Pyrocatechol

Chembox new
Name = Pyrocatechol
ImageFileL1 = Pyrocatechol.svg
ImageSizeL1 = 120px
ImageNameL1 = Pyrocatechol
ImageFileR1 = Pyrocatechol-3d.png ImageSizeR1 = 150px
IUPACName = Pyrocatechol
OtherNames = catechol
benzene-1,2-diol
2-hydroxyphenol
α-hydroxyphenol
"o"-benzenediol
"o"-hydroxyphenol
1,2-dihydroxybenzene
pyrocatechin
Section1 = Chembox Identifiers
SMILES = Oc1c(O)cccc1
CASNo = 120-80-9
RTECS = UX1050000
Section2 = Chembox Properties
Formula = C₆H₆O₂
MolarMass = 110.1 g/mol
Appearance = white solid
Density = 1.344 g/cm³, solid
Solubility = 43 g/100 mL
MeltingPtC = 105
BoilingPtC = 245.5
pKa = 9.5
Section3 = Chembox Structure
Dipole =
Section7 = Chembox Hazards
ExternalMSDS =
EUClass = Harmful (Xn)
NFPA-H = 2
NFPA-F = 1
NFPA-R =
RPhrases = R21/22, R36/38
SPhrases = s2, S22, S26, S37
FlashPt = 127 °C
Section8 = Chembox Related
Function = benzenediols
OtherFunctn = Resorcinol
Hydroquinone
OtherCpds = 1,2-benzoquinone

Pyrocatechol, more commonly known as catechol, is the organic compound with the formula C₆H₄(OH)₂. It is one of three isomeric benzenediols. This colourless compound occurs naturally, but about 20000 tons are manufactured each year, mainly as precursors to pesticides, flavors, and fragrances.

Isolation and synthesis

Catechol was first isolated in 1839 by H. Reinsch by distilling catechin (the juice of "Mimosa catechu" ("Acacia catechu" L.f))Fact|date=October 2007; it occurs free in kino and in beechwood tar; its sulfonic acid is present in the urine of horse and humans. It is produced industrially by the hydroxylation of phenol using hydrogen peroxide: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] :C₆H₅OH + H₂O₂ → C₆H₄(OH)₂ + H₂O

Catechol has been prepared in many ways from phenols, e.g. by fusing 2-phenolsulfonic acid, 2-chlorphenol, 2-bromophenol, or 2,6-phenoldisulfonic acid with potash, or, better, by heating its methyl ether, guaiacol, a constituent of beechwood tar, with hydriodic acid.Fact|date=October 2007 Many pyrocatechin derivatives have been suggested for therapeutic applications.

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.Fact|date=October 2007 It reduces silver solutions in the cold and alkaline copper on heating.Fact|date=October 2007 Catechol can also be conjugated to ruthenium. [Ru^III(NH₃)₄(catechol)] ⁺ oxidizes faster than catechol in the presence of oxygen, but controlled potential electrolysis showed that its oxidation involves only one electron. [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.]

Occurrence

Small amounts of catechol occur naturally in fruits and vegetables, along with the enzyme polyphenol oxidase. Upon mixing the enzyme with the substrate and exposure to oxygen (as when a potato or apple is cut), the colorless catechol oxidizes to reddish-brown benzoquinone derivatives . The enzyme is inactivated by adding an acid, such as lemon juice, or by refrigeration. Excluding oxygen also prevents the browning reaction. Benzoquinone is said to be antimicrobial, which slows the spoilage of wounded fruits and other plant parts. 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, hormones/neurotransmitters, and catechin, which is found in tea.

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. It is a common building block in organic synthesis. [Barner, B. A. "Catechol" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.] Several industrially significant flavors and fragrances are prepared starting from catechol. Guaiacol, 2-methoxyphenol, is prepared by methylation of catechol and then converted to vanillin on a scale of about 10,000 tons/year (1990). The related monoethyl ether of catechol, guethol, is converted to "ethylvanillin," which is a component of chocolate confectionaries. 3-"Trans"-Isocamphylcyclohexanol (CAS#3407-42-9), widely used as a replacement for sandelwood oil, is prepared from catechol via guaiacol and camphor. Piperonal (CAS#120-57-0), a flowery scent, is prepared from the methylene diether of catechol followed by condensation with glyoxal and decarboxylation. [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]

Pyrocatechol is used as a black-and-white photographic developers, but except for some special purpose applications, its use until recently was largely historical. Hobbyist-mixed developers use the "Pyrocat" family of developers.

Nomenclature

Pyrocatechol is the name recommended by the International Union of Pure and Applied Chemistry (IUPAC) in its "1993 Recommendations for the Nomenclature of Organic Chemistry". [cite book | author=Panico, R.; & Powell, W. H. (Eds.) | title=A Guide to IUPAC Nomenclature of Organic Compounds 1993 | location=Oxford | publisher=Blackwell Science | year=1994 | id=ISBN 0-632-03488-2]

ee also

*Urushiol

References

External links

* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc04/icsc0411.htm International Chemical Safety Card 0411]
* [http://www.cdc.gov/niosh/npg/npgd0109.html NIOSH Pocket Guide to Chemical Hazards]
* [http://www-cie.iarc.fr/htdocs/monographs/vol71/012-catechol.html IARC Monograph: "Catechol"]
*ecb
* [http://www.acdlabs.com/iupac/nomenclature/ IUPAC Nomenclature of Organic Chemistry] (online version of the "Blue Book")