Oxidation of aliphatic amides by N-chlorobenzenesulfonamide in acid medium catalyzed by ruthenium(III):a kinetic and mechanistic study

摘要

The kinetics of the ruthenium(III)-catlayzed oxidation of urea and substituted ureas,namely,methylurea,ethylurea and propylurea by sodium N-chlorobenzenesulfonamide or chloramine-B(CAB) in HCl medium have been studied at 30deg.The reaction rate shows a first order dependence each on [CAB],[amide] and [Ru~(III)] and fractional order on [H~+].Additions of halide ions and the reaction product of CAB (benzenesulfonamide) and the variation of ionic strength and dielectric constant of the medium do not have any significant effect on the reaction rate.Activation parameters have been evaluated.The rate increases in D_2O medium.Proton inventory studies were made in H_2O-D_2O mixtures for both the amides.A Taft linear free energy relationship is observed for the reaction with rho*=-0.88 and -3.20 and delta=-0.33,indicating that electron-donating groups enhance the rate.An isokinetic relationis observed with beta=372K confirmed by the Exner criterion protonation constant of monochloramine-B has been evaluated to be 8.6.A mechanism consistent with the observed kinetic data has been propsoed.The rate of oxidation increasesin the order:propylurea>ethylurea>methylurea>urea.