phenol(redirected from phenolic)
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(also hydroxybenzene, carbolic acid), a colorless crystalline compound with a characteristic odor. Phenol turns pink upon storage. It has a melting point of 40.9°C and a boiling point of 181.75°C. The compound is moderately soluble in water and readily soluble in alcohol, ether, and acetone. The structural formula is
Phenol is the simplest of the hydroxyl derivatives of aromatic hydrocarbons and is an important raw material for a number of valuable products. Thus, the industrial chlorination of phenol with elemental chlorine yields 2,4-dichlorophenol, an intermediate in the production of 2,4-dichlorophenoxyacetic acid. The condensation of phenol with aldehydes, principally formaldehyde, yields phenol-aldehyde resins. Condensation with phthalic anhydride yields phenolphthalein (an indicator and drug), and condensation with acetone produces diphenylolpropane, which is used in producing polycarbonates. The hydrogenation of phenol produces cyclohexanol, an intermediate in the synthesis of capro-lactam (the polymerization of which yields polycaproamide), while the compound’s alkylation with olefins produces n-alkyl phenols (RC6H4OH), which are used in the manufacture of surfactants and odoriferous substances. Phenol is also used in the production of picric acid and of various dyes and drugs (salicylic acid, phenyl salicylate).
Phenol can be isolated from coal tar. It is obtained synthetically from benzene through benzenesulfonic acid (C6H5SO2OH) in a process involving the fusion of the acid’s sodium salt with sodium hydroxide. The compound can also be obtained synthetically from chlorobenzene (C6H5Cl) through hydration, but the principal synthetic method involves the breakdown of cumene hydroperoxide.
Phenol is bactericidal. In medicine, where it is better known as carbolic acid, it is used in the form of diluted aqueous solutions to disinfect hospital rooms and equipment. Phenol burns upon contact with the skin. The maximum permissible concentration of phenol in the air is 0.005 mg per liter.
any of the hydroxyl derivatives of aromatic compounds containing one or more hydroxyl groups (—OH) bonded to the aromatic ring. The number of OH groups determines whether the phenol is monohydric, dihydric, or polyhydric. Monohydric phenols include hydroxybenzene (C6H5OH), which is usually referred to simply as phenol, hydroxytoluenes (cresols, CH3C6H4OH), and hydroxynaphthalenes (naphthols). An example of a dihydric phenol is dihydroxybenzene [C6H4(OH)2: hydroquinone, pyrocatechol, and resorcinol]. Polyhydric phenols include pyrogallol and phloroglucinol.
Phenols are colorless crystalline compounds with a characteristic odor; less frequently, they occur as liquids. They are readily soluble in such organic solvents as alcohol, diethyl ether, and benzene. Possessing acid properties, phenols form saltlike products known as phenolates: ArOH + NaOH ⇄ ArONa + H2O (Ar representing an aromatic radical). Alkylation or acylation of phenolates yields ethers (ArOR) and esters (ArOCOR) of phenols, respectively (R being an organic radical). Esters of phenols may be obtained by the direct reaction of phenols with carboxylic acids and with the acids’ anhydrides and acid chlorides. Upon heating, phenols react with CO2 to yield phenolic acids, such as salicylic acid. In contrast to alcohols, the hydroxyl groups of phenols are replaced by halogens only with great difficulty. Electro-philic substitution in the phenol ring (halogenation, nitration, sulfonation, alkylation) occurs much more readily than in unsubstituted aromatic hydrocarbons; here, the substituting groups are directed to positions that are ortho and para relative to the OH group. The catalytic hydrogenation of phenols yields alicyclic alcohols; C6H5OH, for example, is reduced to cyclohexanol. Condensation reactions, such as those with aldehydes and ketones, are typical of phenols; this feature is used in industry in producing phenol-formaldehyde resins, phenolic resins using resorcinol, and diphenylolpropane.
Phenols are produced by, among other methods, the hydrolysis of the corresponding halogen derivatives and the alkaline fusion of arylsulfonic acids (ArSO2OH). They are also obtained by separation from coal tar. Phenols are important raw materials in the production of plastics, adhesives, paints, varnishes, dyes, drugs (phenolphthalein, salicylic acid, phenyl salicylate), surfactants, and odoriferous substances. Certain phenols are used as antiseptics and antioxidants (of polymers, lubricants). Solutions of iron chloride, which reacts with phenols to form colored products, are used for qualitative determination of phenols. Phenols are toxic.