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Not to be confused with Catechin, also sometimes called catechol.
Skeletal formula
Ball-and-stick model
IUPAC name
Other names
120-80-9 YesY
ChemSpider 283 YesY
EC number 204-427-5
Jmol-3D images Image
KEGG C00090 YesY
PubChem 289
RTECS number UX1050000
Molar mass 110.1 g/mol
Appearance white to brown feathery crystals
Odor faint, phenolic odor
Density 1.344 g/cm3, solid
Melting point 105 °C (221 °F; 378 K)
Boiling point 245.5 °C (473.9 °F; 518.6 K) (sublimes)
430 g/L
Solubility very soluble in pyridine
soluble in chloroform, benzene, CCl4, ether, acetate
log P 0.88
Vapor pressure 20 Pa (20 °C)
Acidity (pKa) 9.48
Crystal structure monoclinic
MSDS Sigma-Aldrich
EU classification Harmful (Xn)
R-phrases R21/22, R36/38
S-phrases (S2), S22, S26, S37
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 127 °C (261 °F; 400 K)
510 °C (950 °F; 783 K)
Explosive limits 1.4%-?[1]
300 mg/kg (rat, oral)
US health exposure limits (NIOSH):
TWA 5 ppm (20 mg/m3) [skin][1]
Related compounds
Related benzenediols
Related compounds
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N verify (what isYesY/N?)
Infobox references

Catechol, also known as pyrocatechol or 1,2-dihydroxybenzene, is an organic compound with the molecular formula C6H4(OH)2. It is the ortho isomer of the three isomeric benzenediols. This colorless compound occurs naturally in trace amounts. It was first discovered by destructive distillation of the plant extract catechin. About 20 million kg are now synthetically produced annually as a commodity organic chemical, mainly as a precursor to pesticides, flavors, and fragrances.

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 generally to the catechins.)

Isolation and synthesis[edit]

Catechol was first isolated in 1839 by H. Reinsch by distilling it from the solid tannic preparation catechin, which is the residuum of catechu, the boiled or concentrated juice of Mimosa catechu (Acacia catechu L.f). Upon heating catechin above its decomposition point, a substance Reinsch first named "pyrocatechol" distilled and condensed as a white solid ("pyro" referring to heat). This was a thermal decomposition product of the flavanols in catechin. "Pyrocatechol" is now simply referred to as catechol.

Catechol has since been shown to occur in free-form naturally in kino and in beechwood tar. Its sulfonic acid has been detected in the urine of horses and humans.[2]

Catechol is produced industrially by the hydroxylation of phenol using hydrogen peroxide:[3]

C6H5OH + H2O2 → C6H4(OH)2 + H2O

Previously, catechol was produced by 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 CH3-O bond as promoted by hydriodic acid.[4]


Organic chemistry[edit]

Like other difunctional benzene derivatives, catechol readily condenses to form heterocyclic compounds. Cyclic esters are formed upon treatment with phosphorus trichloride and phosphorus oxychloride, carbonyl chloride, and sulphuryl chloride:

C6H4(OH)2 + XCl2 → C6H4(O2X) + 2 HCl
where X = CO, SO2, PCl, P(O)Cl

Catechols produce quinones with the addition of ceric ammonium nitrate (CAN).

With metal ions[edit]

Catechol is the conjugate acid of a chelating agent used widely in coordination chemistry. Basic solutions of catechol react with iron(III) to give the red [Fe(C6H4O2)3]3−. Ferric chloride 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] It reduces silver solutions in the cold and alkaline copper on heating.[citation needed] Catechol can also be conjugated to ruthenium. [RuIII(NH3)4(catechol)]+ oxidizes faster than catechol in the presence of oxygen, but controlled potential electrolysis showed that its oxidation involves only one electron.[5]

Redox chemistry[edit]

Catechol is produced by a reversible two-electron, two-proton reduction of 1,2-benzoquinone (E° = +795 mV vs SHE; Em (pH 7) = +380 mV vs SHE). [6] [7]

Electrochemical interconversion of 1,2-benzoquinone and catechol

The redox series catecholate dianion, monoanionic semiquinonate, and benzoquinone are collectively called dioxolenes. Dioxolenes are used as ligands.[8]

Natural occurrences[edit]

Small amounts of catechol occur naturally in fruits and vegetables, along with the enzyme polyphenol oxidase (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.

It is one of the main natural phenols in argan oil.[9]

Pyrocatechol is also found in Agaricus bisporus.[10]

It is also a component of castoreum, a substance from castors, used in perfumery.

Presence of the catechol moiety[edit]

Catechol moieties are also found widely within the natural world. Arthropod cuticle consists of chitin linked by a catechol moiety to protein. The cuticle may be strengthened by cross-linking (tanning and sclerotization), in particular, in insects, and of course by biomineralization.[11] Catechols such as DHSA are produced through the metabolism of cholesterol by bacteria such as Mycobacterium tuberculosis.[12]

Urushiols are naturally existing organic compounds that have the catechol skeleton structure and diphenol functionality but with alkyl groups substituted onto the aromatic ring. Urushiols are the skin-irritating poisons found in plants like poison ivy, etc. Catecholamines are biochemically significant hormones/neurotransmitters that are phenethylamines in which the phenyl group has a catechol skeleton structure.

Parts of a molecule of catechin, another natural compound present in tea, has the catechol skeleton structure in it.


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.[3] It is a common building block in organic synthesis.[13] Several industrially significant flavors and 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.[14]

Catechol is used as a black-and-white photographic developer, 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.[citation needed] The Film Developing Cookbook has examples.[15]

Catechol derivatives[edit]

The catechol skeleton occurs in a variety of natural products such as urushiols, which are the skin-irritating poisons found in plants like poison ivy, and catecholamines, drugs imitating them (such as MDMA), hormones/neurotransmitters, and catechin, which is found in tea. Many pyrocatechin derivatives have been suggested for therapeutic applications.


The "preferred IUPAC name" (PIN) of catechol is benzene-1,2-diol.[16] The trivial name pyrocatechol is a retained IUPAC name, according to the 1993 Recommendations for the Nomenclature of Organic Chemistry. [17] [18]

See also[edit]


  1. ^ a b c d "NIOSH Pocket Guide to Chemical Hazards #0109". National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ Zheng, L. T.; Ryu, G. M.; Kwon, B. M.; Lee, W. H.; Suk, K. (2008). "Anti-inflammatory effects of catechols in lipopolysaccharide-stimulated microglia cells: Inhibition of microglial neurotoxicity". European Journal of Pharmacology 588: 106. doi:10.1016/j.ejphar.2008.04.035.  edit
  3. ^ a b Fiegel, Helmut et al. (2002) "Phenol Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH: Weinheim. doi:10.1002/14356007.a19_313.
  4. ^ Alfred, Allen (1889). Commercial Organic Analysis. London: J & A Churchill. p. 65. 
  5. ^ Wagner l. c, A.; Vítor, D. N.; Pereira, M. R. G.; Desá, D. S.; Alvarez, L. D. G.; Pinheiro, A. M.; Costa, S. L.; Costa, M. F. D.; Rocha, Z. N. N. D.; El-Bachá, R. S. (2007). "Redox Properties of Ruthenium Complex with Catechol Are Involved in Toxicity to Glial Cells". Journal of the Chilean Chemical Society 52 (3). doi:10.4067/S0717-97072007000300010.  edit
  6. ^ Horner, Leopold; Geyer, Ekkehard (1965). "Zur Kenntnis der o-Chinone, XXVII: Redoxpotentiale von Brenzcatechin-Derivaten". Chemische Berichte 98 (6): 2016–2045. doi:10.1002/cber.19650980641. 
  7. ^ Nematollahi, D.; Rafiee, M. (2004-05-01). "Electrochemical oxidation of catechols in the presence of acetylacetone". Journal of Electroanalytical Chemistry 566 (1): 31–37. doi:10.1016/j.jelechem.2003.10.044. 
  8. ^ Griffith, W. P. (1993). "Recent advances in dioxolene chemistry". Transition Metal Chemistry 18 (2): 250–256. doi:10.1007/BF00139966.  edit
  9. ^ Charrouf, Z.; Guillaume, D. (2007). "Phenols and Polyphenols from Argania spinosa". American Journal of Food Technology 2 (7): 679. doi:10.3923/ajft.2007.679.683.  edit
  10. ^ Delsignore, A; Romeo, F; Giaccio, M (1997). "Content of phenolic substances in basidiomycetes". Mycological Research 101 (5): 552–6. doi:10.1017/S0953756296003206. 
  11. ^ Briggs DEG (1999). "Molecular taphonomy of animal and plant cuticles: selective preservation and diagenesis". Philosophical Transactions of the Royal Society B: Biological Sciences 354 (1379): 7. doi:10.1098/rstb.1999.0356. 
  12. ^ PDB 2ZI8; Yam KC, D'Angelo I, Kalscheuer R, Zhu H, Wang JX, Snieckus V, Ly LH, Converse PJ, Jacobs WR, Strynadka N, Eltis LD; d'Angelo; Kalscheuer; Zhu; Wang; Snieckus; Ly; Converse; Jacobs Jr; Strynadka; Eltis (March 2009). "Studies of a ring-cleaving dioxygenase illuminate the role of cholesterol metabolism in the pathogenesis of Mycobacterium tuberculosis". PLoS Pathog. 5 (3): e1000344. doi:10.1371/journal.ppat.1000344. PMC 2652662. PMID 19300498. 
  13. ^ Barner, B. A. (2004) "Catechol" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette), J. Wiley & Sons, New York. doi:10.1002/047084289.
  14. ^ Fahlbusch, Karl-Georg et al. (2003) "Flavors and Fragrances" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH: Weinheim doi:10.1002/14356007.a11_141.
  15. ^ Stephen G. Anchell and Bill Troop. The Film Developing Cookbook. ISBN 978-0240802770. 
  16. ^ Preferred IUPAC Names. September 2004, Chapter 6, Sect 60–64, p. 38
  17. ^ IUPAC, Commission on Nomenclature of Organic Chemistry. A Guide to IUPAC Nomenclature of Organic Compounds (Recommendations 1993) R- Alcohols and phenols.
  18. ^ Panico, R.; & Powell, W. H. (Eds.) (1994). A Guide to IUPAC Nomenclature of Organic Compounds 1993. Oxford: Blackwell Science. ISBN 0-632-03488-2. 

Public Domain This article incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press. 

External links[edit]