Inorganic chemistry,phenols, sometimes calledphenolics, are a class ofchemical compounds consisting of one or morehydroxylgroups (−OH)bonded directly to anaromatic hydrocarbon group.^[1] The simplest isphenol,C
₆H
₅OH. Phenolic compounds are classified as simple phenols orpolyphenols based on the number of phenol units in the molecule.

Phenols are both synthesized industrially and produced by plants and microorganisms.^[2]

Phenols are moreacidic than typical alcohols. The acidity of the hydroxyl group in phenols is commonly intermediate between that ofaliphatic alcohols andcarboxylic acids (their pK_a is usually between 10 and 12). Deprotonation of a phenol forms a corresponding negativephenolate ion orphenoxide ion, and the correspondingsalts are calledphenolates orphenoxides (aryloxides according to the IUPAC Gold Book).^{[citation needed]}

Phenols are susceptible toElectrophilic aromatic substitutions. Condensation withformaldehyde gives resinous materials, famouslyBakelite.^{[citation needed]}

Another industrial-scale electrophilic aromatic substitution is the production ofbisphenol A, which is produced by thecondensation withacetone.^[3]

Phenol is readily alkylated at the ortho positions using alkenes in the presence of a Lewis acid such asaluminium phenoxide:^{[citation needed]}

CH₂=CR₂ + C₆H₅OH → R₂CHCH₂-2-C₆H₄OH

More than 100,000 tons oftert-butyl phenols are produced annually (year: 2000) in this way, usingisobutylene (CH₂=CMe₂) as the alkylating agent. Especially important is2,6-ditert-butylphenol, a versatileantioxidant.^[3]

Phenols undergoesterification. Phenol esters areactive esters, being prone to hydrolysis. Phenols arereactive species towardoxidation. Oxidative cleavage, for instance cleavage of 1,2-dihydroxybenzene to the monomethylester of 2,4 hexadienedioic acid with oxygen, copper chloride in pyridine^[4] Oxidative de-aromatization toquinones also known as theTeuber reaction.^[5] andoxone.^[6] In reaction depicted below 3,4,5-trimethylphenol reacts withsinglet oxygen generated fromoxone/sodium carbonate in anacetonitrile/water mixture to a para-peroxyquinole. Thishydroperoxide is reduced to the quinole withsodium thiosulfate.

Phenols are oxidized tohydroquinones in theElbs persulfate oxidation.

Reaction of naphtols and hydrazines and sodium bisulfite in theBucherer carbazole synthesis.

Many phenols of commercial interest are prepared by elaboration ofphenol orcresols. They are typically produced by the alkylation ofbenzene/toluene withpropylene to formcumene thenO
₂ is added withH
₂SO
₄ to form phenol (Hock process). In addition to the reactions above, many other more specialized reactions produce phenols:

• rearrangement of esters in theFries rearrangement^[7][8]
• rearrangement ofN-phenylhydroxylamines in theBamberger rearrangement^[9][10]
• dealkylation of phenolicethers
• reduction ofquinones
• replacement of an aromatic amine by an hydroxyl group with water and sodium bisulfide in theBucherer reaction^[11]
• thermal decomposition of aryldiazonium salts, the salts are converted to phenol^[12]
• by the oxidation of aryl silanes—an aromatic variation of theFleming-Tamao oxidation^[13]
• catalytic synthesis from aryl bromides and iodides usingnitrous oxide^[14]

There are variousclassification schemes.^[15]: 2 A commonly used scheme is based on the number of carbons and was devised byJeffrey Harborne and Simmonds in 1964 and published in 1980:^{[15]: 2 [16]}

More than 371 drugs approved by the FDA between the years of 1951 and 2020 contain either a phenol or a phenolic ether (a phenol with an alkyl), with nearly every class of small molecule drugs being represented, and natural products making up a large portion of this list.^[17]