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Abstract

Kinetics has been studied of cyclization of 2-acetyl-3-methylamino-N-benzoyl-2-betenethioamide (Ia) and 2-acetyl-3-amino-N-benzoyl-2-butenethioamide (Ib) giving 5-acetyl-2-phenyl-1,6-dimethyl-4-(1H)pyrimidinethione (IIa) and 5-acetyl-2-phenyl-6-methyl-4-(3H)-pyrimidinethione (IIb), respectively, in aqueous buffers within pH 2 to 9. Formation of the cyclic intermediate is rate-limiting in the cyclization of Ib within the whole range. In the case of Ia the rate-limiting step consists in acid-catalyzed splitting off of water from the cyclic intermediate above pH 5 and in base-catalyzed splitting off of hydroxyl ion above pH 7.