View source for Catechol

{{Short description|Organic compound (C6H4(OH)2); benzene with two adjacent –OH groups}}
{{Distinguish|text=[[Catechin]], also sometimes called catechol}}
{{Chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 458773191
| Name           = Catechol
| ImageFileL1    = Brenzcatechin.svg
| ImageAltL1     = Skeletal formula
| ImageNameL1    = Pyrocatechol
| ImageFileR1    = Catechol-from-xtal-orientation-2-3D-bs-17.png
| ImageSizeR1    = 135px
| 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 = [[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     = Pyrocatechol<ref name=iupac2013 /><br />1,2-Benzenediol<br />2-Hydroxyphenol<br />1,2-Dihydroxybenzene<br />''o''-Benzenediol<br />''o''-Dihydroxybenzene
| Section1       = {{Chembox Identifiers
| SMILES = Oc1c(O)cccc1
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 13837760
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 18135
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 280998
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 120-80-9
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = LF3AJ089DQ
| RTECS = UX1050000
| PubChem = 289
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C00090
| EINECS = 204-427-5
| Gmelin = 2936
| Beilstein = 471401
| DrugBank = DB02232
 }}
| Section2       = {{Chembox Properties
| C=6 | H=6 | O=2
| Appearance = white to brown feathery crystals
| Odor = faint, phenolic odor
| Density = 1.344 g/cm<sup>3</sup>, solid
| Solubility =  312 g/L at 20 °C<ref name=Ullmann/>
| SolubleOther = very soluble in [[pyridine]] <br> soluble in [[chloroform]], [[benzene]], [[carbon tetrachloride|CCl<sub>4</sub>]], [[diethyl ether|ether]], [[ethyl acetate]]
| MeltingPtC = 105
| BoilingPtC = 245.5
| BoilingPt_notes = (sublimes)
| pKa = 9.45, 12.8
| LogP = 0.88
| RefractIndex = 1.604
| MagSus = {{val|-6.876e-5|u=cm<sup>3</sup>/mol}}
| VaporPressure = 20 Pa (20&nbsp;°C)
| Dipole = {{val|2.62|0.03|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=W. J.|journal=Journal of the American Chemical Society|volume=67|issue=2|pages=322–324|bibcode=1945JAChS..67..322L }}</ref>
 }}
| Section3       = {{Chembox Structure
| CrystalStruct = monoclinic
| Dipole = 
 }}
| Section4       = {{Chembox Thermochemistry
| DeltaHform = −354.1&nbsp;kJ·mol<sup>−1</sup>
| DeltaHfus = 22.8&nbsp;kJ·mol<sup>−1</sup> (at melting point)
 }}
| Section7       = {{Chembox Hazards
| ExternalSDS = [http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=PL&language=EN-generic&productNumber=430749&brand=SIAL&PageToGoToURL=http%3A//www.sigmaaldrich.com/catalog/product/sial/430749%3Flang%3Dpl Sigma-Aldrich]
| 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>) [skin]<ref name=PGCH/>
| IDLH = N.D.<ref name=PGCH/>
 }}
| Section8       = {{Chembox Related
| OtherFunction_label = [[benzenediol]]s
| OtherFunction = [[Resorcinol]]<br />[[Hydroquinone]]
| OtherCompounds = [[1,2-Benzoquinone|1,2-benzoquinone]]
 }}
}}

'''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'' [[isomer]] of the three isomeric [[benzenediol]]s. This colorless compound occurs naturally in trace amounts. It was first discovered by [[destructive distillation]] of the plant extract [[catechin]]. 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 [[fruits]] and [[vegetables]].<ref name=Ullmann/>

==Isolation and synthesis==

Catechol was first isolated in 1839 by Edgar Hugo Emil Reinsch (1809–1884) by [[Distillation|distilling]] it from the solid [[Tannin|tannic]] preparation [[catechin]], which is the residuum of [[catechu]], the boiled or concentrated juice of ''Mimosa catechu'' (''[[Acacia catechu]]'').<ref>Hugo Reinsch  (1839) [http://babel.hathitrust.org/cgi/pt?id=chi.095494244;view=1up;seq=61 "Einige Bemerkungen über Catechu"] (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) [[Sublimation (phase transition)|sublimated]] as a white [[efflorescence]]. This was a thermal decomposition product of the [[Flavan-3-ol|flavanols]] in catechin.  In 1841, both [[Wilhelm Heinrich Wackenroder|Wackenroder]] and Zwenger independently rediscovered catechol; in reporting on their findings, ''[[Philosophical Magazine]]'' coined the name ''pyrocatechin''.<ref>See:
*  H. Wackenroder (1841) [http://babel.hathitrust.org/cgi/pt?id=mdp.39015026322258;view=1up;seq=322 "Eigenschaften der Catechusäure"] (Properties of catechu acid), ''Annalen der Chemie und Pharmacie'', '''37''' : 306-320.
*  Constantin Zwenger (1841) [http://babel.hathitrust.org/cgi/pt?id=mdp.39015026322258;view=1up;seq=336 "Ueber Catechin"] (On catechin), ''Annalen der Chemie und Pharmacie'', '''37''' : 320-336.
*  (Anon.) (1841) [https://books.google.com/books?id=Rx5DAQAAMAAJ&pg=PA194 "On catechin (catechinic acid) and pyrocatechin (pyrocatechinic acid)"], ''Philosophical Magazine'', '''19''' : 194-195.</ref> By 1852, [[Otto Linné Erdmann|Erdmann]] realized that catechol was [[benzene]] with two oxygen atoms added to it; in 1867, [[August Kekulé]] realized that catechol was a [[diol]] of benzene, so by 1868, catechol was listed as ''pyrocatechol''.<ref>See:
*  Rudolf Wagner (1852) [http://babel.hathitrust.org/cgi/pt?id=osu.32435060197167;view=1up;seq=81 "Ueber die Farbstoffe des Gelbholzes (Morus tinctoria.)"] (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; [https://archive.org/stream/zeitschriftfrch16unkngoog#page/n650/mode/2up see p. 643.]
*  Joseph Alfred Naquet, with William Cortis, trans. and Thomas Stevenson, ed., ''Principles of Chemistry, founded on Modern Theories'', (London, England:  Henry Renshaw, 1868), [https://books.google.com/books?id=maxcAAAAcAAJ&pg=PA657 p. 657.]  See also p. 720.</ref> In 1879, the ''[[Journal of the Chemical Society]]'' 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) [https://books.google.com/books?id=xrzmAAAAMAAJ&pg=PA369 "Nomenclature of organic bodies,"] ''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), [https://archive.org/details/elementschemist01grovgoog/page/n563 p.524.]</ref>

Catechol has since been shown to occur in free form naturally in [[Pterocarpus marsupium|kino]] and in [[beech]]wood tar. Its [[sulfonic acid]] has been detected in the [[urine]] 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 [[phenol]] using [[hydrogen peroxide]].<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>
:{{chem2 | C6H5OH  +  H2O2  -> C6H4(OH)2  +  H2O }}

It can be produced by reaction of [[salicylaldehyde]] with base and hydrogen peroxide ([[Dakin oxidation]]),<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 [[hydrolysis]] of 2-substituted phenols, especially [[2-chlorophenol]], with hot aqueous solutions containing alkali metal hydroxides. Its methyl ether derivative, [[guaiacol]], converts to catechol via hydrolysis of the {{chem2|CH3\sO}} bond as promoted by [[hydroiodic acid]] (HI).<ref name=":0" />

== Reactions ==
Like some other difunctional benzene derivatives, catechol readily [[Condensed tannin|condenses]] to form [[heterocyclic compounds]].  For example, using [[phosphorus trichloride]] or [[phosphorus oxychloride]] gives the cyclic chloro[[phosphonite]] or chloro[[phosphonate]], respectively; [[sulfuryl chloride]] gives the [[organosulfate|sulfate]]; and [[phosgene]] ({{chem2|COCl2}}) gives the [[carbonate ester|carbonate]]:<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|[Fe(C6H4O2)3](3-)}}. [[Ferric chloride]] 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 [[dioxygenase]] [[enzyme]]s [[Catalysis|catalyze]] the [[Bond cleavage|cleavage]] of catechol.

=== Redox chemistry ===
Catechols convert to the semiquinone radical.  At {{nowrap|1=pH = 7}}, this conversion occurs at 100&nbsp;mV:{{cn|date=March 2024}}
:{{chem2|C6H4(OH)2  ->  C6H4(O)(OH)  +  ½ H2}}

The semiquinone radical can be reduced to the catecholate dianion, the potential being dependent on pH:
:{{chem2|C6H4(O)(OH)  +  e-  ->  [C6H4O2]^{2-}  +  H+}}

Catechol is produced by a reversible two-electron, two-proton [[Reduction potential|reduction]] of [[1,2-benzoquinone]] ({{nowrap|1=''E''{{sup|0}} = +795 mV}} vs [[Standard hydrogen electrode|SHE]]; {{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 can function as [[ligand]]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>

== Catechol derivatives ==
<gallery widths="180" heights="120" caption="Naturally occurring catechols">
File:DHSA.svg|[[DHSA|3,4-dihydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione]], a metabolite of [[cholesterol]]<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>
File:Catechin structure.svg|[[Catechin]], a component of tea.
File:Piceatannol.svg|[[Piceatannol]], an antioxidant found in some red wines.
File:Urushiol.svg|[[Urushiol]]s, the active agent in [[poison ivy (plant)|poison ivy]] (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)
File:Catecholamine.svg|[[Catecholamine]]s, drugs imitating them (such as [[MDMA]]), [[hormone]]s/[[neurotransmitter]]s
File:Dopamine.svg|[[Dopamine]], a well-known [[neurotransmitter]] with many important roles in cells
File:Quercetin.svg|[[Quercetin]], 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> [[Arthropod]] [[cuticle]] consists of [[chitin]] linked by a catechol [[Moiety (chemistry)|moiety]] to [[protein]]. The cuticle may be strengthened by [[cross-link]]ing ([[Tanning (leather)|tanning]] and [[sclerotization]]), in particular, in [[insect]]s, and of course by [[biomineralization]].<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 [[4-tert-Butylcatechol|4-''tert''-butylcatechol]] is used as an [[antioxidant]] and [[polymerization inhibitor]].

== Uses ==
Approximately 50% of the synthetic catechol is consumed in the production of [[pesticide]]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 [[organic synthesis]].<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 [[Flavoring|flavor]]s and [[Aroma compound|fragrances]] are prepared starting from catechol. [[Guaiacol]] is prepared by [[methylation]] of catechol and is then converted to [[vanillin]] on a scale of about 10M kg per year (1990). The related monoethyl ether of catechol, [[guethol]], is converted to [[ethylvanillin]], a component of [[chocolate]] confectioneries. 3-''trans''-Isocamphylcyclohexanol, widely used as a replacement for [[sandalwood oil]], is prepared from catechol via guaiacol and [[camphor]]. [[Piperonal]], a flowery scent, is prepared from the methylene diether of catechol followed by condensation with [[glyoxal]] and [[decarboxylation]].<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>

[[Josef Maria Eder]] published in 1879 his findings on the use of catechol as a black-and-white [[photographic developer]],<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 |trans-journal=Reports of the German Chemical Society |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 [[Eastman Kodak]]'s HC-110 developer and Anchell supposes it to be a component in [[Tetenal]]'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.{{Citation needed|date=March 2025}} Modern catechol developing was pioneered by noted photographer [[Sandy King (photographer)|Sandy King]], whose "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"/>

== Nomenclature ==
Although rarely encountered, the officially "[[preferred IUPAC name]]" (PIN) of catechol is ''benzene-1,2-diol''.<ref>[http://old.iupac.org/reports/provisional/abstract04/BB-prs310305/Chapter6-Sec60-64.pdf Preferred IUPAC Names]. 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) [http://www.acdlabs.com/iupac/nomenclature/93/r93_414.htm R-5.5.1.1 Alcohols and phenols.]</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>

== See also ==
* [[Enol]]
* [[Pyrogallol]]
* [[Thiotimoline]]

== References ==
{{Reflist|30em}}

{{EB1911|wstitle=Catechu}}

== External links ==
{{Commons category|Pyrocatechol}}
* [http://www.inchem.org/documents/icsc/icsc/eics0411.htm International Chemical Safety Card 0411]
* [https://www.cdc.gov/niosh/npg/npgd0109.html NIOSH Pocket Guide to Chemical Hazards]
* [https://web.archive.org/web/20051012222358/http://www-cie.iarc.fr/htdocs/monographs/vol71/012-catechol.html IARC Monograph: "Catechol"]
* [http://www.acdlabs.com/iupac/nomenclature/ IUPAC Nomenclature of Organic Chemistry] (online version of the "''Blue Book''")

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[[Category:Catechols| ]]
[[Category:5-HT3 receptor positive allosteric modulators]]
[[Category:Antioxidants]]
[[Category:Chelating agents]]
[[Category:Enediols]]
[[Category:IARC Group 2B carcinogens]]
[[Category:Photographic chemicals]]
[[Category:Reducing agents]]
[[Category:Substances discovered in the 19th century]]