Kinetics of oxidation of chloroacetic acids by sodium N-bromo-<i>p</i>-toluenesulphonamide (bromamine-T) in HCl medium and catalysis by Ru(III) ion

Abstract

Kinetics of uncatalysed and Ru(III) catalysed oxidations of mono, di and trichloroacetic acids by bro mamine-T (BAT) in acid medium has been studied at 40°C. The rate laws for the two paths are rate = <i>k</i>[BAT]_t[H⁺]^X and rate= [BAT]_t[S]_t[Ru(III)]^Y[H⁺]^-z where x, y and z are less than unity. Added haIide ions and the reaction product, toluenesulphonamide have no effect on the rate. Variation in ionic str ength of medium has no influence on the reaction. The solvent isotope effect has been studied in D₂O medium. Activation parameters have been evaluated from the Arrhenius plots. Mechanisms consistent with the experimental rate laws have been proposed. The protonation constant of monobromamine- T to form CH₃C₆H₄SO₂NH₂Br is evaluated from the uncatalysed reaction as 9.3 + 1.0 at 40^oC. The value for the same from Ru(III) catalysed reaction is 10.3 ± 1.0. A Taft linear free-energy relation is noted for the catalysed reaction with <i>p* </i>=1.22 and 0.067 indicating that electron withdrawing groups increase the rate. An isokinetic relation is observed with <i>β</i>=457K showing that enthalpy factors control rate of reaction.