Mechanism of the reaction of dialkyl sulphides with bromamine T in alkaline medium

Abstract

Bromamine T (p-MeC₆H₄SO₂NBr^–K⁺) reacts readily with dialkyl sulphides (R₂S) to yield suiphoxides (R₂SO) and sulphimides (R₂SNTs). The kinetics of the reaction were investigated in buffered alkaline water-methanol solutions. In rate-determining steps HOBr and p-MeC₆H₄SO₂NHBr formed in equilibrium reactions convert dialkyl sulphides into bromosulphonium (R₂SBr⁺) intermediates (ρ*–1.22 and –1.11, ρ_I–13.3 and –14.4, respectively). Electrophilic additions of Br⁺ to sulphur atom are significantly hindered by the steric effect of S-alkyl groups (δ 0.713 and 0.765, ρ_s 0.766 and 0.792, respectively). Products are rapidly formed from bromosulphonium ions by nucleophilic displacement with OH^– and p-MeC₆H₄SO₂NH^– nucleophiles. Product distribution depends on pH and the concentration of p-MeC₆H₄SO₂NH₂ but is not influenced markedly by S-alkyl groups in sulphides. Results are compared with those obtained earlier for chloramine T.