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 are useful in diverse applications. A prominent example is quinine, an alkaloid found in plants. 4-Hydroxy-2-alkylquinolines (HAQs) are involved in antibiotic resistance.
|Preferred IUPAC name|
|Systematic IUPAC name
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||129.16 g/mol|
|Appearance||yellowish oily liquid|
|Melting point||−15 °C (5 °F; 258 K)|
|Boiling point||237 °C (459 °F; 510 K) /760 mm Hg, 108 to 110 °C/11 mm Hg|
|Solubility||Soluble in alcohol, ether, and carbon disulfide|
|Acidity (pKa)||4.85 (conjugated acid)|
Std enthalpy of
|174.9 kJ mol−1|
|R-phrases (outdated)||R21, R22|
|S-phrases (outdated)||S26, S27, S28, S29, S30, Template:S31, Template:S32, S33, Template:S34, S35, S36|
|NFPA 704 (fire diamond)|
|Flash point||101 °C (214 °F; 374 K)|
|400 °C (752 °F; 673 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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, or cinchonine 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.
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 species Strain Q1, which was isolated from soil and paper mill sludge.
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-diketones.
- Conrad-Limpach synthesis using anilines and β-ketoesters.
- Doebner reaction using anilines with an aldehyde and pyruvic acid 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, and sulfuric acid.
A number of other processes exist, which require specifically substituted anilines or related compounds:
- Camps quinoline synthesis using an o-acylaminoacetophenone and hydroxide
- Friedländer synthesis using 2-aminobenzaldehyde and acetaldehyde
- Knorr quinoline synthesis, using a β-ketoanilide and sulfuric acid
- Niementowski quinoline synthesis, using anthranilic acid and ketones
- Pfitzinger reaction using an isatin with base and a carbonyl compound to yield substituted quinoline-4-carboxylic acids
- Povarov reaction using an aniline, a benzaldehyde and an activated alkene
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".
- Similar simple aromatic rings
- Pyrroloquinoline quinone (PQQ), a redox cofactor and controversial nutritional supplement
- "QUINOLINE (BENZOPYRIDINE)". Chemicalland21.com. Retrieved 2012-06-14.
- Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. pp. 4, 211. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
The name ‘quinoline’ is a retained name that is preferred to the alternative systematic fusion names ‘1-benzopyridine’ or ‘benzo[b]pyridine’.
- Brown, H.C., et al., in Baude, E.A. and Nachod, F.C., Determination of Organic Structures by Physical Methods, Academic Press, New York, 1955.
- Chisholm, Hugh, ed. (1911). Encyclopædia Britannica. 22 (11th ed.). Cambridge University Press. p. 759..
- F. F. Runge (1834) "Ueber einige Produkte der Steinkohlendestillation" (On some products of coal distillation), Annalen der Physik und Chemie, 31 (5) : 65–78 ; see especially p. 68: "3. Leukol oder Weissöl" (3. White oil [in Greek] or white oil [in German]). From p. 68: "Diese dritte Basis habe ich Leukol oder Weissöl genannt, weil sie keine farbigen Reactionen zeigt." (This third base I've named leukol or white oil because it shows no color reactions.)
- Gerd Collin; Hartmut Höke. "Quinoline and Isoquinoline". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_465.
- Gerhardt, Ch. (1842) "Untersuchungen über die organischen Basen" (Investigations of organic bases), Annalen der Chemie und Pharmacie, 42 : 310-313. See also: (Editor) (1842) "Chinolein oder Chinoilin" (Quinoline or quinoilin), Annalen der Chemie und Pharmacie, 44 : 279-280.
- Initially, Hoffmann thought that Runge's Leukol and Gerhardt's Chinolein were distinct. (See: Hoffmann, August Wilhelm (1843) "Chemische Untersuchungen der organischen Basen im Steinkohlen-Theeröl" (Chemical investigations of organic bases in coal tar oil), Annalen der Chemie und Pharmacie, 47 : 37-87 ; see especially pp. 76-78.) However, after further purification of his Leukol sample, Hoffmann determined that the two were indeed identical. (See: (Editor) (1845) "Vorläufige Notiz über die Identität des Leukols und Chinolins" (Preliminary notice of the identity of leukol and quinoline), Annalen der Chemie und Pharmacie, 53 : 427-428.)
- O'Loughlin, Edward J.; Kehrmeyer, Staci R.; Sims, Gerald K. (1996). "Isolation, characterization, and substrate utilization of a quinoline-degrading bacterium". International Biodeterioration & Biodegradation. 38 (2): 107. doi:10.1016/S0964-8305(96)00032-7.
- GRIBBLE, Gordon W.; HEALD, Peter W. (1975). "Reactions of Sodium Borohydride in Acidic Media; III. Reduction and Alkylation of Quinoline and Isoquinoline with Carboxylic Acids". Synthesis. 1975 (10): 650–652. doi:10.1055/s-1975-23871. ISSN 0039-7881.
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