Kinetics and Mechanism of the Oxidation of Some Secondary Alcohols by Benzimidazolium Dichromate

Abstract

Benzimidazolium dichromate (BIDC), in dimethylsulfoxide, oxidizes secondary alcohols to the corresponding ketones. The reaction is first order with respect to BIDC. The order with respect to alcohol is more than one but less than two. Michaelis - Menten type kinetics were observed with respect to alcohol. The formation constants of the alcohol-BIDC complexes and the rates of their decomposition were determined at different temperatures. The oxidation of deuterated 2-propanol indicated the presence of a substantial primary kinetic isotope effect. The reaction exhibited a second order dependence on hydrogen-ion concentration. The reaction was studied in nineteen organic solvents. The solvent effect was analyzed using multiparametric equations. It was found that the cation-solvating power of the solvent played the major role. The rates of oxidation exhibited an excellent correlation with polar and steric substituent constants. A suitable mechanism has been proposed.