3d-orbital resonance in divalent sulphides—IX : A study on the mechanism of the base catalysed decarboxylation of α-mercaptocarboxylic acids

Abstract

The kinetics of the base-catalysed decarboxylation of a few α-mercaptoacetic acids and other related acids in DMSO using a large excess of triethanolamine has been investigated. The apparent first order rate constant increases gradually as the reaction proceeds, presumably due to the change of the relative concentrations of the carboxylate ion and the undissociated acid, while the major species undergoing the decarboxylation is considered to be the carboxylate ion. There is a linear relation between the p Ka's of these mercapto acids in 50% v/v ethanol—water and the apparent dissociation constants in DMSO in the presence of the amine base (p K A ). The mechanism of the decarboxylation of the mercapto acid is considered to involve the rate-determining decarboxylation from the carboxylate ion to form the corresponding carbanion.