Phenols - aromatic compounds having one or more hydroxyl groups bonded to carbon atoms benzenovogo core.According to the number of OH groups are distinguished one-, two-, and triatomic phenols.
Monohydric phenols - derivatives of benzene and its homologues in the nucleus which one hydrogen atom is substituted with a hydroxyl group.
isomers and nomenclature.In the simplest representative of phenols - carbolic acid (phenol) have isomers, homologs exist in its position isomer benzonovom hydroxyl group at the nucleus (ortho, meta, para position).
to use three names phenols nomenclature - historical, rational and IUPAC.According to historical nomenclature phenols called trivial - phenol (carbolic acid), cresol, etc.
natural source for these substances is coal tar, kernel oil, beech tar, etc.Coal tar is produced during the distillation of coal.Sources for phenols are averages (boiling at 170-230 ° C) and heavy (boiling at 230-270 ° C) of an oil.At their treatment with sodium hydroxide was prepared sodium phenolate.Formula: said substance comprises a residue of phenol and sodium.
in the laboratory often used for aromatic phenols sulfosalts (sodium and potassium salts of sulfonic acids).During chemical reactions, a sodium or potassium phenolate.Then, these compounds are treated with mineral acids to give the free phenols.
chemical properties of phenol are caused by the presence of OH groups in benzelnom core.These substances can enter into reactions which are characteristic of alcohols (ester formation, phenolates, halogen-derivatives) and arenes (replacement of hydrogen atoms on a core benzenovom halogens, nitro group, sulfo group).Therefore, these compounds readily react with metals to form a sodium phenolate.It is in these conditions exhibit features the electronic structure of molecules of alcohols and phenols.
phenolate sodium (or phenoxide) is formed by reacting phenols with alkaline.The acidic properties of phenols is relatively little pronounced.These substances are not stained with litmus paper.Sodium phenate unlike alkoxides can exist in aqueous alkaline solutions, while it does not decompose.Phenolates readily decomposed by reaction with acids (even the weakest, for example, coal).
Yet acidic properties of phenols are more pronounced than in aliphatic alcohols.Introduction into the molecule of the phenol electron-withdrawing substituents (nitro, halogen, a sulfo group, an aldehyde group, etc.) hydrogen gidroksogrupp movement increases, so acidic properties are enhanced.
The presence of phenols positive mesomeric effect causes them to nucleophilic properties, which are less pronounced in comparison with alcohols.This property is used to obtain the esters, but does not participate in the reactions themselves phenols and phenolates and halogenated hydrocarbons.
ester formation occurs by reacting phenols with chlorides or anhydrides of carboxylic acids.As in the formation of esters, the reaction is easier to proceed with potassium phenolate or sodium.
The action of phenols in the form of halogen halogen derivatives.Bromination of phenols used in pharmaceutical analysis: 2,46-tribromophenol poorly soluble in water and precipitates out, which allows the above reaction to determine the phenols in solution.
nitration of phenol.The action to phenol 20% nitric acid, a mixture of o-and p-nitrophenol, which are separated by steam distillation (o-nitrophenol was distilled off, and the p-nitrophenol remains in solution).
