Manufacturing method of S- carboxymethyl -L- cysteine

摘要

PURPOSE:To obtain the above compound in high efficiency, by reacting L- cysteine in the presence of bisulfite ion under specific condition, reacting the produced L-cysteine with a monohalogenoacetic acid ester without separating from the reaction system and hydrolyzing the reaction product. CONSTITUTION:L-cysteine is made to react at pH6.0-5.5 at a temperature below boiling point in the presence of bisulfite ion to produce L-cysteine and S-sulfo-L-cysteine. Without separating the L-cysteine from the reaction liquid, the reaction products are made to react with a monohalogenoacetic acid at pH7.5-5 to selectively form S-carboxymethyl-L-cysteine from L-cysteine, the product is separated from the reaction liquid, and the S-sulfo-L-cysteine is hydrolyzed by reacting the motor liquor with a mineral acid. The produced L-cysteine is again used as a source of raw material. The objective compound useful as a synthetic raw material for pharmaceuticals such as a expectorant can be produced by this process economically at a low cost without using particular reaction apparatus.