To reduce the amts. of p-acetyl aminobenzene sulfochloride (by 50%) and of aq. NH4OH (to nil) used to prep. ST ammonia was replaced by 2-amino sulfathiazole (AT) to dec. Prontyl (4-acetylamino-N-[3-(4-acetylamino-benzenesulfonyl)-3H-thiazol-2-ylidene]benzene sulfonamide). When used in excess, AT neither eliminated Prontyl as an intermediate, nor affected the amt. of resulting 2-(N-4-acetylamino-benzenesulfonamido)-thiazole (AST), and lowered Prontyl's yield and purity. Triethylamine(TEA)-NaHCO3, TEA, MEK, and i-PrOH used as HCl acceptors were ineffective as regards the amt. of AST.