| |||
| Names | |||
|---|---|---|---|
| Preferred IUPAC name Benzene-1,2-diol[1] | |||
| Other names | |||
| Identifiers | |||
| |||
3D model (JSmol) | |||
| 471401 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
| ||
| DrugBank | |||
| ECHA InfoCard | 100.004.025 | ||
| EC Number |
| ||
| 2936 | |||
| KEGG |
| ||
| RTECS number |
| ||
| UNII | |||
| |||
| Properties | |||
| C6H6O2 | |||
| Molar mass | 110.112 g·mol−1 | ||
| 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) | ||
| 312 g/L at 20 °C[2] | |||
| Solubility | very soluble inpyridine soluble inchloroform,benzene,CCl4,ether,ethyl acetate | ||
| logP | 0.88 | ||
| Vapor pressure | 20 Pa (20 °C) | ||
| Acidity (pKa) | 9.45, 12.8 | ||
| −6.876×10−5 cm3/mol | |||
Refractive index (nD) | 1.604 | ||
| 2.62±0.03 D[3] | |||
| Structure | |||
| monoclinic | |||
| Thermochemistry | |||
Std enthalpy of formation(ΔfH⦵298) | −354.1 kJ·mol−1 | ||
Enthalpy of fusion(ΔfH⦵fus) | 22.8 kJ·mol−1 (at melting point) | ||
| Hazards | |||
| GHS labelling: | |||
   | |||
| Danger | |||
| H301,H311,H315,H317,H318,H332,H341 | |||
| P261,P301,P302,P305,P310,P312,P330,P331,P338,P351,P352 | |||
| NFPA 704 (fire diamond) | |||
| Flash point | 127 °C (261 °F; 400 K) | ||
| 510 °C (950 °F; 783 K) | |||
| Explosive limits | 1.4%–?[4] | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) | 300 mg/kg (rat, oral) | ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible) | none[4] | ||
REL (Recommended) | TWA 5 ppm (20 mg/m3) [skin][4] | ||
IDLH (Immediate danger) | N.D.[4] | ||
| Safety data sheet (SDS) | Sigma-Aldrich | ||
| Related compounds | |||
Relatedbenzenediols | Resorcinol Hydroquinone | ||
Related compounds | 1,2-benzoquinone | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Catechol (/ˈkætɪtʃɒl/ or/ˈkætɪkɒl/), also known aspyrocatechol or1,2-dihydroxybenzene, is an organic compound with the molecular formulaC6H4(OH)2. It is theorthoisomer of the three isomericbenzenediols. This colorless compound occurs naturally in trace amounts. It was first discovered bydestructive distillation of the plant extractcatechin. 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 infruits andvegetables.[2]
Catechol was first isolated in 1839 by Edgar Hugo Emil Reinsch (1809–1884) bydistilling it from the solidtannic preparationcatechin, which is the residuum ofcatechu, the boiled or concentrated juice ofMimosa catechu (Acacia catechu).[5] Upon heating catechin above its decomposition point, a substance that Reinsch first namedBrenz-Katechusäure (burned catechu acid)sublimated as a whiteefflorescence. This was a thermal decomposition product of theflavanols in catechin. In 1841, bothWackenroder and Zwenger independently rediscovered catechol; in reporting on their findings,Philosophical Magazine coined the namepyrocatechin.[6] By 1852,Erdmann realized that catechol wasbenzene with two oxygen atoms added to it; in 1867,August Kekulé realized that catechol was adiol of benzene, so by 1868, catechol was listed aspyrocatechol.[7] In 1879, theJournal of the Chemical Society recommended that catechol be called "catechol", and in the following year, it was listed as such.[8]
Catechol has since been shown to occur in free form naturally inkino and inbeechwood tar. Itssulfonic acid has been detected in theurine of horses and humans.[9]
Catechol is produced industrially by thehydroxylation ofphenol usinghydrogen peroxide.[2]
It can be produced by reaction ofsalicylaldehyde with base and hydrogen peroxide (Dakin oxidation),[10] as well as thehydrolysis of 2-substituted phenols, especially2-chlorophenol, with hot aqueous solutions containing alkali metal hydroxides. Its methyl ether derivative,guaiacol, converts to catechol via hydrolysis of theCH3−O bond as promoted byhydroiodic acid (HI).[10]
Like some other difunctional benzene derivatives, catechol readilycondenses to formheterocyclic compounds. For example, usingphosphorus trichloride orphosphorus oxychloride gives the cyclic chlorophosphonite or chlorophosphonate, respectively;sulfuryl chloride gives thesulfate; andphosgene (COCl2) gives thecarbonate:[11]
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, while the alkaline solution rapidly changes to a green and finally to a black color on exposure to the air.[12] Iron-containingdioxygenaseenzymescatalyze thecleavage of catechol.
Catechols convert to the semiquinone radical. AtpH = 7, this conversion occurs at 100 mV:[citation needed]
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-protonreduction of1,2-benzoquinone (E0 = +795 mV vsSHE;Em (at pH 7) = +380 mV vs SHE).[13]
Theredox series catecholate dianion, monoanionic semiquinonate, and benzoquinone are collectively calleddioxolenes. Dioxolenes can function asligands for metal ions.[14]
![3,4-dihydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione, a metabolite of cholesterol[15]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aDHSA.svg)
Catechol derivatives are found widely in nature. They often arise by hydroxylation of phenols.[16]Arthropodcuticle consists ofchitin linked by a catecholmoiety toprotein. The cuticle may be strengthened bycross-linking (tanning andsclerotization), in particular, ininsects, and of course bybiomineralization.[17]
The synthetic derivative4-tert-butylcatechol is used as anantioxidant andpolymerization inhibitor.
Approximately 50% of the synthetic catechol is consumed in the production ofpesticides, the remainder being used as a precursor to fine chemicals such as perfumes and pharmaceuticals.[2] It is a common building block inorganic synthesis.[18] Several industrially significantflavors andfragrances are prepared starting from catechol.Guaiacol is prepared bymethylation of catechol and is then converted tovanillin on a scale of about 10M kg per year (1990). The related monoethyl ether of catechol,guethol, is converted toethylvanillin, a component ofchocolate confectioneries. 3-trans-Isocamphylcyclohexanol, widely used as a replacement forsandalwood oil, is prepared from catechol via guaiacol andcamphor.Piperonal, a flowery scent, is prepared from the methylene diether of catechol followed by condensation withglyoxal anddecarboxylation.[19]
Josef Maria Eder published in 1879 his findings on the use of catechol as a black-and-whitephotographic developer,[20][21] but, except for some special purpose applications, its use is largely historical. It is rumored to have been used briefly inEastman Kodak's HC-110 developer and Anchell supposes it to be a component inTetenal's Neofin Blau developer.[22] It is a key component of Finol from Moersch Photochemie in Germany.[citation needed] Modern catechol developing was pioneered by noted photographerSandy King, whose "PyroCat" formulation is popular among modern black-and-white film photographers.[23] 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.[22]
Although rarely encountered, the officially "preferredIUPAC name" (PIN) of catechol isbenzene-1,2-diol.[24] The trivial namepyrocatechol is a retained IUPAC name, according to the1993 Recommendations for the Nomenclature of Organic Chemistry.[25][26]
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This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Catechu".Encyclopædia Britannica (11th ed.). Cambridge University Press.
