Phenols

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In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group (-O H) attached to an aromatic hydrocarbon group. The simplest of the class is phenol (C₆H₅OH).

Although similar to alcohols, phenols have unique properties and are not classified as alcohols (since the hydroxyl group is not bonded to a saturated carbon atom). They have relatively higher acidities due to the aromatic ring tightly coupling with the oxygen and a relatively loose bond between the oxygen and hydrogen. The acidity of the hydroxyl group in phenols is commonly intermediate between that of aliphatic alcohols and carboxylic acids (their pK_a is usually comprised between 10 and 12). Loss of a positive hydrogen ion (H⁺) from the hydroxyl group of a phenol forms a negative phenolate ion.

Some phenols are germicidal and are used in formulating disinfectants. Others possess estrogenic or endocrine disrupting activity.

Contents 1 Synthesis of phenols 2 Reactions of phenols 3 Phenolic compounds 3.1 Medicinals 4 References

Synthesis of phenols

Several laboratory methods for the synthesis of phenols:

• by an ester rearrangement in the Fries rearrangement
• by a rearrangement of N-phenylhydroxylamines in the Bamberger rearrangement
• by hydrolysis of phenolic esters or ethers
• by reduction of quinones
• by replacement of an aromatic amine by an hydroxyl group with water and sodium bisulfite in the Bucherer reaction
• by hydrolysis of diazonium salts
• by oligomerisation with formaldehyde + base catalysed reaction with epichlorohydrine to epoxi resin components
• by reaction with acetone/ketones to e.g. Bisphenol A, an important monomer for resins, e.g. polycarbonate(PC), epoxi resins
• by a rearrangement reaction of dienones ^[1] in the dienone phenol rearrangement ^[2]:

Reactions of phenols

Phenols react in a wide variety of ways.

• Esterification reactions and ether formation
• Electrophilic aromatic substitutions as the hydroxyl group is activating, for example synthesis of calixarenes ^[3]
• Reaction of naphtols and hydrazines and sodium bisulfite in the Bucherer carbazole synthesis
• 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 to quinones also known as the Teuber reaction. Oxidizing reagents are Fremy's salt ^[5] and oxone ^[6]. In reaction depicted below 3,4,5-trimethylphenol reacts with singlet oxygen generated from oxone/sodium carbonate in an acetonitrile/water mixture to a para-peroxyquinole. This hydroperoxide is oxidized to the quinole with sodium thiosulphate.

• Phenols are oxidized to benzenediols in the Elbs persulfate oxidation
• Phenolate anions (deriving from phenols by the loss of H⁺) can act as ligands towards metal cations

Phenolic compounds

For a full list, see Category:Phenols

Phenol	the parent compound, used as an disinfectant and for chemical synthesis
BHT	(butylated hydroxytoluene) - a fat-soluble antioxidant and food additive
Capsaicin	the pungent compound of chilli peppers
Bisphenol A	and other bisphenols produced from ketones and phenol / cresol
Chavibetol	from betel, used as a flavouring
Cresol	found in coal tar and creosote
Estradiol	estrogen - hormones
Eugenol	the main constituent of the essential oil of clove
Gallic acid	found in gallnuts
Guaiacol	(2-methoxyphenol) - has a smokey flavor, and is found in roasted coffee, whisky, and smoke
4-Nonylphenol	a breakdown product of detergents and nonoxynol-9
Orthophenyl phenol	a fungicide used for waxing citrus fruits
Picric acid	(trinitrophenol) - an explosive material
Phenolphthalein	pH indicator
Polyphenol	e.g. flavonoids and tannins
Raspberry ketone	a compound with an intense raspberry smell
Serotonin / dopamine / adrenaline / noradrenaline	natural neurotransmitters
Thymol	(2-Isopropyl-5-methyl phenol) - an antiseptic that is used in mouthwashes
Tyrosine	an amino acid
Xylenol	-

Medicinals

Cannabinoids	the active constituents of cannabis
Diethylstilbestrol	a synthetic estrogen with a stilbene structure
L-DOPA	a synthetic estrogen with a stilbene structure
Methyl salicylate	the major constituent of the essental oil of wintergreen
Propofol	a short-acting intravenous anesthetic agent
Psilocin	a hallucinogenic alkaloid of Psilocybe mushrooms
Salicylic acid	a plant hormone used for its analgesic, antipyretic and anti-inflammatory properties, also a precursor compound to Aspirin
Trichlorophenylmethyliodosalicyl	the main component of TCP, an antiseptic.

References

1. ↑ related to quinones, see for example the Zincke-Suhl reaction
2. ↑ Advanced organic Chemistry, Reactions, mechanisms and structure 3ed. page Jerry March ISBN 0-471-85472-7
3. ↑ p-tert-butylcalix[8]arene, Organic Syntheses, CV 8, 80 Article
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, Coll. Vol. 6, p.1010 (1988); Vol. 52, p.83 (1972) Abstract.
6. ↑ Oxidative De-aromatization of para-Alkyl Phenols into para-Peroxyquinols and para-Quinols Mediated by Oxone as a Source of Singlet Oxygen M. Carmen Carreño, Marcos González-López, Antonio Urbano Angewandte Chemie International Edition Volume 45, Issue 17 , Pages 2737 - 2741 2006 Abstract

cs:Fenoly

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