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. A 14 gram portion of butyronitrile is 97%. After removal of ammonia, aminoacetonitrile prepared by this method is hy this crude aminonitrile is hydrolyzed by treat drolyzed by boiling for one hour with 28.8 grams ment with boiling 50% sulfuric acid. (2 mols per of 95% sulfuric acid in 100 c.c. of water, to which mol of nitrile) containing 0.1% HgC) (based on 0.3 gram of mercuric oxide promoter has been the weight of the 50% acid) for 24 hours. Upon . added. The aqueous hydrolyzate is then cooled, neutralization of the excess acid with ammonium and brought to a pH of 8 by addition of 35 c. c. of O hydroxide, and removal of water by evaporation concentrated aqueous ammonia. The resulting at diminished pressure there remains a dry resi mixture is evaporated to dryness at a tempera due, containing ammonium sulfate and dl-valine. ture of 110° C., which yields an anhydrous solid This residue is extracted with liquid annonia, residue. This residue, upon being pulverized and and crude dil-valine is obtained by evaporation of extracted with 500 c. c. of anhydrous ammonia, 55 ammonia from the extract. This is decolorized gives an extract which on evaporation yields 15.6 by means of charcoal. The dil-valine is purified grams of aminoacetic acid (83.2% conversion). by recrystallization from water (yield 69%). Eacample 2-The crude aminoacetonitrile pre Eacample 4-A mixture of alpha-methyl-butyr pared in accordance with the preceding example aldehyde and hydrogen cyanide (10% excess), is distilled, yielding aminoacetonitrile having a 50 containing 1% pyridine, is maintained at a tem boiling point of 66 at 10 mm. (80% conversion). perature of about 50 for about 1 hour. The re To determine the effect of the mercuric com Sulting mixture is made acidic with Sulfuric acid pound as a promoter on the hydrolysis of the dis and the excess hydrogen cyanide is removed at tilled aminoacetonitrile, two experiments are reduced pressure. This leaves a residue of alpha made, as follows: 65 methyl-butyraldehyde cyanhydrin, correspond (a) A mixture containing 51 grams conc. sul ing to 98% yield based on the alpha-methyl furic acid and 100 grams of water is heated to butyraldehyde charged. This cyanhydrin con boiling, and a mixture of 14 grams of amino taining the pyridine catalyst is processed with 20 acetonitrile (B. P. 66, 10 mm.) and 14 grams of molal proportions of ammonia at 100° C. under water is slowly introduced. The resulting mix O an autogenously developed pressure of 800 ture is heated at boiling temperature with stir pounds per square inch for 30 minutes. The re ring for a total reaction time of 5 hours. The Sulting product is removed from the reactor, and product is then neutralized with ammonium hy upon evaporation of the ammonia, it yields a resi droxide to a pH of about 8, and the solvent is re due which corresponds to 87.4% yield of isoleu moved at reduced pressure. The resulting dark 75 cine nitrile. A mixture of the crude isoleucine 8,520,812 8 nitrile and 3 equivalents of constant boiling from the shaker tube and the excess ammonia is (20.2%) hydrochloric acid is refluxed for 4 hours, removed under diminished pressure, whereby a during which time a slow stream of dry hydrogen residue containing an alpha-aminonitrile is pro chloride is passed through the flask to maintain duced. A suspension of this amination product the hydrochloric acid concentration approxi in 50 c.c. of cold Water is prepared, and is mixed mately constant. The resulting product is then with 64 grams of cold concentrated hydrochloric made slightly basic with annonium hydroxide. acid. After the initial exothermic reaction has After filtering the mixture, evaporating the so ceased (0.5 to 1.0 hour), the mixture is refluxed vent, and washing the annonium chloride-con and stirred vigorously for four hours. Upon cool taining residue with 58% aqueous methanol, a O ing the resulting reaction mixture a crystalline solution is obtained which upon evaporation precipitate is formed. This is removed by filtra yields isoleucine (yield in the hydrolysis step, tion, after which additional crystals are obtained 75%). by concentrating the filtrate. This crystalline cample 5-Liquid hydrogen cyanide (100 product is a mixture of glutamic acid hydro C. C., corresponding to 10% excess) is added por 5 chloride and ammonium chloride. Pure glutamic tion-wise to a stirred charge of 221.5 grams of acid hydrochloride is obtained by fractional crys isowaleraldehyde and 2.5 cc. of pyridine. The tallization of the product from aqueous hydro reaction temperature is maintained at 25 to 60 chloric acid (yield 82%, based upon the Weight C. for 1 hour, after which time the pyridine of methyl 4-oxobutyrate initially employed). catalyst is neutralized by adding 2.6 c. c. of 85% 20 (b) An amination product (30 grams), pre Orthophosphoric acid. The excess hydrogen cy pared as described in Example 6(a) is suspended anide is then removed by evaporation at 25 C. in 50 c. c. of water, and is added rapidly (5 to 6 under a pressure of 15 m. m. A substantially minutes) to a boiling, vigorously stirred, solution quantitative yield of isovaleraldehyde cyanhydrin containing 16.3 grams of sodium hydroxide in 32 is thus obtained. A mixture consisting of 33.9 25 c. c. of water, and the mixture is refluxed for grams of this cyanhydrin and 102 grams of arm an additional 30 minutes. The resulting product nonia (molar ratio of about 1:20) is processed is concentrated to dryness under reduced pres in an agitated silver-lined bomb for 15 minutes sure, whereby a white crystalline residue is at 110' C. to 114' C. under autogeneous pressure obtained. This residue is washed several times of 1075 to 1210 pounds per square inch. The 30 with methanol and thereafter dried in an Oven bomb is thereafter cooled and the liquid product at 120° C. The product thus obtained is di is discharged. Ammonia and much of the water Sodium glutamate, of reaction are removed by evaporation at 25 C. under a pressure of about 15 mm. The resulting NaOOCCH(N3) CHCHCOONa residue is almost entirely 2-aminoisocapronitrile. which is obtained in 80% yield based upon the A mixture containing 19.3 grams of this 2-amino weight of methyl 4-oxo-butyrate initially em isocapronitrile and 5 grams of constant boiling ployed. hydrochloric acid is heated at the boiling point Eacample 7.-Aminoacetonitrile (28 grams), for 3 hours. The resulting mixture is cooled and prepared in accordance with Example 1, is added thereafter made slightly alkaline with ammonium 4) to about 3 times its weight of water, and the re hydroxide, whereupon a copious precipitate is sulting mixture is introduced dropwise into a boil obtained. This precipitate is removed by filtra ing solution of 22 grams NaOH in 100 c. c. of tion, after which it is washed with 50% aqueous water with vigorous stirring. The boiling is con methanol to remove ammonium chloride. The tinued for 45 minutes to expel ammonia. Sulfuric resulting product is dil-leucine which is obtained acid is then added until a pH of 3 is reached, in 74% yield based upon the isowaleraldehyde after which the pH is brought to 8 with ammonia. initially employed. The resulting mixture is decolorized with char Eacample 6-Methyl 4-oxobutyrate, coal. It is then filtered, and the filtrate is evapo OHCCHCH2COOCE rated to dryness. Extraction of the dry residue with anhydrous ammonia, followed by evapora (116 grams) containing 0.1% by weight of pyri tion of ammonia from the extract gives 31.8 dine as catalyst is mixed with liquid hydrogen grams of aminoacetic acid (conversion, 93.8%, cyanide (54 grams), which is introduced gradu based on aminoacetonitrile). ally at a temperature of 40' to 50° C. over a In the foregoing examples reference is made to period of 20 to 30 minutes. External cooling is an improved method for separating amino acids required to prevent the temperature from rising from the hydrolysis mixtures by adjusting the above 50° C. After the exothermic reaction has pH of the crude hydrolyzate of this invention to ceased, the mixture is cooled to about 5 C., and about 8 with an alkaline reagent, evaporating is held at that temperature for about 0.5 to 1.0 the mixture and extracting the amino acid from hour. The mixture is then made slightly acid the resultant residue by means of liquid am with 85% orthophosphoric acid, and the excess monia. In this way a good separation of amino hydrogen cyanide is removed by evaporation acid from the inorganic constituents is achieved. under diminished pressure. A residue of methyl This method is particularly effective when the 4-cyano-4-hydroxybutyrate corresponding to operations are conducted so as to yield a mixture 97%-98% yield, based upon the weight of s containing inorganic sulfate, especially sodium methyl 4-oxobutyrate initially charged, is ob Sulfate, as when the alkaline agent employed in tained. This product is contaminated with the the hydrolysis, or neutralization of acidic hy pyridine-phosphoric acid salt and with a Small drolysis mixture, is scdium hydroxide, and the quantity of free hydrogen cyanide. acidic agent is sulfuric acid. Ammonium sul (a) A portion of the above product (30 grams 70 fate and sodium sulfate are both Sufficiently in without purification, is heated under a pressure soluble in anhydrous ammonia, but sodium sul of about 40 to 60 atmospheres in a silver-lined fate is less bulky than ammonium sulfate, and shaker tube with 120 grams of ammonia (molar amino acids can be separated from sodium sul ratio of ammonia to cyanhydrin=34) at 60' for fate by extraction with a relatively smaller quan 1 hour. The product is thereafter withdrawn 75 tity of anhydrous liquid ammonia. 2,520,812 7 This invention is not limited to the illustrative REFERENCEs CITED examples given above, since many different em The following references are of record in the bodiments will occur to those skilled in the art. file of this patent: When desired, the aminoacid may be isolated in the form of a salt, amide, or other simple de s UNITED STATES PATENTS rivative. In general, however, the process of this Number Name Date invention may be employed for the manufacture 2,071,282 Gluud et al. ------Feb. 16, 1937 of pure d1-alpha-mono-aminocarboxylic acids, 2,188,340 Dykstra ------Jan. 30, 1940 which are useful in the animal feed industry. 2,364,538 Kirk ------Dec. 5, 1944 We claim: () In a process for the synthesis of aminoacetic FOREIGN PATENTS acid by hydrolysis of aminoacetonitrile with Number Country Date aqueous sulfuric acid containing 30% to 50% by 436,692 Great Britain ------coct. 16, 1935 weight of H2SO4 based on the weight of water 653,099 Germany ------Nov. 15, 1937 and H2SO4 present, the step which comprises car 5 655,563 Germany ------Jan. 18, 1938 rying out the said hydrolysis in the presence of 659,771. Germany ------May 10, 1938 mercuric sulfate as a promoter for the said sul furic acid. WLLAM E. GRESHAMI. CAR. E. SCHWEITZER. 20