GB605311A - Improvements in the manufacture of methionine - Google Patents

Abstract

Methionine is prepared by reacting hydrogen cyamide and methyl mercaptan with acrolein to form alpha - hydroxy - gamma - methylthiol - butyronitrile, reacting the latter with ammonia to convert the hydroxyl group to an amino group and hydrolysing the nitrile group to a carboxyl group. The reaction may also be effected by reacting acrolein with methyl mercaptan to form beta-methylthiol-propion-aldehyde which is then reacted with hydrocyanic acid to form the corresponding cyanhydrin or by reacting acrolein with hydrocyanic acid to form the cyanhydrin which is then reacted with methyl mercaptan. In each case the reaction is completed as above by reacting with ammonia to convert the hydroxyl group to an amino group and hydrolysing the nitrile group. The reaction between acrolein and methyl mercaptan and between acrolein cyanhydrin and methyl mercaptan are preferably conducted in the presence of a small amount of potassium cyanide or other alkali metal cyanide which serves as a catalyst. Anhydrous ammonia is preferred to replace the hydroxyl group by the amino group, but concentrated aqueous ammonia may be used. In examples, methionine is produced by the three methods referred to above, liquid hydrocyanic acid being employed. A small amount of potassium cyanide is used as catalyst and relatively low temperatures are employed for the production of the alpha - hydroxy - gamma - methylthiol butyronitrile. The hydrolysis of the nitrile group is effected in each case by boiling with concentrated hydrochloric acid and after the precipitated ammonium chloride is removed the methionine is precipitated by means of an alcoholic solution of ammonia or of pyridine.