MECHANISTIC STUDIES OF OXIDATION OF DIPHENYLMETHANOLS BY SODIUMN-CHLOROBENZENESULPHONAMIDE CATALYSED BY RUTHENIUM(III)

Abstract

The kinetics of oxidation of six para-substituted diphenyhmethanols (Y-DPM, where Y = H, CI, Br, NO2, CH3 and OCH3) by sodium N-chlorobenzenesulphonamide [chloramine-B (CAB)I In the presence of HCl and catalysed by RuCl3 In 30% (v/v) methanol medium was studied at 35 degrees C, The experimental rate law is rate=k'[CAB](0)[DPM](0)(x)[RuCl3](y)[H+](z), where x, y and z are fractions, Addition of reaction product, benzenesulphonamide (BSA), retards the reaction. An increase in the dielectic constant of the medium decreases the rate, Rate studies in D2O medium showed that the solvent isotope effect k'(H2O)/k(D2O)=0.53, Proton inventory studies were carried out using H2O-D2O mixtures, The rates correlate satisfactorily with the Hammett a relationship and the plot is biphasic, The reaction constant rho is - 2.8 for electron-releasing groups and -0.31 for electron-withdrawing groups at 35 degrees C, The activation parameters Delta H-double dagger, Delta S-double dagger, Delta G(double dagger) and logA were calculated, Delta H-double dagger and Delta S-double dagger are linearly related and an isokinetic relationship is observed with beta=343 Ei indicating enthalpy as a controlling factor, (C) 1997 by John Wiley & Sons, Ltd.