Picoline refers to three different methylpyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...

 isomers, all with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 and a molar mass
Molar mass
Molar mass, symbol M, is a physical property of a given substance , namely its mass per amount of substance. The base SI unit for mass is the kilogram and that for amount of substance is the mole. Thus, the derived unit for molar mass is kg/mol...

 of 93.13 g mol−1. All three are colourless liquids at room temperature and pressure and 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, or 2-picoline, is the compound described with formula C6H7N. 2-picoline is a colorless liquid that has an unpleasant odor similar to pyridine. Pyridines including 2-picoline are most crudely prepared by the reaction of acetylene and hydrogen cyanide.-Synthesis:2-Picoline was the...

, α-picoline
[109-06-8] -66.7 129.4 5.96
3-Methylpyridine, or 3-picoline, is the organic compound with formula 3-CH3C5H4N. It is one of the three isomers of methylpyridine. This colorless liquid is a precursor to pyridine derivatives that have applications in the pharmaceutical and agricultural industries. Like pyridine, 3-methylpyridine...

, β-picoline
[108-99-6] -18 141 5.63
4-Methylpyridine is the organic compound with the formula CH3C5H4N. It is one of the three isomers of methylpyridine. This colourless pungent liquid is a building block for the synthesis of other heterocyclic compounds...

, γ-picoline
[108-89-4] 3.6 145.4 5.98

CAS registry number
CAS Registry Numbersare unique numerical identifiers assigned by the "Chemical Abstracts Service" toevery chemical described in the...

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. 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.
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