Catalysis in aromatic nucleophilic substitution. Part 12.1 Kinetics of the reactions of some 2-phenoxy- and 2-(p-nitrophenoxy)-3-nitro-5-X-thiophenes with benzylamine and N-benzylmethylamine in benzene

Abstract

The rate constants of the title reactions have been measured in benzene at 20 °C. The reactions with benzylamine are not base-catalysed. The second-order kinetic constant for the reactions with N-benzylmethylamine, with the exception of the unsubstituted compound (X = H), increases in a hyperbolical way with increasing nucleophile concentration. A non-linear regression treatment of kinetic data allows the calculation of k₁ and k₃^B/k_–1 for each catalysed system. k₃^B/k_–1 is not a monotonic function of the X substituent. This result has been rationalised on the grounds of a specific base–general acid (SB–GA) mechanism for the base catalysis.