View source for Hydroquinone

You do not have permission to edit this page, for the following reason:

This IP address range has been globally blocked.
This does not affect your ability to read Wikipedia pages.

Most people who see this message have done nothing wrong. Some kinds of blocks restrict editing from specific service providers or telecom companies in response to recent abuse or vandalism, and can sometimes affect other users who are unrelated to that abuse. Review the information below for assistance if you do not believe that you have done anything wrong.

This block affects editing on all Wikimedia wikis.

The IP address or range 62.210.0.0/16 has been globally blocked by ‪Hasley‬ for the following reason(s):

Open proxy/Webhost: See the help page if you are affected:

This block will expire on 16:21, 18 December 2025. Your current IP address is 62.210.136.28.

Even while globally blocked, you will usually still be able to edit pages on Meta-Wiki.

If you believe you were blocked by mistake, you can find additional information and instructions in the No open proxies global policy. Otherwise, to discuss the block please post a request for review on Meta-Wiki. You could also send an email to the stewards VRT queue at stewards@wikimedia.org including all above details.

Other useful links: Global blocks · Help:I have been blocked

You can view and copy the source of this page:

{{Short description|Chemical compound}}
{{Use dmy dates|date=January 2024}}
{{chembox
| Watchedfields = changed
| verifiedrevid = 443862076
| Name = Hydroquinone
| ImageFile_Ref = {{chemboximage|correct|??}}
| ImageFile = Hydrochinon2.svg
| ImageSize =
| ImageName = Hydroquinone
| ImageFile1 = Trans-hydroquinone-from-xtal-3D-balls.png
| ImageSize1 =
| ImageFile2 = Hydroquinone crystal.jpg
| PIN = Benzene-1,4-diol<ref name=iupac2013>{{cite book | title = Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = [[Royal Society of Chemistry|The Royal Society of Chemistry]] | date = 2014 | location = Cambridge | page = 691 | doi = 10.1039/9781849733069-FP001 | isbn = 978-0-85404-182-4| chapter = Front Matter }}</ref>
| OtherNames = Hydroquinone<ref name=iupac2013 /><br />Idrochinone<br />Quinol<br />4-Hydroxyphenol<br />1,4-Dihydroxybenzene<br />''p''-Dihydroxybenzene<br />''p''-Benzenediol
|Section1={{Chembox Identifiers
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 17594
| SMILES = c1cc(ccc1O)O
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 764
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 537
| DrugBank = DB09526
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = XV74C1N1AE
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = D00073
| Beilstein = 605970
| Gmelin = 2742
| PubChem = 785
| EC_number = 204-617-8
| UNNumber = 3077, 2662
| InChI = 1/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H
| InChIKey = QIGBRXMKCJKVMJ-UHFFFAOYAX
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C6H6O2/c7-5-1-2-6(8)4-3-5/h1-4,7-8H
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = QIGBRXMKCJKVMJ-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 123-31-9
| RTECS = MX3500000
  }}
|Section2={{Chembox Properties
| C=6 | H=6 | O=2
| Appearance = White solid
| Density = 1.3 g cm<sup>−3</sup>, solid
| Solubility = 5.9 g/100 mL (15&nbsp;°C)
| MeltingPtC = 172
| BoilingPtC = 287
| pKa = 9.9<ref>{{cite web |url= http://www.inchem.org/documents/sids/sids/123319.pdf |title= Hydroquinone |publisher= UNEP Publications |work= [[OECD SIDS]] |access-date= 17 September 2018 |archive-date= 20 October 2016 |archive-url= https://web.archive.org/web/20161020081945/http://www.inchem.org/documents/sids/sids/123319.pdf |url-status= dead }}</ref>
| VaporPressure = {{val|e=-5|u=mmHg}} (20&nbsp;°C)<ref name=PGCH/>
| MagSus = {{val|-64.63e-6|u=cm<sup>3</sup>/mol}}
  }}
|Section3={{Chembox Structure
| Dipole = {{val|1.4|0.1|u=[[Debye|D]]}}<ref>{{cite journal|doi=10.1021/ja01218a051|title=The Dipole Moments of Catechol, Resorcinol and Hydroquinone|year=1945|last1=Lander|first1=John J.|last2=Svirbely|first2=John J. Lander, W. J.|journal=Journal of the American Chemical Society|volume=67|issue=2|pages=322–324}}</ref>
  }}
| Section6 = {{Chembox Pharmacology
| Pharmacology_ref = 
| ATCCode_prefix = D11
| ATCCode_suffix = AX11
| ATC_Supplemental = 
| ATCvet = 
| Licence_EU = 
| INN = 
| INN_EMA = 
| Licence_US = 
| Legal_status = 
| Legal_AU = 
| Legal_AU_comment = 
| Legal_CA = 
| Legal_CA_comment = 
| Legal_NZ = 
| Legal_NZ_comment = 
| Legal_UK = 
| Legal_UK_comment = 
| Legal_US = 
| Legal_US_comment = 
| Legal_EU = 
| Legal_EU_comment = 
| Legal_UN = 
| Legal_UN_comment = 
| Pregnancy_category = 
| Pregnancy_AU = 
| Pregnancy_AU_comment = 
| Dependence_liability = 
| AdminRoutes = 
| Bioavail = 
| ProteinBound = 
| Metabolism = 
| Metabolites = 
|  HalfLife = 
| DurationOfAction = 
| Excretion = 
  }}
|Section7={{Chembox Hazards
| ExternalSDS =
| NFPA-H = 2
| NFPA-F = 1
| NFPA-R =
| NFPA_ref =<ref>{{cite web |url=http://assets.openstudy.com/updates/attachments/4f0d5cb6e4b084a815fccd72-chmvijay-1326448458607-dipolemoment.pdf |title=Archived copy |access-date=25 January 2014 |url-status=live |archive-url=https://web.archive.org/web/20140202184040/http://assets.openstudy.com/updates/attachments/4f0d5cb6e4b084a815fccd72-chmvijay-1326448458607-dipolemoment.pdf |archive-date=2 February 2014 }}</ref>
| GHSPictograms = {{GHS05}}{{GHS07}}{{GHS08}}{{GHS09}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|302|317|318|341|351|400}}
| PPhrases = {{P-phrases|201|202|261|264|270|272|273|280|281|301+312|302+352|305+351+338|308+313|310|321|330|333+313|363|391|405|501}}
| FlashPtC = 165
| PEL = TWA 2 mg/m<sup>3</sup><ref name=PGCH>{{PGCH|0338}}</ref>
| IDLH = 50 mg/m<sup>3</sup><ref name=PGCH/>
| REL = C 2 mg/m<sup>3</sup> [15-minute]<ref name=PGCH/>
| LD50 = 490 mg/kg (mammal, oral)<br/>245 mg/kg (mouse, oral)<br/>200 mg/kg (rabbit, oral)<br/>320 mg/kg (rat, oral)<br/>550 mg/kg (guinea pig, oral)<br/>200 mg/kg (dog, oral)<br/>70 mg/kg (cat, oral)<ref>{{IDLH|123319|Hydroquinone}}</ref>
  }}
|Section8={{Chembox Related
| OtherFunction_label = [[benzenediol]]s
| OtherFunction = [[Pyrocatechol]]<br />[[Resorcinol]]
| OtherCompounds = [[1,4-Benzoquinone|1,4-benzoquinone]]
  }}
}}

'''Hydroquinone''', also known as '''benzene-1,4-diol''' or '''quinol''', is an [[aromatic]] [[organic compound]] that is a type of [[Phenols|phenol]], a derivative of [[benzene]], having the [[chemical formula]] C<sub>6</sub>H<sub>4</sub>(OH)<sub>2</sub>. It has two [[hydroxyl group]]s [[covalent bond|bonded]] to a [[benzene ring]] in a [[Arene substitution patterns#Ortho, meta, and para substitution|''para'']] position. It is a white granular [[solid]]. Substituted derivatives of this parent compound are also referred to as hydroquinones. The name "hydroquinone" was coined by [[Friedrich Wöhler]] in 1843.<ref>F. Wöhler (1844) "Untersuchungen über das Chinon" (Investigations of quinone), ''Annalen der Chemie und Pharmacie'', '''51''' : 145-163. [http://babel.hathitrust.org/cgi/pt?id=uva.x002457921;view=1up;seq=158 From page 146:] ''"Das so erhaltene Destillat … enthält … einen neuen, krystallisierenden Körper, den ich unter dem Namen ''farbloses Hydrochinon'' weiter unten näher beschreiben werde."'' (The distillate so obtained … contains … a new, crystallizable substance, that I will describe, under the name of ''colorless hydroquinone'', further below in more detail.) [Note: Wöhler's empirical formula for hydroquinone (p. 152) is incorrect because (1) he attributed 25 (instead of 24) carbon atoms to the molecule, and (2) as many chemists at the time did, he used the wrong atomic masses for carbon (6 instead of 12) and oxygen (8 instead of 16). With these corrections, his empirical formula becomes: C<sub>12</sub>H<sub>12</sub>O<sub>4</sub>. Dividing the subscripts by 2, the result is: C<sub>6</sub>H<sub>6</sub>O<sub>2</sub>, which is correct.]</ref>

In 2021, it was the 282nd most commonly prescribed medication in the United States, with more than 800,000 prescriptions.<ref>{{cite web | title=The Top 300 of 2021 | url=https://clincalc.com/DrugStats/Top300Drugs.aspx | website=ClinCalc | access-date=14 January 2024 | archive-date=15 January 2024 | archive-url=https://web.archive.org/web/20240115223848/https://clincalc.com/DrugStats/Top300Drugs.aspx | url-status=live }}</ref><ref>{{cite web | title = Hydroquinone - Drug Usage Statistics | website = ClinCalc | url = https://clincalc.com/DrugStats/Drugs/Hydroquinone | access-date = 14 January 2024}}</ref>

==Production==
Hydroquinone is produced industrially in two main ways.<ref name=Ullmann>Phillip M. Hudnall "Hydroquinone" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. 2005 Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a13_499}}.</ref>
* The most widely used route is similar to the [[cumene process]] in reaction mechanism and involves the dialkylation of [[benzene]] with [[propene]] to give 1,4-diisopropylbenzene. This compound reacts with air to afford the bis(hydroperoxide), which is structurally similar to [[cumene hydroperoxide]] and rearranges in acid to give [[acetone]] and hydroquinone.<ref>Gerhard Franz, Roger A. Sheldon "Oxidation" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim, 2000 {{doi|10.1002/14356007.a18_261}}</ref>
* A second route involves [[hydroxylation]] of [[phenol]] over a catalyst. The conversion uses [[hydrogen peroxide]] and affords a mixture of hydroquinone and its ortho isomer [[catechol]] (benzene-1,2-diol):
*:<chem>C6H5OH  +  H2O2  -> C6H4(OH)2  +  H2O</chem>
Other, less common methods include:
* A potentially significant synthesis of hydroquinone from [[acetylene]] and [[iron pentacarbonyl]] has been proposed<ref name=Cyclization>{{cite journal|author1=Reppe, Walter |author2=Kutepow, N |author3=Magin, A |title=Cyclization of Acetylenic Compounds|journal=Angewandte Chemie International Edition in English|year=1969|volume=8|issue=10|pages=727–733|doi=10.1002/anie.196907271}}</ref><ref>{{cite book|author1=Hubel, Karl |author2=Braye, Henri|title=Process for the preparation of substituted cyclic compounds and products resulting therefrom US3149138 A|year=1960|publisher=Union Carbide Corp.|url=https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US3149138.pdf}}</ref><ref>{{cite book|author1=Pino, Piero |author2=Braca, Giuseppe |author3=Sbrana, Glauco |title=Preparation of hydroquinone US3355503 A|year=1964|publisher=Lonza Ag|url=https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US3355503.pdf}}</ref><ref>{{cite book|author1=Walter, Reppe |author2=Magin, August|title=Production of hydroquinones US3394193 A|year=1966|publisher=Basf Ag|url=https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US3394193.pdf}}</ref><ref>{{cite book|author1=Piero, Pino |author2=Giuseppe, Braca |author3=Frediano, Settimo |author4=Glauco, Sbrana |title=Preparation of hydroquinone US3459812 A|year=1967|publisher=Lonza Ag|url=https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US3459812.pdf}}</ref><ref>{{cite book|author1=Holmes, J. |author2=Hagemeyer, H.|title=Process for the production of hydroquinone US 3742071 A|year=1971|publisher=Eastman Kodak Co.|url=https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US3742071.pdf}}</ref> Iron pentacarbonyl serves as a [[catalyst]], rather than as a [[reagent]], in the presence of free [[carbon monoxide]] gas. [[Rhodium]] or [[ruthenium]] can substitute for iron as the catalyst with favorable chemical yields but are not typically used due to their cost of recovery from the reaction mixture.<ref name=Cyclization />
* Hydroquinone and its [[Derivative (chemistry)|derivatives]] can also be prepared by oxidation of various phenols, such as [[aniline]] and [[Diisopropylbenzene|DIPB]].<ref name=":1">{{Cite journal |vauthors=Shi Y, Xia Y, Xu G, Wen L, Gao G, Zong B |date=28 October 2021 |title=Hydrogen peroxide and applications in green hydrocarbon nitridation and oxidation |doi=10.1016/j.cjche.2021.09.030  |journal=Chinese Journal of Chemical Engineering |type=Review article |volume=41 |pages=145–161|s2cid=240248911 }}</ref> Examples include [[Elbs persulfate oxidation]] and [[Dakin oxidation]].
* Hydroquinone was first obtained in 1820 by the French chemists [[Pierre Joseph Pelletier|Pelletier]] and [[Joseph Bienaimé Caventou|Caventou]] via the [[dry distillation]] of [[quinic acid]].<ref>See:
* Pelletier and Caventou (1820) "Recherches chimiques sur les quinquinas" (Chemical investigations of quinquinas [i.e., the bark of various [[Cinchona]] trees]), ''Annales de Chimie et de Physique'', 2nd series, '''15''' : 289–318, 337-364. [http://babel.hathitrust.org/cgi/pt?id=hvd.hx3dvm;view=1up;seq=347 On pages 341-342], the preparation and properties of ''l'acide pyro-kinique'' (pyroquinic acid or hydroquinone) are discussed.
* {{cite book|last=Roscoe|first=Henry|title=A Treatise on Chemistry, Volume 3, Part 3|year=1891|publisher=Macmillan & Co.|location=London|pages=165|url=https://books.google.com/books?id=HEY9AAAAYAAJ&pg=PA165}}</ref>
* [[Hydrolysis]] of chlorinated [[phenol]], described as being used in China.<ref name=":1" />
Note that methods such as hydrolysis of chlorinated phenol and oxidation of phenols are much more polluting methods than some others.<ref name=":1" />

==Reactions==
The reactivity of hydroquinone's [[hydroxyl]] groups resembles that of other [[phenol]]s, being weakly acidic. The resulting [[conjugate base]] undergoes easy ''O''-alkylation to give [[Ether (chemistry)|mono- and diethers]]. Similarly, hydroquinone is highly susceptible to ring substitution by [[Friedel–Crafts reaction]]s such as alkylation. This reaction is exploited en route to popular antioxidants such as 2-''tert''-butyl-4-methoxyphenol ([[Butylated hydroxyanisole|BHA]]). The useful dye [[1,4-Dihydroxyanthraquinone|quinizarin]] is produced by diacylation of hydroquinone with [[phthalic anhydride]].<ref name=Ullmann/>

===Redox===
Hydroquinone undergoes [[oxidation]] under mild conditions to give [[1,4-Benzoquinone|benzoquinone]]. This process can be reversed. Some naturally occurring hydroquinone derivatives exhibit this sort of reactivity, one example being [[coenzyme Q]]. Industrially this reaction is exploited both with hydroquinone itself but more often with its derivatives where one OH has been replaced by an amine.

When colorless hydroquinone and benzoquinone, a bright yellow solid, are [[cocrystal]]lized in a 1:1 ratio, a dark-green crystalline [[charge-transfer complex]] ([[melting point]] 171&nbsp;°C) called [[quinhydrone]] ({{chem2|C6H6O2*C6H4O2}}) is formed. This complex dissolves in hot water, where the two molecules dissociate in solution.<ref>{{Cite book|title=Introduction to organic chemistry|author=Streitwieser, Andrew|date=1992|publisher=Prentice Hall|others=Heathcock, Clayton H., 1936-, Kosower, Edward M.|isbn=978-0139738500|edition= 4th|location=Upper Saddle River, N.J.|oclc=52836313}}</ref>

===Amination===
An important reaction is the conversion of hydroquinone to the mono- and diamine derivatives. [[Methylaminophenol]], used in photography, is produced in this way:<ref name=Ullmann/>
:<chem>C6H4(OH)2 + \overset{methylamine}{CH3NH2} -> HOC6H4NHCH3 + H2O</chem>
Diamines, useful in the rubber industry as antiozone agents, are similarly produced from [[aniline]]:
:<chem>C6H4(OH)2  +  \overset{aniline}{2 C6H5NH2} ->  C6H4(N(H)C6H5)2  +  2 H2O</chem>

==Uses==
Hydroquinone has a variety of uses principally associated with its action as a reducing agent that is [[soluble]] in water. It is a major component in most black and white [[photographic developer]]s for film and paper where, with the compound [[metol]], it reduces silver [[halides]] to elemental [[silver]].

There are various other uses associated with its [[reducing agent|reducing power]]. As a [[polymerisation inhibitor]], exploiting its [[antioxidant]] properties, hydroquinone prevents polymerization of [[acrylic acid]], [[methyl methacrylate]], [[cyanoacrylate]], and other monomers that are susceptible to radical-initiated [[polymerization]]. By acting as a free radical scavenger, hydroquinone serves to prolong the shelflife of light-sensitive resins such as [[preceramic polymers]].<ref>[https://www.researchgate.net/publication/331309080_Additive_Manufacturing_of_Ceramics_from_Preceramic_Polymers_A_Versatile_Stereolithographic_Approach_Assisted_by_Thiol-Ene_Click_Chemistry Additive manufacturing of ceramics from preceramic polymers] ''Additive manufacturing 2019'' vol. 27. pp 80-90</ref>

Hydroquinone can lose a hydrogen cation from both hydroxyl groups to form a diphenolate ion. The di[[sodium]] diphenolate [[salt (chemistry)|salt]] of hydroquinone is used as an alternating co[[monomer]] unit in the production of the [[polymer]] [[PEEK]].

=== Skin depigmentation ===
Hydroquinone is used as a topical application in [[skin whitening]] to reduce the [[color]] of skin. It does not have the same predisposition to cause [[dermatitis]] as [[metol]] does. This is a prescription-only ingredient in some countries, including the member states of the European Union under [[Directive (European Union)|Directives]] 76/768/EEC:1976.<ref>{{CELEX|31976L0768|text=Council Directive 76/768/EEC of 27 July 1976 on the approximation of the laws of the Member States relating to cosmetic products}}</ref><ref>{{cite web|url=https://www.beskinformed.com/hydroquinone/clear-n-smooth-skin-toning-cream-recalled/|title=Clear N Smooth Skin Toning Cream recalled|date=4 October 2011|access-date=4 April 2018}}</ref>

In 2006, the United States [[Food and Drug Administration]] revoked its previous approval of hydroquinone and proposed a ban on all [[over-the-counter]] preparations.<ref name="FDA 2006">{{cite report | author = United States Food and Drug Administration | year = 2006 | title = Skin Bleaching Drug Products for Over-the-Counter Product Use; Proposed Rule | url = https://www.fda.gov/OHRMS/DOCKETS/98fr/78n-0065-npr0003.pdf | docket = 1978N-0065 | url-status = live | archive-url = https://web.archive.org/web/20110516100158/https://www.fda.gov/OHRMS/DOCKETS/98fr/78n-0065-npr0003.pdf | archive-date = 16 May 2011 }}</ref> The FDA officially banned hydroquinone in 2020 as part of a larger reform of the over-the-counter drug review process.<ref>{{Cite web|title=Congress Enacts OTC Monograph Reform|url=https://www.jdsupra.com/legalnews/congress-enacts-otc-monograph-reform-96907/|access-date=19 December 2021|website=JD Supra|language=en}}</ref> The FDA stated that hydroquinone cannot be ruled out as a potential [[carcinogen]].<ref name=":0">{{Cite web|url=https://www.fda.gov/AboutFDA/CentersOffices/OfficeofMedicalProductsandTobacco/CDER/ucm203112.htm|title=About the Center for Drug Evaluation and Research - Hydroquinone Studies Under The National Toxicology Program (NTP)|last=Research|first=Center for Drug Evaluation and|website=www.fda.gov|language=en|access-date=12 February 2017|url-status=live|archive-url=https://web.archive.org/web/20170122222134/https://www.fda.gov/aboutfda/centersoffices/officeofmedicalproductsandtobacco/cder/ucm203112.htm|archive-date=22 January 2017}}</ref> This conclusion was reached based on the extent of [[absorption (pharmacokinetics)|absorption]] in humans and the incidence of [[neoplasm]]s in rats in several studies where adult rats were found to have increased rates of tumours, including [[thyroid follicular cell hyperplasia]]s, anisokaryosis (variation in nuclei sizes), mononuclear cell leukemia, [[hepatocellular adenoma]]s and [[kidney cancer|renal tubule cell adenoma]]s. The Campaign for Safe Cosmetics has also highlighted concerns.<ref>[http://www.safecosmetics.org/article.php?id=289 Campaign For Safe Cosmetics - Hydroquinone] {{webarchive|url=https://web.archive.org/web/20101127071016/http://safecosmetics.org/article.php?id=289 |date=27 November 2010 }}</ref>

Numerous studies have revealed that hydroquinone, if taken orally, can cause exogenous [[ochronosis]], a disfiguring disease in which blue-black pigments are deposited onto the skin; however, skin preparations containing the ingredient are administered topically. The FDA had classified hydroquinone in 1982 as a safe product - generally recognized as safe and effective (GRASE), however additional studies under the National Toxicology Program (NTP) were suggested in order to determine whether there is a risk to humans from the use of hydroquinone.<ref name="FDA 2006"/><ref>{{cite journal |author1=Olumide, YM |author2=Akinkugbe, AO |author3=Altraide, D |author4=Mohammed, T |author5=Ahamefule, N |author6=Ayanlowo, S |author7=Onyekonwu, C |author8=Essen, N | title=Complications of chronic use of skin lightening cosmetics| date= April 2008 | volume = 47 | issue = 4 | pmid=18377596 |pages = 344–53 | journal = International Journal of Dermatology | doi=10.1111/j.1365-4632.2008.02719.x|s2cid=8159382 }}</ref><ref name=":0" /> NTP evaluation showed some evidence of long-term carcinogenic and genotoxic effects<ref>{{Cite web |title=Hydroquinone 10022-H |url=https://ntp.niehs.nih.gov/static/whatwestudy/testpgm/status/ts-10022-h.html |url-status=live |archive-url=https://web.archive.org/web/20171001031226/https://ntp.niehs.nih.gov/testing/status/agents/ts-10022-h.html |archive-date=1 October 2017 |access-date=18 August 2023 |website=ntp.niehs.nih.gov |language=en-US}}</ref>

While hydroquinone remains widely prescribed for treatment of [[hyperpigmentation]], questions raised about its safety profile by regulatory agencies in the EU, Japan, and USA encourage the search for other agents with comparable efficacy.<ref>{{Cite journal|last=Draelos|first=Zoe Diana|date=1 September 2007|title=Skin lightening preparations and the hydroquinone controversy|journal=Dermatologic Therapy|volume=20|issue=5|pages=308–313|doi=10.1111/j.1529-8019.2007.00144.x|issn=1529-8019|pmid=18045355|s2cid=24913995|doi-access=free}}</ref> Several such agents are already available or under research,<ref>{{Cite journal|last=Bandyopadhyay|first=Debabrata|date=1 January 2009|journal=Indian Journal of Dermatology|volume=54|issue=4|pages=303–309|doi=10.4103/0019-5154.57602|issn=0019-5154|pmc=2807702|pmid=20101327|title=Topical treatment of melasma |doi-access=free }}</ref> including [[azelaic acid]],<ref>{{Cite journal|last1=Mazurek|first1=Klaudia|last2=Pierzchała|first2=Ewa|date=1 September 2016|title=Comparison of efficacy of products containing azelaic acid in melasma treatment|journal=Journal of Cosmetic Dermatology|volume=15|issue=3|pages=269–282|doi=10.1111/jocd.12217|issn=1473-2165|pmid=27028014|s2cid=25303091}}</ref> [[kojic acid]], retinoids, cysteamine,<ref>{{Cite journal|last1=Mansouri|first1=P.|last2=Farshi|first2=S.|last3=Hashemi|first3=Z.|last4=Kasraee|first4=B.|date=1 July 2015|title=Evaluation of the efficacy of cysteamine 5% cream in the treatment of epidermal melasma: a randomized double-blind placebo-controlled trial|journal=The British Journal of Dermatology|volume=173|issue=1|pages=209–217|doi=10.1111/bjd.13424|issn=1365-2133|pmid=25251767|s2cid=21618233}}</ref> topical steroids, [[glycolic acid]], and other substances. One of these, [[4-butylresorcinol]], has been proved to be more effective at treating melanin-related skin disorders by a wide margin, as well as safe enough to be made available over the counter.<ref>{{cite book|title=Phenols—Advances in Research and Application: 2013 Edition|date=2013|page=76|chapter=Hydroquinones|publisher=Scholastic}}</ref>

In the [[anthraquinone process]] substituted hydroquinones, typically anthrahydroquinone are used to produce [[hydrogen peroxide]] which forms spontaneously on reaction with oxygen. The type of substituted hydroquinone is selected depending on reactivity and recyclability.

==Natural occurrences==
Hydroquinones are one of the two primary reagents in the defensive glands of [[bombardier beetle]]s, along with [[hydrogen peroxide]] (and perhaps other compounds, depending on the species), which collect in a reservoir. The reservoir opens through a muscle-controlled valve onto a thick-walled reaction chamber. This chamber is lined with cells that secrete [[catalase]]s and [[peroxidase]]s. When the contents of the reservoir are forced into the reaction chamber, the catalases and peroxidases rapidly break down the hydrogen peroxide and [[catalysis|catalyze]] the [[oxidation]] of the hydroquinones into [[quinone|''p''-quinones]]. These reactions release free oxygen and generate enough heat to bring the mixture to the boiling point and vaporize about a fifth of it, producing a hot spray from the beetle's [[abdomen]].<ref name="Solomons">Organic Chemistry, Solomon and Fryhle, 10th edition, Wiley Publishing, 2010.{{page needed|date=October 2016}}</ref>

Hydroquinone is thought to be the active toxin in ''[[Agaricus hondensis]]'' mushrooms.<ref>{{cite journal | doi=10.1055/s-2006-957852 |author1=Joval, E |author2=Kroeger, P |author3=N | title=Hydroquinone: the toxic compound of Agaricus hondensis| date= April 1996 | volume = 62 | issue = 2 |pages = 185 | journal = Planta Medica | pmid=17252436|s2cid=260249338 }}</ref>

Hydroquinone has been shown to be one of the chemical constituents of the natural product [[propolis]].<ref name="Propolis">{{cite journal | last1 = Burdock | first1 = G.A. | year = 1998 | title = Review of the biological properties and toxicity of bee propolis (propolis) | journal = Food and Chemical Toxicology | volume = 36 | issue = 4| pages = 347–363 | doi = 10.1016/S0278-6915(97)00145-2 | pmid = 9651052 }}</ref>

It is also one of the chemical compounds found in [[castoreum]]. This compound is gathered from the [[beaver]]'s castor sacs.<ref>The Beaver: Its Life and Impact. Dietland Muller-Schwarze, 2003, page 43 ([https://books.google.com/books?id=HZ5WjXB5Pr8C&dq=Castoreum+beekeeping&pg=PA43 book at google books])</ref>

==References==
{{Reflist}}

== External links ==
*[http://www.inchem.org/documents/icsc/icsc/eics0166.htm International Chemical Safety Card 0166]
*[https://www.cdc.gov/niosh/npg/npgd0338.html NIOSH Pocket Guide to Chemical Hazards]

{{Other dermatological preparations}}
{{Authority control}}

[[Category:Hydroquinones| ]]
[[Category:Photographic chemicals]]
[[Category:IARC Group 3 carcinogens]]
[[Category:Reducing agents]]

Pages transcluded onto the current version of this page (help):

Template:Abbr (view source) (protected)
Template:Authority control (view source) (template editor protected)
Template:Button (view source) (template editor protected)
Template:CELEX (view source) (semi-protected)
Template:Cascite (view source) (template editor protected)
Template:Catalog lookup link (view source) (template editor protected)
Template:Category handler (view source) (protected)
Template:Chem2 (view source) (template editor protected)
Template:Chem molar mass (view source) (template editor protected)
Template:Chem molar mass/format (view source) (template editor protected)
Template:Chembox (view source) (template editor protected)
Template:Chembox/styles.css (view source) (template editor protected)
Template:Chembox 3DMet (view source) (template editor protected)
Template:Chembox 3DMet/format (view source) (template editor protected)
Template:Chembox ATCCode (view source) (semi-protected)
Template:Chembox AllOtherNames (view source) (template editor protected)
Template:Chembox AllOtherNames/format (view source) (template editor protected)
Template:Chembox Appearance (view source) (template editor protected)
Template:Chembox Beilstein (view source) (semi-protected)
Template:Chembox BoilingPt (view source) (template editor protected)
Template:Chembox CASNo (view source) (template editor protected)
Template:Chembox CASNo/format (view source) (template editor protected)
Template:Chembox CalcTemperatures (view source) (template editor protected)
Template:Chembox ChEBI (view source) (template editor protected)
Template:Chembox ChEBI/format (view source) (template editor protected)
Template:Chembox ChEMBL (view source) (template editor protected)
Template:Chembox ChEMBL/format (view source) (template editor protected)
Template:Chembox ChemSpiderID (view source) (template editor protected)
Template:Chembox ChemSpiderID/format (view source) (template editor protected)
Template:Chembox CompTox (view source) (template editor protected)
Template:Chembox CompTox/format (view source) (template editor protected)
Template:Chembox Datapage check (view source) (template editor protected)
Template:Chembox Density (view source) (template editor protected)
Template:Chembox Dipole (view source) (semi-protected)
Template:Chembox DrugBank (view source) (template editor protected)
Template:Chembox DrugBank/format (view source) (template editor protected)
Template:Chembox ECHA (view source) (template editor protected)
Template:Chembox ECNumber (view source) (template editor protected)
Template:Chembox ECNumber/format (view source) (template editor protected)
Template:Chembox Elements (view source) (template editor protected)
Template:Chembox Elements/molecular formula (view source) (template editor protected)
Template:Chembox FlashPt (view source) (semi-protected)
Template:Chembox Footer (view source) (template editor protected)
Template:Chembox Footer/tracking (view source) (template editor protected)
Template:Chembox GHS (set) (view source) (extended confirmed protected)
Template:Chembox Gmelin (view source) (semi-protected)
Template:Chembox Hazards (view source) (template editor protected)
Template:Chembox IUPHAR ligand (view source) (template editor protected)
Template:Chembox IUPHAR ligand/format (view source) (template editor protected)
Template:Chembox Identifiers (view source) (template editor protected)
Template:Chembox InChI (view source) (template editor protected)
Template:Chembox InChI/format (view source) (template editor protected)
Template:Chembox Indexlist (view source) (template editor protected)
Template:Chembox Jmol (view source) (template editor protected)
Template:Chembox Jmol/format (view source) (template editor protected)
Template:Chembox KEGG (view source) (template editor protected)
Template:Chembox KEGG/format (view source) (template editor protected)
Template:Chembox Lethal amounts (set) (view source) (semi-protected)
Template:Chembox MagSus (view source) (semi-protected)
Template:Chembox MeltingPt (view source) (template editor protected)
Template:Chembox NFPA (view source) (template editor protected)
Template:Chembox NIOSH (set) (view source) (semi-protected)
Template:Chembox OtherCpds (view source) (semi-protected)
Template:Chembox OtherFunctn (view source) (semi-protected)
Template:Chembox Pharmacology (view source) (template editor protected)
Template:Chembox Properties (view source) (template editor protected)
Template:Chembox PubChem (view source) (template editor protected)
Template:Chembox PubChem/format (view source) (template editor protected)
Template:Chembox RTECS (view source) (template editor protected)
Template:Chembox RTECS/format (view source) (template editor protected)
Template:Chembox Related (view source) (template editor protected)
Template:Chembox SMILES (view source) (template editor protected)
Template:Chembox SMILES/format (view source) (template editor protected)
Template:Chembox SolubilityInWater (view source) (template editor protected)
Template:Chembox Structure (view source) (template editor protected)
Template:Chembox UNII (view source) (template editor protected)
Template:Chembox UNII/format (view source) (template editor protected)
Template:Chembox UNNumber (view source) (semi-protected)
Template:Chembox VaporPressure (view source) (semi-protected)
Template:Chembox headerbar (view source) (template editor protected)
Template:Chembox image (view source) (template editor protected)
Template:Chembox image cell (view source) (template editor protected)
Template:Chembox image sbs (view source) (template editor protected)
Template:Chembox pKa (view source) (semi-protected)
Template:Chembox parametercheck (view source) (template editor protected)
Template:Chembox setDatarow (view source) (extended confirmed protected)
Template:Chembox setHeader (view source) (extended confirmed protected)
Template:Chembox templatePar/formatPreviewMessage (view source) (template editor protected)
Template:Chembox verification (view source) (template editor protected)
Template:Chemboximage (view source) (semi-protected)
Template:Chemspidercite (view source) (template editor protected)
Template:Cite book (view source) (protected)
Template:Cite journal (view source) (protected)
Template:Cite report (view source) (template editor protected)
Template:Cite web (view source) (protected)
Template:Collapsible list (view source) (template editor protected)
Template:Convert (view source) (template editor protected)
Template:DMCA (view source) (template editor protected)
Template:Dated maintenance category (view source) (template editor protected)
Template:Dated maintenance category (articles) (view source) (template editor protected)
Template:Delink (view source) (protected)
Template:Doi (view source) (template editor protected)
Template:Ebicite (view source) (template editor protected)
Template:EditAtWikidata (view source) (protected)
Template:FULLROOTPAGENAME (view source) (template editor protected)
Template:Fdacite (view source) (template editor protected)
Template:First nonempty (view source) (template editor protected)
Template:Fix (view source) (protected)
Template:Fix/category (view source) (protected)
Template:GHS05 (view source) (semi-protected)
Template:GHS07 (view source) (semi-protected)
Template:GHS08 (view source) (semi-protected)
Template:GHS09 (view source) (semi-protected)
Template:GHS corrosion (view source) (semi-protected)
Template:GHS environment (view source) (semi-protected)
Template:GHS exclamation mark (view source) (extended confirmed protected)
Template:GHS health hazard (view source) (semi-protected)
Template:H-phrases (view source) (extended confirmed protected)
Template:Hlist/styles.css (view source) (protected)
Template:IDLH (view source) (semi-protected)
Template:If empty (view source) (protected)
Template:Keggcite (view source) (template editor protected)
Template:KillMarkers (view source) (template editor protected)
Template:Longitem (view source) (template editor protected)
Template:Main other (view source) (protected)
Template:NFPA 704 diamond (view source) (semi-protected)
Template:NFPA 704 diamond/styles.css (view source) (semi-protected)
Template:NFPA 704 diamond/text (view source) (semi-protected)
Template:Navbox (view source) (template editor protected)
Template:Ns has subpages (view source) (protected)
Template:Other dermatological preparations (edit)
Template:P-phrases (view source) (extended confirmed protected)
Template:PGCH (view source) (semi-protected)
Template:Page needed (view source) (template editor protected)
Template:Pagetype (view source) (protected)
Template:ParmPart (view source) (template editor protected)
Template:Plain text (view source) (template editor protected)
Template:Plainlist/styles.css (view source) (protected)
Template:Reflist (view source) (protected)
Template:Reflist/styles.css (view source) (protected)
Template:SDcat (view source) (protected)
Template:Short description (view source) (protected)
Template:Short description/lowercasecheck (view source) (protected)
Template:Stdinchicite (view source) (template editor protected)
Template:Str number/trim (view source) (protected)
Template:Tick (view source) (template editor protected)
Template:Tooltip (view source) (template editor protected)
Template:Tooltip/styles.css (view source) (template editor protected)
Template:Trim (view source) (protected)
Template:Unbulleted list (view source) (template editor protected)
Template:Use dmy dates (view source) (template editor protected)
Template:Val (view source) (template editor protected)
Template:Webarchive (view source) (template editor protected)
Template:Xmark (view source) (template editor protected)
Template:Yesno (view source) (protected)
Template:Yesno-no (view source) (template editor protected)
Template:Yesno-yes (view source) (template editor protected)
Module:Arguments (view source) (protected)
Module:Authority control (view source) (template editor protected)
Module:Authority control/config (view source) (template editor protected)
Module:Catalog lookup link (view source) (template editor protected)
Module:Category handler (view source) (protected)
Module:Category handler/blacklist (view source) (protected)
Module:Category handler/config (view source) (protected)
Module:Category handler/data (view source) (protected)
Module:Category handler/shared (view source) (protected)
Module:Check for unknown parameters (view source) (protected)
Module:Chem2 (view source) (template editor protected)
Module:Chem2/styles.css (view source) (template editor protected)
Module:Citation/CS1 (view source) (protected)
Module:Citation/CS1/COinS (view source) (protected)
Module:Citation/CS1/Configuration (view source) (protected)
Module:Citation/CS1/Date validation (view source) (protected)
Module:Citation/CS1/Identifiers (view source) (protected)
Module:Citation/CS1/Utilities (view source) (protected)
Module:Citation/CS1/Whitelist (view source) (protected)
Module:Citation/CS1/styles.css (view source) (protected)
Module:Collapsible list (view source) (template editor protected)
Module:Convert (view source) (template editor protected)
Module:Convert/data (view source) (template editor protected)
Module:Convert/text (view source) (template editor protected)
Module:Delink (view source) (protected)
Module:Disambiguation/templates (view source) (protected)
Module:EditAtWikidata (view source) (protected)
Module:GHS phrases (view source) (extended confirmed protected)
Module:GHS phrases/data (view source) (extended confirmed protected)
Module:Gapnum (view source) (extended confirmed protected)
Module:GetParameters (view source) (template editor protected)
Module:If empty (view source) (protected)
Module:InfoboxImage (view source) (template editor protected)
Module:List (view source) (protected)
Module:Math (view source) (protected)
Module:Namespace detect/config (view source) (protected)
Module:Namespace detect/data (view source) (protected)
Module:Navbar (view source) (protected)
Module:Navbar/configuration (view source) (protected)
Module:Navbar/styles.css (view source) (protected)
Module:Navbox (view source) (template editor protected)
Module:Navbox/configuration (view source) (template editor protected)
Module:Navbox/styles.css (view source) (template editor protected)
Module:Ns has subpages (view source) (protected)
Module:Pagetype (view source) (protected)
Module:Pagetype/config (view source) (protected)
Module:Pagetype/disambiguation (view source) (protected)
Module:Pagetype/rfd (view source) (protected)
Module:Pagetype/setindex (view source) (protected)
Module:Pagetype/softredirect (view source) (protected)
Module:ParameterCount (view source) (template editor protected)
Module:Plain text (view source) (template editor protected)
Module:SDcat (view source) (protected)
Module:String (view source) (protected)
Module:String2 (view source) (template editor protected)
Module:TableTools (view source) (protected)
Module:TemplatePar (view source) (template editor protected)
Module:Unstrip (view source) (template editor protected)
Module:Unsubst (view source) (protected)
Module:Val (view source) (template editor protected)
Module:Val/units (view source) (template editor protected)
Module:Webarchive (view source) (template editor protected)
Module:Webarchive/data (view source) (template editor protected)
Module:Wikidata (view source) (template editor protected)
Module:Wikitext Parsing (view source) (protected)
Module:Yesno (view source) (protected)

Return to Hydroquinone.

Retrieved from "https://en.wikipedia.org/wiki/Hydroquinone"