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. Quinoline is only slightly soluble in cold water but dissolves readily in hot water and most organic solvents.

Quinoline is mainly used as a building block to other specialty chemicals. Approximately 4 tonnes are produced annually according to a report published in 2005.^{[citation needed]} 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".^[1]

Isolation and synthesis

Quinoline was first extracted from coal tar in 1834 by Friedlieb Ferdinand Runge.^[2] Coal tar remains the principal source of commercial quinoline. It can be synthesized using various methods:

• Combes quinoline synthesis using anilines and β-diketones.
• Conrad-Limpach synthesis using anilines and β-ketoesters.
• Doebner-Miller reaction using anilines and α,β-unsaturated carbonyl compounds.
• Friedländer synthesis using 2-aminobenzaldehyde and acetaldehyde.
• Skraup synthesis using ferrous sulfate, glycerol, aniline, nitrobenzene, and sulfuric acid.
• Povarov reaction using an aniline, a benzaldehyde and an activated alkene.
• Camps quinoline synthesis utilizing an o-acylaminoacetophenone and hydroxide
• Knorr quinoline synthesis, using a β-ketoanilide and sulfuric acid.
• Gould-Jacobs reaction starting from an aniline and ethyl ethoxymethylenemalonate

See also

• Isoquinoline, an analog with the nitrogen atom in position 2.
• Pyridine, an analog without the fused benzene ring.
• Naphthalene, an analog without the nitrogen atom.
• Indole, an analog with only a five-membered nitrogen ring.
• Simple aromatic rings
• Niementowski quinoline synthesis, quinoline derivative synthesis
• Lindlar catalyst, quinoline prevents formation of alkanes

Safety

Quinoline has an LD50 = 331mg/kg (oral dose for rats). ^[3]

References

1. ^ Gerd Collin, Hartmut Höke "Quinoline and Isoquinoline" Ullmann's Encyclopedia of Chemical Technology; 2005 Wiley-VCH, Weinheim. doi:10.1002/14356007.a22_465
2. ^ "Quinoline". Encyclopedia Britannica. 1911. http://www.1911encyclopedia.org/Quinoline. 
3. ^ Wolfram|Alpha™

External links

• International Chemical Safety Card 0071
• Classical methods of synthesizing quinolines
• Quinoline search by Wolfram|Alpha