Phenols
Encyclopedia : P : PH : PHE : Phenols
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. 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[8]arene, Organic Syntheses, CV 8, 80 [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].
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
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