represent a class of organic compound
s that are formally "derived from aromatic
compounds as benzene
by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double bond
s", resulting in "a fully conjugated
structure". The class includes some heterocyclic compound
The prototypical member of the class is 1,4-benzoquinone
or cyclohexadienedione, often called simply "quinone" (thus the name of the class). Other important examples are 1,2-benzoquinone
Quinones are oxidized derivatives of aromatic compounds and are often readily made from reactive aromatic compounds with electron-donating substituents
such as phenols
s, which increase the nucleophilicity of the ring and contributes to the large redox potential
needed to break aromaticity. (Quinones are conjugated but not aromatic). Quinones are electrophilic Michael acceptor
s stabilised by conjugation. Depending on the quinone and the site of reduction, reduction can either rearomatise the compound or break the conjugation. Conjugate addition
nearly always breaks the conjugation.
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.
Occurrence 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 to oxygen:
dihydroanthraquinone + → anthraquinone +
In this way, several billion kilograms of are produced annually.Gustaaf Goor, Jürgen Glenneberg, Sylvia Jacobi "Hydrogen Peroxide" in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim. .
Derivatives of quinones are common in biologically active molecules. Some serve as electron acceptors in electron transport chains such as those in photosynthesis
), and aerobic respiration
). Phylloquinone is also known as Vitamin K1
as it is used by animals to help form certain proteins, which are involved in blood coagulation
formation, and other processes.
A natural example of the oxidation of hydroquinone
to quinone is in the spray of bombardier beetle
s; hydroquinone is reacted with hydrogen peroxide to produce a fiery blast of steam, a strong deterrent in the animal world.
Natural or synthetic quinones show a biological or pharmacological activity, and some of them show anti- tumor
al activity. They embody some claims in herbal medicine
. These applications include purgative ( sennosides
), antimicrobial and antiparasitic (rhein- and saprorthoquinone
), anti-tumor ( emodin
), inhibition of PGE2
biosynthesis ( arnebinone
) and anti- cardiovascular disease
).Liu H., "Extraction and Isolation of Compounds from Herbal Medicines" in 'Traditional Herbal Medicine Research Methods', ed by Willow JH Liu 2011 John Wiley and Sons, Inc.
Many natural and artificial coloring substances ( dye
s and pigment
s) are quinone derivatives. They are second only to azo dyes
in importance as dyestuffs, with particular emphasis on blue colors. Alizarin
(1,2-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
. Strongly oxidizing quinones include chloranil
(also known as DDQ).
Battery charge carrier
9,10-Anthraquinone-2,7-disulphonic acid (AQDS) a quinone similar to one found naturally in rhubarb
has been used as a charge carrier in metal-free flow batteries
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").