Os(VIII) - catalysis on the oxidation of some diaryl sulphoxides with bromamine-B in alkaline medium

Abstract

71-75The effect of substituents reveals the electronic character of Os(VIII)- catalysed N-bromobenzene sulphonamide (bromamine-B) oxidation of some diaryl sulphoxides to sulphones in a strongly alkaline (p͠H~.5) <i style="mso-bidi-font-style: normal">t-butanol-water (1:1 v/v) medium and the conversion appears to be nucleophilic for bromamine-B (BAB). High dielectric constant of the medium favours the reactivity. The kinetic studies reveal that electron-withdrawing groups enhance the reactivity while electron-releasing ones inhibit the rate. It appears that the anion RNBr is the reactive species of bromamine-B. The possibility of the formation of Os(VI)-BAB complex causing a retarding effect on the pseudo-First-order rate coefficients is discussed. Contrary to expectations there is a marked depression in the catalytic activity of Os(VIII) in the presence of other transition metals and pyridine bases such as 2, 2'-bipyridyl and 1, 10-phenanthroline. The probable reaction mechanisms are discussed on the basis of above results