Mechanism of the reaction of sulphides with N-chloroarenesulphonamides

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Abstract
The kinetics of the reaction of R1R2S (R1= R2= alkyl or aryl) and ArSO2NCI–Na+ were investigated in buffered water–ethanol solution. Analytical methods have been elaborated to follow the reaction which affords R1R2-SNSO2Ar and R1R2SO. From the reaction scheme proposed, kinetic equations are deduced and supported experimentally. In fast and slow (kd′) equilibrium reactions, respectively, ArSO2NCl–Na+ in water is transformed into ArSO2NHCl and ArSO2NCl2 which are reactive electrophiles and which, in their turn, react with R1R2S, the first in a slow (k1′) and the second in a relatively fast (k2) step to form reactive intermediates. The rate constants kd′, k1′, and k2 have been determined for different reactants and the observed substituent effects are correlated with the formation of an (R1R2SCl+ArSO2NQ–) ion-pair intermediate (Q = H or Cl). Me2S is converted by TsNHCl (k1′kd′), Ph2S by TsNCl2(k1′kd′), and MeSPh by both chlorinating agents (k1′∼kd′). For the reactions of MeSPh with TsNCl2 and TsNHCl k2/k1′ is 3·5 × 106. MeSPh is chlorinated by TsNCl2 1500 times faster than Ph2S. For XC6H4SMe, electron-donating X groups increase the rate of reaction with both TsNHCl and TsNCl2(ρ–4·25 and –3·56, respectively). For YC6H4SO2NHCl, electron-withdrawing Y groups produce an increase in reactivity toward MeSPh (ρ+ 1·76). From the ion-pair intermediate R1R2SNSO2Ar and R1R2SO are formed, probably via a sulphurane intermediate, in fast, competitive SN reactions under different steric control. The formation of sulphoxides is more hindered by bulky R groups than that of sulphimides. Other product-controlling factors are also discussed.

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