Kinetics and mechanism of oxidation of aliphatic and aromatic ketones by peroxomonosulphate

Abstract

The kinetics of oxidation of ethyl methyl ketone, isobutyl methyl ketone, and acetophenone by peroxomonosulphate (PMS) was carried out in aqueous H₂SO₄ medium (0.20–1.00 mol dm^–3H⁺) and in aqueous acetic acid medium (40% acetic acid v/v) respectively in the temperature range 30–60 °C at constant ionic strength of 1.20 mol dm^–3. The reactions obey total second-order kinetics, first order each with respect to [ketone] and [PMS] for all the ketones. They exhibited acid catalysis with the concurrent occurrence of acid-independent reaction paths conforming to the rate law (i) for the disappearance of –d[PMS]/dt=k_a[PMS][ketone][H⁺]+k_b[PMS][ketone](i) peroxomonosulphate. The reaction stoicheiometry, [ketone] : [PMS] 1:1, for all the ketones indicated the absence of self-decomposition and carbonyl-assisted decomposition of PMS. The kinetic and thermodynamic parameters strongly suggest the mechanism of a fast nucleophilic attack of the oxidant (PMS) on the ketone followed by slow, rate-determining acid-catalysed and uncatalysed decomposition of the intermediate to the product. The reactivity of peroxomonosulphate was compared with those of similar peroxides.