Ruthenium(III)-catalyzed oxidation of amides by sodium N-bromobenzenesulphonamide in hydrochloric acid: a kinetic and mechanistic study |
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Authors: | Swamy Putta Ramachandrappa Rangegowda Ramalingaiah Hulivana |
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Institution: | (1) Department of Post-Graduate Studies in Chemistry, Central College, Bangalore University, Bangalore-, 560001, India;(2) Department of Chemistry, P. E. S. College of Science, Mandya-, 571401, India |
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Abstract: | 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. |
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