Quinolinium
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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 slightly soluble in cold water but dissolves readily in hot water and most organic solvents. Quinoline itself has few applications, but many of its
derivatives The derivative of a function is the rate of change of the function's output relative to its input value. Derivative may also refer to: In mathematics and economics * Brzozowski derivative in the theory of formal languages * Formal derivative, an ...
are useful in diverse applications. A prominent example is quinine, an alkaloid found in plants. Over 200 biologically active quinoline and quinazoline alkaloids are identified.
4-Hydroxy-2-alkylquinoline 4-Hydroxy-2-alkylquinolines (HAQs) are a class of intracellular signaling molecules associated with iron chelation. HAQs are produced by various types of bacteria, such as ''Pseudomonas aeruginosa'', and are involved in quorum sensing. The overpro ...
s (HAQs) are involved in
antibiotic resistance Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...
.


Occurrence and isolation

Quinoline was first extracted from coal tar in 1834 by German chemist Friedlieb Ferdinand Runge; he called quinoline ''leukol'' ("white oil" in Greek). Coal tar remains the principal source of commercial quinoline. In 1842, French chemist Charles Gerhardt obtained a compound by dry distilling quinine,
strychnine Strychnine (, , US chiefly ) is a highly toxic, colorless, bitter, crystalline alkaloid used as a pesticide, particularly for killing small vertebrates such as birds and rodents. Strychnine, when inhaled, swallowed, or absorbed through the eye ...
, or
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 Antima ...
with potassium hydroxide; he called the compound ''Chinoilin'' or ''Chinolein''. Runge's and Gephardt's compounds seemed to be distinct isomers because they reacted differently. However, the German chemist August Hoffmann eventually recognized that the differences in behaviors was due to the presence of contaminants and that the two compounds were actually identical. The only report of quinoline as a natural product is from the Peruvian stick insect ''Oreophoetes peruana''. They have a pair of thoracic glands from which they discharge a malodorous fluid containing quinoline when disturbed. (Eisner, T; Morgan, R.C.; Attygalle A.B., Smedley, S.R.; Herath, K.B., Meinwald, J. (1997) “Defensive Production of quinoline by a phasmid insect (Oreophoetes peruana) J. Exp. Biol. 200, 2493–2500). Like other nitrogen heterocyclic compounds, such as pyridine derivatives, quinoline is often reported as an environmental contaminant associated with facilities processing oil shale or coal, and has also been found at legacy wood treatment sites. Owing to its relatively high solubility in water quinoline has significant potential for mobility in the environment, which may promote water contamination. Quinoline is readily degradable by certain microorganisms, such as ''
Rhodococcus ''Rhodococcus'' is a genus of aerobic, nonsporulating, nonmotile Gram-positive bacteria closely related to ''Mycobacterium'' and ''Corynebacterium''. While a few species are pathogenic, most are benign, and have been found to thrive in a broad ...
'' species Strain Q1, which was isolated from soil and paper mill sludge. Quinolines are present in small amounts in crude oil within the virgin
diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...
fraction. It can be removed by the process called hydrodenitrification.


Synthesis

Quinolines are often synthesized from simple anilines using a number of named reactions. :: Going clockwise from top these are: * Combes quinoline synthesis using anilines and β-di
ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bo ...
s. * Conrad-Limpach synthesis using anilines and β-ketoesters. * Doebner reaction using anilines with an aldehyde and
pyruvic acid Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic aci ...
to form quinoline-4-carboxylic acids * Doebner-Miller reaction using anilines and α,β-unsaturated carbonyl compounds. * Gould-Jacobs reaction starting from an aniline and ethyl ethoxymethylenemalonate * Skraup synthesis using ferrous sulfate, glycerol, aniline,
nitrobenzene Nitrobenzene is an organic compound with the chemical formula C6H5 NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale from benzene as a precursor t ...
, and
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
. A number of other processes exist, which require specifically substituted anilines or related compounds: *
Camps quinoline synthesis The Camps quinoline synthesis (also known as the Camps cyclization) is a chemical reaction whereby an o-acylaminoacetophenone is transformed into two different hydroxyquinolines (products A and B) using hydroxide ion. The relative proportions of ...
using an o-acylaminoacetophenone and hydroxide * Friedländer synthesis using
2-aminobenzaldehyde 2-Aminobenzaldehyde is an organic compound with the formula C6H4(NH2)CHO. It is one of three isomers of aminobenzaldehyde. It is a low-melting yellow solid that is soluble in water. Preparation and reactions It is usually prepared by reduction ...
and
acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the mos ...
*
Knorr quinoline synthesis The Knorr quinoline synthesis is an Intramolecular reaction, intramolecular organic reaction converting a anilide, β-ketoanilide to a 2-hydroxyquinoline using sulfuric acid. This reaction was first described by Ludwig Knorr (1859–1921) in 1886 ...
, using a β-ketoanilide and sulfuric acid *
Niementowski quinoline synthesis The Niementowski quinoline synthesis is the chemical reaction of anthranilic acids and ketones (or aldehydes) to form γ-hydroxyquinoline derivatives. Overview In 1894, Niementowski reported that 2-phenyl-4-hydroxyquinoline was formed when anth ...
, using anthranilic acid and ketones *
Pfitzinger reaction The Pfitzinger reaction (also known as the Pfitzinger-Borsche reaction) is the chemical reaction of isatin with base and a carbonyl compound to yield substituted quinoline-4-carboxylic acids. Several reviews have been published. Reaction mechan ...
using an isatin with base and a carbonyl compound to yield substituted quinoline-4-carboxylic acids * Povarov reaction using an aniline, a
benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. It is a colorless liquid with a characteristic almond-like odor. ...
and an activated alkene


Applications

Quinoline is used in the manufacture of
dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...
s, the preparation of
hydroxyquinoline 8-Hydroxyquinoline (also known as oxine) is a chelating agent which has been used for the quantitative determination of metal ions. In aqueous solution 8-hydroxyquinoline has a pKa value of ca. 9.9 It reacts with metal ions, losing the proton an ...
sulfate and
niacin Niacin, also known as nicotinic acid, is an organic compound and a form of vitamin B3, an essential human nutrient. It can be manufactured by plants and animals from the amino acid tryptophan. Niacin is obtained in the diet from a variet ...
. It is also used as a solvent for resins and terpenes. Quinoline is mainly used as in the production of other specialty chemicals. Approximately 4 tonnes are produced annually according to a report published in 2005. Its principal use is as a precursor to 8-hydroxyquinoline, which is a versatile chelating agent and precursor to pesticides. Its 2- and 4-methyl derivatives are precursors to cyanine dyes. Oxidation of quinoline affords quinolinic acid (pyridine-2,3-dicarboxylic acid), a precursor to the herbicide sold under the name "Assert". The reduction of quinoline with sodium borohydride in the presence of
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
is known to produce Kairoline A. (C.f.
Kairine Kairine is a derivative of tetrahydroquinoline which was first described by Wilhelm Fischer in 1883. Its name comes from the Greek ''kairos'', meaning "the right time". It is an antipyretic, formerly used against typhoid fever, but now largely obs ...
) Quinoline has several
anti-malarial Antimalarial medications or simply antimalarials are a type of antiparasitic chemical agent, often naturally derived, that can be used to treat or to prevent malaria, in the latter case, most often aiming at two susceptible target groups, young c ...
derivatives, including quinine, chloroquine, amodiaquine, and primaquine. Quinolines are reduced to tetrahydroquinolines enantioselectively using several catalyst systems.Reetz, M. T.; Li, X. ''Chem. Commun.'' 2006, 2159. Quinolinium compounds (e.g. salts) can also be used as corrosion inhibitors and intensifiers.


See also

* Quinoline alkaloids *
4-Aminoquinoline 4-Aminoquinoline is a form of aminoquinoline with the amino group at the 4-position of the quinoline. The compound has been used as a precursor for the synthesis of its derivatives. A variety of derivatives of 4-aminoquinoline are antimalarial a ...
* 8-Hydroxyquinoline * Pyrroloquinoline quinone (PQQ), a redox cofactor and controversial nutritional supplement * Quinazoline, an aza derivative of quinoline * Quinine * Similar
simple aromatic ring Simple aromatic rings, also known as simple arenes or simple aromatics, are aromatic organic compounds that consist only of a conjugated planar ring system. Many simple aromatic rings have trivial names. They are usually found as substructures of ...
s ** Isoquinoline, an analog with the nitrogen atom in position 2 ** Pyridine, an analog without the fused benzene ring **
Naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08  ppm by mass. As an aromati ...
, an analog with a carbon instead of the nitrogen ** Indole, an analog with only a five-membered nitrogen ring


References


External links

*
New methods of synthesizing quinolines
{{Authority control Amine solvents Simple aromatic rings Foul-smelling chemicals