8-Hydroxyquinoline
8-Hydroxyquinoline (also known as oxine) is an organic compound derived from the heterocycle quinoline. A colorless solid, its conjugate base is a chelating agent, which is used for the quantitative determination of metal ions.
In aqueous solution 8-hydroxyquinoline has a pKa value of ca. 9.9[1] It reacts with metal ions, losing the proton and forming 8-hydroxyquinolinato-chelate complexes.
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The aluminium complex,[3] is a common component of organic light-emitting diodes (OLEDs). Substituents on the quinoline ring affect the luminescence properties.[4]
In its photo-induced excited-state, 8-hydroxyquinoline converts to zwitterionic isomers, in which the hydrogen atom is transferred from oxygen to nitrogen.[5]
History
8-hydroxyquinoline was first obtained by Hugo Weidel and his student Albert Cobenzl in 1880. They decarboxylated so-called oxycinchoninic acid (from cinchonine) and characterized the resulting compound as melting at about 70°C. They identified that the hydroxy group is on the benzene ring (but not its particular place) and called the compound oxyquinoline and α-quinophenol.[6]
In the following year more chemists found other ways to make the compound. Zdenko Hans Skraup discovered a way to synthesize substituted quinolines from substituted phenols and described three isomers of oxyquinoline, identifying the structure of 8-hydroxyquinoline.[7] Template:Ill and his student Karl Bedall made the compound from a sulphonic acid independently at about the same time, but misidentified its structure.[8][9]
By 1888 azo dyes were made from the compound.[10]
In the 1920s insoluble chelates of 8-hydroxyquinoline were discovered.[11] Script error: No such module "Unsubst".
Bioactivity
The complexes as well as the heterocycle itself exhibit antiseptic, disinfectant, and pesticide properties,[12][13] functioning as a transcription inhibitor.[14] Script error: No such module "Unsubst". Its solution in alcohol is used in liquid bandages. It once was of interest as an anti-cancer drug.[15]
A thiol analogue, 8-mercaptoquinoline is also known.[16]
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.[17]
See also
- Nitroxoline (5-nitro-8-hydroxyquinoline), an antiprotozoal drug
- PBT2
- QUPIC
- Ionophore
- Trace metal detection test
References
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- ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Skraup, Zdenko Hanus, "Verfahren zur Darstellung der Oxychinoline durch Behandlung von Mononitro- und Monamido-Phenolen mit Glycerin und Schwefelsäure", published Script error: No such module "auto date formatter"., issued Script error: No such module "auto date formatter".Script error: No such module "Check for unknown parameters".
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