Nucleophilic substitutions in carbonic acid derivatives. Part I. Kinetics and mechanisms of the reaction of ethyl chloroformate with substituted anilines

Abstract

The second-order rate constants of urethane formation from ethyl chloroformate and meta- or para-substituted anilines were determined conductimetrically in anhydrous acetone. From the obtained activation parameter values (ΔS‡ and ΔH‡) a two-step addition–elimination mechanism is established. By means of a Hammett-type plot as well as a plot of ΔH‡ against ΔS‡ it was possible to postulate the rate-determining step; that is, nucleophilic attack in the case of electron-withdrawing substituted anilines and chloride ion elimination in the case of aniline itself, as well as its electron-releasing substituted derivatives.