Mechanism of the reaction of N-arylsulphonylsulphimides with trivalent phosphorus compounds

Abstract

The reaction of N-arylsulphonylsulphimides with trivalent phosphorus compounds in dimethylformamide (DMF) gave the original sulphide and phosphinimine. The kinetic studies revealed that the rate of the reaction of S-aryl S-methyl N-p-tosylsulphimide with triphenylphosphine follows the second-order kinetic equation v=k₂[Sulphimide][Ph₃P], and the activation parameters for the reaction were ΔH^‡ 26.9 kcal mol^–1 and ΔS^‡–8.8 cal mol^–1 K^–1. Hammett ρ values of the reaction p-XC₆H₄S(NSO₂C₆H₄Y-p) R +(p-ZC₆H₄)₃P, are ρ_X+ 3.7, ρ_Y+ 0.6 (R = CH₃), and ρ_Z–1.3 (R = PhCH₂). These observations suggest that the reaction proceeds via initial nucleophilic attack of the phosphine on the sulphinyl sulphur atom of the sulphimide. Addition of water or alcohol to the reaction mixture changed both the products and kinetic results. The reaction in alcohol gave, besides the original sulphide, an alkylexchanged sulphide in which the alkyl group is derived from the alcohol used. All these observations can be explained by assuming the initial formation of a 1,3-dipolar sulphurane intermediate between the sulphimide and triphenylphosphine.