The decomposition of methionine in sulfuric acid.

The classical procedure for the preparation of homocystine consists of boiling a solution of methionine in 50 per cent sulfuric acid followed by neutralization (1). Although the yields of homocystine account for only 25 to 45 per cent of the methionine, the nature of the reaction has received little attention since originally published by Butz and du Vigneaud (1). These authors noted the formation of dimethyl disulfide and also observed that the complete removal of sulfate by barium hydroxide resulted in a solution of considerable alkalinity. The present study provides experimental evidence for the following mechanism for the reaction (R and Me signify -CH$ZH&H(NH2)COOH and -CH8, respectively) :