Kinetic and Mechanistic Study of Oxidation of Sulfamethoxazole by Alkaline Permanganate

Abstract

The kinetics of the oxidation of sulfamethoxazole (SMZ) by permanganate in aqueous alkaline medium at constant ionic strength of 0.41 mol dm m 3 was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and has apparent less than unit order in both [SMZ] and [alkali]. Addition of products have no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation in alkaline medium has been shown to proceed via an alkali-permanganate species, which forms a complex with SMZ. The latter decomposes slowly, followed by a fast reaction between a free radical of SMZ and another molecule of permanganate to give the products. The reaction constants involved in the mechanism were evaluated and there is a good agreement between observed rate constants and the calculated rate constants. The activation parameters were computed with respect to the slow step of the proposed mechanism.