Phenols can react at both the hydroxyl group and the benzene ring.
1. Reactions on the hydroxyl group
The carbon-oxygen bond in phenols is much stronger than in alcohols. For example, phenol cannot be converted into bromobenzene by the action of hydrogen bromide, while cyclohexanol, when heated with hydrogen bromide, is easily converted into bromocyclohexane:
Like alkoxides, phenoxides react with alkyl halides and other alkylating reagents to form mixed esters:
(23)
Phenetol
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Anisole
Alkylation of phenols with halocarbons or dimethyl sulfate in an alkaline medium is a modification of the Williamson reaction. The alkylation reaction of phenols with chloroacetic acid produces herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D).
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2,4-Dichlorophenoxyacetic acid (2,4-D)
and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).
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2,4,5-trichlorophenoxyacetic acid (2,4,5-T)
The starting 2,4,5-trichlorophenol is obtained according to the following scheme:
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1,2,4,5-Tetrachlorophenol 2,4,5-trichlorophenoxide sodium 2,4,5-trichlorophenol
If overheated at the stage of producing 2,4,5-trichlorophenol, very toxic 2,3,7,8-tetrachlorodibenzodioxine can be formed instead:
2,3,7,8-Tetrachlorodibenzodioxin
Phenols are weaker nucleophiles than alcohols. For this reason, unlike alcohols, they do not enter into an esterification reaction. To obtain phenol esters, acid chlorides and acid anhydrides are used:
Phenylacetate
Diphenyl carbonate
Exercise 17. Thymol (3-hydroxy-4-isopropyltoluene) is found in thyme and is used as a medium-strength antiseptic in toothpastes and mouthwashes. It is prepared by Friedel–Crafts alkylation
m-cresol with 2-propanol in the presence of sulfuric acid. Write this reaction.
2. Substitution into a ring
The hydroxy group of phenol very strongly activates the aromatic ring with respect to electrophilic substitution reactions. Oxonium ions are most likely formed as intermediate compounds:
When carrying out electrophilic substitution reactions in the case of phenols, special measures must be taken to prevent polysubstitution and oxidation.
3. Nitration
Phenol nitrates much more easily than benzene. When it is exposed to concentrated nitric acid, 2,4,6-trinitrophenol (picric acid) is formed:
Picric acid
The presence of three nitro groups in the nucleus sharply increases the acidity of the phenolic group. Picric acid, unlike phenol, is already a fairly strong acid. The presence of three nitro groups makes picric acid explosive and is used to prepare melinite. To obtain mononitrophenols, it is necessary to use dilute nitric acid and carry out the reaction at low temperatures:
It turns out a mixture O- And P- nitrophenols with predominance O- isomer. This mixture separates easily due to the fact that only O- the isomer is volatile with water vapor. Great volatility O- nitrophenol is explained by the formation of an intramolecular hydrogen bond, while in the case
P- nitrophenol, an intermolecular hydrogen bond occurs.
4. Sulfonation
Sulfonation of phenol is very easy and leads to the formation, depending on temperature, predominantly ortho- or pair-phenolsulfonic acids:
5. Halogenation
The high reactivity of phenol leads to the fact that even when it is treated with bromine water, three hydrogen atoms are replaced:
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To obtain monobromophenol, special measures must be taken.
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P-Bromophenol
Exercise 18. 0.94 g of phenol is treated with a slight excess of bromine water. What product and in what quantity is formed?
6. Kolbe reaction
Carbon dioxide adds to sodium phenoxide by the Kolbe reaction, which is an electrophilic substitution reaction in which the electrophile is carbon dioxide
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Phenol Sodium phenoxide Sodium salicylate Salicylic acid
Mechanism:
(M 5)
By reacting salicylic acid with acetic anhydride, aspirin is obtained:
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Acetylsalicylic acid
If both ortho-positions are occupied, then the replacement takes place according to pair- position:
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The reaction proceeds according to the following mechanism:
(M 6)
7. Condensation with carbonyl-containing compounds
When phenol is heated with formaldehyde in the presence of acid, phenol-formaldehyde resin is formed:
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Phenol formaldehyde resin
By condensation of phenol with acetone in an acidic medium, 2,2-di(4-hydroxyphenyl)propane is obtained, industrially named bisphenol A:
Bisphenol A
2,2-di(4-hydroxyphenyl)propane
di(4-hydroxyphenyl)dimethylmethane
By treating bisphenol A with phosgene in pyridine, Lexan is obtained:
In the presence of sulfuric acid or zinc chloride, phenol condenses with phthalic anhydride to form phenolphthalein:
(39)
Phthalic anhydride Phenolphthalein
When phthalic anhydride is fused with resorcinol in the presence of zinc chloride, a similar reaction occurs and fluorescein is formed:
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Resorcinol Fluorescein
Exercise 19. Draw a diagram of the condensation of phenol with formaldehyde. What practical significance does this reaction have?
8. Claisen rearrangement
Phenols undergo Friedel-Crafts alkylation reactions. For example, when phenol reacts with allyl bromide in the presence of aluminum chloride, 2-allylphenol is formed:
(41)
The same product is also formed when allylphenyl ether is heated as a result of an intramolecular reaction called Claisen rearrangement:
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Allylphenyl ether 2-Allylphenol
Reaction
(43)
It takes place according to the following mechanism:
(44)
The Claisen rearrangement also occurs when allyl vinyl ether or 3,3-dimethyl-1,5-hexadiene is heated:
(45)
Allyl vinyl ether 4-Pentenal
(46)
3,3-Dimethyl-2-Methyl-2,6-
1,5-hexadiene hexadiene
Other reactions of this type are also known, for example, the Diels-Alder reaction. They are called pericyclic reactions.
An organic substance from the group of phenols, a simple diatomic phenol. Among chemists, the names resorcinol and 1,3-dihydroxybenzene are also used. The formula of resorcinol is similar to the formulas of hydroquinone and pyrocatechin, the difference is in the structure of the molecule; in the way the OH groups are attached.
Properties
The substance is needle-shaped crystals without color or white crystalline powder with a pungent phenolic odor. Sometimes the powder may have a pinkish or yellowish tint. If it becomes heavily colored, pink-orange or brown, it means that the reagent was not stored correctly and it has oxidized. Resorcinol is a fire hazard. It dissolves well in water, diethyl ether, ethyl alcohol, and acetone. Can be dissolved in oils, glycerin. Almost insoluble in chloroform, carbon disulfide, benzene.
The reagent exhibits the chemical properties of phenols. Strong reducing agent, easily oxidized. Reacts with alkalis, forming phenolate salts; with ammonia, halogens, strong acids (for example, nitric, sulfuric, picric, glacial acetic).
For the qualitative determination of resorcinol, the following reactions are used:
- with ferric chloride - the solution turns deep purple, almost black;
- fusion with phthalic anhydride in the presence of a catalyst leads to the formation of a characteristically colored, green fluorescent substance - fluorescein. Fluorescein itself has a yellow-red color solution (the reaction distinguishes resorcinol from other phenols).
Resorcinol dust and especially its vapors irritate the skin, respiratory organs, and mucous membranes of the eyes. Inhalation of reagent vapors and dust causes coughing, nausea, rapid heartbeat, and dizziness, so you need to work with resorcinol using respirators or masks, safety glasses, special clothing, and a ventilated area. If poisoning is suspected, wash the area where the reagent was exposed with plenty of water, take the victim to fresh air, and call a doctor.
Store resorcinol in an airtight container, in dark, dry, cool rooms, strictly separate from flammable substances.
Application
Resorcinol is in demand in the chemical industry as a raw material 
for the production of artificial dyes, fluorescein, resorcinol-formaldehyde resins, solvents, stabilizers, plasticizers and UV absorbers for plastics.
- In analytical chemistry it is used in colorimetric studies. It is used to determine the content of zinc, lead, carbohydrates, furfural, lignin, etc.
- In the rubber industry.
- In the fur industry, as a dye for fur.
- Very widely used in medicine and pharmaceuticals. It is used as a disinfectant, cauterizing, wound healing agent, and anthelmintic. Included in solutions and ointments for the treatment of various skin diseases, including fungal and purulent; acne, seborrhea, dermatitis, eczema, age spots.
- To obtain explosives.
Goal of the work
The purpose of the work is to carry out oxidation and condensation reactions for phenol and its derivatives.
Theoretical part
Phenols are aromatic compounds that have hydroxyl groups directly attached to the aromatic ring. Based on the number of hydroxyls, monohydric, diatomic and polyatomic phenols are distinguished. The simplest of them, oxybenzene, is called phenol. Hydroxy derivatives of toluene (methylphenols) are called ortho-, meta- and para-cresols, and hydroxy derivatives of xylenes are called xylenols. Phenols of the naphthalene series are called naphthols. The simplest dihydric phenols are called: o - dioxybenzene - pyrocatechol, m - dioxybenzene - resorcinol, n-dioxybenzene - hydroquinone.
Many phenols are easily oxidized, often resulting in a complex mixture of products. Depending on the oxidizing agent and reaction conditions, different products can be obtained. Thus, during the vapor-phase oxidation (t = 540 0) of o - xylene, phthalic anhydride is obtained. A qualitative reaction to phenols is a test with a solution of ferric chloride, which produces a colored ion. Phenol gives a red-violet color, cresols give a blue color, and other phenols give a green color.
A condensation reaction is an intramolecular or intermolecular process of the formation of a new C-C bond, usually occurring with the participation of condensing reagents, the role of which can be very different: it has a catalytic effect, produces intermediate reactive products, or simply binds a split-off particle, shifting the equilibrium in the system.
The condensation reaction with the elimination of water is catalyzed by a variety of reagents: strong acids, strong alkalis (hydroxides, alcoholates, amides, alkali metal hydrides, ammonia, primary and secondary amines).
Work order
In this work, we test the possibility of the oxidation of phenols and the formation of phthaleins by the condensation reaction.
3.1 Oxidation of phenol and naphthol
Oxidation is carried out with a solution of potassium permanganate in the presence of a solution of sodium carbonate (soda).
3.1.1 equipment and reagents:
Test tubes;
Pipettes;
Phenol – aqueous solution;
Naphthol - aqueous solution;
Potassium permanganate (0.5% aqueous solution);
Sodium carbonate (5% aqueous solution);
3.1.2 Conducting the experiment:
a) place 1 ml of an aqueous solution of phenol or naphthol into a test tube;
b) add 1 ml of sodium carbonate solution (soda);
c) add potassium permanganate solution drop by drop while shaking the test tube. Observe the color change of the solution.
The oxidation of phenols usually occurs in different directions and leads to the formation of a complex mixture of substances. The easier oxidation of phenols, compared to aromatic hydrocarbons, is due to the influence of the hydroxyl group, which sharply increases the mobility of hydrogen atoms at other carbon atoms of the benzene poison.
3.2 Formation of phthaleins.
3.2.1 Preparation of phenolphthalein.
Phenolphthalein is formed by the condensation reaction of phenol with phthalic anhydride in the presence of concentrated sulfuric acid.
Phthalic anhydride condenses with phenols to give triphenylethane derivatives. Condensation is accompanied by the elimination of water due to the oxygen of one of the carbonyl groups of the anhydride and the mobile hydrogen atoms of the benzene nuclei of two phenol molecules. The introduction of dewatering agents such as concentrated sulfuric acid greatly facilitates this condensation.
Phenol forms phenolphthalein by the following reaction:
/ \ /
H H C
3.2.1.1 Equipment and reagents:
Test tubes;
Pipettes;
Electric stove;
Phthalic anhydride;
Sulfuric acid diluted 1:5;
3.2.1.2 Conducting the experiment:
b) add approximately twice the amount of phenol to the same test tube;
c) shake the contents of the test tube several times and carefully add 3-5 drops of concentrated sulfuric acid to it, continuing to shake;
d) heat the test tube on a hotplate until a dark red color appears;
e) cool the test tube and add 5 ml of water to it;
f) add an alkali solution drop by drop to the resulting solution and observe the color change;
g) after changing color, add a few drops of diluted sulfuric acid to the contents of the test tube until the original color returns or until discoloration occurs.
3.2.2 Preparation of fluorescein.
Fluorescein is formed by the condensation reaction of resorcinol with phthalic anhydride in the presence of concentrated sulfuric acid.
Diatomic phenols with hydroxyl groups in the meta position, entering condensation, release two water molecules, one due to the oxygen of one of the carbonyl groups of the anhydride and the mobile hydrogen atoms of the benzene nuclei of two phenol molecules. the second water molecule is released due to the hydroxyl groups of two phenol molecules to form a six-membered ring.
Resorcinol forms fluorescein by the following reaction:
OH HO OH HO OH
/ \ / \ /
H H C
3.2.1.1.Equipment and reagents:
Test tubes;
Pipettes;
Electric stove;
Phthalic anhydride;
Resorcinol;
Concentrated sulfuric acid;
Caustic sodium solution (5-10%);
3.2.2.1 Conducting the experiment:
a) weigh 0.1-0.3 g of phthalic anhydride and place in a test tube;
b) add approximately twice the amount of resorcinol to the same test tube and mix by shaking;
c) carefully add 3-5 drops of concentrated sulfuric acid to the contents of the test tube;
d) heat the mixture in a test tube until a dark red color appears. Heat on an electric stove;
e) cool the contents of the test tube and add 5 ml of water to it;
f) add 2-3 drops of the resulting solution into a clean test tube, add 1 ml of alkali solution and dilute with plenty of water. Observe the color change.
3.2.3 Aurin formation
Aurine is obtained by condensation of oxalic acid with phenol in the presence of sulfuric acid.
When heated in the presence of sulfuric acid, oxalic acid condenses with three phenol molecules, splitting off water and carbon monoxide to form aurin.
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H-O- -H H- -OH
-H. OH O =
| . C = O +3H 2 O+CO
H - C
3.2.3.1. Equipment and reagents:
Test tubes;
Pipettes;
Oxalic acid;
Concentrated sulfuric acid;
3.2.3.2 Conducting the experiment:
a) weigh 0.02-0.05 g of oxalic acid and approximately twice as much phenol;
b) place both reagents in a test tube and mix by shaking;
c) add 1-2 drops of concentrated sulfuric acid to the test tube;
d) carefully heat the test tube with the mixture until it begins to boil and an intense yellow color appears;
e) cool the test tube, add 3-4 ml of water and shake. Observe the color that appears;
f) add a few drops of alkali solution to the resulting solution and observe the color change;
3.3 Decomposition of urea (carbomic acid amide) when heated.
When heated above its melting point, urea decomposes, releasing ammonia. At a temperature of 150 0 -160 0 C, two molecules of urea split off one molecule of ammonia and give biureate, which is highly soluble in warm water:
H 2 N-OO-NH 2 +H-NH-OO-NH 2 H 2 N-CO-NH-CO-NH 2 +NH 3
Biureate is characterized by the formation of a bright red complex compound in an alkaline solution with copper salts, which has the following composition in a solution of sodium hydroxide:
(NH 2 CO NH CONH 2) 2 *2NaOH*Cu(OH) 2
3.3.1 Equipment and reagents:
Test tubes;
Electric stove;
Urea (carbamide);
Caustic sodium solution (5-7%);
Copper sulfur solution (1%).
3.3.2 Conducting the experiment:
a) weigh 0.2-0.3 g of urea and place in a dry test tube;
b) heat the test tube on an electric stove;
c) observe the changes taking place: melting, release of ammonia, solidification;
d) cool the test tube;
e) add 1-2 ml of warm water to a cooled test tube, shake and pour into another test tube;
f) add 3-4 drops of caustic soda solution to the resulting cloudy solution until transparent. Then add one drop of copper sulfuric acid solution and observe the color change (a beautiful purple color appears).
Related information.
Phthalic anhydride Phenolphthalein
When phthalic anhydride is fused with resorcinol in the presence of zinc chloride, a similar reaction occurs and fluorescein is formed:
Resorcinol Fluorescein
3.8 Claisen rearrangement
Phenols undergo Friedel-Crafts alkylation reactions. For example, when interacting f
enol with allyl bromide in the presence of aluminum chloride, 2-allylphenol is formed:
The same product is also formed when allylphenyl ether is heated as a result of an intramolecular reaction called the Claisen rearrangement:
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Allylphenyl ether 2-Allylphenol
Reaction:
It takes place according to the following mechanism:
The Claisen rearrangement also occurs when allyl vinyl ether or 3,3-dimethyl-1,5-hexadiene is heated: AAAAAAAAAAAAAAAAAAAAAAAAAAA
3.9 Polycondensation
Polycondensation of phenol with formaldehyde (this reaction results in the formation of phenol-formaldehyde resin:
3.10 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.
3.11 Acid properties
The acidic properties of phenol manifest themselves in reactions with alkalis (the old name “carbolic acid” has been preserved):
C6H5OH + NaOH<->C6H5ONa + H2O
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 suggests that phenol is a weaker acid than carbonic and sulfur dioxide:
C6H5ONa + CO2 + H2O -> C6H5ON + NaHCO3
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.
4. Methods of obtaining
Phenol production on an industrial scale is carried out in three ways:
– Cumene method. This method produces more than 95% of all phenol produced in the world. In a cascade of bubble columns, cumene is subjected to non-catalytic oxidation by air to form cumene hydroperoxide (CHP). The resulting CHP, catalyzed by sulfuric acid, decomposes to form phenol and acetone. In addition, α-methylstyrene is a valuable by-product of this process.
– About 3% of total phenol is obtained by oxidation of toluene, with the intermediate formation of benzoic acid.
– All other phenol is isolated from coal tar.
4.1 Oxidation of cumene
Phenols are isolated from coal tar, as well as from the pyrolysis products of brown coal and wood (tar). The industrial method for producing phenol C6H5OH itself is based on the oxidation of the aromatic hydrocarbon cumene (isopropylbenzene) with atmospheric oxygen, followed by the decomposition of the resulting hydroperoxide diluted with H2SO4. The reaction proceeds with high yield and is attractive in that it allows one to obtain two technically valuable products at once - phenol and acetone. Another method is the catalytic hydrolysis of halogenated benzenes.
4.2 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:
С6Н5-CI + 2NaOH -> С6Н5-ONa + NaCl + Н2O
4.3 Preparation from aromatic sulfonic acids
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:
4.4 Preparation from chlorobenzene
It is known that the chlorine atom is tightly bound to the benzene ring, therefore the reaction of replacing chlorine with a hydroxyl group is carried out under harsh conditions (300 °C, pressure 200 MPa):
C6H5-Cl + NaOH – > C6H5-OH + NaCl
5. Application of phenols
A phenol solution is used as a disinfectant (carbolic acid). Diatomic phenols - pyrocatechol, resorcinol (Fig. 3), as well as hydroquinone (para-dihydroxybenzene) are used as antiseptics (antibacterial disinfectants), added to tanning agents for leather and fur, as stabilizers for lubricating oils and rubber, and also for processing photographic materials and as reagents in analytical chemistry.
Phenols are used to a limited extent in the form of individual compounds, but their various derivatives are widely used. Phenols serve as starting compounds for the production of a variety of polymer products - phenolic resins, polyamides, polyepoxides. Numerous drugs are obtained from phenols, for example, aspirin, salol, phenolphthalein, in addition, dyes, perfumes, plasticizers for polymers and plant protection products.
World consumption of phenol has the following structure:
· 44% of phenol is spent on the production of bisphenol A, which, in turn, is used for the production of polycarbonate and epoxy resins;
· 30% of phenol is spent on the production of phenol-formaldehyde resins;
· 12% of phenol is converted by hydrogenation into cyclohexanol, used to produce artificial fibers - nylon and nylon;
· the remaining 14% is spent on other needs, including the production of antioxidants (ionol), nonionic surfactants - polyoxyethylated alkylphenols (neonols), other phenols (cresols), drugs (aspirin), antiseptics (xeroform) and pesticides.
· 1.4% phenol is used in medicine (oracept) as an analgesic and antiseptic.
6. Toxic properties
Phenol is poisonous. Causes dysfunction of the nervous system. Dust, vapors and phenol solution irritate the mucous membranes of the eyes, respiratory tract, and skin (MPC 5 mg/m³, in reservoirs 0.001 mg/l).
Resorcinum Resorcinum
m-Dioxybenzene
Resorcinol is a diatomic phenol and appears as colorless or slightly pink or yellow needle-shaped crystals or crystalline powder. Sometimes the color of the crystals is almost brown. This is due to improper storage of resorcinol, which oxidizes very easily. Unlike other phenols, resorcinol dissolves very easily in water, alcohol, and easily in ether. Soluble in fatty oil and glycerin. Difficult to dissolve in chloroform. When heated, it evaporates completely.
Resorcinol is an integral part of many resins and tannins, but it is obtained synthetically - from benzene by the method of sulfonation and alkaline melting. Benzene is treated with concentrated sulfuric acid to obtain benzene metadisulfonic acid I.
Then the reaction mixture is treated with lime: sulfonic acid under these conditions forms a water-soluble calcium salt (II), excess sulfuric acid is removed in the form of calcium sulfate:
The resulting resorcinol is purified by distillation.
Resorcinol, like other phenols, is easily oxidized and itself becomes a reducing agent. It can recover silver from ammonia solution of silver nitrate.
Resorcinol gives all reactions characteristic of phenols, including those with formaldehyde-sulfuric acid (a red precipitate forms at the bottom of the test tube). A specific reaction to resorcinol, which distinguishes it from all other phenols, is the reaction of its fusion with phthalic anhydride in the presence of concentrated sulfuric acid with the formation of fluorescein - a yellow-red solution with green fluorescence (pharmacopoeial reaction).
The antiseptic effect of resorcinol is more pronounced than that of monohydric phenol. This is due to its stronger restorative properties.
The reducing ability of resorcinol is especially evident in an alkaline environment.
It is used externally for skin diseases (eczema, fungal diseases, etc.) in the form of 2-5% aqueous and alcohol solutions and 5-10-20% ointments.
Store in well-sealed orange glass jars (light stimulates oxidation).
