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			{{Short description|Organic compound (C6H4(OH)2); benzene with two adjacent –OH groups}}
	{{Distinguish2|], also sometimes called catechol}}
			{{Distinguish|text=], also sometimes called catechol}}
	{{chembox
			{{Chembox
	| Verifiedfields = changed		| Verifiedfields = changed
			| Watchedfields = changed
	| verifiedrevid = 398652770
			| verifiedrevid = 458773191
	| Name = Catechol
			| Name = Catechol
	| ImageFileL1 = Brenzcatechin.svg
			| ImageFileL1 = Brenzcatechin.svg
	| ImageSizeL1 = 120px
	| ImageNameL1 = Skeletal formula		| ImageAltL1 = Skeletal formula
	| ImageNameL1 = Pyrocatechol		| ImageNameL1 = Pyrocatechol
			| ImageFileR1 = Catechol-from-xtal-orientation-2-3D-bs-17.png
	| ImageFileR1 = Pyrocatechol-3D-balls.png
	| ImageSizeR1 = 135px		| ImageSizeR1 = 135px
	| ImageNameR1 = Ball-and-stick model		| ImageNameR1 = Ball-and-stick model
			| PIN = Benzene-1,2-diol<ref name=iupac2013>{{cite book | title = Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = ] | date = 2014 | location = Cambridge | page = 691 | doi = 10.1039/9781849733069-FP001 | isbn = 978-0-85404-182-4| chapter = Front Matter }}</ref>
	| IUPACName = Benzene-1,2-diol
			| OtherNames = Pyrocatechol<ref name=iupac2013 /><br />1,2-Benzenediol<br />2-Hydroxyphenol<br />1,2-Dihydroxybenzene<br />''o''-Benzenediol<br />''o''-Dihydroxybenzene
	| OtherNames = pyrocatechol<br />1,2-benzenediol<br />2-hydroxyphenol<br />1,2-dihydroxybenzene
	| Section1 = {{Chembox Identifiers		| Section1 = {{Chembox Identifiers
	| SMILES = Oc1c(O)cccc1		| SMILES = Oc1c(O)cccc1
	| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}		| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
	| ChemSpiderID = 283		| ChemSpiderID = 13837760
	| ChEMBL_Ref = {{ebicite|changed|EBI}}		| ChEBI_Ref = {{ebicite|correct|EBI}}
			| ChEBI = 18135
	| ChEMBL = <!-- blanked - oldvalue: 280998 -->
	| CASNo_Ref = {{cascite|correct|CAS}}		| ChEMBL_Ref = {{ebicite|correct|EBI}}
	| CASNo = 120-80-9		| ChEMBL = 280998
			| CASNo_Ref = {{cascite|correct|CAS}}
	| RTEhttp://en.wikipedia.org/search/?title=Catechol&action=editCS = UX1050000
	| PubChem = 289		| CASNo = 120-80-9
	| KEGG_Ref = {{keggcite|changed|kegg}}		| UNII_Ref = {{fdacite|correct|FDA}}
			| UNII = LF3AJ089DQ
			| RTECS = UX1050000
			| PubChem = 289
			| KEGG_Ref = {{keggcite|correct|kegg}}
	| KEGG = C00090		| KEGG = C00090
			| EINECS = 204-427-5
	}}
			| Gmelin = 2936
	| Section2 = {{Chembox Properties
			| Beilstein = 471401
	| Formula = C<sub>6</sub>H<sub>6</sub>O<sub>2</sub>
			| DrugBank = DB02232
	| MolarMass = 110.1 g/mol
			}}
	| ExactMass = 110.036779 u
			| Section2 = {{Chembox Properties
	| Appearance = white solid
			| C=6 | H=6 | O=2
	| Density = 1.344 g/cm³, solid
			| Appearance = white to brown feathery crystals
	| Solubility = 43 g/100 mL
			| Odor = faint, phenolic odor
	| MeltingPtC = 105
			| Density = 1.344 g/cm<sup>3</sup>, solid
	| BoilingPtC = 245.5
			| Solubility = 312 g/L at 20 °C<ref name=Ullmann/>
	| pKa = 9.5
			| SolubleOther = very soluble in ] <br> soluble in ], ], ], ], ]
	}}
			| MeltingPtC = 105
	| Section3 = {{Chembox Structure
			| BoilingPtC = 245.5
	| Dipole =
			| BoilingPt_notes = (sublimes)
	}}
			| pKa = 9.45, 12.8
	| Section7 = {{Chembox Hazards
			| LogP = 0.88
	| ExternalMSDS =
			| RefractIndex = 1.604
	| EUClass = Harmful ('''Xn''')
			| MagSus = {{val|-6.876e-5|u=cm<sup>3</sup>/mol}}
	| NFPA-H = 2
			| VaporPressure = 20 Pa (20&nbsp;°C)
	| NFPA-F = 1
			| Dipole = {{val|2.62|0.03|u=]}} <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=W. J.|journal=Journal of the American Chemical Society|volume=67|issue=2|pages=322–324}}</ref>
	| NFPA-R =
			}}
	| RPhrases = {{R21/22}}, {{R36/38}}
			| Section3 = {{Chembox Structure
	| SPhrases = {{s2}}, {{S22}}, {{S26}}, {{S37}}
			| CrystalStruct = monoclinic
	| FlashPt = 127 °C
			| Dipole =
	}}
			}}
	| Section8 = {{Chembox Related
			| Section4 = {{Chembox Thermochemistry
	| Function = ]s
			| DeltaHform = −354.1&nbsp;kJ·mol<sup>−1</sup>
	| OtherFunctn = ]<br />]
			| DeltaHfus = 22.8&nbsp;kJ·mol<sup>−1</sup> (at melting point)
	| OtherCpds = ]
	}}		}}
			| Section7 = {{Chembox Hazards
			| ExternalSDS =
			| NFPA-H = 3
			| NFPA-F = 1
			| NFPA-R = 0
			| GHSPictograms = {{GHS06}}{{GHS08}}{{GHS05}}
			| GHSSignalWord = Danger
			| HPhrases = {{H-phrases|301|311|315|317|318|332|341}}
			| PPhrases = {{P-phrases|261|301|330|331|310|302|352|312|305|351|338}}
			| FlashPtC = 127
			| AutoignitionPtC = 510
			| PEL = none<ref name=PGCH>{{PGCH|0109}}</ref>
			| ExploLimits = 1.4%–?<ref name=PGCH />
			| LD50 = 300&nbsp;mg/kg (rat, oral)
			| REL = TWA 5&nbsp;ppm (20 mg/m<sup>3</sup>) <ref name=PGCH/>
			| IDLH = N.D.<ref name=PGCH/>
			}}
			| Section8 = {{Chembox Related
			| OtherFunction_label = ]s
			| OtherFunction = ]<br />]
			| OtherCompounds = ]
			}}
	}}		}}
	'''Catechol''', also known as '''pyrocatechol''' or '''1,2-dihydroxybenzene''', is an organic compound with the molecular formula C<sub>6</sub>H<sub>4</sub>(OH)<sub>2</sub>. It is the ''ortho'' ] of the three isomeric ]s. This colourless compound occurs naturally in trace amounts. About 20 million kg are produced annually, mainly as a precursor to pesticides, flavors, and fragrances.		'''Catechol''' ({{IPAc-en|ˈ|k|æ|t|ᵻ|tʃ|ɒ|l}} or {{IPAc-en|ˈ|k|æ|t|ᵻ|k|ɒ|l}}), also known as '''pyrocatechol''' or '''1,2-dihydroxybenzene''', is an organic compound with the molecular formula {{chem2|C6H4(OH)2}}. It is the ''ortho'' ] of the three isomeric ]s. This colorless compound occurs naturally in trace amounts. It was first discovered by ] of the plant extract ]. About 20,000 tonnes of catechol are now synthetically produced annually as a commodity organic chemical, mainly as a precursor to pesticides, flavors, and fragrances. Small amounts of catechol occur in ] and ].<ref name=Ullmann/>
	Catechol occurs as feathery white crystals that are very rapidly soluble in water.
	(The name "catechol" has also been used as a chemical class name, where it refers to the ]s.)
	==Isolation and synthesis==		==Isolation and synthesis==
			Catechol was first isolated in 1839 by Edgar Hugo Emil Reinsch (1809–1884) by ] it from the solid ] preparation ], which is the residuum of ], the boiled or concentrated juice of ''Mimosa catechu'' ('']'').<ref>Hugo Reinsch (1839) (Some observations about catechu), ''Repertorium für die Pharmacie'', '''68''' : 49-58. Reinsch describes the preparation of catechol on p. 56: ''"Bekanntlich wird die Katechusäure bei der Destillation zerstört, während sich ein geringer Theil davon als krystallinischer Anflug sublimirt, welcher aber noch nicht näher untersucht worden ist. Diese Säure ist vielleicht dieselbe, welche ich bei der zerstörenden Destillation des Katechus erhalten; … "'' (As is well known, catechu acid is destroyed by distillation, while a small portion of it sublimates as a crystalline efflorescence, which however has still not been closely examined. This acid is perhaps the same one, which I obtained by destructive distillation of catechu; … ). On p. 58, Reinsch names the new compound: ''"Die Eigenschaften dieser Säure sind so bestimmt, dass man sie füglich als eine eigenthümliche Säure betrachten und sie mit dem Namen Brenz-Katechusäure belegen kann."'' (The properties of this acid are so definite, that one can regard it justifiably as a strange acid and give it the name "burned catechu acid".)</ref> Upon heating catechin above its decomposition point, a substance that Reinsch first named ''Brenz-Katechusäure'' (burned catechu acid) ] as a white ]. This was a thermal decomposition product of the ] in catechin. In 1841, both ] and Zwenger independently rediscovered catechol; in reporting on their findings, '']'' coined the name ''pyrocatechin''.<ref>See:
	Catechol was first isolated in 1839 by H. Reinsch by distilling ] from ], the juice of ''Mimosa catechu'' ('']'' L.f). Upon heating catechin above its decomposition point, a substance first named "pyrocatechol" formed ("pyro" referring to heat). This "pyrocatechol" is now simply referred to as catechol. Catechol occurs in free form naturally in ] and in ]wood tar; its ] has been detected in the ] of horse and humans.<ref>Anti-inflammatory effects of catechols in lipopolysaccharide-stimulated microglia cells: Inhibition of microglial neurotoxicity. European Journal of Pharmacology, Volume 588, Issue 1, 24 June 2008, Pages 106-113</ref>
			* H. Wackenroder (1841) (Properties of catechu acid), ''Annalen der Chemie und Pharmacie'', '''37''' : 306-320.
			* Constantin Zwenger (1841) (On catechin), ''Annalen der Chemie und Pharmacie'', '''37''' : 320-336.
			* (Anon.) (1841) , ''Philosophical Magazine'', '''19''' : 194-195.</ref> By 1852, ] realized that catechol was ] with two oxygen atoms added to it; in 1867, ] realized that catechol was a ] of benzene, so by 1868, catechol was listed as ''pyrocatechol''.<ref>See:
			* Rudolf Wagner (1852) (On the coloring matter of Dyer's mulberry (Morus tinctoria.)), ''Journal für praktische Chemie'', '''55''' : 65-76. See p. 65.
			* August Kekulé (1867) "Ueber die Sulfosäuren des Phenols" (On the sulfonates of phenol) ''Zeitschrift für Chemie'', new series, '''3''' : 641–646;
			* Joseph Alfred Naquet, with William Cortis, trans. and Thomas Stevenson, ed., ''Principles of Chemistry, founded on Modern Theories'', (London, England: Henry Renshaw, 1868), See also p. 720.</ref> In 1879, the '']'' recommended that catechol be called "catechol", and in the following year, it was listed as such.<ref>See:
			* In 1879, the Publication Committee of the ''Journal of the Chemical Society'' issued instructions to its abstractors to "Distinguish all alcohols, i.e., hydroxyl-derivations of hydrocarbons, by names ending in ''ol, e.g.'', quinol, catechol, … " See: Alfred H. Allen (June 20, 1879) ''English Mechanic and World of Science'', '''29''' (743) : 369.
			* William Allen Miller, ed., ''Elements of Chemistry: Theoretical and Practical, Part III: Chemistry of Carbon Compounds or Organic Chemistry, Section I … '', 5th ed. (London, England: Longmans, Green and Co., 1880), </ref>
			Catechol has since been shown to occur in free form naturally in ] and in ]wood tar. Its ] has been detected in the ] of horses and humans.<ref>{{Cite journal | doi = 10.1016/j.ejphar.2008.04.035| title = Anti-inflammatory effects of catechols in lipopolysaccharide-stimulated microglia cells: Inhibition of microglial neurotoxicity| journal = European Journal of Pharmacology| volume = 588| issue = 1| pages = 106–13| year = 2008| last1 = Zheng | first1 = L. T. | last2 = Ryu | first2 = G. M. | last3 = Kwon | first3 = B. M. | last4 = Lee | first4 = W. H. | last5 = Suk | first5 = K. | pmid=18499097}}</ref>
	Catechol is produced industrially by the hydroxylation of ] using ]:<ref name=Ullmann>Helmut Fiegel, Heinz-Werner Voges, Toshikazu Hamamoto, Sumio Umemura, Tadao Iwata, Hisaya Miki, Yasuhiro Fujita, Hans-Josef Buysch, Dorothea Garbe, Wilfried Paulus "Phenol Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, 2002: Weinheim. DOI: 10.1002/14356007.a19_313. Article Online Posting Date: June 15, 2000</ref>
	:C<sub>6</sub>H<sub>5</sub>OH + H<sub>2</sub>O<sub>2</sub> → C<sub>6</sub>H<sub>4</sub>(OH)<sub>2</sub> + H<sub>2</sub>O
			Catechol is produced industrially by the ] of ] using ].<ref name=Ullmann>{{citation | doi = 10.1002/14356007.a19_313 | chapter = Phenol Derivatives | title = Ullmann's Encyclopedia of Industrial Chemistry | date = 2000 | last1 = Fiege | first1 = Helmut | last2 = Voges | first2 = Heinz-Werner | last3 = Hamamoto | first3 = Toshikazu | last4 = Umemura | first4 = Sumio | last5 = Iwata | first5 = Tadao | last6 = Miki | first6 = Hisaya | last7 = Fujita | first7 = Yasuhiro | last8 = Buysch | first8 = Hans-Josef | last9 = Garbe | first9 = Dorothea | last10 = Paulus | first10 = Wilfried | isbn = 978-3-527-30385-4 }}</ref>
	Previously, catechol has been produced by hydrolysis of 2-substituted phenols, especially ], with hot aqueous solutions containing alkali metal hydroxides. Its methyl ether derivative, ], converts to catechol via hydrolysis of the CH<sub>3</sub>-O bond as promoted by ].{{Citation needed|date=October 2007}}
			:{{chem2 | C6H5OH + H2O2 -> C6H4(OH)2 + H2O }}
			It can be produced by reaction of ] with base and hydrogen peroxide (]),<ref name=":0">{{Cite journal|title=Catechol|journal=Organic Syntheses|year=1923|volume=3|page=28|doi=10.15227/orgsyn.003.0028|author=H. D. Dakin, H. T. Clarke, E. R. Taylor}}</ref> as well as the ] of 2-substituted phenols, especially ], with hot aqueous solutions containing alkali metal hydroxides. Its methyl ether derivative, ], converts to catechol via hydrolysis of the {{chem2|CH3\sO}} bond as promoted by ] (HI).<ref name=":0" />
	==Reactions==
	===Organic chemistry===
	Like other difunctional benzene derivatives, catechol readily condenses to form ]. Cyclic ]s are formed upon treatment with ] and ], ], and sulphuryl chloride:
	:C<sub>6</sub>H<sub>4</sub>(OH)<sub>2</sub> + XCl<sub>2</sub> → C<sub>6</sub>H<sub>4</sub>(O<sub>2</sub>X) + 2 HCl
	::where X = CO, SO2, PCl, P(O)Cl
			== Reactions ==
	Catechols produce ] with the addition of ] (CAN).
			Like some other difunctional benzene derivatives, catechol readily ] to form ]. For example, using ] or ] gives the cyclic chloro] or chloro], respectively; ] gives the ]; and ] ({{chem2|COCl2}}) gives the ]:<ref>{{cite journal|title=o-Phenylene Carbonate|author=R. S. Hanslick, W. F. Bruce, A. Mascitti|journal=Org. Synth.|year=1953|volume=33|page=74|doi=10.15227/orgsyn.033.0074}}</ref>
			:{{chem2|C6H4(OH)2 + XCl2 -> C6H4(O2X) + 2 HCl}} where X = PCl or POCl; {{chem2|SO2}}; CO
			Basic solutions of catechol react with iron(III) to give the red {{chem2|(3-)}}. ] gives a green coloration with the aqueous solution, while the alkaline solution rapidly changes to a green and finally to a black color on exposure to the air.<ref>{{cite journal | last1 = Anderson | first1 = Bryan F. | last2 = Buckingham | first2 = David A. | last3 = Robertson | first3 = Glen B. | last4 = Webb | first4 = John | last5 = Murray | first5 = Keith S. | last6 = Clark | first6 = Paul E. | year = 1976 | title = Models for the bacterial iron-transport chelate enterochelin | journal = Nature | volume = 262 | issue = 5570| pages = 722–724 | doi = 10.1038/262722a0 | pmid = 134287 | title-link = enterochelin | bibcode = 1976Natur.262..722A | s2cid = 3045676 }}</ref> Iron-containing ] ]s ] the ] of catechol.
	===With metal ions===
	Catechol is the conjugate acid of a chelating agent used widely in ]. Basic solutions of catechol react with iron(III) to give the red <sup>3-</sup>. ] gives a green coloration with the aqueous solution, whilst the alkaline solution rapidly changes to a green and finally to a black color on exposure to the air.{{Citation needed|date=October 2007}} It reduces silver solutions in the cold and alkaline copper on heating.{{Citation needed|date=October 2007}} Catechol can also be conjugated to ]. <sup>+</sup> oxidizes faster than catechol in the presence of oxygen, but controlled potential electrolysis showed that its oxidation involves only one electron.<ref>Almeida, W. L. C.; Vitor, D. N.; Pereira, M. R. G; de Sá, D. S.; Alvarez, L. D. G.; Pinheiro, A. M.; Costa, S. L.; Costa, M. F. D.; Rocha, Z. N.; El-Bachá, R. S. Redox properties of ruthenium complex with catechol are involved in toxicity to glial cells. J. Chil. Chem. Soc. 52 (3): 1240-1243, 2007.</ref>
	===Redox chemistry===		=== Redox chemistry ===
			Catechols convert to the semiquinone radical. At {{nowrap|1=pH = 7}}, this conversion occurs at 100&nbsp;mV:{{cn|date=March 2024}}
	Catechol is produced by a reversible two-electron, two-proton reduction of ] (''E''° = +795 mV vs ]; ''E''<sub>m</sub> (pH 7) = +380 mV vs SHE).
			:{{chem2|C6H4(OH)2 -> C6H4(O)(OH) + ½ H2}}
	<ref>{{Cite journal
	| last = Horner | first = Leopold
	| last2 = Geyer | first2 = Ekkehard
	| title = Zur Kenntnis der ''o''-Chinone, XXVII: Redoxpotentiale von Brenzcatechin-Derivaten
	| journal = Chemische Berichte
	| volume = 98 | issue = 6 | pages = 2016–2045 | year = 1965
	| doi = 10.1002/cber.19650980641 }}</ref>
	<ref>{{Cite journal
	| last = Nematollahi | first = D.
	| last2 = Rafiee | first2 = M.
	| title = Electrochemical oxidation of catechols in the presence of acetylacetone
	| journal = Journal of Electroanalytical Chemistry
	| volume = 566 | issue = 1 | pages = 31–37 | date = 2004-05-01
	| doi = 10.1016/j.jelechem.2003.10.044 }}</ref>
			The semiquinone radical can be reduced to the catecholate dianion, the potential being dependent on pH:
	:]
			:{{chem2|C6H4(O)(OH) + e- -> ^{2-} + H+}}
			Catechol is produced by a reversible two-electron, two-proton ] of ] ({{nowrap|1=''E''{{sup|0}} = +795 mV}} vs ]; {{nowrap|1=''E''{{sub|m}} (at pH&nbsp;7) = +380 mV}} vs SHE).<ref>{{Cite journal| doi = 10.1046/j.1462-2920.2001.00176.x | title = Chemical properties of catechols and their molecular modes of toxic action in cells, from microorganisms to mammals. Minireview | year = 2001 | last1 = Schweigert | first1 = Nina | last2 = Zehnder | first2 = Alexander J. B. |author-link2=Alexander Zehnder | last3 = Eggen | first3 = Rik I. L. | journal = Environmental Microbiology | volume = 3 | issue = 2 | pages = 81–91 | pmid = 11321547 }}</ref>
	The redox series catecholate dianion, monoanionic semiquinonate, and benzoquinone are collectively called '''dioxolenes'''. Dioxolenes are used as ]s.<ref>{{cite DOI|10.1007/BF00139966}}</ref>
			The ] series catecholate dianion, monoanionic semiquinonate, and benzoquinone are collectively called '''dioxolenes'''. Dioxolenes can function as ]s for metal ions.<ref>{{Cite journal| doi = 10.1007/BF00139966| title = Recent Advances in Dioxolene Chemistry| year = 1993| last1 = Griffith | first1 = W. P.| journal = Transition Metal Chemistry| volume = 18| issue = 2| pages = 250–256 | s2cid = 93790780}}</ref>
	==Natural Occurrence==
	Small amounts of catechol occur naturally in fruits and vegetables, along with the enzyme ] (also known as catecholase, or catechol oxidase). Upon mixing the enzyme with the substrate and exposure to oxygen (as when a potato or apple is cut and left out), the colorless catechol oxidizes to reddish-brown melanoid pigments, derivatives of benzoquinone. The enzyme is inactivated by adding an acid, such as lemon juice, and slowed with cooling. Excluding oxygen also prevents the browning reaction. Benzoquinone is said to be antimicrobial, which slows the spoilage of wounded fruits and other plant parts.
			== Catechol derivatives ==
	Catechol ] are also found widely within the natural world. ] ] consists of ] linked by a catechol ] to ]. The cuticle may be strengthened by cross-linking (] and ]), in particular, in ], and of course by ].<ref>{{Cite journal | doi = 10.1098/rstb.1999.0356 | volume = 354 | issue = 1379 | pages = 7 | author = Briggs DEG | title = Molecular taphonomy of animal and plant cuticles: selective preservation and diagenesis | journal = Philosophical Transactions of the Royal Society B: Biological Sciences | year = 1999 }}</ref> Catechols such as ] are produced through the metabolism of ] by bacteria such as '']''.<ref name="pmid19300498">{{PDB|2ZI8}}; {{cite journal | author = Yam KC, D'Angelo I, Kalscheuer R, Zhu H, Wang JX, Snieckus V, Ly LH, Converse PJ, Jacobs WR, Strynadka N, Eltis LD | title = Studies of a ring-cleaving dioxygenase illuminate the role of cholesterol metabolism in the pathogenesis of Mycobacterium tuberculosis | journal = PLoS Pathog. | volume = 5 | issue = 3 | pages = e1000344 | year = 2009 | month = March | pmid = 19300498 | pmc = 2652662 | doi = 10.1371/journal.ppat.1000344 }}</ref>
			<gallery caption="Naturally occurring catechols" widths="180px" heights="120px" >
			DHSA.svg| ], a metabolite of ]<ref name="pmid19300498">{{PDB|2ZI8}}; {{cite journal | vauthors = Yam KC, D'Angelo I, Kalscheuer R, Zhu H, Wang JX, Snieckus V, Ly LH, Converse PJ, Jacobs WR, Strynadka N, Eltis LD | title = Studies of a ring-cleaving dioxygenase illuminate the role of cholesterol metabolism in the pathogenesis of Mycobacterium tuberculosis | journal = PLOS Pathog. | volume = 5 | issue = 3 | pages = e1000344 |date=March 2009 | pmid = 19300498 | pmc = 2652662 | doi = 10.1371/journal.ppat.1000344 | doi-access = free }}</ref>
			Catechin structure.svg| ], a component of tea.
			Piceatannol.svg| ], an antioxidant found in some red wines.
			Urushiol.svg|]s, the active agent in ] (R = (CH<sub>2</sub>)<sub>14</sub>CH<sub>3</sub>, (CH<sub>2</sub>)<sub>7</sub>CH=CHCH<sub>2</sub>CH=CHCH<sub>2</sub>CH=CH<sub>2</sub>, and others)
			catecholamine.svg|]s, drugs imitating them (such as ]), ]s/]s
			Dopamine.svg|], derived from the amino acid tyrosine, an adhesive used by ]s.<ref>{{cite journal |doi=10.1002/anie.201801063|title=The Chemistry behind Catechol-Based Adhesion|year=2019|last1=Saiz-Poseu|first1=J.|last2=Mancebo-Aracil|first2=J.|last3=Nador|first3=F.|last4=Busqué|first4=F.|last5=Ruiz-Molina|first5=D.|journal=Angewandte Chemie International Edition|volume=58|issue=3|pages=696–714|pmid=29573319|hdl=11336/94743|s2cid=4228374}}</ref>
			Quercetin.svg|], which is found in many foods.
			</gallery>
			Catechol derivatives are found widely in nature. They often arise by hydroxylation of phenols.<ref>{{cite journal |doi=10.1016/j.fct.2018.07.050|title=Formation and Biological Targets of Botanical o-Quinones |year=2018 |last1=Bolton |first1=Judy L. |last2=Dunlap |first2=Tareisha L. |last3=Dietz |first3=Birgit M. |journal=Food and Chemical Toxicology |volume=120 |pages=700–707 |pmid=30063944 |pmc=6643002 |s2cid=51887182 |doi-access=free }}</ref>
			] ] consists of ] linked by a catechol ] to ]. The cuticle may be strengthened by ]ing (] and ]), in particular, in ]s, and of course by ].<ref>{{Cite journal | doi = 10.1098/rstb.1999.0356 | volume = 354 | issue = 1379 | pages = 7–17 | author = Briggs DEG | title = Molecular taphonomy of animal and plant cuticles: selective preservation and diagenesis | journal = Philosophical Transactions of the Royal Society B: Biological Sciences | year = 1999 | pmc = 1692454 }}</ref>
			The synthetic derivative ] is used as an ] and ].
	]s are naturally existing organic compounds that have the catechol skeleton structure and diphenol functionality but with ] groups substituted onto the aromatic ring. Urushiols are the skin-irritating ]s found in plants like ], etc. ]s are biochemically significant ]s/]s that are ]s in which the ] group has a catechol skeleton structure.
			== Uses ==
	Parts of a molecule of ], another natural compound present in ], has the catechol skeleton structure in it.
			Approximately 50% of the synthetic catechol is consumed in the production of ]s, the remainder being used as a precursor to fine chemicals such as perfumes and pharmaceuticals.<ref name=Ullmann/> It is a common building block in ].<ref>{{citation | doi=10.1002/047084289X | title=Encyclopedia of Reagents for Organic Synthesis | date=2001 | hdl=10261/236866 | isbn=978-0-471-93623-7 | hdl-access=free }}</ref> Several industrially significant ]s and ] are prepared starting from catechol. ] is prepared by ] of catechol and is then converted to ] on a scale of about 10M kg per year (1990). The related monoethyl ether of catechol, ], is converted to ], a component of ] confectioneries. 3-''trans''-Isocamphylcyclohexanol, widely used as a replacement for ], is prepared from catechol via guaiacol and ]. ], a flowery scent, is prepared from the methylene diether of catechol followed by condensation with ] and ].<ref>{{citation | doi=10.1002/14356007.a11_141 | chapter=Flavors and Fragrances | title=Ullmann's Encyclopedia of Industrial Chemistry | date=2003 | last1=Fahlbusch | first1=Karl-Georg | last2=Hammerschmidt | first2=Franz-Josef | last3=Panten | first3=Johannes | last4=Pickenhagen | first4=Wilhelm | last5=Schatkowski | first5=Dietmar | last6=Bauer | first6=Kurt | last7=Garbe | first7=Dorothea | last8=Surburg | first8=Horst | isbn=978-3-527-30385-4 }}</ref>
			] published in 1879 his findings on the use of catechol as a black-and-white ],<ref>{{Cite journal |last=Eder |first=Josef Maria |date=January 1880 |title=Ueber die chemische Zusammensetzung des Pyroxylins und die Formel der Cellulose |trans-title=About the chemical composition of pyroxylin and the formula of cellulose |url=https://doi.org/10.1002/cber.18800130151 |journal=Berichte der deutschen chemischen Gesellschaft ] |language=de |volume=13 |issue=1 |pages=169–186 |doi=10.1002/cber.18800130151 |issn=0365-9496}}</ref><ref>{{Cite book |last=Eder |first=Josef Maria |title=Der neue Eisenoxalat-Entwickler: und dessen Vergleichung mit dem Pyrogallus-Entwickler |publisher=Verlag der Photographischen Correspondenz: Hermann Vogel |year=1880 |location=Vienna |language=de |trans-title=The new iron oxalate developer: and its comparison with the Pyrogallol developer |oclc=80152687}}</ref> but, except for some special purpose applications, its use is largely historical. It is rumored to have been used briefly in ]'s HC-110 developer and is rumored to be a component in ]'s Neofin Blau developer.<ref name="Stephen G. Anchell">{{Cite book | title=The Darkroom Cookbook | author=Stephen G. Anchell | isbn=978-1136092770 | date=2012-09-10 | publisher=Taylor & Francis }}</ref> It is a key component of Finol from Moersch Photochemie in Germany. Modern catechol developing was pioneered by noted photographer ]. His "PyroCat" formulation is popular among modern black-and-white film photographers.<ref>{{Cite book | title=The Film Developing Cookbook |author1=Stephen G. Anchell |author2=Bill Troop | isbn=978-0240802770 |year=1998 }}</ref> King's work has since inspired further 21st-century development by others such as Jay De Fehr with Hypercat and Obsidian Acqua developers, and others.<ref name="Stephen G. Anchell"/>
	==Uses==
	Approximately 50% of synthetic catechol is consumed in the production of pesticides, the remainder being used as a precursor to fine chemicals such as perfumes and pharmaceuticals.<ref name=Ullmann/> It is a common building block in ].<ref>Barner, B. A. "Catechol" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.</ref> Several industrially significant flavors and fragrances are prepared starting from catechol. ] is prepared by methylation of catechol and is then converted to ] on a scale of about 10M kg per year (1990). The related monoethyl ether of catechol, ], is converted to ], a component of chocolate confectioneries. 3-''Trans''-Isocamphylcyclohexanol, widely used as a replacement for ], is prepared from catechol via guaiacol and ]. ], a flowery scent, is prepared from the methylene diether of catechol followed by condensation with ] and ].<ref>Karl-Georg Fahlbusch, Franz-Josef Hammerschmidt, Johannes Panten, Wilhelm Pickenhagen, Dietmar Schatkowski, Kurt Bauer, Dorothea Garbe, Horst Surburg Flavors and Fragrances" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, 2005: Weinheim. Published online: 15 January 2003</ref>
			== Nomenclature ==
	Catechol is used as a black-and-white ], but, except for some special purpose applications, its use until recently was largely historical. Modern catechol developing was pioneered by noted photographer Sandy King. His "PyroCat" formulation enjoys widespread popularity among modern black-and-white film photographers.
			Although rarely encountered, the officially "preferred ] name" (PIN) of catechol is ''benzene-1,2-diol''.<ref>. September 2004, Chapter 6, Sect 60–64, p. 38</ref> The trivial name ''pyrocatechol'' is a retained IUPAC name, according to the ''1993 Recommendations for the Nomenclature of Organic Chemistry''.<ref>IUPAC, Commission on Nomenclature of Organic Chemistry. A Guide to IUPAC Nomenclature of Organic Compounds (Recommendations 1993) </ref>
			<ref>{{cite book | editor=Panico, R. | editor2= Powell, W. H. | title=A Guide to IUPAC Nomenclature of Organic Compounds 1993 | location=Oxford | publisher=Blackwell Science | year=1994 | isbn=978-0-632-03488-8}}</ref>
	==Catechol derivatives==		== See also ==
			* ]
	The catechol skeleton occurs in a variety of natural products such as ]s, which are the skin-irritating ]s found in plants like ], and ]s, drugs imitating them (such as ]), ]s/]s, and ], which is found in ]. Many pyrocatechin derivatives have been suggested for therapeutic applications.
			* ]
			* ]
	==Nomenclature==		== References ==
			{{Reflist|30em}}
			{{EB1911|wstitle=Catechu}}
	The "preferred ] name" (PIN) of catechol is ''benzene-1,2-diol''.
	<ref>
	September 2004, Chapter 6, Sect 60-64, p.38</ref>
	The trivial name ''pyrocatechol'' is a retained IUPAC name, according to the ''1993 Recommendations for the Nomenclature of Organic Chemistry''.
	<ref>IUPAC, Commission on Nomenclature of Organic Chemistry. A Guide to IUPAC Nomenclature of Organic Compounds (Recommendations 1993) </ref>
	<ref>{{cite book | author=Panico, R.; & Powell, W. H. (Eds.) | title=A Guide to IUPAC Nomenclature of Organic Compounds 1993 | location=Oxford | publisher=Blackwell Science | year=1994 | isbn=0-632-03488-2}}</ref>
	==See also==		== External links ==
			{{Commons category|Pyrocatechol}}
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			* (online version of the "''Blue Book''")
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	==References==
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	{{1911}}
	==External links==
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	* (online version of the "''Blue Book''")
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