• Puttaswamy

      Articles written in Journal of Chemical Sciences

    • Kinetics and mechanism of oxidation of some basic amino acids with bromamine-T

      D S Mahadevappa Puttaswamy N M Made Gowda

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      Kinetics of oxidative decarboxylation of arginine, glutamine, histidine and lysine by bromamine-T (BAT) was investigated in acid and alkaline media at 30° and 20° fespectively. The form of the rate law at low concentrations of HClO4 has been worked out. Proton inventory studies in H2O-D2O mixtures with Arg as a probe have been made. The rate increases in the order: His > Lys > Arg > Glu - NH2. In alkaline media, the rate shows a first order dependence on [BAT]0 and is fractional in [S] and [OH].p-Toluene sulphonamide retards the rate. Mechanisms proposed are consistent with the experimental rate laws.

    • Oxidation of secondary alcohols by sodium N-bromobenzene-sulphonamide: A kinetic study

      K Mohan D S Mahadevappa Puttaswamy

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      The kinetics of oxidation of 2-propanol, 2-butanol, 2-pentanol, 2-hexanol and 2-heptanol to the respective ketones by sodium N-bromobenzenesulphonamide (bromamine-B) in presence of HCl was studied at 40°C. The rate shows a first-order dependence on both [oxidant]0 and [alcohol]0 and is fractional in [H+] and [Cl]. The proposed mechanism assumes the formation of a hypobromite in the rate-limiting step followed by a fast reaction to form products. The magnitude of the solvent isotope effect, $${{k'_{H_2 O} } \mathord{\left/{\vphantom {{k'_{H_2 O} } {k'_{D_2 O} }}} \right.\kern-\nulldelimiterspace} {k'_{D_2 O} }}$$is 0–90. The rates do not correlate satisfactorily with Taft’s substituent constants. An isokinetic relation is observed with β=331 K indicating enthalpy as a controlling factor.

    • Mechanistic investigation of oxidation of a diketone by bromamine-B in acid medium

      T Asha Iyengar D S Mahadevappa Puttaswamy

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      Oxidation of acetylacetone (AA) by bromamine-B (BAB) in HC1 medium (0.1 to 0.6 mol dm−3) at constant ionic strength has been investigated at 40°C. The rate is first order in [BAB]0 and fractional order each in [AA]0 and [H+]. The reaction is also catalysed by chloride ion. Michaelis-Menten type of kinetics is observed. Decrease in dielectric constant of medium increases the rate. A solvent isotope effect κ′H2O/κ′D2O = 0.96 has been noted. Activation parameters for the rate limiting step have been computed. The mechanism involves the enol form of the diketone.

    • Mechanistic investigation of oxidation of paracetamol by sodium N-chlorobenzenesulphonamide in acid medium

      Puttaswamy T M Anuradha

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      Oxidation of paracetamol (PAM) by sodium N-chlorobenzenesulphonamide (chloramine-B or CAB) in HClO4 medium at 30°C was studied. The rate is first order in [CAB]0 and fractional order each in [PAM]0 and [H+]. Variation of ionic strength and addition of the reaction product benzenesulphonamide or halide ions had no significant effect on the reaction rate. The solvent isotope effect was studied using D2O. Decrease in dielectric constant of the medium increases the rate. Activation parameters for the overall reaction have been computed. Michaelis-Menten type of kinetics has been proposed and activation parameters for the rate-limiting step have also been computed. 4-Amino-2,6-dichlorophenol was identified as the oxidation product of PAM. A mechanism consistent with the observed results is proposed and discussed.

    • Kinetics of oxidation of acidic amino acids by sodium N-bromobenzenesulphonamide in acid medium: A mechanistic approach

      Puttaswamy Nirmala Vaz

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      Kinetics of oxidation of acidic amino acids (glutamic acid (Glu) and aspartic acid (Asp)) by sodium N-bromobenzenesulphonamide (bromamine-B or BAB) has been carried out in aqueous HClO4 medium at 30°C. The rate shows first-order dependence each on [BAB]o and [amino acid]o and inverse first-order on [H+]. At [H+] > 0·60 mol dm−3, the rate levelled off indicating zero-order dependence on [H+] and, under these conditions, the rate has fractional order dependence on [amino acid]. Succinic and malonic acids have been identified as the products. Variation of ionic strength and addition of the reaction product benzenesulphonamide or halide ions had no significant effect on the reaction rate. There is positive effect of dielectric constant of the solvent. Proton inventory studies in H2O-D2O mixtures showed the involvement of a single exchangeable proton of the OH ion in the transition state. Kinetic investigations have revealed that the order of reactivity is Asp > Glu. The rate laws proposed and derived in agreement with experimental results are discussed.

    • Kinetics and mechanism of oxidation of chloramphenicol by 1-chlorobenzotriazole in acidic medium

      R C Hiremath R V Jagadeesh Puttaswamy S M Mayanna

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      Chloramphenicol (CAP) is an antibiotic drug having a wide spectrum of activity. The kinetics of oxidation of chloramphenicol by 1-chlorobenzotriazole (CBT) in HClO4 medium over the temperature range 293–323 K has been investigated. The reaction exhibits first-order kinetics with respect to [CBT]o and zero-order with respect to [CAP]o. The fractional-order dependence of rate on [H+] suggests complex formation between CBT and H+. It fails to induce polymerization of acrylonitrile under the experimental conditions employed. Activation parameters are evaluated. The observed solvent isotope effect indicates the absence of hydride transfer during oxidation. Effects of dielectric constant and ionic strength of the medium on the reaction rate have been studied. Oxidation products are identified. A suitable reaction scheme is proposed and an appropriate rate law is deduced to account for the observed kinetic data.

    • Mechanistic chemistry of oxidation of balsalazide with acidic chloramine-T and bromamine-T: A comparative spectrophotometric kinetic study

      Puttaswamy S Dakshayani

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      Balsalazide (BSZ) belongs to a class of non-steroidal anti-inflammatory drugs. Kinetics and mechanism of oxidation of BSZ with sodium N-halo-p-toluenesulfonamides viz., chloramine-T(CAT) and bromamine-T(BAT) in HClO4 medium have been spectrophotometrically investigated ($\lambda_{\max}$ =357nm) at 303 K. Under comparable experimental conditions, reactions with both the oxidants follow a first-order dependence of rate on [BSZ] and fractional-order dependence on each [oxidant] and [HClO4]. Activation parameters and reaction constants have been computed. 2-hydroxy-5-nitroso-benzoic acid and 3-(4-nitroso-benzoylamino)-propionic acid are identified as the oxidation products of BSZ with both CAT and BAT. The rate of oxidation of BSZ is about five-fold faster with BAT than with CAT. Plausible mechanism and related rate law have been deduced for the observed kinetics.

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