Quinoline

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Quinoline is an organic chemical, C₉H₇N, a colourless hygroscopic liquid with a strong odour. It is also known as 1-azanaphthalene, 1-benzazine, or benzo(b)pyridine.

As it ages, if exposed to light, the liquid tends to become yellow and later brown. It is only slightly soluble in water but dissolves readily in many organic solvents.

Quinoline is an intermediate in metallurgical processes and in dye, polymer, and agrochemical production. It is also a preservative, disinfectant, and solvent.

It is toxic: short-term exposure to the vapour causes irritation of the nose, eyes, and throat as well as dizziness and nausea. Longer-term effects are uncertain, but quinoline has been linked to liver damage and is possibly carcinogenic and mutagenic.

As an Additive

It is used as a food additive, known as E104 in terms of E numbers and also Quinoline Yellow. It is a food colourant that induces a dull yellow, or greenish yellow colour. It can be found in ices, scotch eggs and smoked haddock. It is one of the colours that the Hyperactive Childrens Support Group recommends be eliminated from the diet of children. Whilst being a commonly used colour in the UK its use is banned in Australia, Japan, Norway and the United States.

As a Chemical

Quinoline is naturally found in coal tar and was first extracted from this source in 1834 by F. Runge. It can be prepared through the Skraup synthesis using ferrous sulfate, glycerol, aniline, nitrobenzene, and sulphuric acid. Other methods of synthesis are known, usually through a variant on aniline, glycerol and the acid but with different oxidizing agents. The reactions involved can be surprisingly violent.

Its isomer, isoquinoline, was discovered in 1885.