Phenols

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In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group (-OH) 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 External links 5 References

[edit] 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

[edit] Reactions of phenols

Phenols react in a wide variety of ways.

• esterfication reactions and ether formation
• Electrophilic aromatic substitutions as the hydroxyl group is activating, for example synthesis of calixarenes ^[1]
• 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 ^[2]
• Oxidative de-aromatization to quinones also known as the Teuber reaction. Oxidizing reagents are Fremy's salt ^[3] and oxone ^[4]. 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

[edit] 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
• Bisphenol A and other bisphenols produced from ketones and phenol / cresol
• Capsaicin - the pungent compound of chilli peppers
• Chavibetol - from betel, used as a flavouring
• Cresols - 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 / phenol red / bromothymol blue / thymolphthalein / bromophenol blue - pH indicators
• Polyphenols - 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
• Xylenols

[edit] Medicinals

• Cannabinoids - the active constituents of cannabis
• Diethylstilbestrol - a synthetic estrogen with a stilbene structure
• L-DOPA - a drug to treat Parkinson's disease
• 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
• Trichlorophenol - the main component of TCP, an antiseptic

[edit] External links

• National Pollutant Inventory - Phenol Fact Sheet

[edit] References

1. ^ p-tert-butylcalix[8]arene, Organic Syntheses, CV 8, 80 Article
2. ^ 2,4-Hexadienedioic acid, monomethyl ester, (Z,Z)- Organic Syntheses, Coll. Vol. 8, p.490 (1993); Vol. 66, p.180 (1988) Article
3. ^ 2,5-Cyclohexadiene-1,4-dione, 2,3,5-trimethyl Organic Syntheses, Coll. Vol. 6, p.1010 (1988); Vol. 52, p.83 (1972) Abstract.
4. ^ 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