Picolines

(or methylpyridines), homologues of pyridine. All three isomers (α-, β-, and γ-picolines) are known; they are colorless liquids with a pyridine odor. Melting points, –66.6°, –17.7°, and –4.3°C; boiling points, 129.4°, 144.0°, and 145.3° C; densities at 20°C, 0.9940, 0.9572, and 0.9551 g/cm³, respectively. Picolines are stronger bases than pyridine. They are readily soluble in water and organic solvents.

Oxidation of β-picoline yields nicotinic acid (antipellagra vitamin PP, or niacin), the diethylamide of which is cordiamin; oxidation of γ -picoline yields isonicotinic acid, which is the basis of tuberculostatic preparations, such as phthivazid and isoniazid. Pyridoxine (vitamin B6), a derivative of α-picoline, takes part in many important metabolic reactions in its coenzyme form (pyridoxal 5-phosphate).