The stabilities of Meisenheimer complexes. Part 38. Kinetic and equilibrium studies of the reactions of 2,2′,4,4′,6,6′-hexanitrostilbene with aliphatic amines in dimethyl sulphoxide

Abstract

Kinetic and equilibrium data are reported for the reactions of 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) with four aliphatic amines in dimethyl sulphoxide, and are compared with those for related aromatic nitro-compounds. With each amine the most rapid reaction involves σ-adduct formation by attack at the 3(3′)-positions. With the primary amines, n-butylamine and benzylamine, isomerisation to the thermo-dynamically more stable 1(1′)-adducts occurs. However, with the secondary amines piperidine and pyrrolidine, attack at the 1(1′)-positions is not observed, and this is attributed to their high steric requirements. It is shown that the formation of σ-adducts may involve rate-limiting proton transfer from zwitterionic intermediates to amine. A slow reaction is observed between HNS and each amine and is likely to involve amine attack at the olefinic bond.