Kinetics of Oxidation of Thiocyanate and Thiosemicarbazide in the Free and Metal-bound States by Potassium Iodate in Aqueous Perchloric Acid Medium

Department of Post-Graduate Studies and Research in Chemistry, Mangalore University, Mangalagangothri-574 199

Manuscript received 19 March 1990, accepted 9 April 1991

Kinetics of oxidation of thiocyanate ion and thiosemicarbazide (TSC) in the free and metal-bound states by potassium iodate have been studied in aqueous perchioric acid medium under varying conditions. Oxidation of thiocyanate showed first order kinetics in [KIO₃ ] and nearly first order in [NCS^-] The rate was indepen­dent of [H⁺]. Variation in either the ionic strength or dielectric constant of the medium had no effect on the rate of reaction Oxidation of thiosemicarbazide in the free and metal-bound states showed first order kinetics in [KIO₃ ], a little fractional order in [TSC] and inverse fractional order in [H⁺]. Variation in ionic strength of the medium and addition of iodide to reaction mixture slightly decreased the rate. Variation in dielectric constant of the medium by changing the solvent composition with methanol had no significant effect on the rate. Mechanisms consistent with the observed results have been considered and discussed. Activation parameters have also been calculated by measuring rates at different temperatures. The metal com­plexation of the ligand makes the rate independent of its concentration.