Giuseppe Werber

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

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.

Kinetic study of the decarboxylation of 5-amino-1,3,4-oxadiazole-2-carboxylic acid to 2-amino-1,3,4-oxadiazole in water as a function of proton activity

The rate constants of the decarboxylation reaction of 5-amino-1,3,4-oxadiazole-2-carboxylic acid (I) have been measured in water, over a wide range of proton activities (from H0–0.95 to pH 4.77), at various temperatures, and the activation parameters have been determined. We present evidence for the occurrence of a decarboxyprotonation mechanism.

Base-catalysed rearrangement of 2-phenylamino-1,3,4-oxadiazole into 4-phenyl-1,2,4-triazolin-5-one

The behaviour in alkaline media (water, water–dioxane, or water–dimethyl sulphoxide) of 2-phenylamino-1,3,4-oxadiazole (IH) has been studied, together with the title reaction. Chemical and kinetic evidence support the occurrence of a ring conversion through an intermediate cyclic compound (IV–), followed by the formation of an open-chain anion (V–) that cyclizes fast to the triazole derivative (III–).