Aromatic nucleophilic substitution reactions of 1,2-dinitrobenzene with aliphatic primary amines in n-hexane; catalysis by non-nucleophilic bases

Abstract

The kinetics of the reactions of 1,2-dinitrobenzene with n-butyl-, s-butyl-, isobutyl-, n-propyl-, and isopropyl-amine in n-hexane at various temperatures have been investigated. The second-order rate coefficients for these reactions increase linearly with the amine concentrations. The values of the ratio of the rate constant for the catalysed process to the rate constant of the uncatalysed step [k₃^RNH₂/k₂] are dependent on temperature, so that it is possible to minimize the catalysed or uncatalysed processes simply by temperature variation. Kinetic studies in the presence of non-nucleophilic bases [pyridine, triethylamine (TEA), and tributylamine (TBA)] confirmed the proposal that all these reactions are base-catalysed even for the cases where k₃^RNH₂/k₂ is less than 50. The role that electron donor–acceptor complex formation between reactants may play in the mechanism of these reactions is discussed. The influence of electronic and steric effects in the amine structure on the catalytic rate constant has been analysed. It has been shown that the catalysed step is disfavoured by electron-donating substituents and that it is inhibited by steric hindrance. The studies with the addition of the bulky bases TEA and TBA confirmed these conclusions.