monohydric alcohols.

Alcohols are called 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 number of saturated monohydric alcohols can be expressed by the 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 form ketones, further oxidation of aldehydes and ketones leads to the formation 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, triatomic 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). And so on.

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 slightly 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 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 sodium metal 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, metallic sodium cleaves ethers to form an alcoholate and an organosodium compound.

Which in their composition contain one or more hydroxyl groups. Depending on the number of OH groups, these are divided into monohydric alcohols, trihydric, etc. Most often these complex substances are considered as derivatives of hydrocarbons, the molecules of which have undergone changes, tk. one or more hydrogen atoms have been replaced by a hydroxyl group.

The simplest representatives of this class are monohydric alcohols, general formula which looks like this: R-OH or

Cn + H 2n + 1OH.

1. Alcohols containing up to 15 carbon atoms - liquids, 15 or more - solids.
2. Solubility in water depends on molecular weight the higher it is, the worse the alcohol dissolves in water. Thus, lower alcohols (up to propanol) are miscible with water in any proportions, while higher ones are practically insoluble in it.
3. The boiling point also increases with increasing atomic mass, for example, t kip. CH3OH \u003d 65 ° С, and t bp. С2Н5ОН = 78 ° С.
4. The higher the boiling point, the lower the volatility, i.e. the substance does not evaporate well.

These physical properties of saturated alcohols with one hydroxyl group can be explained by the occurrence of an intermolecular hydrogen bond between individual molecules of the compound itself or alcohol and water.

Monohydric alcohols are able to enter into such chemical reactions:

Having considered the chemical properties of alcohols, we can conclude that monohydric alcohols are amphoteric compounds, because. they can react with alkali metals, showing weak properties, and with hydrogen halides, showing basic properties. All chemical reactions go with a gap O-N connections or S-O.

Thus, saturated monohydric alcohols are complex compounds with one OH group that do not have free valencies after the formation C-C connections and exhibiting weak properties of both acids and bases. Due to their physical and chemical properties, they are widely used in organic synthesis, in the production of solvents, fuel additives, as well as in the food industry, medicine, and cosmetology (ethanol).

Alcohols are a large group of organic chemicals. It includes subclasses of monohydric and polyhydric alcohols, as well as all substances of a combined structure: aldehyde alcohols, phenol derivatives, biological molecules. These substances enter into many types of reactions both at the hydroxyl group and at the carbon atom that carries it. These chemical properties of alcohols should be studied in detail.

Types of alcohols

Alcohols contain a hydroxyl group attached to a carrier carbon atom. Depending on the number of carbon atoms to which the carrier C is connected, alcohols are divided into:

• primary (connected to the terminal carbon);
• secondary (connected to one hydroxyl group, one hydrogen and two carbon atoms);
• tertiary (connected to three carbon atoms and one hydroxyl group);
• mixed (polyhydric alcohols in which there are hydroxyl groups at secondary, primary or tertiary carbon atoms).

Alcohols are also divided depending on the number of hydroxyl radicals into monohydric and polyhydric. The former contain only one hydroxyl group at the carrying carbon atom, for example, ethanol. Polyhydric alcohols contain two or more hydroxyl groups on different bearing carbon atoms.

Chemical properties of alcohols: table

It is most convenient to present the material of interest to us through a table that reflects the general principles of the reactivity of alcohols.

Reactive bond, type of reaction	Reagent	Product
O-H bond, substitution	Active metal, active metal hydride, alkali or active metal amides	alcoholates
C-O and O-H bond, intermolecular dehydration	Alcohol when heated acidic environment	Ether
C-O and O-H bond, intramolecular dehydration	Alcohol when heated over concentrated sulfuric acid	Unsaturated hydrocarbon
C-O bond, substitution	Hydrogen halide, thionyl chloride, quasi-phosphonium salt, phosphorus halides	haloalkanes
C-O bond - oxidation	Oxygen donors (potassium permanganate) with primary alcohol	Aldehyde
C-O bond - oxidation	Oxygen donors (potassium permanganate) with secondary alcohol
alcohol molecule	Oxygen (combustion)	carbon dioxide and water.

Reactivity of alcohols

Due to the presence of a hydrocarbon radical in the molecule of monohydric alcohol - the C-O bond and the O-H bond - this class of compounds enters into numerous chemical reactions. They determine the chemical properties of alcohols and depend on the reactivity of the substance. The latter, in turn, depends on the length of the hydrocarbon radical attached to the carrier carbon atom. The larger it is, the lower the polarity of the O-H bond, due to which the reactions proceeding with the elimination of hydrogen from alcohol will proceed more slowly. This also reduces the dissociation constant of the mentioned substance.

The chemical properties of alcohols also depend on the number of hydroxyl groups. One shifts the electron density towards itself along the sigma bonds, which increases the reactivity along O-N groups e. Because it polarizes C-O connection, then reactions with its rupture are more active in alcohols that have two or more O-H groups. Therefore, polyhydric alcohols, whose chemical properties are more numerous, are more likely to react. They also contain several alcohol groups, which is why they can freely react with each of them.

Typical reactions of monohydric and polyhydric alcohols

Typical chemical properties of alcohols appear only in the reaction with active metals, their bases and hydrides, Lewis acids. Also typical are interactions with hydrogen halides, phosphorus halides and other components to produce haloalkanes. Also, alcohols are also weak bases, therefore they react with acids, forming hydrogen halides and esters of inorganic acids.

Ethers are formed from alcohols by intermolecular dehydration. The same substances enter into dehydrogenation reactions with the formation of aldehydes from the primary alcohol and ketones from the secondary. Tertiary alcohols do not enter into such reactions. Also, the chemical properties of ethyl alcohol (and other alcohols) leave the possibility of their complete oxidation with oxygen. it simple reaction combustion, accompanied by the release of water with carbon dioxide and some heat.

Reactions on the hydrogen atom of the О-Н bond

The chemical properties of monohydric alcohols allow the breaking of the O-H bond and the elimination of hydrogen. These reactions proceed when interacting with active metals and their bases (alkalis), with active metal hydrides, and also with Lewis acids.

Alcohols also actively react with standard organic and not organic acids. AT this case reaction products is an ester or a halocarbon.

Reactions for the synthesis of haloalkanes (via the C-O bond)

Halogenalkanes are typical compounds that can be obtained from alcohols by several types of chemical reactions. In particular, the chemical properties of monohydric alcohols make it possible to interact with hydrogen halides, tri- and pentavalent phosphorus halides, quasi-phosphonium salts, and thionyl chloride. Also, haloalkanes from alcohols can be obtained in an intermediate way, that is, by the synthesis of an alkylsulfonate, which will later enter into a substitution reaction.

An example of the first reaction with hydrogen halide is indicated in the graphical appendix above. Here, butyl alcohol reacts with hydrogen chloride to form chlorobutane. In general, the class of compounds containing chlorine and a hydrocarbon saturated radical is called an alkyl chloride. by-product chemical interaction is water.

Reactions with the production of alkyl chloride (iodide, bromide or fluoride) are quite numerous. A typical example is the interaction with phosphorus tribromide, phosphorus pentachloride and other compounds of this element and its halides, perchlorides and perfluorides. They proceed by the mechanism of nucleophilic substitution. Alcohols also react with thionyl chloride to form chloroalkane and release SO 2 .

Visually, the chemical properties of monohydric saturated alcohols containing a saturated hydrocarbon radical are presented in the form of reactions in the illustration below.

Alcohols readily react with the quasi-phosphonium salt. However, this reaction is most advantageous when proceeding with monohydric secondary and tertiary alcohols. They are regioselective and allow the "implantation" of a halogen group in a strictly defined place. The products of such reactions are obtained with a high mass fraction of the yield. And polyhydric alcohols, whose chemical properties are somewhat different from those of monohydric ones, can isomerize during the reaction. Therefore, obtaining the target product is difficult. An example of a reaction in the image.

Intramolecular and intermolecular dehydration of alcohols

The hydroxyl group located at the supporting carbon atom can be cleaved off using strong acceptors. This is how intermolecular dehydration reactions proceed. When one alcohol molecule interacts with another in a solution of concentrated sulfuric acid, a water molecule is split off from both hydroxyl groups, the radicals of which combine to form an ether molecule. With intermolecular dehydration of ethanol, dioxane can be obtained - a dehydration product of four hydroxyl groups.

In intramolecular dehydration, the product is an alkene.

Alcohols- these are derivatives of hydrocarbons, the molecules of which contain one or more hydroxyl OH - groups associated with a saturated carbon atom.

Nomenclature: systematic - the ending - ol is added to the name of the corresponding hydrocarbon, the position of the OH group is indicated by a number; use trivial names.

CLASSIFICATION

By the number of OH - groups alcohols are divided into

● monoatomic

● diatomic (diols)

● triatomic (triols)

● polyhydric (polyols)

Depending on the position of OH groups distinguish

● primary

● secondary

● tertiary

Depending on the nature of the radical R distinguish

● rich

● unsaturated

● aromatic

● alicyclic

isomerism

1. Carbon skeleton

2. Position functional group:

3. Interclass isomerism (alcohols are isomeric to the class of ethers)

§3. Methods for obtaining monohydric alcohols.

1. Hydration of alkenes

Depending on the structure unsaturated hydrocarbon primary, secondary and tertiary alcohols can be formed:

ethylene ethanol

propylene 2-propanol

methylpropene 2-methyl-2-propanol

2. Hydrolysis of halogen derivatives; carried out under the influence water solution alkalis:

3. Hydrolysis of esters:

4. Recovery of carbonyl compounds:

5. Some specific receiving methods:

a) obtaining methanol from synthesis gas (pressure - 50 - 150 atm, temperature - 200 - 300 ° C, catalysts - oxides of zinc, chromium, aluminum):

b) obtaining ethanol by fermentation of sugars:

Physical properties

Methyl alcohol is a colorless liquid with a characteristic alcohol odor.

T bale \u003d 64.7 ° C, burns with a pale flame. Strongly poisonous.

Ethyl alcohol is a colorless liquid with a characteristic alcoholic odor.

T bale \u003d 78.3 o C

Alcohols C 1 - C 11 - liquids, C 12 and above - solids.

alcohols C 4 - C 5 have a suffocating sweet smell;

higher alcohols are odorless.

The relative density is less than 1, i.e. lighter than water.

Lower alcohols (up to C 3) are miscible with water in any ratio.

With an increase in the hydrocarbon radical, the solubility in water decreases, and the hydrophobicity of the molecule increases.

Alcohols are capable of intermolecular association:

In this regard, the boiling and melting points of alcohols are higher than those of the corresponding hydrocarbons and halogen derivatives.

Ability ethyl alcohol to the formation of hydrogen bonds underlies its antiseptic properties.

§5. Chemical properties of monohydric alcohols.

The characteristic reactions of alcohols are determined by the presence of a hydroxyl group in their molecule, which determines their significant reactivity.

1. Interaction with alkali metals:

R-OMe metal alcoholates are colorless solids, easily hydrolyzed by water. They are strong bases.

2.Basic properties

3. Formation of ethers:

4. Formation of esters

with inorganic acids:

with organic acids

5. Reaction of alcohols with hydrogen halides:

The use of phosphorus halides:

6. Dehydration reactions of alcohols.

The splitting of water from alcohols occurs in the presence of acids or over catalysts at elevated temperatures.

The dehydration of alcohols proceeds according to Zaitsev's empirical rule: preferably, hydrogen is split off from the least hydrogenated β-carbon atom.

1) Dehydration of primary alcohols proceeds under harsh conditions:

2) Dehydration of secondary alcohols:

3) Dehydration of tertiary alcohols:

7. Oxidation (oxidizing agents - KMnO 4, K 2 Cr 2 O 7 in an acidic environment)

8.Dehydrogenation of alcohols:

Dihydric alcohols (diols)

Ways to get.

1. Ethylene oxidation

2. Hydrolysis of the dihalogen derivative

Physical properties:

Ethylene glycol is a viscous colorless liquid, sweet in taste, soluble in water; anhydrous ethylene glycol is hygroscopic.

Chemical properties

The reactions are basically similar to the reactions of monohydric alcohols, and the reactions can proceed at one or two hydroxyl groups.

1. Acid properties; ethylene glycol over strong acid than ethanol

(pKa = 14.8). Formation of glycolates

2. Substitution reactions for halogens

3. Formation of ethers

4. Dehydration

5. Oxidation

Trihydric alcohols (triols)

Ways to get.

1. Hydrolysis of fats

2. From allyl chloride

Physical properties:

Glycerin is a viscous liquid with a sweet taste. Let's not limitedly dissolve in water, ethanol; does not dissolve in ether, anhydrous glycerin is hygroscopic (absorbs up to 40% of moisture from the air).

Chemical properties

The reactions are basically similar to the reactions of monohydric alcohols, and the reactions can proceed with one, two or three hydroxyl groups at once.

1. Acid properties; Glycerin is a stronger acid than ethanol and ethylene glycol. pKa = 13.5.

Forms a chelate complex with copper hydroxide:

2. Substitution reactions

3. Dehydration

The use of alcohols

Methanol and ethanol are used as solvents, as well as starting materials in synthesis organic matter. Ethanol is used in pharmacy for the preparation of tinctures, extracts; in medicine - as an antiseptic.

Ethylene glycol is used to produce synthetic polyester fibers (for example, lavsan), as well as antifreeze (50% solution) - an antifreeze liquid for cooling internal combustion engines.

Glycerin is used as a component of cosmetic preparations and ointments. Glycerol trinitrate is a drug used to treat angina pectoris.

Glycerol trinitrate is used in the manufacture of explosives (dynamite).

The use of glycerin in the food and textile industry.

(alcohols) – class organic compounds containing one or more C-OH groups, while the OH hydroxyl group is bonded to an aliphatic carbon atom (compounds in which the carbon atom in the C-OH group is part of the aromatic nucleus are called phenols)

The classification of alcohols is diverse and depends on which feature of the structure is taken as the basis.

1. Depending on the number of hydroxyl groups in the molecule, alcohols are divided into:

a) monoatomic (contain one hydroxyl OH group), for example, methanol CH 3 OH, ethanol C 2 H 5 OH, propanol C 3 H 7 OH

b) polyatomic (two or more hydroxyl groups), for example, ethylene glycol

HO -С H 2 - CH 2 - OH , glycerol HO-CH 2 -CH (OH) -CH 2 -OH, pentaerythritol C (CH 2 OH) 4.

Compounds in which one carbon atom

there are two hydroxyl groups, in most cases they are unstable and easily turn into aldehydes, while splitting off water: RCH (OH) 2 ® RCH \u003d O + H 2 O , does not exist.

2. According to the type of carbon atom to which the OH group is bonded, alcohols are divided into:

a) primary, in which the OH group is bonded to the primary carbon atom. The primary carbon atom is called (highlighted in red), associated with only one carbon atom. Examples of primary alcohols - ethanol C

H 3 - CH 2 - OH, propanol C H 3 - CH 2 - CH 2 - OH. b) secondary, in which the OH group is bonded to a secondary carbon atom. The secondary carbon atom (highlighted in blue) is bonded simultaneously to two carbon atoms, for example, secondary propanol, secondary butanol (Fig. 1).

Rice. one. STRUCTURE OF SECONDARY ALCOHOLS

c) tertiary, in which the OH group is bonded to the tertiary carbon atom. Tertiary carbon atom (isolated in green) is bound simultaneously to three neighboring carbon atoms, for example, tertiary butanol and pentanol (Fig. 2).

Rice. 2. STRUCTURE OF TERTIARY ALCOHOLS

The alcohol group attached to it is also called primary, secondary, or tertiary, according to the type of carbon atom.

In polyhydric alcohols containing two or more OH groups, both primary and secondary HO groups can be present simultaneously, for example, in glycerol or xylitol (Fig. 3).

Rice. 3. COMBINATION OF PRIMARY AND SECONDARY OH-GROUPS IN THE STRUCTURE OF POLYATOMIC ALCOHOLS.

3. According to the structure of organic groups linked by an OH group, alcohols are divided into saturated (methanol, ethanol, propanol), unsaturated, for example, allyl alcohol CH 2 \u003d CH - CH 2 -OH, aromatic (for example, benzyl alcohol C 6 H 5 CH 2 OH), containing in the group

R aromatic group.

Unsaturated alcohols, in which the OH group "adjoins" the double bond, i.e. bound to a carbon atom that simultaneously participates in the formation of a double bond (for example, vinyl alcohol CH 2 \u003d CH–OH), are extremely unstable and isomerize immediately ( cm.ISOMERIZATION) to aldehydes or ketones:

CH 2 \u003d CH–OH ® CH 3 -CH \u003d O Nomenclature of alcohols. For common alcohols with a simple structure, a simplified nomenclature is used: the name of the organic group is converted into an adjective (using the suffix and the ending " new”) and add the word “alcohol”:In the case when the structure of the organic group is more complex, the rules common to all organic chemistry are used. Names compiled according to such rules are called systematic. In accordance with these rules, the hydrocarbon chain is numbered from the end to which the OH group is closest. Further, this numbering is used to indicate the position of various substituents along the main chain, at the end of the name the suffix "ol" is added and a number indicating the position of the OH group (Fig. 4):4. SYSTEMATIC NAMES OF ALCOHOLS. Functional (OH) and substituent (CH 3) groups, as well as their corresponding digital indices, are highlighted in different colors.The systematic names of the simplest alcohols are made according to the same rules: methanol, ethanol, butanol. For some alcohols, trivial (simplified) names that have developed historically have been preserved: propargyl alcohol NSє C-CH 2 -OH, glycerol HO-CH 2 -CH (OH) -CH 2 -OH, pentaerythritol C (CH 2 OH) 4, phenethyl alcohol C 6 H 5 -CH 2 -CH 2 -OH.Physical properties of alcohols. Alcohols are soluble in most organic solvents, the first three simplest representatives - methanol, ethanol and propanol, as well as tertiary butanol (H 3 C) 3 COH - are miscible with water in any ratio. With an increase in the number of C atoms in the organic group, the hydrophobic (water-repellent) effect begins to affect, solubility in water becomes limited, and when R containing more than 9 carbon atoms, practically disappears.

Due to the presence of OH groups, hydrogen bonds form between alcohol molecules.

Rice. 5. HYDROGEN BONDS IN ALCOHOLS(shown by dotted line)

As a result, all alcohols have a higher boiling point than the corresponding hydrocarbons, for example, T. kip. ethanol + 78 ° C, and T. kip. ethane –88.63°C; T. kip. butanol and butane +117.4°C and –0.5°C, respectively.

Chemical properties of alcohols. Alcohols are distinguished by various transformations. The reactions of alcohols have some general patterns: reactivity primary monohydric alcohols is higher than secondary ones, in turn, secondary alcohols are chemically more active than tertiary ones. For dihydric alcohols, in the case when OH groups are located at neighboring carbon atoms, an increased (in comparison with monohydric alcohols) reactivity is observed due to mutual influence these groups. For alcohols, reactions are possible that take place with the cleavage of both C–O and O–H bonds.

1. Reactions proceeding through the О–Н bond.

When interacting with active metals (Na, K, Mg, Al), alcohols exhibit the properties of weak acids and form salts called alcoholates or alkoxides:

CH 3 OH + 2 Na ® 2 CH 3 OK + H 2

Alcoholates are chemically unstable and hydrolyze under the action of water to form alcohol and metal hydroxide:

C 2 H 5 OK + H 2 O

® C 2 H 5 OH + KOH

This reaction shows that alcohols, in comparison with water, are more weak acids(a strong acid displaces a weak one), in addition, when interacting with alkali solutions, alcohols do not form alcoholates. However, in polyhydric alcohols(in the case when OH groups are attached to neighboring C atoms), the acidity of alcohol groups is much higher, and they can form alcoholates not only when interacting with metals, but also with alkalis:

HO–CH 2 –CH 2 –OH + 2NaOH ® NaO–CH 2 –CH 2 –ONa + 2H 2 OWhen the HO groups in polyhydric alcohols are attached to non-adjacent C atoms, the properties of the alcohols are close to monohydric, since the mutual influence of the HO groups does not appear.

When interacting with mineral or organic acids, alcohols form esters - compounds containing a fragment

R-O-A (A is the rest of the acid). The formation of esters also occurs during the interaction of alcohols with anhydrides and acid chlorides. carboxylic acids(Fig. 6).

Under the action of oxidizing agents (K 2 Cr 2 O 7, KMnO 4) primary alcohols form aldehydes, and secondary - ketones (Fig. 7)

Rice. 7. FORMATION OF ALDEHYDES AND KETONES DURING THE OXIDATION OF ALCOHOLS

The reduction of alcohols leads to the formation of hydrocarbons containing the same number of C atoms as the initial alcohol molecule (Fig. 8).

8. RECOVERY OF BUTANOL

2. Reactions taking place at the C–O bond.

In the presence of catalysts or strong mineral acids, alcohols are dehydrated (water is split off), while the reaction can proceed in two directions:

a) intermolecular dehydration with the participation of two molecules of alcohol, while the C–O bonds in one of the molecules break, resulting in the formation of ethers - compounds containing a fragment

R-O-R (Fig. 9A).

b) during intramolecular dehydration, alkenes are formed - hydrocarbons with a double bond. Often, both processes—the formation of an ether and an alkene—occur in parallel (Fig. 9B).

In the case of secondary alcohols, during the formation of an alkene, two directions of the reaction are possible (Fig. 9C), the predominant direction is that in which hydrogen is split off from the least hydrogenated carbon atom during condensation (marked with the number 3), i.e. surrounded by fewer hydrogen atoms (compared to atom 1). Shown in fig. 10 reactions are used to produce alkenes and ethers.

The breaking of the C–O bond in alcohols also occurs when the OH group is replaced by a halogen, or an amino group (Fig. 10).

Rice. ten. REPLACEMENT OF OH-GROUP IN ALCOHOLS WITH HALOGEN OR AMINE GROUP

The reactions shown in fig. 10 are used to produce halocarbons and amines.

Getting alcohols. Some of the reactions shown above (Fig. 6,9,10) are reversible and, under changing conditions, can proceed in the opposite direction, leading to the production of alcohols, for example, during the hydrolysis of esters and halocarbons (Fig. 11A and B, respectively), as well as hydration alkenes - by adding water (Fig. 11B).

Rice. eleven. PRODUCTION OF ALCOHOLS BY HYDROLYSIS AND HYDRATION OF ORGANIC COMPOUNDS

The reaction of hydrolysis of alkenes (Fig. 11, scheme B) underlies industrial production lower alcohols containing up to 4 carbon atoms.

Ethanol is also formed during the so-called alcoholic fermentation of sugars, for example, glucose C 6 H 12 O 6. The process proceeds in the presence of yeast fungi and leads to the formation of ethanol and CO 2:

® 2C 2 H 5 OH + 2CO 2

No more than 15% aqueous alcohol solution can be obtained by fermentation, since yeasts die at a higher concentration of alcohol. Alcohol solutions of higher concentration are obtained by distillation.

Methanol is obtained in industry by the reduction of carbon monoxide at 400

° C under a pressure of 20–30 MPa in the presence of a catalyst consisting of oxides of copper, chromium, and aluminum:® H 3 SON If instead of hydrolysis of alkenes (Fig. 11) oxidation is carried out, then dihydric alcohols are formed (Fig. 12) 12. OBTAINING DIATOMIC ALCOHOLSThe use of alcohols. The ability of alcohols to participate in various chemical reactions allows them to be used to obtain all kinds of organic compounds: aldehydes, ketones, carboxylic acids, ethers and esters used as organic solvents in the production of polymers, dyes and drugs.

Methanol CH 3 OH is used as a solvent, as well as in the production of formaldehyde, used to obtain phenol-formaldehyde resins, in recent times methanol is considered as a promising motor fuel. Large volumes of methanol are used in the production and transportation of natural gas. Methanol is the most toxic compound among all alcohols, the lethal dose when taken orally is 100 ml.

Ethanol C 2 H 5 OH is the starting compound for the production of acetaldehyde, acetic acid, as well as for the production of esters of carboxylic acids used as solvents. In addition, ethanol is the main component of all alcoholic beverages, it is also widely used in medicine as a disinfectant.

Butanol is used as a solvent for fats and resins, in addition, it serves as a raw material for the production of fragrant substances (butyl acetate, butyl salicylate, etc.). In shampoos, it is used as a component that increases the transparency of solutions.

Benzyl alcohol C 6 H 5 -CH 2 -OH in the free state (and in the form of esters) is found in the essential oils of jasmine and hyacinth. It has antiseptic (disinfecting) properties, in cosmetics it is used as a preservative for creams, lotions, dental elixirs, and in perfumery as a fragrant substance.

Phenethyl alcohol C 6 H 5 -CH 2 -CH 2 -OH has the smell of a rose, is found in rose oil, and is used in perfumery.

Ethylene glycol HOCH 2 -CH 2 OH is used in the production of plastics and as an antifreeze (an additive that reduces the freezing point of aqueous solutions), in addition, in the manufacture of textile and printing inks.

Diethylene glycol HOCH 2 -CH 2 OCH 2 -CH 2 OH is used to fill hydraulic brake devices, as well as in the textile industry when finishing and dyeing fabrics.

Glycerol

HOCH 2 - CH (OH) - CH 2 OH used to obtain polyester glyptal resins, in addition, it is a component of many cosmetic preparations. Nitroglycerin (Fig. 6) is the main component of dynamite used in mining and railway construction as an explosive.

Pentaerythritol (

HOCH 2) 4 C is used to produce polyesters (pentaphthalic resins), as a hardener for synthetic resins, as a plasticizer for polyvinyl chloride, and also in the production of tetranitropentaerythritol explosive.

Polyhydric alcohols xylitol HOCH 2 - (CHOH) 3 -CH 2 OH and sorbitol neNOCH 2 - (CHOH) 4 -CH 2 OH have a sweet taste, they are used instead of sugar in the production of confectionery for diabetics and obese people. Sorbitol is found in rowan and cherry berries.

Mikhail Levitsky

LITERATURE Shabarov Yu.S. Organic chemistry . Moscow, "Chemistry", 1994