KINETICS AND MECHANISM OF OXIDATION OF S-PHENYLTHIOACETIC ACIDS BY CE(IV)

The kinetics of oxidation of several S-phenylthioacetic acids by eerie ammonium nitrate (CAN) in presence of perchloric acid has been studie d spectrophoto- metrically in 50%(v/v) aqueous acetic acid. The order with respect to (IV) is one and the order with respect to S-phenylthio acetic acid is found to be 0.8. A linear plot of k(obs)(-1) vs [substr ate](-1) with an intercept on the rate axis suggests the formation of an equilibrium complex between the reactants prior to the rate determi ning step. The added acrylonitrile retards the reaction rate considera bly suggesting that the oxidation process may involve a free radical m echanism. Electron-releasing substituents generally accelerate the rat e, while electron-withdrawing groups retard the rate. A good corrrelat ion is found to exist between log k(1.8) and Hammett sigma constants. [GRAPHICS] where 'S' is the substrate, K-1,K-h are equilibrium constan ts and k(1) is the rate constant for the rate limiting step.