Effects of ortho‐ and para‐Ring Activation on the Kinetics of SNAr Reactions of 1‐Chloro‐2‐nitro‐ and 1‐Phenoxy‐2‐nitrobenzenes with Aliphatic Amines in Acetonitrile
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Crampton, M. R.
Emokpae, T. A.
Batsanov, A. S.,
Howard, J. A., & Mondal, R.
Rate constants are reported for reaction of 4‐substituted 1‐chloro‐2,6‐dinitrobenzenes 1, 6‐substituted 1‐chloro‐2,4‐dinitrobenzenes 2, and some of the corresponding 1‐phenoxy derivatives, 3 and 4, with n‐butylamine, pyrrolidine and piperidine in acetonitrile as solvent. Values of k1, the rate constant for nucleophilic attack at the 1‐position, increase with increasing ring‐activation but may be reduced by steric repulsion at the reaction centre which increases in the order Cl < OPh, and n‐butylamine < pyrrolidine ≈ piperidine. ortho‐Substituents may also have adverse steric effects, and those of the trifluoromethyl group are particularly serious. X‐ray crystal structures of phenyl 2,4‐dinitro‐6‐trifluoromethylphenyl ether and phenyl 2,6‐dinitro‐4‐trifluoromethylphenyl ether are reported. Base catalysis in the 1‐phenoxy derivatives is attributed to rate‐limiting proton transfer from the zwitterionic intermediates 6 to base. Values of rate constants for this process decrease with increasing steric congestion at the reaction centre and in the order n‐butylamine > pyrrolidine > piperidine.
Research Subject Categories::NATURAL SCIENCES::Chemistry::Physical chemistry::Kinetics , Base catalysis , substituents effect , steric hinderance , Nucleophilic aromatic substitution
Crampton, M. R., Emokpae, T. A., Isanbor, C., Batsanov, A. S., Howard, J. A., & Mondal, R. (2006). Effects of ortho‐and para‐Ring Activation on the Kinetics of SNAr Reactions of 1‐Chloro‐2‐nitro‐and 1‐Phenoxy‐2‐nitrobenzenes with Aliphatic Amines in Acetonitrile. European journal of organic chemistry, 2006(5), 1222-1230.