The Effects of Ring Substituents and Leaving Groups on the Kinetics of SNAr Reactions of 1‐Halogeno‐ and 1‐Phenoxy‐nitrobenzenes with Aliphatic Amines in Acetonitrile

Abstract

AbstractRate constants are reported for the reactions of a series of 1‐chloro‐, 1‐fluoro‐ and 1‐phenoxy‐nitrobenzenes activated by CF3 or CN groups or by ring‐nitrogen with n‐butylamine, pyrrolidine or piperidine in acetonitrile. The results are compared with results reported previously for more strongly ring‐activated compounds. Decreasing ring activation leads to lower values of k1 for nucleophilic attack although this may be mediated by reduced steric congestion around the reaction centre. Specific steric effects, leading to rate‐retardation, is noted for the ortho‐CF3 group. The 1‐phenoxy compounds are subject to base catalysis and values of kAm/k–1 are reduced relative to more strongly activated compounds. This is likely to reflect increases in values of k–1 coupled with decreases in values of kAm as the proton transfer from zwitterionic intermediates to catalysing amine becomes less thermodynamically favourable. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)