• Pradeep K Sharma

      Articles written in Journal of Chemical Sciences

    • Kinetics and mechanism of the oxidation of diols by pyridinium hydrobromide perbromide

      Dipti Mathur Pradeep K Sharma Kalyan K Banerji

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      Kinetics of oxidation of five vicinal, four non-vicinal diols, and one of thier monoethers by pyridinium hydrobromide perbromide (PHPB) have been studied. The vicinal diols yield products arising out of the glycol bond fission while the other diols yield hydroxycarbonyl compounds. The reaction is first order with respect to PHPB. Michaelis-Menten type kinetics are observed with respect to the diol. There is no effect of added pyridinium bromide on the reaction. The oxidation of [1,1,2,2-2H4]ethanediol shows the absence of a primary kinetic isotope effect. The values of solvent isotope effect,k(H2O)/k(D2O), at 313K, for the oxidation of ethanediol, propane-1,3-diol and 3-methoxybutan-1-ol are 4·71, 2·17 and 2·23 respectively. A mechanism involving glycol-bond fission has been proposed for the oxidation of the vicinal diols. The other diols are oxidised by a hydride-transfer mechanism as they are monohydric alcohols.

    • Kinetics and mechanism of oxidation of diols bybis(2,2′-bipyridyl) copper(II) permanganate

      Kavita Mohnot Pradeep K Sharma Kalyan K Banerji

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      Kinetics of oxidation of five vicinal, four non-vicinal diols, and one of their monoethers bybis(2,2′-bipyridyl) copper(II) permanganate (BBCP), has been studied. The vicinal diols yielded the products arising out of the glycol bond fission, while the other diols yielded the hydroxycarbonyl compounds. The reaction is first-order with respect to BBCP. Michaelis-Menten type kinetics were observed with respect to the diol. There is no effect of added 2,2′-bipyridine on the reaction. The oxidation of [1,1,2,2-2H4] ethanediol showed the absence of a primary kinetic isotope effect. A mechanism involving a glycol bond fission has been proposed for the oxidation of the vicinal diols. The other diols are oxidised by a hydride-transfer mechanism as are monohydric alcohols.

    • Kinetics and mechanism of the oxidation of diols by bromine in acid solution

      Vinita Sharma Pradeep K Sharma Kalyan K Banerji

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      Kinetics of oxidation of five vicinal diols, four non-vicinal diols, and two of their monoethers by bromine in strong acid solutions have been studied. The vicinal diols yielded the products arising out of glycol bond fission while the other diols yielded the hydroxycarbonyl compounds. The reaction is first order with respect to both bromine and the diol. The rate decreases with an increase in the acidity. The oxidation of [1,1,2,2-2H4] ethanediol showed the absence of a primary kinetic isotope effect. The value of solvent isotope effect, k(H2O)/k(D2O), at 303 K for the oxidation of ethanediol, propane-1,3-diol and 3-methoxybutane-1-ol are 4.71, 1.04 and 1.07 respectively. A mechanism involving a glycol bond fission has been proposed for the oxidation of the vicinal diols. The other diols are oxidised by a hydride-transfer mechanism as are monohydric alcohols.

    • Kinetics and mechanism of the oxidation ofα-hydroxy acids by benzyltrimethylammonium chlorobromate

      Anjana Pradeep K Sharma Kalyan K Banerji

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      The oxidation of glycollic, lactic, malic and a few substituted mandelic acids by benzyltrimethylammonium chlorobromate (BTMACB) in acetic acid-water (1:1) leads to the formation of the corresponding oxoacids. The reaction is of first order in BTMACB as well as the hydroxy acid. Addition of benzyltrimethylammonium chloride or bromide ion does not affect the rate indicating that BTMACB itself is the reactive oxidizing species. The oxidation ofα-deuteriomandelic acid shows the presence of a primary kinetic isotope effect (kH/kD=5·27 at 303 K). The reaction does not exhibit the solvent isotope effect [k(H2O)/k(D2O)=1·01]. The rate decreases with increase in the amount of acetic acid in the solvent mixture. A mechanism is proposed which involves hydride ion transfer to the oxidant.

    • Kinetics and mechanism of oxidation of aliphatic alcohols by tetrabutylammonium tribromide

      Manju Baghmar Pradeep K Sharma

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      Oxidation of nine primary aliphatic alcohols by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to alcohols. The reaction failed to induce the polymerization of acrylonitrile. Tetrabutylammonium chloride has no effect on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The oxidation of [1,1-2H2]ethanol exhibits a substantial kinetic isotope effect. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The reaction is susceptible to both polar and steric effects of substituents. A mechanism involving transfer of a hydride ion in the rate-determining step has been proposed.

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