Mechanism of pyridyne formation from halopyridines

Abstract

Rates of hydrogen-deuterium exchange of 3-chloro- and 3,5-dichloropyridine in MeOD-MeONa were studied. Deuterodeprotonation of 3-chloropyridine at 110·2° is 53 times faster at H-4 than at H-2. At 75° the value of the ortho chloro rate factor for exchange is 800; the para nitrogen rate factor is 3000. Interrupted dehydrohalogenation of 3-chloropyridine-2 or 4- d and 3-iodopyridine-4 d in NH 3NaNH 2 to give 3,4-pyridyne results in no detectable loss of label at 2 in the chloropyridine but reduction and enrichment of 4- d in the chloro and iodo compounds, respectively. Results are interpreted in terms of the reactions of halopyridyl anions.