Picolinic acid
Pyridine-2-carboxylic acid; bidentate chelating agent
From Wikipedia, the free encyclopedia
Picolinic acid is an organic compound with the formula NC5H4CO2H. It is a derivative of pyridine with a carboxylic acid (COOH) substituent at the 2-position. It is an isomer of nicotinic acid and isonicotinic acid, which have the carboxyl side chain at the 3- and 4-positions, respectively. It is a white solid although impure samples can appear tan. The compound is soluble in water.
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| Names | |
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| Preferred IUPAC name
Pyridine-2-carboxylic acid | |
| Other names
Picolinic acid | |
| Identifiers | |
3D model (JSmol) |
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| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.002.472 |
| KEGG | |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| C6H5NO2 | |
| Molar mass | 123.111 g·mol−1 |
| Appearance | White solid |
| Density | 1.526 g/cm³ |
| Melting point | 136 to 138 °C (277 to 280 °F; 409 to 411 K) |
| Slightly soluble (0.41%) in water | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Production
On a commercial scale, picolinic acid is produced by ammoxidation of 2-picoline followed by hydrolysis of the resulting nitrile:
- NC5H4CH3 + 1.5 O2 + NH3 → NC5H4C≡N + 3 H2O
- NC5H4C≡N + 2 H2O → NC5H4CO2H + NH3
It is also produced by oxidation of picoline with nitric acid.[1]
In the laboratory, picolinic acid is formed from 2-methylpyridine by oxidation with potassium permanganate (KMnO4).[2][3]
Reactions
Hydrogenation of picolinic acid gives piperidine-2-carboxylic acid, a precursor to the drug Mepivacaine.
Picolinic acid is a bidentate chelating agent of elements such as chromium, zinc, manganese, copper, iron, and molybdenum in the human body.[4][5]
It is a substrate in the Mitsunobu reaction. In the Hammick reaction, picolinic acid reacts with ketones to give pyridine-2-carbonols:[6]
- NC5H4CO2H + R2C=O → NC5H4CR2(OH) + CO2
Biosynthesis
Picolinic acid is a catabolite of the amino acid tryptophan through the kynurenine pathway.[7][8][9]
The immediate precursor is 2-amino-3-carboxymuconic semialdehyde, which can spontaneously cyclise to quinolinic acid. However, the enzyme aminocarboxymuconate-semialdehyde decarboxylase removes one of its carboxylic acid groups and initially produces 2-aminomuconic semialdehyde.[9]
This intermdiate is chemically unstable and ring-closes to picolinic acid, with loss of water.[9][10]
The function of picolinic acid is unclear, but it has been implicated in a variety of neuroprotective, immunological, and anti-proliferative effects. In addition, it is suggested to assist in the absorption of zinc(II) ions and other divalent or trivalent ions through the small intestine.[11]
Picolinates
Salts of picolinic acid (picolinates) include: