Ruthenium(III)-Mediated Oxidation of D-Mannitol by Cerium(IV) in Aqueous Sulfuric Acid Medium:A Kinetic and Mechanistic Approach

摘要

The oxidation of D-mannitol by cerium(IV) has been studied spectrophotometrically in aqueous sulfuric acid medium at 25°C at constant ionic strength of 1.60 mol dm~(-3). A microamount of ruthenium(III) (10~(-6) mol dm~(-3)) is sufficient to enhance the slow reaction between D-mannitol and cerium(IV). The oxidation products were identified by spot test, IR and GC-MS spectra. The stoichiometry is 1:4, i.e., (D-mannitol]: [Ce(IV)J = 1:4. The reaction is first order in both cerium(IV) and ruthenium(III) concentrations. The order with respect to D-mannitol concentration varies from first order to zero order as the D-mannitol concentration increases. Increase in the sulfuric acid concentration decreases the reaction rate. The added sulfate and bisulfate decreases the rate of reaction. The active species of oxidant and catalyst are Ce(SO4)2 and (Ru(H2O)6]~(3+), respectively. A possible mechanism is proposed. The activation parameters are determined with respect to a slow step and reaction constants involved have been determined.