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UNITED STATES PATENT Office 2,520,312 SYNESS of AMNOACDS William F

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UNITED STATES PATENT Office 2,520,312 SYNESS of AMNOACDS William F Patented Aug. 29, 1950 2,520,312 UNITED STATES PATENT office 2,520,312 SYNESS OF AMNOACDS William F. Gresham and Carl E. Schweitzer, Wi nington, Del, assignors to E. E. du Pont de Nemours & Company, Wilmington, Del, a cor poration of Delaware No Drawing. Original application January 25, 1945, Serial No. 574,626. Divided and this ap plication January 30, 1948, Serial No. 5,512 1. Claim. (C. 260-534) 1. 2 This invention relates to the preparation of C., preferably 60' to 130° C., under a pressure of alpha-monoamino carboxylic acids. More par at least 5 atmospheres, but much more efficiently ticularly it relates to improvements in the prepa at a pressure of about 25 to 1000 atmospheres, ration of alpha-monoamino nitriles, and hy and thereafter hydrolyzing the resulting amino drolysis thereof to alpha-monoamino acids. This nitrile in an aqueous medium containing an alka application is a division of our application S. N. line-reacting or an acid-reacting hydrolytic agent. 574,626, filed January 25, 1945, now abandoned, In a specific embodiment the hydrolysis is con which in turn, is a continuation-in-part of our ducted in the presence of aqueous sulfuric acid copending application Ser. No. 522,966, filed Sep containing a dissolved promoter, such as a salt of tember 18, 1944, now abandoned, wherein it is 10 aheavy metal. For rapid hydrolysis,elevated tem disclosed that alpha-hydroxy-gamma-methyl peratures of about 75° to 125° C., may be employed. mercaptobutyronitrile upon treatment with am The hydrolysis may be conducted in an apparatus monia at a temperature of about 10 to 150 C. equipped with a reflux condenser or, alternatively, under superatmospherie pressure is converted in in a suitable autoclave when the hydrolysis is to be high yield to alpha-amino-gamma-methylmer conducted under pressure. The promoters which captobutyronitrile, which on hydrolysis in an are found to be most useful, according to this aqueous acid medium, gives methionine in high invention, for the hydrolysis of alpha-aminoni yield. It is also disclosed in application Ser. No. triles to alpha-amino-acids are the salts of group 522,966 that the aqueous acidic hydrolyzing agent I-b heavy metals, and the salts of heavy metals may contain Small amounts of mercury, Copper, 20 having atomic numbers adjacent to the heavy or zinc salts. metals of group I-b. These metals are copper, It has been known for some years that hydroxy silver, cobalt, zinc, cadmium, mercury, nickel, acetonitrile may be treated with ammonia at low palladium, and platinum. Of these, one of the temperature to produe aminoacetonitrile, (Brit Outstanding members is mercury. It is to be ish Patent 436,692). It has also been known that 25 understood that soluble salts of these metals need aminoacetonitrile can be hydrolyzed to amino not be introduced as such into the reaction mix acetic acid by treatment with sulfuric acid. ture, but that the oxides, carbonates, etc. may be However, in the synthesis of amino acids by the employed, since they are converted to soluble best heretofore available methods for preparing salts under the hydrolysis conditions. The and hydrolyzing aminonitriles, very low yields amount of heavy metal salt promoter required, (about 6% to 35%) generally were obtained (Or according to the invention, is generally not more ganic Syntheses, Collective Wolume II, Blatt, John than about 5% based on the total weight of re Wiley and Sons, Inc., 1943, pages 29-31, 386). action mixture, the preferred quantity being The present invention, in contrast with the prior about 0.05 to 2.0%. In another embodiment, the art, provides a succession of inter-related steps hydrolysis of the aforesaid aminonitrile is con whereby very high yields of alpha-monoamino ducted in the aforesaid manner in an acidic or acids are obtained. The improvements in each alkaline medium, and amino acid is extracted step are such as to provide intermediate products from the final crude reaction product by means of uniquely suitable for use in each succeeding step, liquid ammonia. and it is a result of the combination of steps, as O Any of the common inorganic acids may be well as the inventive improvements in each step, used as a hydrolytic agent in the practice of this that remarkably high yields are obtained. invention, sulfuric acid or hydrochloric acid being An object of this invention is to provide a com preferred. When a promoter is employed, the mercially feasible process for the preparation of preferred acid is sulfuric acid. While an excess alpha-mono-amino-carboxylic acids. A further 45 of the acid may be employed, it is unnecessary, in object of the invention is to improve the avail the presence of the aforesaid promoters, to use a able methods for preparation and hydrolysis of large excess of the acid. If desired, the amount alpha-aminonitriles So as to produce high yields of acid used may be from about 0.2 to about 10.0 of the amino acids. equivalents per mol of aminonitrile charged, al These and other objects of the invention are 50 though preferably at least 1.0 equivalent of acid accomplished by preparing alpha-aminonitriles, is employed per mol of aminonitrile. The opti generally from the corresponding alpha-hydroxy mum concentration of the acid depends on the nitriles by treatment with an excess of ammonia nature of the acid employed. For example, ex (usually about 10 to 50 mols per mol of hydroxy cellent results are obtained with aqueous sulfuric nitrile) at a temperature of about 50° C. to 150 55 acid containing about 30% to 50% by weight of 2,520,812 3 4. H2SO4, when a promoter is used. In some in brown solid product is dried at 110° C. It is ex stances, if the concentration of promoter is rela tracted with liquid ammonia and the ammonia is tively low (about 0.1%), the optimum concentra evaporated yielding 10.1 grams of crude amino tion and quantity of acid is higher than when acetic acid (conversion 54%). larger concentrations of promoter are employed. (b) A mixture containing 38 grams of conc. Sul The promoters for the sulfuric acid hydrolytic furic acid, 77 grams of water, and 0.15 grammer agent are neither necessary nor markedly advan Curic oxide is heated to boiling, and a solution tageous in all instances, but such promoters are. of mercuric sulfate (about 0.1 by weight) is thus especially valuable and effective in the prepara obtained. During a period of 0.25 hour a mixture tion of aminoacetic acid, d.l-valine and similar O of 14 grams of aminoacetonitrile (B. P. 66, 10 alpha-mono-aminocarboxylic acids. mn.) and 15 grams of water is added. The re The alpha-mono-aminocarboxylic acids which sulting reaction mixture is heated with stirring may be prepared, in accordance with this inven at boiling temperature, under reflux, for an addi tion, from the corresponding alphahydroxyni tional 0.25 hour making the total reaction time triles include aminoacetic acid, d1-leucine, di s 0.5 hour. The product is then withdrawn and is alanine, dil-aspartic acid, d1-glutamic acid and neutralized with ammonium hydroxide to a pH the like. The alpha-mono-aminocarboxylic acids of about 8. The solvent is then removed at a re which may be prepared most satisfactorily, in ac duced pressure, leaving a light yellow, solid resi cordance with this invention, are those alpha due. This is dried at 110° C., and extracted with aminocarboxylic acids which contain (in addition 20 liquid ammonia. Upon evaporation of ammonia to the amino and carboxyl groups) only hydrocar from the extract there remains 17.7 grams of bon groups, or hydrogen, attached to the alpha aminoacetic acid, which corresponds to a con carbon atom. In certain instances, the promoters version of 94.5%. may react with the aminonitrile to form insoluble The product obtained in accordance with ex by products. Thus, in the preparation of 25 periment (b) is not only greater in quantity, but methionine and cysteine in the presence of heavy also is of Superior quality, as compared with the metal Salt promoters, difficulty is encountered due product obtained in experiment (a). Further to the formation of insoluble sulfides. This dif more, a lower ratio of acid is required and the ficulty does not arise in the corresponding prepa processing time is considerably shortened when ration of alpha-amino acids having only an alkyl 30 the promoter is employed. or aralkyl group substituted on the alpha carbon Eacample 3-A mixture of isobutyraldehyde atom. and hydrogen cyanide, having 10% molar excess The invention is illustrated further by means of of hydrogen cyanide, is processed at 50° C. under the following examples. atmospheric pressure in the presence of a pyri Eacample 1.-Into a one-gallon stainless steel 35. dine catalyst (1% by weight based on the alde autoclave containing 300 grams of formaldehyde hyde). The reaction is rapid and essentially cyanhydrin is injected 1400 grams of ammonia, quantitative, the cyanhydrin produced being of the injection requiring 10 seconds. The mixture high quality. The isobutyraldehyde cyanhydrin is maintained at a temperature of 80° C. for 15 thus obtained is processed with an excess of am minutes under a maximum pressure of 35 atmos 40 monia (nol ratio of cyanhydrin to ammonia, pheres. Thereafter the product is withdrawn, 1:15) at a temperature of 120° to 125° C. under and the excess ammonia is removed therefrom by 120 atmospheres pressure, for 15 minutes. Con evaporation. The resulting residue contains 255 version of the cyanhydrin to alpha-aminoiso grams of aminoacetonitrile.
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