Kinetic and mechanistic studies on the oxidation of D-cycloserine by sodium N-bromobenzenesulphonamide in hydrochloric acid medium

Abstract

<span style="font-size:12.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-in;mso-fareast-language:en-in;mso-bidi-language:ar-sa"="" lang="EN-IN">Oxidation of D-cycloserine (CS) by sodium Nbromobenzenesulphonamide or bromamine-B (BAB) in HCI medium (0.1 to 0.6 mol dm^·3) and constant ionic strength (0.8 mol dm^-3) has been investigated at 40^°C. The rate is first order in [BAB]_o and is fractional order each in [CS]_o and <span style="mso-bidi-font-style: italic">[H⁺]<i>. </i>The reaction is catalysed by chloride ion. Addition of reaction product, benzene sulphonamide and variation of ionic strength of the medium have no effect on rate. The reaction fails to induce the polymerisation of acrylonitrile. The rate constant increases with decrease in the dielectric constant of the medium. The rate increases in D₂O medium and the in verse solvent isotope effect <i>k </i>(D₂O) / <i>k</i><span style="mso-bidi-font-style:italic">(H₂O)<i> </i>= 1.70. Proton inventory studies made in H₂O-D₂O mixtures have been employed to calculate the isotopic fractionation factors. Composite activation parameters for the reaction have been determined from Arrhenius plot. Michaelis-Menten type of kinetics is observed and activation parameters for the rate-limiting step have been computed. The proposed mechanism assumes the simultaneous catalysis by H⁺ and CI ions and is consistent with the observed kinetic results.</span></span></span>