The following heterocyclic mercapto compounds are heated in aqueous solution with sodium chloroacetate to give the corresponding carboxymethylmercapto-derivatives; 1-phenyl-2-imidazole-thione, 2-mercaptopyrimidine and its 4, 6-diamino-, 4, 5, 6-triamino, 4-amino-6-hydroxy or 4-hydroxy-6-methylderivatives, 2-mercaptobenzoxazole, 2-mercaptobenzthiazole, 3-phenyl (or amino)-4-amino-5-mercapto- 1, 2, 4-triazole, 3-mercapto-5-hydroxy (or phenyl) 6-methyl-1, 2, 4-triazine and 2-mercapto-imidazoline and its 4-methyl-derivative. 2-Carboxymethylmercapto- 4, 6-diamino-S-triazine is prepared by adding chloroacetic acid to a solution of 4, 6-diamino-2-mercapto-s-triazine in aqueous sodium hydroxide. 2-(1-Carboxyoctylmercapto)-4, 6-diamino-S-triazine is prepared by stirring a solution of a -bromopelargonic acid and 4, 6-diamino-2-mercapto-s-triazine in aqueous sodium hydroxide. 2-Carboxymethylmercapto-imidazoline chloroacetate is prepared by p boiling 2-mercapto-imidazoline and chloroacetic acid in water. Specifications 235,211 and 634,951 are referred to.