Ruthenium(III) mediated oxidation of thiamine hydrochloride by cerium(IV) in perchloric acid medium: a kinetic and mechanistic approach

Oxidation of thiamine hydrochloride (vitamin B1) by cerium(IV) mediated by micro amounts (10−6 mol dm−3) of ruthenium(III) in aqueous perchloric acid medium has been studied spectrophotometrically at 25 °C and I = 1.10 mol dm−3. The reaction is first order in both cerium(IV) and ruthenium(III) concentrations. The order with respect to vitamin B1 concentration varies from first order to zero order as the vitamin B1 concentration increases. An increase in perchloric acid concentratrion decreases the reaction rate. The active species of oxidant and catalyst are [Ce(OH)3+] and [Ru(H2O)6]3+. A possible mechanism is proposed and reaction constants involved have been determined. The activation parameters for the slow step of the mechanism are determined.