Mechanism of oxidation of isoniazid by hypohalites in alkaline medium: A kinetic study

Abstract

Kinetics of oxidation of isoniazid (INH) by sodium hypohalites NaOX (X=Cl or Br) has been investigated at 303 K in NaOH medium. Under comparable experimental conditions the

oxidation behaviour is similar with both the oxidants with first order dependence of rate each on [NaOX] and [INH] and fractional order on [OH^-]. Variation of ionic strength or dielectric

constant of the medium does not have any effect on the reaction while the addition of halide ions slightly retards the rate. The reaction fails to induce polymerisation of acrylonitrile. The rate increases in D₂O medium and the inverse solvent isotope effect <i>k</i>(D₂O)/<i>k </i>(H₂O) is around 1.52. Proton inventory studies have been made in H₂O - D₂O mixtures. Activation parameters for the reaction have been computed from the Arrhenius plots. lsonicotinic acid has been identified as the oxidation product of INH, by GC-MS. Under identical experimental conditions the rate of oxidation of INH is found to be higher with NaOBr than NaOCl by a factor of 3. The proposed reaction mechanism and the derived the law arc consistent with the observed kinetics.