1 THE PREPARATION OF 
 ANHYDROUS OXALIC ACID 
 
 II A NEW METHOD FOR THE 
 PREPARATION OF FURFURAL 
 
 BY 
 
 VANDRRVEER VOORHEES 
 
 THESIS 
 
 FOR THE 
 
 DEGREE OF BACHELOR OF SCIENCE 
 IN 
 
 CHEMICAL ENGINEERING 
 
 COLLEGE OF LIBERAL ARTS AND SCIENCES 
 
 UNIVERSITY OF ILLINOIS 
 
 1921 
 
Digitized by the Internet Archive 
 in 2016 
 
 https://archive.org/details/preparationofanhOOvoor 
 
UNIVERSITY OF ILLINOIS 
 
 
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 THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY 
 
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TAPLE OF CONTENT? 
 
 I Anhydrous Oxalic Acid 
 Introduction 
 Experirr.ental 
 Di scussion 
 
 Drawings of Apparatus 
 II Furfural 
 
 Introduction 
 Di scussion 
 Experimental 
 Notes 
 
 Conclusion 
 Summary 
 Bibliography 
 Drawings of Apparatus 
 
 Page 
 
 1 
 
 3 
 
 6 
 
 Appendix A. 
 
 10 
 
 12 
 
 14 
 
 21 
 
 22 
 
 23 
 
 25 
 
 Appendix B. 
 

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1 
 
 INTRODUCTION 
 
 Certain organic reactions, such as the preparation of oxalic 
 esters, require oxalic acid entirely free from water. Since the 
 pure, crystallized acid contains two molecules of water of crystal- 
 lization, this must he removed before the acid may be used for 
 these purposes. 
 
 Oxalic acid cannot be satisfactorily dried in an ordinary oven, 
 
 since it sublimes arpreciably at temperatures below 100©, and above 
 
 (1) (2) 
 
 this temperature decomposition ensues. Beilstein mentions that 
 the water of crystallization may be removed by standing over cone. 
 HgSO*, but it is obvious that this method would not be applicable 
 to the preparation of any considerable quantity. 
 
 In order to overcome the above difficulties. Dr. H. T. Clarke, 
 of the Eastman Kodak Co. h&s devised the following process (as yet 
 unpublished) which may be carried out in any laboratory. Finely 
 crystallized oxalic acid is boiled with CCI4, the vapor of which 
 carries out the water according to the law of partial pressures. 
 
 The vapors are condensed into a gravity separator where the water 
 flows off and the CCI4 is returned to the flask. This is continued 
 until all water has been distilled out, the product being obtained 
 by filtering off the CCI4, the last of which is removed in a 
 current of dry air. 
 
 (1) Gay Lussac,- Ann. Chera. 1-30, 
 (3) Handbuch - 1 - 639. 
 
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 The purpose of this research was to check over the above metho: 
 and determine the most suitable form of apparatus to use; one 
 which would give the least loss of CCI4 and dry the acid in the 
 shortest time. Previous work with this method showed that*^large I 
 loss of CCI4 could not be avoided, thus making the process an 
 expensive one. To determine where this loss occurred, a number 
 of experiments were made with different forms of apparatus, the 
 loss of CCI4 being observed in each case. 
 
 ETPERIMENTAL 
 
 Experiment 1. - Two Kg. C. ?. oxalic acid were passed through 
 a 30-mesh seive and placed in a 5-1. round bottom flask with 5 Kg. 
 CCI4. The flask was fitted with a glass stir of the vdng type 
 reaching almost to the bottom and sealed by a column of mercury 
 about 3 inches deep. Connection was made to the top of a vertical 
 condenser by a tube 50 inches long and 1/3 inch diameter, wrapped 
 v;ith asbestos to decrease condensation. The condenser, 30 in. long 
 and 5/8 in. diameter was connected at the Icv/er end tc the water 
 separator. In Dr. Clarke's apparatus this separation was effected 
 by means of a simple trap with a funnel set into it to catch the 
 liquid from the condenser. The objection to this is the large 
 surface offered for evaporation, so a modification of this separator 
 was used in this and follcwing experiments. This device, shown in 
 Fig. 1, consisted of a glass tube 8 in. long and 7/8 in. Ham. with 
 a small tube sealed at the side for a water overllow and a second 
 small tube leading up from the bottom to within 1/4 in. of the water 
 

 
 
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outlet where it was bent horizontally and connected to the flask. 
 This maintained the level of CCI4 just below that of the water 
 outlet, and the water, being much lighter, collected on the surface 
 until the layer became sufficient to reach the overflow where it 
 ran out and was collected in a covered beaker. 
 
 The connection between the separator and the conienser was 
 arranged with a capillary open to the air to maintain atmosp'heric 
 pressure and insure the proper adjustment of the liquid levels. 
 
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 containing a capillary to prevent siphoning the contents out of 
 the separator into the flask during operation. The returning CCI4 
 was delivered by a small tube extending well below the surface of 
 the mixture in the flask to prevent vapor rising and escaping 
 through this last mentioned capillary. A small funnel was sealed 
 within the separator just below the condenser to deliver the 00X4 
 below the surface and prevent its being floated out with the water 
 by surface tension. 
 
 Corks were used at the condenser connections, but a rubber 
 stopper was used at the flask, owing to the difficulty of making 
 a large cork stopper carrying two tubes and a stir, sufficiently 
 vapor tight. Hovirever, the rubber was abandoned at the end of this 
 run as it was found impossible to prote ct it from the solvent 
 action of the tetrachloride, altho tinfoil and collodion laquer 
 ware both tried. The rubber also showed a tendency to discolor 
 the product. 
 

 
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 Distillation ovsr a direct flame vias carried on for a total 
 period of 30 hrs. At this time the CCI 4 returning to the flask 
 had lost part of its milkiness due to entrained water, but had not 
 become clear. Gome trouble was occasioned by the return tube 
 becoming closed at the end by an agglomeration of oxalic acid 
 which required frequent removal. After cooling, the acid was 
 filtered off by suction until no more CCI 4 could be obtained. 
 
 The remaining CCI4 w 2 i.s expelled in the oven at lOO , but some 
 sublimation occurred at this temperature, causing the finely 
 powdered acid to sinter together into a mass of delicate needles. 
 
 3900 g. of CCI4 was recovered, denoting a loss of 1100 g. 
 
 1350 g. of anhydrous acid was obtained, which is 94.5^ of 
 the theory. The loss was most likely due to sublimation in the 
 oven. Titration of the product showed a water content of less 
 than .01 mol. HgO. 
 
 Experiment 3. - In this escperiment several changes vyere made 
 in the apparatus. The length of the separator was increased from 
 & in. to 14 in., and the diameter from 7/8 in. to 1-3/8 in. This 
 was done to allow the water more time to separate before the CCI4 
 was returned to the flask. The tube returning the GCI4 was ex- 
 tended just through the stopper in the flask, and a loop was made 
 in it to prevent the reverse passage of vapor. In this way, 
 plugging of the end of the return tube within the flask was effect- 
 ually prevented, A cork stopper was used in the flask and painted 
 with sodium silicate to render it impervious to vapor. The 
 

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 the separator, were replaced by connections to a small vertical 
 condenser as sho'^n in the sketch to prevent any escape of CCI 4 
 vapor. The small funnel which was selaed vdthin the previous 
 separator, was merely rested on a constriction of the wall in 
 this one. This was done to siiiplify construction. The entire 
 apparatus is shown in F'ig. 2 , and was used in succeeding experi- 
 ments. A water-bath entirely surrounding the flask was used in 
 this experiment in place of direct heat. 
 
 2 Kg, oxalic acid graded as before and 5 Kg. CCI4 were placed 
 in the flask. Distillation was carried on for a total period of 
 18-1 /2 hrs, 2500 g. of CCI 4 was recovered by filtration from the 
 anhydrous acid, showing a loss of 2500 g. Part of this loss was 
 due to clogging of the return tube at starting and overflow of 
 the separator. The product 'Afas freed ffom CCI4 by spreading on a 
 paper placed above a radiator for a few hours. 
 
 1450 g. of anhydrous aoid va,s obtained which is a trifle more 
 than the theory (l430 g.). Allowing for .02 mol of water, deter- 
 mined by titration as before, this is practically a quantitative 
 yield. 
 
 The use of the ;vater bath effectually prevented the formation 
 of a crust of acid about the upper part of the flask, this having 
 been previously observed by Dr. Clarke. 
 
 Experiment 3 . - The apparatus was used just as in the pre- 
 ceeding experiment with the exception of the water bath. It was 
 felt that the slight advantage of the crust prevention was more 
 

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 than offset by the inconvenience of handling such a cumbersome 
 water bath and continually supplying v^ater to make up for that 
 lost by evaporation. All connections were wrapped with strips 
 of cloth which were wired on and painted heavily with sodium 
 silicate. Very good seals were obtained in this way. The extracted 
 water was collected in a covered beaker and measured at intervals. 
 
 Distillation was carried on for a total period of 16-1/3 hrs. 
 Water was collected as follows; 
 
 After 7 hrs. - 360 cc. 
 
 ” 13 n - 465 " 
 w 18“l/3" “ 545 « 
 
 The theory requres 570 cc., the discrepancy being undoubtedly 
 due to evaporation from the beaker during operation. 
 
 The product was dried on the radiator as before and the theory 
 yield was obtained (1430 g.) . Titration showed the presence of 
 .03 mol. water. 
 
 Loss of CCI4 was not determined in this run because of an 
 accident which occurred during operation. 
 
 Experiment 4. ~ This run was made largely for the purpose 
 of checking the results of the previous run and determining the 
 loss of CCI 4 . In order to minimize back pressure on the flask, 
 a steam jacket was placed on the vapor tube leading to the con- 
 denser as shown in the sketch. This was advised by Dr. Clarke 
 and entirely prevented condensation in this tube. Apparently 
 the previous losses of CCI 4 were principally due to loss of vapor 
 at the mouth of the flask and around the mercury seal of the stir, 
 
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 and consequently any increase in pressure would increase these vapoi 
 losses proportionately* Greater care was taken to inspire a tight 
 joint at the flask, the stopper being painted with sodium silicate 
 both inside and out and the entire joint wrapped with cloth, 
 securely wired and painted with silicate solution. 
 
 Distillation vvas carried out for a total period of 23-1/2 hrs. 
 during which time 555 cc. of vvater was collected as follows: 
 
 After 4 -I /2 hrs. - 120 c.c. 
 n 13 n » 375 " 
 
 w ie-l/2” ~ 520 « 
 
 « 23-1/3” “ 555 « 
 
 A decrease in volume in the flask during operation, of about 500 c.c. 
 results from the removal of ’water. The anhydrous acid was filtered 
 off and as much CCI4 removed as possible by pressing and suction. 
 
 3950 g. CCI 4 was recovered. The product, which was in a 
 damp condition, was weighed before drying to determine the loss 
 of CCI4. It was then dried on the radiator as before for a period 
 of 3 hrs. after which it was bottled and weighed. 
 
 Yield - 1420 g., practically theoretical. 
 
 Wt . before drying - 2350 g. 
 
 ” after « - 1430 
 
 Loss of CC14 due to drying 930 g. 
 
 930 3 9 50 « 4880 g. or almost 5 Kg., the amount used. 
 
 Titration showed the presence of .03 mol of water. Indications 
 are that some of this, at least, was absorbed while expelling the 
 
 
 
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 last of the CCI 4 on the radiator, the humidity being fairly high, 
 at the time, and a slight crust being formed oer the surface of 
 the acid after exposure. It is to be noted also that the product 
 from the first run, which was placed in the oven to expel’^CCl 4 , 
 contained the least water (.01 mol.) 
 
 DI SOU?? ION 
 
 The success of Dr. Clarke's method for dehydrating oxalic 
 acid is quite evidently dependent on the economy of carbon tetra- 
 chloride consunp tion, for it ^ves unquestionably a pure, dry 
 product. I believe my exr>eriments have shown ;jU3t where the losses 
 of CCI4 occurr, and the manner and extent to which they may be 
 p re vented. 
 
 The apparatus which I employed is practically 100*^ efficient 
 as shown in the last experiment in regard to CCI4 retention. The 
 loss of CCI4 on drying of the product is, in so far as I can see, 
 unavoidable on a laboratory scale. This loss could, however, be 
 greatly minimized if some form of pressing machine were available. 
 When using the laboratory type of suction filter, I think one may 
 figure on a loss of CCI4 equal to 50 "^ of the weight of the crystal- 
 lized acid used. 
 
 The most undesirable feature of the apparatus is the impos- 
 sibility of using rubber stopper connections. Sodium silicate, 
 as I used it, adheres to the flasks and tubes, dr^'ing in horrey 
 lumps which can only be removed by prolonged soaking in water. 
 
 In one experiment the stepper was so securely cemented to the 
 

 
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 flask that it had to be cut and removed in pieces. I see no 
 solution to this difficulty except in the construction of special 
 flasks and connections of glass arranged for ground joints or 
 mercury seals. 
 
 It has been suggested by Dr. Clarke that the use of calcim 
 chloride to dry the returning CCI 4 toward the end of the reaction 
 mig^t considerable shorten the time of operation by removing the 
 entrained water. This was considered but abandoned because of the 
 manipulation and loss of CCI 4 which it would entail, esp^e daily 
 as the drying agent could only be of use during the last 3 or 3 
 hrs. and I felt that this saving in time would be insufficient, 
 particularly as the apparatus which I employed required practically 
 no attention while running. 
 
 I might add that when the reaction is properly controlled, 
 the second condenser is unnecessary and that the capillary arrange- 
 ment described in the first experiment is quite satisfactory. 
 

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A NEW ItETHOD 
 for the 
 
 P REP j9 RATION OF FURFURAL 
 
10 
 
 INTPODUCTTON 
 
 Furfural (furfuraldehyle, furallehyde, furfurole) when pure 
 is a colorless oil, slightly heavier than water 'with a boiling 
 point of 161® (Esilstein) . It is a cyclic ether aldehyde having 
 the following formula with all the 
 
 properties of an aldehyde and many of the properties of the aro- 
 matic series. It is soluble in v;ater to the extent of 1 part in 
 
 11 at 13® , (Beilstein) and considerably more than this at higher 
 
 (l) 
 
 temperatures. It is also quite volatile 'with steam. Cohen 
 gives its formation from pentose by the loss of 3 molecules of 
 water. 
 
 Occurrence - A glance in the literature will show that 
 
 furfural occurrs widely scattered among the processes of annlied 
 
 ( 3 ) 
 
 chemistry. We find it in vdne, beer and fuseloil and in waste 
 
 (3) 
 
 products from sulfite pulp manufacture. It may be obtained by 
 
 (4) (5) (6) (7) 
 
 acid hydrolysis of sugar , bran, lignin, cellulose, and oxy- 
 (S) C9) 
 
 cellulose and also by hydrolysis of bran with zinc chloride. 
 
 It results fromi the acid hydrolysis of pentoses (arabinose and 
 
 , ( 10 ) 
 
 xylose) and pentosans , this reaction being employed in the 
 laboratory for the quantitative estimation of these carbohydrates. 
 In brief, it seems to result from the acid hydrolysis of a great 
 varietv of vegetable products. 
 
 Preparation - A great many processes have been devised for 
 the production of furfural, a number of which have been patented.. 
 Almost vvithout exception they consist of some form of hydrolysis, 
 

- 11 - 
 
 ( 11 ) 
 
 this being accomplished in some cases by steam under pressure 
 
 or by various strengths and kinds of acids. 
 
 The laboratory method which has been in general use is 
 
 ( 12 ) 
 
 essentially that given by Eeilstein as follows; bran is di s- 
 
 tilled with 30“^ KgSO^, the distillate containing less than 1*^ of 
 
 the oil in solution. This distillate is concentrated by saturation 
 
 with salt and redistillation, half the volume being collected. 
 
 The first of the distillate is most concentrated and the oil will 
 
 separate at first and later relissolve. In practice it is rem.oved 
 
 as soon as no more is seen to separate from the water. After each 
 
 distillation, the water solution is saturated with salt and re- 
 
 distilled as before, this procedure being continued until all has 
 
 been obtained as the oil. 
 
 (13) 
 
 Stone found in 1691 that a very much larger yield of fur- 
 fural could be obtained from corn cobs than from most other veg- 
 
 (14) 
 
 etable substances. Following this, Noyes , gave directions for 
 its preparation from cobs using constant boiling (SO^) HCl as 
 hydrolytic agent. During 1917-16, considerable quantities were 
 made by the latter method at the University (Dept. Chem. Mfrs.) 
 Results from this work show that an average yield of 10-12*^ of the 
 weight of air dry cobs was obtained in this 'way. Also, for each 
 150 g, of oil, approximately 30 1 . of solution had to be distilled, 
 which required an average of 15 hrs. 
 
 Use - At present the demand for furfural is rather a limited 
 one. It is used as a reagent for the detection of aromatic primary 
 amines and has been suggested as dyestuff intermediate. Colors 
 

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- 12 
 
 made from it, however, have proven fugitive to light* Some use 
 hae been made of it in perfumery and as a vermicide. 
 
 DI SOT SION 
 
 As far as I am aware, no method has yet been published by 
 which furfural can be obtained from vegetable matter without the 
 distillation of disproportionately great voliimes of water (or acid) 
 and the subsequent concentration of the distillate. This pro- 
 cedure is necessitated by the fact that the distillation must be 
 extended over a long period of hours, since the rate of hydrolysis 
 is only moderate at 100©. The distillation m^ust also be maintained 
 quite rapid thruout this time in order to get a good yield, and 
 consequently a large volume of distillate collects and must be 
 concentrated to obtain the furfural in solution. Several attempts 
 which I made to complete the hydrolysis previous to distillation 
 and then distill off the furfural 'which should have been formed, 
 proved failures, very small yields being obtained. This led me to 
 believe that the furfural formed in the acid solution is in turn 
 destroyed by the acid, the rate of this reaction being naturally 
 dependent on the concentration of the furfural. Later results 
 have also borne cut this theory. It may readily be understood 
 then, that if one wishes to obtain a maximum yield, he must keep the 
 concentration of furfural in the acid solution at a minimum. One 
 way of effecting this is by rapid distillation, the method which 
 has been commonly used. 
 
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- 13 - 
 
 I found th 2 .t this sautne result could be obtained by the 
 addition of a large amount of salt to the acid mixture, for it is 
 well known that furfural is more volatile from a salt solution 
 than from pure water. In this way it is driven off with water 
 vapor at a much lower concentration than when acid is used alone. 
 
 This "salting out" process, then, explains why, in the past, 
 it has been customary to use relatively high concentrations of 
 acid. Experiment had shown that low acid concentrations gave low 
 yields of furfural. It may now be seen that this condition was 
 not due to the lack of hydrogen ion concentration sc much as to 
 the absence of the "salting out" effect. When salt is used, the 
 acid concentration may be reduced to l/5 or l/‘6 the previous 
 value, and it appears that the results are more satisfactory, 
 the lowerthe concentration. This is just what one would expect, 
 since, by the use of salt, the acid concentration may be lowered 
 as wclll as the furfural concentration, and thus still more decrease 
 the speed of the reaction which destroys the product. 
 
 With the knowledge of the above principles and by the use of 
 proper condensing arrangements, I have been able to distil the 
 furfural from a corn-cob-acid mixture, separate the oil, and con- 
 tinuously return the water (together with the furfural in solution) 
 to the flask where it is used over, thus making a complete cycle 
 of operations. The process is entirely automiatic, once started, 
 and the crude furfural (oil) m;ay be drawn off from, the condenser 
 directly, thus making it necessary to handle no water whatsoever, 
 and totally eliminating the laborious procedure of concentrating 
 
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14 - 
 
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 of the experiments which I have male. A number of others which 
 I had in mind could not be performed for want of time, 
 
 ETt^FRIWFNTAL, 
 
 In this work all experiments were condiicted with cobs of the 
 previous year’s crop (1919) of yellow corn. The corn had been 
 shelled only a few months prior to the date of this research 
 (Oct. 1, 1930). The cobs were ground in a coal crusher to approx- 
 imately the size of a pea, there being some pelces considerably 
 larger and also much fine bran-like material. Sulfuric acid used 
 was the ordinary C. 95^ acid. Salt used was the crude barrel 
 product. When weight of cobs is given, it is meant air dry, ground 
 cobs (about 10*^', moisture), and by percent of H^SO^ is meant acid 
 of sp . gr . 1.84, 
 
 Expe riment 1 ,- To study the effect of hydrolysis of the cobs, 
 previouB to distillation by the ordinarv method, 1200 g. of cobs 
 were placed in a 12-h . flask with 6 L, SSf-* KaSO*, The flask was 
 placed on a steam cone and heated for 36 hrs., intimate mixture of 
 acid and cobs being maintained by occasional shaking. The mixture 
 was distilled with a rapid current of steam, 5 L. of distillate 
 being collected. On concentration with salt this yielded about 
 10 g. of oil. 
 
 Experiment 3 ,- This exj^eriment was performed in order to 
 determine if hydrolysis at the boiling temperature would increase 
 the yield of furfural. 1500 g. of cobs were hydrolyzed by boiling 
 
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- 15 - 
 
 gently under a reflux condenser v,lth 7 L, HgSO^ for a long 
 period of hours. The mixture was distilled with steam as before 
 and the furfural obtained by concentration. Tbe yield was still 
 less than in the former experiment. 
 
 Experiment. 3. - Suspecting the decomposition of the product 
 by the acid, I made an attempt in this experiment to effect the 
 hydrolysis with lower acid concentration. 1 Kg. cobs were re~ 
 fluxed gently vTith 5 L. 5^ HgS 04 for a period of 42 hrs. Steam 
 distillation was then used to bring over the furfural which should 
 have been formed, and 2-1 /2 L. of distillate were collected. Very 
 little oil was obtained from this on concentration. 
 
 Experiment 4. - In Experiments ( 2 ) and (3) it was noted that 
 beads of furfural collected in the reflux condenser during hydroly- 
 sis. It occurred to me that if this oil could be kept from return- 
 ing to the acid, the equilibrium between the reaction of formation 
 and that of decomposition of furfural, might be disturbed in the 
 direction of its production. 
 
 To accomplish this a small trap, shown in Fig. 1, was placed 
 below the reflux condenser, thru which tdie condensate was required 
 to flow on its return to the flask, 
 
 1 Kg. cobs were placed in the 12-L . flask with 5-L. lOio H 3 SO 4 . 
 To this was added 2 K'g. salt for the purpose previously discussed. 
 Heat from a large ring burner was applied to the flask. After 3 hrs 
 of refluxing, 40 g. crude oil had been collected in the trap and 
 
 was removed. 7 hrs. longer distillation yielded yet more product. 
 
mmamtarn 
 
 
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16 - 
 
 These portions were comhlned and distilled and amounted to 93 g. 
 pure, dry furfural. This is a yield of 9.3'^ of the weight of the 
 cobs taken. 
 
 Experiment 3. - A test showed that furfural is much more 
 soluble in hot water than in cold, and consequently, a>mong the 
 ideal conditions to be fulfilled by an apparatus for its removal 
 from the condensate, is the return of the separated water (satur- 
 ated with furfural) to the flask at as low a temperature as 
 feasible. This condition was not fulfilled by the simple trap 
 (Fig. l) since the returning condensate was kept at the boiling 
 temperature by the ascending vapor. To correct this, the appar- 
 atus sho’ifinri in Fig. 2 was designed. It is essentially like the 
 former but has a short condenser interposed between the trap and the 
 reflux to.-cool the-^returning condensate and thus precipitate m.cre 
 furfural. It is also provided with a stopcock , below the trap, 
 thus making it unnecessary to take down the apparatus to obtain 
 the product. With this apparatus, the following experiment was 
 made : 
 
 1 Kg. cobs were distilled with 5 L. 10*^ H 5 SO 4 and 2 Kg. salt 
 for 11 hours. 
 
 75 g. of distilled oil were obtained which is a yield of 7.5f^ 
 of the cobs used. 
 
 Experiment 6 . - The apparatus used in the foregoing experi- 
 ment was seen to be inefficient in its cooling of the condensate, 
 partly because of some steam entering the lower condenser from 
 above, and partly because of the warm atmosphere surrounding the 
 trap which must necessarily be above the flask and burner. To insure 
 

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17 
 
 better cooling of the ccnlensate , a water jacket surrounding the 
 trap was seen to be essential. An apparatus including this as 
 well as other features was designed (as shown in Fig. 3). It 
 consists of a vapor tube leading to the top of a vertical conden- 
 ser of large capacity, this resulting from the use of large bore 
 tubing within the condenser thus offering a large cooling surface. 
 This form of condenser was preferred to the ordinary narrow tube 
 type because of the prohibitive length of the latter, cepacities 
 being equal. The lower end of the condenser, v/ithin the water 
 jacket, formed the trap, the water of condensation being led out 
 thru a small tube extending about 5 in. uj: from the end. This 
 tube was bent thru 160® at the inner end to prevent globules of 
 'furfural from falling into it and being carried back to the flask. 
 It was connected by a small rubber tube to a point on the vapor 
 tube sufficiently high to maintain a liquid level within the 
 condenser about 2 in. above the water outlet tube. This was done 
 to allow the condensate sufficient time to become cold before 
 returning, and also to prevent drawdng off the oil which collected 
 on the surface. In order to insure atmospheric preseure within 
 the apparatus, communication vdth the outside was established by 
 a tube of small bore extending from the top of the condenser down 
 within the water jacket and connecting to the inner condenser tubs 
 
 at a point slightly above the level of the liquid vdthin. A stop- 
 cock was provided for the removal of furfural from the trap as 
 
 before . 
 
 It is to be noted that this form of condenser is very compact, 
 having but one water jacket, and the connection to the flask: is 
 

 
 
 
 
 
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- 18 - 
 
 most simple and can be made with the greatest ease and quickness. 
 In operation it was also found to be very efficient for the pur- 
 poses for which it was constructed. It was employed in this and 
 remaining experiments. 
 
 1 Kg. cobs were placed in the IS-L, flask with 5 L. 10^ H 2 S 04 
 and distillation allowed to proceed for 1 hr. No furfural what- 
 ever separated during this time. 2 Kg. salt was added to the 
 mixture and ss distillation was resumed, furfural began to collect 
 at once. Distillation was contained for 7 hrs. luring what time 
 crude furfural was collected as follows: 
 
 First 3 hrs. - 110 g. 
 
 Next l-l/2« - 30 g. 
 
 " 2-1 /2f’ - 5 g. 
 
 This data affords some idea of the course of hydrolysis. 
 
 The product was v^ashed with a small amount of lOfb NagCOs 
 solution followed by water (about 15 c.c. of each) from which it 
 was separated and distilled under dimini shed pressure. The dis- 
 solved water with a few c.c. of furfural was distilled off at 
 first, after which the pure, dry, pale yellow oil was brought 
 over at 110® . 
 
 Yield - 124 g. 12.4 ^ of cobs used. 
 
 Experiment 7. - This run was a check on Exp. . 6 and was -made 
 essentially the same. 
 
 1 Kg, cobs were distilled for 6-1/4 hrs. with 10^ HgS 04 and 
 salt as before. Cru.de furfural was collected as follows: 
 
£ -rrX a 
 
 
 r 
 
 
 
 ^ i i. 
 
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“ 19 
 
 First 2 - 3/4 hrs. 
 
 120 
 
 
 Next hour 
 
 20 
 
 S* 
 
 « 2 - 1/2 hrs. 
 
 10 
 
 g* 
 
 The proluct \ 7 as neutralized and washed as before and dis- 
 tilled at 100 ©, almost colorless. 
 
 Yield - 133 g. = 13.2^ of cobs. 
 
 Experiment 8 . - It was desired to learn if the action of 
 the salt 'was merely physical (salting out) or chemical, since it 
 is well knovrai that a boiling solution of HgSO^ and NaCl must con 
 tain HCl also, and it was of interest to know if the presence of 
 the KCl was essential or ad‘'/antageous . 
 
 In thias exp^sriment, the salt was replaced with NasSO^ and 
 the distillation performed as before. Mo furfural could be 
 obtained. This was later explained by the neutralization of the 
 H 2 SO 4 present to form NaHSC^ which, apparently, did not furnish 
 sufficient acid concentration to effect hydrolysis. 
 
 Experiment 9. - To eliminate the above difficulty, this 
 run was made with the acid sulfate. 
 
 1 Kg. cobs were distilled for 8 hrs. with 5 L. 10^ HgS0 4 
 and 3 Kg. KHSO4 (MaH 804 was not obtainable) . A larger amount 
 of the acid sulfate was used than when salt was employed, partly 
 because of its greater solubility making it possible, and partly 
 tc make the ' comparison favorable to the acid sulfate. Crude 
 furfural was collected as follows: 
 
 First 3 hrs. - 55 g. 
 
 Next 5 ” - 25 g. 
 

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- 20 - 
 
 Yield of distilled product - 73 g» * 7,3^^ of cobs. 
 
 Exceriment 10 . - In order to determine the effect of varying 
 the acid concentration, this and the next experiment were performed 
 using 30v^ and H-SO 4 respectively. 
 
 1 Kg, cobs were distilled 4 hrs. v 7 ith 5 L, 20 f 5 H 2 SO 4 and 
 2 Kg, salt, 75 g, of crude furfural was collected during the first 
 2-1 /2 hrs. after which no more could be obtained. Much more 
 rapid carbonization of the cobs occurred than when 10 ^^ acid was 
 used, and much foaming ensued which necessitated distilling at a 
 very reduced speed. In spite of this, furfural was evolved quite 
 rapidly, more rapi dly, apparently, than in any previous in;in. 
 
 Yield - 62 g. = 6.2 
 
 Experiment 11, - 1 Kg. cobs were distilled with 5 L, 5^- 
 K 2 S 04 and 2 Kg, salt for a period of 6 hrs. At the end of this 
 time, oil was still being evolved but a break in the condenser 
 caused the discontinuance of the experiment. Crude furfural was 
 collected as follows; 
 
 \ 
 
 First 2 hrs. - 52 g. 
 
 Next 1-1/2” - 43 g, 
 
 ” 4-1/2” - 55 g. 
 
 This was neutralized, washed and distilled and gave a yield 
 of 125 g. = 12.5^. 
 
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- 21 
 
 NOTES 
 
 One remarkable feature of the prepa.ration of furfural by 
 hydrolysis, is the unusual purity of the crude product. Distilled 
 from a heterogeneous mixture of unknown comp.osition, the oil may 
 be almost completrely distilled over a range of 1 or 2 degrees, 
 only a trace of high boiling residues remaining. 
 
 Another interesting point in connection 'Alth the purity of 
 furfural is, that, altho it may be quits colorless when distilled, 
 it often darkens and becom.es black on standing a few v/seks, or 
 sometim.es even a few hours. This blackening is probably due to 
 decomposition of associated impurities with form;ation of colloidal 
 carbon. The tendency to blacken seems to be largely influenced by 
 the temperature of distillation, consequently vacuum distillation 
 is advised. I discovered that furfural dried over CaCls, bladkened 
 over night and this led m.e to suspect that the presence of acid 
 on distillation was an important factor. And I found that neutral- 
 ization of the oil before distille.tion greatly increased its 
 stability in respect to color. Some so distilled has thus far 
 as3um»ed only a golden color after two weeks standing, altho it 
 
 was distilled at a relatively hish temperature (ilOo ) . 
 
 ( 12 ) 
 
 Beilstein gives a method of purification which consists 
 of treating the crude oil with small amiounts cf chromic acid to 
 oxidize impurity. It would be interesting to learn how this 
 
 treatment would affect the tendency of the furfural to bla.cken. 
 

 
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- 22 - 
 
 Another Possible ATp-plicatlon of th e Method. 
 
 Because of the greater speed of hydrolysis and the probable 
 increase in furfural yield, it seems quite reasonable to expect 
 that this new method fcr furfural production 'will have wide 
 application in the analytical field and appreciably alter the 
 existing methods for determination of ppentoses, pentosans, oxy- 
 cellulose, etc. It has been impossible in this research because 
 of the limited time at disposal, to attempt experiments along 
 this line . 
 
 COTJCLUSION . 
 
 A study of the experimental data makes the follovdng points 
 seem essential to the preparation of furfural if the maximum 
 yield is to be obtained. 
 
 l) The acid concentration should be as low as possible,, 
 economy of acid being balanced against economy of time. I have 
 shown that high acid strengths, altho it may increase the rate 
 of hydrolysis, tends toward a low yield, and I believe that 
 somewhere between sf? and IS'^- lies the optimum concentration. 
 
 3) The returning furfural solution should be cold in order 
 to return as little furfural as possible, 
 
 3) The returning solution should pass down the tube up 
 which the hot vapors are rising. This has the tendency to steam 
 distil the product from the returning -water and concentrate it 
 in the condenser. The low yield in Exp, 5, indicates this, and I 
 also h-ave observed in the operation of the condenser in Expts, 6- 
 
- 23 
 
 11 that, aftar drawing off oil from the trap v»rhile the distillatioi| 
 was in progress, the rate of furfural separation was greatly 
 diminished, undoubtedly due to the temporary cessation in the 
 flov/ of returning solution resulting from lowering the level in 
 the trap. 
 
 4) The presence of a salt is quite essential to the oper- 
 ation of the method as shewn in Extp . 6. KHSO4 may be used in 
 place of NaCl in the cob-acid mixture, but does not seem to be 
 as satisfactory. This would indicate that HCl is a more satis- 
 factory hydrolytic agent than HgSO^. The use of KCl and NaCl 
 
 to the total exclusion of would probably give quite satis- 
 
 factory results. However, the elimination of KCl might be desir- 
 able in the technical manufacture of furfural where copper or 
 other metallic condensers were employed, because of the volatility 
 of this acid. 
 
 5) Because of the volatility of KCl and the formation of 
 volatile organic acids, (acetic, etc.) during hydrolysi s, the 
 crude furfural -will always be found acidic. I have shown that 
 it is desirable to neutralize these acids and leave the product 
 slightly alkaline on distillation if the color is to be preserved. 
 
 SUMMARY 
 
 1) A theory has been developed concerning the rats of 
 formation and decomposition of furfural in sulfuric acid solution. 
 
 2) A method has been worked out for the preparation of 
 furfural which is practically automatic in regard to labor; 
 
24 - 
 
 7/hich is more eoonomical in regard to chemical consumption, re- 
 quires less time, and is capable of giving a larger yield than 
 any previously existing method* 
 
 3) Several types of apparatus have been constructed and 
 data obtained from each in operation. From this data, conclusions 
 have been dravm which may serve as a godde in the operation of 
 the method, both on a laboratory” scale and commercially. 
 
 4) The effects of varying two important conditions of the 
 process, namely, concentration of acid and kind of salt used, have 
 been studied . 
 
 5) One cause of the discoloration of freshly distilled 
 furfural has been determined. 
 
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- 35 “ 
 
 BIBLIOaHAPHY 
 
 l) Organic Chemistry - 1-269 
 V (C. Nagel - Wochschr. Branw - 30-345 
 (K. Forster - Ber. - 15-230,323 
 
 3) Papierfahr. - 12-1040 
 
 4) Dobereiner - Ann. -3-141 
 
 5) Fovmes - Ann, 54-52 
 
 6) Z. Physiol. Chem . -50-209 
 
 7) Cross and Sevan - Papermaking - 21 
 
 b) Thorpe - 708 
 
 9) Babo - Ann.- 85 - 100 
 
 10) Allen - 1-400 
 
 11) Zeitsch.- Angsw.Chem. 27-654 
 
 12) Handbuch - 3-731 
 
 13) Ber. - 34 - 3019 
 
 14) Lab, Man. - 190 
 
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