Phenols

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. 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.

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

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 p-tert-butylcalix Organic Syntheses, CV 8, 80 [http://www.orgsynth.org/orgsyn/prep.asp?prep=cv8p0080 Article
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 2,4-Hexadienedioic acid, monomethyl ester, (Z,Z)- Organic Syntheses, Coll. Vol. 8, p.490 (1993); Vol. 66, p.180 (1988) Article

Oxidative de-aromatization to quinones also known as the Teuber reaction. Oxidizing reagents are Fremy's salt 2,5-Cyclohexadiene-1,4-dione, 2,3,5-trimethyl Organic Syntheses, Coll. Vol. 6, p.1010 (1988); Vol. 52, p.83 (1972) Abstract.

and oxone 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. In reaction depicted below 3,4,5-trimethylphenol reacts with singlet oxygen generated from oxone/sodium carbonate in a acetonitrile/water mixture to a para-peroxyquinole. This hydroperoxide is oxidized to the quinole with sodium thiosulphate.

Phenolic compounds

Phenol - the parent compound, used as an disinfectant and for chemical synthesis
BHT (butylated hydroxytoluene) - a fat-soluble antioxidant and food additive
Cresols - found in coal tar and creosote
Bisphenol A and other bisphenols produced from ketones and phenol / cresol
Xylenols
Capsaicin - the pungent compound of chilli peppers
Chavibetol - from betel, used as a flavouring
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 isfound 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

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

External links

References