| 145.16 g/mol|
White crystalline needles
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.
It is usually prepared from quinoline-8-sulfonic acid and from Skraup synthesis from 2-aminophenol.
8-Hydroxyquinoline is a monoprotic bidentate chelating agent. 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).
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.
The reaction of 8-hydroxyquinoline with aluminium(III) results in Alq3, a common component of organic light-emitting diodes (OLEDs). Variations in the substituents on the quinoline rings affect its luminescence properties.
The roots of the invasive plant Centaurea diffusa release 8-hydroxyquinoline, which has a negative effect on plants that have not co-evolved with it.
Hydroxyquinoline was used as a stabilizer of hydrogen peroxide in a rocket fuel oxidizer (T-Stoff) for the German Messerschmitt Me 163 Komet in World War 2.
Related ligands include the Schiff bases derived from salicylaldehyde, such as salicylaldoxime, salen, and salicylaldehyde isonicotinoylhydrazone (SIH). 8-Mercaptoquinoline is the thiol analogue of 8-hydroxyquinoline.