Kinetics and mechanism of the oxidation of some unsaturated acids by pyridinium chlorochromate

The oxidation of maleic, fumaric, crotonic and cinnamic acids by pyridinium chlorochromate (PCC) in dimethylsulphoxide (DMSO) leads to the formation of corresponding epoxide. The reaction is of first order with respect to PCC and the acid. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form : k(obs) = a + b [H+]. The oxidation of these acids was studied in nineteen different organic solvents. The solvent effect was analyzed by Kamlet's and Swain's multiparametric equations. Solvent effect indicated the importance of the cation-solvating power of the solvent. A mechanism involving a thee-centre transition state has been postulated.