Kinetics and mechanism of the oxidation of substituted benzyl alcohols by [bis(trifluoroacetoxy)iodo]benzene

The oxidation of substituted benzyl alcohols by bis(trifluoroacetoxy)iodo]benzene in aqueous acetic acid solution results in the formation of the corresponding benzaldehydes. The reaction is first order with respect to each of the alcohol, TFAIB and hydrogen ions. The oxidation of [1,1-H-2(2)]benzyl alcohol exhibited the presence of a substantial primary kinetic isotope effect, indicating the cleavage of the alpha-C-H bond in the rate-determining step. Increase in the amount of water, in the solvent mixture of acetic acid and water, results in a decrease of the reaction rate. The analysis of the substituent effect in terms of Charton's LDR equation yielded an excellent correlation with negative reaction constants. A mechanism involving a hydride-ion transfer in the rate-determining step has been proposed.