Kinetics and mechanism of oxidation of aliphatic aldehydes by peroxomonosulphate

Abstract The kinetics of the oxidation of aliphatic aldehydes, formaldehyde, acetaldehyde, propionaldehyde, n ‐butyraldehyde, and trichloroacetaldehyde by Peroxomonosulphate (PMS) was carried out in aqueous perchloric acid medium (0.1–1 M H + ) at constant ionic strength of 1.2 M in the temperature range 10°–60°C. The reactions of all the aldehydes were found to obey a total second‐order kinetics, first order each with respect to Peroxomonosulphate and aldehyde. Acetaldehyde, propionaldehyde, and n ‐butyraldehyde exhibited acid catalysis with the concurrent occurrence of acid‐independent reaction path conforming to the rate law Formaldehyde was found to undergo oxidation only by acid‐dependent path ( k b = 0) and trichloroacetaldehyde exhibited only the acid‐independent reaction path ( k a = 0). The products of oxidation were found to be the respective carboxylic acids in each case. The stoichiometry of the reaction, Peroxomonosulphate:Aldehyde = 1:1, indicated the absence of carbonyl‐assisted decomposition and self‐decomposition of peroxomonosulphate. The kinetic and thermodynamic parameters evaluated pointed to the mechanism of a fast nucleophilic attack of the oxidant on the aldehyde followed by slow acid catalyzed and/or uncatalyzed decomposition of the intermediate to product. A sharp comparison is made with the corresponding reactions of the similar peroxides, S 2 O and H 2 PO .