Pyridine-N-oxide

Pyridine-N-oxide
Names
	Preferred IUPAC name 1λ5-Pyridin-1-one
	Other names Pyridine-1-oxide
Identifiers
CAS Number	694-59-7 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:29136 ;
ChemSpider	12229 ;
ECHA InfoCard	100.010.705
PubChem CID	12753;
UNII	91F12JJJ4H ;
CompTox Dashboard (EPA)	DTXSID3061007 ;
	InChI InChI=1S/C5H5NO/c7-6-4-2-1-3-5-6/h1-5H Key: ILVXOBCQQYKLDS-UHFFFAOYSA-N ; InChI=1/C5H5NO/c7-6-4-2-1-3-5-6/h1-5H Key: ILVXOBCQQYKLDS-UHFFFAOYAZ;
	SMILES c1cc[n+](cc1)[O-];
Properties
Chemical formula	C5H5NO
Molar mass	95.101 g·mol−1
Appearance	Colourless solid
Melting point	65 to 66 °C (149 to 151 °F; 338 to 339 K)
Boiling point	270 °C (518 °F; 543 K)
Solubility in water	high
Acidity (pKa)	0.8 (of conjugate acid)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Pyridine-N-oxide is the heterocyclic compound with the formula C₅H₅NO. This colourless, hygroscopic solid is the product of the oxidation of pyridine. It was originally prepared using peroxyacids as the oxidising agent. The compound is used infrequently as an oxidizing reagent in organic synthesis.^[1]

Structure

The structure of pyridine-N-oxide is very similar to that of pyridine with respect to the parameters for the ring. The molecule is planar. The N-O distance is 1.34 Å. The C-N-C angle is 124°, 7° wider than in pyridine.^[2]

Synthesis

The oxidation of pyridine can be achieved with a number of peracids including peracetic acid and perbenzoic acid.^[3] Oxidation can also be effected by a modified Dakin reaction using a urea-hydrogen peroxide complex,^[4] and sodium perborate^[5] or, using methylrhenium trioxide (CH
₃ReO
₃) as catalyst, with sodium percarbonate.^[6]

Reactions

Pyridine N-oxide is five orders of magnitude less basic than pyridine: the pK_a of protonated pyridine-N-oxide is 0.8.^[7] Protonated derivatives are isolable, e.g., [C₅H₅NOH]Cl.^[3] Further demonstrating its (feeble) basicity, pyridine-N-oxide also serves as a ligand in coordination chemistry. A host of transition metal complexes of pyridine-N-oxides are known.

Treatment of the pyridine-N-oxide with phosphorus oxychloride gives 4- and 2-chloropyridines.^[8]

Related pyridine-N-oxides

The N-oxides of various pyridines are precursors to useful drugs:^[9]

Nicotinic acid N-oxide, derived from nicotinic acid is a precursor to niflumic acid and pranoprofen.
2,3,5-trimethylpyridine N-oxide is a precursor to the drug omeprazole
2-chloropyridine N-oxide is a precursor to the fungicide zinc pyrithione

Safety

The compound is a skin irritant.^[1]

References

^ ^a ^b Kilényi, S. Nicholas; Mousseau, James J. (20 September 2015). "PyridineN-Oxide". Pyridine N-Oxide. Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. pp. 1–6. doi:10.1002/047084289X.rp283.pub2. ISBN 9780470842898.
^ Ülkü, D.; Huddle, B. P.; Morrow, J. C. (1971). "The Crystal Structure of Pyridine 1-oxide". Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry. 27 (2): 432–436. Bibcode:1971AcCrB..27..432U. doi:10.1107/S0567740871002334.
^ ^a ^b Mosher, H. S.; Turner, L.; Carlsmith, A. (1953). "Pyridine-N-oxide". Org. Synth. 33: 79. doi:10.15227/orgsyn.033.0079.
^ Varma, Rajender S.; Naicker, Kannan P. (1999). "The Urea−Hydrogen Peroxide Complex: Solid-State Oxidative Protocols for Hydroxylated Aldehydes and Ketones (Dakin Reaction), Nitriles, Sulfides, and Nitrogen Heterocycles". Org. Lett. 1 (2): 189–192. doi:10.1021/ol990522n.
^ McKillop, Alexander; Kemp, Duncan (1989). "Further functional group oxidations using sodium perborate". Tetrahedron. 45 (11): 3299–3306. doi:10.1016/S0040-4020(01)81008-5.
^ Jain, Suman L.; Joseph, Jomy K.; Sain, Bir (2006). "Rhenium-Catalyzed Highly Efficient Oxidations of Tertiary Nitrogen Compounds to N-Oxides Using Sodium Percarbonate as Oxygen Source". Synlett. 2006 (16): 2661–2663. doi:10.1055/s-2006-951487.
^ Chmurzyński, L. (1996). "Studies on correlations of acid-base properties of substituted pyridine N-oxides in solutions. Part 1. Correlations of the p Ka values in non-aqueous solvents and water". Analytica Chimica Acta. 321 (2–3): 237–244. doi:10.1016/0003-2670(95)00594-3.
^ Scriven, E. F. V. (1984). "Pyridines and their Benzo Derivatives: (ii) Reactivity at Ring Atoms". In Katritzky, Alan R.; Rees, Charles Wayne; Meth-Cohn, Otto (eds.). Comprehensive Heterocyclic Chemistry: The Structure, Reactions, Synthesis and Uses of Heterocyclic Compounds. Vol. 2. Pergamon Press. pp. 165–314. doi:10.1016/B978-008096519-2.00027-8. ISBN 9780080307015.
^ Shimizu, Shinkichi; Watanabe, Nanao; Kataoka, Toshiaki; Shoji, Takayuki; Abe, Nobuyuki; Morishita, Sinji; Ichimura, Hisao (2000). "Pyridine and Pyridine Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_399. ISBN 3527306730.

[eEROS-1] Kilényi, S. Nicholas; Mousseau, James J. (20 September 2015). "PyridineN-Oxide". Pyridine N-Oxide. Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. pp. 1–6. doi:10.1002/047084289X.rp283.pub2. ISBN 9780470842898.

[2] Ülkü, D.; Huddle, B. P.; Morrow, J. C. (1971). "The Crystal Structure of Pyridine 1-oxide". Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry. 27 (2): 432–436. Bibcode:1971AcCrB..27..432U. doi:10.1107/S0567740871002334.

[pyridine-N-oxide_hydrochloride-3] Mosher, H. S.; Turner, L.; Carlsmith, A. (1953). "Pyridine-N-oxide". Org. Synth. 33: 79. doi:10.15227/orgsyn.033.0079.

[4] Varma, Rajender S.; Naicker, Kannan P. (1999). "The Urea−Hydrogen Peroxide Complex: Solid-State Oxidative Protocols for Hydroxylated Aldehydes and Ketones (Dakin Reaction), Nitriles, Sulfides, and Nitrogen Heterocycles". Org. Lett. 1 (2): 189–192. doi:10.1021/ol990522n.

[5] McKillop, Alexander; Kemp, Duncan (1989). "Further functional group oxidations using sodium perborate". Tetrahedron. 45 (11): 3299–3306. doi:10.1016/S0040-4020(01)81008-5.

[6] Jain, Suman L.; Joseph, Jomy K.; Sain, Bir (2006). "Rhenium-Catalyzed Highly Efficient Oxidations of Tertiary Nitrogen Compounds to N-Oxides Using Sodium Percarbonate as Oxygen Source". Synlett. 2006 (16): 2661–2663. doi:10.1055/s-2006-951487.

[7] Chmurzyński, L. (1996). "Studies on correlations of acid-base properties of substituted pyridine N-oxides in solutions. Part 1. Correlations of the p Ka values in non-aqueous solvents and water". Analytica Chimica Acta. 321 (2–3): 237–244. doi:10.1016/0003-2670(95)00594-3.

[8] Scriven, E. F. V. (1984). "Pyridines and their Benzo Derivatives: (ii) Reactivity at Ring Atoms". In Katritzky, Alan R.; Rees, Charles Wayne; Meth-Cohn, Otto (eds.). Comprehensive Heterocyclic Chemistry: The Structure, Reactions, Synthesis and Uses of Heterocyclic Compounds. Vol. 2. Pergamon Press. pp. 165–314. doi:10.1016/B978-008096519-2.00027-8. ISBN 9780080307015.

[9] Shimizu, Shinkichi; Watanabe, Nanao; Kataoka, Toshiaki; Shoji, Takayuki; Abe, Nobuyuki; Morishita, Sinji; Ichimura, Hisao (2000). "Pyridine and Pyridine Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_399. ISBN 3527306730.

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