Ruthenium(III)-catalyzed oxidation of substituted ethanols by sodium N-bromo-p-toluenesulfonamide in hydrochloric acid medium

The kinetics of oxidation of substituted alcohols, RCH2CH2OH (R = H-, OEt-, OMe-, NH2-, Cl- and Br-) by sodium N-bromo-p-toluenesulfonamide or bromamine-T (BAT), catalyzed by ruthenium(III) chloride in the presence of HCl, has been studied at 303K. The reaction rate shows first order dependence each on [BAT], [alcohol] and [RuIII]. The reaction rate is inversely dependent on [H+]. Addition of halide ions and the reduction product, p-toluenesulfonamide has no significant effect on the rate. Composite activation parameters H, S and G were computed by studying the reaction at different temperatures (298–313K). The rate decreased in D2O medium and the solvent isotope effect k(H2O)|k(D2O) = 1.63 and 1.68 for EtOH and BrCH2CH2OH respectively. Proton inventory studies have been made in H2O–D2O mixtures for both alcohols. The conjugate acid, TsNHBr, is assumed to be the reactive species. The rates do not correlate satisfactorily with Taft substituent constants. The protonation constant (25.3) of monobromamine-T has been evaluated. From enthalpy-entropy relationships and Exner correlations, the isokinetic temperature () was found to be 368 K, which is much higher than the experimental temperature, indicating that enthalpy factors control the rate. The proposed reaction mechanisms and the derived rate laws are consistant with the observed kinetic data. The rate of oxidation of alcohols RCH2CH2OH follows the order: H > Br > OEt > OMe > Cl > NH2.     

Ruthenium(III)-catalyzed oxidation of amides by sodium N-bromobenzenesulphonamide in hydrochloric acid: a kinetic and mechanistic study

The kinetics of the RuIII-catalyzed oxidation of urea and substituted ureas namely: methylurea, ethylurea and propylurea, to the corresponding hydrazines by sodium N- bromobenzenesulphonamide or bromamine-B (BAB) in HCl medium has been studied at 303K. The reaction rate shows a first order dependence each upon [BAB], [amide] and [RuIII] and is dependent on [H+]. Addition of halide ions and benzenesulphonamide do not significantly affect the rate. Proton inventory studies were made in H2O-D2O mixtures for urea and methylurea. A Taft linear free energy relationship is observed for the reaction with *=–2.95 and =–0.25, showing that electron-donating groups enhance the rate. An isokinetic relation is observed with =370K, indicating that enthalpy factors control the rate; this result is also confirmed by Exner Criterion which showed a linear plot for the logarithms of rate constants at the highest and lowest temperatures employed. The protonation constant of monobromamine-B has been evaluated and equals 7.5. A mechanism consistent with the observed kinetic data has been proposed.