Ruthenium(III) Catalyzed Kinetics of Oxidation of Primary Alcohols by Bromamine-b in Hydrochloric Acid Solution

Abstract

The kinetics of the ruthenium(III) catalyzed oxidation of the primary alcohols, methanol, ethanol, 1-propanol, and 1-butanol 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]. Additions of halide ions and the reduction product of BAB (benzenesulfonamide), and variation of the ionic strength of the solvent medium have no effect on the rate. Activation parameters have been evaluated. A general mechanism consistent with the above kinetic data has been proposed. The protonation constant of monobromamine-B has been evaluated to be 12.6. A Taft LFE relationship is noted for the ruthenium(III) catalyzed reaction with p∗ = -0.77 indicating that a positive charge develops on the transition state and the electron-donating groups favor the reaction rate. An isokinetic relationship is observed with β = 386 K indicating that enthalpy factors control the rate.