Kinetic Evidence for Hypervalent Intermediate in Acid Hydrolysis of N-Arylbenzenesulfinamides

Nucleophilic substitution reactions of sulfinic acid derivatives occur with predominent inversion of configuration at sulfur. These results are mainly interpreted by an addition elimination mechanism with a trigonal bipyramidal reaction intermediate (sulfurane) and a concerted SN2 displacement mechanism. The isolation of stabilized bicyclic sulfurances suggests that these species may form as intermediates in nucleophilic substitution reactions of sulfinic acid derivatives. However, despite continuing efforts, there are very rare definitive experiments to demonstrate the formation of these intermediates. Some years ago, we reported acid catalyzed hydrolysis of some simple sulfinamides. In this report, we found downward breaks in the pH-rate profile for acid catalyzed hydrolysis of sulfinamides having electron donating group in the leaving group, aniline. These data provided the first unequivocal evidence that nucleophilic substitution reaction at sulfinyl sulfur may proceed by a two-step mechanism through a hypervalent reaction intermediate. In this study, we have extended our study to identify the hypervalent intermediate in acid catalyzed reactions of sulfinamides having halide or more stronger electron donating group in the leaving group or the sulfinyl group. So, we have performed the acid catalyzed hydrolyses of N-(3methyl-5-methoxyphenyl)-benzenesulfinamide (1-a), N(tolyl)-toluenesulfinamide (1-b), N-(4-fluorophenyl)-toluenesulfinamide (1-c), N-(4-ethylphenyl)-benzenesulfinamide (1-d) and N-(4-fluorophenyl)-benzenesulfinamide (1-e).