18617-77-1Relevant articles and documents
The Mechanisms of Thermal Eliminations. Part 11. Rate Data for Pyrolysis of 2-Alkoxypyridines to 2-Pyridone, and of 2-Ethoxypicolines to 2-Picolones: Nature and Polarity of the Transition State
Al-Awadi, Nouria,Ballam, John,Hemblade, Paul R.,Taylor, Roger
, p. 1175 - 1178 (2007/10/02)
The rates of thermal elimination of 2-ethoxy-, 2-isopropoxy-, 2-t-butoxy-pyridine to 2-pyridone and the corresponding alkene, and of the 2-ethoxy derivatives of 3-, 4-, 5-, and 6-methylpyridines to ethylene and the corresponding 2-picolines have been measured over at least 50 deg for each compound, between 585.1 and 721.1 K.The respective log (A/s-1) and Ea/kJ mol-1 values for the former three compounds are 12.20, 196.5; 12.68, 187.6; and 12.33, 161.0, and these are similar to those for the corresponding acetates.The relative rates of the first-order unimolecular decomposition at 600 K are: Et(1.0), Pri(18.0), But(1645) compared with 1.0:28.8:3316 for the acetates.The polarity of the transition state is thus less than for ester elimination.The difference in the rate ratios k(Pri)/k(Et) for alkoxypyridine and acetate pyrolyses is greater than the difference in the k(But)/k(Pri) ratios and is interpreted in terms of the difference in polarity of the transition states for primary, secondary, and tertiary elimination.Methyl substituents in the 3-, 4-, 5-, and 6-positions of the pyridine ring change the rate at 600 K by factors of 1.57, 1.02, 0.74, and 1.08, respectively.These show the decomposition does not take place via N-alkylpyridone tautomers, and that the reaction is, like ester pyrolysis, sterically accelerated.
