Pyridine

Pyridine
General
Systematic name	Pyridine
Other names	Azabenzene Azine
Molecular formula	C₅H₅N
SMILES	C1=NC=CC=C1
Molar mass	79.10 g/mol
Appearance	colourless liquid
CAS number	^*
Properties
Density and phase	0.9819 g/cm³, liquid
Solubility in water	Miscible
Solubility in ethanol	Miscible
Melting point	−41.6 °C
Boiling point	115.2 °C
Viscosity	0.94 cP at 20 °C
Thermodynamic data
Standard enthalpy of formation Δ_fH°_liquid	101.2 kJ/mol
Standard enthalpy of combustion Δ_cH°_liquid	−2783.2 kJ/mol
Standard molar entropy S°_liquid	? J.K⁻¹.mol⁻¹
Hazards
EU classification	Flammable (F) Harmful (Xn)
NFPA 704
R-phrases	, , ,
S-phrases	, ,
Flash point	20 °C
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Regulatory data	Flash point, RTECS number, etc.
Related compounds
Related amines	Picoline Quinoline
Related compounds	Aniline Pyrimidine
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Chemical infobox

Pyridine is a clear liquid with an odor that is sour, putrid, and fish-like. Pyridine is a simple heterocyclic aromatic organic compound that is structurally related to benzene, with one CH group in the six-membered ring replaced by a nitrogen atom. Pyridine is obtained from crude coal tar or is synthesized from acetaldehyde, formaldehyde and ammonia.

Pyridine has an equatorial lone pair of electrons at the nitrogen atom that does not participate in the aromatic pi-system. This makes pyridine a basic compound with chemical properties similar to tertiary amines with a pKa of the conjugate acid of 5.30. Pyridine is protonated by reaction with acids and forms a positively charged aromatic polyatomic ion called pyridinium cation. The bond lengths and bond angles in pyridine and the pyridinium ion do not differ greatly Tadeusz M. Krygowski, Halina Szatyowicz, and Joanna E. Zachara J. Org. Chem. 2005 70(22) 8859 - 8865; DOI: 10.1021/jo051354h Abstract because protonation does not involve the aromatic pi system.

Pyridine is also a good nucleophile with a donor number of 33.1.

Pyridine is widely used as a solvent and reagent in organic chemistry and it is also a starting material in the synthesis of compounds used as an intermediate in making insecticides, herbicides, pharmaceuticals, food flavorings, dyes, rubber chemicals, adhesives, paints, explosives and disinfectants. Pyridine is also used as a denaturant for antifreeze mixtures, for ethyl alcohol, and for fungicides, and as a dyeing aid for textiles.

Other examples of the pyridine class can be formed by the reaction of 1,5-diketones with ammonium acetate in acetic acid followed by oxidation.

Pyridine is a harmful substance if inhaled, ingested or absorbed through skin, it is known to reduce male fertility and is considered carcinogenic as well. Common symptoms of exposure to pyridine include: headache, coughing, asthmatic breathing, laryngitis, nausea and vomiting.

Related compounds

Structurally or chemically related compounds are

DMAP is short for 4-dimethylaminopyridine
Bipyridine and viologen are simple polypyridine compounds consisting of two pyridine molecules joined by a single bond
Terpyridine, a molecule of three pyridine rings connected together by two single bonds.
Quinoline and Isoquinoline have pyridine and a benzene ring fused together.
Aniline is a benzene derivative with an attached NH₂ group and NOT a pyridine
Diazines are compounds with one more carbon replaced by nitrogen such as Pyrazine and Pyramidine
Triazines are compounds with two more carbons replaced by nitrogen
2,6-lutidine is a trivial name for 2,6-dimethylpyridine.
collidine is a trivial name for 2,4,6-trimethylpyridine.
Pyridinium p-toluenesulfonate (PPTS) is a salt formed by proton exchange between pyridine and p-toluenesulfonic acid

References

External links

Simple aromatic rings | Nitrogen heterocycles | Amines | Solvents | Foul-smelling chemicals

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Related compounds

See also

References

External links