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.
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.
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Several laboratory methods for the synthesis of phenols:
Phenols react in a wide variety of ways.
| 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 |
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 |
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]
The class of phenols (or phenoles) is an important raw material and an additive for industrial purposes in: