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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.

Crampton, M. R. and Emokpae, T. A. and Isanbor, C. and Batsanov, A. S. and Howard, J. A. K. and 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). pp. 1222-1230.

Abstract

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.

Item Type:Article
Keywords:Kinetics, Nucleophilic aromatic substitution, Steric hindrance, Substituent effects.
Full text:Full text not available from this repository.
Publisher Web site:http://dx.doi.org/10.1002/ejoc.200500774
Record Created:26 Apr 2007
Last Modified:08 Apr 2009 16:30

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