Pyridinolysis of phenyl-substituted phenyl chlorophosphates in acetonitrile

The kinetics and mechanism of the reactions of phenyl-substituted phenyl chlorophosphates, I, with pyridines in acetonitrile are investigated at 25.0 degrees C. The rates are much faster and the transition state is much earlier 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 reactions with anilines. The vertical approach of the pyridine ring to an apical position 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 phosphorus with less steric hindrance in a concerted process. The activation parameters are in line with the proposed mechanism.