In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group (—OH) bonded directly to an aromatic hydrocarbon group. The simplest of the class is phenol also called as carbolic acid C6H5OH.

Phenol - the simplest of the phenols.
Phenol resonance structures.

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 higher acidities due to the aromatic ring's tight 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 pKa is usually between 10 and 12).

Loss of a positive hydrogen ion (H+) from the hydroxyl group of a phenol forms a corresponding negative phenolate ion or phenoxide ion, and the corresponding salts are called phenolates or phenoxides, although the term aryloxides is preferred according to the IUPAC Gold Book.

Phenols can have two or more hydroxy groups bonded to the aromatic ring(s) in the same molecule. The simplest examples are the three benzenediols, each having two hydroxy groups on a benzene ring.

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:

The dienone phenol rearrangement

Reactions of phenols

Phenols react in a wide variety of ways.

Oxone Phenol Dearomatization
  • Phenols are oxidized to phediols 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
Bisphenol A and other bisphenols produced from ketones and phenol / cresol
BHT (butylated hydroxytoluene) - a fat-soluble antioxidant and food additive
Capsaicin the pungent compound of chilli peppers
Cresol found in coal tar and creosote
Estradiol estrogen - hormones
Eugenol the main constituent of the essential oil of clove
Gallic acid found in galls
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
Propofol an anesthetic
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 -used in antiseptics & disinfecticides

Adverse health effects of some phenols

Some of the above substances are related to endocrine-disruptive chemicals. GreenPeace report on Hazardous Chemicals in Consumer Products


Cannabinoids the active constituents of cannabis
Diethylstilbestrol a synthetic estrogen with a stilbene structure
L-DOPA a dopamine prodrug
Methyl salicylate the major constituent of the essential oil of wintergreen
Propofol a short-acting intravenous anesthetic agent
Salicylic acid a plant hormone used for its analgesic, antipyretic, and anti-inflammatory properties, also a precursor compound to Aspirin

Natural occurrence

Phenols are found in the natural world, especially in the plant kingdom. In some cases of natural phenols, they are present in vegetative foliage to discourage herbivory, such as in the case of Western poison oak.[8]

Industrial processing

The class of phenols (or phenoles) is an important raw material and an additive for industrial purposes in:

  • laboratory processes
  • chemical industry
  • chemical engineering processes
  • wood processing
  • plastics processing

See also


  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. ^ Sonia Bracegirdle, Edward A. Anderson, Chem. Comm. doi:10.1039/b924135c
  4. ^ p-tert-butylcalix[8]arene, Organic Syntheses, CV 8, 80 Article
  5. ^ 2,4-Hexadienedioic acid, monomethyl ester, (Z,Z)- Organic Syntheses, Coll. Vol. 8, p.490 (1993); Vol. 66, p.180 (1988) Article
  6. ^ 2,5-Cyclohexadiene-1,4-dione, 2,3,5-trimethyl Organic Syntheses, Coll. Vol. 6, p.1010 (1988); Vol. 52, p.83 (1972) Abstract.
  7. ^ 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
  8. ^ C.Michael Hogan (2008) Western poison-oak: Toxicodendron diversilobum, GlobalTwitcher, ed. Nicklas Stromberg [1]

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