Reaction Kinetics of 3-Thiophenesulfonyl Chloride with Anilines in Methanol

The reaction rate constants and the activation parameters for the reaction of 3-thiophenesulfonyl chloride with some meta- and para-substituted anilines have been measured in methanol. The reaction is second order overall and pseudo first order with respect to each reactant. 3-Thiophenesulfonyl chloride is more reactive than 2-thiophenesulfonyl chloride but less than benzenesulfonyl chloride. The slopes of Hammett (ρ = -2.25) and Brønsted plots (β = 0.54) closely resemble those obtained for the analogous reactions of 2-thiophenesulfonyl chloride and benzenesulfonyl chloride, indicating a similar transition-state structure for all three substrates. An addition-elimination mechanism, in which the rate-determining step is the aniline nucleophilic attack to the substrate, is proposed.