Étude de la substitution nucléophile aromatique. II. Cinétique de la réaction du chlorure de picryle avec l'imidazole et schéma réactionnel de l'action des amines sur les chloro-nitro-arènes

In: Bulletin de la Classe des sciences, Band 56, Heft 1, S. 1047-1063

Abstract

Picrylchloride (CP, on mole) reacts quantitatively with imidazole (IA, two moles), in CHC13 as solvent, giving N-picrylimidazole (PI, one mole), as it was already mentionned in the first paper of this series.
This system (CP-IA) does not follow a simple kinetic law : it has been observed that at relatively low concentration in IA ([IA] = b ; [CP] = a. ml-1) the apparent second order rate constant, k'2, depends linearly of b(k'2 = k2o + k3b, if b = 2a) ; at relatively high concentration (b > 20a), on the contrary, k'2 is independent of [IA], being a true second order constant
(k'2 = k2).
Now considering the whole body of our experimental results, relatively to the systems of DNCB-Amines, CP-Amines (first paper), and CP-Imidazoles (this paper), taking also in account the fact that a foreign base (diaza-bicyclo-octane) does not affect the reactivity of the formers, while it accelarates the last, which is also sensitive to the catalysis by the solvent (CHCl3), we developed a reaction scheme consisting of two steps : both reactants (A and B) generate an intermediate (Z), which decomposes in the products. As to the concentration of Z, the kinetic law is based on the steady state treatment which conforms to the experimental equation. The difference in behaviour of the various systems can best be explained in terms of structural differences of Z.