3-methylpyridine

3-Methylpyridine
Identifiers
CAS number 108-99-6 YesY
ChemSpider 7682 YesY
Properties
Molecular formula C6H7N
Molar mass 93.13 g/mol
Appearance Colorless liquid
Density 0.957 g/mL
Melting point

-19 °C

Boiling point

144 °C

Solubility in water Miscible
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.

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.[3] 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.[3]

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.[3] 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.[4] The use of this catalyst/oxidizer combination is greener because it does not produce nitrogen oxides as do traditional ammoxidations.

See also

References

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