Elimination mechanisms in the anilinolysis of sulfamoyl chlorides in chloroform and acetonitrile

The kinetics of the reaction of various sulfamoyl chlorides, R¹R²NSO₂Cl (R¹ = Ph, Me, c-C₆H₁₁, Bu^t, R² = H and R¹ = R² = Me and R¹ = R² = PhCH₂) with anilines in chloroform and acetonitrile have been studied. Reaction is first order in both chloride and aniline and pseudo first order and second order rate constants have been determined for various chlorides and para- and meta-substituted anilines. Hammett p values vary from -4.76 to -2.63 for varying XC₆H₄NH₂ depending on the halide, X. Substituents in XC₆H₄NHSO₂Cl have only small effects on the rates. There is a ca. 10⁶-fold rate difference between PhNHSO₂Cl and (PhCH₂)₂NSO₂Cl reacting with p-anisidine in chloroform at 25°C. This finding, coupled with the observation of hydrogen/deuterium isotope effects, supports the operation of an elimination mechanism involving an N-sulfonylamine, [PhN=SO₂], as a transient species. In chloroform an E2-type mechanism is suggested, while in acetonitrile the activation parameters (ΔH, ΔS) may indicate a more E1cB-like E2 mechanism.