Kinetics and mechanism of oxidation of substituted 5-oxoacids by sodium perborate in aqueous acetic acid medium have been studied. The reaction exhibits first order both in [perborate] and [5-oxoacid] and second order in [H+]. Variation in ionic strength has no effect on the reaction rate, while the reaction rates are enhanced on lowering the dielectric constant of the reaction medium. Electron releasing substituents in the aromatic ring accelerate the reaction rate and electron withdrawing substituents retard the reaction. The order of reactivity among the studied 5-oxoacids is p-methoxy ？ p-methyl > p-phenyl > –H > p-chloro > p-bromo > m-nitro. The oxidation is faster than H2O2 oxidation. The formation of is the reactive species of perborate in the acid medium. Activation parameters have been evaluated using Arrhenius and Eyring’s plots. A mechanism consistent with the observed kinetic data has been proposed and discussed. Based on the mechanism a suitable rate law is derived. 1. Introduction Sodium perborate (NaBO3·4H2O) is a nontoxic cheap large scale industrial chemical primarily used as a source of “active oxygen” in detergents and as a mild antiseptic. This active oxygen has the oxidising properties of hydrogen peroxide. PMR spectral analysis [1] and X-ray diffraction studies [2] conclude that perborate is a true peroxy salt with water of crystallisation. Perborate is a heterocycle and is in a dimeric tetrahedral configuration with dihedral angle of 64° and anionic formula: [3]. Oxidative study suggests perborate as not peroxoborate but borate peroxyhydrate. Hydrogen peroxide acquires stronger electrophilicity by the coordination with borate [4]. It is an effective reagent in organic synthesis and acetic acid is the solvent of choice [5–7]. Perborate in aqueous solution yields hydrogen peroxide and the kinetic studies in aqueous and partly aqueous acidic media confirm that perborate oxidation is hydrogen peroxide oxidation [8–10]. This stable and easily handled crystalline substance oxidizes organic sulphides [11–13], anilines [14], and indole [15]. 5-Oxoacid is an attractive substrate in terms of its enolization. In strong acid medium the substrate undergoes enolization. The reactive species of the substrate has been reported in the literature to be the enol form [16, 17]. In recent years, studies of the oxidation of various organic compounds by perborate have attracted considerable attention. A thorough literature survey reveals that relatively little work on the oxidation of oxoacid has been reported so far [18–21]. Although the perborate
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