ipitation of5-amino-2-sulfonamido-1,3,4-thiadiazole (step p). ##STR16##Thereafter, 5-amino-2-solfonamido-1,3,4-thiadiazole is acylated (step q) by means of a hemiester hemialide of the bicarboxylic acid corresponding to the desired group, i.e.wherein X is a halogen atom and R.sub.2 is different from hydrogen.