- Autocatalytic Oxidation of Thiamine Hydrochloride (Vitamin B1) by Permanganate in Aqueous Sulfuric Acid Medium: A Kinetic and Mechanistic Study
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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.
- Savanur, Anita,Teradale, Amit,Lamani, Shekappa,Chimatadar, Shivamurti
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p. 281 - 291
(2016/04/05)
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- Kinetics and mechanistic study of manganese(II)-catalyzed cerium(IV) oxidation of thiamine hydrochloride in aqueous perchloric acid medium by stopped flow technique
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The kinetics of the manganese(II)-catalyzed oxidation of thiamine hydrochloride by cerium(IV) in aqueous perchloric acid medium at a constant ionic strength of 1.10 mol dm-3 was studied spectrophotometrically at 15, 25, 35, and 45 C by the stopped flow technique. The reaction between thiamine hydrochloride and cerium(IV) in the acid medium exhibits 1:3 stoichiometry. The main products were identified by spot test, IR, 1H NMR, and GC-MS studies. The reaction is first order in cerium(IV) and manganese(II) and has less than unit order in thiamine hydrochloride. As the acid concentration increases the rate of reaction decreases. The added product cerium(III) retards the rate of reaction. The active catalyst and oxidant species were identified as [Mn(H2O)4]2+ and [Ce(OH)]3+, respectively. A probable mechanism involving free radicals and the formation of a complex between substrate and catalyst is proposed. The reaction constants, activation parameters, and thermodynamic quantities are calculated and discussed.
- Naik,Byadagi,Nandibewoor,Chimatadar
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p. 1307 - 1317
(2013/10/01)
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