Free-radical-mediated oxidation of ascorbic acid by peroxomonosulphate

Free-radical-mediated oxidation of ascorbic acid by peroxomonosulphate 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-. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Research on Chemical Intermediates Springer Journals

Free-radical-mediated oxidation of ascorbic acid by peroxomonosulphate

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Publisher
Brill Academic Publishers
Copyright
Copyright © 2003 by VSP 2003
Subject
Chemistry; Inorganic Chemistry; Physical Chemistry
ISSN
0922-6168
eISSN
1568-5675
D.O.I.
10.1163/156856703765694336
Publisher site
See Article on Publisher Site

Abstract

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-.

Journal

Research on Chemical IntermediatesSpringer Journals

Published: Oct 17, 2004

References

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