Pyridinolysis of phenyl-substituted phenyl chlorophosphates in acetonitrile

The kinetics and mechanism of the reactions of phenyl-substituted phenyl ch lorophosphates, I, with pyridines in acetonitrile are investigated at 25.0 degrees C. The rates are much faster and the transition state is much earli er on the reaction coordinate with smaller beta(X) (0.16-0.18) and smaller negative beta(XY) (-0.011) values than those for the corresponding reaction s with anilines. The vertical approach of the pyridine ring to an apical po sition of the trigonal bipyramidal transition state enables the p(pi)-d(pi) overlap between the pi orbital of pyridine and an empty d-orbital of phosp horus with less steric hindrance in a concerted process. The activation par ameters are in line with the proposed mechanism.