Linear free energy ortho-correlations in the reactions of some 2-bromo-5-nitro-3-X-thiophenes with primary and secondary amines in benzene

Abstract

The kinetics of S_NAr reactions of some 2-bromo-3-X-5-nitrothiophenes (X = Me, H, Br, CONH₂, CO₂Me, COMe, SO₂Me, CN and NO₂) with some primary (n-butylamine and benzylamine) and secondary (pyrrolidine, piperidine, morpholine and N-benzylamine) amines have been measured in benzene as a function of nucleophile concentration. Most of the reactions studied show apparent kinetic constants little affected or not affected by an increase in amine concentration, indicating that the overall reaction rate is controlled by the formation of the reaction intermediate. The reactions of the substrates where X = Br and CN with the two primary amines proved to be base-catalysed. The k₃^B/k₋₁ values calculated for these substituents are inconsistent with the hypothesis of a base catalysis for the intermediate decomposition and strongly suggest a catalysis of the first step of the reaction pathway.