Abstract
The kinetics of oxidation of dimedone in perchloric acid medium were studied spectrophotometrically. The reaction showed first order kinetics in quinolinium dichromate (QDC) concentration and an order of less than unity in 5,5-dimethylcyclohexane-1,3-dione [dimedone, (DM)] and acid concentrations. Increasing ionic strength had no effect on the rate, but decreasing dielectric constant of the medium decreased the rate. The oxidation reaction proceeds via a protonated chromium(VI) species, which forms a complex with dimedone. The latter decomposes in a slow step to give a free radical derived from dimedone and chromium(V), which is followed, by subsequent fast steps to give the products. The reaction constants involved in the mechanism have been evaluated. There is good agreement between the observed and calculated rate constants under different experimental conditions. Investigations at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism.