Qualitative reactions to phenol. Preparation of phenols: reactions

Carbolic acid - one of the names of phenol, indicating its special behavior in chemical processes. This substance is lighter than benzene enters the nucleophilic substitution reaction. The acidic properties of the compound are explained by the mobility of the hydrogen atom in the hydroxyl group bonded to the ring. The study of the structure of the molecule and the qualitative reactions to phenol make it possible to classify the substance as aromatic compounds - derivatives of benzene.

Phenol (hydroxybenzene)

In 1834 the German chemist Runge isolated carbolic acid from coal tar, but failed to decipher its composition. Later, other researchers proposed a formula and attributed the new compound to aromatic alcohols. The simplest representative of this group is phenol (hydroxybenzene). In its pure form, this substance is a transparent crystal with a characteristic odor. In air, the color of phenol can change, become pink or red. The aromatic alcohol is characterized by poor solubility in cold water and good in organic solvents. The phenol melts at a temperature of 43 ° C. It is a toxic compound, when it gets on the skin it causes severe burns. The aromatic part of the molecule is represented by the radical phenyl (C6H5-). The oxygen of the hydroxyl group (-OH) is bonded directly to one of the carbon atoms. The presence of each of the particles proves the corresponding qualitative reaction to phenol. Formula showing the total content of atoms of chemical elements in the molecule - C6H6O. The structure reflects structural formulas that include the Kekule cycle and the functional group - hydroxyl. A visual representation of the molecule of aromatic alcohol is provided by spherical rod models.

Features of the structure of the molecule

The interrelation of the benzene nucleus and the OH group determines the chemical reactions of phenol with metals, halogens, and other substances. The presence of an oxygen atom associated with the aromatic cycle leads to a redistribution of the electron density in the molecule. The O-H bond becomes more polar, which leads to an increase in the mobility of hydrogen in the hydroxyl group. The proton can be replaced by metal atoms, which indicates the acidity of the phenol. In turn, the OH group increases the reactivity of the benzene ring. The delocalization of electrons and the ability to electrophilic substitution in the nucleus increase. This increases the mobility of hydrogen atoms associated with carbon in the ortho- and para positions (2, 4, 6). This effect is due to the presence of an electron density donor - a hydroxyl group. Due to its influence, phenol is more active than benzene in reactions with certain substances, and new substituents are oriented to ortho- and para positions.

Acidic properties

In the hydroxyl group of aromatic alcohols, the oxygen atom acquires a positive charge, which attenuates its bond with hydrogen. The release of the proton is facilitated, so phenol behaves like a weak acid, but stronger than alcohols. Qualitative reactions to phenol include a litmus test, which changes color from blue to pink in the presence of protons. The presence of halogen atoms or nitro groups bound to the benzene ring leads to an increase in the activity of hydrogen. The effect is observed in molecules of nitro derivatives of phenol. Reduces the acidity of such substituents as the amino group and alkyl (CH3-, C2H5- and others). To compounds that combine a benzene ring, a hydroxyl group and a methyl radical in their composition, cresol is included. Its properties are weaker than carbolic acid.

Reaction of phenol with sodium and alkali

Like acids, phenol interacts with metals. For example, it reacts with sodium: 2C6H5-OH + 2Na = 2C6H5-ONa + H2 ↑. Sodium phenolate is formed , and hydrogen gas is released. Phenol reacts with soluble bases. There is a neutralization reaction with the formation of salt and water: C6H5-OH + NaOH = C6H5-ONa + H2O. The ability to give hydrogen in the hydroxyl group of phenol is lower than in most inorganic and carboxylic acids. It displaces it from salts even dissolved in water carbon dioxide (carbonic acid). Reaction equation: C6H5-ONa + CO2 + H2O = C6H5-OH + NaHCO3.

Reactions of the benzene ring

Aromatic properties are due to delocalization of electrons in the benzene nucleus. Hydrogen from the ring is replaced by halogen atoms, nitro group. A similar process in the phenol molecule is easier than in benzene. One example is bromination. The halogen acts on the benzene in the presence of a catalyst, bromobenzene is obtained. Phenol reacts with bromine water under normal conditions. As a result of the interaction, a white precipitate of 2,4,6-tribromophenol is formed, the appearance of which makes it possible to distinguish the test substance from similar aromatic compounds. Bromination is a qualitative reaction to phenol. Equation: C6H5-OH + 3Br2 = C6H2Br3 + HBr. The second product of the reaction is hydrogen bromide. When the phenol reacts with dilute nitric acid , nitro derivatives are obtained. The reaction product with concentrated nitric acid - 2,4,6-trinitrophenol or picric acid is of great practical importance.

Qualitative reactions to phenol. List

In the interaction of substances, certain products are obtained, which allow us to establish the qualitative composition of the initial substances. A number of color reactions indicate the presence of particles, functional groups, which is convenient for chemical analysis. Qualitative reactions to phenol prove the presence in the molecule of the substance of the aromatic ring and the OH group:

1. In the phenol solution, the blue litmus paper turns red.
2. Color reactions to phenols are also carried out in a weak alkaline medium with diazonium salts. Yellow or orange azo dyes are formed.
3. Reacts with bromine water of brown color, a white precipitate of tribromophenol appears.
4. As a result of reaction with a solution of ferric chloride, ferric phenoxide is obtained - a substance of blue, violet or green color.

Preparation of phenols

The production of phenol in industry goes in two or three stages. In the first stage, cumene (trivial name of isopropylbenzene) is obtained from propylene and benzene in the presence of aluminum chloride . Friedel-Crafts equation of reaction: C6H5-OH + C3H6 = C9H12 (cumene). Benzene and propylene in a 3: 1 ratio are passed over the acid catalyst. Increasingly, instead of the traditional catalyst - aluminum chloride - environmentally friendly zeolites are used. At the final stage, oxygenation in the presence of sulfuric acid is carried out: C6H5-C3H7 + O2 = C6H5-OH + C3H6O. Phenols can be obtained from coal by distillation, are intermediates in the production of other organic substances.

Use of phenols

Aromatic alcohols are widely used in the production of plastics, dyes, pesticides and other substances. The production of carbolic acid from benzene is the first step in the development of a number of polymers, including polycarbonates. Phenol reacts with formaldehyde, phenol-formaldehyde resins are obtained.

Cyclohexanol serves as a raw material for the production of polyamides. Phenols are used as antiseptics and disinfectants in deodorants, lotions. Used to produce phenacetin, salicylic acid and other medications. Phenols are used in the manufacture of resins, which are used in electrical products (switches, sockets). They are also used in the preparation of azo dyes, for example phenylamine (aniline). Picric acid, which is a nitro derivative of phenol, is used for dyeing fabrics, making explosives.