Kinetics and mechanism of the oxidation of secondary alcohols by pyridinium hydrobromide perbromide

The oxidation of secondary alcohols by pyridinium hydrobromide perbromide (PHPB) in aqueous acetic acid leads to the formation of the corresponding ketones. The reaction is first order with respect to PHPB and the alcohols. The reaction rates have been determined at different temperatures and the activation parameters calculated. The oxidation of benzhydrol-alpha-d exhibited a substantial kinetic isotope effect (k(H)/k(D) = 4.83). With an increase in the amount of acetic acid in the solvent mixture of acetic acid and water, the rate increases. Addition of pyridinium hydrobromide and acrylonitrile has no effect on the rate. Suitable mechanisms have been proposed.