u THE PREPARATION OF MONO- BROMACETIC ACID AND ITS ESTER BY ROBERT T. REED THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN CHEMISTRY COLLEGE OF LIBERAL ARTS AND SCIENCES UNIVERSITY OF ILLINOIS 1!)22 . Digitized by the Internet Archive in 2016 https://archive.org/details/preparationofmonOOreed ACKNOWLEDGMENT The author wishes to express his sincere thanks to Dr. B. L. Souther for his valuable help and direction throughout this investigation. * . . . TABLE OE CONTENTS Page Introduction 1 Historical 2 Experimental 6 Summary. 9 Bibliography 10 •1 INTRODUCTION Bromacetic acid is not a commercial product, "but is used to some extent in the laboratory in carrying out the Reformatsky Reaction. This is a reaction between zinc, an aldehyde, and brom- acetic ester to give a B-hydroxy ester which w r hen hydrolyzed gives the B-hydroxy acid. Chloracetic acid^ is made commercially and used to a great extent in the preparation of indigo from aniline. It is made by passing dry chlorine gas through glacial acetic acid. A small amount of acetic anhydride is added to act as a catalyzer. This method givei a very good yield and it was conceived that bromacetic acid might be prepared in the same manner. 2 HISTORICAL Mono -bromacetic acid has teen prepared in many different ways to get a product free from impurities and also free from di- and tri-bromacetic acids. Another difficulty has been to get a good yield from the reaction. One of the methods very commonly used is employing p phosphorus^ as a catalyzer. The use of phosphorus as a halogen carrier was first discovered by Corenweinder. It was later found by Personne that red phosphorus worked better than yellow phosphorus or a mixture of the two. The bromination of acids in the presence of phosphorus was first discovered by a German chemist named Hell. One necessity in using phosphorus is that all materials be dry, therefore since red phosphorus always contains a little phosphoric acid, the acid must be washed out and then the red phosphorus dried again. For every mole of acetic acid used about 5 grams of red phosphorus were used. The pip cess was carried out in a reflux condenser. The bromin was forced through the acetic acid as a gas. The reaction was heated over a water bath and in direct sunlight. The sunlight seemed to act as a catalyzer since the reaction went much faster when it was used. The total time for it to go to completion was between one and two days. The bromacetic acid was recovered by distilling under diminished pressure. It came over at a temperature of 110° U. under 50 mm. pressure. The difficulty with this reaction was that the product after distillation was a very sluggish mixture from which it was difficult to extract the final product. Another difficulty i3 that often the bromacetic acid has sorae di- and tri-bromacetic acid in it . . -3 Use of Phosphorus Pen tabromide 3 When phosphorus pentabronide was used, the reaction w s carried out in a similar manner as in the case when only phosphorus was used. Acetyl "bromide was first generated and then the anhydride was formed which reacted with hydrobromic acid to give one molecule of bromacetic acid and one molecule of acetyl bromide. The acetyl bromide reacted again with more acetic acid to give more of the anhydride. This reaction went fairly smooth, but it also gave a sluggish mixture which was very hard to work with. The reactions were as follows: 1. P 4 Br^ — P Br 5 2. CH 3 COOH 4 P Br- -*■ CH S COBr + POBr 3 4 HBr. 3. CH 3 COBr + CK 3 COOH — CH 3 qo + H Br ,0 CH 3 CO 4 CHpO !o + Br, — CHpO 5. CH* BrCO 0 4 H Br CH 3 C0 CHg BrCO 04 E Br CH 3 CO CH a BrCOOH 4 CH 3 CO Br Preparation of Mono -Bromacetic Acid Using Sulphur as a Catalyzer (4) A reflux condenser was used into which five parts of sulphur were added for every one hundred parts of acid used. The bromine was added in small portions, using a small excess of the theoretical amount. After the reaction was complete which was shown by the fact that no more hydrogen bromide gas was being given off, the mixture was distilled under atmospheric pressure. .4 The acid distilled over at 207° C. and crystallized immediately. The objection to this method was that di-bromacetic acid was found unless extreme precautions were taken. As soon as an excess of the theoretical amount of bromine was added the mono -bromacetic acid would react with it to give the di-bromacetic acid. It was very hard to add just the theoretical amount of bromine because it was never known how much bromine had escaped during the reaction. Some compounds were formed by the reaction of bromine on the sulphur. This not only cut down the yield but these compounds were very hard to get rid of when the pure bromacetic acid was recovered. Process of Heating Bromine and Acetic Acid in a Closed Tube 5 Equal portions of glacial acetic acid and bromine were heated in a closed tube to the temperature of 150° C. When the solution became colorless or an amber color, the tube was then cooled thoroughly and broken. A large amount of hydrogen bromide escaped. The residue was then placed in a retort, or reflux condenser and boiled until all of the hydrogen bromide gas had been given off. This was told by passing the gas through silver nitrate solution. The solution then contained bromacetic acid, di-bromacetic acid, and a little hydrogen bromine. The mixture was then heated to 150° C. and CO 2 gas was passed through it until the very last traces of hydrogen bromide gas were given off. An excess of lead carbonate and 10 times its volume of water were then added to the acid and the solution was heated to 100° C. and allowed to stand for a few hours. After standing the liquid was filtered from the separated crystalline precipitate. The crystals v/ere . ■ . . . ; . ; - . < • ■ ' . , ' . . f * < - * , *v ' , . . washed with cold water and then suspended in water into which hydrogen sulphide was conducted until the solution was saturated. The liquid when filtered and concentrated gave the pure crystalline acid. The latter part of this preparation was a method of separating the bromacetic acid from the di-brornacetic acid. The lead salt of the dibrom acid is far more soluble than that of the mono -bromacetic acid. ■ - . ■ - 6 - EXPERIMENTAL In all of these reactions acetic anhydride was used as a catalyzer. It must he free from water. Common acetic anhydride contains a large amount of acid,, therefore, it must he distilled before using. The advantages of acetic anhydride were that it did not give a mixture of the mono- and di-bromacetic acids and also the final product was easily recovered. The first reaction was run using a common round bottom flask with a rubber stopper connection to the condenser. The bromine reacted very violently with the rubber and at the end all that was left was a gummy mass from which it was impossible to recover the bromacetic acid. A glass stoppered flask and condenser were then obtained. This was a great advantage in that there was no rubber to react with the bromine and it also made a water tight connection. A little water would ruin the reaction because the acetic anhydride would react with it to give acetic acid. From the top of the condenser the hydrogen bromide gases were passed over water and absorbed. This prevented their escape into the room, 120 grams of glacial acetic acid and lOcc. of acetic anhydride were first placed in the flask to which 160 grams of bromine were added. The flask, heated by means of a water bath, was heated very slowly at first. This prevented the reaction, which was violent at first from boiling over the top of the condenser. A red substance crystallized out in the condenser but after the reaction had gone for sometime before these crystals melted. They were probably bromacetic acid crystals with some bromine mixed in with them. -7- Aftsr the reaction had gone for 2 hours the solution assumed a light yellow color. This was due to the fact that all of the "bromine had reacted. Another portion of 160 grams of "bromine was added and the solution was again heated very slowly. The water, however, was kept "boiling constantly after it was started. When the refluxing had gone for another 2 hours the solution again became colorless. Since the theoretioal amount of bromine had been added it assumed that the reaction was complete. However upon extracting i the pure bromacetic acid, the yield was found to be only 56 %, From these results it was concluded that 44# of the bromine had escaped and not reacted. In the next run an excess of 44# of bromine was added in three portions af about 154 grains each. The first two portions were not added until the solution became colorless, when no more hydro geii bromide gas was given off after the last portion had been added the reaction was considered to be complete. The time for one complete reaction was between 7 and 8 hours. The pure bromacetic acid was recovered by distilling the mixture unaer diminished pressure. First, the excess bromine distilled over followed by the acetic acid which did not react. Finally, at a temperature of about 105-108° C. and under a pressure of 50 mm. a colorless solution began to distill over. It solidified as soon as it came in contact with the cold receiving flask. The product under ordinary conditions is a colorless crystalline substance which melts at 50° C. and boils at 208° u. It has little or no odor when free from hydrogen bromide. when a little of it gets on the hands it is hardly noticed at the time but the next morning there will be a large blister there. It is very - 8 - painful then and will be an open sore for a few days. Nine runs were made using practical ly the same amounts as stated before. The yields ran between 72$ and 87.21$ of the theoretical yield. The theoretical yield was calculated from the amount of acetic acid that was used. The be3t yield of 255 grams of pure bromacetic acid was obtained by using 120 grams of acetic acid, 467 grams of bromine, and lOcc. of acetic anhydride. The theoretical yeidl from acetic acid was 278 and from the acetic anhydride it was 14.4 making a total yield of 292.4 grams. fin- ' 87 - 21 * At first it was thought that the work on bro.macetic acid would be short enough to allow for some work on the ester but it was found that the whole semester was taken up -with the work on the acid. SUMMARY It was found that hromacetic acid could be prepared in good yields by using acetic anhydride as a catalyzer. ' . . - 10 - B IBL 10 GRAPHY 1. Martin. Industrial Chemistry, Organic, vol. 1, page 332. 2. Gattermann, Practical Methods of Organic Chemistry, Page 163 3. Gattermann, Practical Methods of Organic Chemistry, page 165 4. Bulletin de la Societie chimique senes 3. vol 7, page 365 5. Annalen der Chimie. Vol. 108, page 106.