Patented June 19, 1934 1,963,138 UNITED STATES PATENT OFFICE 1963,138 PREPARATION OF AMIDES Herbert E. Martin and Robert Finley Thompson, - Cumberland, Md., assignors to Celanese Corpo ration of America, a corporation of Delaware No Drawing. Application September 20, 1930, Serial No. 483,374 6 Claims. (CI. 260-124) This invention relates to the preparation of The acid formed is then distilled from the amide acid amides and relates more particularly to the which remains as a residue...... preparation of acetamide or other aliphatic acid While this invention is of greatest importance amides. - in the making of acetamide, it may be also em 5 An object of Our invention is to produce acid ployed for making other amides such as propion- 60. amides more cheaply than has heretofore been amide or butyramide and also for making Substi pOSsible. A further object of our invention is to tuted acid amides such as acetanilid. prepare acid amides which are purer than those If ordinary acid amides are to be made, anhy made previously on a commercial Scale. Other drous ammonia, is caused to react With the acid 10 objects of this invention will appear from the foll anhydride. If substituted ammonias Or amines, 65. lowing detailed description. whether a primary amine such as aniline or a, The method heretofore employed for making secondary amine, are employed, substituted acid acetamide commercially consists in reacting am amides Will be formed. monium carbonate Or ammonia. With an excess of Appropriate organic acid anhydrides, such as 15 acetic acid to form ammonium acetate and acetic anhydride, propionic anhydride, butyric 70. then distilling off the excess acetic acid. Dur anhydride or higher acid anhydrides are caused ing distillation the ammonium acetate is con to react with the ammonia, or substituted ann verted into acetamide which remains as a nonia. residue in the still. This method is open The ammonia and the acid anhydride are re 20 to many objections, among which are the facts acted in Substantially equimolecular proportion, 75. that low yields are obtained, a long time so that in the case of making acetamide, the re is required for Conversion and distillation, deCon action proceeds as follows: position with the formation of methyl cyanide takes place, and the resulting product contains CEC=O 25 an appreciable amount of impurities. O--NH=CH3CONH2+. CHCOOH 80. Furthermore, in the reaction between ammoni um carbonate and acetic acid water is produced, CH3C-O which water adds considerably to the corrosive acetican ana- acetamide acetic acid action of the mixture and the products of the dis hydride mo 30 tillation. The reaction or conversion of am la 85. monium acetate to acetamide by the ammonium We have found that if equimolecular propor carbonate process is slow and separation of the tions of the reactants are used, no appreciable products by vacuum distillation cannot be car amount of ammonium acetate is formed. This is ried out. This necessitates distilling at atmos a great advantage, since if ammonium acetate is 35 pheric pressure and consequently much higher formed, it must be converted to acetamide which 90. temperatures which involves special and more complicates the process. complicated apparatus for temperature control. The reaction of the ammonia. With the acid We have found that acetamide or other acid anhydride should preferably take place within amides of great purity may be made cheaply if certain temperature range. Thus in the case of 40 ammonia, is caused to react with acetic anhydride making acetamide by reacting ammonia. With ace 95: or other organic acid anhydrides in substantially tic anhydride the temperature should not be allowed to rise above 90 C., say below 70° C. and equimolecular proportions, preferably under con preferably should be kept below 40° C. At the trolled temperatures. The reaction between am lower temperature no methyl cyanide is formed monia, and acetic anhydride resultS in immediate whereas traces are produced at the higher tem 100 45 formation of acetamide. The by-product of the peratures. reaction can thus be removed by the most eco The acid formed by the reaction is distilled off nomical means, which yields a pure product, from the acid amide and in order to avoid de such as crystallizing or low temperature distilla composition, this distillation is preferably carried 50tion obtained by the use of vacuum. out under reduced pressure say from 1 to 10' of 105 In accordance with our invention, we form mercury absolute pressure. acid amides by reacting anhydrous ammonia. Or By this process, excellent yields are obtained substituted ammonias with an acid anhydride in in a relatively short time. Moreover the product Substantially equimolecular proportions and pref is of high degree of purity. Acetamide formed 55 erably under controlled temperature conditions. by this process may be used to make methylamine O 2 1,968,138 by reaction with a hypochlorite and an alkali, of anhydride to each molecular proportion of particularly as described in the U. S. patent of ammonia. Bader et al. No. 1,489,380 of April 8, 1924. 2. The method of forming acetamide compris In order further to illustrate our invention, but ing reacting ammonia, with acetic anhydride in Without being limited thereto the following ex substantially equimolecular proportions at ten 80 ample is given. peratures below 90° C. Eacample 3. The method of forming acetamide compris 17 parts by weight of anhydrous ammonia gas ing reacting ammonia. With acetic anhydride in are bubbled into 102 parts by weight of acetic substantially equimolecular proportions at tem O peratures below 40 C. 85 anhydride, the temperature being maintained at 4. In the method of producing acid amides 40° C. The mixture, consisting essentially of comprising reacting ammonia. With anhydrides of acetamide and acetic acid, with but traces of am monium acetate and methyl cyanide, is then dis monobasic lower aliphatic acids the step of main tilled in a vacuum still provided with a fractionat taining in the reaction mixture at least one molec 5 ular proportion of anhydride to each molecular 90 ing column at a pressure of 1' to 10' mercury proportion of ammonia, and then distilling off the absolute, the acetic acid distilling off and being acid that is formed under Subatmospheric pres condensed as glacial acetic acid which may be SLe, used as such. The residue remaining in the Still 5. The method of forming acetamide compris is acetamide practically free of impurities. The ing reacting ammonia. With acetic anhydride in 95 20 yield is high, being over 98% of theoretical. Substantially equimolecular proportions at tem It is to be understood that the foregoing de peratures below 90° C. and then distilling off the scription is given merely by way of illustration acetic acid that is formed under Subatmospheric and that many variations may be made therein, preSSLIre. 25 without departing from the Spirit of our inven 6. The method of forming acetamide compris 100 tion. ing reacting ammonia. With acetic anhydride in Having described our invention, what we de Substantially equimolecular proportions at tem sire to secure by Letters Patent is: peratures below 40 C. and then distilling off the 1. In the method of producing acid amides COin acetic acid that is formed under Subatmospheric prising reacting at temperatures below 90° C. preSSure. 30 ammonia. With anhydrides of nonobasic lower 105 aliphatic acids the step of maintaining in the re HEREBERT E. MARTIN. action mixture at least One molecular proportion ROBERT FINLEY THOMPSON.

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