Osmium(VIII) Catalysed Oxidation of Diclofenac Sodium by Diperiodato- argentate(III) Complex in Aqueous Alkaline Medium

The kinetics of Osmium(VIII) (Os(VIII)) catalysed oxidation of diclofenac sodium (DFS) by diperiodatoargentate(III) (DPA) in alkaline medium at a constant ionic strength of 0.60 mol dm -3 has been studied spectrophotometrically. The stoichiometry was found to be 1:1 i.e, one mole of DFS reacted with one mole of DPA. The reaction was first order with respect to [DPA] and [Os(VIII)], less than unit order in both [DFS] and [alkali] and negative fractional order in [periodate]. The effect of added products, ionic strength and dielectric constant of the medium was studied. The oxidation reaction in alkaline medium has been shown to proceed via a Os(VIII)-DFS complex, which further reacts with one molecule of monoperiodatoargentate in a rate determining step followed by other fast steps to give the products. The oxidation products were identified by LC-ESI-MS, NMR and IR spectral studies. The reaction constants involved in different steps of the mechanism were calculated. The activation parameters with respect to slow step of the mechanism were computed and discussed and thermodynamic quantities were also determined. The catalytic constant (Kc) was also calculated for Os(VIII) catalysis at different temperatures and values of activation parameters with respect to the catalyst have been evaluated. The active species of catalyst and oxidant have been identified.