Kinetics of the reaction between 1,2-dinitrobenzene and piperidine in n-hexane. Role of electron donor–acceptor complexes in the mechanism. Catalysis by pyridine

Abstract

The denitration of 1,2-dinitrobenzene (1,2-DNB) by piperidine (PIP) in n-hexane follows a wholly base-catalysed S_NAr mechanism. The curvilinear dependence of the apparent second-order rate constant (K_A) on PIP concentration is explained in terms of an electron donor–acceptor (EDA) complex between 1,2-DNB and PIP prior to the formation of the σ-intermediate. The fact that the association constant for this complex calculated from kinetic data agrees quite well with the spectroscopic measurements supports this proposal. The kinetics of the reaction in the presence of pyridine are best explained in terms of an association between piperidine and pyridine in an effect that could be described as catalysis of catalysis.