Organic Syntheses Collective Volume 1

Organic Syntheses, Coll. Vol. 1, p.1 (1941); Vol. 3, p.1 (1923).

ACETAL

Submitted by Homer Adkins and B. H. Nissen. Checked by H. T. Clarke and J. H. Bishop.

1. ProcedureIn a 1-gallon (4-l.) bottle are placed 1050 g. (1305 cc., 21.7 moles) of 95 per cent ethyl alcohol and 200 g. (1.8 moles) of granulated anhydrous calcium chloride (Note 1). The mixture is cooled to 8 or below by immersion in ice water, and 500 g. (620 cc., 11.4 moles) of freshly distilled acetaldehyde (b. p. 2022) is slowly added down the sides of the bottle so that it forms a layer on the alcoholic calcium chloride. The bottle is then tightly closed with a cork stopper and shaken vigorously for a few minutes (Note 2). It is then allowed to stand at room temperature with intermittent shaking for one to two days. The mixture divides into two layers after one to two hours; after the first twenty-four hours no appreciable change in volume of the two layers takes place. The upper layer, which weighs 12801285 g., is separated and washed three times with 330 cc. portions of water. The weight has now fallen to 990995 g. The oil is dried by standing over 25 g. of anhydrous potassium carbonate and is then fractionally distilled with the use of an efficient column at least 90 cm. long (Note 3), and the fraction which boils at 101103.5 collected as pure acetal. In this way 700720 g. can be obtained by one or two fractionations. The yield can be further increased by washing the low-boiling fractions and residue with small quantities of water, drying, and again fractionally distilling, so that a total of 790815 g. is obtained (6164 per cent of the theoretical amount). (Note 4)

2. Notes1. It is essential that the calcium chloride should be anhydrous; if it contains water of crystallization, stratification may be long delayed and the yield be much decreased. On the other hand, no great advantage is observed by substituting absolute alcohol for the 95 per cent material. 2. On mixing the acetaldehyde and the alcoholic calcium chloride solution, a considerable rise in temperature takes place; for this reason it is necessary to chill the reagents and to close the stopper before mixing intimately, otherwise losses might occur by volatilization. 3. A fractionating column containing a condensing unit at the head1 has been found satisfactory. 4. It is suggested that acetaldehyde be distilled directly into the mixture of alcohol and calcium chloride. The aldehyde is generated by warming paraldehyde with a little sulfuric acid. The yield of acetal thus obtained is somewhat lower than that in the procedure described (V. H. Wallingford, private communication).

3. DiscussionAcetal can be prepared by the action of acetaldehyde upon alcohol in the presence of small quantities of mineral acid,2 or Twitchell's reagent,3 or certain metallic salts;4 by the action of acetylene on alcohol in the presence of sulfuric acid and mercuric salts;5 by the action of acetaldehyde on tetraethyl silicate with hydrogen chloride as a catalyst;6 from paraldehyde and ethyl alcohol with hydrogen chloride or p-toluenesulfonic acid as catalyst;7 and from metaldehyde and ethyl alcohol in the presence of calcium chloride and a trace of hydrogen chloride.8 The procedure described is essentially that of Adkins and Nissen.9

References and Notes1. 2. 3. 4. 5. 6. 7. 8. 9. Clarke and Rahrs, Ind. Eng. Chem. 15, 349 (1923). Geuther, Ann. 126, 62 (1863); Fischer and Giebe, Ber. 30, 3053 (1897). Zaganiaris, Ber. 71, 2002 (1938). King and Mason, Brit. pat. 101,428 [C. A. 11, 86 (1917)]; U. S. pat. 1,312,186 [C. A. 13, 2536 (1919)]. Reichert, Bailey and Nieuwland, J. Am. Chem. Soc. 45, 1552 (1923); Consortium Elektrochem. Ind. Ges., Brit. pat. 257,622 [C. A. 21, 3057 (1927)]; 264,791 [C. A. 22, 243 (1928)]. Helferich and Hansen, Ber. 57, 795 (1924). Beduwe, Bull. soc. chim. Belg. 34, 41 (1925). Soc. anon. des distilleries des Deux-Sevres, Brit. pat. 283, 112 [C. A. 22, 3893 (1928)]; Fr. pat. 646,666 [C. A. 23, 2191 (1929)]. Fouque and Cabanac, Bull. soc. chim. (4) 39, 1184 (1926). Adkins and Nissen, J. Am. Chem. Soc. 44, 2749 (1922); Adams and Adkins, ibid. 47, 1358 (1925); Adkins and Broderick, ibid. 50, 178 (1928).

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)Twitchell's reagent mercuric salts metaldehyde ACETAL (105-57-7) ethyl alcohol, alcohol (64-17-5) calcium chloride (10043-52-4) acetaldehyde (75-07-0) potassium carbonate (584-08-7) sulfuric acid (7664-93-9) acetylene (74-86-2) tetraethyl silicate (78-10-4) hydrogen chloride (7647-01-0) p-toluenesulfonic acid (104-15-4) paraldehyde (123-53-7)Copyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


ACETAMIDE

Submitted by G. H. Coleman and A. M. Alvarado. Checked by H. T. Clarke and E. R. Taylor.

1. ProcedureIn a 5-l. flask is placed 3 kg. (2860 cc., 50.0 moles) of glacial acetic acid and to this is added a weight of ammonium carbonate corresponding to 400 g. (23.5 moles) of ammonia (Note 1). The flask is fitted with a one-hole stopper holding an efficient fractionating column 90 cm. long with condenser and receiver. An air condenser 150200 cm. long may be employed. The mixture in the flask is heated to gentle boiling and the flame so regulated that the rate of distillation does not exceed 180 cc. per hour. The distillation is continued in this way for eight to ten hours, until the temperature at the head of the column reaches 110. The distillate, which is a mixture of water and acetic acid, amounts to 14001500 cc. The receiver is changed, the flame under the flask is gradually increased, and the distillation is continued at about the same rate until the temperature at the head of the column rises to 140. The distillate, which amounts to 500700 cc., is largely acetic acid and may be used in the next run. The contents of the flask are transferred to a 2-l. flask for fractional distillation (p. 130), having a column 4050 cm. long, and distilled under atmospheric pressure, using an air condenser. The fraction boiling below 210, amounting to 250300 cc., is collected separately. The material remaining in the flask is nearly pure acetamide and may all be distilled, 11501200 g. passing over at 210216. By redistilling the fraction boiling below 210, the yield may be increased to 12001250 g. (8790 per cent of the theoretical amount). The acetamide thus obtained is pure enough for most purposes, but if a purer product is desired it may be recrystallized from a mixture of benzene and ethyl acetate; 1 l. of benzene and 300 cc. of ethyl acetate are used for 1 kg. of acetamide (Note 2). Colorless needles melting at 81 are thus obtained (Note 3). The solvent and the acetamide it contains may be recovered by distillation.

2. Notes1. Ammonium carbonate of commerce is often extremely impure, and care must be taken to obtain a representative sample for the determination of the ammonia content by titration with standard acid. The ammonium carbonate used in this preparation contained 27.2 per cent of ammonia, and 1470 g. was used in each run. 2. Crystallization of acetamide, by solution in hot methyl alcohol (0.8 cc. per g.) and dilution with ether (810 cc. per g.), has been recommended as the best method of purification.1 3. As acetamide is somewhat hygroscopic, it cannot be exposed to the air unless precautions are taken to have the air dry.

3. DiscussionAcetamide can be prepared by the rapid distillation of ammonium acetate;2 by heating ammonium acetate in a sealed tube and distilling the product;3 by treating acetic anhydride with ammonia;4 by heating a mixture of ammonium chloride and sodium acetate to 240;5 by the action of cold aqueous ammonia on ethyl acetate;6 by boiling a mixture of glacial acetic acid and ammonium thiocyanate for four days;7 by saturating glacial acetic acid with dry ammonia and then refluxing;8 by distillation of ammonium acetate through a reflux condenser filled first with glacial acetic acid and then with aniline until the temperature of the mixture reaches 220;9 by passing a stream of ammonia through heated acetic acid;10 and from formamide and hydrogen at 200500.11

The procedure described is based on the method of Noyes and Goebel,12 in which equimolecular proportions of ammonium acetate and acetic acid are heated together, the acetic acid having been shown to accelerate both the dehydration of ammonium acetate and the hydrolysis of acetamide.

References and Notes1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Wagner, J. Chem. Education 7, 1135 (1930). Kundig, Ann. 105, 277 (1858). Hofmann, Ber. 15, 977 (1882). Gerhardt, Ann. chim. phys. (3) 37, 327 (1853). Dunlap, J. Am. Chem. Soc. 24, 762 (1902). Phelps and Phelps, Am. J. Sci. (4) 24, 429 (1907). Schulze, J. prakt. Chem. (2) 27, 514 (1883). Grant and James, J. Am. Chem. Soc. 39, 933 (1917). Francois, J. pharm. chim. (6) 23, 230 (1906) [Chem. Zentr. I, 1089 (1906)]. Mitchell and Reid, J. Am. Chem. Soc. 53, 1879 (1931). Soc. franaise de catalyse gnralise, Fr. pat. 708,084 [C. A. 26, 995 (1932)]. Noyes and Goebel, J. Am. Chem. Soc. 44, 2286 (1922); Rosanoff, Gulick and Larkin, ibid. 33, 974 (1911); Hitch and Gilbert, ibid. 35, 1780 (1913).

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)Acetamide (60-35-5) acetic acid (64-19-7) ammonium carbonate (506-87-6) ammonia (7664-41-7) Benzene (71-43-2) ethyl acetate (141-78-6) methyl alcohol (67-56-1) ether (60-29-7) ammonium acetate (631-61-8) acetic anhydride (108-24-7) ammonium chloride (12125-02-9) sodium acetate (127-09-3) ammonium thiocyanate (1762-95-4)

aniline (62-53-3) formamide (75-12-7) hydrogen (1333-74-0)Copyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


ACETAMIDINE HYDROCHLORIDE

Submitted by A. W. Dox Checked by Frank C. Whitmore

1. ProcedureDry hydrogen chloride (p. 293) (Note 1) is passed into a solution of 100 g. (2.44 moles) of thoroughly dry acetonitrile (Note 2) in 113 g. (143 cc., 2.5 moles) of absolute ethyl alcohol (Note 1) contained in a 1-l. weighed suction flask (Note 3) surrounded by a freezing mixture of ice and salt, until an increase in weight of 95 g. (2.6 moles) is obtained. This requires about four hours (Note 4) but the time is diminished considerably if proper mechanical stirring is used. The flask is now tightly stoppered, the side arm being attached to a calcium chloride tube, and allowed to stand until the mixture has set to a solid mass of crystals. Usually this requires two or three days. A solution of dry ammonia gas in absolute ethyl alcohol is prepared and titrated against standard hydrochloric acid, using methyl orange as the indicator. The solution should contain at least 9 per cent of ammonia by weight (Note 5). The solid crystalline mass of acetimido ethyl ether hydrochloride is broken up and transferred to a dry mortar in which it is ground to a paste with 100 cc. of absolute alcohol and returned to the flask (Note 6). It is then stirred mechanically with an excess of the alcoholic ammonia solution (500 cc. of 9 per cent solution or an equivalent amount of a more concentrated solution). The crystals gradually dissolve and ammonium chloride separates. After stirring for three hours the ammonium chloride is filtered by suction and the filtrate evaporated on the steam bath to a volume of about 200 cc. when a considerable quantity of crystals separates. On cooling, the acetamidine hydrochloride separates in long colorless prisms. These are filtered by suction, washed with 10 cc. of cold alcohol, and dried in a desiccator over sulfuric acid. Concentration of the mother liquor gives a second crop. The product melts at 164166 and is readily soluble in alcohol and in water. The yield varies from 185 to 210 g. (8091 per cent of the theoretical amount). The product is somewhat deliquescent and should be kept in a tightly stoppered bottle.

2. Notes1. Moisture in the reagents affects the yield seriously because of the ease with which the intermediate imido ether is hydrolyzed. The hydrogen chloride must be thoroughly dried by passing it through two wash bottles containing sulfuric acid. If the wash bottles are not effective, a tube containing glass beads mixed with phosphorus pentoxide should be used after the wash bottles. It is well to protect the side arm of the flask by means of a calcium chloride tube. The absolute alcohol used should be at least 99.5 per cent (p. 249). 2. If commercial acetonitrile is used directly, the yields are poor. It should be dried over calcium chloride for at least a week, filtered, and distilled, the fraction boiling at 7681 being used. 3. If a thinner flask is used, there is danger of its being cracked during the experiment. 4. If a proper safety bottle is placed between the drying train and the flask of acetonitrile, the treatment with hydrogen chloride does not require constant attention during this time. 5. When weaker solutions of ammonia were used, the yields were lower.

6. The grinding of the imido ether hydrochloride is very important, as lumps of this material become coated with ammonium chloride, which prevents the complete action of the ammonia. 7. By a similar procedure benzamidine hydrochloride can be prepared. Dry hydrogen chloride is passed into a cooled solution of 51.5 g. (51 cc., 0.5 mole) of benzonitrile in 25 g. of absolute ethyl alcohol until 21.3 g. of the gas is absorbed. The reaction mixture is allowed to stand for forty-eight hours, and the solid cake of imido ether hydrochloride is quickly crushed in a dry mortar. The solid is transferred to a liter flask, and an 8 per cent solution of dry ammonia in absolute ethyl alcohol containing 12 g. of ammonia is added slowly in small portions. The reaction mixture is shaken for twenty-four hours, then allowed to stand for forty-eight hours and filtered to remove the ammonium chloride which has precipitated. (During the shaking the solution may develop a faint pink color. This is probably due to the presence of traces of glyoxal in the alcohol for this material in basic solution furnishes colored condensation products with benzamidine.) The filtrate is allowed to evaporate to dryness in the open air, and the benzamidine hydrochloride thus obtained is dissolved in water. The solution is acidified with concentrated hydrochloric acid, decolorized with charcoal, filtered, and the filtrate is evaporated almost to dryness at room temperature. The crystals of benzamidine hydrochloride dihydrate are filtered and air-dried. The yield is 6070 g. of material which melts at 7073. The filtrate on evaporation to dryness furnishes 1530 g. of less pure product, melting at 7482, which contains a small amount of ammonium chloride but which can be used satisfactorily in most reactions. The total yield is 8095 per cent. (A. R. Ronzio and J. B. Ekeley, private communication.)

3. DiscussionThe only practical method of preparation is that of Pinner,1 on which the procedure described is based.

References and Notes1. Pinner, Ber. 16, 1654 (1883), 17, 178 (1884).

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)acetimido ethyl ether hydrochloride imido ether imido ether hydrochloride ethyl alcohol, alcohol (64-17-5) calcium chloride (10043-52-4) sulfuric acid (7664-93-9) hydrogen chloride, hydrochloric acid (7647-01-0) ammonia (7664-41-7)

ammonium chloride (12125-02-9) Acetamidine hydrochloride (124-42-5) acetonitrile (75-05-8) Benzamidine hydrochloride (1670-14-0) benzonitrile (100-47-0) glyoxal (107-22-2) benzamidine (618-39-3) benzamidine hydrochloride dihydrate phosphorus pentoxide (1314-56-3)Copyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


p-ACETAMINOBENZENESULFINIC ACID[Benzenesulfinic acid, p-acetamido-]

Submitted by S. Smiles and C. M. Bere. Checked by Henry Gilman and F. Schulze.

1. ProcedureThe crude p-acetaminobenzenesulfonyl chloride (p. 8) obtained from 67.5 g. (0.5 mole) of acetanilide is shaken for two hours with a solution of 252 g. (1 mole) of crystallized sodium sulfite (Na2SO3 7H2O) in 500 cc. of water. The reaction mixture is kept slightly alkaline by the addition at intervals of small portions of 50 per cent sodium hydroxide solution. The total volume of alkali used varies from 10 to 50 cc. After the alkaline mixture has been shaken for the two-hour period (Note 1) it is filtered, and the filtrate is acidified with 60 per cent sulfuric acid. If the acid is added slowly, the sulfinic acid comes down in fine crystals which, after filtering and drying, melt at 155 with decomposition (Note 2). The yield is 5055 g.. (4347 per cent of the theoretical amount based on the acetanilide used). The product may be purified by crystallization from 400 cc. of hot water, but this is unnecessary when the above procedure is followed carefully.

2. Notes1. The solution does not clear up when reduction is complete on account of the formation of a gelatinous impurity. Two hours suffice for the completion of reduction. 2. The melting point given in the literature (180) is incorrect, its publication being due to a typographical error. The observed melting point varies slightly with the rate of heating during the determination of the melting point.

3. Discussionp-Acetaminobenzenesulfinic acid can be prepared by the reduction of p-acetaminobenzenesulfonyl chloride.1 This preparation is referenced from: Org. Syn. Coll. Vol. 1, 8 Org. Syn. Coll. Vol. 6, 727

References and Notes1. Bere and Smiles, J. Chem. Soc. 125, 2361 (1924).

Appendix

Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)sulfinic acid sulfuric acid (7664-93-9) Acetanilide (103-84-4) sodium sulfite (7757-83-7) sodium hydroxide (1310-73-2) p-Acetaminobenzenesulfonyl chloride (121-60-8) p-Acetaminobenzenesulfinic acid, Benzenesulfinic acid, p-acetamido- (710-24-7)Copyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


p-ACETAMINOBENZENESULFONYL CHLORIDE[Sulfanilyl chloride, N-acetyl-]

Submitted by S. Smiles and Jessie Stewart. Checked by Henry Gilman and F. Schulze.

1. ProcedureIn a 500-cc. round-bottomed flask, fitted with a mechanical stirrer, is placed 290 g. (165 cc., 2.49 moles) of chlorosulfonic acid (Note 1). The flask is surrounded by a cooling bath and cooled with running water to about 1215. To the chlorosulfonic acid is added gradually 67.5 g. (0.5 mole) of acetanilide. This requires about fifteen minutes if the temperature is maintained at approximately 15. Since large volumes of hydrogen chloride are evolved, the reaction should be conducted in a good hood, or a gas absorption trap (Fig. 7 on p. 97) might be used. After all the acetanilide has been added, the mixture is heated to 60 for two hours to complete the reaction (Note 2). The sirupy liquid is poured slowly, with stirring (Note 3), into 1 kg. of ice to which just enough water has been added to make stirring easy. This decomposition of the excess chlorosulfonic acid should be carried out in the hood. The solid sulfonyl chloride which separates is collected on a suction funnel (Note 4) and washed with water. The yield of crude material is 9095 g. (7781 per cent of the theoretical amount based on the acetanilide). This crude material may be used directly in many preparations such as p-acetaminobenzenesulfinic acid (p. 7). If a pure product is desired, the crude material is dried by pressing on a porous plate and then crystallized from dry benzene. The acid chloride is slightly soluble in benzene, and only 1.5 to 2 g. will dissolve in 100 cc. of hot benzene. On cooling, about 75 per cent of the material separates from the benzene in thick, colorless prisms melting at 149 (Note 5).

2. Notes1. The chlorosulfonic acid should be freshly distilled. Smaller amounts of this reagent may be used without reducing the yield or affecting the quality of the product. However, with smaller amounts the time required for the reaction must be increased. Thus, if 175 g. (1.5 moles) of chlorosulfonic acid is used with 67.5 g. (0.5 mole) of acetanilide, an additional hour of heating is required to obtain the yields mentioned above. 2. The hydrogen chloride which is liberated during the reaction fills the mixture with tiny bubbles. When these disappear the reaction is complete. 3. Mechanical stirring is most convenient but not necessary. 4. A rather large suction funnel (125 mm. or more) should be used in the filtration as the sulfonyl chloride has a tendency to clog the filter. 5. The purification is the least satisfactory part of the preparation. The material must not be heated while water is still present, or excessive decomposition will occur. As the sulfonyl chloride is only slightly soluble in hot benzene, it is inconvenient to crystallize more than a small amount at a time. The crude product does not keep well and must be used at once. After recrystallization it may be kept indefinitely.

3. Discussionp-Acetaminobenzenesulfonyl chloride can be prepared by the action of phosphorus pentachloride1 or chlorosulfonic acid2 on sodium p-acetaminobenzenesulfonate and by the action of chlorosulfonic acid

on acetanilide.3 This preparation is referenced from: Org. Syn. Coll. Vol. 1, 7

References and Notes1. Schroeter, Ber. 39, 1563 (1906). 2. Goldyrev and Postovskii, J. Applied Chem. (U.S.S.R.) 11, 316 (1938) [C. A. 32, 5800 (1938)]. 3. Stewart, J. Chem. Soc. 121, 2558 (1922).

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)sulfonyl chloride acid chloride hydrogen chloride (7647-01-0) Benzene (71-43-2) Acetanilide (103-84-4) Sulfanilyl chloride, N-acetyl-, p-Acetaminobenzenesulfonyl chloride (121-60-8) chlorosulfonic acid (7790-94-5) phosphorus pentachloride (10026-13-8) p-Acetaminobenzenesulfinic acid (710-24-7) sodium p-acetaminobenzenesulfonateCopyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


ACETONEDICARBOXYLIC ACID[Glutaric acid, -oxo]

Submitted by Roger Adams, H. M. Chiles, and C. F. Rassweiler. Checked by H. T. Clarke and T. F. Murray.

1. ProcedureIn a 5-l. round-bottomed flask (Note 1), fitted with a mechanical stirrer, is placed 3 kg. (1555 cc.) of fuming sulfuric acid (20 per cent of free sulfur trioxide). Then the flask is cooled very efficiently with a thick pack of ice and salt, until the temperature of the acid reaches 5 (Note 2). The stirring is started, and 700 g. (3.64 moles) of finely powdered u. s. p. citric acid is added gradually. The speed of the addition is regulated according to the temperature of the reaction mixture. The temperature should not rise above 0 until half of the citric acid has been added, after which the temperature should not be allowed to exceed 10 until the reaction is complete. The addition requires three to four hours, provided efficient cooling is used. The citric acid should be in solution at the end of this time; if not, the stirring should be continued until it has dissolved completely. The temperature of the reaction mixture is allowed to rise gradually until a vigorous evolution of gas commences; at this point the flask is cooled with ice water to stop the excessive frothing, but cooling is not carried far enough to stop the evolution of gas entirely (Note 3). After the more vigorous foaming has ceased, the reaction mixture is raised to about 30 and kept there until no more foaming occurs. A convenient way of determining this point is to stop the stirring for a moment and allow the mixture to remain quiet. After a minute or so, a clear brown liquid giving off very few gas bubbles should result. This general procedure requires two to three hours. The reaction mixture is cooled down again with ice and salt until the temperature reaches 0, then 2400 g. of finely cracked ice is added in small portions at such a rate that the temperature does not rise above 10 until one-third of the ice has been added. Then the temperature may be allowed to rise to 25 30. The addition of the ice requires about two hours; after this, the mixture is cooled again to 0 (Note 4) and then filtered as rapidly as possible through a funnel fitted with a filtros plate (Note 5). The crystals are thoroughly pressed and sucked as dry as possible. The acetonedicarboxylic acid is light gray to white in color. After the suction and pressing have removed practically all of the sulfuric acid, the crystals are transferred to a beaker and stirred with sufficient ethyl acetate (about 200250 cc.) to make a thick paste. The crystals are filtered with suction. If acetonedicarboxylic acid entirely free from sulfuric acid is desired, the washing with ethyl acetate should be repeated. The yield of practically dry acetonedicarboxylic acid varies from 450475 g. (8590 per cent of the theoretical amount) (Note 6). This may be used directly for the preparation of the ester (p. 237). The acid itself is not stable and after a few hours gradually decomposes (Note 7).

2. Notes1. The reaction must be carried out in a good hood, since a large amount of carbon monoxide is liberated. 2. The use of a very efficient ice and salt mixture around the reaction flask is necessary if the reaction is to be carried out within the time indicated. It is very necessary to regulate the temperature as directed, since a considerably lower yield is obtained if the temperature rises. 3. Some cooling is necessary, or the rapid evolution of gas will cause the reaction mixture to foam over with consequent loss of material. 4. Vigorous cooling before final filtration of the acetonedicarboxylic acid is essential to good yields,

since the acid is fairly soluble in the reaction mixture. 5. The filtros plate for filtration can be very conveniently sealed into the Bchner funnel with a paste of water-glass and amorphous silica which is then hardened with concentrated sulfuric acid. 6. If the acid is to be esterified at once, careful drying from ethyl acetate is not necessary. 7. However, it has been observed that if the acid is purified by recrystallization from ethyl acetate and thoroughly dried it undergoes no decomposition, at least over a seven-month period, when kept at room temperature in a desiccator.1

3. DiscussionAcetonedicarboxylic acid can be prepared from citric acid by the action of concentrated2 or fuming sulfuric acid.3 The procedure described is a slight modification of that by Willsttter and Pfannenstiehl.3 While it is more complex than the details given by Ingold and Nickolls,3 it gives somewhat higher yields. The method of Ingold and Nickolls has been checked and found to have the advantage of requiring much less time. This preparation is referenced from: Org. Syn. Coll. Vol. 1, 237 Org. Syn. Coll. Vol. 1, 408 Org. Syn. Coll. Vol. 1, 485 Org. Syn. Coll. Vol. 4, 816

References and Notes1. Wiig, J. Phys. Chem. 32, 961 (1928). 2. Pechmann, Ber. 17, 2543 (1884). 3. Pechmann, Ann. 261, 155 (1891); Peratoner and Strazzeri, Gazz. chim. ital. 21, I, 295 (1891) [Chem. Zentr. I, 967 (1891)]; Jerdan, J. Chem. Soc. 75, 809 (footnote) (1889); Willsttter and Pfannenstiel, Ann. 422, 5 (1921); Ingold and Nickolls, J. Chem. Soc. 121, 1642 (1922); Wiig, J. Phys. Chem. 32, 961 (1928).

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)sulfuric acid (7664-93-9) ethyl acetate (141-78-6) Acetonedicarboxylic acid Glutaric acid, -oxo (542-05-2) sulfur trioxide (7446-11-9) citric acid (77-92-9) carbon monoxide (630-08-0)

Copyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


ACETYLMANDELIC ACID and ACETYLMANDELYL CHLORIDE[(Mandelic acid, acetate) (Mandelyl chloride, acetate)]

Submitted by F. K. Thayer Checked by Roger Adams and E. E. Dreger.

1. Procedure(A) In a 500-cc. Claisen distilling flask with a low side tube connected to a condenser, are placed 105 g. (0.69 mole) of mandelic acid (p. 336) (m.p. 118) and 151 g. (137 cc., 1.92 moles) of acetyl chloride. A reaction sets in without the application of heat (Note 1). As soon as a clear solution results, the flask is warmed on a water bath and the excess acetyl chloride is distilled. The last trace of acetyl chloride may be removed by prolonged drying in a vacuum. The acetylmandelic acid then crystallizes in large, round, white clusters after one or two days' standing. The yield is 130133 g. (9799 per cent of the theoretical amount) (Note 2). (B) To the crude acetylmandelic acid still containing some acetyl chloride obtained as described above, is added 250 g. (149 cc., 2.1 moles) of thionyl chloride. The reaction starts at once without warming but it is necessary to reflux for four hours to complete the reaction (Note 3). The excess thionyl chloride is then distilled and the residue distilled under reduced pressure (Note 4). The yield is 115120 g. (7982 per cent of the theoretical amount) of almost colorless liquid boiling at 125130/10 mm. (150155/33 mm.).

2. Notes1. Occasionally the application of a little heat is necessary to bring about a more rapid acetylation. 2. The melting points given in the literature range from 39 to 80. The acetylmandelic acid is difficult to crystallize but may be purified from benzene or chloroform, preferably the former. The product thus obtained melts at about 7980. 3. Prolonged refluxing of the acetylmandelic acid with the thionyl chloride tends to lower the yield. 4. The boiling point of acetylmandelyl chloride has been reported1 as 129/10 mm. The pressure should be reduced as low as possible, to avoid the formation of tar during the distillation.

3. DiscussionAcetylmandelic acid can be prepared by the action of acetyl chloride1 or acetic anhydride2 on mandelic acid. Acetylmandelyl chloride can be prepared by the action of phosphorus pentachloride1 or thionyl chloride3 on acetylmandelic acid.

References and Notes

1. Anschtz and Bcker, Ann. 368, 57, 59 (1909). 2. Kaufler and Herzog, Ber. 42, 3872 (1909). 3. v. Braun and Mller, Ber. 51, 244 (1918).

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)Benzene (71-43-2) acetic anhydride (108-24-7) phosphorus pentachloride (10026-13-8) Acetylmandelic acid Acetylmandelyl chloride (1638-63-7) Mandelic acid, acetate (5438-68-6) Mandelyl chloride, acetate Mandelic acid (90-64-2) acetyl chloride (75-36-5) thionyl chloride (7719-09-7) chloroform (67-66-3)Copyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


ACID AMMONIUM o-SULFOBENZOATE[Benzoic acid, o-sulfo-, ammonium H salt]

Submitted by H. T. Clarke and E. E. Dreger. Checked by Henry Gilman and J. E. Kirby.

1. ProcedureIn a 12-l. flask fitted with a stirrer and reflux condenser are placed 188 g. (1 mole) of o-sulfobenzoic imide ("saccharin insoluble"), 565 cc. of distilled water and 188 g. (158 cc.) of concentrated hydrochloric acid (sp. gr. 1.19). The mixture is boiled over a free flame with continual stirring (Note 1) until all the solid is in solution; this requires two and one-half to three hours. A second quantity of 188 g. of o-sulfobenzoic imide is then added, and the mixture again heated with stirring until a clear solution results, which requires one and one-half to two hours. Heating is then continued for one hour longer, whereupon the solution is poured into a crock and allowed to cool. The crystals which separate are collected on a suction funnel, washed as free from hydrochloric acid as possible (Note 2) with ice-cold distilled water, and dried. The mother liquor and washings are concentrated on a steam bath under reduced pressure until the separation of crystals causes bumping, when the solution is again allowed to crystallize. This procedure is repeated, the final mother liquor being evaporated nearly to dryness. The main product, together with that from the mother liquors, weighs 410427 g. (9195 per cent of the theoretical amount) and is sufficiently pure for conversion into o-sulfobenzoic anhydride (p. 495). In order to obtain a purer product the material may be recrystallized from an equal weight of distilled water; the yield on recrystallizing is about 90 per cent.

2. Notes1. The mixture tends to foam somewhat during the first few minutes of boiling. 2. If much hydrochloric acid is allowed to remain with the crystals, drying is extremely difficult.

3. DiscussionAcid ammonium o-sulfobenzoate can be prepared by the hydrolysis of saccharin with concentrated hydrochloric acid.1 The procedure described is a modification of that of White and Acree.2 This preparation is referenced from: Org. Syn. Coll. Vol. 1, 495

References and Notes1. Fahlberg and Barge, Ber. 22, 755 (1889); Remsen and Linn, Am. Chem. J. 11, 74 (1889). 2. White and Acree, J. Am. Chem. Soc. 41, 1197 (1919).

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)ACID AMMONIUM o-SULFOBENZOATE hydrochloric acid (7647-01-0) saccharin (81-07-2) o-Sulfobenzoic anhydride (81-08-3) Benzoic acid, o-sulfo-, ammonium o-sulfobenzoic imideCopyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


ACROLEIN

Submitted by Homer Adkins and W. H. Hartung. Checked by Frank C. Whitmore and M. L. Wolfrom.

1. ProcedureThe apparatus is assembled according to Fig. 1. B and D are 5-l. round-bottomed flasks, immersed to about two-thirds of their height in deep oil baths heated by large burners. Each bath is provided with a thermometer reaching to the level of the bottom of the flask. Flask B is fitted with a specially treated two-holed cork stopper (Note 1), in one hole of which is fitted a 500-cc. separatory funnel A and in the other a delivery tube C of 12-mm. diameter. The tubes must not extend more than 3 mm. below the stopper. Flask D is fitted with a three-holed cork stopper connected with a separatory funnel, the delivery tube from B, and the delivery tube E of 12-mm. tubing leading to flask F. F is a 500-cc. roundbottomed flask immersed to two-thirds of its height in an oil bath heated by a Bunsen burner and provided with a thermometer. Fig. 1.

Flask F is provided with a two-holed cork stopper connected with tube E, and with tube G which connects with the first condenser H and may be of smaller bore than tubes C and E. H is a condenser with a 30-cm. water jacket. H is connected with I by means of an adapter. I is a 1-l. round-bottomed flask supported in a pan which is at first filled with ice and later used as a water bath. Flask I is fitted with a two-holed cork stopper carrying the adapter connected with condenser H and a Vigreux column K of 2-cm. diameter and a length of 30 cm. to the side arm. Flask I and condenser H are covered with black cloth (Note 2). The side arm of K is connected with a 90-cm. water-jacketed condenser L which leads into M through an adapter. M is a 750-cc. Erlenmeyer flask immersed in an ice bath. Flask M is provided with a two-holed stopper connected with the adapter from L and an upright bulb condenser that is provided with a tube leading through a window or to a hood.

Before the final assembling of the apparatus, the flasks are charged as follows: One kilo of freshly fused and finely powdered acid potassium sulfate, 200 g. of powdered potassium sulfate, and 300 g. (238 cc.) of dry glycerol (Note 3) are thoroughly mixed in each of flasks B and D. In each of flasks I and M is placed about 1 g. of hydroquinone to act as a stabilizer for the acrolein.1 The apparatus is assembled as indicated and the oil baths under B and D are heated to about 190 200 (Note 4), and the oil bath under F to about 110120. The bath under I is filled with ice. The volatile products are collected in I which is kept carefully protected from light. When the reaction is well started 300 g. of dry glycerol is placed in each separatory funnel, and added drop by drop during the heating. After the first violent reaction has abated (about one hour) the baths under B and D are raised to 215230 and maintained there until no more volatile product comes over (a total time of heating of about four and one-half hours). After B and D have been heated about four hours the ice under I is replaced by water which is heated to 7580 to distil the acrolein into flask M, which is packed in ice. Near the end of the distillation the water under I is heated to boiling. The product in M is treated with small amounts of solid sodium bicarbonate to neutralize any acid present. The cold liquid is filtered through a small filter into a 1500-cc. distilling flask containing about 1 g. of hydroquinone. It is then distilled into a tared dark bottle containing about 1 g. of hydroquinone. The yield of product boiling at 52.555.5 (Note 5) obtained from 1200 g. (13 moles) of dry glycerol is 240350 g. (3348 per cent of the theoretical amount).

2. Notes1. The corks used in the apparatus are made tight and heat-resistant by treatment with sodium silicate solution. After being properly fitted and bored they are placed in the silicate solution contained in a bottle that is connected with a suction pump. The solution is forced into the pores of the corks by alternately making and breaking the reduced pressure and shaking the solution vigorously. After the excess of solution has been wiped off, the corks are put in place while still wet. After this the outside of each cork is given an extra coat of the silicate solution. When corks treated in this way were used no odor of acrolein was noted in the laboratory. Acrolein has pronounced lachrymatory properties and is also highly toxic. 2. The exclusion of light slows up the polymerization of the acrolein. If the condensers are not protected from light a solid polymer collects in them. 3. The glycerol is dried by heating slowly in an open dish in a hood until the temperature of the liquid is 170. A sand bath is used and the heating requires about three hours. "Dynamite glycerine," 9698 per cent, may be used instead of the dried glycerol. 4. The heating must not be too rapid nor too high at first as there is danger of frothing followed by a clogging of the apparatus. 5. Pure acrolein boils at 52.5/760 mm.2

3. DiscussionAcrolein can be prepared by heating glycerol with magnesium or alkali sulfates under various conditions,3 by heating glycerol with a "bleaching earth" catalyst,4 from glycerol with iron and lithium phosphates as catalysts,5 from epichlorohydrin by heating with water and an inorganic acid,6 and from propylene with aqueous sulfuric acid and mercuric sulfate.7 This preparation is referenced from: Org. Syn. Coll. Vol. 1, 166 Org. Syn. Coll. Vol. 1, 506 Org. Syn. Coll. Vol. 2, 137 Org. Syn. Coll. Vol. 3, 502

References and Notes

1. Moureu, Compt. rend. 170, 26 (1920). 2. Moureu, Boutaric and Dufraisse, J. chim. phys. 18, 333 (1921). 3. Wohl and Mylo, Ber. 45, 2046 (1912); Witzemann, J. Am. Chem. Soc. 36, 1766 (1914); Moureu and Lepape, Compt. rend. 169, 885 (1919); Ann. chim. (9) 15, 176 (1921); Evans and Haas, J. Am. Chem. Soc. 48, 2703 (1926). 4. Freund, U. S. pat. 1,672,378 [C. A. 22, 2571 (1928)]. 5. Schering-Kahlbaum A.-G., Fr. pat. 695,931 [C. A. 25, 2740 (1931)]. 6. Shell Development Company, U. S. pat. 2,106,347 [C. A. 32, 2542 (1938)]. 7. E. I. du Pont de Nemours and Co., U. S. pat. 2,197,258 [C. A. 34, 5468 (1940)].

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)acid potassium sulfate Dynamite glycerine alkali sulfates lithium phosphates sulfuric acid (7664-93-9) Acrolein (107-02-8) potassium sulfate (37222-66-5) glycerol (56-81-5) hydroquinone (123-31-9) sodium bicarbonate (144-55-8) sodium silicate silicate (15593-90-5) magnesium (7439-95-4) iron (7439-89-6) Epichlorohydrin (106-89-8) propylene (115-07-1)Copyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


ADIPIC ACID

Submitted by B. A. Ellis Checked by Roger Adams and C. D. Thompson.

1. ProcedureIn a 5-l. round-bottomed flask fitted with a mechanical stirrer, a thermometer, and a 1-l. separatory funnel, is placed 2100 g. (16.6 moles) of 50 per cent nitric acid (sp. gr. 1.32) (Hood). The acid is heated nearly to boiling, and 1 g. of ammonium vanadate (Note 1) is added. The stirrer is started, and 500 g. (5 moles) of cyclohexanol (Note 2) is introduced slowly through the separatory funnel. At first 4050 drops of cyclohexanol are admitted and the reaction mixture is stirred until the reaction has started (four to five minutes) as is indicated by the evolution of oxides of nitrogen (Note 3). Then the reaction flask is placed in an ice-water bath and cooled until the temperature of the oxidizing mixture is 5560. The cyclohexanol is then added as rapidly as possible while the temperature of the mixture is kept within these limits. Toward the end of the oxidation (after about 475 g. of cyclohexanol has been added) the ice bath must be removed and sometimes heat must be applied in order to maintain the temperature and avoid crystallization of adipic acid. Stirring is continued for about one hour after the addition of the last of the cyclohexanol. Then the mixture is cooled to about 0 and the adipic acid is collected on a suction filter, washed with 500 cc. of ice water, and dried in the air overnight. The yield is 395410 g. of white crystals which melt at 146 149. Evaporation of the nitric acid mother liquors yields an additional 3040 g. of product which melts at 141144 (Note 4). The total yield of crude adipic acid is 425440 g. (5860 per cent of the theoretical amount) (Note 5). This product is pure enough for most purposes. However, a purer product may be obtained by recrystallizing this crude material from 700 cc. of concentrated nitric acid (sp. gr. 1.42). The loss in this purification is about 5 per cent. The recrystallized acid melts at 151152 (Note 6) and (Note 7).

2. Notes1. It is suggested that no catalyst is necessary if the temperature of the reaction mixture, once the reaction has started, is maintained at 8590. (W. W. Hartman, private communication.) 2. The cyclohexanol used was a commercial grade, which contained practically no phenol. Over 90 per cent of the product boiled between 158163. 3. It is important that the oxidation start before a large amount of cyclohexanol has been added or the reaction will become violent. The reaction must be carried out in a good hood. 4. The nitric acid mother liquors contain considerable amounts of adipic acid mixed with glutaric and succinic acids. It has not proved practicable to separate these acids by crystallization. However, if the nitric acid is removed by evaporation and the resulting mixture of acids is esterified with ethyl alcohol, a mixture of ethyl succinate (b.p. 121126/20 mm.), ethyl glutarate (b.p. 133138/20 mm.), and ethyl adipate (b.p. 142147/20 mm.) can be obtained. These esters can be separated quite satisfactorily by distillation. 5. The following modified procedure is reported to give better yields. In a 3-l. three-necked flask provided with a stirrer, reflux condenser, and dropping funnel set in asbestos-sodium silicate stoppers, are placed 1900 cc. of 50 per cent nitric acid (1262 cc. of nitric acid, sp. gr. 1.42, diluted to 1900 cc.) and 1 g. of ammonium vanadate. The flask is surrounded by a water bath heated to 5060, and, while the mixture is stirred, 357 g. (3.5 moles) of commercial cyclohexanol is added very slowly so that the temperature of the bath is maintained at 5060. This requires about six to eight hours. The reaction is

completed by heating the water bath to boiling until the evolution of nitrogen oxides has ceased (about one hour). The hot reaction mixture is siphoned off and allowed to cool. The yield of crude adipic acid is 372 g. (72 per cent of the theoretical amount). (Duncan G. Foster, private communication.) The asbestos-sodium silicate stoppers are prepared by cutting thin asbestos paper into strips about 2.5 cm. wide, moistening the strips in water-glass solution, and then winding them around the end of the condenser, for example, until a stopper of the correct size is obtained. After the apparatus is assembled the stoppers are coated with water-glass and allowed to harden overnight. 6. The nitric acid mother liquors from the crystallization may be used as part of the acid for a subsequent oxidation. 7. Adipic acid may also be recrystallized from 2.5 times its weight of water or 50 per cent alcohol. However, these solvents are less satisfactory than nitric acid.

3. DiscussionAdipic acid can be prepared by the oxidation of cyclohexanol and cyclohexanone with nitric acid1 or potassium permanganate.2 The procedure described is adapted from the patent of the Deutsche Hydrierwerke A.-G.1 Other methods of preparing adipic acid are the oxidation of cyclohexene with dichromate and sulfuric acid3 and the interaction of -bromobutyric ester with sodium malonic ester followed by hydrolysis and decarboxylation of the resulting triethyl 1,4,4-butanetricarboxylate.4 This preparation is referenced from: Org. Syn. Coll. Vol. 1, 123 Org. Syn. Coll. Vol. 1, 192 Org. Syn. Coll. Vol. 1, 289 Org. Syn. Coll. Vol. 2, 169

References and Notes1. Zelinsky, J. Russ. Phys. Chem. Soc. 35, 1280 (1903) [Bull. soc. chim. (3) 34, 208 (1905)]; Holleman, Van Der Laan and Slijer, Rec. trav. chim. 24, 23 (1905); Bouveault and Locquin, Bull. soc. chim. (4) 3, 438 (1908); Chavanne and Simon, Compt. rend. 168, 1326 (1919); Thorpe and Kon, Org. Syn. 5, 9; Deutsche Hydrierwerke A.-G., Ger. pat. 473,960 (1926) [C. A. 23, 2988 (1929)]; Claasen, Fr. pat. 32,991 (1927) [C. A. 23, 846 (1929)]; Edwards and Reid, J. Am. Chem. Soc. 52, 3235 (1930); E. I. du Pont de Nemours and Co., U. S. pat. 1,921,101 [C. A. 27, 5084 (1933)]. 2. Rosenlew, Ber. 39, 2202 (1906); Mannich and Hncu, Ber. 41, 575 (1908); Blaise and Koehler, Bull. soc. chim. (4) 5, 682 (1909); v. Braun and Lemke, Ber. 55B, 3529 (1922); Wagner, J. Chem. Education 10, 114 (1933); D. A. Howes (private communication) prepared adipic acid in quite satisfactory yields by the permanganate oxidation method. 3. Zal'kind and Markov, Russ. pat. 50,394 [C. A. 31, 8548 (1937)]; Zal'kind and Markov, C. A. 31, 3875 (1937). 4. Boorman, Linstead, and Rydon, J. Chem. Soc. 1933, 573.

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)oxides of nitrogen

glutaric succinic acids asbestos-sodium silicate nitrogen oxides -bromobutyric ester sodium malonic ester ethyl alcohol, alcohol (64-17-5) sulfuric acid (7664-93-9) Adipic acid (124-04-9) nitric acid (7697-37-2) ammonium vanadate (7803-55-6) Cyclohexanol (108-93-0) phenol (108-95-2) ethyl succinate ethyl glutarate (1070-62-8) Ethyl adipate (626-86-8) Cyclohexanone (108-94-1) potassium permanganate (7722-64-7) Cyclohexene (110-83-8) dichromate triethyl 1,4,4-butanetricarboxylateCopyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


dl-ALANINE

Submitted by E. C. Kendall and B. F. McKenzie. Checked by C. S. Marvel and W. W. Moyer.

1. ProcedureOne hundred and thirty-one grams (3 moles) of freshly distilled acetaldehyde (Note 1) is added to 100 cc. of ether in a 2-l. bottle and cooled to 5 in an ice bath (Note 2). One hundred and eighty grams (3.4 moles) of ammonium chloride dissolved in 550 cc. of water is then added, followed by an ice-cold solution of 150 g. (3.1 moles) of sodium cyanide in 400 cc. of water. The sodium cyanide must be added slowly and with frequent cooling to prevent loss of acetaldehyde by volatilization. After the sodium cyanide solution is added, the bottle is stoppered securely, placed in a mechanical shaker, and shaken for four hours at room temperature. At the end of this time the solution is transferred to a 3-l. distilling flask and 600 cc. of concentrated hydrochloric acid (sp. gr. 1.19) is added (Hood) (Note 3). The solution in the flask is distilled over a free flame until separation of salt prevents further heating. It is then transferred to a large evaporating dish, placed on a steam bath and evaporated to dryness (Note 4). The residue remaining in the dish after evaporation is stirred thoroughly with 800 cc. of 95 per cent alcohol. After filtration the alcohol is distilled on a steam bath and the last traces are removed under vacuum. While still warm the residue is dissolved in 500 cc. of 95 per cent alcohol containing 2 per cent of hydrochloric acid, and cooled. Two hundred cubic centimeters of ether is added, and the solution is filtered. This treatment should remove all but the last traces of sodium chloride and ammonium chloride. The alcohol and ether are removed by distillation and the last of the free hydrochloric acid is removed by distillation under diminished pressure. The alanine hydrochloride remaining in the flask is dissolved in 1500 cc. of water, and transferred to a metal pail of about 2-l. capacity. Two hundred and twenty grams of yellow lead oxide is added and the mixture is boiled gently for one hour. During the boiling small amounts of water are added at intervals in order to maintain the original volume (Note 5). Upon cooling, the lead chloride crystallizes; it is filtered off and the solution is again boiled one hour with 100 g. of lead oxide. Twenty grams of freshly precipitated lead hydroxide is added slowly and the boiling is continued for ten minutes. Following this the solution is again cooled and filtered (Note 6). The chloride content should now be equivalent to not more than 5075 cc. of a normal solution (Note 7). The solution is again brought to a boil and the calculated amount of silver oxide (Note 7) is added to remove the last of the chlorides. The silver chloride is filtered off and the lead is precipitated with hydrogen sulfide. After filtering off the lead sulfide, a light strawcolored solution remains. The solution is evaporated by boiling to a volume of about 400 cc., and 600 cc. of 95 per cent alcohol is added. When thoroughly cooled, 100120 g. of alanine is filtered off. This is washed with 200 cc. of alcohol and a pure white product is obtained. A further crop of 4050 g. may be obtained by removing the alcohol and water until a volume of about 100 cc. remains, and then adding 250 cc. of alcohol and cooling to 0. The total yield is 140160 g. (5260 per cent of the theoretical amount) (Note 8). Alanine so prepared is sufficiently pure for most purposes. It may be recrystallized by dissolving in

the least amount of hot water (about 450 cc.) and adding two volumes of alcohol.

2. Notes1. Acetaldehyde may be conveniently prepared by distilling from paraldehyde in the presence of a trace of sulfuric acid; an efficient fractionating column should be used. 2. A one-half gallon (2-l.) ginger-ale bottle is convenient for this purpose. The necks of these bottles are small and will hold a wire securely. 3. Caution must be observed during the addition of the hydrochloric acid as much hydrogen cyanide is evolved. During the first part of the subsequent distillation it is necessary to prevent fumes from escaping from the receiver into the room. 4. During the evaporation a layer of crystals forms on the surface and must be continually broken. A blast of air blowing over the surface agitates the liquid sufficiently and allows free evaporation. 5. The volume of the solution must be kept large during the treatment with lead oxide as lead chloride will not crystallize from concentrated alanine solutions. 6. If the solution at this point still contains ammonium salts another treatment with 100 g. of lead oxide is necessary. 7. An aliquot portion of the solution is titrated with silver nitrate by the Volhard method. The result of this titration is used in calculating the amount of silver oxide which must be added. 8. A slightly lower yield of alanine may be obtained conveniently from the evaporated alanine hydrochloride by treatment with aniline (Benedict,1 and G. J. Cox and Harriette King, private communications).

Submitted by Walter C. Tobie and Gilbert B. Ayres. Checked by John R. Johnson and R. B. Hasbrouck.

1. ProcedureSlowly and with stirring, 100 g. (0.65 mole, 59 cc.) of cold (14) -bromopropionic acid (Note 1) is added to 3 l. (44.5 moles, 2700 g.) of cold (14) concentrated aqueous ammonia (sp. gr. 0.9) (Note 2) in a 1-gal. glass-stoppered bottle, and the mixture is allowed to stand at room temperature for at least four days (Note 3). The solution is concentrated to a volume of 300 cc. (Note 4), filtered, and concentrated further to 200 cc. The solution is cooled to room temperature and 1 l. of methyl alcohol (Note 5) added. After chilling overnight in a refrigerator (04) the crystals are filtered with suction and washed with 250 cc. each of methyl alcohol and ether (Note 6). The yield is 4248 g. of crude alanine. For purification the crude product is dissolved in 200 cc. of water (warming if necessary), 1 l. of methyl alcohol is added, and the mixture chilled overnight. After washing as before, the yield is about 3842 g. (6570 per cent of the theoretical amount) of purified dl-alanine, m. p. 295 (dec.) on the Maquenne block (Note 7). This product is free of bromide and contains only traces of ammonia. If an especially pure product is desired the material may be reprecipitated from methyl alcohol once more in the same manner (Note 8).

2. Notes1. -Bromopropionic acid may be prepared in 8085 per cent yields by bromination of propionic acid, the general procedure given for -bromoisovaleric acid (Org. Syn. 20, 106) being followed and a fraction boiling at 100102 at 15 mm. being collected. The commercially available -bromopropionic acid boiling over the same range is also satisfactory. The use of -chloropropionic acid gives a poorer yield (4346 per cent of theoretical) and the product is more difficult to purify owing to the fact that ammonium chloride is less soluble than the bromide in methyl alcohol.

2. The use of a large excess of ammonia (70 moles) minimizes the production of ,'-iminodipropionic acid and similar by-products. 3. Temperatures above 40 reduce the yield, and chilling after mixing does not increase it. Less than four days' standing gives a reduced yield, but longer standing does not increase the yield. 4. Evaporation may be done in an evaporating dish under a hood, or better by distillation at reduced pressure, using a water pump with a trap. Heating should be gentle at first to avoid violent ebullition. The ammonia may be recovered if desired by absorption in ice water. 5. The grade of technical methyl alcohol known as "Columbian Spirits" may be employed. Ethyl alcohol is much less satisfactory, since it does not dissolve ammonium bromide as well as methyl alcohol does. 6. Filtration is best done with suction on a Bchner funnel. Washing with ether can be omitted without reducing the yield. 7. In a capillary tube the product melts with decomposition at 275280, and the melting point varies somewhat with the rate of heating. 8. The last traces of ammonia may be removed by adding 10 g. of permutit when dissolving for the second time, then shaking the mixture thoroughly for three minutes and filtering before the methyl alcohol is added.

3. Discussiondl-Alanine can be prepared by heating ethyl -chloropropionate with concentrated aqueous ammonia at 100;2 by treatment of -bromopropionic acid with alcoholic or aqueous ammonia;3 by the catalytic reduction of a solution of ammonia and ammonium pyruvate,4 or of the oxime of pyruvic acid;5 by the action of hydrocyanic acid on aldehyde ammonia;6 by the action of ammonium cyanide and ammonia on acetaldehyde followed by alkaline hydrolysis;7 and by methylation of ethyl benzaminomalonate with subsequent hydrolysis and decarboxylation.8 The procedure described in part A above is based on the modification by Zelinsky and Stadnikov9 of the hydrocyanic acid and aldehyde ammonia method. A thorough study has been made of the preparation of alanine by the hydrogen cyanide-acetaldehyde method.10 This preparation is referenced from: Org. Syn. Coll. Vol. 2, 28

References and Notes1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Benedict, J. Am. Chem. Soc. 51, 2277 (1929). Kolbe, Ann. 113, 221 (1860). Kekul, Ann. 130, 18 (1864); Tobie and Ayres, J. Am. Chem. Soc. 59, 950 (1937). Aubel and Bourguel, Compt. rend. 186, 1844 (1928). Shemin and Herbst, J. Am. Chem. Soc. 60, 1951 (1938). Strecker, Ann. 75, 29 (1850). I. G. Farbenind, A.-G., French pat. 746,641 [C. A. 27, 4541 (1933)]. Redemann and Dunn, J. Biol. Chem. 130, 341 (1939). Zelinsky and Stadnikov, Ber. 41, 2061 (1908); Benedict, J. Am. Chem. Soc 51, 2277 (1929). Cocker and Lapworth, J. Chem. Soc. 1931, 1399.

Appendix Chemical Abstracts Nomenclature (Collective Index Number); (Registry Number)oxime of pyruvic acid

aldehyde ammonia ethyl alcohol, alcohol (64-17-5) acetaldehyde (75-07-0) sulfuric acid (7664-93-9) hydrochloric acid (7647-01-0) ammonia (7664-41-7) methyl alcohol (67-56-1) ether (60-29-7) ammonium chloride (12125-02-9) aniline (62-53-3) sodium cyanide (143-33-9) sodium chloride (7647-14-5) alanine hydrochloride lead oxide lead chloride lead hydroxide silver oxide (20667-12-3) silver chloride (7783-90-6) lead (7439-92-1) hydrogen sulfide (7783-06-4) lead sulfide alanine (56-41-7) hydrogen cyanide, hydrocyanic acid (74-90-8) silver nitrate (7761-88-8) -bromopropionic acid (598-72-1)

bromide (24959-67-9) propionic acid (79-09-4) -Bromoisovaleric acid (565-74-2) -chloropropionic acid (598-78-7) ,'-iminodipropionic acid ammonium bromide (12124-97-9) ethyl -chloropropionate (535-13-7) ammonium pyruvate ammonium cyanide ethyl benzaminomalonate DL-Alanine (302-72-7) paraldehyde (123-53-7)Copyright 1921-2005, Organic Syntheses, Inc. All Rights Reserved


ALKYL AND ALKYLENE BROMIDES[I. HYDROBROMIC ACID METHOD]

Submitted by Oliver Kamm and C. S. Marvel. Checked by H. T. Clarke and Anne W. Davis.

1. ProcedureA given primary alcohol is treated with 25 per cent excess of aqueous (48 per cent) hydrobromic acid (Note 1) together with sulfuric acid (Note 2). The mixture is refluxed (Note 3) in order to convert the alcohol as completely as possible into the corresponding bromide, and the latter is then removed from the reaction mixture by distillation. The water-insoluble layer is separated; washed successively with water, cold concentrated sulfuric acid (Note 4), and a sodium carbonate solution; separated; dried with calcium chloride (Note 5); and distilled. Slight variations from this procedure depend upon the physical and chemical properties of the alcohol used, or of the bromide formed in the reaction. For example, in the preparations of ethyl and allyl bromides, the reaction mixture is not refluxed because of the volatility of the former compound, and because of the chemical reactivity of the latter; in the preparation of iso-amyl bromide, too large a proportion of sulfuric acid may produce appreciable decomposition, whereas halides of high molecular weight, because of their low volatility, are separated from the reaction mixture mechanically, instead of by distillation. The use of a modified sodium bromide-sulfuric acid method (Note 6) for the preparation of alkyl bromides is described in connection with the preparation of n-butyl bromide. This method has been used also for the preparations of iso-amyl and trimethylene bromides, but, in general, the yields were found to be somewhat lower than those obtained with the hydrobromic-sulfuric acid method. Preparation of Hydrobromic Acid.Hydrobromic acid may be prepared conveniently by the interaction of bromine and sulfur dioxide in the presence of water1 (Note 7). In a 3-l. round-bottomed flask are placed 1200 g. (377 cc., 7.5 moles) of bromine, 500 cc. of water, and 1500 g. of crushed ice. A fairly rapid stream of sulfur dioxide is allowed to pass from a pressure tank into the flask, the outlet of the gas-tube being placed below the surface of the bromine layer. The flow of sulfur dioxide is adjusted at such a rate that the gas is completely absorbed. It is advisable to agitate the mixture occasionally during the first stage of the reduction (Note 8). About two hours will serve for the completion of the reduction, at which time the mixture will assume a yellow color (Note 9) which is not removed by further addition of sulfur dioxide, an excess of which is to be avoided (Note 10). To prevent loss by gaseous hydrogen bromide, it is advisable to cool the mixture during the progress of the reduction. When the reduction is completed, the flask is connected with a condenser and the mixture subjected to distillation. The boiling point of constant boiling hydrobromic acid is 125126 /760 mm., but it must be remembered that, in distilling the product from the sulfuric acid mixture, the thermometer reading should not be relied upon as an index to the composition of the distillate. Towards the end of the distillation the thermometer may rise to 130 and above, when water with only traces of acid distils from the sulfuric acid residue. Upon redistillation of the product the thermometer reading may be relied upon. For many uses a product free from traces of sulfuric acid is not required and one distillation is sufficient. In such cases the progress of the distillation is followed by determinations of the specific gravity of the distillate.

According to the above procedure, 20 kg. of 48 per cent hydrobromic acid (92 per cent of the theoretical amount) may be prepared from 10.3 kg. of bromine. The actual time required by one person for the preparation of this quantity is twenty-three hours. For the preparation of alkyl bromides on a relatively large scale the hydrobromic acid need not be distilled but may be used directly for the subsequent preparation. The fact that 0.5 mole of sulfuric acid is present for each mole of hydrobromic acid is not a disadvantage, since the presence of sulfuric acid is desired, and consequently a correspondingly smaller quantity need be added.

(A) ALLYL BROMIDE, CH2=CHCH2BrIn a 3-l. round-bottomed flask, a hydrobromic acid solution is prepared (p. 26) by the sulfur dioxide reduction of 480 g. (150.5 cc., 3 moles) of bromine in the presence of 510 g. of ice water or a mixture is made of 1 kg. (5.9 moles) of aqueous 48 per cent hydrobromic acid and 300 g. (162 cc.) of concentrated sulfuric acid. To this is added 385 cc. of aqueous allyl alcohol (p. 42), which, according to bromine titration, contains 233 g. (4 moles) of pure allyl alcohol. The 3-l. round-bottomed flask is fitted with a mechanical stirrer (Note 11), separatory funnel, and an efficient condenser set for downward distillation. Stirring is started, and 300 g. (162 cc.) of concentrated sulfuric acid is added gradually through the separatory funnel to the warm solution. The allyl bromide distils over completely in about one-half to one hour. The crude allyl bromide is washed with dilute sodium carbonate solution, dried over calcium chloride, and then distilled. The yield of product boiling at 6972 from a number of experiments varies from 445465 g. (9296 per cent of the theoretical amount). A small high-boiling fraction is also obtained and examination has shown this to consist of propylene bromide.

[Propene, 3-bromo-]

(B) iso-AMYL BROMIDE, (CH3)2CHCH2CH2BrIn a 5-l. round-bottomed flask, a hydrobromic acid solution is prepared (p. 26) by passing sulfur dioxide into a mixture of 1100 g. of crushed ice and 1 kg. (314 cc., 6.25 moles) of bromine. This is equivalent to a mixture of 2.1 kg. (12.5 moles) of 48 per cent hydrobromic acid and 600 g. of concentrated sulfuric acid. There are then added, in the order mentioned, 880 g. (1086 cc., 10 moles) of iso-amyl alcohol (b.p. 130132) and 100 g. (54.5 cc.) of concentrated sulfuric acid. The clear homogeneous solution is refluxed gently during a period of five to six hours. Even during the early stages of the heating, the separation of iso-amyl bromide is observed, and the reaction appears to be complete after about one hour. The product is isolated as in the preparation of n-butyl bromide below. A yield of 1435 g. of crude product is obtained. After purification with concentrated sulfuric acid the product weighs 1410 g. (93 per cent of the theoretical amount). Upon fractionation, however, it is found that appreciable amounts of a high-boiling product are present, and therefore the yield of fractionated material boiling over the range 116120 varies in different experiments from 1330 to 1360 g. (8890 per cent of the theoretical amount).

[Butane, 1-bromo-3-methyl-]

(C) n-BUTYL BROMIDE, CH3(CH2)3BrHydrobromic-Sulfuric Acid Method.In a 5-l. round-bottomed flask are placed 1300 g. of crushed ice and 1200 g. (376 cc., 7.5 moles) of bromine. The flask is cooled in an ice-water bath and sulfur dioxide is passed into the mixture until the red color due to free bromine has just disappeared (p. 26). This mixture is equivalent to 2500 g. (14.8 moles) of 48 per cent hydrobromic acid to which 750 g. of concentrated sulfuric acid has been added. To the sulfuric-hydrobromic acid mixture is added 888 g. (1096 cc., 12 moles) of n-butyl alcohol. Following this, 600 g. (324 cc.) of concentrated sulfuric acid is added in several portions, with shaking. The flask is then attached to a reflux condenser and the mixture is refluxed during a period of five to six hours, during which time the formation of butyl bromide is carried practically to completion. The flask is now fitted with a condenser set downward and the product removed from the reaction mixture by

[Butane, 1-bromo-]

direct distillation (about one hour). The water-insoluble layer is separated, washed first with water, then with 200 g. (109 cc.) of cold concentrated sulfuric acid, and finally with a sodium carbonate solution (50 g. of sodium carbonate in 500 cc. of water). The product is separated as completely as possible from the aqueous layer, dried during several hours with a small quantity (1525 g.) of calcium chloride, and distilled. The yield of product boiling between 101104 is 1560 g. (95 per cent of the theoretical amount). Sodium Bromide Method.In a 5-l. round-bottomed flask is placed 1350 cc. of water, and then with stirring 1545 g. (15 moles) of finely powdered sodium bromide is added. It is advisable to add the salt to the water in this manner in place of the reverse procedure, in order to avoid caking of the sodium bromide. First, 888 g. (12 moles) of n-butyl alcohol and then gradually 2 kg. (1087 cc.) of concentrated sulfuric acid are added. The last half of the acid is added through a dropping funnel after the flask has been connected with a reflux condenser. The mixture is shaken occasionally during the addition of the sulfuric acid because of a tendency to separate into layers, and is finally refluxed during a period of two hours. The condenser is then set downward and the butyl bromide removed by distillation. The product is purified as in the preceding experiment for the preparation of n-butyl bromide by the hydrobromicsulfuric acid method. The yield of n-butyl bromide boiling between 101104 is 1480 g. (90 per cent of the theoretical amount).

(D) n-DODECYL BROMIDE, CH3(CH2)10CH2BrIn a 250-cc. round-bottomed flask are placed 70 g. (0.42 mole) of hydrobromic acid (48 per cent) (p. 26) and 22 g. (12 cc.) of concentrated sulfuric acid. To this mixture is added 40 g. (0.22 mole) of lauryl alcohol (b.p. 188192 /110 mm.) (Org. Syn. 10, 62), and the mixture is then refluxed for five to six hours. The bromide is isolated as described in the preparation of n-octyl bromide (p. 30). The product is distilled under reduced pressure and is collected from 175180 /45 mm. The yield is 49 g. (91 per cent of the theoretical amount) (Note 12).

[Lauryl Bromide]

(E) ETHYL BROMIDE, CH3CH2BrIn the preparation of hydrobromic acid for the manufacture of ethyl bromide, particular care must be taken to avoid the presence of any excess of sulfur dioxide gas. The evolution of gas during the distillation of the ethyl bromide will invariably result in a large loss of this volatile product (b.p. 38 39). A hydrobromic acid solution is prepared (p. 26) in a 5-l. round-bottomed flask by the reduction of 1 kg. (314 cc., 6.25 moles) of bromine in the presence of 1.1 kg. of cracked ice. A mixture of 2075 g. (12.3 moles) of 48 per cent hydrobromic acid and 600 g. (324 cc.) of concentrated sulfuric acid may be used in place of the above reduction mixture. After the addition of 500 g. (622 cc., 10 moles) of 95 per cent ethyl alcohol, the flask is attached to a long condenser set ready for distillation, and 1 kg. (544 cc.) of concentrated sulfuric acid is slowly added through a separatory funnel. Because of the volatility of ethyl bromide, the mixture is not heated under a reflux condenser, but is subjected instead to slow distillation. The end of the condenser is provided with an adapter tube, and the distillate is collected in a flask containing ice water. The crude ethyl bromide, weighing 1055 g., is purified as directed under the n-butyl bromide experiment (p. 28). The washing with concentrated sulfuric acid is almost superfluous unless a product of special purity is desired; for instance, in the present experiment a washing with 300 g. of concentrated acid results in a decrease in weight of only 10 g. The ethyl bromide is distilled from a water bath and boils at 38.539.5 provided that chips of porous plate are added to prevent superheating. Final yields vary from 980 to 1035 g. (9095 per cent of the theoretical amount) according to the precautions taken to prevent losses due to evaporation.

[Ethane, bromo-]

(F) n-OCTYL BROMIDE, CH3(CH2)6CH2Br[Octane, 1-bromo-]

In a 500-cc. round-bottomed flask are placed 240 g. (1.4 moles) of hydrobromic acid (48 per cent) (p. 26), 62 g. (34 cc.) of concentrated sulfuric acid, and 71 g. (0.55 mole) of n-octyl alcohol (b.p. 135 140 /100 mm.). The mixture is boiled under reflux for five to six hours. The solution is diluted with water and the bromide layer is separated, washed once with a little cold concentrated sulfuric acid, then with water and finally with dilute sodium carbonate solution, after the procedure described for n-butyl bromide. The crude yield is 102 g.; this is dried over a little calcium chloride and distilled. The product is collected at 196200 (9193 /22 mm.) and amounts to 96 g. (91 per cent of the theoretical amount).

(G) TRIMETHYLENE BROMIDE, Br(CH2)3BrHydrobromic-Sulfuric Acid Method.In a 5-l. round-bottomed flask are placed 1200 g. (377 cc., 7.5 moles) of bromine and 1300 g. of crushed ice, and the bromine is reduced with sulfur dioxide to hydrobromic acid (p. 26). In place of the above reduction mixture, there may be used a mixture of 2.5 kg. (14.8 moles) of aqueous 48 per cent hydrobromic acid and 750 g. (408 cc.) of concentrated sulfuric acid. First, 456 g. (433 cc., 6 moles) of trimethylene glycol (b.p. 210215) is added, and then 1200 g. (652 cc.) of concentrated sulfuric acid, the sulfuric acid being added slowly. The mixture is refluxed (Note 13) during a period of five to six hours and is then subjected to distillation until no waterinsoluble product appears in the distillate (about one hour). The trimethylene bromide is purified (Note 14) in accordance with the method used for n-butyl bromide (p. 28). A yield of 10651142 g. boiling at 162165 (8895 per cent of the theoretical amount) is obtained. Sodium Bromide Method.The yields of trimethylene bromide by the sodium bromide method as described for n-butyl bromide (p. 29) are slightly lower than those given above. Thus, from 1350 g. of water, 1545 g. (15 moles) of sodium bromide, 456 g. (6 moles) of trimethylene glycol, and 2500 g. of sulfuric acid, a yield of 1110 g. of crude product is obtained, from which, after purification (Note 14) and distillation, a yield of 1030 g. of bromide (85 per cent of the theoretical amount) is obtained.

[Propane, 1,3-dibromo-]

2. Notes1. When an alcohol is heated with aqueous 48 per cent hydrobromic acid, a partial conversion takes place into the corresponding bromide. The reaction is more rapid and more complete, however, in the presence of sulfuric acid. Although the constant boiling hydrobromic acid obtainable on the market may be used in all the preparations described, its formation by the sulfur dioxide reduction of bromine will be considerably less expensive and equally convenient, provided that a cylinder of sulfur dioxide is available. For use in the preparation of alkyl bromides, distillation of the bromine-sulfur dioxide reduction mixture is superfluous. 2. The procedure described is quite general for the preparation of primary bromides. The presence of sulfuric acid would usually be objectionable in the preparation of secondary and tertiary bromides because of the ease of dehydration of the corresponding alcohols and the formation of isomers. This is also true of iso-butyl bromide and to some extent of iso-amyl bromide. These bromides may be obtained in good yields by the phosphorus tribromide method described in Org. Syn. 13, 20. In the preparations described, a more dilute hydrobromic acid solution may be used, provided that the proportion of sulfuric acid is increased. Aqueous solutions of alcohols may also be used if the proportion of sulfuric acid is suitably adjusted. In the allyl alcohol experiment, material was used as obtained from the glycerol-formic acid preparation (p. 42) after one salting out with potassium carbonate. 3. The reaction mixture is heated under the reflux condenser for several hours preliminary to the first distillation of the alkyl bromide. This is done in order to convert the alcohol as completely as possible into the corresponding bromide and thus to prevent its volatilization with the bromide. Direct distillation of the reaction mixture without refluxing will usually result in a decrease in yield of 515 per cent. Alkyl bromides of low molecular weight may, however, be distilled directly from the reaction mixture without the necessity of refluxing, providing the process of distillation is conducted very slowly. Alkyl

halides of high molecular weight are separated from the reaction liquors mechanically instead of by distillation. This is done in order to avoid the decomposition due to heating the slightly volatile material with a gradually increasing concentration of sulfuric acid. 4. The main impurities usually found in alkyl halides are the corresponding alcohols and ethers. Cold concentrated sulfuric acid is an efficient reagent for the removal of these impurities in all cases where the alkyl halide itself is not attacked by this reagent. Whenever a product contains a considerable quantity of unchanged alcohol, several washings with the cold concentrated acid may be required. 5. In many organic preparations too large a quantity of drying agent is usually employed, with the resulting loss of a considerable amount of material due to absorption by the drying agent. In the present experiments it is found that after a careful separation of the alkyl halide from the water layer as small a quantity as 15 g. of calcium chloride is sufficient for the drying of 1500 g. of alkyl halide. 6. The favorable results obtained in the preparation of alkyl bromides with aqueous hydrobromic acid to which sulfuric acid has been added suggest that practically the same result might be accomplished by the use of sodium bromide, water, and sulfuric acid in such ratios as approximate the proportions used in the first instance. In actual practice this modified sodium bromide method was found fairly satisfactory for the preparation of n-butyl bromide and of trimethylene bromide. Slightly lower yields are due to the decreased solubilities of the alcohols in the reaction mixtures because of the presence of dissolved salts. One would therefore predict that, with alcohols of still higher molecular weights, even lower yields would be obtained with the sodium bromide method. This prediction is substantiated in experiments with iso-amyl alcohol, where the sodium bromide method gives yields of only 70 per cent of the theoretical amount, whereas the hydrobromic acid method gives yields of almost 90 per cent. The sodium bromide method is therefore not recommended for the preparation of alkyl bromides of high molecular weight. 7. In the sulfur dioxide reduction of bromine, it should be noted that the proportion of water used depends upon whether the reduction mixture is to be distilled for the preparation of 48 per cent hydrobromic acid, or whether it is to be used directly for the manufacture of alkyl bromides. 8. During the first stage of the reduction, the flask should be shaken from time to time in order to avoid the accumulation of sulfur dioxide, or possibly of sulfuryl bromide, which would result in a violent reaction owing to a large quantity of the material reacting at one time. In more than a hundred reduction experiments conducted with quantities of bromine varying from 0.5 to 2 kg., this sudden reaction was noted in only one or two instances, in spite of the fact that there was usually no agitation other than that furnished by the entering gas stream. Mechanical stirring is frequently important in obtaining successful yields. In Fig. 2, A and B represent two convenient types of stirring devices2 where refluxing and stirring are desired at the same time. When the stopper of the flask is so small that it will hold only the mechanical stirrer, a Y-tube such as is shown in Fig. 3 B fitted with either form of stirrer is suitable. It often happens that a separatory funnel or thermometer must also be inserted in the flask in addition to the reflux condenser. A three-necked flask such as is shown in Fig. 3 A is especially convenient, the middle opening being used for the stirrer, the two smaller ones for thermometer and reflux condenser. Fig. 2.

Fig. 3.

9. The intensity of the color in the reduced bromine solution depends somewhat on the quality of bromine used, and with the technical product special care is needed in noting the end point of the reduction, i.e., the transition from the bromine color to a yellowish-brown color. 10. An excess of sulfur dioxide is to be avoided for the reason that evolution of gas during the distillation of the product will result in a considerable loss of alkyl bromide through volatilization. This loss is especially marked in the preparations of ethyl and allyl bromides if this precaution is not observed. 11. In the preparation of allyl bromide, appreciable loss may occur, not only because of carbonization

but primarily because of the reaction of the allyl bromide with hydrobromic acid to form propylene bromide. Stirring during the formation of the alkyl bromide prevents the formation of two layers in the reaction mixture and thus assures a rapid and smooth distillation. An efficient condenser is of course essential. 12. The troublesome emulsions often encountered when lauryl bromide is shaken with sulfuric acid may be avoided by the following alternative method of purification. The reaction mixture, after the heating is completed, is diluted with water and the layer of lauryl bromide is separated. The bromide is washed with water and then with potassium carbonate solution. The washing with water should be sufficiently thorough so that there is no appreciable foaming on shaking with the carbonate. The bromide is then dried with calcium chloride and distilled. Lauryl bromide and the bromides of other primary alcohols of high molecular weight can also be prepared by saturating the alcohol at 100120 with hydrogen bromide as described in Org. Syn. 15, 24. This hydrogen bromide procedure has been reported to be superior for preparing lauryl bromide to the hydrobromic acid-sulfuric acid method described above. 13. Trimethylene bromide, prepared by direct distillation of the reaction mixture without the preliminary refluxing period, contains appreciable amounts of trimethylene bromohydrin. 14. In the purification of trimethylene bromide with sulfuric acid the high specific gravity of the former (1.987) must be borne in mind. Vigorous shaking with sulfuric acid may result in the formation of emulsions.

[II. PHOSPHORUS AND BROMINE METHOD]

Submitted by R. H. Goshorn, Thomas Boyd, and E. F. Degering. Checked by R. L. Shriner and F. J. Wolf.

1. Procedure

(A) ETHYL BROMIDE, CH3CH2BrA 1-l. three-necked, round-bottomed flask is fitted with an Allihn condenser and a dropping funnel, the stem of which reaches to the bottom of the flask. By means of a bent glass tube the top of the Allihn condenser is connected to a Liebig condenser the end of which dips just beneath the surface of a mixture of ice and water (about 800 g.) contained in a 2-l. beaker (Note 1). In the reaction flask are placed 363 g. of 95 per cent ethyl alcohol (7.5 moles), 25 g. of red phosphorus, and 15 g. of yellow phosphorus (1.29 gram atoms) (Note 2). The mixture is heated by means of the oil bath until gentle refluxing takes place (bath temperature at 100110), and 377 g. of bromine (121 cc., 2.36 moles) is slowly added through the dropping funnel over a period of three hours (Note 3), (Note 4). The water is drained from the Allihn condenser, and distillation is continued at a rate of forty to fifty drops per minute up to a temperature of about 94 (a thermometer may be placed in the flask in place of the dropping funnel) (bath at about 155). When the distillation is complete the two condensers are disconnected first and the burner removed (Note 5). The distillate is washed with 20 cc. of ice-cold 5 per cent sodium hydroxide solution, then with 50 cc. of ice-water. The product is dried over anhydrous calcium chloride and distilled through a short column, the distillate being collected in a dry receiver packed in an ice-salt mixture. The yield of colorless ethyl bromide distilling between 37 and 40 is 420465 g. (8290 per cent of the theoretical amount based on the bromine) (Note 6).

[Ethane, bromo-]

(B) iso-PROPYL BROMIDE, (CH3)2CHBrThe procedure for the preparation of iso-propyl bromide is similar to that for ethyl bromide except for the quantities of the reactants and the temperature of the bath. A mixture of 180 g. (228 cc., 3.0 moles) of iso-propyl alcohol, 6 g. of red phosphorus, and 4 g. of yellow phosphorus (0.3 gram atom) is placed in the reaction flask. Then, 135 g. (43.2 cc., 0.84 mole) of bromine is added over a period of three hours, the temperature of the oil bath being maintained between 85 and 95 (preferably at 90). The distillate is collected up to a temperature of 145 (bath temperature 155185). In the second distillation after washing and drying the crude product, the fraction boiling between 59 and 62 is collected. The yield of product is 143152 g. or 6973 per cent of the theoretical amount (Note 7).

[Propane, 2-bromo-]

(C) n-PROPYL BROMIDE, CH3CH2CH2BrThe procedure for the preparation of n-propyl bromide is similar to that for ethyl bromide except for the quantities of the reactants and the temperature of the bath. A mixture of 180 g. (224 cc., 3.0 moles) of n-propyl alcohol, 6 g. of red phosphorus, and 4 g. of yellow phosphorus (0.3 gram atom) is placed in the reaction flask. Then 135 g. (43.2 cc., 0.84 mole) of bromine is added slowly over a period of three hours, the temperature of the oil bath being maintained between 125 and 140. The distillate is collected up to a temperature of 140 (bath temperature 190210). In the second distillation, after washing and drying the crude product, the fraction boiling between 7073 (Note 8) is collected. The yield of n-propyl bromide is 170186 g. (8290 per cent of the theoretical amount).

[Propane, 1-bromo-]

(D) n-BUTYL BROMIDE, CH3(CH2)3BrThe same apparatus as described in the preparation of ethyl bromide may be used with the omission of the Liebig condenser. In the reaction flask are placed 138 g. (170 cc., 1.86 moles) of n-butyl alcohol, 6 g. of red phosphorus, and 4 g. of yellow phosphorus (0.3 gram atom). The oil bath is heated to 175, and 94 g. (30.1 cc., 0.58 mole) of bromine is added slowly through the dropping funnel at such a rate that the dense white vapors which form remain near the top of the Allihn condenser. The optimum period for the addition of bromine is about one hour, during which time the bath temperature slowly decreases to 165. The mixture is distilled directly from the reaction flask which is attached to a condenser set for downward distillation. When the distillation becomes slow about 25 cc. of water is added through the dropping funnel to assist in carrying over the butyl bromide. The final bath temperature is about 210. The distillate is washed with 20 cc. of 5 per cent sodium hydroxide solution and then with 50 cc. of water. The product is dried with calcium chloride and distilled through a Vigreux column. The fraction boiling from 97 to 99.5 is collected and amounts to 145150 g. (9093 per cent of the theoretical amount).

[Butane, 1-bromo-]

(E) sec.-BUTYL BROMIDE, CH3CH2CHBrCH3The procedure for secondary butyl bromide is similar to that used in the preparation of n-butyl bromide, except that bromine is added at a bath temperature of 140150, and the distillate (bath temperature up to 190) from the reaction mixture is washed with water and dried over anhydrous sodium sulfate before redistilling. The yield (b.p. 8687) is about 135137 g. (8485 per cent of the theoretical amount).

[Butane, 2-bromo-]

(F) tert.-BUTYL BROMIDE, (CH3)3CBr[Propane, 2-bromo-2-methyl-]

In a 500-cc. three-necked, round-bottomed flask fitted with a dropping funnel and a mechanical stirrer is placed 5 g. (0.16 gram atom) of red phosphorus. The flask is cooled on a bath of cold water, and 47 g. (15 cc., 0.29 mole) of bromine is added very slowly at first (Note 9). After the initial reaction has moderated the remainder of the bromine is added over a period of one and a half to two hours. The stirrer is started, and 69 g. (0.93 mole) of tert-butyl alcohol is placed in the separatory funnel and added slowly to the phosphorus bromide. The stirrer and separatory funnel are removed; the flask is connected to a condenser and arranged for vacuum distillation. By means of a water pump the pressure is gradually reduced to 2030 mm. and the bromide distilled by raising the bath temperature slowly to 7080. The distillate is washed quickly with 50 cc. of ice-water, dried with anhydrous calcium chloride, and redistilled. The fraction boiling from 69 to 71 is collected. The yield is 32 to 34 g. (3942 per cent of the theoretical amount).

2. Notes1. A diagram of the apparatus used is shown in Fig. 4. Fig. 4.

2. Nearly as good yields are obtained if yellow phosphorus is used alone. However, a much smoother and more readily controllable reaction is obtained if some red phosphorus is used along with the yellow phosphorus. Care must be exercised in handling yellow phosphorus since it ignites spontaneously in the air. It should be kept under water and transferred quickly to the flask which already contains the alcohol. 3. A vigorous reaction, with some bumping and the formation of white vapors, accompanies the first addition. As the density of the vapors decreases, the rate of addition of bromine may be increased to the extent that some of the white vapors are carried over into the Liebig condenser. 4. There is a tendency for water to be sucked from the ice bath into the apparatus because of sudden changes in pressure within the system. This difficulty may be avoided by adding the bromine at a constant rate, by maintaining a constant reflux rate, and by maintaining the temperature of the oil bath

nearly constant, allowing any changes in temperature, especially lowering, to take place slowly. If water is sucked into the reaction flask, the addition of bromine may as well be discontinued because the alcohol has become diluted and the yield will be low. 5. Care must be exercised in the disposal of the residue in the flask since it sometimes contains unreacted phosphorus which ignites spontaneously when dry and exposed to the air. After the residue has cooled, it should be drowned in a large volume of water and the mixture washed down the drain with a good stream of water. 6. Ethyl bromide is quite volatile, and hence care must be taken to keep it cold during the washing operations and to use efficient condensing systems. 7. In washing the product a lachrymator is noticed, and in the final distillation a residue of 3036 g. possessing highly lachrymatory properties is observed. 8. The residue has lachrymatory properties and a pungent odor. 9. Care should be taken to add the bromine very slowly at first since sometimes the heat of the reaction is sufficient to ignite the phosphorus and it burns until all the oxygen is removed from the flask.

3. DiscussionAlkyl bromides are prepare

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Organic Syntheses Collective Volume 1