Autocatalytic Oxidation of Thiamine Hydrochloride (Vitamin B1 ) by Permanganate in Aqueous Sulfuric Acid Medium: A Kinetic and Mechanistic Study

The reaction kinetics of autocatalytic oxidation of thiamine hydrochloride (vitamin B1) by the permanganate ion in aqueous sulfuric acid medium has been investigated spectrophotometrically under the pseudo–first-order condition at 25°C. The observed stoichiometry is 6:5 in terms of the mole ratio of permanganate ions and thiamine hydrochloride. Formation of products was confirmed by UV–vis, IR, GC-MS, and NMR spectral data. Usually in the permanganate oxidation–reduction reactions, one of the products, Mn2+ autocatalyzes the reaction, but in the present investigation the autocatalytic effect is due to the (4-methyl–thiazol-5-yl) acetic acid, a product formed from the oxidation of vitamin B1, which is a rare case. The added Mn2+ does not have any significant effect on the rate of reaction. The reaction is first order with respect to both permanganate and thiamine hydrochloride concentrations. An increase in the sulfuric acid concentration decreases the rate of reaction. A composite scheme and rate laws were proposed. The activation parameters with respect to the slow step and reaction constants involved in the mechanism were determined and discussed.