Mechanism of SO2 elimination from the aromatic sulfonamide anions: A theoretical study

Based on the density functional theory (DFT), the mechanism of SO2 elimination from the aromatic sulfonamide anions has been analyzed in this paper. Three reaction pathways have been proposed. Calculations indicate that the most favorable reaction pathway is Pathway I, namely the nucleophilic attack of the nitrogen anion followed by a three-membered ring rearrangement to lose SO2. It is found there exists good linear relationship between the activation enthalpies and the reaction enthalpies in Pathway I. The corresponding correlation coefficient is as high as 0.931. The Marcus theory analyses suggest that the major driving force for the acceleration effect of the substituent is the intrinsic factor. Moreover, as for the N-phenyl-benzenesulfonamide anion series, the effect of the substituent in the p-position of the benzene ring has also been studied and moderate linear relationship between the activation enthalpies and the substituent constants can be obtained. Meanwhile, the electron-withdrawing group in the N-substituted benzene ring can hold back the three-membered ring rearrangement to lose SO2, while the similar group in the S-substituted benzene ring has the opposite effect.