Abstract on the topic:

"Phenols"

Teacher: Petrishek

Irina Alexandrovna

Completed:

2nd year student, 9th group

Faculty of Pharmacy

Vladlen Ardislamov

General characteristics of phenols

Phenols are derivatives of arenes in which one or more hydrogen atoms are replaced by hydroxyl groups

The OH groups of phenols are called phenolic hydroxyl groups.

Many phenols and their derivatives are present in the plant world (pigments, tannins, lignin components of wood). Phenols are used in medicine (they are a powerful antifungal and antibacterial antiseptic; if they enter the human body in sufficient quantities, they cause poisoning, affecting most organs and systems), in the pharmaceutical industry, in the production of polymers, dyes, fragrances, and plant protection products. Phenols and their derivatives are used in the oil industry (as antipolarimizers). Hydroquinone is used as a cosmetic to eliminate skin defects; as an inhibitor of the free radical polymerization reaction of methyl methacrylate, it is part of chemically cured dental composite materials. Pyrocatechol is used in photography as a developer, in the production of dyes, and medicinal substances (for example, adrenaline).

Based on the number of hydroxyl groups in the aromatic ring, single and polyhydric phenols are distinguished. For most phenols and some of their homologues, the trivial names adopted by the IUPAC nomenclature are used.

Representatives:

O-Cresol m-Cresol p-Cresol

a-naphthol b-naphthol

Pyrocatechol Resorcinol Hydroquinone

Pyrogallol

Physical properties of phenols

Phenol and its lower homologues are colorless, low-melting crystalline substances or liquids with a rather strong characteristic odor. The smell of phenol in the air at low concentrations (4 mg/m3). Diatomic and trihydric phenols are solid, odorless substances with fairly high melting points. Phenols are less volatile than alcohols with similar molecular weights, as they form stronger intermolecular hydrogen bonds.

Phenol is moderately soluble in water (8.2% at 15C*). Other monohydric phenols are slightly soluble in water, but readily dissolve in ether, benzene, alcohol and chloroform. An increase in the number of hydroxyl groups causes an increase in the solubility of polyhydric phenols in water. Polyhydric phenols are also highly soluble in polar polyhydric solvents.

Phenols and especially naphthols are highly toxic substances. Their release into water bodies causes irreparable harm to nature.

Preparation of phenols

Cumene method (Sergeeva)

Most phenol is currently produced from isopropylbenzene - cumene. By oxidizing cumene with air, cumene hydroperoxide is obtained, which decomposes under the action of aqueous solutions of mineral acids into phenol and acetone. Cumene is synthesized from benzene and propylene.

Cumene hydroperoxide

Mechanism:

(M 3)

Second-butyl hydroperoxide behaves similarly.

Hydrolysis of aryl halides

Chlorine in chlorobenzene is inactive and therefore hydrolysis is carried out with an 8% NaOH solution in an autoclave at 250°C in the presence of copper salts:

Sodium phenoxide

According to the Raschig method, chlorobenzene is obtained by the oxidation of benzene in the presence of hydrogen chloride:

Hydrolysis of chlorobenzene is carried out with superheated steam in the presence of a copper catalyst. The resulting hydrogen chloride is returned to the first stage of the process:

Hydrolysis in the presence of alkali occurs at a lower temperature, but this results in the loss of valuable hydrochloric acid, which is preserved in the Raschig method.

Fusion of arylsulfonates with alkali

When fused with alkali, arylsulfonates undergo a substitution reaction:

Benzenesulfonic acid Sodium benzenesulfonate

The conversion of sodium phenolate into phenol is carried out using sulfur dioxide, which is formed in the second stage:

Phenol is obtained in the form of an aqueous solution, from which it is isolated by distillation. This method of phenol synthesis is the oldest (1890). The method is used to obtain other phenols, for example:

Decomposition of diazonium salts

Direct oxidation of benzene

C6H6+O2 (bauxite, 300-750C*) C6H5OH

The difficulty of this transformation was that benzene is oxidized more easily than phenol. It is known both as catalytic oxidation with atmospheric oxygen (in the reaction diagram) and with the use of various combinations of oxidizing agents (peroxides) and catalysts (salts of copper, iron, titanium, etc.).

Isolation from natural raw materials

Phenols are isolated from coal tar through distillation and chemical treatment to produce a mixture of phenols; from oil refining waste.

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 also polyhydric phenols containing three or more hydroxyl groups in 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 cass - phenols.

Physical properties of phenol

Phenol is a solid, colorless crystalline substance, melting point = 43°C, boiling point = 181°C, with a sharp characteristic odor. Toxic. Phenol is slightly soluble in water at room temperature. An aqueous solution of phenol is called carbolic acid. On contact with skin it causes burns, Therefore, phenol must be handled very carefully!

Chemical properties of phenol

In most reactions, phenols are more active at the O–H bond, since this bond is more polar due to the shift of electron density from the oxygen atom towards the benzene ring (participation of the lone electron pair of the oxygen atom in the p-conjugation system). The acidity of phenols is much higher than that of alcohols. For phenols, rupture reactions S-O connections are not characteristic, since the oxygen atom is firmly bonded to the carbon atom of the benzene ring due to the participation of its lone electron pair in the conjugation system. The mutual influence of atoms in the phenol molecule is manifested not only in the behavior of the hydroxy group, but also in the greater reactivity of the benzene ring. The hydroxyl group increases the electron density in the benzene ring, especially at the ortho and para positions (OH groups)

Acid properties of phenol

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

The acidity of phenols depends on the nature of the substituents (electron density donor or acceptor), position relative to the OH group and the number of substituents. The greatest influence on the OH-acidity of phenols is exerted by groups located in the ortho- and para-positions. Donors increase strength O-N connections(thereby reducing hydrogen mobility and acidic properties), acceptors reduce the strength of the O-H bond, while acidity increases:

However, the acidic properties of phenol 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:

Qualitative reaction to phenol

Phenol reacts with ferric chloride to form an intensely purple complex compound. 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 give a bright blue-violet color in reaction with ferric chloride(3).

Reactions of the benzene ring of phenol

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(3) bromide). In addition, the interaction with phenol occurs selectively: bromine atoms are directed to ortho- And pair- positions, replacing the hydrogen atoms located there. The selectivity of substitution is explained by the features of the electronic structure of the phenol molecule discussed above.

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

This reaction, like the reaction with iron(3) chloride, serves to 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 is formed ortho- And paro isomers of nitrophenol:

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

3. Hydrogenation of the aromatic ring of phenol in the presence of a catalyst passes easily:

4.Polycondensation of phenol with aldehydes, in particular, with formaldehyde it 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:

Reaction polycondensation, those. the polymer production reaction, which 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 the same 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 phenol-formaldehyde resin with a linear structure with an excess of aldehyde, solid plastic masses are obtained with unique properties. Polymers based on phenol-formaldehyde resins are used for the manufacture of varnishes and paints, plastic products that are resistant to heating, cooling, water, alkalis, and acids. They have high dielectric properties. The most critical and important parts of electrical appliances, power unit housings and machine parts, and the polymer base of printed circuit boards for radio devices are made from polymers based on phenol-formaldehyde resins. 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 adhesive is used to attach the metal base of lighting lamps to a glass bulb. Thus, phenol and products based on it are widely used.

Application of phenols

Phenol - solid, with a characteristic odor, causes burns upon contact with skin. Poisonous. It dissolves in water, its solution is called carbolic acid (antiseptic). She was the first antiseptic introduced into surgery. Widely used in plastic production, medicines (salicylic acid and its derivatives), dyes, explosives.

According to the number of hydroxyl groups:

Monatomic; For example:

Diatomic; For example:

Triatomic; For example:

There are phenols of higher atomicity.

The simplest 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;

An increase in the polarity of the O-H bond, leading to an increase in the acidic properties of phenols compared to alcohols.

Unlike alcohols, phenols partially dissociate in aqueous solutions for 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. They are toxic substances and 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

The formation of a white precipitate of tribromophenol is sometimes considered 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.

a) Acetylene can be obtained from methane when heated:

In the presence of a catalyst, acetylene is converted to benzene (trimerization reaction):

Phenol can be obtained from benzene in two stages. Benzene reacts with chlorine in the presence of ferric chloride to form chlorobenzene:

When chlorobenzene is exposed to alkali at high temperature the chlorine atom is replaced by a hydroxyl group and phenol is obtained:

When phenol is exposed to bromine, 2,4,6-tribromophenol is formed:

b) Ethane can be obtained from methane in two stages. When methane is chlorinated, chloromethane is formed. When methane is chlorinated in light, chloromethane is formed:

When chloromethane reacts with sodium, ethane is formed (Wurtz reaction):

Propane can also be produced from ethane in two stages. When ethane is chlorinated, chloroethane is formed:

When chloroethane reacts with chloromethane in the presence of sodium, propane is formed:

Hexane can be obtained from propane in two stages. When propane is chlorinated, a mixture of isomers is formed - 1-chloropropane and 2-chloropropane. The isomers have different boiling points and can be separated by distillation.

When 1-chloropropane reacts with sodium, hexane is formed:

When hexane is dehydrogenated over a catalyst, benzene is formed:

Picric acid (2,4,6-trinitrophenol) can be obtained from benzene in three stages. When benzene reacts with chlorine in the presence of ferric chloride, chlorobenzene is formed.

The main purpose of this process is to produce metallurgical coke. Liquid coking products and gas are formed as by-products. By distilling liquid coking products, along with benzene, toluene and naphthalene, phenol, thiophene, pyridine and their homologues, as well as more complex analogues with condensed nuclei, are obtained. The proportion of coal tar phenol, compared to that obtained by the cumene method, is insignificant.

2. Halogen substitution in aromatic compounds

The replacement of a halogen with a hydroxyl group occurs under harsh conditions and is known as the “Dow” process (1928)

Previously, phenol (from chlorobenzene) was obtained by this method, but now its importance has decreased due to the development of more economical methods that do not involve the consumption of chlorine and alkali and the formation of large amounts of wastewater.

In activated halogenarenes (containing, along with halogen, a nitro group in O- And p- positions) halogen substitution occurs under milder conditions:

This can be explained by the electron-withdrawing effect of the nitro group, which absorbs the electron density of the benzene ring and thus participates in the stabilization of the σ-complex:

3. Raschig method

This is a modified chlorine method: benzene is subjected to oxidative chlorination by the action of hydrogen chloride and air, and then, without isolating the resulting chlorobenzene, it is hydrolyzed with water vapor in the presence of copper salts. As a result, chlorine is not consumed at all, and the overall process is reduced to the oxidation of benzene to phenol:

4.Sulfonate method

Phenols can be obtained in good yield by fusing aromatic sulfonic acids Ar-SO 3 H with a mixture of sodium and potassium hydroxides (reaction alkaline melting) at 300°C, followed by neutralization of the resulting alcoholate by adding acid:

The method is still used in industry (for the production of phenol) and is used in laboratory practice.

5. Cumene method

The first large-scale production of phenol using the cumene method was carried out in 1949 in the Soviet Union. Currently, this is the main method for producing phenol and acetone.

The method includes two stages: oxidation of isopropylbenzene (cumene) with atmospheric oxygen to hydroperoxide and its acid decomposition:

The advantage of this method is the absence of by-products and the high need for final products - phenol and acetone. The method was developed in our country by R.Yu. Udris, B.D. Krutalov et al. in 1949

6. From diazonium salts

The method involves heating diazonium salts in dilute sulfuric acid, which leads to hydrolysis - the replacement of the diazo group with a hydroxy group. The synthesis is very convenient for obtaining hydroxyarenes in the laboratory:

1. Structure of phenols

The structure and distribution of electron density in a phenol molecule can be depicted by the following diagram:

The dipole moment of phenol is 1.55 D and is directed towards the benzene ring. The hydroxyl group exhibits a –I effect and a +M effect in relation to the benzene ring. Since the mesomeric effect of the hydroxy group prevails over the inductive one, the conjugation of lone electron pairs of the oxygen atom with the -orbitals of the benzene ring has an electron-donating effect on the aromatic system, which increases its reactivity in electrophilic substitution reactions.