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Nucleophilic substitutions at the pyridine ring: Kinetics of the reaction of 2-chloro-3-nitro and 2-chloro-5-nitropyridines with piperidine and morpholine in methanol and benzene

✍ Scribed by Ezzat A. Hamed

Publisher: John Wiley and Sons
Year: 1997
Tongue: English
Weight: 148 KB
Volume: 29
Category: Article
ISSN: 0538-8066
DOI: 10.1002/(sici)1097-4601(1997)29:8<599::aid-kin5>3.0.co;2-p

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✦ Synopsis

The kinetics of the reactions of 2-chloro-3-nitropyridine (ortho-like) and 5-nitro ( para-like) isomer with morpholine and piperidine were studied in methanol and benzene at several amine concentrations and temperatures in the range 25 -45°C. The data show that k 3-NO 2 /k 5-NO 2 ratios are less than unity in methanol. The steric hindrance in the transition state of the 3-nitro (ortho-like) isomer retards o-substitution while the stability of p-quinonoid structure of the 5-nitro ( para-like) isomer favors p-substitution. In benzene, the k 3-NO2 /k 5-NO2 ratios are greater than unity. The hydrogen bonding formation between the ammonium hydrogen and the ortho-nitro group in the transition state of 3-nitro isomer favors the o-substitution.

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