Kinetics and mechanism of the reaction of para‐chlorophenyl aryl chlorophosphates with anilines in acetonitrile

The kinetics and mechanism of the nucleophilic substitution reactions of p‐chlorophenyl aryl chlorophosphates ( 2 ) with anilines are investigated in acetonitrile at 55°C. Relatively large magnitudes of ρ_X and β_X values are indicative of a large degree of bond making in the TS. Smaller magnitudes of ρ_X (0.20 for X = H) and ρ_XY (?0.30) than those for the corresponding reactions with phenyl aryl chlorophosphates ( 1 ) (ρ_X = 0.54 for X = H and ρ_XY = ?1.31) are interpreted to indicate partial electron loss, or shunt, towards the electron acceptor equatorial ligand (p‐ClC₆H₄O‐) in the bipyramidal pentacoordinated transition state. The inverse secondary kinetic isotope effects (k_H/k_D = 0.64–0.87) involving deuterated aniline (ND₂C₆H₄X) nucleophiles, and small ΔH^? and large negative ΔS^? are obtained. These results are consistent with a concerted nucleophilic substitution mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 632–637, 2002