2-Pyridone

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2-Pyridone
2-Pyridone
2-Pyridone
2-Pyridone molecule (lactam form)
2-Pyridone molecule (lactim form)
Names
Preferred IUPAC name
Pyridin-2(1H)-one
Other names
2(1H)-Pyridinone
2(1H)-Pyridone
1H-Pyridine-2-one
2-Pyridone
1,2-Dihydro-2-oxopyridine
1H-2-Pyridone
2-Oxopyridone
2-Pyridinol
2-Hydroxypyridine
Identifiers
3D model (
JSmol
)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.005.019 Edit this at Wikidata
EC Number
  • 205-520-3
KEGG
RTECS number
  • UV1144050
UNII
  • InChI=1S/C5H5NO/c7-5-3-1-2-4-6-5/h1-4H,(H,6,7) checkY
    Key: UBQKCCHYAOITMY-UHFFFAOYSA-N checkY
  • InChI=1/C5H5NO/c7-5-2-1-3-6-4-5/h1-4,7H
    Key: GRFNBEZIAWKNCO-UHFFFAOYAT
  • InChI=1/C5H5NO/c7-5-3-1-2-4-6-5/h1-4H,(H,6,7)
    Key: UBQKCCHYAOITMY-UHFFFAOYAK
  • lactim: Oc1ccccn1
  • lactam: C1=CC=CNC(=O)1
Properties
C5H5NO
Molar mass 95.101 g·mol−1
Appearance Colourless crystalline solid
Density 1.39 g/cm3
Melting point 107.8 °C (226.0 °F; 380.9 K)
Boiling point 280 °C (536 °F; 553 K) decomp.
Solubility in other solvents Soluble in
water,
methanol, acetone
Acidity (pKa) 11.65
UV-vis (λmax) 293 nm (ε 5900, H2O soln)
Structure
Orthorhombic
planar
4.26 D
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 irritating
GHS labelling:
GHS06: ToxicGHS07: Exclamation mark
Danger
H301, H315, H319, H335
P261, P264, P270, P271, P280, P301+P310, P302+P352, P304+P340, P305+P351+P338, P312, P321, P330, P332+P313, P337+P313, P362, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability (yellow): no hazard codeSpecial hazards (white): no code
2
1
Flash point 210 °C (410 °F; 483 K)
Related compounds
Other anions
 2-Pyridinolate
Other cations
 2-Hydroxypyridinium-ion
lactim,
pyridine, ketone
Related compounds
 pyridine, thymine, cytosine,
uracil, benzene
Supplementary data page
2-Pyridone (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

2-Pyridone is an organic compound with the formula C
5H
4NH(O). It is a colourless solid. It is well known to form hydrogen bonded dimers and it is also a classic case of a compound that exists as tautomers.

Tautomerism

tautomerism

The second

lactim tautomerism can also be exhibited in many related compounds.[1]

Tautomerism in the solid state

The amide group can be involved in hydrogen bonding to other nitrogen- and oxygen-containing species.

The predominant solid state form is 2-pyridone. This has been confirmed by X-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), and IR-spectroscopy, which shows that the C=O longitudinal frequency is present whilst the O-H frequencies are absent.[2][3][4][5]

Tautomerism in solution

The tautomerization has been exhaustively studied. The energy difference appears to be very small.

alcohols and water favour the 2-pyridone.[1][6][7]

The energy difference for the two tautomers in the gas phase was measured by IR-spectroscopy to be 2.43 to 3.3 kJ/mol for the solid state and 8.95 kJ/mol and 8.83 kJ/mol for the liquid state.[8][9][10]

Tautomerisation mechanism A

The single molecular tautomerisation has a forbidden

energy barrier for this tautomerisation, which was calculated with theoretical methods to be 125 or 210 kJ/mol. The direct tautomerisation is energetically not favoured. There are other possible mechanisms for this tautomerisation.[10]

Dimerisation

dimer

2-Pyridone and 2-hydroxypyridine can form dimers with two hydrogen bonds.[11]

Aggregation in the solid state

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 by X-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]

Aggregation in solution

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 the

equilibrium constants in the system is extremely difficult.[11][12][13][14][15][16][17][18][19][20]

(

molecules
).

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.

Tautomerisation mechanism B

The direct tautomerisation is not energetically favoured, but a

dimerisation followed by a double proton transfer and dissociation
of the dimer is a self catalytic path from one tautomer to the other. Protic solvents also mediate the proton transfer during the tautomerisation.

Synthesis

2-Pyrone can be obtained by a cyclisation reaction, and converted to 2-pyridone via an exchange reaction with ammonia:

2-Pyridone synthesis from 2-pyran

Pyridine forms an N-oxide with some oxidation agents such as hydrogen peroxide. This pyridine-N-oxide undergoes a rearrangement reaction to 2-pyridone in acetic anhydride:[21][22][23]

2-Pyridone synthesis from pyridine-N-oxide

In the Guareschi-Thorpe condensation

2-pyridone.[12][13] The reaction is named after Icilio Guareschi and Jocelyn Field Thorpe.[14][15]

Chemical properties

Catalytic activity

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 with

quantum chemical methods.[16][17][24]

Coordination chemistry

2-Pyridone and some

ligands in coordination chemistry, usually as a 1,3-bridging ligand akin to carboxylate.[18]

In nature

2-Pyridone is not naturally occurring, but a derivative has been isolated as a cofactor in certain hydrogenases.[19]

Environmental behavior

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 bacterium Arthrobacter crystallopoietes,[25] a member of the phylum Actinomycetota 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 of Arthrobacter 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 in quinoline degradation,[27] also owing to transformation of metabolites, however the yellow pigments often reported in degradation of many pyridine solvents, such as unsubstituted pyridine or picoline, generally result from overproduction of riboflavin 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]

See also

References

  1. ^ a b c Forlani L., Cristoni G., Boga C., Todesco P. E., Del Vecchio E., Selva S., Monari M. (2002). "Reinvestigation of tautomerism of some substituted 2-hydroxypyridines".
    hdl:2027/spo.5550190.0003.b18
    .
  2. ^
    S2CID 9505447
    .
  3. ^
    doi:10.1107/S0365110X5300168X
    .
  4. ^
    S2CID 97575334
    .
  5. ^
    doi:10.1107/S0567740871003753
    .
  6. doi:10.1021/ja00500a001
    .
  7. doi:10.1039/p29760001428
    .
  8. doi:10.1021/ja00523a050
    .
  9. doi:10.1021/ar50113a006
    .
  10. ^
    PMID 11765793
    .
  11. ^
    doi:10.1021/ja00729a012
    .
  12. ^
    ISBN 0-470-20481-8
  13. ^
    doi:10.1107/S1600536803029295
    .
  14. ^ a b I. Guareschi (1896). "Mem. Reale Accad. Sci. Torino II". {{cite journal}}: Cite journal requires |journal= (help)
  15. ^
    doi:10.1039/ct9048501726. Archived
    from the original on 2020-09-14. Retrieved 2020-06-05.
  16. ^ a b Fischer 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
    .
  17. ^
    doi:10.1002/jlac.199619961003. Archived
    from the original on 2021-09-01. Retrieved 2021-09-01.
  18. ^
    doi:10.1016/0010-8545(94)01117-T
    .
  19. ^ a b Shima, 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.
  20. ^
    doi:10.2134/jeq1985.00472425001400040022x. Archived from the original
    on 2008-08-30.
  21. doi:10.1248/yakushi1947.67.3-4_51
    .
  22. doi:10.1021/jo01133a010
    .
  23. doi:10.1021/jo01061a037
    .
  24. S2CID 98273691. Archived from the original
    (subscription required) on 2008-10-30. Retrieved 2006-11-07.
  25. S2CID 6389661
    .
  26. ^
    doi:10.1080/10643388909388372. Archived from the original
    (PDF) on 2010-05-27.
  27. doi:10.1016/S0964-8305(96)00032-7
    .
  28. PMID 16348793
    .

Further reading

General

  1. Engdahl K., Ahlberg P. (1977). Journal of Chemical Research: 340–341. {{cite journal}}: Missing or empty |title= (help)
  2. 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".
    doi:10.1021/ja00490a046
    .
  3. Bensaude O, Dreyfus G, Dodin G, Dubois J (1977). "Intramolecular Nondissociative Proton Transfer in Aqueous Solutions of Tautomeric Heterocycles: a Temperature-Jump Kinetic Study".
    doi:10.1021/ja00455a037
    .
  4. Bensaude O, Chevrier M, Dubois J (1978). "Influence of Hydration upon Tautomeric Equilibrium".
    doi:10.1016/S0040-4039(01)86850-7
    .
  5. Hammes GG, Park AC (1969). "Kinetic and Thermodynamic Studies of Hydrogen Bonding".
    doi:10.1021/ja01032a028
    .
  6. Hammes GG, Spivey HO (1966). "A Kinetic Study of the Hydrogen-Bond Dimerization of 2-Pyridone".
    PMID 5942979
    .
  7. 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".
    doi:10.1021/ja00441a079
    .
  8. 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".
    doi:10.1021/jo01296a001
    .
  9. 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".
    doi:10.1021/jo01296a002
    .

Tautomerism
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