On Air


Buy this Domain?
Do you interesting about this domain and the running project?
Feel free to send your offer to webmaster.
pay with Paypal



|Section2={{Chembox Properties | Formula = C6H6O2 | MolarMass = 110.1 g/mol | Appearance = white to brown feathery crystals | Odor = faint, phenolic odor | Density = 1.344 g/cm3, solid | Solubility = 430 g/L | SolubleOther = very soluble in pyridine soluble in chloroform, benzene, CCl4, ether, ethyl acetate | MeltingPtC = 105 | BoilingPtC = 245.5 | BoilingPt_notes = (sublimes) | pKa = 9.48 | LogP = 0.88 | RefractIndex = 1.604 | MagSus = -68.76·10−6 cm3/mol | VaporPressure = 20 Pa (20 °C) | Dipole = 2.62±0.03 D }} |Section3={{Chembox Structure | CrystalStruct = monoclinic | Dipole = }} |Section7={{Chembox Hazards | ExternalSDS = Sigma-Aldrich | EUClass = Harmful (Xn) | NFPA-H = 3 | NFPA-F = 1 | NFPA-R = 0 | RPhrases = , | SPhrases = , , , | FlashPtC = 127 | AutoignitionPtC = 510 | PEL = none | ExploLimits = 1.4%-? | LD50 = 300 mg/kg (rat, oral) | REL = TWA 5 ppm (20 mg/m3) skin | IDLH = N.D. }} |Section8={{Chembox Related | OtherFunction_label = benzenediols | OtherFunction = Resorcinol Hydroquinone | OtherCompounds = 1,2-benzoquinone }} }} 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

Catechol was first isolated in 1839 by Edgar Hugo Emil Reinsch (1809 - 1884) 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).Hugo Reinsch (1839) "Einige Bemerkungen über Catechu" (Some observations about catechu), Repertorium für die Pharmacie, 68 : 49-58. Reinsch describes the preparaton 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".) Upon heating catechin above its decomposition point, a substance that Reinsch first named Brenz-Katechusäure (burned catechu acid) sublimated as a white efflorescence. This was a thermal decomposition product of the flavanols in catechin. In 1841, both Wackenroder and Zwenger independently rediscovered catechol; in reporting on their findings, Philosophical Magazine coined the name pyrocatechin.See:
  • H. Wackenroder (1841) "Eigenschaften der Catechusäure" (Properties of catechu acid), Annalen der Chemie und Pharmacie, 37 : 306-320.
  • Constantin Zwenger (1841) "Ueber Catechin" (On catechin), Annalen der Chemie und Pharmacie, 37 : 320-336.
  • (Anon.) (1841) "On catechin (catechinic acid) and pyrocatechin (pyrocatechinic acid)", Philosophical Magazine, 19 : 194-195. By 1852, 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.See:
  • Rudolf Wagner (1852) "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 ; 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), p. 657. See also p. 720. In 1879, the Journal of the Chemical Society recommended that catechol be called "catechol", and in the following year, it was listed as such.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) "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), p.524.
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. Catechol is produced industrially by the hydroxylation of phenol using hydrogen peroxide.Fiegel, Helmut et al. (2002) "Phenol Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH: Weinheim. . C6H5OH + H2O2 → C6H4(OH)2 + H2O Previously, it was produced by hydroxylation of salicylaldehyde using hydrogen peroxide, 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 CH3-O bond as promoted by hydriodic acid.


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)33−. 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. Iron-containing dioxygenase enzymes catalyze the cleavage of catechol.

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).
"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Catechol, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Catechol&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany