Reaction of 2,4-dinitrochlorobenzene with aniline. Solvent effects and molecular complex formation

Abstract

The kinetics of the reaction of aniline with 2,4-dinitrochlorobenzene (2,4-DNClB) were studied in several benzene–n-hexane mixtures at 40 °C in the presence of variable amounts of aniline. A linear dependence of the second-order rate coefficients, k_A, with [B] is observed, with a null intercept. Taking into account the non-polar character of the solvent, and the excellent nucleofugacity of chlorine, this kinetic behaviour is interpreted as evidence of the aggregation of aniline, the hydrogen-bonded dimer acting as the nucleophile. Consistent with this interpretation, when the solvent is changed to THF, a good hydrogen-bond acceptor (HBA), the k_A is no longer dependent on [B]. Electron donor–acceptor (EDA) molecular complexes of 2,4-DNClB with benzene and with aniline, and also between aniline and the product, were clearly recognized and the stability constants of each one of these complexes were determined.