Oxidation of xylitol by a silver(III) periodate complex in the presence of osmium(VIII) as a homogeneous catalyst

The kinetics of the osmium (Os(VIII)) catalyzed oxidation of xylitol (XYL) by a silver(III) periodate complex (diperiodatoargentate(III)) (DPA) in an aqueous alkaline medium at 298 K and at a constant ionic strength of 0.06 mol dm (3) was studied spectrophotometrically. The reaction between DPA and xylitol in an alkaline medium exhibits 1 : 2 stoichiometry (XYL : DPA). The reaction is of first order in [Os(VIII)] and [DPA] and has a negative fractional order in [IO4-]. It is apparent that it has less than the unit order in [XYL] and [OH-] under the experimental conditions. The main oxidation product was identified as 2,3,4,5-tetrahydroxypentanoic acid by FT-IR and LC-MS spectral studies. A probable mechanism was proposed and discussed. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also calculated. The active species of the catalyst and oxidant have been identified.