What substances are used to produce phenol. Preparation, chemical properties and use of phenol. The simplest monohydric phenols
Phenols- derivatives aromatic hydrocarbons, which may include one or more hydroxyl groups connected to benzene ring.
What are phenols called?
According to IUPAC rules, the name " phenol" The numbering of atoms comes from the atom that is directly bonded to the hydroxy group (if it is the senior one) and is numbered so that the substituents receive the lowest number.
Representative - phenol - C 6 H 5 OH:
The structure of phenol.
The oxygen atom has a lone electron pair at its outer level, which is “pulled” into the ring system (+M effect HE-groups). As a result, 2 effects can occur:
1) increasing the electron density of the benzene ring to the ortho- and para- positions. Basically, this effect manifests itself in electrophilic substitution reactions.
2) the density on the oxygen atom decreases, as a result of which the bond HE weakens and may tear. The effect is associated with increased acidity phenol compared to saturated alcohols.
Mono-substituted derivatives phenol(cresol) can be in 3 structural isomers:
Physical properties of phenols.
Phenols are crystalline substances at room temperature. Poorly soluble in cold water, but well soluble in hot and aqueous solutions alkalis. They have a characteristic odor. Due to the formation of hydrogen bonds, they have a high boiling and melting point.
Preparation of phenols.
1. From halobenzenes. When chlorobenzene and sodium hydroxide are heated under pressure, sodium phenolate is obtained, which, after reacting with acid, turns into phenol:
2. Industrial method: the catalytic oxidation of cumene in air produces phenol and acetone:
3. From aromatic sulfonic acids by fusion with alkalis. The reaction most often carried out to produce polyhydric phenols is:
Chemical properties of phenols.
R-orbital of the oxygen atom forms with the aromatic ring unified system. Therefore, the electron density on the oxygen atom decreases, and on the benzene ring it increases. Communication polarity HE increases, and the hydrogen of the hydroxyl group becomes more reactive and can easily be replaced by a metal atom even under the action of alkalis.
The acidity of phenols is higher than that of alcohols, so the following reactions can be carried out:
But phenol is a weak acid. If carbon dioxide or sulfur dioxide is passed through its salts, phenol is released, which proves that carbonic and sulfurous acids are stronger acids:
The acidic properties of phenols are weakened by the introduction of type I substituents into the ring and enhanced by the introduction of type II.
2) Formation of esters. The process occurs under the influence of acid chlorides:
3) Electrophilic substitution reaction. Because HE-group is a substituent of the first kind, then reactivity of the benzene ring in the ortho and para positions increases. When phenol is exposed to bromine water, a precipitate is observed - this is a qualitative reaction to phenol:
4) Nitration of phenols. The reaction is carried out with a nitrating mixture, resulting in the formation of picric acid:
5) Polycondensation of phenols. The reaction occurs under the influence of catalysts:
6) Oxidation of phenols. Phenols are easily oxidized by atmospheric oxygen:
7) A qualitative reaction to phenol is the effect of a solution of ferric chloride and the formation of a violet complex.
Application of phenols.
Phenols are used in the production of phenol-formaldehyde resins, synthetic fibers, dyes and medicines, disinfectants. Picric acid is used as explosives.
Formed on the basis of benzene. At normal conditions They are solid toxic substances with a specific aroma. In modern industry, these chemical compounds play an important role. In terms of volume of use, phenol and its derivatives are among the twenty most popular chemical compounds in the world. They are widely used in the chemical and light industries, pharmaceuticals and energy. Therefore, obtaining phenol in industrial scale- one of the main tasks of the chemical industry.
Phenol designations
The original name of phenol is carbolic acid. Later, this compound was given the name “phenol”. The formula of this substance is shown in the figure:
The phenol atoms are numbered from the carbon atom that is connected to the OH hydroxo group. The sequence continues in such an order that the other substituted atoms receive the lowest numbers. Phenol derivatives exist in the form of three elements, the characteristics of which are explained by the differences in their structural isomers. Various ortho-, meta-, para-cresols are only a modification of the basic structure of the compound of the benzene ring and hydroxyl group, the basic combination of which is phenol. The formula of this substance is chemical notation looks like C6H5OH.
Physical properties of phenol
Visually, phenol appears as solid, colorless crystals. On outdoors they oxidize, giving the substance its characteristic pink tint. Under normal conditions, phenol is quite poorly soluble in water, but with an increase in temperature to 70 o this figure increases sharply. In alkaline solutions this substance is soluble in any quantity and at any temperature.
These properties are also preserved in other compounds, the main components of which are phenols.
Chemical properties
The unique properties of phenol are explained by its internal structure. In the molecule of this chemical substance, the p-orbital of oxygen forms unified p-system with a benzene ring. This tight interaction increases the electron density of the aromatic ring and decreases this indicator for the oxygen atom. In this case, the polarity of the bonds of the hydroxo group increases significantly, and the hydrogen included in its composition is easily replaced by any alkali metal. This is how various phenolates are formed. These compounds do not decompose with water like alcoholates, but their solutions are very similar to salts of strong bases and weak acids, so they have a fairly pronounced alkaline reaction. Phenolates react with various acids; as a result of the reaction, phenols are reduced. The chemical properties of this compound allow it to react with acids, forming esters. For example, the interaction of phenol and acetic acid leads to the formation of finyl ester (phenyacetate).
The nitration reaction is widely known, in which, under the influence of 20% nitric acid, phenol forms a mixture of para- and orthonitrophenols. When phenol is treated with concentrated nitric acid, it produces 2,4,6-trinitrophenol, which is sometimes called picric acid.
Phenol in nature
As an independent substance, phenol is found in nature in coal tar and in certain types of oil. But for industrial needs this quantity does not play any role. Therefore, the production of phenol artificially has become a priority for many generations of scientists. Fortunately, this problem was resolved and artificial phenol was eventually obtained.
Properties, receiving
The use of various halogens makes it possible to obtain phenolates, from which further processing benzene is formed. For example, heating sodium hydroxide and chlorobenzene produces sodium phenolate, which, when exposed to acid, breaks down into salt, water and phenol. The formula for such a reaction is given here:
C 6 H 5 -CI + 2NaOH -> C 6 H 5 -ONa + NaCl + H 2 O
Aromatic sulfonic acids are also a source for the production of benzene. Chemical reaction carried out by simultaneous melting of alkali and sulfonic acid. As can be seen from the reaction, phenoxides are formed first. When treated with strong acids, they are reduced to polyhydric phenols.
Phenol in industry
In theory, the simplest and most promising way to obtain phenol looks like this: with the help of a catalyst, benzene is oxidized with oxygen. But until now, a catalyst for this reaction has not been selected. Therefore, other methods are currently used in industry.
Continuous industrial method The production of phenol consists of the interaction of chlorobenzene and a 7% solution of sodium hydroxide. The resulting mixture is passed through a one and a half kilometer system of pipes heated to a temperature of 300 C. Under the influence of temperature and maintained high pressure the starting substances react to produce 2,4-dinitrophenol and other products.
Not long ago, an industrial method for producing phenol-containing substances using the cumene method was developed. This process consists of two stages. First, isopropylbenzene (cumene) is obtained from benzene. To do this, benzene is alkalated with propylene. The reaction looks like this:
After this, cumene is oxidized with oxygen. The output of the second reaction is phenol and another important product, acetone.
Phenol can be produced on an industrial scale from toluene. To do this, toluene is oxidized on oxygen contained in the air. The reaction occurs in the presence of a catalyst.
Examples of phenols
The closest homologues of phenols are called cresols.
There are three types of cresols. Meta-cresol is a liquid under normal conditions, para-cresol and ortho-cresol are solids. All cresols are poorly soluble in water, and their chemical properties are almost similar to phenol. In their natural form, cresols are found in coal tar; in industry they are used in the production of dyes and some types of plastics.
Examples of diatomic phenols include para-, ortho-, and meta-hydrobenzenes. All of them are solids, easily soluble in water.
The only representative of trihydric phenol is pyrogallol (1,2,3-trihydroxybenzene). Its formula is presented below.
Pyrogallol is a fairly strong reducing agent. It oxidizes easily, so it is used to produce oxygen-free gases. This substance is well known to photographers; it is used as a developer.
The main purpose of this process is to produce metallurgical coke. By-products are formed liquid products coking and gas. 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:
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.
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.
Formed on the basis of benzene. Under normal conditions, they are solid toxic substances with a specific aroma. In modern industry, these chemical compounds play an important role. In terms of volume of use, phenol and its derivatives are among the twenty most popular chemical compounds in the world. They are widely used in the chemical and light industries, pharmaceuticals and energy. Therefore, the production of phenol on an industrial scale is one of the main tasks of the chemical industry.
Phenol designations
The original name of phenol is carbolic acid. Later, this compound was given the name “phenol”. The formula of this substance is shown in the figure:
The phenol atoms are numbered from the carbon atom that is connected to the OH hydroxo group. The sequence continues in such an order that the other substituted atoms receive the lowest numbers. Phenol derivatives exist in the form of three elements, the characteristics of which are explained by the differences in their structural isomers. Various ortho-, meta-, para-cresols are only a modification of the basic structure of the compound of the benzene ring and hydroxyl group, the basic combination of which is phenol. The formula of this substance in chemical notation looks like C 6 H 5 OH.
Physical properties of phenol
Visually, phenol appears as solid, colorless crystals. In open air they oxidize, giving the substance a characteristic pink tint. Under normal conditions, phenol is quite poorly soluble in water, but with an increase in temperature to 70 o this figure increases sharply. In alkaline solutions this substance is soluble in any quantity and at any temperature.
These properties are also preserved in other compounds, the main components of which are phenols.
Chemical properties
The unique properties of phenol are explained by its internal structure. In the molecule of this chemical substance, the p-orbital of oxygen forms a single p-system with the benzene ring. This tight interaction increases the electron density of the aromatic ring and decreases this indicator for the oxygen atom. In this case, the polarity of the bonds of the hydroxo group increases significantly, and the hydrogen included in its composition is easily replaced by any alkali metal. This is how various phenolates are formed. These compounds do not decompose with water like alcoholates, but their solutions are very similar to salts of strong bases and weak acids, so they have a fairly pronounced alkaline reaction. Phenolates react with various acids; as a result of the reaction, phenols are reduced. The chemical properties of this compound allow it to react with acids, forming esters. For example, the reaction of phenol and acetic acid leads to the formation of phenyl ester (phenyacetate).
The nitration reaction is widely known, in which, under the influence of 20% nitric acid, phenol forms a mixture of para- and orthonitrophenols. When phenol is treated with concentrated nitric acid, it produces 2,4,6-trinitrophenol, which is sometimes called picric acid.
Phenol in nature
As an independent substance, phenol is found in nature in coal tar and in certain types of oil. But for industrial needs this quantity does not play any role. Therefore, obtaining phenol artificially has become a priority for many generations of scientists. Fortunately, this problem was resolved and artificial phenol was eventually obtained.
Properties, receiving
The use of various halogens makes it possible to obtain phenolates, from which benzene is formed upon further processing. For example, heating sodium hydroxide and chlorobenzene produces sodium phenolate, which, when exposed to acid, breaks down into salt, water and phenol. The formula for such a reaction is given here:
C 6 H 5 -CI + 2NaOH -> C 6 H 5 -ONa + NaCl + H 2 O
Aromatic sulfonic acids are also a source for the production of benzene. The chemical reaction is carried out by simultaneous melting of alkali and sulfonic acid. As can be seen from the reaction, phenoxides are formed first. When treated with strong acids, they are reduced to polyhydric phenols.
Phenol in industry
In theory, the simplest and most promising way to obtain phenol looks like this: with the help of a catalyst, benzene is oxidized with oxygen. But until now, a catalyst for this reaction has not been selected. Therefore, other methods are currently used in industry.
A continuous industrial method for producing phenol consists of the interaction of chlorobenzene and a 7% sodium hydroxide solution. The resulting mixture is passed through a one and a half kilometer system of pipes heated to a temperature of 300 C. Under the influence of temperature and maintained high pressure, the starting substances react, resulting in 2,4-dinitrophenol and other products.
Not long ago, an industrial method for producing phenol-containing substances using the cumene method was developed. This process consists of two stages. First, isopropylbenzene (cumene) is obtained from benzene. To do this, benzene is alkalated with propylene. The reaction looks like this:
After this, cumene is oxidized with oxygen. The output of the second reaction is phenol and another important product, acetone.
Phenol can be produced on an industrial scale from toluene. To do this, toluene is oxidized on oxygen contained in the air. The reaction occurs in the presence of a catalyst.
Examples of phenols
The closest homologues of phenols are called cresols.
There are three types of cresols. Meta-cresol under normal conditions is a liquid, para-cresol and ortho-cresol are solids. All cresols are poorly soluble in water, and their chemical properties are almost similar to phenol. In their natural form, cresols are found in coal tar; in industry they are used in the production of dyes and some types of plastics.
Examples of diatomic phenols include para-, ortho-, and meta-hydrobenzenes. All of them are solids, easily soluble in water.
The only representative of trihydric phenol is pyrogallol (1,2,3-trihydroxybenzene). Its formula is presented below.
Pyrogallol is a fairly strong reducing agent. It oxidizes easily, so it is used to produce oxygen-free gases. This substance is well known to photographers; it is used as a developer.
