Catechol ( or ), also known as pyrocatechol or 1,2-dihydroxybenzene, is an organic compound with the molecular formula . It is the ortho isomer of the three isomeric . 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.[
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Isolation and synthesis
Catechol was first isolated in 1839 by Edgar Hugo Emil Reinsch (1809–1884) by Distillation it from the solid Tannin preparation catechin, which is the residuum of catechu, the boiled or concentrated juice of Mimosa catechu ( Acacia catechu).[Hugo Reinsch (1839) "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".)] 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:
] 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 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.
It can be produced by reaction of salicylaldehyde with base and hydrogen peroxide (Dakin oxidation),
Reactions
Like some other difunctional benzene derivatives, catechol readily Condensed tannin to form heterocyclic compounds. For example, using phosphorus trichloride or phosphorus oxychloride gives the cyclic chlorophosphonite or chlorophosphonate, respectively; sulfuryl chloride gives the organosulfate; and phosgene () gives the carbonate ester:
- where X = PCl or POCl; ; CO
Basic solutions of catechol react with iron(III) to give the red . 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.
Redox chemistry
Catechols convert to the semiquinone radical. At , this conversion occurs at 100 mV:
The semiquinone radical can be reduced to the catecholate dianion, the potential being dependent on pH:
Catechol is produced by a reversible two-electron, two-proton reduction of 1,2-benzoquinone ( vs SHE; vs SHE).
The redox series catecholate dianion, monoanionic semiquinonate, and benzoquinone are collectively called dioxolenes. Dioxolenes can function as for metal ions.
Catechol derivatives
File:DHSA.svg|DHSA, a metabolite of cholesterol[; ]
File:Catechin structure.svg|Catechin, a component of tea.
File:Piceatannol.svg|Piceatannol, an antioxidant found in some red wines.
File:Urushiol.svg|, the active agent in poison ivy (R = (CH2)14CH3, (CH2)7CH=CHCH2CH=CHCH2CH=CH2, and others)
File:Catecholamine.svg|, drugs imitating them (such as MDMA), /
File:Dopamine.svg|Dopamine, a well-known neurotransmitter with many important roles in cells
File:Quercetin.svg|Quercetin, which is found in many foods.
Catechol derivatives are found widely in nature. They often arise by hydroxylation of phenols.
The synthetic derivative 4- tert-butylcatechol is used as an antioxidant and polymerization inhibitor.
Uses
Approximately 50% of the synthetic catechol is consumed in the production of , the remainder being used as a precursor to fine chemicals such as perfumes and pharmaceuticals.[ It is a common building block in organic synthesis.]
Josef Maria Eder published in 1879 his findings on the use of catechol as a black-and-white photographic developer,
Nomenclature
Although rarely encountered, the officially "preferred IUPAC name" (PIN) of catechol is benzene-1,2-diol.[ Preferred IUPAC Names. September 2004, Chapter 6, Sect 60–64, p. 38] The trivial name pyrocatechol is a retained IUPAC name, according to the 1993 Recommendations for the Nomenclature of Organic Chemistry.[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.]
See also
External links
