The kinetics and mechanism of the spontaneous hydrolysis of 4-chlorophenyl isocyanate in diethyl ether solution

Abstract

The kinetics of hydrolysis of 4-chlorophenyl isocyanate have been studied at low concentrations in diethyl ether solution at three temperatures. When the ratio [H₂O] : [RNCO] is sufficiently large the final organic product is 4-chloroaniline only, which arises from the loss of carbon dioxide from the initially formed carbamic acid, RNHCO₂H. In the presence of a sufficient excess of water, the overall process comprises two consecutive first-order reactions [equation (4)], whose pseudo-first-order rate constants k₁ and k₂ both depend on the third power of the stoicheiometric water concentration. For the first reaction ΔH^‡≃ 22 kJ mol^–1 and ΔS^‡≃–202 J mol^–1 K^–1; for the second reaction ΔH^‡= 22 ± 1 kJ mol^–1 and ΔS^‡=–216 ± 3 J mol^–1 K^–1. We interpret our results in terms of cyclic transition states involving trimeric water. Ours is the first kinetic investigation to detect the two-stage process of aniline formation.