Kinetics and mechanism of the aminolysis of aryl propanedithioates in acetonitrile†
Abstract
The kinetics and mechanism of the aminolysis of aryl proanedithioates with benzylamines are investigated in acetonitrile at −35.0 °C. A large magnitude of the Hammett (ρX and ρZ) and Brönsted (βX and βZ) coefficients and exceptionally large cross-interaction constant ρXZ(= 3.5) are consistent with a stepwise mechanism in which leaving group expulsion from an intermediate, T±, is the rate-determining step. The faster rates observed for dithio esters (II) than for thio esters (I), and the validity of the reactivity-selectivity principle (RSP) are also in line with the mechanism proposed. The kH/kD values (= 1.0–1.8) determined with deuterated benzylamines (XC6H4CH2ND2) and the activation parameters, ΔH≠(≃ 8 kcal mol−1) and ΔS≠(= −16 to −23 e.u.), suggest that proton transfer occurs concurrently with leaving group departure in the transition state.