Kinetics and Mechanism of the Oxidation of Substituted Benzaldehydes by [Bis(Trifluoroacetoxy)Iodo]Benzene

Abstract

The oxidation of monosubstituted benzaldehydes by [bis(trifluoroacetoxy)iodo]-benzene (TFAIB), in acidic solution, leads to the formation of the corresponding benzoic acids. The reaction is first-order with respect to each the aldehydes, TFAIB and hydrogen ions. The reaction failed to induce the polymerization of acrylonitrile. The oxidation of [2H]benzaldehyde (PhCDO) indicated the presence of a substantial kinetic isotope effect. The effect of solvent composition indicated that the reaction rate increases with a decrease in the polarity of the medium. The rates of oxidation of meta- and para-substituted benzaldehydes showed excellent correlations in terms of Charton's triparametric LDR equation whereas the oxidation of ortho-substituted benzaldehydes correlated well with tetraparametric LDRS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalization effect but the oxidation of ortho- and meta-substituted compounds displayed a greater dependence on the field effect. The positive value of η suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric acceleration when ortho-substituents are present.