Alcohols, chemical compounds and names. Chemical properties of monohydric and polyhydric alcohols

Alcohols(or alkanols) are organic substances whose molecules contain one or more hydroxyl groups (-OH groups) connected to a hydrocarbon radical.

Classification of alcohols

According to the number of hydroxyl groups(atomicity) alcohols are divided into:

Monatomic, For example:

Diatomic(glycols), for example:

Triatomic, For example:

According to the nature of the hydrocarbon radical The following alcohols are released:

Limit containing only saturated hydrocarbon radicals in the molecule, for example:

Unlimited containing multiple (double and triple) bonds between carbon atoms in the molecule, for example:

Aromatic, i.e. alcohols containing a benzene ring and a hydroxyl group in the molecule, connected to each other not directly, but through carbon atoms, for example:

Organic substances containing hydroxyl groups in the molecule, connected directly to the carbon atom of the benzene ring, differ significantly in chemical properties from alcohols and therefore are classified as an independent class of organic compounds - phenols.

For example:

There are also polyhydric (polyhydric alcohols) containing more than three hydroxyl groups in the molecule. For example, the simplest hexahydric alcohol hexaol (sorbitol)

Nomenclature and isomerism of alcohols

When forming the names of alcohols, a (generic) suffix is ​​added to the name of the hydrocarbon corresponding to the alcohol. ol.

The numbers after the suffix indicate the position of the hydroxyl group in the main chain, and the prefixes di-, tri-, tetra- etc. - their number:

In the numbering of carbon atoms in the main chain, the position of the hydroxyl group takes precedence over the position of multiple bonds:

Starting from the third member of the homologous series, alcohols exhibit isomerism of the position of the functional group (propanol-1 and propanol-2), and from the fourth, isomerism of the carbon skeleton (butanol-1, 2-methylpropanol-1). They are also characterized by interclass isomerism - alcohols are isomeric to ethers:

Let's give a name to the alcohol, the formula of which is given below:

Name construction order:

1. The carbon chain is numbered from the end closest to the –OH group.
2. The main chain contains 7 C atoms, which means the corresponding hydrocarbon is heptane.
3. The number of –OH groups is 2, the prefix is ​​“di”.
4. Hydroxyl groups are located at 2 and 3 carbon atoms, n = 2 and 4.

Alcohol name: heptanediol-2,4

Physical properties of alcohols

Alcohols can form hydrogen bonds both between alcohol molecules and between alcohol and water molecules. Hydrogen bonds arise from the interaction of a partially positively charged hydrogen atom of one alcohol molecule and a partially negatively charged oxygen atom of another molecule. It is thanks to hydrogen bonds between molecules that alcohols have abnormally high boiling points for their molecular weight. Thus, propane with a relative molecular weight of 44 under normal conditions is a gas, and the simplest of alcohols is methanol, having a relative molecular weight of 32, under normal conditions it is a liquid.

The lower and middle members of a series of saturated monohydric alcohols containing from 1 to 11 carbon atoms are liquids. Higher alcohols (starting from C12H25OH) at room temperature - solids. Lower alcohols have an alcoholic odor and a pungent taste; they are highly soluble in water. As the carbon radical increases, the solubility of alcohols in water decreases, and octanol no longer mixes with water.

Chemical properties of alcohols

The properties of organic substances are determined by their composition and structure. Alcohols confirm the general rule. Their molecules include hydrocarbon and hydroxyl groups, so the chemical properties of alcohols are determined by the interaction of these groups with each other.

The properties characteristic of this class of compounds are due to the presence of a hydroxyl group.

1. Interaction of alcohols with alkali and alkaline earth metals. To identify the effect of a hydrocarbon radical on a hydroxyl group, it is necessary to compare the properties of a substance containing a hydroxyl group and a hydrocarbon radical, on the one hand, and a substance containing a hydroxyl group and not containing a hydrocarbon radical, on the other. Such substances can be, for example, ethanol (or other alcohol) and water. The hydrogen of the hydroxyl group of alcohol molecules and water molecules is capable of being reduced by alkali and alkaline earth metals (replaced by them)
2. Interaction of alcohols with hydrogen halides. Substitution of a hydroxyl group with a halogen leads to the formation of haloalkanes. For example:
   This reaction is reversible.
3. Intermolecular dehydrationalcohols- splitting off a water molecule from two alcohol molecules when heated in the presence of water-removing agents:
   As a result of intermolecular dehydration of alcohols, ethers. Thus, when ethyl alcohol is heated with sulfuric acid to a temperature of 100 to 140°C, diethyl (sulfur) ether is formed.
   
4. The interaction of alcohols with organic and inorganic acids to form esters (esterification reaction)
   
   The esterification reaction is catalyzed by strong inorganic acids. For example, when ethyl alcohol and acetic acid react, ethyl acetate is formed:
   
   
5. Intramolecular dehydration of alcohols occurs when alcohols are heated in the presence of water-removing agents to a higher temperature than the temperature of intermolecular dehydration. As a result, alkenes are formed. This reaction is due to the presence of a hydrogen atom and a hydroxyl group at adjacent carbon atoms. An example is the reaction of producing ethene (ethylene) by heating ethanol above 140°C in the presence of concentrated sulfuric acid:
   
6. Oxidation of alcohols usually carried out with strong oxidizing agents, for example, potassium dichromate or potassium permanganate in an acidic environment. In this case, the action of the oxidizing agent is directed to the carbon atom that is already bonded to the hydroxyl group. Depending on the nature of the alcohol and the reaction conditions, various products can be formed. Thus, primary alcohols are oxidized first to aldehydes and then to carboxylic acids:
   The oxidation of secondary alcohols produces ketones:
   
   Tertiary alcohols are quite resistant to oxidation. However, under harsh conditions (strong oxidizing agent, high temperature), oxidation of tertiary alcohols is possible, which occurs with the rupture of carbon-carbon bonds closest to the hydroxyl group.
7. Dehydrogenation of alcohols. When alcohol vapor is passed at 200-300 °C over a metal catalyst, such as copper, silver or platinum, primary alcohols are converted into aldehydes, and secondary alcohols into ketones:
   
   
8. Qualitative reaction to polyhydric alcohols.
   The presence of several hydroxyl groups in the alcohol molecule at the same time determines the specific properties of polyhydric alcohols, which are capable of forming bright blue complex compounds soluble in water when interacting with a freshly obtained precipitate of copper (II) hydroxide. For ethylene glycol we can write:
   
   Monohydric alcohols are not able to enter into this reaction. Therefore, it is a qualitative reaction to polyhydric alcohols.
   

Preparation of alcohols:

Use of alcohols

Methanol(methyl alcohol CH 3 OH) is a colorless liquid with a characteristic odor and a boiling point of 64.7 ° C. Burns with a slightly bluish flame. The historical name of methanol - wood alcohol is explained by one of the ways of its production by distilling hard wood (Greek methy - wine, get drunk; hule - substance, wood).

Methanol requires careful handling when working with it. Under the action of the enzyme alcohol dehydrogenase, it is converted in the body into formaldehyde and formic acid, which damage the retina, cause death of the optic nerve and complete loss of vision. Ingestion of more than 50 ml of methanol causes death.

Ethanol(ethyl alcohol C 2 H 5 OH) is a colorless liquid with a characteristic odor and a boiling point of 78.3 ° C. Flammable Mixes with water in any ratio. The concentration (strength) of alcohol is usually expressed as a percentage by volume. “Pure” (medicinal) alcohol is a product obtained from food raw materials and containing 96% (by volume) ethanol and 4% (by volume) water. To obtain anhydrous ethanol - “absolute alcohol”, this product is treated with substances that chemically bind water (calcium oxide, anhydrous copper (II) sulfate, etc.).

In order to make alcohol used for technical purposes unsuitable for drinking, small amounts of difficult-to-separate toxic, bad-smelling and disgusting-tasting substances are added to it and tinted. Alcohol containing such additives is called denatured or denatured alcohol.

Ethanol is widely used in industry for the production of synthetic rubber, medicines, is used as a solvent, is part of varnishes and paints, and perfumes. In medicine, ethyl alcohol is the most important disinfectant. Used for preparing alcoholic drinks.

When small amounts of ethyl alcohol enter the human body, they reduce pain sensitivity and block inhibition processes in the cerebral cortex, causing a state of intoxication. At this stage of the action of ethanol, water separation in the cells increases and, consequently, urine formation accelerates, resulting in dehydration of the body.

In addition, ethanol causes dilation of blood vessels. Increased blood flow in the skin capillaries leads to redness of the skin and a feeling of warmth.

In large quantities, ethanol inhibits brain activity (inhibition stage) and causes impaired coordination of movements. An intermediate product of ethanol oxidation in the body, acetaldehyde, is extremely toxic and causes severe poisoning.

Systematic consumption of ethyl alcohol and drinks containing it leads to a persistent decrease in brain productivity, death of liver cells and their replacement with connective tissue - liver cirrhosis.

Ethanediol-1,2(ethylene glycol) is a colorless viscous liquid. Poisonous. Unlimitedly soluble in water. Aqueous solutions do not crystallize at temperatures significantly below 0 °C, which makes it possible to use it as a component of non-freezing coolants - antifreeze for internal combustion engines.

Prolactriol-1,2,3(glycerin) is a viscous, syrupy liquid with a sweet taste. Unlimitedly soluble in water. Non-volatile. As a component of esters, it is found in fats and oils.

Widely used in cosmetics, pharmaceutical and food industries. In cosmetics, glycerin plays the role of an emollient and soothing agent. It is added to toothpaste to prevent it from drying out.

Glycerin is added to confectionery products to prevent their crystallization. It is sprayed onto tobacco, in which case it acts as a humectant that prevents the tobacco leaves from drying out and crumbling before processing. It is added to adhesives to prevent them from drying out too quickly, and to plastics, especially cellophane. In the latter case, glycerin acts as a plasticizer, acting like a lubricant between polymer molecules and thus giving plastics the necessary flexibility and elasticity.

Hydrocarbon derivatives with one or more hydrogen atoms in the molecule replaced by an -OH group (hydroxyl group or hydroxy group) are alcohols. Chemical properties are determined by the hydrocarbon radical and hydroxyl group. Alcohols form a separate group in which each subsequent representative differs from the previous member by a homological difference corresponding to =CH2. All substances in this class can be represented by the formula: R-OH. For monoatomic saturated compounds, the general chemical formula is CnH2n+1OH. According to international nomenclature, names can be derived from hydrocarbons with the addition of the ending -ol (methanol, ethanol, propanol, and so on).

This is a very diverse and broad class of chemical compounds. Depending on the number of -OH groups in the molecule, it is divided into one-, two-, triatomic and so on - polyatomic compounds. The chemical properties of alcohols also depend on the content of hydroxy groups in the molecule. These substances are neutral and do not dissociate into ions in water, such as strong acids or strong bases. However, they can weakly exhibit both acidic (they decrease with increasing molecular weight and branching of the hydrocarbon chain in the series of alcohols) and basic (increasing with increasing molecular weight and branching of the molecule) properties.

The chemical properties of alcohols depend on the type and spatial arrangement of atoms: molecules come with chain isomerism and positional isomerism. Depending on the maximum number of single bonds of a carbon atom (linked to the hydroxy group) with other carbon atoms (with 1, 2 or 3), primary (normal), secondary or tertiary alcohols are distinguished. Primary alcohols have a hydroxyl group attached to the primary carbon atom. In secondary and tertiary - to secondary and tertiary, respectively. Starting with propanol, isomers appear that differ in the position of the hydroxyl group: propyl alcohol C3H7-OH and isopropyl alcohol CH3-(CHOH)-CH3.

It is necessary to name several main reactions that characterize the chemical properties of alcohols:

1. When reacting with or their hydroxides (deprotonation reaction), alcoholates are formed (the hydrogen atom is replaced by a metal atom), depending on the hydrocarbon radical, methylates, ethylates, propylates and so on are obtained, for example, sodium propoxide: 2CH3CH2OH + 2Na → 2CH3CH2ONa + H2.
2. When interacting with concentrated hydrohalic acids, HBr + CH3CH2OH ↔ CH3CH2Br + H2O are formed. This reaction is reversible. As a result, nucleophilic substitution of the hydroxyl group with a halogen ion occurs.
3. Alcohols can be oxidized to carbon dioxide, to aldehydes, or to ketones. Alcohols burn in the presence of oxygen: 3O2 + C2H5OH →2CO2 + 3H2O. Under the influence of a strong oxidizing agent (chromic acid, etc.), primary alcohols are converted into aldehydes: C2H5OH → CH3COH + H2O, and secondary alcohols are converted into ketones: CH3—(CHOH)—CH3 → CH3—(CHO)—CH3 + H2O.
4. The dehydration reaction occurs when heated in the presence of water-removing substances (sulfuric acid, etc.). As a result, alkenes are formed: C2H5OH → CH2=CH2 + H2O.
5. The esterification reaction also occurs when heated in the presence of water-subtracting compounds, but, unlike the previous reaction, at a lower temperature and with the formation of 2C2H5OH → C2H5-O-C2H5O. With sulfuric acid the reaction occurs in two stages. First, an ester of sulfuric acid is formed: C2H5OH + H2SO4 → C2H5O—SO2OH + H2O, then when heated to 140 ° C and in excess of alcohol, diethyl (often called sulfuric) ether is formed: C2H5OH + C2H5O—SO2OH → C2H5—O—C2H5O + H2SO4 .

The chemical properties of polyhydric alcohols, by analogy with their physical properties, depend on the type of hydrocarbon radical forming the molecule and, of course, the number of hydroxyl groups in it. For example, ethylene glycol CH3OH-CH3OH (boiling point 197 °C), which is a 2-atomic alcohol, is a colorless liquid (has a sweetish taste), which mixes with H2O, as well as lower alcohols in any ratio. Ethylene glycol, like its higher homologues, enter into all reactions characteristic of monohydric alcohols. Glycerol CH2OH—CHOH—CH2OH (boiling point 290 °C) is the simplest representative of 3-hydroxy alcohols. This is a thick, sweet-tasting liquid that cannot be mixed with it in any proportion. Dissolves in alcohol. Glycerol and its homologues are also characterized by all reactions of monohydric alcohols.

The chemical properties of alcohols determine the areas of their use. They are used as fuel (bioethanol or biobutanol and others), as solvents in various industries; as a raw material for the production of surfactants and detergents; for the synthesis of polymer materials. Some representatives of this class of organic compounds are widely used as lubricants or hydraulic fluids, as well as for the manufacture of medicines and biologically active substances.

Alcohols are a diverse and broad class of chemical compounds.

Alcohols are chemical compounds whose molecules contain hydroxyl OH groups connected to a hydrocarbon radical.

A hydrocarbon radical consists of carbon and hydrogen atoms. Examples of hydrocarbon radicals - CH 3 - methyl, C 2 H 5 - ethyl. Often a hydrocarbon radical is simply denoted by the letter R. But if different radicals are present in the formula, they are denoted by R." R ", R """, etc.

The names of alcohols are formed by adding the suffix –ol to the name of the corresponding hydrocarbon.

Classification of alcohols

Alcohols are monohydric and polyhydric. If there is only one hydroxyl group in an alcohol molecule, then such an alcohol is called monohydric. If the number of hydroxyl groups is 2, 3, 4, etc., then it is a polyhydric alcohol.

Examples of monohydric alcohols: CH 3 -OH - methanol or methyl alcohol, CH 3 CH 2 -OH - ethanol or ethyl alcohol.

Accordingly, a molecule of a dihydric alcohol contains two hydroxyl groups, a molecule of a trihydric alcohol contains three, etc.

Monohydric alcohols

The general formula of monohydric alcohols can be represented as R-OH.

Based on the type of free radical included in the molecule, monohydric alcohols are divided into saturated (saturated), unsaturated (unsaturated) and aromatic alcohols.

In saturated hydrocarbon radicals, carbon atoms are connected by simple C – C bonds. Unsaturated radicals contain one or more pairs of carbon atoms connected by double C = C or triple C ≡ C bonds.

Saturated alcohols contain saturated radicals.

CH 3 CH 2 CH 2 -OH – saturated alcohol propanol-1 or propylene alcohol.

Accordingly, unsaturated alcohols contain unsaturated radicals.

CH 2 = CH - CH 2 - OH – unsaturated alcohol propenol 2-1 (allylic alcohol)

And the molecule of aromatic alcohols includes a benzene ring C 6 H 5.

C 6 H 5 -CH 2 -OH – aromatic alcohol phenylmethanol (benzyl alcohol).

Depending on the type of carbon atom bonded to the hydroxyl group, alcohols are divided into primary ((R-CH 2 -OH), secondary (R-CHOH-R) and tertiary (RR"R""C-OH) alcohols.

Chemical properties of monohydric alcohols

1. Alcohols burn to form carbon dioxide and water. When burning, heat is released.

C 2 H 5 OH + 3O 2 → 2CO 2 + 3H 2 O

2. When alcohols react with alkali metals, sodium alkoxide is formed and hydrogen is released.

C 2 H 5 -OH + 2Na → 2C 2 H 5 ONa + H 2

3. Reaction with hydrogen halide. As a result of the reaction, a haloalkane (bromoethane and water) is formed.

C 2 H 5 OH + HBr → C 2 H 5 Br + H 2 O

4. Intramolecular dehydration occurs when heated and under the influence of concentrated sulfuric acid. The result is unsaturated hydrocarbon and water.

H 3 – CH 2 – OH → CH 2 = CH 2 + H 2 O

5. Oxidation of alcohols. At ordinary temperatures, alcohols do not oxidize. But with the help of catalysts and heating, oxidation occurs.

Polyhydric alcohols

As substances containing hydroxyl groups, polyhydric alcohols have chemical properties similar to those of monohydric alcohols, but their reaction occurs at several hydroxyl groups at once.

Polyhydric alcohols react with active metals, hydrohalic acids, and nitric acid.

Preparation of alcohols

Let's consider methods for producing alcohols using the example of ethanol, the formula of which is C 2 H 5 OH.

The oldest of them is the distillation of alcohol from wine, where it is formed as a result of the fermentation of sugary substances. The raw materials for the production of ethyl alcohol are also starch-containing products, which are converted into sugar through the fermentation process, which is then fermented into alcohol. But the production of ethyl alcohol in this way requires a large consumption of food raw materials.

A much more advanced synthetic method for producing ethyl alcohol. In this case, ethylene is hydrated with water vapor.

C 2 H 4 + H 2 O → C 2 H 5 OH

Among polyhydric alcohols, the most famous is glycerin, which is obtained by splitting fats or synthetically from propylene, which is formed during high-temperature oil refining.

The content of the article

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

The classification of alcohols is varied and depends on which structural feature is taken as a 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–CH 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 has two hydroxyl groups are in most cases unstable and easily turn into aldehydes, eliminating water: RCH(OH) 2 ® RCH=O + H 2 O

2. Based on 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. A carbon atom (highlighted in red) that is bonded to just one carbon atom is called primary. Examples of primary alcohols - ethanol CH 3 - C H 2 –OH, propanol CH 3 –CH 2 – C H2–OH.

b) secondary, in which the OH group is bonded to a secondary carbon atom. A secondary carbon atom (highlighted in blue) is bonded to two carbon atoms at the same time, for example, secondary propanol, secondary butanol (Fig. 1).

Rice. 1. STRUCTURE OF SECONDARY ALCOHOLS

c) tertiary, in which the OH group is bonded to the tertiary carbon atom. The tertiary carbon atom (highlighted in green) is bonded to three neighboring carbon atoms simultaneously, for example, tertiary butanol and pentanol (Figure 2).

Rice. 2. STRUCTURE OF TERTIARY ALCOHOLS

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

In polyhydric alcohols containing two or more OH groups, both primary and secondary HO groups may 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 connected by an OH group, alcohols are divided into saturated (methanol, ethanol, propanol), unsaturated, for example, allyl alcohol CH 2 =CH–CH 2 –OH, aromatic (for example, benzyl alcohol C 6 H 5 CH 2 OH) containing an aromatic group in the R group.

Unsaturated alcohols in which the OH group is “adjacent” to the double bond, i.e. bonded to a carbon atom simultaneously involved in the formation of a double bond (for example, vinyl alcohol CH 2 =CH–OH), are extremely unstable and immediately isomerize ( cm ISOMERIZATION) to aldehydes or ketones:

CH 2 =CH–OH ® CH 3 –CH=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 ending “ new") and add the word "alcohol":

In the case where the structure of an organic group is more complex, 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 located closest. Next, this numbering is used to indicate the position of various substituents along the main chain; at the end of the name, the suffix “ol” and a number indicating the position of the OH group are added (Fig. 4):

Rice. 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 follow the same rules: methanol, ethanol, butanol. For some alcohols, trivial (simplified) names that have developed historically have been preserved: propargyl alcohol HCє C–CH 2 –OH, glycerin 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 СОН - are mixed with water in any ratio. With an increase in the number of C atoms in the organic group, a hydrophobic (water-repellent) effect begins to take effect, solubility in water becomes limited, and when R contains more than 9 carbon atoms, it practically disappears.

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

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

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

Chemical properties of alcohols.

Alcohols have a variety of transformations. The reactions of alcohols have some general principles: the reactivity of 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, increased (compared to monohydric alcohols) reactivity is observed due to the mutual influence of these groups. For alcohols, reactions are possible that involve the breaking of both C–O and O–H bonds.

1. Reactions occurring at the O–H bond.

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

2CH 3 OH + 2Na ® 2CH 3 OK + H 2

Alcoholates are chemically unstable and, when exposed to water, hydrolyze 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 are weaker acids compared to water (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 the 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 O

When HO groups in polyhydric alcohols are attached to non-adjacent C atoms, the properties of alcohols are close to monoatomic ones, since the mutual influence of HO groups does not appear.

When interacting with mineral or organic acids, alcohols form esters - compounds containing the R-O-A fragment (A is the acid residue). The formation of esters also occurs during the interaction of alcohols with anhydrides and acid chlorides of carboxylic acids (Fig. 6).

Under the action of oxidizing agents (K 2 Cr 2 O 7, KMnO 4), primary alcohols form aldehydes, and secondary alcohols form 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 molecule of the original alcohol (Fig. 8).

Rice. 8. BUTANOL RESTORATION

2. Reactions occurring at the C–O bond.

In the presence of catalysts or strong mineral acids, dehydration of alcohols (elimination of water) occurs, and the reaction can proceed in two directions:

a) intermolecular dehydration involving two alcohol molecules, in which the C–O bonds of one of the molecules are broken, resulting in the formation of ethers—compounds containing the R–O–R fragment (Fig. 9A).

b) intramolecular dehydration produces alkenes - 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 reaction directions are possible (Fig. 9B), the predominant direction is in which, during the condensation process, hydrogen is split off from the least hydrogenated carbon atom (marked by 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 cleavage of the C–O bond in alcohols also occurs when the OH group is replaced by a halogen or amino group (Fig. 10).

Rice. 10. REPLACEMENT OF OH-GROUP IN ALCOHOLS WITH HALOGEN OR AMINO GROUP

The reactions shown in Fig. 10 is used for the production of halocarbons and amines.

Preparation of alcohols.

Some of the reactions shown above (Fig. 6,9,10) are reversible and, when conditions change, 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 by hydration alkenes - by adding water (Fig. 11B).

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

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

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

C 6 H 12 O 6 ® 2C 2 H 5 OH + 2CO 2

Fermentation can produce no more than a 15% aqueous solution of alcohol, since at a higher concentration of alcohol the yeast fungi die. Higher concentration alcohol solutions are obtained by distillation.

Methanol is produced industrially by the reduction of carbon monoxide at 400° C under a pressure of 20–30 MPa in the presence of a catalyst consisting of copper, chromium, and aluminum oxides:

CO + 2 H 2 ® H 3 COH

If instead of hydrolysis of alkenes (Fig. 11) oxidation is carried out, then dihydric alcohols are formed (Fig. 12)

Rice. 12. PREPARATION OF DIOHOMIC ALCOHOLS

Use of alcohols.

The ability of alcohols to participate in a variety of chemical reactions allows them to be used to produce 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 produce phenol-formaldehyde resins; methanol has recently been 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 ingested 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 carboxylic acid esters used as solvents. In addition, ethanol is the main component of all alcoholic beverages; it is 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 a rose scent, 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 for finishing and dyeing fabrics.

Glycerol HOCH 2 –CH(OH)–CH 2 OH is used to produce polyester glyphthalic 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 the explosive tetranitropentaerythritol.

Polyhydric alcohols xylitol СОН2–(СНН)3–CH2ОН and sorbitol СОН2– (СНН)4–СН2ОН have a sweet taste; they are used instead of sugar in the production of confectionery products for patients with diabetes and people suffering from obesity. Sorbitol is found in rowan and cherry berries.

Mikhail Levitsky