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 (S_N2) mechanism in methanol. In the aminolysis, both bond formation and cleavage are well under way in a late S_N2 transition state with high ρ_X (β_X) and ρ_Z (β_Z) values. However, cross interactions between the nucleophile and leaving group are extensive with large negative constants (ρ_XZ=−1.7, β_XZ=−0.27), which are suggestive of an S_N2 reaction with frontside attack. The inverse secondary kinetic isotope effects involving deuterated anilines (k_H/k_D=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.