Oxidation kinetics of some sulfoxides with N,N-dibromobenzene sulfonamide

Department of Chemistry, Annamalai University, Annamalainagar-608 002, Tamilnadu, India
E-mail : meenas1957@gmail.com
Manuscript received 1 February 2006, revised Jl May 2007, accepted 15 May 2007

The kinetics of oxidation of some sulfoxides with dibromamine-B yielding sulfones was investigated in presenceof Hg^II , and the rate equation,

 \(k_{obs} = {k_3K_2k_h[S] \ \over [RNH_2]+k_h}\), was found to be valid.

The reaction involves two distinct pathways namely initial fast step and a subsequent slow step. The chloride ions have no effect on the reactivity of sulfoxides. Sulfoxides containing electron-attracting substituents retard the reactivity while those containing electron-releasing constituents accelerate the rate of oxidation. Exner plot confirms the operation of same mechanism in all the sulroxides studied. Electrophilic addition of Br⁺ to sulfur atom results in an electron-deficient sulfonium centre which decomposes in a slow rate-limiting step. The rate coefficients are treated in terms of multiparametric extensions of the Hammett equation to have more insight into the mechanistic aspects.