8-Hydroxyquinoline (also known as oxine) is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

derived from the heterocycle

quinoline Quinoline is a heterocyclic aromatic organic compound with the chemical formula C9H7N. It is a colorless hygroscopic liquid with a strong odor. Aged samples, especially if exposed to light, become yellow and later brown. Quinoline is only sl ...

. A colorless solid, its conjugate base is a

chelating agent Chelation () is a type of bonding of ions and their molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These l ...

, which is used for the quantitative determination of metal ions. In aqueous solution 8-hydroxyquinoline has a pK_a value of ca. 9.9 It reacts with metal ions, losing the proton and forming 8-hydroxyquinolinato- chelate complexes. The aluminium complex, is a common component of

organic light-emitting diode An organic light-emitting diode (OLED), also known as organic electroluminescent (organic EL) diode, is a type of light-emitting diode (LED) in which the emissive electroluminescent layer is an organic compound film that emits light in respon ...

s (OLEDs). Substituents on the quinoline ring affect the

luminescence Luminescence is a spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment. A luminescent object emits ''cold light'' in contrast to incandescence, where an obje ...

properties. In its photo-induced excited-state, 8-hydroxyquinoline converts to

zwitterion In chemistry, a zwitterion ( ; ), also called an inner salt or dipolar ion, is a molecule that contains an equal number of positively and negatively charged functional groups. : (1,2- dipolar compounds, such as ylides, are sometimes excluded from ...

ic isomers, in which the hydrogen atom is transferred from oxygen to nitrogen.

History

8-hydroxyquinoline was first obtained by Hugo Weidel and his student Albert Cobenzl in 1880. They decarboxylated so-called oxycinchoninic acid (from

cinchonine Cinchonine is an alkaloid found in ''Cinchona officinalis''. It is used in asymmetric synthesis in organic chemistry. It is a stereoisomer and pseudo-enantiomer of cinchonidine. It is structurally similar to quinine, an antimalarial drug. It i ...

) and characterized the resulting compound as melting at about 70°C. They identified that the

hydroxy group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

is on the benzene ring (but not its particular place) and called the compound oxyquinoline and α-quinophenol. 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. and his student Karl Bedall made the compound from a sulphonic acid independently at about the same time, but misidentified its structure. By 1888

azo dyes Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C−N=N−C li ...

were made from the compound. In the 1920s insoluble chelates of 8-hydroxyquinoline were discovered.

Bioactivity

The complexes as well as the heterocycle itself exhibit

antiseptic An antiseptic ( and ) is an antimicrobial substance or compound that is applied to living tissue to reduce the possibility of sepsis, infection, or putrefaction. Antiseptics are generally distinguished from ''antibiotics'' by the latter's abil ...

disinfectant A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than ...

, and pesticide properties, functioning as a transcription inhibitor. Its solution in alcohol is used in

liquid bandage Liquid bandage is a topical skin treatment for minor wounds which binds to the skin to form a protective polymeric layer that keeps dirt and germs out and moisture in.Petkewich, R. "Liquid Bandages" (2008) ''Chemical & Engineering News.'' vol. 8 ...

s. It once was of interest as an anti-cancer drug. A thiol analogue, 8-mercaptoquinoline is also known. 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.

References

{{DEFAULTSORT:Hydroxyquinoline, 8- Antiseptics Quinolinols

History

Bioactivity

See also

References