acidpyridine

Acidpyridine is not a standard chemical term in current nomenclature. It is often used informally to refer to pyridine derivatives that bear a carboxyl group, i.e., pyridine carboxylic acids. These compounds form a class in which a carboxylic acid function is attached directly to the pyridine ring, and they exist as three principal isomers: 2-pyridine carboxylic acid (picolinic acid), 3-pyridine carboxylic acid (nicotinic acid or niacin), and 4-pyridine carboxylic acid (isonicotinic acid).

Nicotinic acid is best known as a vitamin (vitamin B3) essential for human metabolism, functioning as a precursor to the coenzymes NAD and NADP. It is used as a dietary supplement and in pharmaceutical formulations. Picolinic acid and isonicotinic acid are important in coordination chemistry and medicinal chemistry as ligands and building blocks for more complex molecules; picolinic acid, in particular, acts as a chelating agent for metal ions and has roles in biological metal handling. Isonicotinic acid derivatives, including isoniazid, are well-known in drug development and in the synthesis of dyes and agrochemicals.

These acids are weak carboxylic acids; their conjugate bases form water-soluble salts that impact solubility and formulation. Synthesis of pyridine carboxylic acids typically involves oxidation or carboxylation steps on pyridine precursors, or conversion of suitable 2-, 3-, or 4-substituted pyridines into the corresponding carboxylates.

See also: nicotinic acid, picolinic acid, isonicotinic acid.