Picoline

Picoline refers to three different methylpyridine isomers, all with the chemical formula C₆H₇N and a molar mass of 93.13 g mol⁻¹. All three are colourless liquids at room temperature and pressure, with a characteristic smell similar to pyridine. They are miscible with water and most organic solvents. Data for the three compounds are summarized in the table.

Name(s)	CAS#	m.p. (°C)	b.p. (°C)	pKa of pyridinium ion	structure
2-Methylpyridine, α-picoline, 2-picoline	[109-06-8]	-66.7	129.4	5.96
3-Methylpyridine, β-picoline, 3-picoline	[108-99-6]	-18	141	5.63
4-Methylpyridine, γ-picoline, 4-picoline	[108-89-4]	3.6	145.4	5.98

The CAS number of an unspecified picoline isomer is [1333-41-1]

Environmental properties

Picolines exhibit greater volatility and are more slowly degraded than their carboxylic acid counterparts. Volatilization is much less extensive in soil than water, owing to sorption of the compounds to soil clays and organic matter.^[1] Picoline degradation appears to be mediated primarily by bacteria, with the majority of isolates belonging to the Actinobacteria. 3-Methylpyridine degrades more slowly than the other two isomers, likely due to the impact of resonance in the heterocyclic ring. Like most simple pyridine derivatives, the picolines contain more nitrogen than is needed for growth of microorganisms, and excess nitrogen is generally excreted to the environment as ammonium during the degradation process.^[2]

Derivatives

Pyridoxal

The most well known picoline derivatives are the vitamin B₆ vitamers such as pyridoxine and pyridoxal.

References

1. Sims, G. K. and L.E. Sommers. 1985. Degradation of pyridine derivatives in soil. J. Environmental Quality. 14:580-584.
2. Sims, G. K. and L.E. Sommers. 1986. Biodegradation of pyridine derivatives in soil suspensions. Environmental Toxicology and Chemistry. 5:503-509.

External links

• Picolines at the US National Library of Medicine Medical Subject Headings (MeSH)