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

Kinetics of oxidation of isoniazid (INH) by sodium hypohalites NaOX (X=Cl o r Br) has been investigated at 303 K in NaOH medium. Under comparable exper imental conditions the oxidation behaviour is similar with both the oxidant s with first order dependence of rate each on [NaOX] and [INH] and fraction al 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 hali de ions slightly retards the rate. The reaction fails to induce polymerisat ion of acrylonitrile. The rate increases in D2O medium and the inverse solv ent isotope effect k(D2O)/k (H2O) is around 1.52. Proton inventory studies have been made in H2O - D2O mixtures. Activation parameters for the reactio n have been computed from the Arrhenius plots. Isonicotinic acid has been i dentified as the oxidation product of INH, by CC-MS. Under identical experi mental conditions the rate of oxidatian of INH is found to be higher with N aOBr than NaOCl by a factor of 3. The proposed reaction mechanism and the d erived the law are consistent with the observed kinetics.