Title: Pyridine
CAS Registry Number: 110-86-1
Molecular Formula: C5H5N
Molecular Weight: 79.10
Percent Composition: C 75.92%, H 6.37%, N 17.71%
Literature References: Discovered in coal tar: T. Anderson, Ann. 60, 86 (1846). Physical data: B. A. Middleton, J. R. Partington, Nature 141, 516 (1938). Acute toxicity study: H. F. Smyth Jr. et al., Arch. Ind. Hyg. Occup. Med. 4, 119 (1951). Books: H. Maier-Bode, Das Pyridin und Seine Derivate in Wissenschaft und Technik (Edwards Bros., Ann Arbor, Mich., 1943); Hill in Chemistry of Coal Utilization vol 2, H. H. Lowry, Ed. (Wiley, New York, 1945), Chapter 27; The Chemistry of Heterocyclic Compounds vol. 14, a series of books entitled "Pyridine and its Derivatives": Parts 1-4, E. Klingsberg, Ed. (1960-1964); Suppl. Parts 1-4, R. A. Abramovitch, Ed. (1974-1975); Part 5, G. R. Newkome, Ed. (1984) (Wiley-Interscience, New York). Review: G. L. Goe in Kirk-Othmer Encyclopedia of Chemical Technology vol. 19 (Wiley-Interscience, New York, 3rd ed., 1982) pp 454-483. Review of commercial synthesis and uses of pyridine and derivatives: D. J. Berry, Spec. Chem. 3, 13 (1983); of occurrence of pyridine and derivatives in foods, tobacco and essential oils: G. Vernin, Perfum. Flavor. 7, 23-26 (1982); of use in the study of surface properties of transition metal oxides: M. C. Kung, H. H. Kung, Catal. Rev. Sci. Eng. 27, 425-460 (1985). Review of toxicology and environmental fate: A. Jori et al., Ecotoxicol. Environ. Saf. 7, 251 (1983); and human exposure: Toxicological Profile for Pyridine (PB93-110831, 1992) 108 pp.
Properties: Flammable, colorless liq; characteristic disagreeable odor; sharp taste. d420 0.98272. Flash pt, closed cup: 68°F (20°C). mp -41.6°. bp 115.2-115.3°. nD20 1.50920. Dipole moment in benzene: 2.26. Forms an azeotropic mixture with 3 mols water, boiling at 92-93°. Volatile with steam. Miscible with water, alcohol, ether, petr ether, oils and many other organic liquids. Good solvent for many organic and inorganic compds. Weak base; forms salts with strong acids. pKa 5.19. pH of 0.2 molar soln in H2O: 8.5. LD50 orally in rats: 1.58 g/kg (Smyth).
Melting point: mp -41.6°
Boiling point: bp 115.2-115.3°; Forms an azeotropic mixture with 3 mols water, boiling at 92-93°
Flash point: Flash pt, closed cup: 68°F (20°C)
pKa: pKa 5.19
Index of refraction: nD20 1.50920
Density: d420 0.98272
Toxicity data: LD50 orally in rats: 1.58 g/kg (Smyth)
CAUTION: Potential symptoms of overexposure are headache, nervousness, dizziness and insomnia; nausea, anorexia; eye irritation; dermatitis; liver and kidney damage. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 272.
Use: As solvent for anhydr mineral salts. Synthetic intermediate in laboratory and industry.
Pyridine 1-Oxide Pyridinium Bromide Perbromide Pyridinium Chlorochromate Pyridinol Carbamate Pyridofylline

Full structural formula of pyridine Skeletal formula of pyridine, showing the numbering convention
Ball-and-stick diagram of pyridine Space-filling model of pyridine
Pyridine sample.jpg
CAS number 110-86-1 YesY
PubChem 1049
ChemSpider 1020 YesY
EC number 203-809-9
KEGG C00747 YesY
Jmol-3D images Image 1
Molecular formula C5H5N
Molar mass 79.10 g mol−1
Appearance colorless liquid
Density 0.9819 g/mL[1]
Melting point −41.6 °C; −42.9 °F; 231.6 K
Boiling point 115.2 °C; 239.4 °F; 388.3 K
Solubility in water Miscible
Vapor pressure 18 mmHg
Acidity (pKa) 5.25 (for the conjugate acid)[2][3]
Refractive index (nD) 1.5093
Viscosity 0.88 cP
Dipole moment 2.2 D[4]
MSDS External MSDS
EU classification Flammable (F)
Harmful (Xn)
R-phrases R20 R21 R22 R34 R36 R38
NFPA 704
NFPA 704.svg
Flash point 21 °C; 70 °F; 294 K
Threshold Limit Value 5 ppm (TWA)
Related compounds
Related amines Picoline
Related compounds Aniline
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one methine group (=CH-) replaced by a nitrogen atom. The pyridine ring occurs in many important compounds, including azines and the vitamins niacin and pyridoxal.

Pyridine was discovered in 1849 by the Scottish chemist Thomas Anderson as one of the constituents of bone oil. Two years later, Anderson isolated pure pyridine through fractional distillation of the oil. It is a colorless, highly flammable, weakly alkaline, water-soluble liquid with a distinctive, unpleasant fish-like odor.

Pyridine is used as a precursor to agrochemicals and pharmaceuticals and is also an important solvent and reagent. Pyridine is added to ethanol to make it unsuitable for drinking (see denatured alcohol). It is used in the in vitro synthesis of DNA,[6] in the synthesis of sulfapyridine (a drug against bacterial and viral infections), antihistaminic drugs tripelennamine and mepyramine, as well as water repellents, bactericides, and herbicides. Some chemical compounds, although not synthesized from pyridine, contain its ring structure. They include B vitamins niacin and pyridoxal, the anti-tuberculosis drug isoniazid, nicotine and other nitrogen-containing plant products.[7] Historically, pyridine was produced from coal tar and as a by-product of the coal gasification. However, increased demand for pyridine resulted in the development of more economical methods of synthesis from acetaldehyde and ammonia, and more than 20,000 tonnes per year are manufactured worldwide.