|Density||0.9819 g/cm³, liquid|
|Solubility in water||Miscible|
|Viscosity||0.94 cP at 20 °C|
|EU classification||Flammable (F)
|Flash point||21 °C|
|Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Pyridine is a fundamentally important chemical compound with the formula C5H5N. It is a liquid with a distinctively putrid, fishy odor. Its molecules have a six-membered ring structure that can be found in many compounds, including the nicotinamides.
This compound has numerous applications. It is both a versatile solvent and a building block for a variety of other organic compounds. It is a starting material in the manufacture of insecticides, herbicides, pharmaceuticals, food flavorings, dyes, rubber chemicals, adhesives, paints, explosives, and disinfectants. In addition, it is a denaturant for antifreeze mixtures and is sometimes used as a ligand in coordination chemistry.
Pyridine can be classified as a heterocyclic aromatic organic compound. Each molecule of pyridine is a six-membered ring related to the structure of benzene—one CH group in the benzene ring is replaced by a nitrogen atom.
Pyridine has a lone pair of electrons at the nitrogen atom. Because this lone pair is not delocalized into the aromatic system of "pi" electrons, pyridine is basic, with chemical properties similar to those of tertiary amines.
Pyridine is protonated by reaction with acids and forms a positively charged aromatic polyatomic ion called a pyridinium cation. This cation is the conjugate acid of pyridine and its pKa has a value of 5.30.
The bond lengths and bond angles in pyridine and the pyridinium ion are almost identical. This is because protonation of pyridine does not affect the aromatic pi system.
Pyridine was originally isolated industrially from crude coal tar. There are now many methods in industry and in the laboratory for the synthesis of pyridine and its derivatives.
By substituting other aldehydes for acetaldehyde, one can obtain alkyl and aryl substituted pyridines. 26,000 tons were produced worldwide in 1989.
In organic reactions, pyridine behaves as a tertiary amine with protonation, alkylation, acylation and N-oxidation at the nitrogen atom. It also behaves as an aromatic compound with nucleophilic substitutions.
Pyridine is toxic. (Its oral lethal dose LD50 in rats was found to be 891 mg kg–1). It is volatile and can be absorbed through the skin. Available data indicate that "exposure to pyridine in drinking-water led to reduction of sperm motility at all dose levels in mice and increased estrous cycle length at the highest dose level in rats".
Currently, its evaluations as a possible carcinogenic agent showed there is inadequate evidence for the carcinogenicity of pyridine in humans, albeit there is limited evidence of carcinogenic effects on animals.
Effects of acute pyridine intoxication include dizziness, headache, nausea, and anorexia. Further symptoms include abdominal pain and pulmonary congestion. Though resistant to oxidation, pyridine is readily degraded by bacteria, releasing ammonium and carbon dioxide as terminal degradation products.
Structurally or chemically related compounds are:
|Chemical class: Alcohol • Aldehyde • Alkane • Alkene • Alkyne • Amide • Amine • Azo compound • Benzene derivative • Carboxylic acid • Cyanate • Ester • Ether • Haloalkane • Imine • Isocyanide • Isocyanate • Ketone • Nitrile • Nitro compound • Nitroso compound • Peroxide • Phosphoric acid • Pyridine derivative • Sulfone • Sulfonic acid • Sulfoxide • Thioether • Thiol • Toluene derivative|
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