Characteristics of alcohols chemistry. Physical and chemical properties of alcohols

Alcohols are hydrocarbon derivatives containing one or more -OH groups, called a hydroxyl group or hydroxyl.

Alcohols are classified:

1. According to the number of hydroxyl groups contained in the molecule, alcohols are divided into monohydric (with one hydroxyl), diatomic (with two hydroxyls), triatomic (with three hydroxyls) and polyatomic.

Like saturated hydrocarbons, monohydric alcohols form a naturally constructed series of homologues:

As in other homologous series, each member of the alcohol series differs in composition from the previous and subsequent members by a homologous difference (-CH 2 -).

2. Depending on which carbon atom the hydroxyl is located at, primary, secondary and tertiary alcohols are distinguished. The molecules of primary alcohols contain a -CH 2 OH group associated with one radical or with a hydrogen atom in methanol (hydroxyl at the primary carbon atom). Secondary alcohols are characterized by a >CHOH group linked to two radicals (hydroxyl at the secondary carbon atom). In the molecules of tertiary alcohols there is a >C-OH group associated with three radicals (hydroxyl at the tertiary carbon atom). Denoting the radical by R, we can write the formulas of these alcohols in general view:

In accordance with the IUPAC nomenclature, when constructing the name of a monohydric alcohol, the suffix -ol is added to the name of the parent hydrocarbon. If a compound contains higher functions, the hydroxyl group is designated by the prefix hydroxy- (in Russian the prefix oxy- is often used). The longest unbranched chain of carbon atoms, which includes a carbon atom bound to a hydroxyl group, is selected as the main chain; if the compound is unsaturated, then a multiple bond is also included in this chain. It should be noted that when determining the beginning of numbering, the hydroxyl function usually takes precedence over the halogen, double bond and alkyl, therefore, numbering begins from the end of the chain closer to which the hydroxyl group is located:

The simplest alcohols are named by the radicals with which the hydroxyl group is connected: (CH 3) 2 CHOH - isopropyl alcohol, (CH 3) 3 SON - tert-butyl alcohol.

A rational nomenclature for alcohols is often used. According to this nomenclature, alcohols are considered as derivatives of methyl alcohol - carbinol:

This system is convenient in cases where the name of the radical is simple and easy to construct.

2. Physical properties of alcohols

Alcohols have higher boiling points and are significantly less volatile, have higher melting points, and are more soluble in water than the corresponding hydrocarbons; however, the difference decreases with increasing molecular weight.

The difference in physical properties is due to the high polarity of the hydroxyl group, which leads to the association of alcohol molecules due to hydrogen bonding:

Thus, the higher boiling points of alcohols compared to the boiling points of the corresponding hydrocarbons are due to the need to break hydrogen bonds when molecules pass into the gas phase, which requires additional energy. On the other hand, this type of association leads to an increase in molecular weight, which naturally causes a decrease in volatility.

Alcohols with low molecular weight are highly soluble in water, this is understandable if we take into account the possibility of forming hydrogen bonds with water molecules (water itself is associated to a very large extent). In methyl alcohol, the hydroxyl group makes up almost half the mass of the molecule; It is not surprising, therefore, that methanol is miscible with water in all respects. As the size of the hydrocarbon chain in alcohol increases, the influence of the hydroxyl group on the properties of alcohols decreases; accordingly, the solubility of substances in water decreases and their solubility in hydrocarbons increases. The physical properties of monohydric alcohols with high molecular weight are already very similar to the properties of the corresponding hydrocarbons.

Structure

Alcohols (or alkanols) are called organic matter, the molecules of which contain one or more hydroxyl groups (-OH groups) connected to a hydrocarbon radical.

Based on the number of hydroxyl groups (atomicity), alcohols are divided into:

Monatomic
dihydric (glycols)
triatomic.

The following alcohols are distinguished by their nature:

Saturated, containing only saturated hydrocarbon radicals in the molecule
unsaturated, containing multiple (double and triple) bonds between carbon atoms in the molecule
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.

Organic substances containing hydroxyl groups in the molecule, bonded directly to the carbon atom benzene ring, significantly differ in chemical properties from alcohols and therefore stand out in a separate class organic compounds- phenols. For example, hydroxybenzene phenol. We will learn more about the structure, properties and use of phenols later.

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

It should be noted that alcohols containing two hydroxyl groups on one carbon atom are unstable and spontaneously decompose (subject to rearrangement of atoms) to form aldehydes and ketones:

Unsaturated alcohols containing a hydroxyl group at the carbon atom connected by a double bond are called ecols. It is not difficult to guess that the name of this class of compounds is formed from the suffixes -en and -ol, indicating the presence of a double bond and a hydroxyl group in the molecules. Enols, as a rule, are unstable and spontaneously transform (isomerize) into carbonyl compounds - aldehydes and ketones. This reaction is reversible, the process itself is called keto-enol tautomerism. Thus, the simplest enol, vinyl alcohol, isomerizes extremely quickly into acetaldehyde.

Based on the nature of the carbon atom to which the hydroxyl group is bonded, alcohols are divided into:

Primary, in the molecules of which the hydroxyl group is bonded to the primary carbon atom
secondary, in the molecules of which the hydroxyl group is bonded to a secondary carbon atom
tertiary, in the molecules of which the hydroxyl group is bonded to a tertiary carbon atom, for example:

Nomenclature and isomerism

When naming alcohols, the (generic) suffix -ol is added to the name of the hydrocarbon corresponding to the alcohol. The numbers after the suffix indicate the position of the hydroxyl group in the main chain, and the prefixes di-, tri-, tetra-, etc. indicate their number:

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.

Roda, which is part of the hydroxyl group of alcohol molecules, differs sharply from hydrogen and carbon atoms in its ability to attract and hold electron pairs. Due to this, alcohol molecules contain polar C-O and O-H bonds.

Physical properties of alcohols

Given the polarity O-N connections and significant partial positive charge, localized (focused) on a hydrogen atom, the hydrogen of the hydroxyl group is said to be “acidic” in nature. In this way, it differs sharply from the hydrogen atoms included in the hydrocarbon radical.

It should be noted that the oxygen atom of the hydroxyl group has a partial negative charge and two lone electron pairs, which allows alcohols to form special, so-called hydrogen bonds between molecules. Hydrogen bonds occur when a partially positively charged hydrogen atom of one alcohol molecule interacts with a partially negatively charged oxygen atom of another molecule. It is thanks to hydrogen bonds between molecules that alcohols have boiling points that are abnormally high 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 a liquid.

The lower and middle members of a series of saturated monohydric alcohols, containing from one to eleven carbon atoms, are liquids. Higher alcohols (starting from C 12 H 25 OH) at room temperature - solids. Lower alcohols have a characteristic alcoholic odor and pungent taste; they are highly soluble in water. As the hydrocarbon radical increases, the solubility of alcohols in water decreases, and octanol no longer mixes with water.

Chemical properties

The properties of organic substances are determined by their composition and structure. Alcohols confirm general rule. Their molecules include hydrocarbon and hydroxyl radicals, therefore Chemical properties alcohols are determined by the interaction and influence of these groups on 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).

With water this interaction is much more active than with alcohol, is accompanied by a large release of heat, and can lead to an explosion. This difference is explained by the electron-donating properties of the radical closest to the hydroxyl group. Possessing the properties of an electron donor (+I-effect), the radical slightly increases the electron density on the oxygen atom, “saturates” it at its own expense, thereby reducing the polarity of the O-H bond and the “acidic” nature of the hydrogen atom of the hydroxyl group in alcohol molecules by compared to water molecules.

2. Interaction of alcohols with hydrogen halides. Substitution of a hydroxyl group with a halogen leads to the formation of haloalkanes.

For example:

C2H5OH + HBr<->C2H5Br + H2O

This reaction is reversible.

3. Intermolecular dehydration of alcohols - the splitting of 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 are formed. 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, the interaction of ethyl alcohol and acetic acid produces ethyl acetate - ethyl acetate:

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 is usually carried out with strong oxidizing agents, such as 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:

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:

The presence of several hydroxyl groups in the alcohol molecule at the same time is due to specific properties polyhydric alcohols that are capable of forming water-soluble bright blue complex compounds when interacting with a freshly obtained precipitate of copper(II) hydroxide.

Monohydric alcohols are not able to enter into this reaction. Therefore, it is a qualitative reaction to polyhydric alcohols.

Alcoholates of alkali and alkaline earth metals undergo hydrolysis when interacting with water. For example, when sodium ethoxide is dissolved in water, a reversible reaction occurs

C2H5ONa + HON<->C2H5OH + NaOH

the balance of which is almost completely shifted to the right. This also confirms that water is superior to alcohols in its acidic properties (the “acidic” nature of the hydrogen in the hydroxyl group). Thus, the interaction of alcoholates with water can be considered as the interaction of a salt of a very weak acid (in this case, the alcohol that formed the alcoholate acts as this) with a stronger acid (water plays this role here).

Alcohols can exhibit basic properties when reacting with strong acids, forming alkyloxonium salts due to the presence of a lone electron pair on the oxygen atom of the hydroxyl group:

The esterification reaction is reversible (the reverse reaction is ester hydrolysis), the equilibrium shifts to the right in the presence of water-removing agents.

Intramolecular dehydration of alcohols proceeds in accordance with Zaitsev's rule: when water is removed from a secondary or tertiary alcohol, a hydrogen atom is detached from the least hydrogenated carbon atom. Thus, dehydration of 2-butanol results in 2-butene rather than 1-butene.

Presence of alcohols in molecules hydrocarbon radicals cannot but affect the chemical properties of alcohols.

The chemical properties of alcohols caused by the hydrocarbon radical are different and depend on its nature. So, all alcohols burn; unsaturated alcohols containing a double C=C bond in the molecule enter into addition reactions, undergo hydrogenation, add hydrogen, react with halogens, for example, decolorize bromine water, etc.

Methods of obtaining

1. Hydrolysis of haloalkanes. You already know that the formation of haloalkanes when alcohols interact with hydrogen halogens is a reversible reaction. Therefore, it is clear that alcohols can be obtained by hydrolysis of haloalkanes - the reaction of these compounds with water.

Polyhydric alcohols can be obtained by hydrolysis of haloalkanes containing more than one halogen atom per molecule.

2. Hydration of alkenes - the addition of water at the tg bond of an alkene molecule - is already familiar to you. Hydration of propene leads, in accordance with Markovnikov’s rule, to the formation of a secondary alcohol - propanol-2

HE
l
CH2=CH-CH3 + H20 -> CH3-CH-CH3
propene propanol-2

3. Hydrogenation of aldehydes and ketones. You already know that the oxidation of alcohols under mild conditions leads to the formation of aldehydes or ketones. It is obvious that alcohols can be obtained by hydrogenation (reduction with hydrogen, addition of hydrogen) of aldehydes and ketones.

4. Oxidation of alkenes. Glycols, as already noted, can be obtained by oxidation of alkenes with an aqueous solution of potassium permanganate. For example, ethylene glycol (ethanediol-1,2) is formed by the oxidation of ethylene (ethene).

5. Specific methods for producing alcohols. Some alcohols are obtained using methods that are unique to them. Thus, methanol is produced industrially by the reaction of hydrogen with carbon monoxide (II) (carbon monoxide) at high blood pressure and high temperature on the surface of the catalyst (zinc oxide).

The mixture required for this reaction carbon monoxide and hydrogen, also called (think why!) “synthesis gas”, is obtained by passing water vapor over hot coal.

6. Fermentation of glucose. This method of producing ethyl (wine) alcohol has been known to man since ancient times.

Let's consider the reaction of producing alcohols from haloalkanes - the hydrolysis reaction of halogenated hydrocarbons. It is usually carried out in an alkaline environment. The released hydrobromic acid is neutralized, and the reaction proceeds almost to completion.

This reaction, like many others, proceeds through the mechanism of nucleophilic substitution.

These are reactions the main stage of which is substitution, which occurs under the influence of a nucleophilic particle.

Let us recall that a nucleophilic particle is a molecule or ion that has a lone electron pair and is capable of being attracted to a “positive charge” - regions of the molecule with a reduced electron density.

The most common nucleophilic species are ammonia, water, alcohol, or anions (hydroxyl, halide, alkoxide ion).

The particle (atom or group of atoms) that is replaced by a reaction with a nucleophile is called a leaving group.

The replacement of the hydroxyl group of an alcohol with a halide ion also occurs through the mechanism of nucleophilic substitution:

CH3CH2OH + HBr -> CH3CH2Br + H20

Interestingly, this reaction begins with the addition of a hydrogen cation to the oxygen atom contained in the hydroxyl group:

CH3CH2-OH + H+ -> CH3CH2- OH

Under the influence of the added positively charged ion, the bond S-O yet shifts more towards oxygen, the effective positive charge on the carbon atom increases.

This leads to the fact that nucleophilic substitution with a halide ion occurs much more easily, and a water molecule is split off under the action of a nucleophile.

CH3CH2-OH+ + Br -> CH3CH2Br + H2O

Preparation of ethers

When sodium alkoxide reacts with bromoethane, the bromine atom is replaced by an alkoxide ion and an ether is formed.

The nucleophilic substitution reaction in general can be written as follows:

R - X +HNu -> R - Nu +HX,

if the nucleophilic particle is a molecule (HBr, H20, CH3CH2OH, NH3, CH3CH2NH2),

R-X + Nu - -> R-Nu + X - ,

if the nucleophile is an anion (OH, Br-, CH3CH2O -), where X is a halogen, Nu is a nucleophilic particle.

Individual representatives of alcohols and their significance

Methanol (methyl alcohol CH3OH) 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 methods of its production - distillation of hard wood (Greek - wine, to get drunk; substance, wood).

Methanol is very poisonous! It 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 C2H5OH) 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.).

To make the alcohol used in 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 to produce synthetic rubber, medicines, used as a solvent, included in varnishes and paints, 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.

Propanetriol-1,2,3 (glycerol) 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.

1. What substances are called alcohols? By what criteria are alcohols classified? What alcohols should be classified as butanol-2? butene-Z-ol-1? penten-4-diol-1,2?

2. Write down the structural formulas of the alcohols listed in exercise 1.

3. Are there quaternary alcohols? Explain your answer.

4. How many alcohols have the molecular formula C5H120? Make up the structural formulas of these substances and name them. Can this formula only correspond to alcohols? Make up the structural formulas of two substances that have the formula C5H120 and are not alcohols.

5. Name the substances whose structural formulas are given below:

6. Write the structural and empirical formulas of a substance whose name is 5-methyl-4-hexen-1-inol-3. Compare the number of hydrogen atoms in the molecule of this alcohol with the number of hydrogen atoms in the molecule of an alkane with the same number of carbon atoms. What explains this difference?

7. Comparing the electronegativity of carbon and hydrogen, explain why the O-H covalent bond is more polar than S-O connection.

8. Which alcohol do you think - methanol or 2-methylpropanol-2 - will react more actively with sodium? Explain your answer. Write down equations for the corresponding reactions.

9. Write down reaction equations for the interaction of 2-propanol (isopropyl alcohol) with sodium and hydrogen bromide. Name the reaction products and indicate the conditions for their implementation.

10. A mixture of propanol-1 and propanol-2 vapors was passed over heated copper(P) oxide. What reactions could occur in this case? Write down equations for these reactions. What classes of organic compounds do their products belong to?

11. What products can be formed during the hydrolysis of 1,2-dichloropropanol? Write down equations for the corresponding reactions. Name the products of these reactions.

12. Write down equations for the reactions of hydrogenation, hydration, halogenation and hydrohalogenation of 2-propenol-1. Name the products of all reactions.

13. Write down equations for the interaction of glycerol with one, two and three moles of acetic acid. Write the equation for the hydrolysis of an ester - the product of the esterification of one mole of glycerol and three moles of acetic acid.

14*. When the primary saturated monohydric alcohol reacted with sodium, 8.96 liters of gas (n.e.) were released. When the same mass of alcohol is dehydrated, an alkene weighing 56 g is formed. Determine all possible structural formulas of the alcohol.

15*. Volume carbon dioxide, released during the combustion of saturated monohydric alcohol, is 8 times greater than the volume of hydrogen released during the action of excess sodium on the same amount of alcohol. Establish the structure of an alcohol if it is known that its oxidation produces a ketone.

Use of alcohols

Since alcohols have various properties, their area of ​​application is quite wide. Let's try to figure out where alcohols are used.

Alcohols in the food industry

Alcohol such as ethanol is the basis of all alcoholic beverages. And it is obtained from raw materials that contain sugar and starch. Such raw materials can be sugar beets, potatoes, grapes, as well as various cereals. Thanks to modern technologies When producing alcohol, it is purified from fusel oils.

Natural vinegar also contains ethanol-based raw materials. This product is obtained through oxidation by acetic acid bacteria and aeration.

But in the food industry they use not only ethanol, but also glycerin. This food additive promotes the connection of immiscible liquids. Glycerin, which is part of liqueurs, can give them viscosity and a sweet taste.

Also, glycerin is used in the manufacture of bakery, pasta and confectionery products.

Medicine

In medicine, ethanol is simply irreplaceable. In this industry, it is widely used as an antiseptic, as it has properties that can destroy microbes, delay painful changes in the blood and prevent decomposition in open wounds.

Ethanol is used by medical workers before performing various procedures. This alcohol has disinfecting and drying properties. During artificial ventilation of the lungs, ethanol acts as an antifoam. Ethanol can also be one of the components of anesthesia.

When you have a cold, ethanol can be used as a warming compress, and when cooling, as a rubbing agent, since its substances help restore the body during heat and chills.

In case of poisoning with ethylene glycol or methanol, the use of ethanol helps to reduce the concentration toxic substances and acts as an antidote.

Also huge role alcohols have pharmacological properties, as they are used to prepare medicinal tinctures and all kinds of extracts.

Alcohols in cosmetics and perfumes

In perfumery, it is also impossible to do without alcohol, since the basis of almost all perfume products is water, alcohol and perfume concentrate. Ethanol in this case acts as a solvent for fragrant substances. But 2-phenylethanol has a floral scent and can replace natural rose oil in perfumery. It is used in the manufacture of lotions, creams, etc.

Glycerin is also the base for many cosmetics, as it has the ability to attract moisture and actively moisturize the skin. And the presence of ethanol in shampoos and conditioners helps moisturize the skin and makes it easier to comb hair after washing your hair.

Fuel

Well, alcohol-containing substances such as methanol, ethanol and butanol-1 are widely used as fuel.

Thanks to the processing of plant materials such as sugar cane and corn, it was possible to obtain bioethanol, which is an environmentally friendly biofuel.

IN Lately Bioethanol production has become popular in the world. With its help, the prospect of renewing fuel resources appeared.

Solvents, surfactants

In addition to the applications of alcohols already listed, it can be noted that they are also good solvents. The most popular in this area are isopropanol, ethanol, and methanol. They are also used in the production of bit chemicals. Without them, proper care of a car, clothing, household utensils, etc. is not possible.

The use of alcohols in various areas of our activities has a positive effect on our economy and brings comfort to our lives.

DEFINITION

Alcohols– compounds containing one or more hydroxyl groups –OH associated with a hydrocarbon radical.

The general formula of the homologous series of saturated monohydric alcohols is C n H 2 n +1 OH. The names of alcohols contain the suffix – ol.

Depending on the number of hydroxyl groups, alcohols are divided into one- (CH 3 OH - methanol, C 2 H 5 OH - ethanol), two- (CH 2 (OH)-CH 2 -OH - ethylene glycol) and triatomic (CH 2 (OH )-CH(OH)-CH 2 -OH - glycerol). Depending on which carbon atom the hydroxyl group is located at, primary (R-CH 2 -OH), secondary (R 2 CH-OH) and tertiary alcohols (R 3 C-OH) are distinguished.

Saturated monohydric alcohols are characterized by isomerism of the carbon skeleton (starting from butanol), as well as isomerism of the position of the hydroxyl group (starting from propanol) and interclass isomerism with ethers.

CH 3 -CH 2 -CH 2 -CH 2 -OH (butanol – 1)

CH 3 -CH (CH 3) - CH 2 -OH (2-methylpropanol - 1)

CH 3 -CH (OH) -CH 2 -CH 3 (butanol - 2)

CH 3 -CH 2 -O-CH 2 -CH 3 (diethyl ether)

Chemical properties of alcohols

1. Reactions that occur with the rupture of the O-H bond:

— acid properties alcohols are very weakly expressed. Alcohols react with alkali metals

2C 2 H 5 OH + 2K → 2C 2 H 5 OK + H 2

but do not react with alkalis. In the presence of water, alcoholates are completely hydrolyzed:

C 2 H 5 OK + H 2 O → C 2 H 5 OH + KOH

This means that alcohols are weaker acids than water.

- formation of esters under the influence of mineral and organic acids:

CH 3 -CO-OH + H-OCH 3 ↔ CH 3 COOCH 3 + H 2 O

- oxidation of alcohols under the action of potassium dichromate or permanganate to carbonyl compounds. Primary alcohols are oxidized to aldehydes, which in turn can be oxidized to carboxylic acids.

R-CH 2 -OH + [O] → R-CH = O + [O] → R-COOH

Secondary alcohols are oxidized to ketones:

R-CH(OH)-R’ + [O] → R-C(R’) = O

Tertiary alcohols are more resistant to oxidation.

2. Reaction with breaking of the C-O bond.

- intramolecular dehydration with the formation of alkenes (occurs when alcohols with water-removing substances (concentrated sulfuric acid) are strongly heated):

CH 3 -CH 2 -CH 2 -OH → CH 3 -CH = CH 2 + H 2 O

— intermolecular dehydration of alcohols with the formation of ethers (occurs when alcohols are slightly heated with water-removing substances (concentrated sulfuric acid)):

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

— weak basic properties of alcohols manifest themselves in reversible reactions with hydrogen halides:

C 2 H 5 OH + HBr → C 2 H 5 Br + H 2 O

Physical properties of alcohols

Lower alcohols (up to C 15) are liquids, higher alcohols are solids. Methanol and ethanol are mixed with water in any ratio. As the molecular weight increases, the solubility of alcohols in alcohol decreases. Alcohols have high boiling and melting points due to the formation of hydrogen bonds.

Preparation of alcohols

The production of alcohols is possible using a biotechnological (fermentation) method from wood or sugar.

Laboratory methods for producing alcohols include:

- hydration of alkenes (the reaction occurs when heated and in the presence of concentrated sulfuric acid)

CH 2 = CH 2 + H 2 O → CH 3 OH

— hydrolysis of alkyl halides under the influence of aqueous solutions of alkalis

CH 3 Br + NaOH → CH 3 OH + NaBr

CH 3 Br + H 2 O → CH 3 OH + HBr

— reduction of carbonyl compounds

CH 3 -CH-O + 2[H] → CH 3 – CH 2 -OH

Examples of problem solving

EXAMPLE 1

Exercise	The mass fractions of carbon, hydrogen and oxygen in the molecule of saturated monohydric alcohol are 51.18, 13.04 and 31.18%, respectively. Derive the formula of alcohol.
Solution	Let us denote the number of elements included in the alcohol molecule by the indices x, y, z. Then, the formula of alcohol in general will look like C x H y O z. Let's write down the ratio: x:y:z = ω(С)/Ar(C): ω(Н)/Ar(Н) : ω(О)/Ar(О); x:y:z = 51.18/12: 13.04/1: 31.18/16; x:y:z = 4.208: 13.04: 1.949. Let's divide the resulting values ​​by the smallest, i.e. at 1.949. We get: x:y:z = 2:6:1. Therefore, the formula of alcohol is C 2 H 6 O 1. Or C 2 H 5 OH is ethanol.
Answer	The formula of saturated monohydric alcohol is C 2 H 5 OH.

Goals:

Educational: familiarize students with the classification of alcohols, their nomenclature and isomerism. Consider the influence of the structure of alcohols on their properties. Developmental: Strengthen skills of working in groups, develop skills for finding relationships between new and studied material. Educational: developing teamwork skills Student - student, Student - teacher. Be able to analyze the information received.

Lesson type: Combined

Organizational form: frontal survey, laboratory work, independent work, conversation on problematic issues, analysis of the information received.

Equipment:

1. Set of slides ( Annex 1) tables, individual sheets with tasks for independent work, assignment for laboratory work.
2. On student tables: bottles with alcohols (ethyl, isopropyl, glycerin), sodium, copper oxide (2), acetic acid, phenolphthalein, potassium permanganate, sand, sodium hydroxide, hydrochloric acid, tap water, chemical glassware, safety regulations.

Lesson plan:

1. 1.Definition of the class of alcohols, the structure of the molecule of monohydric saturated alcohols.
2. Classification of alcohols according to three criteria.
3. Nomenclature of alcohols.
4. Types of isomerism of monohydric saturated alcohols.
5. Physical properties alcohols The influence of hydrogen bonding on the physical properties of alcohols.

2. 6.Chemical properties.
7. Consolidation of new material.

DURING THE CLASSES

I. Organizational moment

Teacher: We have completed the study of a large class of organic compounds consisting of only two chemical elements - carbon and hydrogen. What else chemical elements most often found in organic compounds?

Student: Oxygen, nitrogen, phosphorus, sulfur and others.

II. Learning new material

Teacher: We are beginning to study a new class of organic compounds, which, in addition to carbon and hydrogen, include oxygen. They are called oxygen-containing. (Slide No. 1).
As we see, there are several classes of organic compounds consisting of carbon, hydrogen and oxygen. Today we are starting to study a class called “Alcohols”. Alcohol molecules contain a hydroxyl group, which is the functional group (FG) for this class. What do we call FG? (Slide No. 1).

Student: A group of atoms (or an atom) that determines whether a compound belongs to a certain class and determines its most important chemical properties is called a FG.

Teacher: Alcohols, a large class of organic compounds in terms of diversity and properties, are widely used in various areas National economy. (Slides No. 2-8)
As we see, this is pharmaceuticals, cosmetics production, food industry, and also as a solvent in the production of plastics, varnishes, paints, etc. Let's look at the table.

Table 1.

SOME IMPORTANT REPRESENTATIVES OF THE CLASS OF ALCOHOLS

Teacher: If we talk about the effect on the human body, then all alcohols are poisons. Alcohol molecules have a detrimental effect on living cells. (Slide No. 9) Spit - alkanes have an outdated name for alcohol. Alcohols are derivatives of hydrocarbons in which one or more hydrogen atoms are replaced by hydroxyl groups - OH.
In the very simple case The structure of alcohol can be expressed by the following formula:

R–OH,

where R is a hydrocarbon radical.

Alcohols can be classified according to three criteria:

1. The number of hydroxyl groups (monoatomic, diatomic, polyatomic).

Table 2.

CLASSIFICATION OF ALCOHOLS ACCORDING TO THE NUMBER OF HYDROXYL GROUPS (–OH)

2. The nature of the hydrocarbon radical (saturated, unsaturated, aromatic).

Table 3.

CLASSIFICATION OF ALCOHOLS BY NATURE OF RADICAL

3. The nature of the carbon atom to which the hydroxyl group is connected (primary, secondary, tertiary)

Table 4.

CLASSIFICATION OF ALCOHOLS BY THE CHARACTER OF THE CARBON ATOM ASSOCIATED WITH THE FUNCTIONAL GROUP –OH

There are no quaternary alcohols because the quaternary C atom is bonded to 4 other C atoms, so there are no more valences to bind to the hydroxyl group.

Let's consider the basic principles of constructing the names of alcohols according to the substitutive nomenclature, using the scheme:

Name of alcohol = name HC + (prefix) + - OL +(n1, n2 ..., nn), where prefix denotes the number of –OH groups in the molecule: 2 – “di”, 3 – “three”, 4 – “tetra”, etc.
n indicates the position of hydroxyl groups in the carbon chain, for example:

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

In our school course we will study in detail monohydric saturated alcohols with the general formula: CnH2n+1OH

Let's consider models of molecules of individual representatives of these alcohols (methyl, ethyl, glycerol). (Slides No. 10-13)

Homologous series of these alcohols starts with methyl alcohol:

CH3 – OH – methyl alcohol
CH3 – CH2 – OH – ethyl alcohol
CH3 – CH2 – CH2 – OH – propyl alcohol
CH3 – CH2 – CH2 – CH2 – OH – butyl alcohol
CH3 – CH2 – CH2 – CH2 – CH2 – OH – amyl alcohol or pentanol

Isomerism

The following are characteristic of saturated monohydric alcohols: types of isomerism:

1) positions of functional groups

2) carbon skeleton.

Please note– numbering of carbon atoms begins from the end close to the –OH group.

3) interclass isomerism (with ethers R – O – R)

Physical properties of alcohols

The first ten members of the homologous series of representatives of monohydric alcohols are liquids, higher alcohols are solids. (Slides 14, 15)
The hydrogen bond formed between alcohol molecules has a strong influence on the physical properties of alcohols. You are familiar with hydrogen bonding from the 9th grade program, topic “Ammonia”. Now your classmate, who received an individual assignment in the last lesson, will remind us what a hydrogen bond is.

Student answer

A hydrogen bond is a bond between the hydrogen atoms of one molecule and the highly electronegative atoms of another molecule. (F, O, N, CL). On the letter it is indicated by three dots. (Slides 16,17). Hydrogen bond is special kind intermolecular bonding, which is weaker than normal covalent bond 10-20 times, but it has a great influence on the physical properties of the compounds.
Two consequences of hydrogen bonding: 1) good solubility of substances in water; 2) increase in melting and boiling points. For example: the dependence of the boiling point of some compounds on the presence of a hydrogen bond.

Teacher: What conclusions can we draw about the effect of hydrogen bonding on the physical properties of alcohols?

Students: 1) In the presence of a hydrogen bond, the boiling point increases greatly.
2) The higher the atomicity of the alcohol, the more hydrogen bonds are formed.

This also helps to increase the boiling point.

CHEMICAL PROPERTIES OF ALCOHOLS

(Repeat PTB)

Burning of alcohols.

2. Interaction of alcohols with alkali metals.

3. Oxidation of alcohols ( qualitative reaction) - production of aldehydes.

4. The interaction of alcohols with acids to form esters (esterification reaction).

5. Intramolecular dehydration of alcohols with the formation of unsaturated hydrocarbons.

6. Intermolecular dehydration of alcohols to form ethers.

7. Dehydrogenation of alcohols - obtaining aldehydes.

Teacher: write a five-line poem (Cinquain)

1st keyword

2nd two adjectives

3rd three verbs

4th sentence

5th word associated with the keyword.

Student. Alcohols.

Poisonous, liquid

They strike, they destroy, they destroy

They have a narcotic effect on the human body.

Drugs.

IV. Homework: paragraph No. 9, pp. 66-70 ex. No. 13 b.

Individual tasks. Using additional literature: 1) talk about the areas of application of glycerin and ethylene glycol; 2) talk about the production of alcohols from cellulose and fats; 3) how do these alcohols act on the human body?

V. Lesson summary Let's sum it up in the form of doing independent work in two options

Literature:

1. Chemistry 10th grade. Textbook for general education educational institutions. Bustard Moscow 2008. Basic level. 4th ed. stereotypical.
2. Chemistry 100 class workbook to the textbook. A basic level of. Bustard, 2007.
3. Lesson developments in chemistry. To the textbooks of O. S. Gabrielyan, . Grade 10
4. , . Chemistry 9th grade Smolensk Association XXI century 2006
5. . CHEMISTRY. New school aid for applicants to universities. Ed. 4th, corrected and supplemented. Rostov-on-Don. Phoenix 2007.

Ethyl alcohol or wine alcohol is a widespread representative of alcohols. There are many known substances that contain oxygen, along with carbon and hydrogen. Among the oxygen-containing compounds, I am primarily interested in the class of alcohols.

Ethanol

Physical properties of alcohol . Ethyl alcohol C 2 H 6 O is a colorless liquid with a peculiar odor, lighter than water (specific gravity 0.8), boils at a temperature of 78 °.3, and dissolves well many inorganic and organic substances. Rectified alcohol contains 96% ethyl alcohol and 4% water.

The structure of the alcohol molecule .According to the valency of the elements, the formula C 2 H 6 O corresponds to two structures:

To resolve the question of which of the formulas actually corresponds to alcohol, let us turn to experience.

Place a piece of sodium in a test tube with alcohol. A reaction will immediately begin, accompanied by the release of gas. It is not difficult to establish that this gas is hydrogen.

Now let’s set up the experiment so that we can determine how many hydrogen atoms are released during the reaction from each alcohol molecule. To do this, add a certain amount of alcohol, for example 0.1 gram molecule (4.6 grams), drop by drop from a funnel to a flask with small pieces of sodium (Fig. 1). The hydrogen released from the alcohol displaces water from the two-necked flask into the measuring cylinder. The volume of displaced water in the cylinder corresponds to the volume of released hydrogen.

Fig.1. Quantitative experience in producing hydrogen from ethyl alcohol.

Since 0.1 gram molecules of alcohol were taken for the experiment, it was possible to obtain hydrogen (in terms of normal conditions) about 1.12 liters This means that sodium displaces 11.2 from a gram molecule of alcohol liters, i.e. half a gram molecule, in other words 1 gram atom of hydrogen. Consequently, sodium displaces only one hydrogen atom from each alcohol molecule.

Obviously, in the alcohol molecule, this hydrogen atom is in a special position compared to the other five hydrogen atoms. Formula (1) does not explain this fact. According to it, all hydrogen atoms are equally bonded to carbon atoms and, as we know, are not displaced by metallic sodium (sodium is stored in a mixture of hydrocarbons - in kerosene). On the contrary, formula (2) reflects the presence of one atom located in a special position: it is connected to carbon through an oxygen atom. We can conclude that it is this hydrogen atom that is less tightly bound to the oxygen atom; it turns out to be more mobile and is replaced by sodium. Hence, structural formula ethyl alcohol:

Despite the greater mobility of the hydrogen atom of the hydroxyl group compared to other hydrogen atoms, ethyl alcohol is not an electrolyte and aqueous solution does not dissociate into ions.

To emphasize that the alcohol molecule contains a hydroxyl group - OH, connected to a hydrocarbon radical, the molecular formula of ethyl alcohol is written as follows:

Chemical properties of alcohol . We saw above that ethyl alcohol reacts with sodium. Knowing the structure of alcohol, we can express this reaction with the equation:

The product of replacing hydrogen in alcohol with sodium is called sodium ethoxide. It can be isolated after the reaction (by evaporation of excess alcohol) as a solid.

When ignited in air, alcohol burns with a bluish, barely noticeable flame, releasing a lot of heat:

If you heat ethyl alcohol with a hydrohalic acid, for example with HBr, in a flask with a refrigerator (or a mixture of NaBr and H 2 SO 4, which gives hydrogen bromide during the reaction), then an oily liquid will be distilled off - ethyl bromide C 2 H 5 Br:

This reaction confirms the presence of a hydroxyl group in the alcohol molecule.

When heated with concentrated sulfuric acid as a catalyst, the alcohol easily dehydrates, that is, it splits off water (the prefix “de” indicates the separation of something):

This reaction is used to produce ethylene in the laboratory. When alcohol is heated weaker with sulfuric acid (not higher than 140°), each molecule of water is split off from two molecules of alcohol, resulting in the formation of diethyl ether - a volatile, flammable liquid:

Diethyl ether (sometimes called sulfuric ether) is used as a solvent (tissue cleaning) and in medicine for anesthesia. He belongs to the class ethers - organic substances whose molecules consist of two hydrocarbon radicals connected through an oxygen atom: R - O - R1

Use of ethyl alcohol . Ethyl alcohol has a large practical significance. A lot of ethyl alcohol is consumed to produce synthetic rubber using the method of Academician S.V. Lebedev. By passing ethyl alcohol vapor through a special catalyst, divinyl is obtained:

which can then polymerize into rubber.

Alcohol is used to produce dyes, diethyl ether, various “fruit essences” and a number of other organic substances. Alcohol as a solvent is used to make perfumes and many medicines. Various varnishes are prepared by dissolving resins in alcohol. High calorific value alcohol determines its use as a fuel (motor fuel = ethanol).

Obtaining ethyl alcohol . World alcohol production is measured in millions of tons per year.

A common method for producing alcohol is the fermentation of sugary substances in the presence of yeast. These lower plant organisms (fungi) produce special substances - enzymes, which serve as biological catalysts for the fermentation reaction.

Cereal seeds or potato tubers rich in starch are taken as starting materials in the production of alcohol. Starch is first converted into sugar using malt containing the enzyme diastase, which is then fermented into alcohol.

Scientists have worked hard to replace food raw materials for alcohol production with cheaper non-food raw materials. These searches were crowned with success.

Recently, due to the fact that when cracking oil a lot of ethylene is formed, steel

The reaction of ethylene hydration (in the presence of sulfuric acid) was studied by A. M. Butlerov and V. Goryainov (1873), who also predicted its industrial significance. A method of direct hydration of ethylene by passing it in a mixture with water vapor over solid catalysts has also been developed and introduced into industry. Producing alcohol from ethylene is very economical, since ethylene is part of the cracking gases of oil and other industrial gases and, therefore, is a widely available raw material.

Another method is based on the use of acetylene as the starting product. Acetylene undergoes hydration according to the Kucherov reaction, and the resulting acetaldehyde is catalytically reduced with hydrogen in the presence of nickel into ethyl alcohol. The entire process of acetylene hydration followed by reduction with hydrogen on a nickel catalyst into ethyl alcohol can be represented by a diagram.

Homologous series of alcohols

In addition to ethyl alcohol, other alcohols are known that are similar to it in structure and properties. All of them can be considered as derivatives of the corresponding saturated hydrocarbons, in the molecules of which one hydrogen atom is replaced by a hydroxyl group:

Table

Hydrocarbons	Alcohols	Boiling point of alcohols in º C
Methane CH 4	Methyl CH 3 OH	64,7
Ethane C 2 H 6	Ethyl C 2 H 5 OH orCH 3 - CH 2 - OH	78,3
Propane C 3 H 8	Propyl C 4 H 7 OH or CH 3 - CH 2 - CH 2 - OH	97,8
Butane C 4 H 10	Butyl C 4 H 9 OH orCH 3 - CH 2 - CH 2 - OH	117

Being similar in chemical properties and differing from each other in the composition of the molecules by a group of CH 2 atoms, these alcohols form a homologous series. Comparing the physical properties of alcohols, in this series, as well as in the series of hydrocarbons, we observe the transition of quantitative changes into qualitative changes. The general formula of alcohols in this series is R - OH (where R is a hydrocarbon radical).

Alcohols are known whose molecules contain several hydroxyl groups, for example:

Groups of atoms that determine the characteristic chemical properties of compounds, i.e., their chemical function, are called functional groups.

Alcohols are organic substances whose molecules contain one or more functional hydroxyl groups connected to a hydrocarbon radical .

In their composition, alcohols differ from hydrocarbons corresponding to them in the number of carbon atoms by the presence of oxygen (for example, C 2 H 6 and C 2 H 6 O or C 2 H 5 OH). Therefore, alcohols can be considered as products of partial oxidation of hydrocarbons.

Genetic relationship between hydrocarbons and alcohols

It is quite difficult to directly oxidize hydrocarbons into alcohol. In practice, it is easier to do this through a halogen derivative of a hydrocarbon. For example, to obtain ethyl alcohol starting from ethane C 2 H 6, you can first obtain ethyl bromide by the reaction:

and then convert ethyl bromide into alcohol by heating with water in the presence of alkali:

In this case, an alkali is needed to neutralize the resulting hydrogen bromide and eliminate the possibility of its reaction with alcohol, i.e. move this reversible reaction to the right.

In a similar way, methyl alcohol can be obtained according to the following scheme:

Thus, hydrocarbons, their halogen derivatives and alcohols are in a genetic connection with each other (relationship by origin).