Pyridine-N-oxide

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Pyridine-N-oxide
Pyridine-N-oxide.png
Pyridine-N-oxide-3D-balls.png
Names
Preferred IUPAC name
1λ5-Pyridin-1-one
Other names
Pyridine-1-oxide
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.010.705 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 211-774-6
PubChem CID
UNII
  • InChI=1S/C5H5NO/c7-6-4-2-1-3-5-6/h1-5H Yes check.svgY
    Key: ILVXOBCQQYKLDS-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C5H5NO/c7-6-4-2-1-3-5-6/h1-5H
    Key: ILVXOBCQQYKLDS-UHFFFAOYAZ
  • c1cc[n+](cc1)[O-]
Properties
C5H5NO
Molar mass 95.101 g·mol−1
AppearanceColourless solid
Melting point 65 to 66 °C (149 to 151 °F; 338 to 339 K)
Boiling point 270 °C (518 °F; 543 K)
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).
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Pyridine-N-oxide is the heterocyclic compound with the formula C5H5NO. This colourless, hygroscopic solid is the product of the oxidation of pyridine. Its synthesis was first reported by Jakob Meisenheimer, who used peroxybenzoic acid as the oxidant. [1] The compound is used infrequently as an oxidizing reagent in organic synthesis. [2]

Contents

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. [3]

Synthesis

The oxidation of pyridine can be achieved with a number of peroxy acids, including peracetic acid and peroxybenzoic acid. [4] Oxidation can also be effected by a modified Dakin reaction using a urea–hydrogen peroxide complex, [5] and sodium perborate [6] or, using methylrhenium trioxide (CH
3ReO
3) as catalyst, with sodium percarbonate. [7]

Reactions

Pyridine N-oxide is five orders of magnitude less basic than pyridine: the pKa of protonated pyridine-N-oxide is 0.8. [8] Protonated derivatives are isolable, e.g., [C5H5NOH]Cl. [4] 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. [9]

Pyridine-N-oxides are uncommon in nature. 2-(Methyldithio)pyridine-N-oxide and related compounds have been isolated from species of Allium. [10]

The N-oxides of various pyridines are precursors to useful drugs: [11]

Safety

The compound is a skin irritant. [2]

Further reading

References

  1. ↑ Meisenheimer, Jakob (1926). "Über Pyridin-, Chinolin- und Isochinolin-N-oxyd". Ber. Dtsch. Chem. Ges. (in German). 59 (8): 1848–1853. doi:10.1002/cber.19260590828.
  2. 1 2 Kilényi, S. Nicholas; Mousseau, James J. (20 September 2015). "Pyridine N-Oxide". Encyclopedia of Reagents for Organic Synthesis . John Wiley & Sons. pp. 1–6. doi:10.1002/047084289X.rp283.pub2. ISBN   9780470842898.
  3. ↑ 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.
  4. 1 2 Mosher, H. S.; Turner, L.; Carlsmith, A. (1953). "Pyridine-N-oxide". Org. Synth. 33: 79. doi:10.15227/orgsyn.033.0079.
  5. ↑ 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.
  6. ↑ 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.
  7. ↑ 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.
  8. ↑ 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.
  9. ↑ 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.
  10. ↑ o'Donnell, Gemma; Poeschl, Rosemarie; Zimhony, Oren; Gunaratnam, Mekala; Moreira, Joao B. C.; Neidle, Stephen; Evangelopoulos, Dimitrios; Bhakta, Sanjib; Malkinson, John P.; Boshoff, Helena I.; Lenaerts, Anne; Gibbons, Simon (2009). "Bioactive Pyridine- N -oxide Disulfides from Allium stipitatum". Journal of Natural Products. 72 (3): 360–365. Bibcode:2009JNAtP..72..360O. doi:10.1021/np800572r. PMC   2765505 . PMID   19093848.
  11. ↑ 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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