The stabilities of Meisenheimer complexes. Part 34. Kinetic studies of σ-adduct formation and nucleophilic substitution in the reactions of 2,4,6-trinitrophenetole with aliphatic amines in dimethyl sulphoxide

Abstract

The reaction of 2,4,6-trinitrophenetole with aliphatic amines in dimethyl sulphoxide results in the formation of anionic σ-adducts via zwitterionic intermediates. Rapid attack at the 3-position is followed by attack at the ethoxy-substituted 1-position. The 1-adducts formed by reaction with n-butylamine and benzylamine undergo acid-catalysed expulsion of ethoxide to yield N-substituted picramides; that formed by reaction with piperidine is relatively stable. Rate and equilibrium data for these reactions have been determined and compared with data for reactions of related compounds. Increased steric crowding at the reaction centre caused by a change from primary amines to piperidine results in reductions in the rate of proton transfer from zwitterionic intermediates to amine catalyst and in the rate of leaving-group expulsion.