Mechanism of Oxidation of Thiocyanate Ion by Bromamine-T and Hypobromite Ion in Alkaline Medium. A Kinetic Study

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

Manuscript received 17 June 1986, revised 8 October 1987, accepted 27 January 1988

Kinetics and mechanism of oxidation of thiocyanate ion by bromamine-T (BAT) and hypobromite ion have been Investigated In alkaline medium. The rate followed first order kinetics In (oxidant) with both BAT and OBr^-, but fractional and Inverse fractional orders In [OH^-] with BAT and OBr^-, respectively. The rate was independent of (NCS^-) with BAT and small fractional order In (NCS^-) with OBr^-. Increase in ionic strength of the medium Increased the rate with BAT and had no effect In hypobromite oxidations. Decrease in dielectric constant of the medium by changing the solvent composition with methanol increased the rate with BAT and had no significant effect with OBr^- oxidation. Activation parameters have been computed from the Arrhenius plots. Mechanism, consistent with the observed kinetics have been proposed and the related rate laws deduced. The formation equilibrium constant and the rate constant for the rate-controlling step have been computed from the double reciprocal plots. Comparison of kinetic results In acid and alkaline media reveal that BAT is more powerful oxidant in alkaline medium than in the former.