Kinetics and Mechanism of the Pyridinolysis of Diisopropyl ThiophosphinicChloride in Acetonitrile

摘要

The kinetic studies on the pyridinolysis of diisopropyl thiophosphmic chloride have been carried out in acetonitrile at 55.0 °C. The free energy correlations for substituent X variations in the X-pyridines are biphasic concave upwards with a break point at X = 3-Ph. A concerted S_n2 mechanism is proposed with a change of the attacking direction of the X-pyridine from a frontside attack for the strongly basic pyridines to a backside attack for the weakly basic pyridines. The factors to determine the rates and thio effects on the rates for the pyridinolyses of thiophophinic chloride, chlorothiophosphate, phosphinic chloride, phosphonochloridothioate, and chlorophosphate systems are briefly reviewed on the basis of the magnitude of the positive charge of the reaction center P atom and steric effects of the two ligands.