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Effects of ortho ‐ and para ‐Ring Activation on the Kinetics of S N Ar Reactions of 1‐Chloro‐2‐nitro‐ and 1‐Phenoxy‐2‐nitrobenzenes with Aliphatic Amines in Acetonitrile
Author(s) -
Crampton Michael R.,
Emokpae Thomas A.,
Isanbor Chukwuemeka,
Batsanov Andrei S.,
Howard Judith A. K.,
Mondal Raju
Publication year - 2006
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200500774
Subject(s) - chemistry , piperidine , pyrrolidine , steric effects , reaction rate constant , medicinal chemistry , nucleophile , trifluoromethyl , butylamine , ether , stereochemistry , photochemistry , kinetics , catalysis , organic chemistry , amine gas treating , physics , alkyl , quantum mechanics
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 k 1 , 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)