Mechanistic Investigations of Uncatalyzed and Ruthenium(III) Catalyzed Oxidation of D-Mannitol by Diperiodatoargentate(III) Complex in Aqueous Alkaline Medium

The kinetics of oxidation of D-Mannitol (D-Manni) by diperiodatoargentate(III) (DPA) both in the absence and presence of ruthenium(III) catalyst in alkaline medium at 298K and at a constant ionic strength of 0.10mol dm3 was studied spectrophotometrically. The reaction exhibits a 1:2 stoichiometry ([D-Manni]:[DPA]) and first order in [DPA], less than unit order in [D-mannitol] in both cases. The OH had retarding effect and added periodate had no effect on the rate of the reaction in both cases. The order with respect to [Ru(III)] was unity. The main products were identified by spot tests, FT-IR, and LC-MS spectral studies. Based on the experimental results possible mechanisms were proposed. The reaction constants involved in the different steps of the mechanisms were evaluated. The catalytic constant (K C) was also calculated for Ru(III) catalysis at different temperatures. The values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to slow step of the mechanisms were computed and discussed and thermodynamic quantities were also determined. Kinetic studies suggest that the active species of DPA and ruthenium(III) were found to be [Ag(H3IO6)2] and [Ru(H2O)5OH]2+, respectively.