Ruthenium(III) catalyzed kinetics of chloroacetic acids oxidation by sodium n-bromobenzenesulfonamide in hydrochloric acid medium

Article abstract of DOI:10.1002/kin.550250906

Kinetics of uncatalyzed and Ru(III)-catalyzed oxidations of mono-, di, and tri-chloroacetic acids by the title compound (bromamine-B or BAB) in HCl medium has been studied at 40°. The uncatalyzed reaction shows a first-order dependence of the rate on [BAB], and fractional and zero orders in [acid] at low and high [HCl] ranges, respectively. The Ru(III)-catalyzed reaction, on the other hand, shows a first-order behavior on each of [BAB] and [substrate], second-order dependence on [Ru(III)], and inverse first orders in [acid] at low and high [HCl] ranges. Addition of halide ions and the reduction product of BAB, benzenesulfonamide, has no effect of on the reaction rate. Variation of ionic strength of the medium has no influence on the reaction. Solvent isotope effect was studied using D₂O. Activation parameters have been evaluated from the Arrhenius plots. Mechanisms consistent with the above kinetic data have been proposed. The protonation constant of monobromamine B evaluated from the uncatalyzed reaction is 12.4 while that evaluated from Ru(III) catalyzed reaction is 12.7. A Taft linear free-energy relationship is noted for the catalyzed reaction with ρ^* = 1.2 and 0.07 indicating that electron withdrawing groups enhance the rate. An isokinetic relation is observed with B = 338 K indicating that enthalpy factors control the reaction rate.