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Benzoquinone, or quinone is one of the two isomers of cyclohexadienedione. These compounds have the molecular formula C6H4O2. Orthobenzoquinone is the 1,2-dione, whereas parabenzoquinone is the 1,4-dione.
Orthobenzoquinone is the oxidized form of catechol (1,2-dihydroxybenzene), while parabenzoquinone is the oxidized form of hydroquinone. An acidic potassium iodide solution reduces a solution of benzoquinone to hydroquinone, which is oxidized back with a solution of silver nitrate.
Quinone is also the name for the class of compounds containing either benzoquinone isomers as part of their structure. Quinones are not aromatic, but are diketones.
 p-chloranil |
 DDQ |
Biochemistry
Quinone is a common constituent of biologically relevant molecules (e.g. Vitamin K1 is phylloquinone). Others serve as electron acceptors in electron transport chains such as those in Photosystems I & II of photosynthesis, and aerobic respiration. A natural example of the oxidization of hydroquinone to quinone is the spray of bombardier beetles. Hydroquinone is reacted with hydrogen peroxide to produce a fiery blast of steam, a strong deterrent in the animal world. Quinones can be partially reduced to quinols.
Oxidizing agents
Benzoquinone is used in organic chemistry as an oxidizing agent. Stronger quinone oxidising agents exist; for instance: 2,3,5,6-tetrachloro-parabenzoquinone (also known as p-chloranil) and 2,3-dicyano-5,6-dichloro-parabenzoquinone (also known as DDQ). 1
References
- ^ March, Jerry (1985). Advanced Organic Chemistry, Reactions, Mechanisms and Structure, third Edition, John Wiley & Sons. ISBN 0-471-85472-7.
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- This page was last modified on 30 October 2008, at 07:27.
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