Kinetics and mechanism of the oxidation of dimedone by alkaline permanganate

The kinetics of oxidation of dimedone (DM) by permanganate in low and high alkali concentrations at a constant ionic strength has been studied spectro photometrically The reaction seems to proceed by two different mechanisms. At higher concentrations of alkali the reaction exhibits first, less than u nity and zero order dependence of the rate on [permanganate ion], [DM] and [alkali], respectively, while at lower concentrations of alkali, all the or ders are the same except for [OH-] the order of [OH] is less than unity. In both the cases of [OH-], the initial addition of products does not affect the rate significantly, while an increase in ionic strength and decrease in dielectric constant enhance the rate of the reaction. Plausible mechanisms consistent with the kinetic data were proposed and constants involved in t he mechanisms have been evaluated. There is good agreement between observed and calculated rate constants at varying conditions of the experiments. Th e activation parameters with respect to the slow step of the mechanism have been computed.