What do polyhydric alcohols react with? table. Polyhydric alcohols, glucose. Chemical properties of alcohols

Let us recall that polyhydric alcohols are organic compounds whose molecules contain several hydroxyl groups. The general formula of polyhydric alcohols is CnH2n+1(OH)k, where n and k are integers greater than 2. The classification, structure, isomerism and nomenclature of alcohols were discussed earlier in. In this section we will consider the properties and preparation of polyhydric alcohols.

The most important representatives of polyhydric alcohols contain from two to six hydroxyl groups. Dihydric alcohols(glycols) or alkanediols containing two hydroxyl groups in their molecule, trihydric alcohols(alcantriols) – three hydroxyl groups. Tetra-, penta- and hexahydric alcohols(erythrites, pentites and hexites) contain 4, 5 and 6 OH groups, respectively.

Physical properties of polyhydric alcohols

Polyhydric alcohols dissolve well in water and alcohols, worse in other organic solvents. Alcohols with a small number of carbon atoms are viscous liquids with a sweetish taste. The higher members of the series are solids. Compared to monohydric alcohols, they have higher densities and boiling points. Trivial names, names and physical properties of some alcohols are presented in the table:

Preparation of polyhydric alcohols

Preparation of glycols

Glycols can be obtained by almost everyone. Let’s highlight the main ones:

1. Hydrolysis of dihalogenated alkanes :
2. Hydrolysis of chlorohydrins proceeds as follows:
   
3. Reduction of esters dibasic acids using the Bouveau method:
   
4. according to Wagner:
   
5. Incomplete reduction of ketones under the influence of magnesium (in the presence of iodine). This is how you get pinacons:
   

Obtaining glycerin

1. Chlorination of propylene in Lvov:
   
2. Beresh and Yakubovich method consists of the oxidation of propylene to acrolein, which is then reduced to allylic alcohol followed by its hydroxylation:
   
3. Catalytic hydrogenation of glucose leads to the restoration of the aldehyde group and at the same time the rupture of the C3-C4 bond:
   

Due to the cleavage of the C2-C3 bond, a small amount of ethylene glycol and threitol (a stereoisomer of erythritol) is formed.

In addition to glucose, other polysaccharides containing glucose units, such as cellulose, can be subjected to catalytic hydrogenation.

4. Hydrolysis of fats alkali is used to obtain soap (potassium or sodium salts of complex carboxylic acids):
This process is called saponification.

Preparation of tetrahydric alcohols (erythritols)

In nature erythritol (butantetraol-1,2,3,4) found both in free form and in the form of esters in algae and some molds.

It is produced artificially from 1,4-butadiene in several stages:

Pentaerythritol (tetraoxyneopentane) are not found in nature. Synthetically can be obtained by reacting formaldehyde with an aqueous solution of acetaldehyde in an alkaline medium:

Chemical properties of polyhydric alcohols

The chemical properties of polyhydric alcohols are similar to. However, the presence of several hydroxyl groups in the molecules of polyhydric alcohols increases their acidity. Therefore, they can react with alkalis and heavy metal hydroxides, forming salts.

Substitution of the second hydroxo group of ethylene glycol is more difficult (under the influence of PCl5 or SOCl2, the substitution occurs more easily).

1. Interaction with acids leads to the formation of esters:

Interaction with nitric acid

These compounds are explosives. Trinitroglycerin is also used in medicine as a medicinal drug.

Interaction with acetic acid

If the esterification reaction of ethylene glycol involves diacid, then it is possible to obtain polyester (polycondensation reaction):

Typically, R is terephthalic acid. The product of this reaction is terylene, lavsan:

At ethylene glycol dehydration a compound is obtained that has 2 tautomeric forms (keto-enol tautomerism):

Dehydration of ethylene glycol can occur with its simultaneous dimerization:

At dehydration of 1,4-butanediol You can get tetrahydrofuran (oxolane):

Dehydration of other glycols is accompanied by a process pinacoline rearrangement:

• Oxidation of polyhydric alcohols leads to the formation of aldehydes or ketones.

At ethylene glycol oxidation First, glycolaldehyde is obtained, then glyoxal, which upon further oxidation turns into dicarboxylic acid:

At glycerol oxidation a mixture of the corresponding aldehyde and ketone is formed:

Categories ,

Lecture No. 3.

Polyhydric alcohols, their structure and properties.

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 - glycerols, or triols.

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

Physical properties

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

Receipt

Di- and trihydric alcohols are obtained by the same methods 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

Polyhydric alcohols have chemical properties similar to monohydric alcohols. However, the chemical properties of polyhydric alcohols have 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 alcohols, which is explained by the presence in the molecule of additional hydroxyl groups that have a negative inductive effect. Therefore, polyhydric alcohols, unlike monohydric alcohols, react with alkalis, forming salts. For example, ethylene glycol reacts not only with alkali metals, but also with heavy metal hydroxides.

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

When ethylene glycol reacts 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 glycerin 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.

Polyhydric alcohols react with acids to form esters (see §7). When glycerin reacts with nitric acid in the presence of concentrated sulfuric acid, nitroglycerin (glycerol trinitrate) is formed:

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

Application

Ethylene glycol is used mainly for the production of lavsan and for the preparation of antifreeze - aqueous solutions that freeze well below 0 ° C (using them to cool engines allows cars to operate 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 use of glycerin is in the production of glycerol trinitrate (incorrectly called nitroglycerin), a powerful explosive that explodes on impact, and also a medicine (vasodilator). Sorbitol (hexahydric alcohol) is used as a sugar substitute for diabetics.

Test No. 4.

Properties of polyhydric alcohols

1. Which of the following substances will glycerin react with?

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

2. Glycerol 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) glycerol;

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

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

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

6. Glycerol in an aqueous solution can be detected using

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

7. Which alcohol reacts with copper (II) hydroxide?

1) CH 3 OH 2) CH 3 CH 2 OH 3) C 6 H 5 OH 4) HO-CH 2 CH 2 -OH

8. A characteristic reaction for polyhydric alcohols is interaction with

1) H 2 2) Cu 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 No. 4.

Phenols, their structure. Properties of phenol, mutual influence of atoms in the phenol molecule. Ortho-, vapor-orienting effect of the hydroxyl group. Preparation and use of phenol

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

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

Rice. 1. ONE-, DUAL AND TRICHATIC PHENOLS

In accordance with the number of condensed aromatic rings in the molecule, they are distinguished (Fig. 2) into phenols themselves (one aromatic ring - benzene derivatives), naphthols (2 condensed rings - naphthalene derivatives), anthranols (3 condensed rings - anthracene derivatives) and phenanthroles (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. Substituting groups and corresponding digital indices are highlighted in different colors for clarity.

Chemical properties of phenols

The benzene ring and the OH group, combined in a phenol molecule, influence each other, significantly increasing each other's reactivity. The phenyl group absorbs a lone pair of electrons 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 the d+ symbol), 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–), transferring to the phenyl group, is concentrated in the ortho- and para-positions (relative to the OH group). These reaction points can be attacked by reagents that gravitate toward electronegative centers, so-called electrophilic (“electron-loving”) reagents.

Rice. 4. ELECTRON DENSITY DISTRIBUTION IN PHENOL

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

1. It has weak acidic properties; when exposed to 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 undergoes 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 substitution to the ortho and para positions. Phenol is easily alkylated, acylated, halogenated, nitrated and sulfonated.

Kolbe-Schmidt reaction.

2. Interaction with sodium metal:

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 produces 2,4,6 tribromophenol

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) dichloridephenolate is formed (violet color )

Methods for obtaining phenols.

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 H3SO4 (Fig. 8A). 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 (Fig. 8B).

Rice. 8. METHODS FOR OBTAINING PHENOL

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 various polymer products - phenolic resins (Fig. 7), polyamides, polyepoxides. Numerous drugs are obtained from phenols, for example, aspirin, salol, phenolphthalein, in addition, dyes, perfumes, plasticizers for polymers and plant protection products.

Test No. 5 Phenols

1. How many phenols of the composition C 7 H 8 O are there? 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) the phenol molecule contains a larger mass fraction of hydrogen ions

3) in phenols, the electronic system is 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 O-H 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) ether; 4) alkane

6. The effect of the benzene ring on the hydroxyl group in the phenol molecule is proven 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 is

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) Cu(OH) 2

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

13. When phenol reacts 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 the 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

B) 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

B) 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) [Аg(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 hydrogen in the aromatic ring is replaced by a hydroxyl group, the following is formed:

1) ester; 2) ether; 3) limiting 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

Interconnection, 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) 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 when copper (II) hydroxide reacts 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 transformation scheme C 6 H 12 O 6 à X à C 2 H 5 -O- C 2 H 5 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 transformation scheme ethanolà Xà butane substance X is

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

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

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

29.Aqueous solutions of ethanol and glycerol 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 ether using:

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

33. You can distinguish glycerin from 1-propanol 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 in the laboratory?

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

Video tutorial 2: Phenol: Chemical properties

Lecture: Characteristic chemical properties of saturated monohydric and polyhydric alcohols, phenol

Alcohols and phenols

Depending on the type of hydrocarbon radical, as well as, in some cases, the characteristics of the attachment of the -OH group to this hydrocarbon radical, compounds with a hydroxyl functional group are divided into alcohols and phenols.

There is a division of organic compounds into alcohols and phenols. This division is based on the type of hydrocarbon radical and the characteristics of the attachment of -OH groups to it.

Alcohols (alkanols)- derivatives of saturated and unsaturated hydrocarbons, in which the OH group is connected to a hydrocarbon radical without direct attachment to the aromatic ring.

Phenols- organic substances that have in their structure OH groups directly attached to an aromatic ring.

The mentioned features of the position of OH groups significantly affect the difference in the properties of alcohols and phenols. In phenol compounds, the O-H bond is more polar compared to alcohols. This increases the mobility of the hydrogen atom in the OH group. Phenols have much more pronounced acidic properties than alcohols.

Classification of alcohols

There are several classifications of alcohols. So, by the nature of the hydrocarbon radical alcohols are divided into:

• Limit containing only saturated hydrocarbon radicals. In their molecules, one or more hydrogen atoms are replaced by an OH group, for example:

Ethanediol-1,2 (ethylene glycol)

• Unlimited containing double or triple bonds between carbon atoms, for example:

Propen-2-ol-1 (allylic alcohol)

• Aromatic containing a benzene ring and an OH group in the molecule, which are connected to each other through carbon atoms, for example:

Phenylmethanol (benzyl alcohol)

By atomicity, i.e. number of OH groups, alcohols are divided into:

• Monatomic, For example:

• Diatomic (glycols) , For example:

Triatomic, For example:

Polyatomic containing more than three OH groups, for example:

By the nature of the bond between the carbon atom and the OH group alcohols are divided into:

• Primary, in which the OH group is bonded to the primary carbon atom, for example:

• Secondary, in which the OH group is bonded to a secondary carbon atom, for example:

Tertiarye, in which the OH group is bonded to a tertiary carbon atom, for example:

The Unified State Exam codifier in chemistry requires you to know the chemical properties of saturated monohydric and polyhydric alcohols, let’s look at them.
Chemical properties of saturated monohydric alcohols

1. Substitution reactions

Interaction with alkali and alkaline earth metals , as a result, metal alcoholates are formed and hydrogen is released. For example, when ethyl alcohol and sodium react, sodium ethoxide is formed:

2C 2 H 5 OH+ 2Na→ 2C 2 H 5 ONa+ H2

It is important to remember the following rule for this reaction: alcohols must not contain water, otherwise the formation of alcoholates will become impossible, since they are easily hydrolyzed.

Esterification reaction , i.e. the interaction of alcohols with organic and oxygen-containing inorganic acids leads to the formation of esters. This reaction is catalyzed by strong inorganic acids. For example, the interaction of ethanol with acetic acid forms ethyl acetate (ethyl acetate):

The mechanism of the esterification reaction looks like this:

This is a reversible reaction, therefore, to shift the equilibrium towards the formation of an ester, the reaction is carried out with heating, as well as in the presence of concentrated sulfuric acid as a water-removing substance.

Interaction of alcohols with hydrogen halides . When alcohols are exposed to hydrohalic acids, the hydroxyl group is replaced by a halogen atom. As a result of this reaction, haloalkanes and water are formed. Eg:

C 2 H 5 OH+ HCl → C 2 H 5 Cl+ H 2 O.

This is a reversible reaction.

2. Elimination reactions

Dehydration of alcohols can be intermolecular or intramolecular.

In intermolecular, one molecule of water is formed as a result of the abstraction of a hydrogen atom from one molecule of alcohol and a hydroxyl group from another molecule. As a result, ethers (R-O-R) are formed. The reaction conditions are the presence of concentrated sulfuric acid and heating to 140 0 C:

C 2 H 5 OS 2 H 5 → C 2 H 5 -O-C 2 H 5 +H 2 O

Dehydration of ethanol with ethanol resulted in the formation of diethyl ether (ethoxyethane) and water.

CH 3 OS 2 H 5 → CH 3 -O-C 2 H 5 +H 2 O

Dehydration of methanol with ethanol resulted in the formation of methyl ethyl ether (methoxyethane) and water.

Intramolecular dehydration of alcohols, unlike intermolecular dehydration, proceeds as follows: one molecule of water is split off from one molecule of alcohol:

This type of dehydration requires high heat. As a result, one molecule of alcohol and one molecule of water are formed from one molecule of alcohol.

Since the methanol molecule contains only one carbon atom, intramolecular dehydration is impossible for it. During the intermolecular dehydration of methanol, only an ether (CH 3 -O-CH 3) can be formed:

2CH 3 OH → CH 3 -O-CH 3 + H 2 O.

It must be remembered that in the case of dehydration of unsymmetrical alcohols, intramolecular elimination of water will proceed in accordance with Zaitsev’s rule, that is, hydrogen will be eliminated from the least hydrogenated carbon atom.

Dehydrogenation of alcohols:

a) Dehydrogenation of primary alcohols when heated in the presence of copper metal leads to the formation of aldehydes:

b) In the case of secondary alcohols, similar conditions will lead to the formation of ketones:

c) Tertiary alcohols are not subject to dehydrogenation.

3. Oxidation reactions

Combustion. Alcohols easily react in combustion. This generates a large amount of heat:

2CH 3 - OH + 3O 2 → 2CO 2 + 4H 2 O + Q.

Oxidation alcohols occurs in the presence of catalysts Cu, Cr, etc. when heated. Oxidation also occurs in the presence of a chromium mixture (H 2 SO 4 + K 2 Cr 2 O 7) or magnesium permanganate (KMnO 4). Primary alcohols form aldehydes, for example:

C 2 H 5 OH+ CuO → CH 3 COH + Cu + + H 2 O.

As a result, we obtained acetaldehyde (ethanal, acetaldehyde), copper, and water. If the resulting aldehyde is not removed from the reaction medium, the corresponding acid is formed.

Secondary alcohols under the same conditions form ketones:

For tertiary alcohols, the oxidation reaction is not typical.

Chemical properties of polyhydric alcohols

Polyhydric alcohols are stronger acids than monohydric ones.

Polyhydric alcohols are characterized by the same reactions as monohydric ones with alkali and alkaline earth metals. In this case, a different number of hydrogen atoms of OH groups are replaced in the alcohol molecule. As a result, salts are formed. Eg:

Since polyhydric alcohols have more acidic properties than monohydric ones, they readily react not only with metals, but also with their heavy metal hydroxides. The reaction with copper hydroxide 2 is a qualitative reaction to polyhydric alcohols. When interacting with a polyhydric alcohol, the blue precipitate turns into a bright blue solution.

• The esterification reaction, i.e. interaction with organic and oxygen-containing inorganic acids to form esters:

C 6 H 5 ONa + CH 3 COCl → C 6 H 5 OCOCH 3 + NaCl

Alcohols are derivatives of hydrocarbons, in the molecules of which one or more hydrogen atoms near the saturated carbon atom are replaced by a hydroxy group - OH. It has been experimentally proven that the number of hydroxyls in an alcohol molecule cannot exceed the number of hydrocarbon atoms. Depending on the nature of the radical, acyclic (aliphatic series) and cyclic alcohols are distinguished; by the number of hydroxyl groups - one-, two-, three- and polyhydric alcohols; according to saturation - saturated and unsaturated; the location of the hydroxyl group in the hydrocarbon chain - primary, secondary and tertiary alcohols.

Polyhydric alcohols are derivatives of alkanes, in the molecules of which more than three hydrogen atoms are replaced by hydroxy groups - OH. Polyhydric alcohols as derivatives of monosaccharides are characterized by optical isomerism and isomerism of the position of the OH group in the hydrocarbon chain. Optical isomerism is associated with the ability of certain groups of organic substances in solutions to exhibit optical activity. The optical activity of substances is determined using a polarimeter.

For polyhydric alcohols

The most common qualitative reaction to polyhydric alcohols is their interaction with During the reaction, the hydroxide dissolves, and a violet chelate complex is formed.

Tetrahydric alcohols C4H6(OH)4 are called tetrites, pentaatomic alcohols C5H7(OH)5 are called pentites, hexahydric alcohols C6H8(OH)6 are called hexites. In each such group, individual alcohols are distinguished, which have historical names: erythritol, arabitol, sorbitol, xylitol, dulcitol, mannitol, etc.

Preparation of polyhydric alcohols

These alcohols are synthesized by reduction of monosaccharides, condensation of aldehydes with formaldehyde in an alkaline medium. Very often, polyhydric alcohols are obtained from natural raw materials. Some alcohols are extracted from rowan fruits.

Polyhydric alcohols are optically active compounds that are highly soluble in water. In the IR and UV spectra they have absorption bands typical of OH groups due to the presence of an OH group. When these substances interact with alcohols, they form saccharates. During the oxidation of hydroxyl, which is localized near the first carbon atom (C1), monosaccharides are formed.

Polyhydric alcohols: main representatives

Erythritol HOCH2(CHOH)2CH2OH is a crystalline substance, melts at 121.5 °C. This alcohol is found in lichens and mosses. Erythritol can be obtained by reducing 1,3-butadiene and erythrose. This alcohol is used in the manufacture of explosive compounds, quick-drying paints, and emulsifiers.

Xylitol HOCH2(CHOH)3CHOH - sweet crystals, highly soluble in water, melt at a temperature of 61.5 degrees. This alcohol can be synthesized by reducing xylose. Xylitol is used in the food industry in the manufacture of foods for diabetics, as well as in the production of alkyd resins, drying oils and surfactants.

Pentaerythritol C(CH2OH)4 is a solid substance, poorly soluble in water. Obtained by the reaction of formaldehyde with acetaldehyde in the presence of Ca(OH)2. Used in the production of polyesters, alkyd resins, tetrapentaerythritol, surfactants, plasticizers for the production of polyvinyl chloride, and synthetic oils. Exhibits narcotic properties.

Manit HOCH2(CHOH)4CH2OH is a sweet-tasting substance that melts at a temperature of 165 degrees. Contained in mosses, mushrooms, algae, and higher plants. Used as a diuretic and as a component of cosmetic products (ointments).

D-Sorbitol NOCH2(CHOH)4CH2OH - melts at a temperature of 96 degrees. Rowan fruits are rich in this alcohol. Sorbitol is obtained by reducing glucose. This alcohol is an intermediate product in the synthesis of vitamin C, has a diuretic effect, and is used as a sucrose substitute for diabetics.

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.

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

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

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

CH 2 = CH 2 + [O] + H 2 O → H O CH 2 -CH 2 OH.

3. Glycerin is obtained by hydrolysis of fats.

Chemical properties./>Di- and trihydric alcohols are characterized by the basic reactions of monohydric alcohols. One or two hydroxyl groups may participate in the reactions. 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 alcohols, react with alkalis, forming salts. By analogy with alcoholates, salts of dihydric alcohols are called glycolates, and trihydric alcohols are called glycerates.

The qualitative reaction to polyhydric alcohols containing OH groups at adjacent carbon atoms is a bright blue color when exposed to 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 (the latter name is incorrect from a chemical point of view, since in nitro compounds the group is NO 2 directly bonded to the carbon atom):

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

dioxane

Glycerin is widely used in cosmetics, the food industry, pharmacology, and the production of explosives. Pure nitroglycerin explodes even with a slight impact; it serves as a raw material for the production of 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 the fields of 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 blood supply to the heart muscle.