Ruthenium(III) Catalyzed Kinetics of Oxidation of Substituted Ethanols by Bromamine-B in Hydrochloric Acid Solution

Abstract

The kinetics of the ruthenium(III) catalyzed oxidation of ethanol and substituted ethanols, RCH2CH2OH (R ˭ H, OC2H5, OCH3, NH2, CI and Br) by sodium N-bromobenzenesulfonamide (bromamine-B or BAB) in HCI solution has been studied at 30°C. The reaction rate shows a first-order dependence each on [BAB], [alcohol] and [ruthenium(III)]. The reaction also shows an inverse fractional-order dependence on [acid]. Added halide ions and the reduction product of BAB (benzenesulfonamide), and variation of ionic strength of the solvent medium have no effect on the rate. Activation parameters have been evaluated. Proton inventory studies have been made in H2O-D2O mixtures for ethanol and 2-bromoethanol. A general mechanism consistent with the above kinetic data has been proposed. The protonation constant of monobromamine-B has been evaluated to be 24.2 M−1. The rates do not correlate satisfactorily with the Taft substituent constant. An isokinetic relationship is observed with β = 372 K indicating that enthalpy factors control the rate.