CHEMICAL KINETIC AND MECHANISTIC STUDY OF OXIDATION OF ISONIAZID BY AMMONIUM METAVANADATE IN AN ACIDIC MEDIUM BY SPECTROPHOTOMETRY

Abstract

The chemical kinetic and mechanistic study of oxidation of Isoniazid by ammonium metavanadate in an acidic medium has been studied spectrophotometrically by maintaining pseudo-first order reaction condition in which concentration of Isoniazid was in excess than oxidizing agent. The concentration dependence of Isoniazid, ammonium metavanadate, medium of the reaction, ionic strength, specific ions, temperature, dielectric constant and various solvents on the rate of oxidation reaction was observed. The determination of reactive intermediate, intervention of free radical, stoichiometry and end product analysis was carried out using standard parameters of the reaction. The order of reaction with respect to oxidant is one. The decrease in rate constant with increase in the concentration of Isoniazid is attributed to greater stability of the complex due to solvation. The specific rate of the reaction increases with increase in the concentration of acid. The oxidation rate is not influenced by increase in ionic strength and changing the various salts. The specific rate ofthe oxidation of Isoniazid is directly proportional to the dielectric constant of the reaction medium. The thermodynamic parameters temperature coefficient (1.97), energy of activation (Ea=56.57 KJmol-1), enthalpy of activation (ΔH #=53.35 KJmol-1), entropy of activation (ΔS #=-135.75 J K-1mol-1) and free energy of activation (ΔG # = 95.84 KJmol-1) were obtained by carrying out the reaction at seven different temperatures. The mol ratio of Isoniazid: ammonium metavanadate is found to be 1:4 and it was independent of concentration of medium of the reaction. The mechanism in terms of the active species of the oxidant and Isoniazid is proposed.