Studies on decarboxylation reactions. Part 7. Kinetic study of the decarboxylation of 2-amino- and 2-phenylamino-thiazole-5-carboxylic acids

Abstract

The rate constants of the decarboxylation reaction of 2-amino- and 2-phenylamino-thiazole-5-carboxylic acid (3a–b), and, for comparison, of 5-phenylamino-1,3,4-thiadiazole-2-carboxylic acid (2b) have been measured in water over a range of proton activities. The results obtained suggest: (i) compound 2b decarboxylates, in the whole range of proton activity studied, through a unimolecular decarboxyprotonation mechanism characteristic of 1,3,4-oxa- and 1,3,4-thiadiazole derivatives; (ii) in contrast, 3a-b decarboxylate via either a unimolecular decarboxyprotonation or a bimolecular protiodecarboxylation mechanism as a function of proton activity.