2-Pyridone is anorganic compound with the formulaC 5H 4NH(O). It is a colourless solid. It is well known to formhydrogen bonded dimers and it is also a classic case of a compound that exists astautomers.
The predominantsolid state form is 2-pyridone. This has been confirmed byX-ray crystallography which shows that the hydrogen in solid state is closer to the nitrogen than to the oxygen (because of the low electron density at the hydrogen the exact positioning is difficult), andIR-spectroscopy, which shows that the C=O longitudinal frequency is present whilst the O-H frequencies are absent.[2][3][4][5]
The tautomerization has been exhaustively studied. The energy difference appears to be very small.Non-polar solvents favour 2-hydroxypyridine whereaspolar solvents such asalcohols andwater favour the 2-pyridone.[1][6][7]
The energy difference for the two tautomers in the gas phase was measured byIR-spectroscopy to be 2.43 to 3.3kJ/mol for the solid state and 8.95 kJ/mol and 8.83 kJ/mol for the liquid state.[8][9][10]
The single molecular tautomerisation has a forbidden1-3 suprafacialtransition state and therefore has a highenergy barrier for thistautomerisation, which was calculated withtheoretical methods to be 125 or 210 kJ/mol. The direct tautomerisation is energetically not favoured. There are other possible mechanisms for this tautomerisation.[10]
In the solid state the dimeric form is not present; the 2-pyridones form a helical structure over hydrogen bonds. Some substituted 2-pyridones form the dimer in solid state, for example the 5-methyl-3-carbonitrile-2-pyridone. The determination of all these structures was done byX-ray crystallography.In the solid state the hydrogen is located closer to the nitrogen so it could be considered to be right to call the colourless crystals in the flask 2-pyridone.[1][2][3][4][5]
In solution the dimeric form is present; the ratio of dimerisation is strongly dependent on the polarity of the solvent. Polar and protic solvents interact with thehydrogen bonds and moremonomer is formed.Hydrophobic effects innon-polar solvents lead to a predominance of the dimer. The ratio of the tautomeric forms is also dependent on the solvent. All possible tautomers and dimers can be present and form an equilibrium, and the exact measurement of all theequilibrium constants in the system is extremely difficult.[11][12][13][14][15][16][17][18][19][20]
Some publications only focus one of the two possible patterns, and neglect the influence of the other. For example, to calculation of the energy difference of the two tautomers in a non-polar solution will lead to a wrong result if a large quantity of the substance is on the side of the dimer in an equilibrium.
The direct tautomerisation is not energetically favoured, but adimerisation followed by a double proton transfer anddissociation of the dimer is a self catalytic path from one tautomer to the other. Protic solvents also mediate the proton transfer during the tautomerisation.
2-Pyridone catalyses a variety of proton-dependent reactions, for example the aminolysis of esters. In some cases, molten 2-pyridone is used as a solvent. 2-Pyridone has a large effect on the reaction from activated esters withamines innonpolarsolvent, which is attributed to its tautomerisation and utility as a ditopic receptor. Proton transfer from 2-pyridone and its tautomer have been investigated byisotope labeling,kinetics andquantum chemical methods.[16][17][24]
2-Pyridone is rapidly degraded by microorganisms in the soil environment, with a half life less than one week.[20] Organisms capable of growth on 2-pyridone as a sole source of carbon, nitrogen, and energy have been isolated by a number of researchers. The most extensively studied 2-pyridone degrader is the gram positive bacteriumArthrobacter crystallopoietes,[25] a member of the phylumActinomycetota which includes numerous related organisms that have been shown to degrade pyridine or one or more alkyl-, carboxyl-, or hydroxyl-substituted pyridines. 2-Pyridone degradation is commonly initiated by mono-oxygenase attack, resulting in a diol, such as 2,5-dihydroxypyridine, which is metabolized via the maleamate pathway. Fission of the ring proceeds via action of 2,5-dihydroxypyridine monooxygenase, which is also involved in metabolism of nicotinic acid via the maleamate pathway. In the case ofArthrobacter crystallopoietes, at least part of the degradative pathway is plasmid-borne.[26] Pyridine diols undergo chemical transformation in solution to form intensely colored pigments. Similar pigments have been observed inquinoline degradation,[27] also owing to transformation of metabolites, however the yellow pigments often reported in degradation of many pyridine solvents, such as unsubstitutedpyridine orpicoline, generally result from overproduction ofriboflavin in the presence of these solvents.[28] Generally speaking, degradation of pyridones, dihydroxypyridines, and pyridinecarboxylic acids is commonly mediated by oxygenases, whereas degradation of pyridine solvents often is not, and may in some cases involve an initial reductive step.[26]
Cox RH, Bothner-By AA (1969). "Proton magnetic resonance spectra of tautomeric substituted pyridines and their conjugate acids".The Journal of Physical Chemistry.73 (8): 2465.doi:10.1021/j100842a001.
Roberts JD, Von Ostwalden PW (1971). "Nuclear magnetic resonance specroscopy. Proton spectra of 2-pyridones".The Journal of Organic Chemistry.36 (24): 3792.doi:10.1021/jo00823a029.
^abOhms U., Guth H., Heller E., Dannöhl H., Schweig A. (1984). "Comparison of Observed and Calculated Electron-Density 2-Pyridone, C5H5NO, Crystal-Structure Refinements at 295K and 120K, Experimental and Theoretical Deformation Density Studies".Z. Kristallogr.169:185–200.doi:10.1524/zkri.1984.169.14.185.S2CID97575334.
^abAlmlöf J., Kvick A., Olovsson I. (1971). "Hydrogen Bond Studies Crystal Structure of Intermolecular Complex 2-Pyridone-6-Chloro-2-Hdroxypyridine".Acta Crystallogr. B.27 (6):1201–1208.doi:10.1107/S0567740871003753.
^Frank J.,Alan R. Katritzky (1976). "Tautomeric pyridines. XV. Pyridone-hydroxypyridine equilibria in solvents of different polarity".J Chem Soc Perkin Trans 2 (12):1428–1431.doi:10.1039/p29760001428.
^Brown R. S., Tse A., Vederas J. C. (1980). "Photoelectro-Determined Core Binding Energies and Predicted Gas-Phase Basicities for the 2-Hydroxypyridine 2-Pyridone System".Journal of the American Chemical Society.102 (3):1174–1176.doi:10.1021/ja00523a050.
^Beak P. (1977). "Energies and Alkylation of Tautomeric Heterocyclic-Compounds - Old Problems New Answers".Acc. Chem. Res.10 (5):186–192.doi:10.1021/ar50113a006.
^abAbdulla H. I., El-Bermani M. F. (2001). "Infrared studies of tautomerism in 2-hydroxypyridine 2-thiopyridine and 2-aminopyridine".Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy.57 (13):2659–2671.Bibcode:2001AcSpA..57.2659A.doi:10.1016/S1386-1425(01)00455-3.PMID11765793.
^abHammes GG, Lillford PJ (1970). "A Kinetic and Equilibrium Study of Hydrogen Bond Dimerization of 2-Pyridone in Hydrogen Bonding Solvent".J. Am. Chem. Soc.92 (26):7578–7585.doi:10.1021/ja00729a012.
^abFischer C. B., Steininger H., Stephenson D. S., Zipse H. (2005). "Catalysis of Aminolysis of 4-Nitrophenyl Acetate by 2-Pyridone".Journal of Physical Organic Chemistry.18 (9):901–907.doi:10.1002/poc.914.
^abRawson J. M., Winpenny R. E. P. (1995). "The coordination chemistry of 2-pyridones and its derivatives".Coordination Chemistry Reviews.139 (139):313–374.doi:10.1016/0010-8545(94)01117-T.
^abShima, S.; Lyon, E. J.; Sordel-Klippert, M.; Kauss, M.; Kahnt, J.; Thauer, R. K.; Steinbach, K.; Xie, X.; Verdier, L. and Griesinger, C., "Structure elucidation: The cofactor of the iron-sulfur cluster free hydrogenase Hmd: structure of the light-inactivation product", Angew. Chem. Int. Ed., 2004, 43, 2547-2551.
^Ochiai E (1953). "Recent Japanese Work on the Chemistry of Pyridine 1-Oxide and Related Compounds".The Journal of Organic Chemistry.18 (5):534–551.doi:10.1021/jo01133a010.
^Boekelheide V, Lehn WL (1961). "The Rearrangement of Substituted Pyridine N-Oxides with Acetic Anhydride1.2".The Journal of Organic Chemistry.26 (2):428–430.doi:10.1021/jo01061a037.
^Oloughlin E, Kehrmeyer S, Sims G (1996). "Isolation, characterization, and substrate utilization of a quinoline-degrading bacterium".International Biodeterioration & Biodegradation.38 (2):107–118.Bibcode:1996IBiBi..38..107O.doi:10.1016/S0964-8305(96)00032-7.
Engdahl K., Ahlberg P. (1977).Journal of Chemical Research:340–341.{{cite journal}}:Missing or empty|title= (help)
Bensaude O, Chevrier M, Dubois J (1978). "Lactim-Lactam Tautomeric Equilibrium of 2-Hydroxypyridines. 1.Cation Binding, Dimerization and Interconversion Mechanism in Aprotic Solvents. A Spectroscopic and Temperature-Jump Kinetic Study".J. Am. Chem. Soc.100 (22):7055–7066.Bibcode:1978JAChS.100.7055B.doi:10.1021/ja00490a046.
Bensaude O, Dreyfus G, Dodin G, Dubois J (1977). "Intramolecular Nondissociative Proton Transfer in Aqueous Solutions of Tautomeric Heterocycles: a Temperature-Jump Kinetic Study".J. Am. Chem. Soc.99 (13):4438–4446.Bibcode:1977JAChS..99.4438B.doi:10.1021/ja00455a037.
Beak P, Covington JB, Smith SG (1976). "Structural Studies of Tautomeric Systems: the Importance of Association for 2-Hydroxypyridine-2-Pyridone and 2-Mercaptopyridine-2-Thiopyridone".J. Am. Chem. Soc.98 (25):8284–8286.Bibcode:1976JAChS..98.8284B.doi:10.1021/ja00441a079.
Beak P, Covington JB, White JM (1980). "Quantitave Model of Solvent Effects on Hydroxypyridine-Pyridone and Mercaptopyridine-Thiopyridone Equilibria: Correlation with Reaction-Field and Hydrogen-Bond Effects".J. Org. Chem.45 (8):1347–1353.doi:10.1021/jo01296a001.
Beak P, Covington JB, Smith SG, White JM, Zeigler JM (1980). "Displacement of Protomeric Equilibria by Self-Association: Hydroxypyridine-Pyridone and Mercaptopyridine-Thiopyridone Isomer Pairs".J. Org. Chem.45 (8):1354–1362.doi:10.1021/jo01296a002.
Vögeli U., von Philipsborn W. (1973). "C-13 and H-1 NMR Spectroscopie Studies on Structure of N-Methyle-3-Pyridone and 3-Hydroypyridine".Org Magn Reson.5 (12):551–559.doi:10.1002/mrc.1270051202.
Specker H., Gawrosch H. (1942). "Ultraviolet absorption of benztriaxole, pryridone and its salts".Chem. Ber. (75):1338–1348.doi:10.1002/cber.19420751115.
Albert A., Phillips J. N. (1956). "Ionisation Constants of Heterocyclic Substances Hydroxy-Derivates of Nitrogenous Six-Membered Ring-Compounds".J. Chem. Soc.:1294–1304.doi:10.1039/jr9560001294.
Cox R. H., Bothner-By A. A (1969). "Proton Magnetic Resonance Spectra of Tautomeric Substituted Pyridines and Their Conjugated Acides".J. Phys. Chem.73 (8):2465–2468.doi:10.1021/j100842a001.
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