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Nucleophilic substitution at the pyridine ring. Kinetics of the reaction of 2-chloro-3,5-dinitropyridine with arylthiolates in methanol

✍ Scribed by Ezzat A. Hamed

Publisher: John Wiley and Sons
Year: 1997
Tongue: English
Weight: 129 KB
Volume: 29
Category: Article
ISSN: 0538-8066
DOI: 10.1002/(sici)1097-4601(1997)29:7<515::aid-kin5>3.0.co;2-x

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✦ Synopsis

The reaction rates of 2-chloro-3,5-dinitropyridine 1 with a series of arylthiolates 2a-h in methanol have been measured at 25°C. The products are the corresponding 2-thioaryl-3,5-dinitropyridine 3a-h. Good Hammett correlation with value Ϫ1.19 was obtained suggesting an elimination-addition mechanism S N Ar and the formation of Meisenheimer-like intermediates. Plot of log k 2 vs. pK a values of arylthiols gave straight line with ␤ ϭ 0.38 indicating that the -bond breaking in the pyridine ring is so much advanced over bond making between the nucleophile and the carbon that bears the chlorine atom. Excellent correlation between log k 2 and log K (carbon basicity of arylthiolates) was obtained.

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