quinone
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Dictionary:
qui·none (kwĭ-nōn', kwĭn'ōn') 
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n.
Any of a class of aromatic compounds found widely in plants, especially the yellow crystalline form, C6H4O2, used in making dyes, tanning hides, and photography.
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Britannica Concise Encyclopedia:
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quinone
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Sci-Tech Encyclopedia:
Quinone |
One of a class of aromatic diketones in which the carbon atoms of the carbonyl groups are part of the ring structure. The name quinone is applied to the whole group, but it is often used specifically to refer to p-benzoquinone (1), o-Benzoquinone (2) is also known but the meta isomer does not exist. 1
Quinones are prepared by oxidation of the corresponding aromatic ring systems containing amino (NH2) or hydroxyl (OH) groups on one or both of the carbon atoms being converted to the carbonyl group.
Three of the several possible quinones derived from naphthalene are known: 1,4-naphthoquinone (3), 1,2-naphthoquinone, and 2,6-naphthoquinone (4). 3
Important naturally occurring naphthoquinones are vitamins K1 and K2 which are found in blood and are responsible for proper blood clotting reaction. A number of quinone pigments have been isolated from plants and animals. Illustrative of these are juglone found in unripe walnut shells and spinulosin from the mold Penicillium spinuhsum. 9,10-Anthraquinone derivatives form an important class of dyes of which alizarin is the parent type. p-Benzoquinone is manufactured for use as a photographic developer. See also Aromatic hydrocarbon; Dye; Ketone.
Wikipedia:
Quinone |
A quinone is a class of organic compounds that are formally derived from aromatic compounds (such as benzene or naphthalene) by exchanging an even number of –CH= groups by –C(=O)– groups, with any necessary rearrangement of double bonds, resulting in a fully conjugated cyclic dione structure. The class includes derivatives of heterocyclic aromatic compounds.[1]
The prototypical member of the class are 1,4-benzoquinone or cyclohexadienedione, often called simply quinone (whence the name of the class). Other important examples are 1,2-benzoquinone (ortho-quinone), 1,4-naphthoquinone and 9,10-anthraquinone.
The term quinone is also used more generally for a large class of compounds formally derived from aromatic quinones through replacement of some hydrogen atoms by other atoms or radicals.
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Contents
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Occurence and uses
Production of hydrogen peroxide
A large scale industrial application of quinones is for the production of hydrogen peroxide. 2-Alkylanthraquinones are hydrogenated to the corresponding hydroquinones (quinizarins), which then transfer H2 to oxygen:
- dihydroanthraquinone + O2 → anthraquinone + H2O2
In this way, several billion kilograms of H2O2 are produced annually.[2]
Biochemistry
Derivatives of quinones are common constituents 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 oxidation of hydroquinone to quinone is in 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. Many natural or synthetic quinones show a biological or pharmacological activity, and some of them show antitumoral activity.[3]
Dyes
Many natural and artificial coloring substances (dyes and pigments) are quinone derivatives. They are second only to azo dyes in importance as dyestuffs, with particular emphasis on blue colors. Alizarin (2,3-dihydroxy-9,10-anthraquinone), extracted from the madder plant, was the first natural dye to be synthesized from coal tar.
Reagents in organic chemistry
Benzoquinone is used in organic chemistry as an oxidizing agent. Stronger quinone oxidising agents exist; for instance: chloranil and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (also known as DDQ).[4]
Nomenclature
Quinones are commonly named with a prefix that indicates the parent aromatic hydrocarbon ("benzo-" for benzene, "naphtho-" for naphthalene, "anthra-" for anthracene, etc.) and the "-quinone" suffix. Infix multipliers "-di-", "-tri-", "-tetra-" (etc.) are used when there are 4, 6, 8 (etc.) carbonyls. The position of the carbonyl groups can be indicated before the prefix (as in "1,4,5,8-naphthodiquinone") or after it ("anthra-1,4-quinone").
See also
References
- ^ International Union of Pure and Applied Chemistry (1995). "Quinones". Compendium of Chemical Terminology Internet edition.
- ^ Gustaaf Goor, Jürgen Glenneberg, Sylvia Jacobi “Hydrogen Peroxide” in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim. doi: 10.1002/14356007.a13_443.pub2.
- ^ Michel Baron (1982), Ph'D Sciences Pharmacologiques et Biologiques, Series E N°70, Paris Descartes University.
- ^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7
External links
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
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