The term 'phenol' may refer to either a specific compound or a family of compounds. Phenols are aromatic compounds in which a hydroxide group is directly bonded to an aromatic ring system. They are very weak acids, and, like alcohols, form ethers and esters. They are very liable to undergo electrophilic substitution (see electrophile), and hence condense with methanal (formaldehyde) to form resins. The main phenols are phenol itself, cresol, resorcinol, pyrogallol (see gallic acid), and picric acid.
Phenol itself (C6H5OH), also known as carbolic acid, is a white, hygroscopic crystalline solid, insoluble from coal tar, but made by acid hydrolysis of cumene hydroperoxide, or by fusion of sodium benzenesulfonate (see sulfonic acid) with sodium hydroxide. Formerly used as an antiseptic, phenol has more latterly been used to make bakelite and other resins, plastics, dyes, detergents, and drugs. Molecular weight 94.1, melting point 43°C, boiling point 182°C.