Reaction of N-p-tolylsulphonylsulphimides with halide ion in dimethylformamide

Abstract

The halide ion catalysed rearrangement of N-p-tolylsulphonylsulphimides [Ar–S(Ts)–R; R = Me or PhCH₂] was found to afford nearly quantitatively the corresponding sulphenamide [ArSN(Ts)R] and is considered to proceed through a Stevens-type intramolecular rearrangement. The kinetic study revealed that the rate of the reaction of S-aryl-S-methyl-N-p-tolylsulphonylsulphimides with lithium chloride in dimethylformamide obeys a second-order kinetic equation v=k₂[Sulphimide][LiCl]. However, the lithium chloride concentration remained constant throughout the reaction, i.e. v=k_app[Sulphimide]. This suggests that the reaction is catalysed by chloride ion. Furthermore, with only a 1/10 molar amount of lithium chloride the sulphimide afforded the rearranged product quantitatively. The activation parameters for the reaction are ΔH^‡ 26·7 kcal mol^–1 and ΔS^‡–4·1 cal mol^–1 K^–1 respectively, and a Hammett ρ value of +1·7 was obtained. When the reaction of S-methyl-S-phenyl-N-p-tolylsulphonylsulphimide with LiCl was carried out in the presence of benzyl chloride, the only rearranged product obtained was N-benzyltoluene-p-sulphonamide. Methyl chloride formed in this reaction was trapped as methyl p-tolyl sulphide upon addition of toluene-p-thiolate. These observations suggest that the catalytic rearrangement proceeds through initial formation of alkyl halide and subsequent alkylation of sulphenamide anion involving a rate-determining nucleophilic attack of halide ion on the α-carbon atom attached to the trivalent sulphur atom of the sulphimide.