• B Thimme Gowda

      Articles written in Journal of Chemical Sciences

    • Kinetics and mechanism of Ru(III)-catalysed oxidation of amino acids by N-chloro-N-sodio-toluene-p-sulphonamide in acid media

      B Thimme Gowda P Ramachandra

      More Details Abstract Fulltext PDF

      The kinetics of Ru(III)-catalysed oxidations of several amino acids (AA) (glycine, alanine, valine, leucine and phenyl alanine) by N-chloro-N-sodio-toluene-p-sulphonamide have been studied in aqueous perchloric acid medium under various conditions. Catalysed oxidations of all the amino acids show second-order kinetics in [oxidant], fractional order each in [AA] and Ru(III), and inverse fractional order in [H+] as compared to the second order dependence in [oxidant], first order in [AA] and inverse first order in [H+], generally observed for the uncatalysed oxidations. Variation in ionic strength of the medium or the addition of reduced product of the oxidant had no significant effect on the rates of reactions. Decrease in dielectric constant of the medium by changing the solvent composition with methanol decreased the rate in all the cases. A two-pathway mechanism has been considered to explain the observed kinetics and other effects. The rate-controlling steps have been identified in all cases and coefficients of these steps are calculated at different temperatures by varying [AA] at each temperature. Hence the activation parameters associated with the rate-controlling steps have been computed. The rate constants were also predicted from the rate laws as [AA] and [Ru(III)] were varied.

    • Kinetics of oxidation of S-N donor ligands by hydrogen peroxide

      B Thimme Gowda Pardhasaradhi Vasireddy

      More Details Abstract Fulltext PDF

      The kinetics of oxidation of thiosemicarbazide (TSC) in aqueous perchloric and sulphuric acid media, and also that of thiocarbohydrazide (TCH), its metal complex and its hydrazone in perchloric acid medium, by hydrogen peroxide have been investigated under varying conditions. The rates show first order kinetics each in [oxidant] and [substrate] in all the cases. The rate dependences in [H+] are different. Inverse first order kinetics in [H+] are observed for TCH oxidations and varying inverse orders in [H+] (depending upon its concentration) are seen for TSC oxidations. Effects of varying ionic strength, dielectric constant of the medium etc. have also been investigated. Mechanisms consistent with the observed results have been considered and discussed. The metal complexation of thiocarbohydrazide and its conversion into hydrazone enhance the rate of oxidations but have little effects on the kinetic orders.

    • Kinetics and mechanism of oxidation of carbohydrazide by chloramine-T and bromamine-T in aqueous perchloric acid medium

      B Thimme Gowda P Ramachandra

      More Details Abstract Fulltext PDF

      Kinetics of oxidation of carbohydrazide by chloramine-T (CAT) and bromamine-T (BAT) have been studied in aqueous medium over a wide acid range, and are found to be [H+] dependent. At low [H+] (0-0005-0-0075 mol dm−3), oxidation by both CAT and BAT shows first-order kinetics in [oxidant], fractional order in [substrate] and inverse fractional order in [H+]. At [HClO4]>0-005 mol dm−3, the rate dependence in [H+] is zero and fractional order for CAT and BAT oxidations respectively and the kinetics in [oxidant] and [substrate] are the same as before. Two pathways as well as Michaelis-Menten type mechanisms have been discussed to explain the observed kinetics and other effects. The rate controlling steps have been identified and the coefficients of these steps and the corresponding activation parameters are calculated. The rate constants are also predicted from the rate laws as [substrate] and [H+] are varied. The predicted values are in reasonable agreement with the experimental rate constants.

    • Kinetics and mechanism of oxidation of carbohydrazide and thiocarbo-hydrazide by N-bromoacetamide

      B Thimme Gowda P Jagan Mohana Rao

      More Details Abstract Fulltext PDF

      Kinetics of oxidation of carbobydrazide (ch) by N-bromoacetamide (NBA) in aqueous perchloric acid medium and thiocarbohydrazide (tch) in the free state and in its metal complex by NBA both in the presence and absence of added bromide ion have been investigated in aqueous perchloric acid medium. Oxidation of carbohydrazide showed first order kinetics in [NBA], nearly first order in [ch] and inverse fractional order in [H+]. The rate slightly decreased with increase in ionic strength of the medium. Addition of either the reduced product of the oxidant or bromide had no significant effect on the rate of CH oxidation. Oxidation of thiocarbohydrazide in the free and metal-bound states both in the presence and absence of added bromide showed first order kinetics in [NBA] and fractional order in both [tch] and [H+]. But the fractional order in [H+] for the oxidation of tch in the presence of Br¯ was almost twice that in its absence. The rate increased with increase in [Br¯] with a fractional order of about 0–3. Variation in ionic strength of the medium had very negligible effects. Addition of acetamide, the reduced product of the oxidant, had no effect on the rate. Michaelis-Menten type mechanisms have been considered to explain the observed results. Activation parameters have been computed for all the oxidations by measuring rates at different temperatures. Detailed mechanisms of oxidations have also been suggested.

  • Journal of Chemical Sciences | News

© 2021-2022 Indian Academy of Sciences, Bengaluru.