English

Abstract

Oxidation of thiamine hydrochloride (Vit. B1) by PDP mediated by micro amounts (10 -6 mol dm -3 to 10 - 4 ) of Ru (III) in aqueous nitric acid medium has been studied at 25˚C. The reaction is second order in both PDP and Ru (III) concentrations. The order with respect to B1 concentration varies first order to zero order as the vitamin B1 concentration increases, An increase in HNO3 concentration decrease the reation rate. The active species of Oxidant and catalyst are (PDP) and (Ru(H2O)6) 3 A possible mechanism is proposed and reaction constants involved have been determined. Ruthenium (III) is an efficient catalyst in many redox reactions involving different complexities due to the formation of intermediate complexes, free radicals and multiple oxidation states of ruthenium PDP is a well Known oxidant in acidic media PDP was act as predominant active species in the concentration range 0.30 - 2.0 moldm-3 of Nitric acid, but it role has not received much attention so far the oxidation of thiamine hydrochloride with alkaline potassium ferricyanide, hypo iodide, chlorite and N-chloro benzene sulphonamide were studied. The literature survey reveals that there were no report on the oxidation of thiamine hydrochloride by PDP the mechanism may be quite complicated due to the formation of different PDP and Ru (III) Complexes in the form of active complexes in nitric acid medium. Hence, we have investigated the Ru(III) mediated oxidation of vit B1 by PDP in order to understand the behaviour of active species of oxidant and catalyst to propose a suitable mechanism. Reagent grade chemicals were used double distilled water was used through for the preparation of solutions. The stock solution of the oxidant has obtained by dissolving PDP in 1.0 mol dm -3 H2SO4. The solution was standardized by a Known method. A stock solution of thiamine hydrochloride was prepared by dissolving thiamine hydrochloride in distilled water. The Ruthenium (III) stock solution was prepared by dissolving Rucl3 in 0.20 mol dm -3 Hcl and its concentration was assayed by EDTA titration. The stock solution was diluted as required before use. KNO3 and HNO3 were used to provide the required ionic strength and acidity All Kinetic measurement were carried out under Pseudo first order conditions, where thiamine hydrochloride was in excess over PDP at a constant ionic strength of 1.10 mol dm -3 . The reaction was initiated by mixing thermally equilibrated (25