Table comparative characteristics of polyhydric alcohols. Chemical properties of monohydric and polyhydric alcohols

28.08.2020

The most important polyhydric alcohols are ethylene glycol and glycerin:

Ethylene glycol glycerin

These are viscous liquids, sweet in taste, highly soluble in water and poorly soluble in organic solvents.

Receipt. />

1. Hydrolysis of alkyl halides (similar to monohydric alcohols):

ClCH 2 - CH 2 Cl + 2 NaOH → NOCH 2 -CH 2 OH + 2 NaCl.

2. Ethylene glycol is formed during the oxidation of ethylene with an aqueous solution of potassium permanganate:

CH 2 \u003d CH 2 + [O] + H 2 O → H O CH 2 -CH 2 OH.

3. Glycerin is obtained by hydrolysis of fats.

Chemical properties. />Dihydric and trihydric alcohols are characterized by the main reactions of monohydric alcohols. The reactions may involve one or two hydroxyl groups. The mutual influence of hydroxyl groups is manifested in the fact that polyhydric alcohols are stronger acids than monohydric alcohols. Therefore, polyhydric alcohols, unlike monohydric ones, react with alkalis, forming salts. By analogy with alcoholates, salts of dihydric alcohols are called glycolates, and trihydric ones are called glycerates.

A qualitative reaction to polyhydric alcohols containing OH groups at adjacent carbon atoms is a bright blue coloration upon the action of freshly precipitated copper hydroxide ( II ). The color of the solution is due to the formation of complex copper glycolate:

Polyhydric alcohols are characterized by the formation of esters. In particular, when glycerol reacts with nitric acid in the presence of catalytic amounts of sulfuric acid, glycerol trinitrate is formed, known as nitroglycerin ( last title incorrect from a chemical point of view, since in nitro compounds the group - NO 2 directly bonded to the carbon atom)

Application .Ethylene glycol is used for the synthesis of polymeric materials and as an antifreeze. It is also used in large quantities to produce dioxane, an important (albeit toxic) laboratory solvent. Dioxane is obtained by intermolecular dehydration of ethylene glycol:

dioxane

Glycerin is widely used in cosmetics, food industry, pharmacology, and the production of explosives. Pure nitroglycerin explodes even with a slight impact; it serves as a raw material for obtaining smokeless gunpowder and dynamite -an explosive that, unlike nitroglycerin, can be safely thrown. Dynamite was invented by Nobel, who founded the world famous Nobel Prize for outstanding scientific achievements in physics, chemistry, medicine and economics. Nitroglycerin is toxic, but in small quantities it serves as a medicine, as it dilates the heart vessels and thereby improves the blood supply to the heart muscle.

Representatives of polyhydric alcohols are ethylene glycol and glycerin. Dihydric alcohols containing two hydroxyl groups-OH are called glycols, or diols, trihydric alcohols containing three hydroxyl groups are called glycerols, or triols.

The position of the hydroxyl groups is indicated by numbers, on-

Physical properties

Polyhydric alcohols are colorless syrupy liquids of a sweetish taste, highly soluble in water, poorly soluble in organic solvents; have high boiling points. For example, t boiling ethylene glycol 198 ° C, density (r) 1.11 g/cm 3 ; t bale (glycerin) \u003d 290 ° C, r glycerin \u003d 1.26 g / cm 3.

Receipt

Dihydric and trihydric alcohols are obtained in the same ways as monohydric ones. Alkenes, halogen derivatives, and other compounds can be used as starting compounds. For example:

Glycerin is obtained from fats, as well as synthetically from petroleum cracking gases (propylene), i.e. from non-food raw materials.

Chemical properties

Polyhydric alcohols are chemically similar to monohydric alcohols. However, in the chemical properties of polyhydric alcohols there are features due to the presence of two or more hydroxyl groups in the molecule.

The acidity of polyhydric alcohols is higher than that of monohydric ones, which is explained by the presence of additional hydroxyl groups in the molecule, which have a negative inductive effect. Therefore, polyhydric alcohols, unlike monohydric ones, react with alkalis, forming salts. For example, ethylene glycol reacts not only with alkali metals but also with hydroxides of heavy metals.

By analogy with alcoholates, salts of dihydric alcohols are called glycolates, and trihydric alcohols are called glycerates.

When ethylene glycol interacts with hydrogen halides (HCl, HBr), one hydroxyl group is replaced by a halogen:

The second hydroxo group is more difficult to replace, under the action of PCl 5 .

When copper (II) hydroxide reacts with glycerol and other polyhydric alcohols, the hydroxide dissolves and a bright blue complex compound is formed.

The Yuta reaction is used to detect polyhydric alcohols having hydroxyl groups at adjacent carbon atoms -CH(OH)-CH(OH)-:

In the absence of alkali, polyhydric alcohols do not react with | copper (II) hydroxide - their acidity is insufficient for this.

Polyhydric alcohols interact with acids, forming esters (see § 7). When glycerol interacts with nitric acid in the presence of concentrated sulfuric acid, nitroglycerin (glycerol trinitrate) is formed:

Alcohols are characterized by reactions resulting in the formation of cyclic structures:

Application

Ethylene glycol is used mainly for the production of lavsan and for the preparation of antifreezes - aqueous solutions freezing well below 0°C (using them to cool engines allows cars to run in winter).

Lecture number 3.

Polyhydric alcohols, their structure and properties.

The position of the hydroxyl groups is indicated by numbers at the end of the name.

Physical properties

Polyhydric alcohols are colorless syrupy liquids of a sweetish taste, highly soluble in water, poorly soluble in organic solvents; have high boiling points. For example, boiling point of ethylene glycol is 198°C, density () is 1.11 g/cm3; tboil (glycerin) = 290°С, glycerol = 1.26 g/cm3.

Receipt

Dihydric and trihydric alcohols are obtained in the same ways as monohydric ones. Alkenes, halogen derivatives, and other compounds can be used as starting compounds.

1. Ethylene glycol (ethanediol-1,2) is synthesized from ethylene in various ways:

3CH 2 =CH 2 + 2KMnO 4 + 4H 2 O ® 3HO–CH 2 –CH 2 –OH + 2MnO 2 + 2KOH

2. Glycerin (propanetriol -1,2,3) is obtained from fats, as well as synthetically from petroleum cracking gases (propylene), i.e. from non-food raw materials.

Chemical properties

By analogy with alcoholates, salts of dihydric alcohols are called glycolates, and trihydric alcohols are called glycerates.

When ethylene glycol interacts with hydrogen halides (HCl, HBr), one hydroxyl group is replaced by a halogen:

The second hydroxo group is more difficult to replace, under the action of PCl5.

When copper (II) hydroxide reacts with glycerol and other polyhydric alcohols, the hydroxide dissolves and a bright blue complex compound is formed.

This reaction is used to detect polyhydric alcohols having hydroxyl groups at adjacent carbon atoms -CH(OH)-CH(OH)-:

In the absence of alkali, polyhydric alcohols do not react with | copper (II) hydroxide - their acidity is insufficient for this.

Alcohols are characterized by reactions resulting in the formation of cyclic structures:

Application

Ethylene glycol is used mainly for the production of lavsan and for the preparation of antifreezes - aqueous solutions that freeze well below 0 ° C (their use for engine cooling allows cars to work in winter).

Glycerin is widely used in the leather and textile industries for finishing leather and fabrics and in other areas of the national economy. The most important area of application of glycerin is the production of glycerol trinitrate (incorrectly called nitroglycerin) - a strong explosive that explodes on impact, as well as a drug (vasodilator). Sorbitol (hexahydric alcohol) is used as a sugar substitute for diabetics.

Test number 4.

Properties of polyhydric alcohols

1. With which of the following substances will glycerin react?

1) HBr 2) HNO 3 3) H 2 4) H 2 O 5) Cu(OH) 2 6) Ag 2 O/NH 3

2. Glycerin does not react with 1) HNO 3 2) NaOH 3) CH 3 COOH 4) Cu (OH) 2

3. Ethylene glycol does not react with 1) HNO 3 2) NaOH 3) CH 3 COOH 4) Cu (OH) 2

4. The following will not interact with freshly precipitated copper (II) hydroxide: 1) glycerin;

2) butanone 3) propanal 4) propanediol-1,2

5. A freshly prepared precipitate of Cu (OH) 2 will dissolve if you add to it

1) propanediol-1,2 2) propanol-1 3) propene 4) propanol-2

6. Glycerin in aqueous solution can be detected using

1) bleach 2) iron (III) chloride 3) copper (II) hydroxide 4) sodium hydroxide

7. Which of the alcohols reacts with copper (II) hydroxide?

1) CH 3 OH 2) CH 3 CH 2 OH 3) C 6 H 5 OH 4) NO-CH 2 CH 2 -OH

8. A characteristic reaction for polyhydric alcohols is the interaction with

1) H 2 2) Сu 3) Ag 2 O (NH 3 solution) 4) Cu (OH) 2

9. A substance that reacts with Na and Cu (OH) 2 is:

1) phenol; 2) monohydric alcohol; 3) polyhydric alcohol 4) alkene

10. Ethanediol-1,2 can react with

1) copper (II) hydroxide

2) iron oxide (II)

3) hydrogen chloride

4) hydrogen

6) phosphorus

Lecture number 4.

Phenols, their structure. Properties of phenol, mutual influence of atoms in a phenol molecule. Ortho-, vapor-orienting action of the hydroxyl group. Obtaining and using phenol

PHENOLS - class of organic compounds. They contain one or more C–OH groups, while the carbon atom is part of an aromatic (for example, benzene) ring.

Classification of phenols. There are one-, two-, three-atomic phenols depending on the number of OH groups in the molecule (Fig. 1)

Rice. 1. SINGLE-, TWO-, AND TRI-ATOMIC PHENOLS

In accordance with the number of fused aromatic cycles in the molecule, there are (Fig. 2) phenols themselves (one aromatic ring - benzene derivatives), naphthols (2 fused rings - naphthalene derivatives), anthranols (3 fused rings - anthracene derivatives) and phenantrols (Fig. 2).

Rice. 2. MONO- AND POLYNUCLEAR PHENOLS

Nomenclature of phenols

For phenols, trivial names that have developed historically are widely used. The names of substituted mononuclear phenols also use the prefixes ortho-, meta- and para- used in the nomenclature of aromatic compounds. For more complex compounds, the atoms that make up the aromatic rings are numbered and the position of the substituents is indicated using digital indices (Fig. 3).

Rice. 3. NOMENCLATURE OF PHENOLS. Substituent groups and corresponding numerical indices are highlighted in different colors for clarity.

Chemical properties of phenols

The benzene nucleus and the OH group combined in the phenol molecule affect each other, significantly increasing the reactivity of each other. The phenyl group pulls the lone electron pair away from the oxygen atom in the OH group (Fig. 4). As a result, the partial positive charge on the H atom of this group increases (indicated by d+), the polarity of the O–H bond increases, which manifests itself in an increase in the acidic properties of this group. Thus, compared to alcohols, phenols are stronger acids. The partial negative charge (denoted by d–), passing to the phenyl group, is concentrated in the ortho and para positions (with respect to the OH group). These reaction sites can be attacked by reagents that tend to electronegative centers, the so-called electrophilic ("electron loving") reagents.

Rice. 4. ELECTRON DENSITY DISTRIBUTION IN PHENOL

As a result, two types of transformations are possible for phenols: the substitution of a hydrogen atom in the OH group and the substitution of the H-atomobenzene nucleus. A pair of electrons of the O atom, drawn to the benzene ring, increases the strength of the C–O bond, so reactions that occur with the breaking of this bond, which are characteristic of alcohols, are not typical for phenols.

1. It has weak acidic properties, under the action of alkalis it forms salts - phenolates (for example, sodium phenolate - C6H6ONa):

C 6 H 5 OH + NaOH = C 6 H 5 ONa + H 2 O

It enters into electrophilic substitution reactions on the aromatic ring. The hydroxy group, being one of the strongest donor groups, increases the reactivity of the ring to these reactions and directs the substitution to the ortho and para positions. Phenol is readily alkylated, acylated, halogenated, nitrated, and sulfonated.

Kolbe-Schmidt reaction.

2. Interaction with metallic sodium:

C 6 H 5 OH + Na = C 6 H 5 ONa + H 2

3. Interaction with bromine water (qualitative reaction to phenol):

C 6 H 5 OH + 3Br 2 (aq.) → C 6 H 2 (Br) 3 OH + 3HBr 2,4,6 tribromophenol is formed

4. Interaction with concentrated nitric acid:

C 6 H 5 OH + 3HNO 3 conc → C 6 H 2 (NO 2) 3 OH + 3H 2 O 2,4,6 trinitrophenol is formed

5. Interaction with iron (III) chloride (qualitative reaction to phenol):

C 6 H 5 OH + FeCl 3 → 2 + (Cl) 2- + HCl iron (III) dichloride phenolate is formed (violet color )

Methods for obtaining phenols.

Phenols are isolated from coal tar, as well as from pyrolysis products of brown coal and wood (tar). The industrial method for obtaining C6H5OH phenol itself is based on the oxidation of the aromatic hydrocarbon cumene (isopropylbenzene) with atmospheric oxygen, followed by decomposition of the resulting hydroperoxide diluted with H3SO4 (Fig. 8A). The reaction proceeds with a high yield and is attractive in that it allows obtaining two technically valuable products at once - phenol and acetone. Another method is the catalytic hydrolysis of halogenated benzenes (Fig. 8B).

Rice. 8. METHODS FOR OBTAINING PHENOL

The use of phenols.

A solution of phenol is used as a disinfectant (carbolic acid). Dihydric phenols - pyrocatechol, resorcinol (Fig. 3), as well as hydroquinone (para-dihydroxybenzene) are used as antiseptics (antibacterial disinfectants), are added to tanning agents for leather and fur, as stabilizers of lubricating oils and rubber, as well as for processing photographic materials and as reagents in analytical chemistry.

In the form of individual compounds, phenols are used to a limited extent, but their various derivatives are widely used. Phenols serve as starting compounds for obtaining a variety of polymer products - phenol-aldehyde resins (Fig. 7), polyamides, polyepoxides. Based on phenols, numerous drugs are obtained, for example, aspirin, salol, phenolphthalein, in addition, dyes, perfumes, plasticizers for polymers and plant protection products.

Test #5 Phenols

1. How many phenols of composition C 7 H 8 O exist? 1) One 2) Four 3) Three 4) two

2. The oxygen atom in the phenol molecule forms

1) one σ-bond 2) two σ-bonds 3) one σ- and one π-bond 4) two π-bonds

3. Phenols are stronger acids than aliphatic alcohols because...

1) a strong hydrogen bond is formed between alcohol molecules

2) in the phenol molecule, the mass fraction of hydrogen ions is greater

3) in phenols electronic system shifted towards the oxygen atom, which leads to greater mobility of the hydrogen atoms of the benzene ring

4) in phenols, the electron density of the О-Н bond decreases due to the interaction of the lone electron pair of the oxygen atom with the benzene ring

4. Choose the correct statement:

1) phenols dissociate to a greater extent than alcohols;

2) phenols exhibit basic properties;

3) phenols and their derivatives do not have a toxic effect;

4) the hydrogen atom in the hydroxyl group of phenol cannot be replaced by a metal cation under the action of bases.

Properties

5. Phenol in aqueous solution is

1) strong acid 2) weak acid 3) weak base 4) strong base

1. A substance that reacts with Na and NaOH, giving a violet color with FeCl 3 is:

1) phenol; 2) alcohol 3) simple ether; 4) alkane

6. The effect of the benzene ring on the hydroxyl group in the phenol molecule is proved by the reaction of phenol with

1) sodium hydroxide 2) formaldehyde 3) bromine water 4) nitric acid

7. Chemical interaction is possible between substances whose formulas are:

1) C 6 H 5 OH and NaCl 2) C 6 H 5 OH and HCl 3) C 6 H 5 OH and NaOH 4) C 6 H 5 ONa and NaOH.

8. Phenol does not interact with

1) methanal 2) methane 3) nitric acid 4) bromine water

9. Phenol interacts with

1) hydrochloric acid 2) ethylene 3) sodium hydroxide 4) methane

10. Phenol does not interact with a substance whose formula

1) HBr 2) Br 2 3) HNO 3 4) NaOH

11. Phenol does not react with 1) HNO 3 2) KOH 3) Br 2 4) Сu (OH) 2

12. Acid properties are most pronounced in 1) phenol 2) methanol 3) ethanol 4) glycerin

13. When phenol interacts with sodium,

1) sodium phenolate and water 2) sodium phenolate and hydrogen

3) benzene and sodium hydroxide 4) sodium benzoate and hydrogen

14. Establish a correspondence between the starting substances and products that are predominantly formed during their interaction.

STARTING SUBSTANCES INTERACTION PRODUCTS

A) C 6 H 5 OH + K 1) 2,4,6-tribromophenol + HBr

B) C 6 H 5 OH + KOH 2) 3,5-dibromophenol + HBr

C) C 6 H 5 OH + HNO3 3) potassium phenolate + H 2

D) C 6 H 5 OH + Br 2 (solution) 4) 2,4,6-trinitrophenol + H 2 O

5) 3,5-dinitrophenol + HNO 3

6) potassium phenolate + H 2 O

15. Establish a correspondence between the starting materials and the reaction products.

STARTING SUBSTANCES REACTION PRODUCTS

A) C 6 H 5 OH + H 2 1) C 6 H 6 + H 2 O

B) C 6 H 5 OH + K 2) C 6 H 5 OK + H 2 O

C) C 6 H 5 OH + KOH 3) C 6 H 5 OH + KHCO 3

D) C 6 H 5 OK + H 2 O + CO 2 4) C 6 H 11 OH

5) C 6 H 5 OK + H 2

6) C 6 H 5 COOH + KOH

16. Phenol interacts with solutions

3) [Ag (NH 3) 2] OH

17. Phenol reacts with

1) oxygen

2) benzene

3) sodium hydroxide

4) hydrogen chloride

5) sodium

6) silicon oxide (IV)

Receipt

18. When replacing hydrogen in the aromatic ring with a hydroxyl group, the following is formed:

1) ester; 2) a simple ether; 3) saturated alcohol; 4) phenol.

19. Phenol can be obtained in the reaction

1) dehydration of benzoic acid 2) hydrogenation of benzaldehyde

3) hydration of styrene 4) chlorobenzene with potassium hydroxide

Relationship, qualitative reactions.

20. Methanol. ethylene glycol and glycerin are:

1) homologues; 2) primary, secondary and tertiary alcohols;

32) isomers; 4) monohydric, dihydric, trihydric alcohols

21. A substance that does not react with either Na or NaOH, obtained by intermolecular dehydration of alcohols is: 1) phenol 2) alcohol 3) simple ether; 4) alkene

22. Interact with each other

1) ethanol and hydrogen 2) acetic acid and chlorine

3) phenol and copper (II) oxide 4) ethylene glycol and sodium chloride

23. Substance X can react with phenol, but does not react with ethanol. This substance:

1) Na 2) O 2 3) HNO 3 4) bromine water

24. A bright blue solution is formed by the interaction of copper (II) hydroxide with

1) ethanol 2) glycerin 3) ethanal 4) toluene

25. Copper(II) hydroxide can be used to detect

1) Al 3+ ions 2) ethanol 3) NO 3 ions - 4) ethylene glycol

26. In the scheme of transformations C 6 H 12 O 6 à X à C 2 H 5 -O- C 2 H 5, the substance "X" is

1) C 2 H 5 OH 2) C 2 H 5 COOH 3) CH 3 COOH 4) C 6 H 11 OH

27. In the scheme of transformations ethanolà Xà butane substance X is

1) butanol-1 2) bromoethane 3) ethane 4) ethylene

28. In the scheme of transformations propanol-1à Xà propanol-2 substance X is

1) 2-chloropropane 2) propanoic acid 3) propyne 4) propene

29. Aqueous solutions of ethanol and glycerin can be distinguished using:

1) bromine water 2) ammonia solution of silver oxide

4) metallic sodium 3) freshly prepared precipitate of copper (II) hydroxide;

30. You can distinguish ethanol from ethylene glycol using:

31. You can distinguish phenol from methanol using:

1) sodium; 2) NaOH; 3) Cu(OH) 2 4) FeCl 3

32. You can distinguish phenol from a simple ether using:

1) Cl 2 2) NaOH 3) Cu(OH) 2 4) FeCl 3

33. You can distinguish glycerin from propanol-1 using:

1) sodium 2) NaOH 3) Cu(OH) 2 4) FeCl 3

34. What substance should be used in order to distinguish ethanol and ethylene glycol from each other under laboratory conditions?

1) Sodium 2) Hydrochloric acid 3) Copper (II) hydroxide 4) Sodium hydroxide

Polyhydric alcohols – organic compounds, the molecules of which contain several hydroxyl groups (-OH) connected to a hydrocarbon radical

Glycols (diols)

Syrup-like, viscous colorless liquid, has an alcoholic smell, mixes well with water, greatly lowers the freezing point of water (60% solution freezes at -49 ˚С) - this is used in engine cooling systems - antifreeze.
Ethylene glycol is toxic - a strong Poison! Depresses the central nervous system and affects the kidneys.

triplets

Colorless, viscous syrupy liquid, sweet in taste. Not poisonous. Without smell. Mixes well with water.
Widespread in wildlife. It plays an important role in metabolic processes, as it is part of the fats (lipids) of animal and plant tissues.

Nomenclature

In the names of polyhydric alcohols ( polyols) the position and number of hydroxyl groups are indicated by the corresponding numbers and suffixes -diol(two OH groups), -triol(three OH groups), etc. For example:

Obtaining polyhydric alcohols

I. Obtaining dihydric alcohols

In industry

1. Catalytic hydration of ethylene oxide (production of ethylene glycol):

2. Interaction of dihalogenated alkanes with aqueous solutions of alkalis:

3. From synthesis gas:

2CO + 3H2 250°,200 MPa,kat→CH 2 (OH)-CH 2 (OH)

In the laboratory

1. Alkene oxidation:

II. Obtaining trihydric alcohols (glycerol)

In industry

Saponification of fats (triglycerides):

Chemical properties of polyhydric alcohols

Acid properties

1. With active metals:

HO-CH 2 -CH 2 -OH + 2Na → H 2 + NaO-CH 2 -CH 2 -ONa(sodium glycolate)

2. With copper hydroxide( II ) is a qualitative reaction!

Simplified scheme

Basic properties

1. With hydrohalic acids

HO-CH 2 -CH 2 -OH + 2HCl H+↔ Cl-CH 2 -CH 2 -Cl + 2H 2 O

2. FROM nitric acid

T rinitroglycerin - the basis of dynamite

Application

ethylene glycol lavsan production , plastics, and for cooking antifreeze - aqueous solutions that freeze well below 0°C (their use for engine cooling allows cars to work in winter); raw materials in organic synthesis.
Glycerol widely used in leather, textile industry for finishing leather and fabrics and in other areas National economy. Sorbitol (hexahydric alcohol) is used as a sugar substitute for diabetics. Glycerin is widely used in cosmetics , Food Industry , pharmacology , production explosives . Pure nitroglycerin explodes even with a slight impact; it serves as a raw material for smokeless powder and dynamite An explosive that, unlike nitroglycerin, can be safely thrown. Dynamite was invented by Nobel, who founded the world famous Nobel Prize for outstanding scientific achievements in the fields of physics, chemistry, medicine and economics. Nitroglycerin is toxic, but in small quantities serves as a medicine , as it expands the heart vessels and thereby improves the blood supply to the heart muscle.

monohydric alcohols.

Alcohols are derivatives of hydrocarbons, which are products of substitution of a hydrogen atom (atoms) in a hydrocarbon molecule by a hydroxyl group -OH. Depending on how many hydrogen atoms are replaced, alcohols are monohydric and polyhydric. Those. the number of -OH groups in an alcohol molecule characterizes the atomicity of the latter.

Limiting monohydric alcohols are of the greatest importance. The composition of the members of a series of saturated monohydric alcohols can be expressed general formula-- СnH2n+1OH or R-OH.

The first few members of the homologous series of alcohols and their names according to the radical-functional, substitutional and rational nomenclature, respectively, are given below:

According to the radical-functional nomenclature, the name of alcohols is formed from the name of the radicals and the word "alcohol", expressing the functional name of the class.

Chemical properties

1. Alcohols react with alkali metals (Na, K, etc.) to form alcoholates:
2R--OH + 2Na ® 2R--ONa + H2
2. Substitution of the hydroxyl group of alcohols by halogen

R--OH + H--X « R--X + H2O

3. The interaction of alcohols with acids is called the esterification reaction. As a result, esters are formed:

R--OH + HO--C--R1 « R--O--C--R1 + H2O

4. At high temperatures, air oxygen oxidizes alcohols to form CO2 or H2O (combustion process). Methanol and ethanol burn with an almost non-luminous flame, higher ones with a brighter smoky one. This is due to the increase in the relative increase in carbon in the molecule.

Solutions of KMnO4 and K2Cr2O7 (acid) oxidize alcohols. The KMnO4 solution becomes colorless, the K2Cr2O7 solution turns green.

In this case, primary alcohols form aldehydes, secondary alcohols - ketones, further oxidation of aldehydes and ketones leads to the production of carboxylic acids.

5. When passing vapors of primary and secondary alcohols over the surface of the heated finely divided metals (Cu, Fe), their dehydrogenation occurs:

CH3--CH--H CH3--C--H

polyhydric alcohols.

Dihydric alcohols are called glycols, trihydric alcohols are called glycerols. According to the international substitution nomenclature, dihydric alcohols are called alkanediols, trihydric alcohols are called alkanetriols. Alcohols with two hydroxyls at one carbon atom usually do not exist in free form; when trying to get them, they decompose, releasing water and turning into a compound with a carbonyl group - aldehydes or ketones

Trihydric alcohols with three hydroxyls at one carbon atom are even more unstable than similar dihydric ones, and are not known in free form:

Therefore, the first representative of diatomic alcohols is an ethane derivative of the composition C2H4 (OH) 2 with hydroxyl groups at different carbon atoms - 1,2-ethanediol, or otherwise - ethylene glycol (glycol). Propane already corresponds to two dihydric alcohols - 1,2-propadiol, or propylene glycol, and 1,3-propanediol, or trimethylene glycol:

Glycols in which two alcohol hydroxyl groups are located side by side in a chain - at adjacent carbon atoms, are called a-glycols (for example, ethylene glycol, propylene glycol). Glycols with alcohol groups located through one carbon atom are called b-glycols (trimethylene glycol). Etc.

Among the dihydric alcohols, ethylene glycol is of the greatest interest. It is used as an antifreeze for cooling the cylinders of automobile, tractor and aircraft engines; upon receipt of lavsan (polyester of alcohol with terephthalic acid).

It is a colorless syrupy liquid, odorless, sweet in taste, poisonous. Miscible with water and alcohol. Tbp.=197 °C, Tm.= -13 °C, d204=1.114 g/cm3. combustible liquid.

Gives all the reactions characteristic of monohydric alcohols, and one or both alcohol groups can participate in them. Due to the presence of two OH groups, glycols have somewhat more acidic properties than monohydric alcohols, although they do not give an acid reaction to litmus, do not conduct electric current. But unlike monohydric alcohols, they dissolve hydroxides of heavy metals. For example, when ethylene glycol is added to a blue gelatinous precipitate of Cu (OH) 2, a blue solution of copper glycolate is formed:

Under the action of PCl5, both hydroxide groups are replaced by chlorine, and under the action of HCl, one is replaced, and the so-called glycol chlorohydrins are formed:

During dehydration, diethylene glycol is formed from 2 molecules of ethylene glycol:

The latter, by releasing intramolecularly one molecule of water, can turn into a cyclic compound with two ether groups - dioxane:

On the other hand, diethylene glycol can react with the next molecule of ethylene glycol, forming a compound also with two ether groups, but with an open chain - triethylene glycol. Sequential interaction of this kind of reaction of many glycol molecules leads to the formation of polyglycols - high molecular weight compounds containing many ether groups. Polyglycol formation reactions are referred to as polycondensation reactions.

Polyglycols are used in the production of synthetic detergents, wetting agents, foaming agents.

Chemical properties

The main feature of ethers is their chemical inertness. Unlike esters, they are not hydrolyzed and are not decomposed by water into initial alcohols. Anhydrous (absolute) ethers, unlike alcohols, do not react with metallic sodium at ordinary temperatures, because there is no active hydrogen in their molecules.

The cleavage of ethers occurs under the action of certain acids. For example, concentrated (especially fuming) sulphuric acid absorbs ether vapors, and in this case an ester of sulfuric acid (ethylsulfuric acid) and alcohol are formed.

Hydroiodic acid also decomposes ethers, resulting in haloalkyl and alcohol.

When heated, sodium metal cleaves ethers to form an alcoholate and an organosodium compound.