AbstractThe 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, andn‐butyraldehyde exhibited acid catalysis with the concurrent occurrence of acid‐independent reaction path conforming to the rate law\documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm PMS]}}}{{dt}} = k_a [{\rm PMS] [aldehyde] [H}^ +] + k_b [{\rm PMS] [aldehyde]} $$\end{document}Formaldehyde was found to undergo oxidation only by acid‐dependent path (kb= 0) and trichloroacetaldehyde exhibited only the acid‐independent reaction path (ka= 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 peroxide