The kinetics of ruthenium (III)-catalyzed oxidative cleavage of thiamine hydrochloride (THM, Vitamin B-1) with N-bromosuccinimide (NBS) in HCl medium has been investigated at 308 K. The oxidation reaction follows the rate law, -d[NBS]/dt=k[NBS] [Ru(III)](a) [THM](b) [H+](-c) [Cl-](-d), where a, b, c and d are less than unity. The stiochiometry of the reaction was found to be 1: 1, and 2-(4-methyl thiazol-5-yl) ethanol and 4-amino-2-methylpyrimidine-5-carbaldehyde were identified as the oxidation products of THM. The reaction was examined with reference to variation of ionic strength of the medium and addition of the deduction product NBS. succinamide (RNH). The change in relative permittivity of the medium affected by changing the solvent composition with acetonitrile has been studied. The reaction constants involved in the mechanism were computed. The overall activation parameters have been evaluated from the Arrhenius plot. HOBr has been postulated as the reactive oxidizing species. The observed results have been explained by plausible mechanisms and the relative rate laws have been deduced. (C) 2008 Elsevier B.V. All rights reserved.