3-Methylpyridine

3-Methylpyridine
Names

Other names 3-picoline
Identifiers
CAS Registry Number	108-99-6^Y
ChEBI	CHEBI:39922^Y
ChEMBL	ChEMBL15722^N
ChemSpider	7682^Y
InChI InChI=1S/C6H7N/c1-6-3-2-4-7-5-6/h2-5H,1H3 Key: ITQTTZVARXURQS-UHFFFAOYSA-N
Jmol-3D images	Image
SMILES Cc1cccnc1
Properties
Chemical formula	C₆H₇N
Molar mass	93.13 g/mol
Appearance	Colorless liquid
Density	0.957 g/mL
Melting point	−19 °C (−2 °F; 254 K)
Boiling point	144 °C (291 °F; 417 K)
Solubility in water	Miscible
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
N verify (what is: Y/N?)
Infobox references

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 is a colourless liquid with a strong odor. It is classified as a weak base.

Synthesis

3-Methylpyridine is produced industrially by the reaction of acrolein with ammonia:

2 CH₂CHCHO + NH₃ → 3-CH₃C₅H₄N + 2 H₂O

This reaction is nonselective and a more efficient route starts with acrolein, propionaldehyde, and ammonia:

CH₂CHCHO + CH₃CH₂CHO + NH₃ → 3-CH₃C₅H₄N + 2 H₂O + H₂

It may also be obtained as a co-product of pyridine synthesis from acetaldehyde, formaldehyde, and ammonia via Chichibabin pyridine synthesis. Approximately 9,000,000 kilograms were produced worldwide in 1989. ^[1]

Uses

3-Picoline is a useful precursor to agrochemicals, such as chlorpyrifos.^[2] Chlorpyrifos is produced from 3,5,6-trichloro-2-pyridinol, which is generated from 3-picoline by way of cyanopyridine. This conversion involves the ammoxidation of 3-methylpyridine:

3-CH₃C₅H₄N + 1.5 O₂ + NH₃ → 3-NCC₅H₄N + 3 H₂O

3-Cyanopyridine is also a precursor to 3-pyridinecarboxamide, which is a precursor to pyridinecarbaldehydes:

3-NCC₅H₃N + [H] + catalyst → 3-HC(O)C₅H₄N

Pyridinecarbaldehydes are used to make antidotes for poisoning by organophosphate acetylcholinesterase inhibitors.

Environmental Behavior

Pyridine derivatives (including 3-methylpyridine) are environmental contaminants, generally associated with processing fossil fuels, such as oil shale or coal.^[3] They are also found in the soluble fractions of crude oil spills. They have also been detected at legacy wood treatment sites. The high water solubility of 3-methyl pyridine increases the potential for the compound to contaminate water sources. 3-methyl pyridine is biodegradable, although it degrades more slowly and volatilize more readily from water samples than either 2-methyl- or 4-methyl-pyridine.,^[4]^[5]

Niacin

3-Methylpyridine is the main precursor to niacin, one of the B vitamins. Niacin is the generic name for both nicotinic acid and nicotinamide (pyridine 3-carboxylic acid and pyridine 3-carboxylic acid amide). Nicotinic acid was first synthesized in 1867 by oxidative degradation of nicotine.^[6] Niacin is also an important food additive for domestic and farm animals; more than 60% of the niacin produced is consumed by poultry, swine, ruminants, fish, and pets. Along with its use as an essential vitamin, niacin is also a precursor to many of commercial compounds including cancer drugs, antibacterial agents, and pesticides. Approximately 10,000,000 kilograms of niacin are produced annually worldwide.^[6]

Niacin is prepared by hydrolysis of nicotinonitrile, which, as described above, is generated by oxidation of 3-picoline. Oxidation can be effected by air, but ammoxidation is more efficient.^[6] The catalysts used in the reaction above are derived from the oxides of antimony, vanadium, and titanium. New “greener” catalysts are being tested using manganese-substituted aluminophosphates that use acetyl peroxyborate as non-corrosive oxidant.^[7] The use of this catalyst/oxidizer combination is greener because it does not produce nitrogen oxides as do traditional ammoxidations.

References