Kinetics and mechanism of the aminolysis of Z-thiophenyl acetates with X-benzylamines are investigated in acetonitrile at 45.0∩. The magnitudes of Bronsted coefficients モx (=1.3~-1.6) and モz (= -2.1~-2.4) are all large and cross-interaction constant ヱxz is relatively large and positive (0.90). These trends are consistent with the rate-limiting breakdown of a tetrahedral intermediate, T【. The proposed mechanism is also supported by adherence of the rate data to the reactivity-selectivity principle (RSP). The kinetic isotope effects, kH/kD, are greater than unity (1.3-1.4) suggesting a possibility of hydrogen-bonded four-centered transition state. The activation parameters, ツH × and ツS × , are consistent with this transition-state structure.
展开▼
