8-Hydroxyquinoline

8-Hydroxyquinoline is an organic compound with the formula C₉H₇NO. It is a derivative of the heterocycle quinoline by placement of an OH group on carbon number 8. This light yellow compound is widely used commercially, although under a variety of names.

Synthesis

It is usually prepared from quinoline-8-sulfonic acid and from a Skraup synthesis from 2-aminophenol.

As a chelating agent

8-Hydroxyquinoline is a monoprotic bidentate chelating agent. Related ligands are the Schiff bases derived from salicylaldehyde, such as salicylaldoxime, salen and salicylaldehyde isonicotinoylhydrazone (SIH). In neutral solution, the hydroxyl is in the protonated form (pKa=9.89) and the nitrogen is not protonated (pKa=5.13). However, an excited-state zwitterionic isomer exists in which H⁺ is transferred from the oxygen (giving an oxygen anion) to the nitrogen (giving a protonated nitrogen cation).

Applications

The complexes as well as the heterocycle itself exhibit antiseptic, disinfectant, and pesticide properties, functioning as a transcription inhibitor. Its solution in alcohol is used in liquid bandages. It once was of interest as an anti-cancer drug.