Oxidation of 3,4,5-trimethoxybenzaldehyde by pyridinium fluorochromate in N,N-dimethyl formamide medium: A kinetic and mechanistic study

Kinetics of oxidation of 3,4,5-trimethoxybenzaldehyde (TMBA) by pyridinium fluorochromate (PFC) in N, N-dimethyl formamide (DMF) medium in the presence of toluene para-sulfonic acid (TsOH) has been studied. The reaction is first order each in [PFC], [TMBA] and [TsOH]. The rate of oxidation remains unaltered by the variation of NaClO4 but addition of MnSO4 decreases the rate. The effects of the dielectric constant of the medium and the ionic strength indicate the reaction to be of ion-dipole type. The stoichiometry of the reaction is 1: 1 and the product of oxidation is the corresponding 3,4,5-trimethoxybenzoic acid and Cr(III). The reaction rates have been determined at different temperatures and the activation parameters were calculated. The reaction failed to induce the polymerization of acrylonitrile, i.e.,absence of free radicals. A suitable mechanism involving the slow formation of an unstable chromate ester and a rate law has been proposed. (C) 2011 Production and hosting by Elsevier B.V. on behalf of King Saud University.