Pyridine-N-oxide

Pyridine-N-oxide

Names
IUPAC name Pyridine-N-oxide
Other names pyridine-1-oxide
Identifiers
CAS Number	694-59-7
3D model (Jmol)	Interactive image
ChEBI	CHEBI:29136
ChemSpider	12229
ECHA InfoCard	100.010.705
PubChem	12753
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
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).
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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 peracids as the oxidising agent.^[1] The molecule is planar. The compound is used infrequently as an oxidizing reagent in organic synthesis.^[2] It also serves as a ligand in coordination chemistry.

Synthesis and reactions

The oxidation of pyridine is effected with peracetic acid, a reaction that affords the protonated derivative. Subsequent treatment with base liberates the neutral oxide.^[3]

Pyridine N-oxide is about 10⁵ less basic than pyridine. It does however form an isolable hydrochloride [C₅H₅NOH]Cl. Chlorination of the N-oxide with phosphorus oxychloride gives 4- and 2-chloropyridines.^[4]

Safety

The compound is a skin irritant.

References

1. J. Meisenheimer (1926). "Über Pyridin-, Chinolin- und Isochinolin-N-oxyd". Berichte der deutschen chemischen Gesellschaft. 59 (8): 1848–1853. doi:10.1002/cber.19260590828.
2. S. Nicholas Kilényi "Pyridine N-Oxide" in Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons, New York. doi:10.1002/047084289X.rp283 Article Online Posting Date: April 15, 2001
3. H. S. Mosher, L. Turner, and A. Carlsmith (1963). "Pyridine-N-oxide". Org. Synth.; Coll. Vol., 4, p. 828
4. E. F. V. Scriven "Pyridines and their Benzo Derivatives: (ii) Reactivity at Ring Atoms" in Comprehensive Heterocyclic Chemistry 1984, Volume 2, Pages 165–314. doi:10.1016/B978-008096519-2.00027-8