisted 
 by sodium nitrite or mercuric sulphate, in presence of boric acid. It seems, however, 
 to be difficult to obtain unitary products by these methods. 
 
 Quinizarin can also be prepared from 1-hydroxyanthraquinone by chlorination 
 to the 4-chloro derivative, and replacement of the chlorine atom by hydroxyl through 
 heating with sulphuric acid and boric acid at a high temperature (Ullmann and 
 Conzetti, Ber., 1920, 58, 826). Ullmann and Conzetti used sulphuryl chloride for the 
 chlorination of 1-hydroxyanthraquinone, but chlorine gas can also be used, as described 
 in E.P. 209694 (Thomas and Scottish Dyes). 
 
 A solution of 120 Ibs. of 1-hydroxyanthraquinone in 640 Ibs. of 98 per cent. 
 sulphuric acid is circulated at 70° to 75° through a tower up which chlorine is passing 
 at the rate of 5 to 6 Ibs. per hour. After 80 lbs. of chlorine have been passed, a sample 
 of the solution is taken and the crude 1-hydroxy-4-chloroanthraquinone precipitated 
 by pouring into water, filtered, and washed acid-free. The chlorine content is 
 determined. If this is about 13-7 per cent. and the melting-point is 180° to 181”, 
 the chlorination is complete. 
 
 Without isolating the 4-chloro body, 80 Ibs. of boric acid is added to the solution, 
 which is then heated for twelve hours at 160°, or for eight hours at 180°. The cooled 
 solution is then run into water and the precipitated quinizarin isolated in the usual 
 way. The yield obtained is slightly over 120 parts. 
 
232 INTERMEDIATES FOR DYESTUFFS 
 
 «-Anthrol— ee 
 YY) 
 
 Nat ONS 
 
 —yellow plates, m.p. 152°, almost insoluble in water, but soluble in most organic 
 solvents, the solutions showing a blue fluorescence. 
 
 This derivative of anthracene is prepared by fusion of the corresponding sulphonic 
 acid with alkali. Reference has been made to the difficulty of preparing directly 
 from anthracene in pure condition the anthracenemonosulphonic acids (p. 214). The 
 a«-sulphonic acid of anthracene is, therefore, usually prepared by reduction of anthra- 
 quinone-«-sulphonic acid or its salts. The method is described by R. E. Schmidt 
 (Ber., 1904, 37, 70). 
 
 30 gms. of potassium anthraquinone-«-sulphonate is warmed with 500 to 750 c.c. 
 of 20 per cent. ammonia and 70 gms. of zinc dust for ten to twelve hours on the 
 water-bath. The solution, at first intensely reddish-yellow, slowly decolourises. 
 When the reduction is finished, the solution is filtered hot, and, on cooling, potassium 
 anthracene-«-sulphonate crystallises in colourless leaflets. 
 
 The sulphonate is then fused at 270° to 280° (the paper referred to gives 170° to 
 180° as the fusion temperature, but this is probably a misprint) with 5 parts of caustic 
 potash. The finished melt is dissolved as quickly as possible in water, the solution 
 acidified with hydrochloric acid and the «-anthrol, which separates as pale grey 
 flocks, filtered off. It is purified by dissolving it in boiling glacial acetic acid, adding 
 animal charcoal and boiling a short time to decolourise the solution. After filtering, 
 
 water is added till a slight cloudiness appears, when, on cooling, the a-anthrol — 
 
 crystallises in pale yellow lustrous plates. 
 
 Sircar (J.C.S., 1916, 109, 774) carried out the fusion at 250° to 260° for twenty-five 
 minutes, using 2 gms. of the «-sulphonate and 10 gms. of caustic potash. The cooled 
 melt was then diluted with 4 to 5 c.c. of water, 6 to 7 c.c. of concentrated hydrochloric 
 acid added, and the whole poured into 100 c.c. of water. Onrecrystallising the crude 
 product from acetic acid a yield of 1 gm. of «-anthrol was obtained. 
 
 a-Anthrol is used in making vat dyes by condensing it with isatin derivatives. 
 Apparently in such condensations it reacts in its ketonic form : 
 
 OH 
 Wee ahgeay Co 
 | ; | 5 eee eee ce) i + OK OH, 
 NOAA weak pe 
 
 NAO. 
 
 Using dibromoisatin, Alizarin Indigo is obtained. 
 
ANTHRACENE AND ANTHRAQUINONE 233 
 
 Anthrarufin— OH 
 OTS. 
 
 Cs 
 
 —crystallises in yellow needles or tablets, m.p. 280°, insoluble in water, sparingly 
 soluble in alcohol, ether, or glacial acetic acid, but moderately soluble in benzene. Its 
 solution in sulphuric acid is intense crimson in colour. In caustic alkalies it dissolves 
 to a red solution. 
 
 This substance is obtained from anthraquinone-l : 5-disulphonic acid by heating 
 at high temperatures with milk of lime (E.P. 25541 of 1903; G.P. 170108, Bayer). 
 
 In an autoclave fitted with a stirrer, 20 parts of sodium anthraquinone-l : 5- 
 disulphonate, 30 parts of slaked lime, and 400 parts of water, are heated at 180° to 
 190° for twelve hours. The product is acidified with hydrochloric acid, and the 
 precipitated anthrarufin filtered off. 
 
 According to a patent of Iljinskij and Wedekind and Co. (E.P. 25738 of 1903), 
 if a salt (sodium or potassium) of the anthraquinonedisulphonic acid is used, as in 
 the Bayer patent, the caustic alkali set free in the reaction, which proceeds mainly as 
 in the equation— 
 
 C,4H,0,(SO,Na), + 2Ca(OH), = CyH,0,0H), + 2CaSO, + 2Na0H 
 
 —causes the production of much dark smeary impurity, reduction taking place to 
 some extent. They proposed, therefore, to use the calcium salt of the disulphonic 
 acid, together with some calcium chloride, and recommended the following method : 
 100 parts of the calcium anthraquinone-1 : 5-disulphonate are stirred with 500 parts 
 of hot water, in this are slaked 100 parts of lime, and 30 parts of sodium nitrate and 
 100 parts of 20 per cent. calcium chloride solution added. The whole is stirred under 
 pressure in a digester at 180° to 220° until no trace of hydroxysulphonic acid can be 
 detected. The product is then precipitated by addition of hydrochloric acid. The 
 yield obtained is 50 parts of pure anthrarufin. 
 
 The conversion of the disulphonate to anthrarufin can also be carried out with 
 aqueous sodium carbonate at 190° to 200° (G.P. 197649, Bayer). 
 
 Anthrarufin is used for the preparation of Alizarin Saphirol B and SE. 
 
 Diaminoanthrarufin— 
 HN go Of 
 SE AONE ae ae 
 
 —dark violet needles, insoluble in water. 
 
 Diaminoanthrarufin can be prepared by dinitration of anthrarufin and reduction 
 of the product, but it is difficult to obtain it pure in this way, since the nitro groups 
 enter other positions besides the 4- and 8-, and a complex mixture of several nitro- 
 anthrarufins is obtained. 
 
234 INTERMEDIATES FOR DYESTUFFS 
 
 It is more satisfactorily prepared by a method described in two patents of Bayer’s, 
 G.P. 158531 and 170728. Anthraquinone-1 : 5-disulphonic acid is converted into 
 1: 5-diphenoxyanthraquinone by heating with phenol and caustic potash. On 
 nitrating the diphenoxy compound, the nitro groups first enter the phenyl nuclei, and 
 then enter the 4- and 8-positions only of the anthraquinone nucleus. The resulting 
 compound is easily hydrolysed with dilute alkali to 4: 8-dinitroanthrarufin, which 
 may then be reduced to diaminoanthrarufin : 
 
 SO,K 00,H 
 Ny one Pa 
 | | ) oreo? | | J ae 
 Koy 00” ony’ co” 
 Ose 
 O,N o¢ DO: O.N OH 
 WA 0. ON JO a 
 HNOs: 0 | | S ) Dil. alkali me | | J 
 . NEN ms BY oo” YG, 
 O.N O 
 Sed 
 NO, 
 N OH 
 BN cit AN 
 NaoS | ) | 
 nv CO” Sir, 
 
 A mixture of 160 kg. of phenol and 50 kg. of caustic potash is heated to 140°, and 
 20 kg. of sodium anthraquinone-1 : 5-disulphonate added. The whole mass is then 
 heated to 180°, and kept at this temperature until the sulphonate has nearly all 
 disappeared. After cooling, the melt is stirred with hot water and filtered. The 
 diphenoxy compound so obtained may be purified by crystallisation from glacial 
 acetic acid or nitrobenzene, and is obtained as long yellow needles, m.p. 215°, which 
 dissolve in most organic solvents to yellow solutions. Its solution in sulphuric acid 
 is pure blue in colour, but on warming, changes to orange-red. 
 
 The nitration is carried out by dissolving 20 kg. of diphenoxyanthraquinone in 
 250 kg. of 100 per cent. sulphuric acid, and adding, at 0° to 5°, 40 to 50 litres of mixed 
 acid containing about 50 per cent. of nitric acid. The solution is then stirred at the 
 ordinary temperature until the hexanitro compound, which is very sparingly soluble in 
 sulphuric acid, has completely separated. The mixture is poured into water, and the 
 product filtered off, washed, and dried. It may be purified by crystallisation from 
 nitrobenzene, and forms fine grey needles. It dissolves at 200° in boric-sulphuric acid 
 to a blue-violet solution. It is hydrolysed, by warming with dilute alkali, to 
 dinitroanthrarufin and 2:4-dinitrophenol. The former is then reduced in the usual 
 way with sodium sulphide to diaminoanthrarufin. 
 
 Diaminoanthrarufin, on acylation of the amino groups with benzoyl chloride, 
 anisoyl chloride, etc., yields blue or violet vat dyes of great fastness. 
 
ANTHRACENE AND ANTHRAQUINONE 235 
 
 Nitration of Anthraquinone. 
 
 The direct nitration of anthraquinone by the ordinary method produces chiefly 
 x-derivatives—that is, 1-nitro- and 1:5- and 1:8-dinitroanthraquinones. As in 
 sulphonation, nitration of anthraquinone cannot be carried out so as to form the 
 mononitro compound without at the same time forming a large proportion of dinitro 
 compounds, and the general experience of workers on these substances has been that 
 they are difficult to prepare in a reasonable state of purity. This, no doubt, accounts 
 for the fact that most anthraquinone derivatives are obtained through the sulphonic 
 acids. Ullmann, however, claims good results for the following preparation of a-nitro- 
 anthraquinone (Ullmann and van der Schalk, Ann., 388, 203), based on a method 
 given by Lauth (C. r., 1903, 187, 662): 
 
 20-8 gms. of anthraquinone are dissolved in 125 ¢.c of concentrated sulphuric acid, 
 and the solution is warmed to 50°. At this temperature 7-6 c.c. of nitric acid (D 1-4— 
 i.e., 65 per cent.) are slowly added, the temperature being maintained about 50°. 
 This quantity of nitric acid is about 10 per cent. in excess of the theoretical require- 
 ment for mononitroanthraquinone. When the nitric acid is all added, the mixture 1s 
 cooled and poured on ice. The precipitate is filtered off, and washed acid-free with 
 hot water. The yield of this product is 25 gms., and its melting-point 217°. But it 
 contains besides «-nitroanthraquinone some unchanged anthraquinone and dinitro- 
 anthraquinones. This crude product is extracted with toluene, which leaves 2 gms. 
 of dinitro compounds undissolved, and on evaporation of the toluene solution to 
 crystallising point the g-nitroanthraquinone is obtained, though even then it is con- 
 taminated with anthraquinone and with 1 : 8-dinitroanthraquinone, etc. 
 
 Another method of purification of the crude product is given in G.P. 281490 
 (Ullmann). This depends on distillation in a vacuum under 7 mm., when the a-nitro 
 compound distils undecomposed at 270° to 971° as a pale yellow liquid. 
 
 For the preparation of «-aminoanthraquinone, however, according to Ulimann and 
 van der Schalk (loc. cit.), the moist crude nitro product as obtained above may be used 
 direct. It isrubbed with 40 gms. of crystalline sodium sulphide (Na,8.9H,O) and the 
 dark thick paste gradually diluted, while being stirred, with 700 c.c. of boiling water. 
 The mixture is then heated until a test portion, on filtering off the solid and rubbing it 
 up with a little sodium sulphide, no longer becomes green. About twenty minutes is 
 required to reach this point. The suspended «-aminoanthraquinone is then filtered 
 off and boiled up twice with water. The yield is 21-9 gms. (from 20-8 gms. of anthra- 
 quinone) or 98 per cent. The melting-point of the product is given as 243°, which is 
 the melting-point of the pure substance as obtained by Ullmann. This is probably 
 not the case, however, the figure 243° being more probably the melting-point of the 
 several times recrystallised product. 
 
 When anthraquinone 1s nitrated with more than two molecular equivalents of 
 concentrated nitric acid, a mixture olf dinitroanthraquinones is formed. Romer 
 (Ber., 16, 366) gives the following particulars: A solution of 10 gms. of anthraquinone 
 in concentrated sulphuric acid is treated with 10 gms. of nitric acid (D 1-48, or 86 per 
 cent.). The mixture is allowed to stand for several days, and is then poured into 
 
236 INTERMEDIATES FOR DYESTUFFS 
 
 water and the precipitate filtered off, washed acid-free, and dried. A mixture of 
 dinitroanthraquinones obtained in some such way as this was found by Battegay and 
 Claudin (Bull. Soc. Ind. Mulhouse, 1920, 86, 628-631) to contain 37 per cent. of 1: 5-, 
 37 per cent. of 1: 8-, 4-2 per cent. of 1: 7-, 3-6 per cent. of 1 : 6-, 6 per cent. of 2 : 6-, 
 and 4 per cent. of 2 : 7-dinitroanthraquinones. 
 
 The mixture of dinitro compounds is used in the preparation of the Anthracene 
 Blues. But 1: 5-dinitroanthraquinone, owing to its exceptional properties, may be 
 separated fairly readily from the mixture by extracting the other dinitro compounds 
 with alcohol or acetone in which the 1 : 5-dinitro compound is insoluble. The extrac- 
 tion is continued until a test portion of the residue dissolves in potassium stannite 
 solution with a pure bluecolour. The residue is then recrystallised from nitrobenzene, 
 and 1 : 5-dinitroanthraquinone thus obtained as large yellow prisms, m.p. 422°. 
 
 Noelting and Wortmann (Ber., 39, 643) have shown that 1 : 5- and 1 : 8-diamino- 
 anthraquinones may be obtained from the crude mixture of dinitro compounds as 
 prepared by Romer by reducing the whole mixture, and then separating the diamino 
 compounds by differences in basicity. 
 
 250 gms. of the dinitroanthraquinone mixture, as obtained by Rémer’s method, is 
 stirred into an aqueous solution of sodium sulphide. The mixture dissolves to a green 
 solution, and this is gently boiled for an hour, during which the red diamines separate. 
 The precipitate is filtered off, washed, and dried. The yield is almost quantitative, 
 about 200 gms. This mixture is then rubbed with 400 c.c. of water and 800 c.c. of 
 concentrated sulphuric acid added, which effects complete solution of the diamines. 
 The solution is diluted with 400 c.c. of water, heated to boiling, and filtered, if necessary, 
 through glass wool. After standing for twenty-four hours, a considerable precipitate 
 has separated, and this is filtered off. It consists of the sulphate of 1 : 5-diaminoanthra- 
 quinone, and this is dissociated by stirring with a large volume of water, the diamine 
 being filtered off, washed, and dried. The yieldis78 gms. It may be purified by crystal- 
 lisation as sulphate from a mixture of equal volumes of water and sulphuric acid, the 
 sulphate being afterwards dissociated. It is thus obtained in pure condition, m.p. 319°. 
 
 The sulphuric acid filtrate from the 1 : 5-diaminoanthraquinone sulphate is poured 
 into several litres of cold water. The precipitated bases are filtered off, boiled up with 
 water, again filtered, washed, and dried. The dry product weighs about 120 gms. 
 It is boiled up with two and a half times its weight of acetic anhydride, and an equal 
 weight of glacial acetic acid for an hour under reflux. After standing for twenty-four 
 hours, the separated diacetyl compound is filtered off, washed, and dried. It is then 
 hydrolysed by heating for half an hour with ten times its weight of sulphuric acid at 
 80°. The solution is poured into water and partly neutralised by ammonia to set free 
 the base, which is then filtered off. It may be crystallised from alcohol, glacial acetic 
 acid, nitrobenzene, or pyridine. In this way, a yield of 70 gms. of 1: 8-diamino- 
 anthraquinone, m.p. 262°, is obtained. 
 
 C 
 
 nt ‘1 
 1 : 5-Dichloroanthraquinone— Son aN PAN 
 
 We) U 
 
 cede Say 
 
ANTHRACENE AND ANTHRAQUINONE 237 
 
 —pale yellow crystals, m.p. 251°. Insoluble in water, soluble in organic solvents. 
 Best crystallised from glacial acetic acid. 
 
 It is prepared from anthraquinone-I : 5-disulphonic acid by the action of sodium 
 chlorate and hydrochloric acid, as described in G.P. 205195. 
 
 20 parts of sodium anthraquinone-! : 5-disulphonate are dissolved in a mixture of 
 400 parts of water and 40 parts of hydrochloric acid (20° Bé). The solution is heated 
 to boiling, and a solution of 40 parts of sodium chlorate in 300 parts of water 
 slowly added until no further precipitate of the dichloro compound is formed. This 
 usually requires several hours’ boiling. The dichloro compound is then filtered 
 off, washed with water, and purified if necessary by recrystallisation from glacial 
 acetic acid. 
 
 1 : 5-Dichloroanthraquinone is used in making Indanthrene Violet RN. 
 
 Benzanthrone— iN 
 
 a OT fac 
 
 ee 
 
 A ee SA 
 CO 
 
 —crystallises in fine pale yellow needles, m.p. 170°, soluble in alcohol and other 
 organic solvents. It dissolves in sulphuric acid to an orange-red solution with an 
 olive-green fluorescence. 
 
 Benzanthrone is prepared by heating anthranol, an acid reduction product of 
 anthraquinone, with glycerol and sulphuric acid, the reaction being analogous with 
 the formation of quinoline from aniline: 
 
 CH 
 OH J 
 ‘ a CH 
 ONAN VA tas IK 
 | | | | “Reduction ~ | | | ~“HyS0s+C,Be05 | | | | 
 rg \co” es are ~ fe NN ike av ee 
 Anthranol Benzanthrone 
 
 (a) Anthranol.—This is best prepared, as in G.P. 201542 (Bayer), by dissolving 
 10 parts of anthraquinone in 150 parts of concentrated sulphuric acid and gradually 
 adding to the well-stirred solution 2-5 parts of aluminium powder, the temperature 
 being kept at 30° to 40°. Much frothing takes place. When the reaction is over, the 
 anthranol may be precipitated by running the solution into water, and is filtered off. 
 Recrystallised from glacial acetic acid, it forms lustrous pale yellow needles, m.p. 
 163° to 170°. The melting-point, even of the pure substance, 1s indefinite because, on 
 fusion, anthranol changes partly into its tautomeride, anthrone (m.p. 154°) : 
 
 Lr fee ae) 
 
 Ur Gane 
 
238 INTERMEDIATES FOR DYESTUFFS 
 
 (6) Benzanthrone.—To a solution or suspension of 10 parts of anthranol in 150 
 parts of sulphuric acid (62° Bé=82 per cent.), 10 parts of glycerol are added. The 
 mixture is cautiously heated. At about 120°, a vigorous reaction sets in, the solution 
 becomes red and sulphur dioxide is evolved. After four hours’ further heating at 
 120°, the cooled solution is poured into water and the benzanthrone separates as olive- 
 green flocks, which are filtered off, washed, and boiled for half an hour with thirteen 
 times the weight of 1 per cent. caustic soda solution, then filtered and dried. It may 
 be purified by crystallisation from alcohol (G.P. 176018, Badische). 
 
 Benzanthrone forms the starting-point of a series of very fast blue, violet, and 
 green vat dyes, of which the first, Indanthrene Dark Blue BO, is obtained by fusing 
 benzanthrone with caustic potash. 
 
CHAPTER XV 
 STABILISED DIAZO COMPOUNDS 
 
 A LARGE number of insoluble azo colours—the so-called “ice colours ’’—are pro- 
 duced on the fibre (cotton) by padding the material with a solution of sodium f- 
 naphtholate, or other suitable phenolic compound, drying off and then passing the 
 padded material through a solution of a diazotised amine, when coupling takes place 
 and the colour is formed on the fibre. This method of dyeing was initiated by the 
 firm of Read, Holliday, and Sons in 1880, and has been greatly extended within the 
 last ten years by the introduction of f-oxynaphthoic anilide (Naphthol AS), and 
 similar substances by the Griesheim-Hlektron firm as variants on B-naphthol, which 
 was formerly the only substance used as second component in such colours. 
 
 As is well known, the diazo compounds of aromatic amines are very unstable 
 substances, and are generally formed in an ice-cold acid solution of the amine by 
 addition of sodium nitrite solution. In the dry state the pure diazo compounds are 
 extremely explosive. The troublesome nature of the diazotisation process, and the 
 difficulty of keeping the temperature low enough to avoid decomposition, led to efforts 
 to obtain diazo compounds in a form which would be sufficiently stable to be capable 
 of being stored, transported, and used by the dyer as required by simple solution in 
 water. This problem was successfully solved in several different ways chiefly by the 
 Badische Anilin- und Soda-Fabrik, Meister Lucius and Briining, and Cassella and Co. 
 These firms, and others using their processes, now market a large range of stabilised 
 diazo compounds. 
 
 (a) Nitrosamines or Isodiazotates. 
 
 The first, and probably the most successful, solution of the problem was discovered 
 by Schraube and Schmidt, and patented by the Badische Anilin- und Soda-Fabrik in 
 G.P. 78874, and a series of additional patents. It consists in the transformation of 
 the ordinary diazonium salt by the action of alkali into a tautomeric form, which is 
 stable at moderate temperatures even when dry. The diazonium salt produced in 
 the ordinary diazotisation is considered to have the constitution : 
 
 NO | 
 N 
 When its solution is poured into excess of warm alkali, the diazonium salt is trans- 
 formed into a substance whose constitution is still a matter of controversy. Schraube 
 and Schmidt attributed to it the structure of a metallic derivative of a nitrosamine 
 (I), while others consider it a salt of the anti-form of an isodiazotic acid (II), of which 
 two stereoisomeric forms are theoretically possible : 
 
 > R.N(Na).NO + NaCl + H,O0 
 
 (I) R—N—Cl + 2Na0H 
 | 
 N 
 
 (II) R—N—Cl 4+ 2Na0OH ——> ar + NaCl + H,O 
 K N.ONa 
 
 239 
 
240 INTERMEDIATES FOR DYESTUFFS 
 
 The evidence for either formula cannot be entered into here. The important practical 
 points are (1) that substances of this nature are stable, (2) that they do not couple 
 with phenols in alkaline solution, (3) that they are sparingly soluble in concentrated 
 alkali or in common salt solution, and are, therefore, readily isolated, (4) that they 
 can be transformed back into diazonium salts simply by dissolving them in water and 
 acidifying the solution. 
 
 The method of preparation of these nitrosamines or isodiazotates is indicated by 
 the following example from G.P. 78874 : 
 
 The diazonium chloride, prepared from 138 parts of p-nitroaniline in the usual way 
 in a solution of about 10 per cent. concentration, is run into 8,000 parts of hot 18 per 
 cent. caustic soda solution with good stirring. Stirring is continued until a sample of 
 the solution no longer produces a colour on adding it to an alkaline solution of 
 f-naphthol. This stage is reached in a very short time. On cooling, the product 
 separates in yellow needles, which are filtered off and pressed. 
 
 The amines which most readily undergo this transformation are those containing 
 negative substituent groups, such as the nitro-, chloro-, or nitrochloro-amines. These 
 can be transformed at 10° to 15°, using caustic soda, or at 40° to 50°, using sodium 
 carbonate as alkali. Thus, the preparation of the stable diazo compound of 2: 5- 
 dichloroaniline is thus described in G.P. 81134: 
 
 168 parts of 2 : 5-dichloroaniline are dissolved in 350 parts of concentrated hydro- 
 chloric acid and 800 parts of water by heating. On cooling, the solution sets to a thick 
 paste of crystals of the hydrochloride. To this, 300 parts of ice are added, the mixture 
 is stirred, and a solution of 75 parts of sodium nitrite in 150 parts of water slowly run 
 in. The 10 per cent. solution of diazonium salt so obtained is filtered from a little 
 insoluble matter and quickly stirred into a solution of 2,400 parts of soda ash in 10,000 
 parts of water at 45°. After conversion to the nitrosamine is shown to be complete 
 by the B-naphthol test, the yellow solution is filtered and solid caustic soda added until 
 a cooled sample shows crystallisation. The whole is then allowed to stand until 
 the separation is complete and the product filtered off. 
 
 Amines, such as the toluidines, p-anisidine, «-naphthylamine, benzidine, etc., 
 which contain no negative substituents require a much higher temperature for the 
 transformation which, in their case, proceeds best at 110° to 120° (G.P. 81202). 
 
 (b) Stabilisation by the Addition of Inorganic Salts. 
 
 It is shown in G.P. 85387 (Meister Lucius and Briining) that solutions of diazo- 
 nium salts can be made much more stable by addition of large excess of mineral acid. 
 This increased stability enabled the solutions to be evaporated under reduced pressure 
 at 45°. The explosive nature of the dry compounds is overcome by mixing the 
 partially evaporated solution with an anhydrous inorganic salt, such as sodium 
 sulphate, calcined alum, etc., which takes up the remaining water to form the hydrated 
 salt, and thus gives a dry powder, said to be quite stable. 
 
 Thus, for example, in the case of p-nitroaniline, the stable diazonium salt is pre- 
 pared by diazotising 14 kg. of p-nitraniline with 7 kg. of sodium nitrite and 17 kg. of 
 
STABILISED DIAZO COMPOUNDS 241 
 
 sulphuric acid (66° Bé) in the usual way at the highest possible concentration. The 
 filtered solution of the diazonium sulphate is then evaporated in a lead- or copper- 
 lined vacuum pan at 45° until it reaches a syrupy consistency. On mixing this with 
 an equal weight of anhydrous sodium sulphate or calcined alum a dry powder is 
 obtained. This comes on the market as Azophor Red PN. A stabilised tetrazo 
 compound similarly prepared from dianisidine is sold as Azophor Blue D. 
 
 These products merely require to be dissolved in water to be ready for use. 
 
 In certain cases, particularly aminoazobenzene and other aminoazo compounds, 
 addition of zinc chloride solution to the solution of diazonium chloride results in the 
 formation of sparingly soluble double chlorides, which are stable (G.P. 89437, ee 
 Lucius and Briining). 
 
 Cassella and Co. (G.P. 97933) found that a mixture of the diazonium sulphate with 
 sodium bisulphate was remarkably stable. It is prepared as follows : 
 
 Into 80 kg. of concentrated sulphuric acid, a stream of nitrous fumes is led until 
 10 kg. has been absorbed. The solution of nitrosylsulphuric acid so formed is cooled 
 and 30 kg. of p-nitroaniline added gradually. <A clear and colourless solution of 
 diazotised p-nitroaniline is formed. To this is added 120 kg. of anhydrous sodium 
 sulphate. After a short time the mass sets solid. Itis ground to a powder, which is not 
 sensitive either to mechanical shock or to heat. It is sold under the name Nitrazol C. 
 
 Other stable diazo and tetrazo compounds are made in similar fashion. 
 
 A later patent of the same firm, G.P. 281098, states that the stability of the product 
 is increased by partly neutralising the sulphuric acid with magnesia or magnesite 
 before adding the sodium sulphate. 
 
 (c) Stable Diazonium Naphthalenesulphonates. 
 
 It was discovered by Becker (G.PP. 81039, 86367, etc.) that diazonium salts, on 
 addition to solution of naphthalenesulphonic acids, form diazonium naphthalene- 
 sulphonates—e.g., NO,.C,H,.N,.SO,.C,)H,. Those derived from naphthalene-«- 
 sulphonic acid are sparingly soluble, and thus easily isolated. They are found to be 
 quite stable if protected from sunlight and moisture. The naphthalene-f-sulphonates 
 are too soluble to be isolated. 
 
 O. N. Witt, however, was able to prepare a double salt of p-nitrobenzenediazonium 
 naphthalene-f-sulphonate with sodium naphthalene-f-sulphonate, which is sparingly 
 soluble and separates as lemon yellow needles having the formula : 
 
 NO,.CH4-No-803.C,,H, + NaSO;.CyH, + H,O 
 
 This is prepared as follows (G.P. 264268): 
 
 _ A solution of 13-8 parts of p-nitroaniline in 100 parts of 50 per cent. sulphuric acid 
 is cooled with ice and diazotised with 7 parts of sodium nitrite in concentrated solution. 
 After filtering from traces of insoluble matter, a concentrated solution of 45 parts of 
 free naphthalene-f-sulphonic acid (C,)H,SO;H-+H,O) is added. The solution 
 becomes orange-red in colour, and after a short time the double salt separates. The 
 separation is completed at the lowest possible temperature, and the salt filtered, 
 washed, pressed, and dried. It is sold as Paranil A. 
 
 16 
 
CHAPTER XVI 
 MISCELLANEOUS INTERMEDIATES 
 
 I. Derivatives of the Cresols. 
 
 Tue three cresols— 
 CH, CH, CH, 
 (Nou aN € 
 { | jou ) 
 U ~ a 
 OH 
 o-Cresol, m-Cresol, p-Cresol, 
 b.p. 191° b.p. 202° b.p. 203° 
 
 —are obtained chiefly from that fraction of the middle oil of coal tar which boils 
 between 185° and 220°, the fraction which contains also most of the naphthalene. 
 They are separated from the associated hydrocarbons and bases by extraction with 
 caustic soda, and a crude mixture of the three isomers boiling between 185° and 205° is 
 finally obtained, which constitutes the ordinary “ cresylic acid.”” From this mixture 
 pure o-cresol is obtained by fractional distillation, since its boiling-point is sufficiently 
 distant from those of m- and p-cresols. The separation of m- and p-cresols is accom- 
 plished by chemical methods. The following methods of separation have been used: 
 
 (a) Sulphonation Method.—The mixture is sulphonated with rather less than its 
 own weight of 94 per cent. sulphuric acid at about 100°. This produces a mixture of 
 the monosulphonic acids— 
 
 ch ) ( » 
 OH Jao 
 a Wa 
 
 —from which p-cresolsulphonic acid can be separated by crystallisation fairly, but 
 not quite, completely. The cresols are then recovered from their sulphonic acids by 
 hydrolysis with superheated steam. -Cresol is thus obtained in good purity, but the 
 m-cresol contains a substantial proportion of p-compound. 
 
 (6) Separation through the Calcium Salts.—The mixture of m- and p-cresols is 
 converted into calcium salts by treatment with lime. The calcium salts are then 
 distilled with superheated steam, which decomposes the calcium salt of m-cresol only, 
 so that m-cresol distils over, while the calcium salt of p-cresol remains unchanged, and 
 is acidified to recover the p-cresol (G.P. 267210). 
 
 o-Cresol and -cresol are used to a small extent as end components in azo dyes. 
 
 o-Cresotinic acid (o-Cresotic acid)— 
 
 CH, 
 
 ( ‘oH 
 
 x coon 
 
 —crystallises in long flat needes, m.p. 163° to 164°, volatile in steam. 
 242 
 
MISCELLANEOUS INTERMEDIATES 243 
 
 This is prepared from o-cresol by the same method as that used in preparing 
 salicylic acid from phenol. It is important to note that the sodium salt of o-cresol 
 is spontaneously inflammable, so that the whole preparation must be carried through 
 in one vessel. The product always contains some unchanged o-cresol (about 20 per 
 cent.),and the cresotinic acid must, therefore, be purified by crystallisation from water. 
 
 Cresotinic acid is used, like salicylic acid, as an end componentinazo dyes, especially 
 in conjunction with diamines of the benzidine series. It is also used in the preparation 
 of a few triphenylmethane dyes by condensation with benzaldehyde derivatives. 
 
 m-Amino-p-cresol methyl ether (Cresidine)— 
 
 —crystallises in long rhombic prisms, m.p. 51-5°, b.p. 235°. It is almost insoluble 
 in cold water, but sparingly soluble in hot water, and easily soluble in alcohol, ether, 
 and benzene. Its hydrochloride is soluble in water. 
 
 Cresidine is prepared from p-cresol by the same series of operations as is used in 
 making o-anisidine from phenol—+.e., nitration, methylation, and reduction (Hofmann 
 and Miller, Ber., 1881, 14,573). Very little information is available with regard to the 
 details of the process. 
 
 CH, CH, CH, CH; 
 ey @) wos, 
 a. ie. en. 
 
 OH OH OCH, OCH, 
 
 Nitro-p-cresol forms yellow flat needles, m.p. 33-5°. According to Staedel (Ann., 
 217, 53), some dinitro-p-cresol is always formed along with the mononitro compound. 
 The latter, however, can be separated by its volatility in steam. 
 
 Nitrocresol methyl ether forms pale yellow crystals, m.p. 8-5°, b.p. 274°. It is 
 almost insoluble in alcohol. 
 
 Cresidine is used as a first and also as a middle component in azo dyes. In the 
 former case it imparts to the colours derived from it, which are mostly reds containing 
 naphtholsulphonic acids as end components, a brilliant bluish tone similar to that 
 observed in dyes derived from o-anisidine. 
 
 Il. Derivatives of Acenaphthene. 
 1 g 
 H,C—-CH, 
 Spe wR 
 
 WU : 
 6 5 
 
 Acenaphthene crystallises in characteristic long needles, melting at 95° and boiling 
 
 at 278°. It occurs in the last fractions of the heavy oil of coal tar, and in the fore- 
 
244, INTERMEDIATES FOR DYESTUFFS 
 
 runnings of the anthracene oil. Its separation is somewhat difficult, owing to the 
 occurrence of a number of substances of similar properties in the same fractions. 
 Fractional distillation and crystallisation are used to some extent, but these, applied 
 in the ordinary way, do not yield a pure product. The fraction boiling between 
 275° and 285° gives a mass of crystals which, after separation from oil, contain about 
 50 per cent. of acenaphthene. 
 
 By a method described in G.P. 277110, pure acenaphthene may readily be separated 
 from these mixed crystals. On mixing 50 kg. of the crystals with 50 kg. of the 240° 
 to 260° fraction of coal tar (containing chiefly methyl naphthalenes), and distilling, 
 the first fraction, up to 245°, remains liquid on cooling. The next fraction, 245° to 
 275°, about 30 kg. in weight, on cooling, deposits 6 kg. of fairly pure acenaphthene 
 crystals. The third fraction, up to 285°, yields 11 kg. of an impure acenaphthene 
 (60 to 70 per cent.), which can be purified by mixing it again with the 240° to 260° 
 fraction and redistilling. A final purification can be given by recrystallising from 
 alcohol. 
 
 Acenaphthenequinone— oc——CO 
 
 —crystallises and sublimes as yellow needles, m.p. 261°, very sparingly soluble in 
 water. 100 gms. of glacial acetic acid at 15° dissolve 0-15 gm. 
 
 This, the only important derivative of acenaphthene, is prepared by oxidation of 
 acenaphthene with chromic acid (Graebe and Gfeller, Ann., 1893, 276, 4). The 
 yields obtained under the best conditions are not good, owing to the tendency for 
 the oxidation to proceed further to form naphthalic acid. Another by-product 
 formed is bisacenaphthylidene diketone : 
 
 HOOC COOH y ye 
 \A a 
 @ To do L$ 
 ae ols 
 Naphthalic Acid Bisacenaphthylidene Diketone 
 
 The preparation is described by Graebe and Gfeller as follows: 
 
 10 gms. of acenaphthene and 70 c.c. of glacial acetic acid are mixed in a basin of 
 2 to 1 litre capacity and heated to 95° to 100°. The flame is then removed and 
 40 to 45 gms. of finely powdered commercial sodium dichromate (89 to 90 per cent.) 
 added with good stirring. In a few moments a vigorous reaction sets in, the acetic 
 acid boils, and the mass foams up. Ina few minutes the reaction is over, and a thick 
 green paste remains. Hot water (200 to 250 c.c.) is added, and after the chromium 
 compounds have dissolved, the liquid is filtered. The red crystalline filter-cake is 
 washed, then heated with 60 to 75 c.c. of 10 per cent. sodium carbonate solution to 
 dissolve out naphthalic anhydride, and filtered again. The residue of crude acenaph- 
 thenequinone is boiled for a short time with 40 c.c. of 40 per cent. bisulphite solution, 
 
MISCELLANEOUS INTERMEDIATES 245 
 
 then 75 c.c. of water added, boiled a littlelonger, and filtered hot. The filtrate contains 
 the bisulphite compound of acenaphthenequinone, which crystallises out partly on 
 cooling. The undissolved residue is extracted again with 20 to 25 c.c. of bisulphite 
 solution. The united filtrates are heated to boiling and excess of sulphuric acid 
 added. After boiling for some time, the acenaphthenequinone separates as fine yellow 
 needles. The yield is 40 to 41 per cent. According to Graebe, even this 40 per cent. 
 yield is only attained by adhering accurately to the specified conditions. 
 
 Another method of preparation, depending on the action of amyl nitrite and 
 hydrochloric acid on acenaphthene, is patented by Kalle and Co. (G.PP. 228698, 
 233473; see also Reissert, Ber., 1911, 44, 1749). 
 
 Acenaphthenequinone is condensed with thioindoxyl and its derivatives to 
 bright scarlet and red vat dyes of the type— 
 
 —lnown as Ciba Scarlet G, Ciba Red R, etc. 
 
 III. Derivatives of Carbazole. 
 
 Se, 
 
 Carbazole crystallises in colourless leaflets, m.p. 238°, b.p. 335°. It is insoluble 
 in water and sparingly soluble in most organic solvents. 100 parts of alcohol at 14° 
 dissolve 0-92 part, and at the boiling-point 3-88 parts. 100 parts of toluene at 16-5° 
 dissolve 0-55 part, and at 100° 5-46 parts. It sublimes easily. It is not appreciably 
 basic in properties. 
 
 As already mentioned (p. 213), it occurs with anthracene in the solid which 
 separates from anthracene oil, and is roughly separated from the anthracene by the - 
 pyridine treatment described. The crude carbazole recovered from the pyridine 
 solution is purified by heating with caustic potash at a high temperature (about 220° 
 to 240°), when a potassium derivative is formed : 
 
 7, Sa A 
 
 WM 
 
 K 
 
 This is non-volatile, and any accompanying anthracene, phenanthrene, etc., can be 
 distilled off under low pressure. The residual potassium compound, on heating with 
 water, is converted back into carbazole, which is then distilled for a final purification 
 (G.P. 178764). 
 
 E.P. 139981 (Burt, Boulton, and Haywood, and F. D. Miles) describes a modifica- 
 
246 INTERMEDIATES FOR DYESTUFFS 
 
 tion of this method of purification. Crude carbazole is heated under pressure with 
 an alkali metal, or oxide or hydroxide of the metal, in presence of an indifferent 
 solvent, such as naphthalene or toluene, at a temperature below the melting-point of 
 the carbazole-metal compound. The solvent is subsequently removed, and the 
 carbazole-metal compound decomposed by boiling with water. 
 
 Carbazole itself is used in the preparation of Hydron Blue R, a vat dyestuff of 
 unknown constitution. For this purpose, the carbazole is first condensed with 
 p-nitrosophenol to form the indophenol : 
 
 aD SIF ean ee aia a LC 
 eral a) 
 Sue Narra 
 
 This indophenol is then converted into the dyestufi by heating with sodium poly- 
 sulphide. 
 N-Ethylcarbazole— oe 
 
 hs © 
 C,H, 
 
 —is prepared by the action of ethylating agents—e.g., ethyl chloride, on potassium- 
 carbazole. It crystallises in leaflets, m.p. 67° to 68°, very soluble in ether and hot 
 alcohol. It is used in making Hydron Blue G. 
 
 3 : 6-Diaminocarbazole— 
 H,N ( Tree NH, 
 ou y 
 
 —crystallises in silvery leaflets (melting-point above 290°), sparingly soluble in hot 
 water, alcohol, or benzene. 
 
 This is prepared by first nitrating carbazole to the dinitro derivative (G.P. 46438, 
 Badische; G.P. 128853, Wirth), and then reducing this with sodium sulphide 
 (G.P. 139568, Wirth). | 
 
 It yields a tetrazo compound, and is used as a component in azo dyes, to which, 
 like benzidine, it imparts the property of dyeing cotton without the aid of a mordant. 
 
 IV. Isoquinoline. 
 Oa 
 oe 
 Crystallises in tables, m.p. 24°, b.p. 242° (760 mm.), D*? 10986. It has an odour 
 like that of quinoline, and is volatile in steam. It is more basic than quinoline. 
 It occurs with quinoline and quinaldine in the heavy coal tar bases, and is most 
 
 conveniently obtained from this source, although the separation is rather troublesome. 
 A partial separation from quinoline and quinaldine can be accomplished by taking 
 
 baal acai. ~ P = 
 eS en a 
 
MISCELLANEOUS INTERMEDIATES 247 
 
 advantage of the greater basicity of isoquinoline (G.P. 285666). But the main 
 purification depends on the fact that the acid sulphates of quinoline and quinaldine 
 are more soluble in alcohol than that of isoquinoline. 
 
 A method is described by Forsyth, Kelly, and Pyman (J.C.S., 1925, 127, 1661) as 
 follows: Three gallons of “ crude pyridine bases’ (corresponding to 6 tons of coal 
 tar) are dehydrated by shaking three times with aqueous sodium hydroxide (80° Tw.), 
 and the product (10-85 litres) is distilled up to 170°, and then fractionated through a 
 twelve-pear column. The various fractions, b.p. 200° to 280°, are fractionated 
 similarly twice more, when 2:3 litres (2,470 g.) of heavy quinoline bases, b.p. 230° to 
 255°, are obtained. This fraction is converted into acid sulphate and crystallised 
 fractionally from alcohol, when 185 g. of pure isoquinoline hydrogen sulphate, m.p. 
 207-5° (corr.), are obtained. This gives 102 g. of the base, b.p. 242° (corr.) over a range 
 of 0-5°; m.p. 24° (corr.). The yield of isoquinoline from the heavy quinoline bases is 
 thus about 4 per cent. 
 
 Another and more laborious method js given by Harris and Pope (J.C.S., 1922, 
 121, 1029). 
 
 Isoquinoline is used for the preparation of Quinoline Red. 
 
INDEXES 
 INDEX OF ABBREVIATIONS 
 
 A.G.F.A. =Actien-Gesellschaft fiir Anilin-Fabrika- 
 tion. 
 
 Ann. =Liebig’s Annalen der Chemie. 
 
 B.D.C. =British Dyestuffs Corporation. 
 
 Ber.=Berichte der deutschen chemischen Gesell- 
 schaft. 
 
 Bull. Soc. Chim.=Bulletin de la Société Chimique 
 de Paris. 
 
 Bull. Soc. Ind. Mulhouse=Bulletin de la Société 
 Industrielle de Mulhouse. 
 
 Chem. Ztg.=Chemiker-Zeitung. 
 
 C.r.=Comptes rendus de |’Académie des Sciences. 
 
 Dingl. Polytech. J.=Dingler’s Polytechnisches 
 Journal. 
 
 K.P.=English Patent. 
 
 G.P.=German Patent. 
 
 Helv. Chim. Acta=Helvetica Chimica Acta. 
 
 J. Am. Chem. Soc.=Journal of the American 
 Chemical Society. 
 
 J.C.S.=Journal of the Chemical Society. 
 
 J. Ind. Eng. Chem.=Journal of Industrial and 
 Engineering Chemistry. 
 
 J.S.C.I.=Journal of the Society of Chemical 
 Industry. 
 
 J. pr. Chem. =Journal fiir praktische Chemie. 
 
 Mon.=Monatshefte fiir Chemie. 
 
 Mon. Sci.=Moniteur Scientifique. 
 
 Rec. trav. chim.=Recueil des Travaux chimiques 
 des Pays-Bas. 
 
 Rev. peas Chim. =La Revue des Produits chimi- 
 
 USP. ~ United States Patent. 
 
 Zeit. angew. Ch.=Zeitschrift fiir angewandte 
 Chemie. 
 
 Zeit. Farb. Ind.=Zeitschrift fiir Farben-In- 
 dustrie. 
 
 Zeit. physik. Chem. =Zeitschrift fiir physikalische 
 Chemie. 
 
 INDEX OF OPERATIONS 
 
 Halogenations : 
 
 (a) with chlorine of: 
 1-Acetylaminoanthraquinone, 228 
 Anthracene, 214 
 Benzaldehyde, 129 
 Benzene, 1 
 o-Chlorotoluene (side chain), 128 
 1-Hydroxyanthraquinone, 231 
 B-Methylanthraquinone, 211 
 p-Nitrochlorobenzene, 9 
 Phthalic anhydride, 202, 203 
 Toluene (side chain), 120, 121 
 Toluene (nuclear), 126 
 Toluene-p-sulphonic acid, 127, 129 
 
 (6) with chlorate and acid of: 
 Anthraquinone-1: 5-disulphonic acid, 237 
 Anthraquinone-a-sulphonic acid, 229 
 Anthraquinone-f-sulphonic acid, 222 
 meso - Dichloroanthracene - 2: 7 - disulphonic 
 
 acid, 216 
 
 (c) with hypochlorite and acid of: 
 Diacetylbenzidine, 34 
 
 (d) with sulphuryl chloride of: 
 B-Methylanthraquinone, 211 
 
 (e) with bromine of: 
 a-Aminoanthraquinone, 226, 227 
 1-Methylaminoanthraquinone, 228 
 
 Nitration of: 
 
 a-Acetylaminoanthraquinone, 225 
 Acetanilide, 38 
 
 Acetylmetanilic acid, 24 
 Acet-o-anisidide, 88 
 Acet-p-phenetidine, 91 
 Acet-p-toluidide, 117 
 Acet-o-toluidide, 109 
 
 Nitration of: 
 o-Aminophenol-p-sulphonic acid, 94 
 Aniline, 138 
 Anthraquinone, 235 fi. 
 Benzaldehyde, 124 
 Benzene, 16 
 Benzidine, 34 
 Benzylideneaniline, 39 
 Chlorobenzene, 2, 4 
 p- -Dichlorobenzene, 14 
 1: 5- “Diphenoxpaitheaeatyiee 234 
 fB-Methylanthraquinone, 211 
 Naphthalene, 137, 141, 148 
 Naphthalene-1: 5- disul phonic acid, 138, 179 
 Naphthalene-1: 6-disulphonic acid, 138, 179 
 Naphthalene-2: 7-disulphonic acid, 175 
 Naphthalene-a-sulphonic acid, 138, 154 
 Naphthalene-f-sulphonic acid, 138, 162 
 Naphthalene-1: 3: 6-trisulphonic acid, 
 
 170 
 
 o-Nitrochlorobenzene-p-sulphonic acid, 11 
 a-Nitronaphthalene, 148 
 Phenol, 83, 92 
 Phenol-p-sulphonic acid, 95 
 Toluene, 102 ff. 
 p-Toluenesulphonyl- o-toluidide, 109 
 o-Toluidine, 118 
 
 138, 
 
 Sulphonation : 
 
 (a) with sulphuric acid of: 
 Alkylanilines, 54 
 Aminoazobenzene, 64 
 o-Aminophenol, 94 
 Aniline, 57 
 Anthracene, 214 
 Anthraquinone, 218, 222 (catalytic) 
 
 248 
 
INDEXES 
 
 Sulphonation : 
 Benzene, 77, 78, 80, 98 
 Benzidine, 32 ff. 
 Benzylethylaniline, 50 
 Chlorotoluenes, 127 
 Cresols, 242 
 Dehydrothiotoluidine, 115 
 Diethylaniline, 55 
 Dimethylaniline, 55 
 2: 5-Dichloroaniline, 14 
 Naphthalene, .135, 151, 159, 160, 166, 167, 
 168, 169, 170 
 Naphthalene-1: 5-disulphonic acid, 174, 175 
 Naphthasultone, 156 
 Naphthionic acid, 150 
 B-Naphthol, 185, 187 ff., 184, 182 
 B-Naphthylamine, 191 ff. 
 1-Naphthylamine-4: 8-disulphonic acid, 158 
 1-Naphthylamine-8-sulphonic acid, 156 
 Nitrobenzene, 22 
 o-Nitrochlorobenzene, 10 
 p-Nitrochlorobenzene, 8, 9 
 p-Nitrotoluene, 110 
 Phenol, 92, 95 
 Toluene, 128, 130 
 m-Tolylenediamine, 118 
 
 (b) by bake process applied to: | 
 
 Benzidine sulphate, 32 
 Aniline sulphate, 57 
 Dehydrothiotoluidine sulphate, 116 
 (c) with sodium sulphite or bisulphite of: 
 o-Nitrochlorobenzene-p-sulphonic acid, 10 
 o-Chlorobenzaldehyde, 130 
 1-Nitroso-2-naphthol, 97 
 (d) with chlorsulphonie acid of: 
 Naphthalene, 164 
 Naphthalene-f-sulphonic acid, 166 
 B-Naphthol, 184 
 Toluene, 130 
 meso-Dichloroanthracene, 216 
 
 Reduction : 
 
 (a) with tron and acid of: 
 
 1-Chloro-2 : 6-dinitrobenzene-4-sulphonic acid, 
 12 
 
 1: 4-Dichloro-2-nitrobenzene, 14 
 
 m-Dinitrobenzene, 20, 21 
 
 Dinitrostilbenedisulphonic acid, 112 
 
 2: 4-Dinitrotoluene, 117 
 
 Dithiosalicylic acid, 207 
 
 p-Nitroacetanilide, 40 
 
 p-Nitroaniline, 41 
 
 o-Nitroanisole, 86 
 
 Nitrobenzene-2: 5-disulphonic acid, 11 
 
 m-Nitrobenzenesulphonic acid, 23 
 
 p-Nitrochlorobenzene, 7 
 
 a-Nitronaphthalene, 142 
 
 1-Nitronaphthalene-3: 8- and 4: 8-disulphonic 
 acids, 179 
 
 1-Nitronaphthalene-3: 6-disulphonic acid, 175 
 
 1-Nitronaphthalene-5- and 8-sulphonic acids, 
 154 
 
 1-Nitronaphthalene-6- and 7-sulphonic acids, 
 163 
 
 1-Nitronaphthalene-3: 6: 8-trisulphonic acid, 
 170 
 
 p-Nitrophenetole, 90 | 
 
 249 
 
 Reduction : 
 
 o-Nitrophenol, 85 
 
 p-Nitrophenol, 89 
 
 o-Nitrotoluene, 105 
 
 p-Nitrotoluene, 110 
 
 (b) with alkaline sulphides or disulphides of: 
 
 1: 5- and 1: 8-Dinitroanthraquinones, 236 
 
 4: 8-Dinitroanthrarufin, 234 
 
 m-Dinitrobenzene, 19 
 
 2:4-Dinitrophenol, 6 
 
 a-Nitroanthraquinone, 235 
 
 1-Nitro-2-methylanthraquinone, 211 
 
 p-Nitrosophenol, 89 
 
 Picric acid, 93 
 
 (c) miscellaneous reductions: 
 
 Anthraquinone to anthranol by aluminium 
 powder and sulphuric acid, 237 
 
 Anthraquinone-a-sulphonic acid to anthra- 
 cene-a-sulphonic acid by zinc dust and 
 ammonia, 231 
 
 pp’ -Diethoxyazobenzene to p-phenetidine by 
 tin and hydrochloric acid, 91 
 
 2:4-Dinitrophenol to 4-nitro-2-aminophenol 
 by iron and sulphurous acid, 6 
 
 2: 6-Dinitrophenol-4-sulphonic acid with zine 
 dust and acid, 95 
 
 o-Nitroanisole to hydrazoanisole by zinc dust 
 and alkali, 86 
 
 Nitrobenzene to hydrazobenzene by iron or 
 zinc and alkali, 29 ff. 
 
 m-Nitrobenzaldehyde to m-aminobenzalde- 
 hyde by ferrous sulphate and chalk, 
 124 
 
 p-Sulphobenzenediazonium chloride to p- 
 sulphophenylhydrazine by sodium bisul- 
 phite, 59 
 
 Alkali Fusions of (or action of dilute or concen- 
 trated alkali on): 
 
 Anthracene-a-sulphonic acid, 232 
 Benzenesulphonic acid, 81 
 Benzene-m-disulphonic acid, 99 
 Dimethylaniline-m-sulphonic acid, 55 
 Metanilic acid, 24 
 Naphthalene-1: 5-disulphonic acid, 178 
 Naphthalene-2: 7-disulphonic acid, 177 
 Naphthalene-a-sulphonic acid, 152 
 Naphthalene-f-sulphonic acid, 160 
 1 : 8-Naphthasultam-2: 4-disulphonic 
 158 
 1-Naphthylamine-4: 8-disulphonic acid, 157 
 2-Naphthylamine-6: 8-disulphonic acid, 194 
 1-Naphthylamine-3:6:8-trisulphonic acid, 
 
 acid, 
 
 171 
 Phenylthioglycol-o-carboxylic acid, 208 
 
 Amidations of: 
 
 Anthraquinone-a-sulphonic acid, 224 
 
 Anthraquinone-f-sulphonic acid, 221 
 
 a-Chloroanthraquinone (by p-toluenesulphon- 
 amide), 229 
 
 p-Chloroanthraquinone, 222 
 
 Chlorobenzene, 28 
 
 1: 4-Dichloro-2-nitrobenzene, 14 
 
 1: 2-Dichloro-4-nitrobenzene, 9 
 
 p-Naphthol, 190 
 
 2-Naphthol-1-sulphonic acid, 185 
 
250 
 
 Amidations of: 
 2-Naphthol-7-sulphonic acid, 177 
 4-Nitroaniline-3-sulphonic acid, 25 
 o-Nitrochlorobenzene, 12 
 p-Nitrochlorobenzene, 8 
 Resorcinol, 100 
 
 Alkylations of: 
 
 1-Amino-2-bromoanthraquinone 
 methyl sulphate), 226 
 
 Aniline (with ethyl alcohol and hydrochloric 
 acid), 46 
 
 Aniline (with methyl alcohol and sulphuric 
 acid), 44, 45 
 
 Aniline (with methyl chloride), 45 
 
 Aniline (with formaldehyde and a reducing 
 agent), 44 
 
 Diphenylamine, 61 
 
 a-Hydroxyanthraquinone (with p-toluene- 
 sulphonic methyl] ester), 231 
 
 a-Naphthylamine, 144 
 
 o-Nitropheny! (with methyl! chloride), 85 
 
 p-Nitrophenol (with ethyl chloride), 90 
 
 m-Phenylenediamineoxamic acid with ethyl 
 bromide), 22 
 
 o-Toluidine, 106 
 
 (with di- 
 
 Oxidations of: 
 
 Acenaphthene, 244 
 
 Anthracene, 217, 218 
 1-Chloro-2-methylanthraquinone, 212 
 Indoxy] (to isatin), 75 
 
 Naphthalene, 199, 200 
 p-Nitrotoluenesulphonic acid, 111 
 Tetramethyldiaminodiphenylmethane, 53 
 Toluene, 123, 125 
 
 Condensations of: 
 
 2: 4-Dinitrochlorobenzene 
 phenol, 6 
 
 with p-amino- 
 
 INTERMEDIATES FOR DYESTUFFS 
 
 Condensations of : 
 
 Anthraquinone-1: 5-disulphonic acid with 
 phenol, 234 
 
 Phthalic anhydride with benzene (Friedel- 
 Crafts reaction), 209 
 
 Phthalic anhydride with toluene (Friedel- 
 Crafts reaction), 210 
 
 Phthalic anhydride with p-chlorophenol, 208 
 
 Aniline with chloroacetic acid, 65 
 
 Anthranilic acid with chloroacetic acid, 205 
 
 Thiosalicylic acid with chloroacetic acid, 207 
 
 Nitrosations of: 
 Dimethylaniline, 51 
 Ethyl-o-toluidine, 107 
 B-Naphthol, 197 
 Phenol, 83 
 
 Hydrolyses of: 
 Benzal chloride, 122 
 Benzotrichloride, 125 
 o-Chlorobenzalchloride, 128 
 Naphthionic acid, 146 
 a-Naphthylamine, 145 
 1-Naphthylamine-3: 6: 8-trisulphonic 
 
 173 
 
 Miscellaneous Reactions: 
 
 Replacement of Cl by OH in p-dichloro- 
 benzene, 13 
 
 Replacement of Cl by OH in 2: 4-dinitro- 
 chlorobenzene, 5 
 
 Transformation of hydrazobenzene to benzi- 
 dine, 31 
 
 Transformation of hydrazoanisole to dianisi- 
 dine, 87 
 
 Sandmeyer reaction applied to diazotised 
 o-toluidine, 108 
 
 Hofmann transformation applied to phthal- 
 imide, 204 ; 
 
 acid, - 
 
 ee 
 
GENERAL INDEX 
 
 (Main references in bold type) 
 
 ACENAPHTHENE, 243 
 
 —— oxidation of, 244 
 
 Acenaphthenequinone, 244 
 
 Acetaldehyde, 71 
 
 Acetanilide, 36 
 
 nitration of, 38 
 
 Acet-o-anisidide, 88 
 
 Acet-p-phenetidide (phenacetine), 91 
 
 Acet-o-toluidide, 105, 109, 204 
 
 Acet-p-toluidide, 110, 117 
 
 a-Acetylaminoanthraquinone, 224 
 
 nitration of, 225 
 
 chlorination of, 228 
 
 1-Acetylamino-4-chloroanthraquinone, 228 
 
 1-Acetylamino-4-nitroanthraquinone, 225 
 
 Acrolein, 69 
 
 Alkylated m-aminophenols, 54 
 
 Alkylanilines, sulphonation of, 54 
 
 Alkylanilinesulphonic acids, alkali fusion of, 54-56 
 
 te a (see 2-naphthylamine-7-sulphonic 
 aci 
 
 Amido-G-acid 
 sulphonic acid) 
 
 Amido-R-acid 
 sulphonic acid) 
 
 p-Aminoacetanilide, 40 
 
 hydrolysis of, 41 
 
 a-Aminoanthraquinone, 97, 222, 223, 229, 235 
 
 —— acetylation of, 224 
 
 benzoylation of, 224 
 
 bromination of, 226, 227 
 
 p-Aminoanthraquinone, 216, 220, 222 
 
 a-Aminoanthraquinoneoxamic acid, 225 
 
 nitration of, 226 
 
 Aminoazobenzene, 62, 148 
 
 stable diazo derivative of, 241 
 
 Aminoazobenzenedisulphonic acid, 64 
 
 Aminoazobenzenesulphonic acids, 64 
 
 Aminoazotoluene, 105, 148 
 
 m-Aminobenzaldehyde, 124 
 
 1-Amino-2-bromoanthraquinone, 226 
 
 methylation of, 226 
 
 1-Amino-2-bromo-4-hydroxyanthraquinone, 227 
 
 1-Amino-2: 4-dibromoanthraquinone, 227 
 
 1-Amino-4-chloroanthraquinone, 228 
 
 m-Amino-p-cresol methyl! ether, 243 
 
 1-Amino-2-methylanthraquinone, 211 
 
 1-Amino-5-naphthol, 158 
 
 1: 8-Aminonaphthol-2: 4-disulphonic acid, 158 
 
 1: 8-Aminonaphthol-3 : 6-disulphonic acid, 168 ff., 
 172 
 
 (see 2-naphthylamine-6: 8-di- 
 
 (see 2-naphthylamine-3: 6-di- 
 
 coe 
 
 —_ = 
 
 alkali fusion of, 173 
 
 1: 8-Aminonaphthol-4: 6-disulphonic acid, 174 
 1: 8-Aminonaphthol-4-sulphonic acid, 156, 157 
 1-Amino-2-naphthol-4-sulphonic acid, 197, 198 
 2-Amino-5-naphthol-7-sulphonic acid, 195 
 2-Amino-8-naphthol-6-sulphonic acid, 194 
 1-Amino-4-nitroanthraquinone, reduction of, 225 
 Aminophenazoxine, 85 
 
 o-Aminophenol, 85 
 
 sulphonation of, 94 
 
 m-Aminophenol, 24, 101 
 
 p-Aminophenol, 88, 89 
 o-Aminophenol-p-sulphonic acid, 11, 94, 178 
 Aminosalicylic acid, 97 
 
 | 
 
 Aniline, 26 ff., 36, 110, 145, 172, 195, 196 
 —— alkylation of, 42 ff. 
 
 —— condensation with chloracetic acid, 65 
 —— —— with formaldehyde and cyanide, 67 
 —— —— with trichloroethylene, 68 
 diazotisation of, 98 
 
 —— methyl-w-sulphonate of, 67 
 
 —— nitration of, 38 
 
 —— sulphonation of, 57 
 
 Aniline-2: 5-disulphonic acid, 10 
 
 o-Anisidine, 86 
 
 Anisoyl! chloride, 234 
 
 Anthracene, 213, 245 
 
 —— oxidation of, 217, 218 
 
 —— chlorination of, 214 
 
 —— sulphonation of, 214 
 Anthracene-a-sulphonic acid, 214, 232 
 
 alkali fusion of, 232 
 Anthracene-f-sulphonic acid, 214 
 
 Anthranilic acid, 204 
 
 condensation with chloroacetic acid, 205 
 conversion to thiosalicylic acid, 206 
 Anthranilodiacetic acid, 205 
 
 Anthranol, 237 
 
 condensation with glycerol, 238 
 Anthraquinone, 209, 216 ff. 
 
 —— nitration of, 235 ff. 
 
 —— reduction of, 237 
 
 sulphonation of, 218, 222 
 
 : Anthraquinone-1 : 5-disulphonic acid, 218, 223 
 
 —— —— —— hydrolysis of, 233 
 chlorination of, 237 
 Anthraquinone-1 : 8-disulphonic acid, 218, 223 
 Anthraquinone-2: 6-disulphonic acid, 218, 220 
 Anthraquinone-2: 7-disulphonic acid, 218, 220 
 Anthraquinone-a-sulphonic acid, 218, 222 _ 
 action of methylamine on, 228 
 amidation of, 224 
 
 ——- —— —— chlorination of, 229 
 
 —_— —— —— hydrolysis by dilute alkali, 230 
 ——- —_—- —— reduction of, 232 
 Anthraquinone-f-sulphonic acid, 218, 219 
 —— —— —— amidation of, 221 
 
 chlorination of, 222 
 Anthrarufin, 233 
 
 a-Anthrol, 74, 282 
 
 Anthrone, 237 
 
 Azobenzene, 30 
 
 Azophor Blue D, 241 
 
 Azophor Red PN, 241 
 
 Azoxybenzene, 30 
 
 Benzal chloride, 120, 122 
 Benzaldehyde, 39, 117, 122 ff., 133 
 nitration of, 124 
 
 chlorination of, 129 
 Benzaldehyde-o-sulphonic acid, 129 
 Benzanthrone, 237 
 
 Benzene, chlorination of, 1, 2 
 nitration of, 16 
 
 sulphonation of, 77 ff., 98 
 condensation with phthalic anhydride, 209 
 Benzene-m-disulphonic acid, 98 
 —_—__ —— —— alkali fusion of, 99 
 Benzene-p-disulphonic acid, 98 
 
 251 
 
INTERMEDIATES 
 
 Benzenesulphonic acid, 77 ff. 
 Benzidine, 29 ff., 172, 240 
 sulphonation of, 32 ff. 
 —— nitration of, 34 
 Benzidine-3: 3’-disulphonic acid, 32, 109 
 Benzidinesulphone, 33 
 Benzidinesulphonedisulphonic acid, 33 
 Benzoic acid, 125, 126 
 Benzotrichloride, 120, 122, 125 
 Benzoylchloride, 126, 234 
 a-Benzoylaminoanthraquinone, 224 
 Benzyl] alcohol, 50, 120 
 Benzyl chloride, 49, 120 
 Benzylethylaniline, 47, 49, 123 
 Benzylethylanilinedisulphonic acid, 50 
 Benzylethylanilinesulphonic acid, 50 
 Benzylideneaniline, 38, 39 
 nitration of, 39 
 Benzylmethylaniline, 44, 49 
 Bisacenaphthylidene diketone, 244 
 Bronner acid (see 2-naphthylamine-6-sulphonic 
 acid 
 Reriat reaction, 100, 139 
 n-Butylaniline, 71 
 
 252 
 
 Carbazole, 83, 213, 245 
 
 w-Chloroacetanilide, 65 
 
 Chloroacetic acid, 65, 68, 105 
 
 -Chloroaniline, 7 
 
 a-Chloroanthraquinone, 229 
 
 amidation of, 229 
 
 B-Chloroanthraquinone, 220, 222 
 
 amidation of, 222 
 
 1-Chloroanthraquinone-2-carboxylic 
 212 
 
 o-Chlorobenzalchloride, 128 
 
 o-Chlorobenzaldehyde, 128, 129 
 
 Chlorobenzene, 1 
 
 o-Chlorobenzoic acid, 128 
 
 1-Chloro-2: 6-dinitrobenzene-4-sulphonic acid, 11 
 
 1-Chloro-2: 6-diaminobenzene-4-sulphonic acid, 
 12 
 
 1-Chloro-2-methylanthraquinone, 211 
 
 —— oxidation of, 212 
 
 o-Chloro-p-nitroaniline, 10 
 
 p-Chloro-o-nitroaniline, 14, 15 
 
 p-Chlorophenol, 13, 208 
 
 Chloropicrin, 70 
 
 o-Chlorotoluene, 108, 126 
 
 —— side-chain chlorination of, 128 
 
 p-Chlorotoluene, 127 
 
 Chlorotoluenes, sulphonation of, 127 
 
 o-Chlorotoluene-p-sulphonic acid, 127 
 
 p-Chlorotoluene-o-sulphonic acid, 127 
 
 Chromotrope acid (see 1 : 8-dihydroxynaphthalene- 
 3: 6-disulphonic acid) 
 
 Cleve’s acids (see 1l-naphthylamine-6- and 7- 
 sulphonic acids) 
 
 Cresidine (see m-amino-p-cresol methyl ether) 
 
 o-Cresol, 242 
 
 m-Cresol, 242 
 
 p-Cresol, 242 
 
 Cresols, sulphonation of, 242 
 
 o-Cresotinic (o-cresotic) acid, 242 
 
 Crocein acid (see 2-naphthol-8-sulphonic acid) 
 
 Crotonaldehyde, 71 
 
 Crotonylideneaniline, 71 
 
 acid, 191, 
 
 FOR DYESTUFEFS 
 
 Dahl’s acids II. and III. (see 1-naphthylamine- 
 4: 6-and 4: 7-disulphonic acids) 
 
 Dehydrothiotoluidine, 113 
 
 Dehydrothiotoluidinesulphonic acids, 115, 116 
 
 Dehydrothio-m-xylidene, 134 
 
 iso- Dehydrothio-m-xylidene, 134 
 
 Diacetylbenzidine, 34 
 
 Diacetyldianisidine, 86 
 
 1: 4-Diaminoanthraquinone, 224 
 
 1: 5-Diaminoanthraquinone, 236 
 
 1: 8-Diaminoanthraquinone, 236 
 
 Diaminoanthrarufin, 233 
 
 3: 6-Diaminocarbazole, 246 
 
 pp’ -Diaminodi-p-xylylphenylmethane, 133 
 
 2: 6-Diaminophenol-4-sulphonic acid, 95 
 
 Diaminostilbenedisulphonic acid, 112 
 
 Dianisidine, 86 
 
 Diazoaminobenzene, 62, 63 
 
 Diazo compounds, stabilised, 239 ff. 
 
 Diazonium naphthalenesulphonates, 241 
 
 Diazonium salts, action of alkalies on, 239 
 
 Dibenzyl, 123 
 
 5: 7-Dibromoisatin, 76, 232 
 
 5: 7-Dibromoisatin chloride, 76 
 
 2: 5-Dichloroaniline, 14, 240 
 
 sulphonation of, 14 
 
 2: 5-Dichloroaniline-4-sulphonic acid, 14 
 
 meso-Dichloroanthracene, 214 
 
 meso-Dichloroanthracene-2: 6- 
 phonic acids, 216 
 
 meso-Dichloroanthracene-8-sulphonic acid, 216 
 
 Id: 5-Dichloroanthraquinone, 236 
 
 2: '7-Dichloroanthraquinone, 216 
 
 2: 5-Dichlorobenzaldehyde, 128 
 
 3: 4-Dichlorobenzaldehyde, 129 
 
 o-Dichlorobenzene, 1 
 
 p-Dichlorobenzene, 1 
 
 —— nitration of, 14 ; 
 
 : 3’-Dichlorobenzidine, 34 
 
 : 2-Dichloro-4-nitrobenzene, 9 
 
 : 4-Dichloro-2-nitrobenzene, 14 
 
 : 4-Dichlorophthalic anhydride, 202 
 
 : 4-Dichlorophthalic anhydride, 202 
 
 : 6-Dichlorophthalic anhydride, 202 
 
 : §-Dichlorophthalic anhydride, 202 
 
 : 5-Dichlorotoluene, 129 
 
 : 5-Dichlorotoluenesulphonic acid, 129 
 
 and 2: 7-disul- 
 
 bo bo BGO 09 CO 
 
 Dichloroviny] ether, 68 
 
 pp’ -Diethoxyazobenzene, 91 
 
 Diethyl-m-aminophenol, 55 
 
 Diethylaniline, 46 
 
 sulphonation of, 55 
 
 Diethylaniline-m-sulphonic acid, alkali fusion of, 
 6 
 
 5) 
 4-Dihydroxyanthraquinone (see quinizarin) 
 5-Dihydroxynaphthalene, 159,178 — 
 8-Dihydroxynaphthalene-3: 6-disulphonic acid 
 173, 174 
 
 1: 8-Dihydroxynaphthalene-4-sulphonic acid, 157 
 Dimethylamine sulphite, 101 
 
 1: 
 1 
 1: 
 
 Dimethyl-m-aminophenol, 54, 101 
 
 Dimethylaniline, 44 ff., 123 
 
 —— nitrosation of, 51 
 
 —— sulphonation of, 55 
 
 Dimethylaniline-m-sulphonic acid, alkali fusion of, 
 55 
 
 2: 2’-Dimethyl-1: 1’-dianthraquinonyl, 210 
 
INDEXES 
 
 sym. Dimethyl-m-phenylenediamine, 101 
 
 Dimethy! sulphate, 46 
 
 Bp’-Dinaphthol, 161 
 
 BB’-Dinaphthylene oxide, 161 
 
 Bp’-Dinaphthylamine, 190 
 
 1: 5-Dinitroanthraquinone, 235 
 
 1: 8-Dinitroanthraquinone, 235 
 
 4: 8-Dinitroanthrarufin, 234 
 
 m-Dinitrobenzene, 18 
 
 1: 3-Dinitrobenzene-4-sulphuric acid, 7 
 
 3: 3’-Dinitrobenzidine, 35 
 
 2: 4-Dinitrochlorobenzene, 4, 90 
 
 2: 6-Dinitrochlorobenzene, 4 
 
 Dinitrodibenzyldisulphonic acid, 111 
 
 2: 4-Dinitro-4’-hydroxydiphenylamine, 6, 90 
 
 1: 5-Dinitronaphthalene, 148 
 
 1: 8-Dinitronaphthalene, 148 
 
 action of sodium sulphite on, 149 
 
 2: 4-Dinitrophenol, 5, 95 
 
 2: 6-Dinitrophenol-4-sulphonic acid, 95 
 
 Dinitrostilbenedisulphonic acid, 111, 116 
 
 Dinitrothiophene, 18 
 
 2: 3-Dinitrotoluene, 105 
 
 2: 4-Dinitrotoluene, 104 
 
 reduction of, to diamine, 117 
 
 of, to nitroamine, 118 
 
 2: 6-Dinitrotoluene, 105 
 
 Dioxy-S-acid (see 1: 8-dihydroxynaphthalene-4- 
 sulphonic acid) 
 
 1: 5-Diphenoxyanthraquinone, 234 
 
 Diphenylamine, 60 
 
 methylation of, 61, 62 
 
 Diphenyline, 31 
 
 Diphenyldiketopiperazine, 65 
 
 Diphenylsulphone, 78 
 
 Dithiosalicylic acid, 206 
 
 —— reduction of, 207 
 
 e-Acid (see 1-naphthol-3: 8-disulphonic acid) 
 
 Erithroxyanthraquinone (see a-hydroxyanthra- 
 quinone) 
 
 Ethyl-m-aminophenol, 22, 56 
 
 Ethylaniline, 46, 71 
 
 Ethylbenzene, 132 
 
 Ethylbenzylaniline, 49 
 
 Ethylbenzylanilinesulphonic acid, 50 
 
 N-Ethylcarbazole, 246 
 
 Ethyl chloride, 47 
 
 Ethylenetriphenyltriamine, 68 
 
 Ethylideneaniline, 71 
 
 Ethylmethylaniline, 44 
 
 Ethyl-a-naphthylamine, 144 
 
 6-Ethylquinaldine, 72 
 
 Ethyl-o-toluidine, 106, 125, 128 
 
 nitrosation of, 107 
 
 F-Acid (see 2-naphthol-7-sulphonic acid) 
 
 Formaldehyde, 44, 52, 67, 97, 117 
 
 ‘* Formaldehyde-bisulphite,’’ 67, 205, 206 ; 
 
 Freund’s acid (see 1-naphthylamine-3: 6-disul- 
 phonic acid) 
 
 Friedel-Crafts reaction, 209, 210 
 
 G-acid (see 2-naphthol-6: 8-disulphonic acid) 
 
 Gamma acid (see 2-amino-8-naphthol-6-sulphonic 
 
 acid) 
 lycerol, 69, 238 
 
 253 
 
 pee (see 1: 8-aminonaphthol-3: 6-disulphonic 
 aci 
 
 Hydrazoanisole, 86 
 
 Hydrazobenzene, 29-31 
 
 Hydrazotoluene, 108 
 Hydrocyancarbodiphenylimide, 73 
 a-Hydroxyanthraquinone, 230 
 
 methylation of, 231 
 
 chlorination of, 231 
 m-Hydroxybenzaldehyde, 125 
 1-Hydroxy-4-chloroanthraquinone, 231 
 2-Hydroxy-3-naphthoic acid, 196 
 2-Hydroxy-3-naphthoic anilide, 196 
 2-Hydroxythionaphthene (thioindoxyl), 74, 207 
 2-Hydroxythionaphthene-1-carboxylic acid, 207 
 
 Indoxyl, oxidation to isatin, 75 
 Indoxylic acid, oxidation to isatin, 75 
 Isatin, 74, 232 
 
 a-Isatinanilide, 72 
 
 hydrolysis to isatin, 75 
 
 a-Isatin chloride, 76 
 
 Isodiazotates, 239 
 
 Tsoquinoline, 246 
 
 J-acid (see 2-amino-5-naphthol-7-sulphonic acid) 
 
 K-acid (see 1: 8-Aminonapthhol-4: 6-disulphonic 
 acid) 
 
 Koch acid (see 1-naphthylamine-3: 6: 8-trisul- 
 phonic acid) 
 
 Laurent’s acid (see 1-naphthylamine-5-sulphonic 
 acid) 
 Leucoquinizarin, 209 
 
 Metanilic acid, 23 
 
 ‘*Methane base”’ 
 phenylmethane) 
 
 a-Methoxyanthraquinone, 230 
 
 Methylamine, 101, 228 
 
 1-Methylaminoanthraquinone, 228 
 
 bromination of, 228 
 
 1-Methylamino-2-bromoanthraquinone, 226 
 
 1-Methylamino-4-bromoanthraquinone, 228 
 
 Methyl-m-aminophenol, 101 
 
 Methylaniline, 43, 44 
 
 p-Methylanthraquinone, 209 
 
 chlorination of, 211 
 
 nitration of, 211 
 
 Methylbenzylaniline, 44, 49 
 
 Methyldiphenylamine, 61 
 
 Methylenedianiline, 44 
 
 o-Methylphenylglycine, 105 
 
 Methy]-o-toluidine, 106 
 
 ‘*Michler’s hydrol’’? (see tetramethyldiamino- 
 benzhydrol) 
 
 ‘¢Michler’s ketone’? (see tetramethyldiamino- 
 benzophenone) 
 
 (see tetramethyldiaminodi- 
 
 Naphthalene, 114, 141 
 
 nitration of, 137, 141, 148 
 
 —— oxidation of, 199, 200 
 
 —— sulphonation of, 135, 151, 159 ff., 164, 166, 
 167 ff. 
 
 Naphthalene-1: 5-disulphonic acid, 136, 164, 168 
 
 alkali fusion of, 178 
 
md 
 
 254 INTERMEDIATES 
 
 Naphthalene-1 :5-disulphonic acid, nitration of,179 
 
 sulphonation of, 174, 175 
 
 Naphthalene-1: 6-disulphonic acid, 136, 164, 166, 
 168 
 
 —— nitration of, 179 
 Naphthalene-2: 6-disulphonic acid, 136, 164, 167, 
 177 
 
 Naphthalene-2: 7-disulphonic acid, 136, 164, 167, 
 177 
 
 nitration of, 175 
 
 Naphthalene-a-sulphonic acid, 135, 151 ff. 
 
 alkali fusion of, 152 
 
 nitration of, 138, 154 
 
 Naphthalene-B-sulphonic acid, 135, 159 ff. 
 
 ——_— —-— alkali fusion of, 160 
 
 —— —— nitration of, 138, 162 
 
 —— —— sulphonation of, 166 
 
 —— —— use in stabilisation of diazo compounds, 
 241 
 
 Naphthalene-1: 3: 5-trisulphonic acid, 136 
 
 Naphthalene-1: 3: 6-trisulphonic acid, 136, 169, 
 176 
 
 nitration of, 170 
 
 Naphthalene-1: 3: 7-trisulphonic acid, 136 
 
 Naphthalene-1: 3: 5: 7-tetrasulphonic acid, 137 
 
 Naphthalic acid, 244 
 
 1: 8-Naphthasultam-2: 4-disulphonic acid, 157 
 
 —— —— alkali fusion of, 158 
 
 1: 8-Naphthasultone, 156 
 
 —— sulphonation of, 156 
 
 1: 8-Naphthasultonedisulphonic acid, 173 
 
 1: 8-Naphthasultone-3-sulphonic acid, 180 
 
 Naphthionic acid (see 1 naphthylamine-4-sulphonic 
 acid) 
 
 a-Naphthol, 74, 145, 152, 182 
 
 B-Naphthol, 52, 105, 117, 119, 133, 160 ff., 177, 
 194, 239 
 
 amidation of, 190 
 
 —— nitrosation of, 197 
 
 —— sulphonation of, 185, 187 ff., 182 
 
 —— sulphonation with chlorsulphonic acid, 184 
 
 Naphthol AS (2-hydroxy-3-naphthoic anilide), 88, 
 117, 119, 239 
 
 1-Naphthol-3: 6-disulphonic acid, 176 
 
 1-Naphthol-3: 8-disulphonic acid, 180 
 
 1-Naphthol-4: 8-disulphonic acid, 156 
 
 2-Naphthol-3: 6-disulphonic acid, 184, 186, 187 
 
 2-Naphthol-6: 8-disulphonic acid, 184, 187 
 
 Naphthol pitch, 161 
 
 1-Naphthol-4-sulphonic acid, 140, 147 
 
 1-Naphthol-5-sulphonic acid, 178 
 
 1-Naphthol-8-sulphonic acid, 156 
 
 2-Naphthol-1-sulphonic acid, 182, 184 
 
 —— —— amidation of, 185 
 
 2-Naphthol-6-sulphonic acid, 177, 182, 185, 186 
 
 2-Naphthol-7-sulphonic acid, 176 
 
 ——amidation of, 177 
 
 2-Naphthol-8-sulphonic acid, 182, 185 
 
 1-Naphthol-2: 4: 7-trisulphonic acid, 145 
 
 1-Naphthol-3: 6: 8-trisulphonic acid, 173 
 
 alkali fusion of, 174 
 
 a-Naphthylamine, 98, 142, 145, 155, 159, 176, 246 
 
 ethylation of, 144 
 
 —— hydrolysis of, 139 
 
 —— sulphonation of, 146 
 
 B-Naphthylamine, 140, 190, 212 
 
 —— sulphonation of, 191 ff. 
 
 FOR DYESTUFFS 
 
 1-Naphthylamine-3: 6-disulphonic acid, 175 
 
 1-Naphthylamine-3: 8-disulphonic acid, 179 
 
 1-Naphthylamine-4: 6-disulphonic acid, 149 
 
 1-Naphthylamine-4: 7-disulphonic acid, 149 
 
 1-Naphthylamine-4: 8-disulphonic _ acid, 
 179 ff. 
 
 —— —— alkali fusion of, 157 
 
 —— sulphonation of, 158 
 
 2-Naphthylamine-1: 5-disulphonic acid, 191, 192 
 
 2-Naphthylamine-3: 6-disulphonic acid, 189 
 
 ae aphthylamine-4: 7- and 4: 8-disulphonic acids, 
 
 79 
 
 2-Naphthylamine-5: 7-disulphonic 191, 
 192 ff., 195 
 
 2-Naphthylamine-6: 8-disulphonic acid, 189, 191, 
 192 ff. 
 
 —— alkali fusion of, 194 
 
 1-Naphthylamine-4-sulphonic acid (naphthionic 
 acid), 140, 146 
 
 —— —— hydrolysis of, 147 
 
 —— sulphonation of, 150 
 
 1-Naphthylamine-5-sulphonic acid, 146, 154 
 
 —— alkali fusion of, 158, 159 
 
 1-Naphthylamine-6- and 7-sulphonic acids (Cleve’s — 
 acids), 162 
 
 1-Naphthylamine-6-sulphonic acid, 152 ff. 
 
 condensation with arylamines, 155 
 
 —— —— conversion to naphthasultone, 156 
 
 —— sulphonation of, 156 
 
 2-Naphthylamine-1-sulphonic acid, 184 
 
 2-Naphthylamine-5-sulphonic acid, 191 
 
 2-Naphthylamine-6-sulphonic acid, 187, 191 
 
 2-Naphthylamine-7-sulphonic acid, 177, 191 
 
 2-Naphthylamine-8-sulphonic acid, 191 
 
 1-Naphthylamine-3: 6: 8-trisulphonic acid, 170, 
 171, 174 
 
 alkali fusion of, 171 
 
 —— —— hydrolysis of, 173 
 
 —— —— elimination of the 8-sulpho group from, 
 176 
 
 2-Naphthylamine-1: 5: 7-trisulphonic acid, 192 
 
 B-Naphthylsulphuric ester, 182 
 
 Nitrazol C, 241 
 
 o-Nitroacetanilide, 38 
 
 p-Nitroacetanilide, 38 
 
 reduction of, 40 
 
 hydrolysis of, 39 
 
 p-Nitro-o-aminophenol, 5 
 
 2-Nitro-6-aminophenol-4-sulphonic acid, 94 
 
 3-Nitro-4-aminotoluene, 117 
 
 4-Nitro-2-aminotoluene, 118, 119 
 
 5-Nitro-2-aminotoluene, 109, 118 
 
 6-Nitro-2-aminotoluene, 118 
 
 o-Nitroaniline, 12, 18, 38 
 
 m-Nitroaniline, 19 
 
 156, 
 
 acid, 
 
 p-Nitroaniline, 8, 36, 39, 161, 172 
 
 reduction, 41 
 
 stabilisation of its diazo compound, 240, 
 241 
 
 p-Nitroaniline-o-sulphonic acid, 9 
 
 4-Nitroaniline-3-sulphonic acid, 24 
 
 4-Nitro-2-anisidine, 87 
 
 5-Nitro-2-anisidine, 88 
 
 o-Nitroanisole, 13, 85 
 
 —— alkaline reduction of, 86 
 
 —— acid reduction of, 86 
 
 a-Nitroanthraquinone, 235 
 
INDEXES 
 
 o-Nitrobenzaldehyde, 124 
 
 m-Nitrobenzaldehyde, 124 
 
 Nitrobenzene, 16, 69 
 
 alkaline reduction of, 29 
 
 acid reduction of, 26 
 
 electrolytic reduction of, 89 
 
 Nitrobenzene-2: 5-disulphonic acid, 10 
 
 m-Nitrobenzenesulphonic acid, 22 
 
 2-Nitrobenzidine, 34 
 
 o-Nitrochlorobenzene, 2 
 
 sulphonation of, 10 
 
 -Nitrochlorobenzene, 2 
 
 amidation of, 8 
 
 reduction of, 7 
 
 sulphonation of, 8 
 
 o-Nitrochlorobenzene-p-sulphonic acid, 10, 94 
 
 p-Nitrochlorobenzene-o-sulphonic acid, 8 
 
 m-Nitro-p-cresol, 243 
 
 m-Nitro-p-cresol methyl ether, 243 
 
 1-Nitro-2-methylanthraquinone, 211 
 
 a-Nitronaphthalene, 137, 144 
 
 nitration of, 148 
 
 reduction of, 142 
 
 1-Nitronaphthalene-3: 6-disulphonic acid, 175 
 
 1-Nitronaphthalene-3: 8-disulphonic acid, 179 
 
 1-Nitronaphthalene-4: 8-disulphonic acid, 179 
 
 1:6- and 1: 7-Nitronaphthalenesulphonic acids, 
 154, 155 
 
 reduction of, 162 
 
 1:5 and 1:8-Nitronaphthalenesulphonic acids, 
 152 
 
 —— 
 
 reduction of, 154 
 1-Nitronaphthalene-3: 6: 8-trisulphonic acid, 170 
 1-Nitronaphthalene-4: 6: 8-trisulphonic acid, 174 
 o-Nitro-p-phenetidine, 91 
 p-Nitrophenetole, 90 
 
 o-Nitrophenol, 83 
 
 methylation of, 85 
 
 reduction of, 85 
 
 p-Nitrophenol, 83 
 
 ethylation of, 90 
 
 reduction of, 89 
 o-Nitrophenol-p-sulphonic acid, 11 
 4-Nitro-m-phenylenediamine, 25 
 Nitrosamines (isodiazotates), 239 
 p-Nitrosodiethylaniline, 51 
 p-Nitrosodimethylaniline, 51, 100, 162 
 p-Nitrosoethyl-o-toluidine, 107 
 p-Nitrosomethyl-o-toluidine, 107 
 a-Nitroso-B-naphthol, 197 
 p-Nitrosophenol, 82, 246 
 
 reduction of, 89 
 
 o-Nitrotoluene, 102, 108 
 
 reduction of, 105 
 
 m-Nitrotoluene, 102 
 
 p-Nitrotoluene, 102 
 
 —— reduction of, 110 
 
 sulphonation of, 110 
 p-Nitrotoluene-o-sulphonic acid, 110 
 Nitroxylenes, 132 
 
 NW-acid (see 1-naphthol-4-sulphonic acid) 
 
 Oxanthol, 217 
 
 Oxy-Koch acid (see 1-naphthol-3: 6: 8-trisulphonic 
 acid) 
 
 B-Oxynaphthoic acid (see 2-hydroxy-3-naphthoic 
 acid) 
 
 255 
 
 Para-anthracene, 213 
 
 Paraldehyde, 70 
 
 Paranil A, 241 
 
 Peri-acid (see 1-naphthylamine-8-sulphonic acid) 
 
 Phenacetine, 91 
 
 Phenanthrene, 213 
 
 p-Phenetidine, 90 
 
 —— diazotisation of, 91 
 
 Phenol, 78, 80 ff., 172 
 
 condensation of, with anthraquinone-1: 5- 
 
 disulphonic acid, 234 
 
 nitration of, 83, 92 
 
 —— nitrosation of, 83 
 
 —— sulphonation of, 95 
 
 Phenol-p-sulphonic acid, 95 
 
 2-Phenylamino-5-naphthol-7-sulphonic acid, 195 
 
 2-Phenylamino-8-naphthol-6-sulphonic acid, 195 
 
 m-Phenylenediamine, 20, 100, 172, 194 
 
 p-Phenylenediamine, 44 : 
 
 m-Phenylenediamineoxamic acid, 21 
 
 m-Phenylenediamine-4-sulphonic acid, 6 
 
 Phenylgamma acid (see 2-phenylamino-8-naphthol- 
 6-sulphonic acid) 
 
 Phenylglycine, 65 ff. 
 
 Phenylglycineanilide, 66, 68 
 
 Phenylglycine-o-carboxylic acid, 205 
 
 Phenylhydrazine-p-sulphonic acid, 58 
 
 Phenyliminodiacetic acid, 65 
 
 Phenyl-J-acid (see 2-phenylamino-5-naphthol-7- 
 sulphonic acid) 
 
 Phenyl-a-naphthylamine, 144 
 
 1-Phenylnaphthylamine-8-sulphonic acid (Pheny]- 
 peri acid), 155 
 
 Phenylthioglycol-o-carboxylic acid, 207 
 
 alkali fusion of, 208 
 
 Phosgene, 53 
 
 Phthalic acid, 199 
 
 Phthalic anhydride, 57, 72, 100, 199 ff. 
 
 —— —— chlorination of, 202, 203 
 
 condensation with p-chlorophenol, 208 
 
 condensation with benzene, 209 
 
 condensation with toluene, 210 
 
 Phthalimide, 203 
 
 —— Hofmann transformation applied to, 204 
 
 Picramic acid, 93 
 
 Picric acid, 92 
 
 Primuline, 113, 115, 117 
 
 Pyranthrone, 210 
 
 Pyridine bases as solvent, 149, 213 
 
 Quinaldine, 70, 246 
 Quinizarin, 14, 110, 208, 231 
 Quinoline, 69, 246 
 
 R-acid (see 2-naphthol-3: 6-disulphonic acid) 
 Resorcinol, 52, 99, 101 
 amidation of, 100 
 
 Sabanejefi’s base, 68 ; < 
 
 S-acid (see 1: 8-aminonaphthol-4-sulphonic acid) 
 
 Salicylic acid, 95 ff. 
 
 Schaffer acid (see 2-naphthol-6-sulphonic acid) 
 
 ‘* Silver salt? (sodium anthraquinone-B-sulphon- 
 ate), 219 aol 
 
 Sodium phenate, action of carbon dioxide on, 96 
 
 Stilbene derivatives, 110 
 
 Sucéinic anhydride, 57, 
 
256 INTERMEDIATES 
 
 Sulphanilic acid, 57 
 diazotisation of, 59 
 
 Tetrachlorophthalic anhydride, 203 
 
 Tetrahydroquinaldine, 71 
 
 Tetramethyldiaminobenzhydrol, 53 
 
 Tetramethyldiaminobenzophenone, 53 
 
 Tetramethyldiaminodiphenylmethane, 52 
 
 ** Thioamide ”’ (thio-oxamidediphenylamidine), 73 
 
 Thiocarbanilide, 72, 73 
 
 Thioindoxyl (see also 2-hydroxythionaphthene), 
 74, 245 
 
 Thiophene, 16 
 
 Thiosalicylic acid, 206 
 
 —— condensation with chloroacetic acid, 207 
 
 Thio-p-toluidine, 114 
 
 Tobias acid (see 2-naphthylamine-1-sulphonic acid) 
 
 o-Tolidine, 108, 178 
 
 o-Tolidinedisulphonic acid, 109 
 
 Toluene, side-chain chlorination of, 120 ff. 
 
 —— nuclear chlorination of, 126 ff. 
 
 —— condensation with phthalic anhydride, 210 
 
 nitration of, 102 ff. 
 
 —— oxidation of, 123, 125 
 
 ——  sulphonation of, 127, 130 
 
 Toluene-p-sulphoamide, 131, 229 
 
 Toluene-o-sulphonic acid, 130 
 
 FOR DYESTUFFS 
 
 Toluene-p-sulphonic acid, 130 
 
 —— chlorination of, 127, 129 
 Toluene-p-sulphonic alkyl esters, 131 
 Toluene-p-sulphonyl-o-toluidide, 109 
 Toluene-o-sulphonyl] chloride, 130 
 Toluene-p-sulphony] chloride, 64, 127, 130 
 o-Toluidine, 105, 106 
 
 —— alkylation of, 106 
 
 —— diazotisation of, 108 
 
 —— nitration of, 118 
 
 —— sulphonation of, 105 
 
 p-Toluidine, 109 ff., 145, 209 
 
 —— action of sulphur on, 113 ff. 
 o-Toluidinesulphonic acid, 105 
 m-Tolylenediamine, 117, 123 
 sulphonation of, 118 
 m-Tolylenediaminesulphonic acid, 118 
 p-Tolyl-a-naphthylamine, 145 
 Tribromoresorcinol, 99 
 
 Trichloroethylene, condensation with aniline, 68 
 2: 5: 6-Trichlorotoluene-4-sulphonic acid, 129 
 
 Xylenes, 132 
 
 Xylidenes, 132 
 
 m-Xylidene, 132 
 
 p-Xylidene, 133 
 m-Xylidene-o-sulphonic acid, 134 
 
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