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Phenols

From Wikipedia, the free encyclopedia
Chemical compounds in which hydroxyl group is attached directly to an aromatic ring
This article is about the class of chemicals containing a phenol group. For the molecule alone, seePhenol.

Inorganic chemistry,phenols, sometimes calledphenolics, are a class ofchemical compounds consisting of one or morehydroxylgroups (−OH)bonded directly to anaromatic hydrocarbon group.[1] The simplest isphenol,C
6
H
5
OH
. Phenolic compounds are classified as simple phenols orpolyphenols based on the number of phenol units in the molecule.

Phenol – the simplest of the phenols
Chemical structure ofsalicylic acid, theactive metabolite ofaspirin

Phenols are both synthesized industrially and produced by plants and microorganisms.[2]

Properties

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Acidity

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Phenols are moreacidic than typical alcohols. The acidity of the hydroxyl group in phenols is commonly intermediate between that ofaliphatic alcohols andcarboxylic acids (their pKa is usually between 10 and 12). Deprotonation of a phenol forms a corresponding negativephenolate ion orphenoxide ion, and the correspondingsalts are calledphenolates orphenoxides (aryloxides according to the IUPAC Gold Book).[citation needed]

Condensation with aldehydes and ketones

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Phenols are susceptible toElectrophilic aromatic substitutions. Condensation withformaldehyde gives resinous materials, famouslyBakelite.[citation needed]

Another industrial-scale electrophilic aromatic substitution is the production ofbisphenol A, which is produced by thecondensation withacetone.[3]

C-Alkylation with alkenes

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Phenol is readily alkylated at the ortho positions using alkenes in the presence of a Lewis acid such asaluminium phenoxide:[citation needed]

CH2=CR2 + C6H5OH → R2CHCH2-2-C6H4OH

More than 100,000 tons oftert-butyl phenols are produced annually (year: 2000) in this way, usingisobutylene (CH2=CMe2) as the alkylating agent. Especially important is2,6-ditert-butylphenol, a versatileantioxidant.[3]

Other reactions

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Phenols undergoesterification. Phenol esters areactive esters, being prone to hydrolysis. Phenols arereactive species towardoxidation. Oxidative cleavage, for instance cleavage of 1,2-dihydroxybenzene to the monomethylester of 2,4 hexadienedioic acid with oxygen, copper chloride in pyridine[4] Oxidative de-aromatization toquinones also known as theTeuber reaction.[5] andoxone.[6] In reaction depicted below 3,4,5-trimethylphenol reacts withsinglet oxygen generated fromoxone/sodium carbonate in anacetonitrile/water mixture to a para-peroxyquinole. Thishydroperoxide is reduced to the quinole withsodium thiosulfate.

Oxone phenol dearomatization

Phenols are oxidized tohydroquinones in theElbs persulfate oxidation.

Reaction of naphtols and hydrazines and sodium bisulfite in theBucherer carbazole synthesis.

Synthesis

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Many phenols of commercial interest are prepared by elaboration ofphenol orcresols. They are typically produced by the alkylation ofbenzene/toluene withpropylene to formcumene thenO
2
is added withH
2
SO
4
to form phenol (Hock process). In addition to the reactions above, many other more specialized reactions produce phenols:

Classification

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The best-selling drug in the U.S.,Acetaminophen, also known as Paracetamol, is a phenol.

There are variousclassification schemes.[15]: 2  A commonly used scheme is based on the number of carbons and was devised byJeffrey Harborne and Simmonds in 1964 and published in 1980:[15]: 2 [16]

Phenolthe parent compound, used as adisinfectant and forchemical synthesis
Bisphenol Aand other bisphenols produced from ketones and phenol / cresol
BHT(butylated hydroxytoluene) - a fat-solubleantioxidant andfood additive
4-Nonylphenola breakdown product ofdetergents andnonoxynol-9
Orthophenyl phenolafungicide used for waxingcitrus fruits
Picric acid(trinitrophenol) - anexplosive material
PhenolphthaleinpH indicator
Xylenolused in antiseptics & disinfectants

Drugs and bioactive natural products

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More than 371 drugs approved by the FDA between the years of 1951 and 2020 contain either a phenol or a phenolic ether (a phenol with an alkyl), with nearly every class of small molecule drugs being represented, and natural products making up a large portion of this list.[17]

tyrosineone of the 20 standard amino acids
L-DOPAdopamine prodrug used to treatParkinson's disease
propofolshort-acting intravenousanesthetic agent
vitamin K hydroquinoneblood-clotting agent that converts
levothyroxine (L-thyroxine)Top-selling drug to treat thyroid hormone deficiency.
amoxicillinTop-selling antibiotic
estradiolthe major female sex hormone

References

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  1. ^IUPAC,Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "phenols".doi:10.1351/goldbook.P04539
  2. ^Hättenschwiler, Stephan; Vitousek, Peter M. (2000)."The role of polyphenols in terrestrial ecosystem nutrient cycling".Trends in Ecology & Evolution.15 (6):238–243.doi:10.1016/S0169-5347(00)01861-9.PMID 10802549.
  3. ^abFiege H; Voges H-W; Hamamoto T; Umemura S; Iwata T; Miki H; Fujita Y; Buysch H-J; Garbe D; Paulus W (2000). "Phenol Derivatives".Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH.doi:10.1002/14356007.a19_313.ISBN 978-3-527-30673-2.
  4. ^2,4-Hexadienedioic acid, monomethyl ester, (Z,Z)-Organic Syntheses, Coll. Vol. 8, p. 490 (1993); Vol. 66, p. 180 (1988)Article.
  5. ^"2,5-Cyclohexadiene-1,4-dione, 2,3,5-trimethyl".Organic Syntheses.52: 83. 1972.
  6. ^Carreño, M. Carmen; González-López, Marcos; Urbano, Antonio (2006). "Oxidative De-aromatization of para-Alkyl Phenols into para-Peroxyquinols and para-Quinols Mediated by Oxone as a Source of Singlet Oxygen".Angewandte Chemie International Edition.45 (17):2737–2741.doi:10.1002/anie.200504605.PMID 16548026.
  7. ^Fries, K.; Finck, G. (1908)."Über Homologe des Cumaranons und ihre Abkömmlinge".Chemische Berichte.41 (3):4271–4284.doi:10.1002/cber.190804103146.
  8. ^Fries, K.; Pfaffendorf, W. (1910)."Über ein Kondensationsprodukt des Cumaranons und seine Umwandlung in Oxindirubin".Chemische Berichte.43 (1):212–219.doi:10.1002/cber.19100430131.
  9. ^Bamberger, E. (1894)."Ueber die Reduction der Nitroverbindungen".Chemische Berichte.27 (2):1347–1350.doi:10.1002/cber.18940270229.
  10. ^Bamberger, E. (1894)."Über das Phenylhydroxylamin".Chemische Berichte.27 (2):1548–1557.doi:10.1002/cber.18940270276.
  11. ^H. Bucherer (1904)."Über die Einwirkung schwefligsaurer Salze auf aromatische Amido- und Hydroxylverbindungen".J. Prakt. Chem. (in German).69 (1):49–91.doi:10.1002/prac.19040690105.
  12. ^H. E. Ungnade, E. F. Orwoll (1943). "3-Bromo-4-hydroxytoluene".Organic Syntheses.23: 11.doi:10.15227/orgsyn.023.0011.
  13. ^Bracegirdle, Sonia; Anderson, Edward A. (2010). "Arylsilane oxidation—new routes to hydroxylated aromatics".Chem. Comm.46 (20):3454–6.doi:10.1039/b924135c.PMID 20582346.S2CID 31736757.
  14. ^Le Valliant, Franck; Mateos Calbet, Ana; González-Pelayo, Silvia; Reijerse, Edward J.; Ni, Shengyang; Busch, Julia; Cornella, Josep (2022)."Catalytic synthesis of phenols with nitrous oxide".Nature.604 (7907):677–683.Bibcode:2022Natur.604..677L.doi:10.1038/s41586-022-04516-4.PMC 9046086.PMID 35478236.
  15. ^abWilfred Vermerris and Ralph Nicholson.Phenolic Compound Biochemistry Springer, 2008.
  16. ^Harborne, J. B. (1980). "Plant phenolics". In Bell, E. A.; Charlwood, B. V. (eds.).Encyclopedia of Plant Physiology, volume 8 Secondary Plant Products. Berlin Heidelberg New York: Springer-Verlag. pp. 329–395.
  17. ^Scott, Kevin A.; Cox, Philip B.; Njardarson, Jon T. (2022-05-26)."Phenols in Pharmaceuticals: Analysis of a Recurring Motif".Journal of Medicinal Chemistry.65 (10):7044–7072.doi:10.1021/acs.jmedchem.2c00223.ISSN 0022-2623.PMID 35533692.S2CID 248667453.
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