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quinone

 
Dictionary: qui·none   (kwĭ-nōn', kwĭn'ōn') pronunciation
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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: quinone
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Any member of a class of cyclic organic compounds comprising a six-membered unsaturated ring (see saturation) to which two oxygen atoms are bonded as carbonyl groups (-C=O; see functional group). This structure plays an important role in theories of chemical structure and colour, since quinones occur as pigments in bacteria, fungi, and certain higher plants; animals containing quinones obtain them from plants they eat. The K vitamins (see vitamin K) are naphthoquinones. The term quinone often specifically denotes para-benzoquinone (C6H4O2), a bright yellow solid with a sharp odour used in manufacturing dyes and fungicides and in photography.

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Sci-Tech Encyclopedia: Quinone
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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

2

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

4

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
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Quinones are "compounds having a fully conjugated cyclic dione structure, such as that of benzoquinones, derived from aromatic compounds by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double bonds (polycyclic and heterocyclic analogues are included)."[1]

Benzoquinone, sometimes referred to simply as "quinone", is either 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.

Some examples of quinones:

1,2-Benzoquinone

1,4-Benzoquinone

DDQ

Anthraquinone

Chloranil


Contents

Biochemistry

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.[2]

Oxidizing agents

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).[3]

References

  1. ^ International Union of Pure and Applied Chemistry (1995). "Quinones". Compendium of Chemical Terminology Internet edition.
  2. ^ Michel Baron (1982), Ph'D Sciences Pharmacologiques et Biologiques, Series E N°70, Paris DescartesUniversity.
  3. ^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7 

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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
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Quinone".  Read more