Mechanistic investigation of ruthenium (III) catalysed oxidation of vitamin B 6 by diperiodatoargentate (III) in aqueous alkaline medium

Abstract

The oxidation of a Vitamin B₆ by diperiodatoargentate (III) (DPA) was carried out in presence of ruthenium (III) catalyst in the alkaline medium at 25°C and at a constant ionic strength of 0.50 mol dm⁻³ spectrophotometrically. The reaction was first order with respect to [DPA] whereas the apparent order with respect to Vitamin B₆, Ru (III) and alkali concentrations were less than unity. The order changes from first order to zero order as the Vitamin B₆ and alkali concentrations were increased. Addition of periodate had no effect on the rate of the reaction. Effect of added products, ionic strength and dielectric constant of the reaction medium has been investigated in the presence of Ru (III). The reaction in an alkaline medium proceeds via Ru(III)-Vitamin B₆ complex, which further reacts with one mole of DPA in the rate determining step to give the product. The reaction constants involved in the different steps of the mechanism were calculated. The catalytic constant (K_C) was also calculated at different temperatures. The activation parameters with respect to the slow step of the mechanism were determined and discussed.