Kinetic Aspects of the Direct Electrochemical Oxidation of p-Xylene in Methanol using Graphite Electrodes

Abstract

The kinetics of the electrochemical oxidation of p-xylene (A) in methanol solutions containing tetraethylammonium p-toluene sulphonate as supporting electrolyte using graphite electrodes were investigated. It was shown that p-xylene is first oxidized to the intermediate 4-methylbenzyl methyl ether (B), which is then further oxidized to the corresponding acetal, 4-methyl benzaldehyde dimethyl acetal (C). The stepwise reaction A->B->C was first tested for first order consecutive kinetics and this approach was shown to be invalid. A model based on parallel consecutive second order kinetics was then proposed in which solvent participation assists in the electrochemical oxidation of the substrate, through free radical reactions. Using the ratios of the relevant k values, instead of their absolute values, the concentrations of each reactant are expressed as ratios with respect to the initial concentration of A. These are calculated using expressions based on the fraction of A remaining at a particular time. It is shown that the calculated curves agree well with those based on the observed values, indicating that the proposed kinetic model is acceptable.


Key words: p-xylene. Electrochemical oxidation, Parallel second order consecutive kinetics


South African Journal of Chemistry Vol.57 2004: 53-56