Aromatic nucleophilic substitutions with o- and p-fluoronitrobenzenes in aprotic solvents. Steric effects on the base-catalysed step

Abstract

The kinetics of the reaction between o- and p-fluoronitrobenzene with n- and iso-propylamine were studied in toluene and DMSO at several amine concentrations and temperatures in the range 30–100 °C. The results show that, contrary to the previous assumption, primary steric effects due to branching in the amine do not produce a large decrease in the reaction rate when the first step is rate determining. However, reactions with bulky amines can be extremely slow because of the reduced power of the amine as a hydrogen-bond acceptor catalyst, when the second step is rate determining. The reaction rate may be increased by the addition of a non-nucleophilic base of another hydrogen-bond acceptor catalyst such as dimethyl sulphoxide.