8-Hydroxyquinoline
Encyclopedia
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 colorless compound is widely used commercially, although under a variety of names.
.
. Related ligands are the Schiff base
s derived from salicylaldehyde
, such as salicylaldoxime
and salen
. 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).
, disinfectant, and pesticide properties. Its solution in alcohol is used as liquid bandage
s. 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 diode
s (OLED's). 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.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
C9H7NO. It is a derivative of the heterocycle quinoline
Quinoline
Quinoline is a heterocyclic aromatic organic compound. It has the formula C9H7N and is a colourless hygroscopic liquid with a strong odour. Aged samples, if exposed to light, become yellow and later brown...
by placement of an OH group on carbon number 8. This colorless 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-aminophenol2-Aminophenol
2-Aminophenol is an organic compound with the formula C6H4NH2. Along with its isomer 4-aminophenol, it is an amphoteric molecule and a reducing agent. It is a useful reagent for the synthesis of dyes and heterocyclic compounds...
.
As a chelating agent
8-Hydroxyquinoline is a monoprotic bidentate chelating agentChelation
Chelation is the formation or presence of two or more separate coordinate bonds between apolydentate ligand and a single central atom....
. Related ligands are the Schiff base
Schiff base
A Schiff base, named after Hugo Schiff, is a compound with a functional group that contains a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group, not hydrogen....
s derived from salicylaldehyde
Salicylaldehyde
Salicylaldehyde is the chemical compound with the formula C6H4CHO-2-OH. Along with 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, it is one of the three isomers of hydroxybenzaldehyde. This colorless oily liquid has a bitter almond odor at higher concentration and a characteristic buckwheat...
, such as salicylaldoxime
Salicylaldoxime
Salicylaldoxime is a chemical compound described by the formula C6H4CH=NOH-2-OH. It is the oxime of salicylaldehyde. This crystalline solid is a chelator and sometimes used in the analysis of samples containing transition metal ions, with which it often forms brightly-coloured coordination...
and salen
Salen ligand
Salen is the abbreviation for a popular chelating ligand used in coordination chemistry and homogeneous catalysis. The name salen is a contraction for salicylaldehyde and ethylenediamine. The ligand is a bright yellow micaceous solid that is soluble in polar organic solvents.-Nomenclature:The...
. 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 antisepticAntiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...
, disinfectant, and pesticide properties. Its solution in alcohol is used as liquid bandage
Liquid bandage
Liquid bandage is a topical skin treatment for minor cuts and sores that is sold by several companies. The products are mixtures of chemicals which create a polymeric layer which binds to the skin...
s. It once was of interest as an anti-cancer drug.
The reaction of 8-hydroxyquinoline with aluminium(III) results in Alq3
Tris(8-hydroxyquinolinato)aluminium
Trisaluminium is the chemical compound with the formula Al3. Widely abbreviated Alq3, it is a coordination complex wherein aluminium is bonded in a bidentate manner to the conjugate base of three 8-hydroxyquinoline ligands....
, a common component of organic light-emitting diode
Organic light-emitting diode
An OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...
s (OLED's). Variations in the substituents on the quinoline rings affect its luminescence
Luminescence
Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...
properties.
The roots of the invasive plant Centaurea diffusa
Diffuse knapweed
Diffuse Knapweed , also known as White Knapweed or Tumble Knapweed, is a member of the genus Centaurea in the family Asteraceae. It is native to Asia Minor , the Balkans, , Ukraine, and southern Russia. Diffuse knapweed is an annual or biennial plant, generally growing to between 10 and 60 cm...
release 8-hydroxyquinoline, which has a negative effect on plants that have not co-evolved
Co-evolution
In biology, coevolution is "the change of a biological object triggered by the change of a related object." Coevolution can occur at many biological levels: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits between different...
with it.
Hydroxyquinoline was used as a stabilizer of hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
in a rocket fuel oxidizer (T-Stoff
T-Stoff
T-Stoff was the oxidizer part of a bipropellant rocket fuel combination used in Germany during World War II. It is a stabilized high test peroxide...
) for the German Messerschmitt Me 163
Messerschmitt Me 163
The Messerschmitt Me 163 Komet, designed by Alexander Lippisch, was a German rocket-powered fighter aircraft. It is the only rocket-powered fighter aircraft ever to have been operational. Its design was revolutionary, and the Me 163 was capable of performance unrivaled at the time. Messerschmitt...
Komet in World War 2.