Kinetics and mechanism of the aminolysis of diphenyl phosphinic chloride with anilines

The aminolyses of diphenyl phosphinic chloride (1) with substituted anilines in acetonitrile at 55.0°C are investigated kinetically. Large Hammett ρX ( ρnuc = -4.78) and Brönsted βX (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 (XC 6H4ND2) 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.