METHOD OF SYNTHESIS OF D,L-METHIONINE OR ITS SALT (VARIANTS) Russian patent published in 2001 - IPC

FIELD: organic chemistry, amino acids, chemical technology. SUBSTANCE: invention describes method of synthesis of D,L-methionine or its salt by conversion of the following components: 3-methylmercaptopropionic aldehyde, hydrogen cyanide or hydrocyanic acid salt, ammonium or ammonium salt and carbon dioxide or carbonic acid salt in the presence of water to 5-(2-methylmercaptoethyl)-hydantoin followed by its hydrolysis to the corresponding end product. Before conversion of components a mixture is prepared preliminary that contains predominant part, at least 5/10, of 3- methylmercaptopropionic aldehyde, at least 1/10 of hydrogen cyanide or hydrocyanic acid salt and less 5/10 of each components of ammonium or ammonium salt, carbon dioxide or carbonic acid salt. Then mixture is mixed with at least one component to yield 5-(2-methylmercapto- -ethyl)-hydantoin being the latter at least one component can be stirred preliminary with a single or some mixtures. Invention describes also method of continuous synthesis of D, L-methionine or its salt. Also, invention describes two variants of method. The first variant involves hydrolysis in the presence of from 0.1 to 7 equivalents of ammonia per each equivalent of 5-(2-methylmercaptoethyl)-hydantoin. The second variant involves hydrolysis in the presence of metallic zirconium or zirconium alloy containing at least 10 wt.-% of zirconium. Also, invention describes method of isolation of D,L-methionine from alkaline metal methionate. EFFECT: enhanced degree of purification, increased yield of end product. 41 cl, 3 dwg, 7 ex