NUCLEOPHILIC-SUBSTITUTION REACTIONS OF PHENYL CHLOROFORMATES

Methanolysis and aminolysis of phenyl chloroformates in acetonitrile have been investigated. The rates are slow due to initial-state stabilization by strong resonance electron donation form the phenoxy group. In both reactions the large positive values of rho(Y) = 0.8-1.6 and low Delta H-double dagger and Delta S double dagger values show that the transition state is strongly associative with little bond breaking. This mechanism is supported by the relatively large solvent isotope effect, k(MeOH)/k(MeOD) congruent to 2.3-2.5, and by the relatively strong inverse secondary kinetic isotope effect, k(H)/k(D) congruent to 0.74-0.94, involving deuteriated aniline nucleophiles, in addition to a negative value of rho(XY). The dependence of aniline basicity, beta(X)(beta(nuc)) congruent to 0.8, and the rho(X) values of -2.3 are similar to those corresponding values for the reactions of benzoyl chlorides which have been predicted to react by an associative S(N)2 mechanism. These observations are consistent with a concerted displacement mechanism for the methanolysis and aminolysis of phenyl chloroformates.