The stabilities of Meisenheimer complexes. Part 33. Kinetic studies of the formation of isomeric σ-adducts from 2,4,6-trinitrobenzyl chloride and aliphatic amines in dimethyl sulphoxide

Abstract

Kinetic and equilibrium data are reported for the reversible colour-forming reactions of 2,4,6-trinitro-benzyl chloride with some aliphatic amines in dimethyl sulphoxide and are compared with data for reactions of 1,3,5-trinitrobenzene. With n-butylamine and benzylamine three processes are observable : attack at the 3-position, attack at the 1-position, and transfer of a side-chain proton. For piperidine and pyrrolidine only two-of these are observable, attack at the 1-position being disfavoured for steric reasons. The formation of anionic σ-adducts occurs via zwitterionic intermediates and it is shown that the proton-transfer step may be kinetically significant. Reductions of rate constants for proton-transfer below the values expected for diffusion-controlled reaction are attributed to steric effects which are increased when reaction involves secondary amines and when the CH₂Cl group is at the reaction site. Specific effects of chloride ions are noted and are attributed to their interaction with substituted ammonium ions.