Kinetics and Mechanism of the Aminolysis of Diphenyl Phosphinic Chloride with Anilines

Abstract

The aminolyses of diphenyl phosphinic chloride (1) with substituted anilines in acetonitrile at 55.0 oC are investigated kinetically. Large Hammett ρ X (ρnuc = ?4.78) and Bronsted β X (βnuc = 1.69) values suggest extensive bond formation in the transition state. The primary normal kinetic isotope effects (kH/kD = 1.42-1.82) involving deuterated aniline (XC6H4ND2) nucleophiles indicate that hydrogen bonding results in partial deprotonation of the aniline nucleophile in the rate-limiting step. The faster rate of diphenyl phosphinic chloride (1) than diphenyl chlorophosphate (2) is rationalized by the large proportion of a frontside attack in the reaction of 1. These results are consistent with a concerted mechanism involving a partial frontside nucleophilic attack through a hydrogen-bonded, four-center type transition state.