Kinetics and mechanism of the aminolysis of cycloalkyl arenesulfonates

Abstract

Nucleophilic substitution reactions of cycloalkyl arenesulfonates (C_nH_2n–1OSO₂C₆H₄Z) with anilines in acetonitrile at 65.0 °C are studied. The reactivity decreases in the order n= 5 > 7 > 4 > 6, which is influenced by angular deformation energies in the transition state (TS), steric effect and exoergicity of the reaction. The cross-interaction constants, ρ_xz, between substituents in the nucleophile (X) and nucleofuge (Z) for all the cycloalkyl compounds, irrespective of the ring size, are uniformly the same (0.11) as those observed for isopropyl arenesulfonates. This indicates that the TS for S_N2 processes at a secondary carbon atom is substantially looser than that at a primary carbon for which a greater ρ_xz value (0.33) has been reported, regardless of the size of the group attached to the reaction centre. The TS shifts toward an earlier position along the reaction coordinate, and becomes more asymmetric, as the ring size decreases, n= 7→4, in accordance with the Bell–Evans–Polanyi principle.