Kinetics and mechanism of oxidation of primary alcohols by pyridinium hydrobromide perbromide

Abstract

Oxidation of nine primary aliphatic alcohols by pyridinium hydrobromide perbromide (PHPB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to PHPB. Michaelis-Menten-type kinetics are observed with respect to the alcohol. The oxidation of [1,1-²H₂]ethanol (MeCD₂OH) exhibits a substantial kinetic isotopic effect. The effect of solvent composition indicates that the transition state is more polar than the reactants. The reaction is susceptible to both polar and steric effects of the substituents. A mechanism involving transfer of a hydride ion from the alcohol to the oxidant has been proposed.