The kinetics of the oxidation of ascorbic acid (AH2) by peroxomonosulphate (PMS) were determined in aqueous medium in acidic (pH 4.4), neutral (pH 7.0) and alkaline (pH 9.0) conditions over the temperature range 13-28°C. The reactions were found to obey total second-order kinetics, first-order each with respect to peroxomonosulphate and ascorbic acid concentration, obeying-d[AH2]/dt = k 2[PMS][AH2]. Dehydroascorbic acid was detected as the product of the reaction. The stoichiometry of the reaction, [peroxomonosulphate]/[ascorbicacid] = 1 : 1, indicated the absence of self-decomposition of peroxomonosulphate. The influence of neutral salt (NaClO4) was found to increase the reaction rate. Evidence for the formation of radical intermediates was obtained. A mechanism involving the formation of hydroxyl, sulphate and ascorbate free radicals as intermediates is proposed. The rate and activation parameters were evaluated to substantiate the mechanism proposed. A comparison is made with the corresponding reactions of the similar peroxides, S2O8 2- and P2O8 4-.
Research on Chemical Intermediates – Springer Journals
Published: Oct 17, 2004
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