2-hydroxypyridine <--> 2-pyridone tautomerization: catalytic influence of formic acid.
A 1:1 hydrogen-bonded complex between 2-pyridone and formic acid has been characterized using laser-induced-fluorescence excitation and dispersed fluorescence spectroscopy in a supersonic jet expansion. Under the same expansion condition, the fluorescence signal of the tautomeric form of the complex (2-hydroxypyridine...formic acid) is absent, although both the bare tautomeric molecules exhibit well-resolved laser-induced-fluorescence spectra. Quantum chemistry calculation at the DFT/B3LYP/6-311++G** level predicts that in the ground electronic state the activation barrier for tautomerization from hydroxy to keto form in bare molecules is very large (approximately 34 kcal/mol). However, the process turns out to be nearly barrierless when assisted by formic acid, and double proton transfer occurs via a concerted mechanism.
Hazra
Montu K
MK
Department of Chemistry, Indian Institute of Technology, Kanpur, UP 208016, India.
Chakraborty
Tapas
T
D002384:Catalysis; D004583:Electrons; D005561:Formates / Q000737:chemistry*; D007536:Isomerism; D008958:Models, Molecular; D008968:Molecular Conformation; D011728:Pyridones / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
D005561:Formates; D011728:Pyridones; C030544:formic acid; C017679:2-hydroxypyridine