Kinetics and Mechanism of the Aminolysis of O-Methyl-S-Phenylthiocarbonates in Methanol

2003

Kinetic studies of the reaction of O-methyl-S-phenylthiocarbonates with benzylamines in methanol at 45.0 ℃ have been carried out. The reaction proceeds by a stepwise mechanism in which the rate-determining step is the breakdown of the zwitterionic tetrahedral intermediate, , with a hydrogen-bonded four-center type transition state (TS). These mechanistic conclusions are drawn based on (ⅰ) the large magnitude of , (ⅱ) the normal kinetic isotope effects $(k_H/k_D\;>\;1.0)$ involving deuterated benzylamine nucleophiles, (ⅲ) the positive sign of and the larger magnitude of than that for normal processes, and lastly (ⅳ) adherence to the reactivity-selectivity principle (RSP) in all cases.

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