Oxidation of vanillin by peroxomonosulphate-thermodynamic and kinetic investigation

The oxidation of vanillin by peroxomonosulphate (PMS) in acetic acid–sodium acetate buffered medium was carried out at 308 K. The rate was first order with respect to [vanillin] and [PMS]. The rate increased with increase in pH and the rate was too fast to be measured at pH 5.2. The rate increased with increase in [acetate] and the plot of kobs versus [acetate] was a straight line with positive intercept. Variation of ionic strength had no effect on the rate of the reaction. Effects of polarity were studied with five different solvents and in all the cases, log kobs versus 1/ɛ were linear with negative slope. The reaction had been carried out at four different temperatures and the activation and thermodynamic parameters were calculated. The product of oxidation was confirmed as vanillic acid by IR, 1H NMR and GC-MS spectral analysis. Based on the results obtained a reaction scheme had been proposed and the rate law was derived.