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

Abstract

The kinetics of the ruthenium(III)-catalyzed oxidation of urea and substituted ureas, namely, methylurea, ethylurea and propylurea by sodium N-chlorobenzenesulfonamide or chloramine-B (CAB) in HCI medium have been studied at 30°. The reaction rate shows a first order dependence each on CAB, amide and RuIII 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 D2O medium. Proton inventory studies were made in H2O-D2O mixtures for both the amides. A Taft linear free energy relationship is observed for the reaction with I�* = -0.88 and -3.20 and I´ = -0.33, indicating that electron-donating groups enhance the rate. An isokinetic relation is observed with I² = 372 K confirmed by the Exner criterion. The protonation constant of monochloramine-B has been evaluated to be 8.6. A mechanism consistent with the observed kinetic data has been proposed. The rate of oxidation increases in the order: propylurea > ethylurea > methylurea > urea.