Kinetics of formation and decomposition of the intermediate complex in the reaction of methyl 4-methoxy-3,5-dinitrobenzoate with n-butylamine in dimethyl sulphoxide

Abstract

A stopped-flow spectrophotometric study of the reaction of methyl 4-methoxy-3,5-dinitrobenzoate with n-butylamine in dimethyl sulphoxide has confirmed the formation of an intermediate complex, and kinetic and equilibrium constants have been obtained for its formation and decomposition. The observable intermediate is the conjugate base (M^–) of the zwitterionic complex (MH). Proton transfer between MH and M^– is rapid and intermediate formation is not base-catalysed. The decomposition of M^– is first order in n-butylamine hydrochloride. The mechanism of the overall reaction is shown to involve rapid equilibrium deprotonation of MH, followed by general-acid-catalysed leaving group departure.