Chemical properties phenols are determined by the presence of a hydroxyl group and a benzene ring in the molecule.

Reactions by hydroxyl group

Phenols, like aliphatic alcohols, have acidic properties, i.e. capable of forming salts - phenolates. However, they are stronger acids and therefore can interact not only with alkali metals (sodium, lithium, potassium), but also with alkalis and carbonates:

Acidity constant rK A phenol is equal to 10. The high acidity of phenol is associated with the acceptor property of the benzene ring ( coupling effect) and is explained by the resonance stabilization of the resulting phenolate anion. The negative charge on the oxygen atom of the phenolate anion can be redistributed throughout the aromatic ring due to the conjugation effect; this process can be described by a set of resonance structures:

None of these structures alone describes the actual state of the molecule, but their use allows us to explain many reactions.

Phenolates easily interact with haloalkanes and acid halides:

The interaction of phenol salts with haloalkanes is the reaction of O-alkylation of phenols. This is a method for preparing ethers (Williamson reaction, 1852).

Phenol is able to react with acid halides and anhydrides to produce esters (O-acylation):

The reaction occurs in the presence of small amounts of mineral acid or by heating.

Reactions on the benzene ring

Hydroxyl is an electron-donating group and activates ortho- And pair-positions in electrophilic substitution reactions:

Halogenation

Halogenation of phenols by the action of halogens or halogenating agents occurs at high speed:

Nitration

When exposed to nitric acid acetic acid(in the presence of a small amount of sulfuric acid) to phenol, 2-nitrophenol is obtained:

Under the action of concentrated nitric acid or a nitrating mixture, phenol is intensively oxidized, which leads to deep destruction of its molecule. When using dilute nitric acid, nitration is accompanied by strong tarring despite cooling to 0°C and leads to the formation O- And p- isomers with a predominance of the first of them:

When phenol is nitrated with dinitrogen tetroxide in an inert solvent (benzene, dichloroethane), 2,4-dinitrophenol is formed:

Nitration of the latter with a nitrating mixture proceeds easily and can serve as a method for the synthesis of picric acid:

This reaction occurs with self-heating.

Picric acid is also obtained through the sulfonation step. To do this, phenol is treated at 100°C with an excess amount of sulfuric acid, a 2,4-disulfo derivative is obtained, which is treated with fuming nitric acid without isolating it from the reaction mixture:

The introduction of two sulfo groups (as well as nitro groups) into the benzene ring makes it resistant to the oxidizing action of fuming nitric acid; the reaction is not accompanied by tarring. This method of obtaining picric acid is convenient for production on an industrial scale.

Sulfonation . Sulfonation of phenol, depending on temperature, occurs in ortho- or pair-position:

Alkylation and acylation according to Friedel-Crafts . Phenols form inactive salts ArOAlCl 2 with aluminum chloride; therefore, protic acids (H 2 SO 4) or acid-type metal oxide catalysts (Al 2 O 3) are used as catalysts for the alkylation of phenols. This allows only alcohols and alkenes to be used as alkylating agents:

Alkylation occurs sequentially with the formation of mono-, di- and trialkylphenols. At the same time, an acid-catalyzed rearrangement occurs with migration of alkyl groups:

Condensation with aldehydes and ketones . When alkaline or acid catalysts act on a mixture of phenol and fatty aldehyde, condensation occurs in O- And n- provisions. This reaction is of very great practical importance, since it underlies the production of important plastics and varnish bases. At ordinary temperatures, the growth of a molecule due to condensation proceeds in a linear direction:

If the reaction is carried out with heating, condensation begins with the formation of branched molecules:

As a result of joining all available O- And n-positions, a three-dimensional thermosetting polymer is formed – bakelite. Bakelite has high electrical resistance and heat resistance. This is one of the first industrial polymers.

The reaction of phenol with acetone in the presence of a mineral acid leads to the production of bisphenol:

The latter is used to obtain epoxy compounds.

Kolbe–Schmidt reaction. Synthesis of phenylcarboxylic acids.

Sodium and potassium phenolates react with carbon dioxide, forming ortho- or para-isomers of phenylcarboxylic acids, depending on the temperature:

Oxidation

Phenol is easily oxidized by chromic acid to n-benzoquinone:

Recovery

Reduction of phenol to cyclohexanone is used to produce polyamide (nylon-6,6)

The hydroxyl group in molecules of organic compounds can be associated with aromatic core directly, or can be separated from it by one or more carbon atoms. It can be expected that, depending on this property, substances will differ significantly from each other due to the mutual influence of groups of atoms. And indeed, organic compounds containing the aromatic radical phenyl C 6 H 5 - directly bonded to the hydroxyl group, exhibit special properties, different from the properties of alcohols. Such connections are called phenols.

Organic substances whose molecules contain a phenyl radical linked to one or more hydroxo groups. Just like alcohols, phenols are classified by atomicity, i.e., by the number of hydroxyl groups.

Monohydric phenols contain one hydroxyl group in the molecule:

Polyhydric phenols contain more than one hydroxyl group in molecules:

There are other polyhydric phenols containing three or more hydroxyl groups on the benzene ring.

Let's take a closer look at the structure and properties of the simplest representative of this class - phenol C 6 H 5 OH. The name of this substance formed the basis for the name of the entire class - phenols.

Phenol is a solid, colorless crystalline substance, t° = 43 °C, t° = 181 °C, with a sharp characteristic odor. Poisonous. Phenol is slightly soluble in water at room temperature. An aqueous solution of phenol is called carbolic acid. Upon contact with skin it causes burns, so phenol must be handled with care!

Chemical properties of phenols

Acid properties. The hydrogen atom of the hydroxyl group is acidic in nature. The acidic properties of phenol are more pronounced than that of water and alcohols. Unlike alcohols and water, phenol reacts not only with alkali metals, but also with alkalis to form phenolates:

However, the acidic properties of phenols are less pronounced than those of inorganic and carboxylic acids. For example, the acidic properties of phenol are approximately 3000 times less than those of carbonic acid. Therefore, by passing carbon dioxide through an aqueous solution of sodium phenolate, free phenol can be isolated.

Adding hydrochloric or sulfuric acid to an aqueous solution of sodium phenolate also leads to the formation of phenol:

Phenol reacts with iron (III) chloride to form an intensely colored purple complex connection.

This reaction allows it to be detected even in very limited quantities. Other phenols containing one or more hydroxyl groups on the benzene ring also produce bright blue-violet colors when reacted with iron(III) chloride.

The presence of a hydroxyl substituent greatly facilitates the occurrence of electrophilic substitution reactions in the benzene ring.

1. Bromination of phenol.

Unlike benzene, the bromination of phenol does not require the addition of a catalyst (iron (III) bromide). In addition, the interaction with phenol proceeds selectively: bromine atoms are directed to the ortho and para positions, replacing the hydrogen atoms located there. The selectivity of substitution is explained by the above-discussed features of the electronic structure of the phenol molecule.

Thus, when phenol reacts with bromine water, a white precipitate of 2,4,6-tribromophenol is formed:

This reaction, like the reaction with iron (III) chloride, serves for the qualitative detection of phenol.

2. Nitration of phenol also occurs more easily than benzene nitration. The reaction with dilute nitric acid occurs at room temperature. As a result, a mixture of ortho- and para-isomers of nitrophenol is formed:

When concentrated nitric acid is used, 2,4,6-trinitrophenol is formed - picric acid, an explosive:

3. Hydrogenation of the aromatic core of phenol in the presence of a catalyst occurs easily:

4. Polycondensation of phenol with aldehydes, in particular, with formaldehyde occurs with the formation of reaction products - phenol-formaldehyde resins and solid polymers.

The interaction of phenol with formaldehyde can be described by the following scheme:

The dimer molecule retains “mobile” hydrogen atoms, which means that further continuation of the reaction is possible with a sufficient number of reagents:

The polycondensation reaction, i.e., the reaction of producing a polymer that occurs with the release of a low-molecular-weight by-product (water), can continue further (until one of the reagents is completely consumed) with the formation of huge macromolecules. The process can be described by the summary equation:

The formation of linear molecules occurs at ordinary temperatures. Carrying out this reaction when heated leads to the fact that the resulting product has a branched structure, it is solid and insoluble in water. As a result of heating a linear phenol-formaldehyde resin with an excess of aldehyde, hard plastic masses with unique properties. Polymers based on phenol-formaldehyde resins are used for the manufacture of varnishes and paints, plastic products resistant to heating, cooling, water, alkalis and acids. They have high dielectric properties. The most responsible and important details electrical appliances, power unit housings and machine parts, polymer base printed circuit boards for radio devices. Adhesives based on phenol-formaldehyde resins are capable of reliably connecting parts of a wide variety of natures, maintaining the highest joint strength over a very wide temperature range. This glue is used to attach the metal base of lighting lamps to a glass bulb. Thus, phenol and products based on it are widely used.

According to the number of hydroxyl groups:

Monatomic; For example:

Diatomic; For example:

Triatomic; For example:

There are phenols of higher atomicity.

Protozoa monohydric phenols

C 6 H 5 OH - phenol (hydroxybenzene), the trivial name is carbolic acid.

The simplest diatomic phenols

Electronic structure of the phenol molecule. Mutual influence of atoms in a molecule

The hydroxyl group -OH (like alkyl radicals) is a substituent of the 1st kind, i.e., an electron donor. This is due to the fact that one of the lone electron pairs of the hydroxyl oxygen atom enters into p, π-conjugation with the π-system of the benzene ring.

The result of this is:

An increase in electron density on carbon atoms in the ortho- and para-positions of the benzene ring, which facilitates the replacement of hydrogen atoms in these positions;

Increasing polarity O-N connections, leading to increased acidic properties of phenols compared to alcohols.

Unlike alcohols, phenols partially dissociate in aqueous solutions into ions:

i.e., they exhibit weakly acidic properties.

Physical properties

The simplest phenols under normal conditions are low-melting, colorless crystalline substances with a characteristic odor. Phenols are slightly soluble in water, but dissolve well in organic solvents. Are toxic substances, cause skin burns.

Chemical properties

I. Reactions involving the hydroxyl group (acidic properties)

(neutralization reaction, unlike alcohols)

Phenol is a very weak acid, so phenolates are decomposed not only by strong acids, but even by such a weak acid as carbonic acid:

II. Reactions involving the hydroxyl group (formation of esters and ethers)

Like alcohols, phenols can form ethers and esters.

Esters are formed by the reaction of phenol with anhydrides or acid chlorides of carboxylic acids (direct esterification with carboxylic acids is more difficult):

Ethers (alkylaryl ethers) are formed by the interaction of phenolates with alkyl halides:

III. Substitution reactions involving the benzene ring

Education white sediment tribromophenol is sometimes regarded as a qualitative reaction to phenol.

IV. Addition reactions (hydrogenation)

V. Qualitative reaction with iron (III) chloride

Monohydric phenols + FeCl 3 (solution) → Blue-violet color, disappearing upon acidification.

The names of phenols are compiled taking into account the fact that for the parent structure, according to IUPAC rules, the trivial name “phenol” is retained. The numbering of the carbon atoms of the benzene ring starts from the atom directly bonded to the hydroxyl group (if it is the highest function), and continues in such a sequence that the available substituents receive the lowest numbers.

Mono-substituted phenol derivatives, for example methylphenol (cresol), can exist in the form of three structural isomers - ortho-, meta- and para-cresols.

Physical properties.

Phenols are mostly crystalline substances (-cresol - liquid) at room temperature. They have a characteristic odor, are rather poorly soluble in water, but dissolve well in aqueous solutions of alkalis (see below). Phenols form strong hydrogen bonds and have quite high temperatures boiling.

Methods of obtaining.

1. Preparation from halobenzenes. When chlorobenzene and sodium hydroxide are heated under pressure, sodium phenolate is obtained, upon further processing of which with acid, phenol is formed:

2. Preparation from aromatic sulfonic acids (see reaction 3 in the section “Chemical properties of benzene”, § 21). The reaction is carried out by fusing sulfonic acids with alkalis. The initially formed phenoxides are treated with strong acids to obtain free phenols. The method is usually used to obtain polyhydric phenols:

Chemical properties.

In phenols, the p-orbital of the oxygen atom forms with the aromatic ring a unified system. As a result of this interaction, the electron density of the oxygen atom decreases and that of the benzene ring increases. The polarity of the O-H bond increases, and the hydrogen of the OH group becomes more reactive and is easily replaced by a metal even under the action of alkalis (unlike saturated monohydric alcohols).

In addition, as a result of such mutual influence in the phenol molecule, the reactivity of the benzene ring in the ortho and cara positions in electrophilic substitution reactions (halogenation, nitration, polycondensation, etc.) increases:

1. The acidic properties of phenol manifest themselves in reactions with alkalis (the old name “carbolic acid” has been preserved):

Phenol, however, is a very weak acid. When carbon dioxide or sulfur dioxide gases are passed through a solution of phenolates, phenol is released - this reaction proves that phenol is a weaker acid than carbonic and sulfur dioxide:

The acidic properties of phenols are weakened by the introduction of substituents of the first kind into the ring and enhanced by the introduction of substituents of the second kind.

2. Formation of esters. Unlike alcohols, phenols do not form esters when exposed to carboxylic acids; For this purpose, acid chlorides are used:

3. Halogenation. When phenol is exposed to bromine water (compare with the conditions for the bromination of benzene - § 21), a precipitate of 2,4,6-tribromophenol is formed:

This is a qualitative reaction for the detection of phenol.

4. Nitration. Under the action of 20% nitric acid, phenol is easily converted into a mixture of ortho- and para-nitrophenols. If phenol is nitrated with concentrated nitric acid, 2,4,6-trinitrophenol is formed - a strong acid (picric acid).

5. Oxidation. Phenols are easily oxidized even under the influence of atmospheric oxygen.

Thus, when standing in air, phenol gradually turns pinkish-red. During the vigorous oxidation of phenol with a chromium mixture, the main oxidation product is quinone. Diatomic phenols are oxidized even more easily. The oxidation of hydroquinone produces quinone:

They can be found in nature, but the ones most known to man are those obtained artificially. They are now widely used in chemical industry, construction, plastics production and even in medicine. Due to its high toxic properties, the stability of its compounds and the ability to penetrate the human body through the skin and respiratory system, phenol poisoning often occurs. Therefore, this substance was classified as a highly dangerous toxic compound and its use was strictly regulated.

What are phenols

Naturally occurring and produced in artificial conditions. Natural phenols can be beneficial - they are antioxidants, polyphenols, which make some plants healing for humans. And synthetic phenols are toxic substances. If they come into contact with the skin, they cause a burn; if they enter the human body, they cause severe poisoning. These complex compounds, related to volatile aromatic hydrocarbons, pass into gaseous state already at a temperature of just over 40 degrees. But under normal conditions it is a transparent crystalline substance with a specific odor.

The definition of phenol is studied at school in the course of organic chemistry. At the same time, it talks about its composition, molecular structure and harmful properties. Many people know nothing about the natural substances of this group, which play a large role in nature. How can phenol be characterized? The composition of this chemical compound is very simple: a benzoic group molecule, hydrogen and oxygen.

Types of phenols

These substances are present in many plants. They provide color to their stems, scent the flowers, or repel pests. There are also synthetic compounds that are poisonous. These substances include:

1. Natural phenolic compounds are capsaicin, eugenol, flavonoids, lignins and others.
2. The most famous and poisonous phenol is carbolic acid.
3. Compounds butylphenol, chlorophenol.
4. Creosote, Lysol and others.

But mostly ordinary people Only two names are known: and phenol itself.

Properties of these compounds

These chemicals They are not only toxic. They are used by humans for a reason. To determine what qualities phenol has, the composition is very important. The combination of carbon, hydrogen and oxygen gives it special properties. This is why phenol is so widely used by humans. The properties of this connection are as follows:

The role of phenols in nature

These substances are found in many plants. They participate in creating their color and aroma. Capsaicin gives hot peppers their spiciness. Anthocyanins and flavonoids color the bark of trees, and ketol or eugenol provide the aroma of flowers. Some plants contain polyphenols, substances formed by the combination of several phenol molecules. They are good for human health. Polyphenols include lignins, flavonoids and others. These substances are in olive oil, fruits, nuts, tea, chocolate and other products. Some of them are believed to have an anti-aging effect and protect the body from cancer. But there are also toxic compounds: tannins, urushiol, carbolic acid.

Harm of phenols to humans

This substance and all its derivatives easily penetrate the body through the skin and lungs. In the blood, phenol forms compounds with other substances and becomes even more toxic. The higher its concentration in the body, the more harm it can cause. Phenol disrupts the activity of the nervous and cardiovascular systems, affecting the liver and kidneys. It destroys red blood cells, causing allergic reactions and ulcers.

Most often, phenol poisoning occurs through drinking water, as well as through the air in rooms where its derivatives were used in construction, paint or furniture production.

Inhalation of its compounds causes burns. respiratory tract, irritation of the nasopharynx and even pulmonary edema. If phenol gets on the skin, a severe chemical burn results, after which poorly healing ulcers develop. And if more than a quarter is affected skin of a person, this leads to his death. If small doses of phenol are accidentally ingested, for example through contaminated water, stomach ulcers, impaired coordination of movements, infertility, heart failure, bleeding and cancer develop. Large doses lead to death immediately.

Where are phenols used?

After the discovery of this substance, its ability to change color in air was discovered. This quality was used for the production of dyes. But then its other properties were discovered. And the substance phenol has become widely used in human activities:

Application in medicine

When the bactericidal properties of phenol were discovered, it began to be widely used in medicine. Mainly for disinfecting premises, tools and even the hands of staff. In addition, phenols are the main components of some popular drugs: aspirin, purgen, drugs for the treatment of tuberculosis, fungal diseases and various antiseptics, for example, xeroform.

Now phenol is often used in cosmetology for deep skin peeling. In this case, its property of burning is used top layer epidermis.

Using phenol for disinfection

There are also special drug in the form of ointment and solution for external use. It is used to disinfect things and indoor surfaces, tools and linen. Under medical supervision, phenol is used to treat condylomas, pyoderma, impetigo, folliculitis, purulent wounds and other skin diseases. The solution in combination with is used for disinfecting premises and soaking laundry. If you mix it with kerosene or turpentine, it acquires pest control properties.

Large areas of skin, as well as rooms intended for preparing and storing food, should not be treated with phenol.

How can you be poisoned by phenol?

The lethal dosage of this substance for an adult can be from 1 g, and for a child - 0.05 g. Phenol poisoning can occur for the following reasons:

• failure to comply with safety precautions when working with toxic substances;
• in case of an accident;
• in case of non-compliance with the dosage of medications;
• when using plastic products containing phenol, such as toys or dishes;
• if household chemicals are stored incorrectly.

In acute cases, they are immediately visible and help can be provided to the person. But the danger of phenol is that when taking small doses it may not be noticed. Therefore, if a person lives in a room where they were used finishing materials, paint products or furniture that emit phenol, chronic poisoning occurs.

Symptoms of poisoning

It is very important to recognize the problem in time. This will help start treatment on time and prevent death. The main symptoms are the same as for any other poisoning: nausea, vomiting, drowsiness, dizziness. But there are also characteristic signs by which you can find out that a person has been poisoned by phenol:

• characteristic odor from the mouth;
• fainting;
• a sharp decrease in body temperature;
• dilated pupils;
• pallor;
• dyspnea;
• cold sweat;
• decreased heart rate and blood pressure;
• stomach ache;
• bloody diarrhea;
• white spots on the lips.

You also need to know the signs of chronic poisoning. When small doses enter the body, there are no strong signs of this. But phenol undermines health. Symptoms of chronic poisoning are:

• frequent migraines, headaches;
• nausea;
• dermatitis and allergic reactions;
• insomnia;
• intestinal disorders;
• severe fatigue;
• irritability.

First aid and treatment of poisoning

The victim must be given first aid and taken to a doctor as soon as possible. The measures that need to be taken immediately after contact with phenol depend on the place of its penetration into the body:

1. If the substance gets on the skin, rinse with plenty of water; do not treat burns with ointment or fat.
2. If phenol gets on the oral mucosa, rinse and do not swallow anything.
3. If it gets into the stomach, drink a sorbent, for example, charcoal, "Polysorb", it is not recommended to rinse the stomach to avoid burns to the mucous membrane.

IN medical institution Treatment of poisoning is complex and lengthy. Ventilation of the lungs, detoxification therapy are carried out, an antidote is administered - calcium gluconate, sorbents, antibiotics, cardiac drugs are used,

Safety rules for using phenols

Sanitary and epidemiological standards in all countries have established maximum permissible level phenol concentrations in indoor air. A safe dose is considered to be 0.6 mg per 1 kg of human weight. But these standards do not take into account that even with such a concentration of phenol regularly entering the body, it gradually accumulates and can cause serious harm to health. This substance can be released into the air from plastic products, paints, furniture, construction and decoration materials, and cosmetics. Therefore, it is necessary to carefully monitor the composition of the products you purchase, and if you notice an unpleasant sweetish odor from something, it is better to get rid of it. When using phenol for disinfection, it is necessary to strictly observe the dosage and storage rules for solutions.