Nucleophilic substitution reactions of anilino thioethers with anilines in methanol

Abstract

Kinetic studies have been carried out on the solvolysis and aminolysis with anilines of anilino thioethers, N-methyl-N-[(Z-phenylthio)methyl]-Y-anilines, YC6H4N(CH3)CH2SC6H4Z, I, in methanol at 45.0°C. In contrast to the iminium cations with significant lifetimes produced in water, the solvolysis proceeds by a direct displacement (SN2) mechanism in methanol. In the aminolysis, both bond formation and cleavage are well under way in a late SN2 transition state with high ρX (βX) and ρZ (βZ) values. However, cross interactions between the nucleophile and leaving group are extensive with large negative constants (ρXZ=−1.7, βXZ=−0.27), which are suggestive of an SN2 reaction with frontside attack. The inverse secondary kinetic isotope effects involving deuterated anilines (kH/kD=0.84–0.88) along with low ΔH≠ (4.2–5.2 kcal mol−1) and ΔS≠ (−46–−59 e.u.) values are consistent with the proposed mechanism.