Sodium phenolate: preparation, chemical properties
Phenols are aromatic compounds that haveone or more hydroxyl groups bonded to the carbon atoms of the benzene nucleus. By the number of OH groups, one-, two- and three-atom phenols are distinguished.
Monohydric phenols are derivatives of benzene and its homologues, in the nucleus of which one hydrogen atom is replaced by a hydroxyl group.
Isomerism and nomenclature. The simplest representative of phenols - carbolic acid (phenol) is not isomers, in its homologues there is an isomerism of the position of the hydroxyl group in the benzon nucleus (ortho-, meta-, paraposition).
For the name of phenols use three nomenclatures - historical, rational and IUPAC. According to the historical nomenclature, phenols are called trivial - carbolic acid (carbolic acid), cresols, etc.
A natural source for obtaining these substancesis a coal tar, stone oil, beech tar, etc. Coal tar is formed during the dry distillation of coal. The sources for the preparation of phenols are medium (boiling at 170-230 ° C) and heavy (boiling at 230-270 ° C) oils. When they are treated with sodium hydroxide, sodium phenolate is obtained. The formula of this substance consists of the remainder of phenol and sodium.
In the laboratory, most often to obtainphenols use aromatic sulfosalts (sodium and potassium salts of sulfonic acids). In the course of chemical reactions, phenolic sodium or potassium is formed. After that, these compounds are treated with mineral acids, resulting in free phenols.
The chemical properties of phenol are determined bythe presence of an OH group in the benzene nucleus. These substances can enter into reactions that are characteristic of alcohols (the formation of esters, phenolates, halogenated derivatives) and arenes (replacement of hydrogen atoms in the benzene nucleus with halogens, nitro group, sulfo group). Therefore, these substances easily interact with metals, forming sodium phenolate. It is under such conditions that the features of the electronic structure of molecules of alcohols and phenols are manifested.
Sodium phenolate (or phenoxide) is formed wheninteraction of alkalis with phenols. Acidic properties of phenols are relatively small. These substances do not stain litmus paper. Sodium phenolate, unlike alcoholates, can exist in aqueous solutions of alkalis, but it does not decompose. Phenolates easily decompose upon interaction with acids (even the weakest, for example, coal).
Yet the acid properties of phenols are expressedstronger than in aliphatic alcohols. The introduction of electron-withdrawing substituents (nitro group, halogens, sulfo group, aldehyde group, etc.) into the phenol molecule increases the hydrogen movement of the hydroxo group, so the acid properties are enhanced.
The presence of a positive mesomer in phenolseffect determines their nucleophilic properties, which are less pronounced in comparison with alcohols. This property is used to produce esters, but phenols and phenols and halogenated hydrocarbons do not participate in the reactions themselves.
The formation of esters occurs when phenols react with acid chlorides or carboxylic acid anhydrides. As in the formation of esters, the reactions take place more readily with phenols of potassium or sodium.
When halogens react on phenols, they are formedhalogenated derivatives. Bromination of phenols is used in pharmaceutical analysis: 2,46-tribromophenol is poorly soluble in water and precipitates, which allows using this reaction to determine phenols in solutions.
Nitration of phenol. When a 20% nitric acid acts on phenol, a mixture of o- and p-nitrophenols is formed, which is separated by steam distillation (o-nitrophenol is distilled off, and p-nitrophenol remains in solution).
