Catechol

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Not to be confused with Catechin, also sometimes called catechol.
Catechol
IUPAC name

Benzene-1,2-diol

Other names

pyrocatechol
1,2-benzenediol
2-hydroxyphenol
1,2-dihydroxybenzene

Identifiers
CAS number 120-80-9 YesY
PubChem 289
ChemSpider 283 YesY
EC number 204-427-5
KEGG C00090 YesY
ChEMBL CHEMBL280998 N
RTECS number UX1050000
Jmol-3D images Image 1
Properties
Molecular formula C6H6O2
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)
Solubility in water 43 g/100 mL
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
Refractive index (nD) 1.604
Structure
Crystal structure monoclinic
Hazards
MSDS Sigma-Aldrich
EU classification Harmful (Xn)
R-phrases R21/22, R36/38
S-phrases (S2), S22, S26, S37
NFPA 704
1
3
0
Flash point 127 °C; 261 °F; 400 K
Autoignition temperature 510 °C; 950 °F; 783 K
Related compounds
Related benzenediols Resorcinol
Hydroquinone
Related compounds 1,2-benzoquinone
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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 basic 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

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.[1]

Catechol is produced industrially by the hydroxylation of phenol using hydrogen peroxide:[2]

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.[3]

Reactions

Organic chemistry

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

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.[4]

Redox chemistry

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). [5] [6]

The redox series catecholate dianion, monoanionic semiquinonate, and benzoquinone are collectively called dioxolenes. Dioxolenes are used as ligands.[7]

Natural occurrences

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.[8]

Pyrocatechol is also found in Agaricus bisporus.[9]

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

Presence of the catechol moiety

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.[10] Catechols such as DHSA are produced through the metabolism of cholesterol by bacteria such as Mycobacterium tuberculosis.[11]

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.

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.[2] It is a common building block in organic synthesis.[12] 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.[13]

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]

Catechol derivatives

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.

Nomenclature

The "preferred IUPAC name" (PIN) of catechol is benzene-1,2-diol. [14] The trivial name pyrocatechol is a retained IUPAC name, according to the 1993 Recommendations for the Nomenclature of Organic Chemistry. [15] [16]

See also

References

  1. ↑ 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
  2. ↑ 2.0 2.1 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
  3. ↑ Alfred, Allen (1889). Commercial Organic Analysis. London: J & A Churchill. p. 65. 
  4. ↑ 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.
  5. ↑ 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. 
  6. ↑ 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. 
  7. ↑ Griffith, W. P. (1993). "Recent advances in dioxolene chemistry". Transition Metal Chemistry 18 (2): 250–256. doi:10.1007/BF00139966. 
  8. ↑ Phenols and Polyphenols from Argania spinosa. Z. Charrouf and D. Guillaume, American Journal of Food Technology, 2007, 2, pages 679-683, doi:10.3923/ajft.2007.679.683
  9. ↑ Delsignore, A; Romeo, F; Giaccio, M (1997). "Content of phenolic substances in basidiomycetes". Mycological Research 101: 552–6. doi:10.1017/S0953756296003206. 
  10. ↑ 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. 
  11. ↑ 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 (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. 
  12. ↑ Barner, B. A. "Catechol" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289.
  13. ↑ 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
  14. ↑ Preferred IUPAC Names September 2004, Chapter 6, Sect 60-64, p.38
  15. ↑ IUPAC, Commission on Nomenclature of Organic Chemistry. A Guide to IUPAC Nomenclature of Organic Compounds (Recommendations 1993) R-5.5.1.1 Alcohols and phenols.
  16. ↑ 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 domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press 

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