Editing Quinone (section)

== Occurrence and uses ==
=== Production of hydrogen peroxide ===
{{Main|Anthraquinone process}}
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 {{chem|H|2}} to oxygen:

: dihydroanthraquinone  +  {{chem|O|2}}   →   [[anthraquinone]]  +  {{chem|H|2|O|2}}

in this way, several million metric tons of {{chem|H|2|O|2}} are produced annually.<ref>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}}.</ref>

1,4-[[Naphthoquinone]], derived by oxidation of naphthalene with [[chromium trioxide]].<ref>{{ OrgSynth | author = Braude E. A. | author2 = Fawcett, J. S. | title = 1,4-Naphthoquinone | year = 1953 | volume = 33 | page = 50 | collvol = 4 | collvolpages = 698 | doi=10.15227/orgsyn.033.0050}}</ref> It is the precursor to anthraquinone.

=== Biochemistry ===
Numerous quinones are significant roles in biology.  Vitamin K, which is involved in coagulation of blood, is a quinone. [[Ubiquinone]]-10 is a naturally occurring 1,4-benzoquinone involved in [[Cellular respiration|respiration]] apparatus. [[Plastoquinone]] is a redox relay involved in photosynthesis.  [[Pyrroloquinoline quinone]] is another biological redox cofactor.

[[File:Ubiquinone.svg|thumb|class=skin-invert-image|right|Ubiquinones, as their name implies, are ubiquitous in living creatures, being components of respiratory apparatus.]]
[[File:Gentisyl quinone isovalerate.png|class=skin-invert-image|Blattellaquinone, a sex pheromone in cockroaches|thumb|right]]
Quinones are conjectured to occur in all respiring organisms.<ref name=Obrien>{{cite journal|doi=10.1016/0009-2797(91)90029-7|title=Molecular mechanisms of quinone cytotoxicity|year=1991|last1=O'Brien|first1=P.J.|journal=Chemico-Biological Interactions|volume=80|issue=1|pages=1–41|pmid=1913977}}</ref> Some serve as electron acceptors in electron transport chains such as those in [[photosynthesis]] ([[plastoquinone]], [[phylloquinone]]), and [[aerobic respiration]] ([[ubiquinone]]). Phylloquinone is also known as [[Vitamin K|vitamin K<sub>1</sub>]] as it is used by animals to carboxylate certain proteins, which are involved in [[blood coagulation]], [[bone]] formation, and other processes. Conversely, the toxicity of [[paracetamol]] is due to its metabolism to a [[NAPQI|quinone imine]], which then reacts with liver proteins to cause liver failure.

The auto-oxidation of the neurotransmitter [[dopamine]] and its precursor L-Dopa generates the comparatively stable dopamine quinone which inhibits the functioning of dopamine transporter (DAT) and the [[Tyrosine hydroxylase|TH]] enzyme and leads to low mitochondrial [[Adenosine triphosphate|ATP]] production.<ref>{{Cite journal|title=Molecular Effects of L-dopa Therapy in Parkinson's Disease|last1=Dorszewska|first1=Jolanta|last2=Prendecki|first2=Michal|date=2014-01-31|journal=Current Genomics|volume=15|issue=1|pages=11–17|language=en|doi=10.2174/1389202914666131210213042|pmc=3958954|pmid=24653659|last3=Kozubski|first3=Margarita Lianeri and Wojciech}}</ref>

The  benzoquinone [[blattellaquinone]] is a sex [[pheromone]] in [[cockroach]]es. In the spray of [[bombardier beetle]]s, hydroquinone reacts with hydrogen peroxide to produce a fiery blast of steam, a deterrent in the animal world.

=== Medical ===
Several quinones are of pharmacological interest.  They form a major class of anticancer cytotoxins.  One example is [[daunorubicin]], which is antileukemic.<ref name=Obrien/> Some of them show anti-[[tumor]]al activity. They embody some claims in [[herbal medicine]]. These applications include purgative ([[sennosides]]), antimicrobial and antiparasitic ([[rhein (molecule)|rhein]] and [[saprorthoquinone]], [[atovaquone]]), anti-tumor ([[emodin]] and [[juglone]]), inhibition of [[PGE2]] biosynthesis ([[arnebinone]] and [[arnebifuranone]]) and anti-[[cardiovascular disease]] ([[Salvia miltiorrhiza|tanshinone]]).<ref>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.</ref>  [[Malbranchea cinnamomea]] is a thermophilic fungus, which produces a quinone antibiotic.

Another quinone-containing drug is [[Mecarbinate]] ([[dimecarbine]]), made by the reaction of ethyl [[N-methyl-β-aminocrotonate]] with para-benzoquinone. Others include [[Amendol]], [[Oxyphemedol]], [[Phemedol]] all in FR5142 (M) ― 1967-06-05.{{clarify|date=July 2018}} Note: These are all indoles made via the [[Nenitzescu indole synthesis]]. The antineoplastic [[Apaziquone]].

Benzoquinone compounds are a metabolite of [[paracetamol]].<ref>{{Cite journal
 | doi = 10.1073/pnas.81.5.1327
 | last1 = Dahlin | first1 = D. C.
 | last2 = Miwa | first2 = G. T.
 | last3 = Lu | first3 = A. Y.
 | last4 = Nelson | first4 = S. D.
 | title = N-acetyl-p-benzoquinone imine: a cytochrome P-450-mediated oxidation product of acetaminophen
 | journal = Proceedings of the National Academy of Sciences of the United States of America
 | volume = 81
 | issue = 5
 | pages = 1327–1331
 | year = 1984
 | pmid = 6424115
 | pmc = 344826
| bibcode = 1984PNAS...81.1327D | doi-access = free }}</ref>

=== Dyes ===
Many natural and artificial coloring substances ([[dye]]s and [[pigment]]s) are quinone derivatives, for instance [[lawsone]] is the active dye compound in [[henna]]. 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 [[Rubia|madder]] plant, was the first natural dye to be synthesized from coal tar.

=== Photography ===
A commercial application of quinones is in [[Monochrome photography|black-and-white photography]]. Black-and-white film is covered with an emulsion containing silver bromide or silver iodide crystals, which exposure to light activates. Hydroquinone is used to reduce the activated silver ions to metallic silver. During this process, hydroquinone is oxidized to quinone. All silver halide not activated by light or reduced by hydroquinone is removed, leaving a negative by deposited silver where the film had been struck by light.<ref>{{Cite book |last1=Brown |first1=William Henry |url=https://www.worldcat.org/oclc/974377227 |title=Organic chemistry |last2=Iverson |first2=Brent L. |last3=Anslyn |first3=Eric V. |last4=Foote |first4=Christopher S. |date=2018 |publisher=Cengage Learning |isbn=978-1-305-58035-0 |edition=8th |location=Boston, MA |oclc=974377227}}</ref>