3-Methylpyridine or 3-picoline, is an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...

with formula 3-CH₃C₅H₄N. It is one of three

positional isomer In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct bonds between them. The term meta ...

s of methylpyridine, whose structures vary according to where the

methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...

is attached around the

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...

ring. This colorless liquid is a precursor to pyridine derivatives that have applications in the pharmaceutical and agricultural industries. Like pyridine, 3-methylpyridine is a colorless liquid with a strong odor and is classified as a

weak base A weak base is a base that, upon dissolution in water, does not dissociate completely, so that the resulting aqueous solution contains only a small proportion of hydroxide ions and the concerned basic radical, and a large proportion of undissociat ...

Synthesis

3-Methylpyridine is produced industrially by the reaction of

acrolein Acrolein (systematic name: propenal) is the simplest unsaturated aldehyde. It is a colorless liquid with a piercing, acrid smell. The smell of burnt fat (as when cooking oil is heated to its smoke point) is caused by glycerol in the burning fa ...

, with

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

. These ingredients are combined as gases which flows over an oxide-based

heterogeneous catalyst In chemistry, heterogeneous catalysis is catalysis where the phase of catalysts differs from that of the reactants or products. The process contrasts with homogeneous catalysis where the reactants, products and catalyst exist in the same phase. Ph ...

. The reaction is multistep, culminating in cyclisation. :2 CH₂CHCHO + NH₃ → CH₃C₅H₄N + 2H₂O This process also affords substantial amounts of pyridine, which arises by demethylation of the 3-methylpyridine. A route that gives better control of the product starts with

propionaldehyde Propionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is the 3-carbon aldehyde. It is a colourless, flammable liquid with a slightly fruity odour. It is produced on a large scale industrially. Production Propionalde ...

, and

: :CH₂CHCHO + CH₃CH₂CHO + NH₃ → 3-CH₃C₅H₄N + 2 H₂O + H₂ It may also be obtained as a co-product of pyridine synthesis from

acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the mos ...

formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...

, and

via

Chichibabin pyridine synthesis The Chichibabin pyridine synthesis () is a method for synthesizing pyridine rings. The reaction involves the condensation reaction of aldehydes, ketones, α,β-Unsaturated carbonyl compounds, or any combination of the above, with ammonia. It was ...

. Approximately 9,000,000 kilograms were produced worldwide in 1989. It has also been prepared by dehydrogenation of 3-methylpiperidine, derived from hydrogenation of 2-Methylglutaronitrile.

Uses

3-Picoline is a useful precursor to agrochemicals, such as

chlorpyrifos Chlorpyrifos (CPS), also known as Chlorpyrifos ethyl, is an organophosphate pesticide that has been used on crops, animals, and buildings, and in other settings, to kill several pests, including insects and worms. It acts on the nervous systems ...

. 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 In organic chemistry, ammoxidation is a process for the production of nitriles () using ammonia () and oxygen (). It is sometimes called the SOHIO process, acknowledging that ammoxidation was developed at Standard Oil of Ohio. The usual substrate ...

of 3-methylpyridine: :CH₃C₅H₄N + 1.5O₂ + NH₃ → NCC₅H₄N + 3H₂O 3-Cyanopyridine is also a precursor to 3-pyridinecarboxamide, which is a precursor to pyridinecarbaldehydes: :3-NCC₅H₃N + + 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. 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.,Sims, G. K. and L.E. Sommers. 1985. Degradation of pyridine derivatives in soil. J. Environmental Quality. 14:580-584. 3-Methylpyridine is the main precursor to

niacin Niacin, also known as nicotinic acid, is an organic compound and a form of vitamin B3, an essential human nutrient. It can be manufactured by plants and animals from the amino acid tryptophan. Niacin is obtained in the diet from a variet ...

, one of the

B vitamins B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells. Though these vitamins share similar names (B1, B2, B3, etc.), they are chemically distinct compounds that often coexist ...

. Approximately 10,000 tons of niacin are produced annually worldwide.

Toxicity

Like most alkylpyridines, the

LD50 In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the ...

of 2-methylpyridine is modest, being 400 mg/kg (oral, rat).

References

{{DEFAULTSORT:Methylpyridine, 3- 3-Pyridyl compounds

Synthesis

Uses

Environmental behavior

See also

Toxicity

References