Isomers c2n5on. The structure of saturated monohydric alcohols

Glycols. Hydroxyl groups in glycols are found at various carbon atoms. Glycols with two hydroxyls at one carbon atom are unstable. They split off water to form aldehydes or ketones.

Isomerism of glycols is determined by the mutual arrangement of hydroxyl groups and the isomerism of the carbon skeleton. Depending on the relative position of the OH– groups, there are α-, β-, γ-, δ-, ... glycols. Depending on the nature of the carbon atoms carrying hydroxyls, glycols can be primary-secondary, primary-tertiary, two-primary, two-secondary, etc.

Glycol names can be given in two ways. According to the IUPAC nomenclature, the suffix is added to the name of the main carbon chain –Diol and indicate the carbon numbers of the longest carbon chain bearing hydroxyl groups. Names α- glycols can be derived from the name of the corresponding ethylene carbon with the addition of the word glycol... The classification and names of glycols are given below for butanediols:

Methods of obtaining. In principle, glycols can be obtained by all conventional synthetic methods for preparing alcohols.

An example is the following reactions.

- Hydrolysis of dihalogenated derivatives of saturated hydrocarbons and halogenhydrins:

- Hydration α -oxides in an acidic environment:

- Oxidation of olefins potassium permanganate in a dilute aqueous weakly alkaline solution (Wagner reaction) or hydrogen peroxide in the presence of catalysts (CrO 3):

Physical properties. Lower glycols are readily soluble in water. Their density is higher than that of monohydric alcohols. Accordingly, the boiling point is also higher due to the significant association of molecules: for example, ethylene glycol boils at a temperature of 197.2 ° C; propylene glycol at 189 ° C and butanediol-1,4 at 230 ° C.

Chemical properties. Everything said earlier about the properties of the corresponding monohydric alcohols is also applicable to glycols. It should be remembered that both one hydroxyl can enter into the reaction, or both at once. - Oxidation of two-primary glycols gives aldehydes:

- During oxidation α- glycols with iodic acid the bond between the carbon atoms carrying the hydroxyls is broken, and the corresponding aldehydes or ketones are formed:

The method is of great importance for establishing the structure α- glycols.

-Results intramolecular elimination of water glycols to a large extent depend on the type of glycol.

Dehydration of α-glycols proceeds with the formation of aldehydes or ketones, γ-glycols due to the atoms of hydroxyl groups, water is eliminated with the formation of heterocyclic compounds - tetrahydrofuran or its homologues:

The first reaction proceeds through the formation of a carbonium ion, followed by the movement of a hydrogen atom with its electron pair:

At vapor phase dehydration over Al 2 O 3 α- two-tertiary glycols, called pinacons, diene hydrocarbons are obtained:

– Intermolecular dehydration leads to the formation of hydroxyesters or cyclic ethers:

The boiling point of diethylene glycol is 245.5 ° C. It is used as a solvent for filling brake hydraulic systems, when finishing and dyeing fabrics.

Among cyclic ethers, dioxane is most widely used as a solvent. It was obtained for the first time by A.E. Favorsk heating ethylene glycol with sulfuric acid:

Ethylene glycol Is a viscous, colorless liquid, sweetish in taste, bale t = 197.2 ° C. It is produced on an industrial scale from ethylene in three ways.

Ethylene glycol mixed with water greatly lowers its freezing point. For example, 60% aqueous glycol solution freezes at -49 ° C and is successfully used as antifreeze... The high hygroscopicity of ethylene glycol is used for the preparation of printing inks. A large amount of ethylene glycol is used to obtain film-forming materials, varnishes, paints, synthetic fibers (for example, lavsan - polyethylene terephthalate), dioxane, diethylene glycol and other products.

Polyhydric alcohols

Polyhydric alcohols are alcohols with several hydroxyl groups OH.
Polyhydric alcohols with a small number of carbon atoms are viscous liquids, while higher alcohols are solids. Polyhydric alcohols can be obtained by the same synthetic methods as saturated polyhydric alcohols.

1. Obtaining ethyl alcohol (or wine alcohol) by fermentation of carbohydrates:
C2H12O6 => C2H5-OH + CO2

The essence of fermentation lies in the fact that one of the simplest sugars - glucose, obtained in technology from starch, under the influence of yeast fungi decomposes into ethyl alcohol and carbon dioxide. It has been established that the fermentation process is caused not by the microorganisms themselves, but by the substances they release - zymases. To obtain ethyl alcohol, plant materials rich in starch are usually used: potato tubers, grain grains, rice grains, etc.

2. Hydration of ethylene in the presence of sulfuric or phosphoric acid
CH2 = CH2 + KOH => C2H5-OH

3. In the reaction of haloalkanes with alkali:

4. In the reaction of oxidation of alkenes

5. Hydrolysis of fats: this reaction produces the well-known alcohol - glycerin

Properties of alcohols

1) Combustion: Like most organic substances, alcohols burn with the formation of carbon dioxide and water:
C2H5-OH + 3O2 -> 2CO2 + 3H2O
When they burn, a lot of heat is released, which is often used in laboratories. Lower alcohols burn with an almost colorless flame, while higher alcohols have a yellowish flame due to incomplete combustion of carbon.

2) Reaction with alkali metals
C2H5-OH + 2Na -> 2C2H5-ONa + H2
In this reaction, hydrogen is released and sodium alcoholate is formed. Alcoholates are similar to very weak acid salts and are readily hydrolyzed. Alcoholates are extremely unstable and, when exposed to water, decompose into alcohol and alkali.

3) Reaction with hydrogen halide C2H5-OH + HBr -> CH3-CH2-Br + H2O
This reaction forms a haloalkane (bromoethane and water). This chemical reaction of alcohols is due not only to the hydrogen atom in the hydroxyl group, but also to the entire hydroxyl group! But this reaction is reversible: for its course you need to use a dehydrating agent, such as sulfuric acid.

4) Intramolecular dehydration (in the presence of H2SO4 catalyst)

The elimination of a hydrogen atom from alcohol can occur in its own. This reaction is an intermolecular dehydration reaction. For example, like this:

During the reaction, ether and water are formed.

5) reaction with carboxylic acids:

If you add a carboxylic acid, for example, acetic acid, to the alcohol, an ether will form. But esters are less stable than ethers. While the ether formation reaction is almost irreversible, the ester formation is a reversible process. Esters are easily hydrolyzed, decomposing into alcohol and carboxylic acid.

6) Oxidation of alcohols. Alcohols are not oxidized by oxygen in the air at normal temperatures, but when heated in the presence of catalysts, oxidation occurs. An example is copper oxide (CuO), potassium permanganate (KMnO4), chromium mixture. Under the action of oxidants, various products are obtained and depend on the structure of the initial alcohol. Thus, primary alcohols are converted to aldehydes (reaction A), secondary alcohols - into ketones (reaction B), and tertiary alcohols are resistant to oxidants.
- a) for primary alcohols

- b) for secondary alcohols

- c) tertiary alcohols are not oxidized by copper oxide!

As for polyhydric alcohols, they have a sweetish taste, but some of them are poisonous. The properties of polyhydric alcohols are similar to monohydric alcohols, with the difference that the reaction proceeds not one by one to the hydroxyl group, but several at once.
One of the main differences is that polyhydric alcohols easily react with copper hydroxide. This results in a clear solution of bright blue-violet color. It is this reaction that can reveal the presence of polyhydric alcohol in any solution.
Interact with nitric acid:

Ethylene glycol is a typical representative of polyhydric alcohols. Its chemical formula is CH2OH - CH2OH. - dihydric alcohol. It is a sweet liquid that dissolves perfectly in water in any proportion. Chemical reactions can involve either one hydroxyl group (-OH), or two at the same time. Ethylene glycol - its solutions - is widely used as an anti-icing agent (antifreeze). The ethylene glycol solution freezes at a temperature of -340C, which in the cold season can replace water, for example, for cooling cars.
For all the benefits of ethylene glycol, one must take into account, it is a very strong poison!

Municipal budgetary educational institution

"Novoshimkus secondary school

Yalchik region of the Chuvash Republic "

Abstract open lesson in chemistry
in 10th grade

« The structure of saturated monohydric alcohols.

Isomerism and nomenclature»

Prepared by a chemistry teacher

with. New Shimkus

Motto: To know the invisible,

Look closely at what you see.

(Ancient wisdom)

Target: Familiarization of students with the structure of saturated monohydric alcohols, with isomerism and nomenclature , the influence of alcohols on a living organism.

Tasks:

educational:

chemical experiment

developing:

logical thinking

educational

Equipment and reagents:

supporting notes, reagents (water, ethyl alcohol, egg white solution), laboratory equipment; multimedia projector, screen, computer; disk "Lessons of chemistry by Cyril and Methodius. Grade 10-11".

During the classes:

Organizing time. Repetition of the main classes of hydrocarbons - exercises, chemical dictation. Learning new material.

3.1. Statement of the cognitive task of the lesson.

3.2. The concept of alcohols: composition and structure of alcohols.

3.3. Nomenclature of alcohols and classification of alcohols.

3.4. Isomerism of alcohols.

3.5. Group work.

3.6. Student's speech "The effect of ethanol on the human body."

4. Fastening.

5. Reflection.

6.Homework par. 20, exercise. 5-7, p. 88

1. Organizational moment.

2. Repetition of the composition and properties of hydrocarbons.

What hydrocarbons are the riddles talking about?

We are similar in properties to alkenes

We also interact with bromine water.
In P-bond molecules - punishment,
Our suffix -in will tell you the name ... (Alkyne)

upper class

Now let's do a little chemical dictation.

The teacher reads the statement, can selectively ask any student to explain their answer. The dictation is carried out in writing, the work of students is organized in pairs. One of the students completes the task at the blackboard, the other works on the computer, passes the test.

1. The names have the suffix - an. (Alkanes)

(2) They are characterized by sp2 hybridization of atomic orbitals. (Alkenes, dienes,)

3. The molecules contain only sigma - bonds. (Alkanes, cycloalkanes)

4. There is one double bond in the molecules. (Alkenes)

5. A cyclic fragment is required in the molecule. (Cycloalkanes)

6. They are characterized by sp-hybridization of atomic orbitals (Alkyne)

7. The general formula of these hydrocarbons is СН2п. (Alkenes, cycloalkanes)

8. They are characterized mainly by substitution reactions. (Alkanes, cycloalkanes)

9. There is always a triple bond in molecules. (Alkyne)

10. The names have the suffix -in (Alkyne)

o Select structural formulas homologues and isomers of butene-1 and give them names:

3. Statement of the cognitive task of the lesson.

We are not simple substances
And they have been known since ancient times.
In medicine, the following are applicable:
Fight back infection.
We are not so simple in properties,
And we are called ... (alcohols)

So, the topic of our lesson today is -

“The structure of saturated monohydric alcohols. Isomerism and nomenclature ”.

Today we will get acquainted with the composition, structure, isomerism and nomenclature of these compounds. We will also find out what alcohols are and what dangers may be hidden in the physical properties of alcohols.

4. Composition and structure of alcohols.

Task: The substance has been known to man since ancient times.Its name means since Arabic"Intoxicating". It is widely used in various areas of the national economy. Possesses disinfectant properties. What substance are we talking about if it is known that during the combustion of 3.45 g of it, 6.6 g of CO2 and water weighing 4.05 g were formed? The vapor density of this substance in the air is 1.59. (The answer is ethanol C2H5OH.)

The general formula of all monohydric alcohols is СН2п + 1ОН or ROH. Let us consider the structure of an alcohol molecule using the example of C2H5OH - ethyl alcohol.

One of the hydrogen atoms is different from other atoms. (Student question - Why?) It is connected to a carbon atom through oxygen. Hence, it can be assumed that it will behave differently. What is this assumption based on? You will answer this question yourself, since you know that oxygen has a higher electronegativity. It will pull off the electrons of the hydrogen atom. Communication O-N turns out to be polar. This is indicated by a directional arrow:

O  N. It is this group - OH in alcohols and will determine their chemical properties, that is, their chemical function. Such groups are called functional.

Functional is called a group of atoms that determines the chemical properties of a substance.

What remains in the alcohol molecule after mentally removing the functional group is called a hydrocarbon radical.

Now we can deduce the definition of alcohols ... (students themselves formulate, suggest different variants determination of alcohols)

Alcohols organic substances are called, the molecules of which contain one or more functional hydroxyl groups attached to a hydrocarbon radical.

Alcohols - these are derivatives of hydrocarbons, in the molecules of which one or more hydrogen atoms are replaced by functional (hydroxyl) groups.

Alcohols Are organic compounds, the molecules of which contain one or more hydroxyl groups connected to a hydrocarbon radical.

5.Nomenclature of alcohols .

Trivial nomenclature- the names of alcohols come from the names of radicals:

CH3OH - methyl alcohol. (С2Н5ОН, С3Н7ОН - they are called independently.)

Systematic nomenclature- the names of alcohols are formed from the names of saturated hydrocarbons by adding the suffix - ol:

CH3OH - methanol.

Basic principles of the nomenclature of alcohols:

The longest carbon chain is selected and numbered from the end of the chain to which the hydroxo group is closer. Substituents in the main carbon chain are named and their positions are indicated by numbers. Name the backbone alkane and add the suffix -ol. The position of the OH group is indicated by a number.

(Students complete the assignment on the nomenclature of alcohols on the chalkboard.)

Task on the board: Name the alcohols by the systematic nomenclature:

6. Classification of alcohols . ( Cyril and Methodius disc )

(On the students' tables - a scheme for the classification of alcohols)

Alcohols are classified in different ways.

alcohols are: limit unsaturated aromatic

There are alcohols: monatomic diatomic triatomic

3. By the nature of the carbon atom. Depending on the valence of the alcohol group alcohols are: primary - contain a monovalent alcohol group - CH2OH (for example, CH3-CH2OH ethanol); secondary - contain a divalent alcohol group = CHOH (for example, CH3-CHOH-CH3 propanol-2); tertiary - contain a trivalent alcohol group = C-OH (for example, 2-methylbutanol-2:

(From the formulas presented earlier, students find alcohols, formulas for alcohols of different classifications)

Exercise 1 ... Which of the following alcohols are: a) primary; b) secondary; c) tertiary?

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Task 3.

(On the students' tables there is a diagram of the types of isomerism of alcohols; the concepts of “isomer” and “isomerism” are repeated.)

7. Isomerism of alcohols

The following types of isomerism are characteristic of alcohols:

Carbon skeleton isomerism

For example,

Interclass isomerism

For example,

Exercise:

8 group work (5 groups work. Group 1 - builders make a ball-and-stick model of ethanol and methanol. Group 2 - practitioners, exploring the physical properties of ethanol. Group 3 - theorists, using additional information, talk about methyl alcohol. Group 4 - theorists, using additional information, talks about ethyl alcohol. Group 5 - practitioners exploring the effect of ethanol on protein molecules) Each group answers the questions posed.

9. Student presentation "The influence of ethanol on the human body."

4. Anchoring.

5. Reflection. What new things did you learn from today's lesson? Where can you apply the acquired knowledge in practice? Did you like our lesson? Why?

6. Homework. Par. 20. ex. 5,6,7. Page 88.

С2Н5ОН is a drug. Under the influence of ethanol, a person's attention is weakened, the reaction is inhibited, the correlation of movements is disturbed. Causes profound disturbances with prolonged use nervous system, diseases of the cardiovascular system, digestive tract, a serious illness occurs - alcoholism.

Classification of alcohols.

1.By the nature of the hydrocarbon radical alcohols are: limit - the hydrocarbon radical contains only single bonds (for example, CH3OH methanol, C4H9OH butanol); unsaturated - contain an unsaturated hydrocarbon radical (for example, CH2 = CH-CH2OH allyl alcohol); aromatic - contain an aromatic hydrocarbon radical (for example, C6H5-CH2OH benzyl alcohol).

2. By the number of hydroxyl groups there are alcohols: monatomic - contain one OH-group (for example, CH3-CH2-OH ethanol); diatomic - contain two OH-groups (for example, HO-CH2-CH2-OH ethylene glycol or ethanediol-1,2); triatomic - contain three OH groups in the molecule (for example, HO-CH2-CHOH-CH2-OH glycerin or propanetriol-1,2,3).

Carbon skeleton isomerism

For example,

Functional group position isomerism

For example,

Interclass isomerism: Alcohols are isomeric to ethers.

For example,

(Students complete the assignment on separate cards.)

Exercise: Find the isomers of pentanol-1 among the given formulas and determine the type of isomerism. Give names to all compounds:

Task 3. Write down all possible isomers of C4H9OH.

Alcohols refers to compounds containing one or more hydroxyl groups directly linked to a hydrocarbon radical.

Classification of alcohols

Alcohols are classified according to various structural characteristics.

1. By the number of hydroxyl groups, alcohols are subdivided into

o monatomic(one group -OH)

For example, CH 3 – OH methanol,CH 3 – CH 2 – OH ethanol

o polyatomic(two or more groups -OH).

The modern name for polyhydric alcohols is polyols(diols, triols, etc.). Examples:

dihydric alcohol -ethylene glycol(ethanediol)

HO – CH 2 –CH 2 –OH

trihydric alcohol -glycerol(propanetriol-1,2,3)

HO – CH 2 –CH (OH) –CH 2 –OH

Dihydric alcohols with two OH groups at the same carbon atom R – CH (OH) 2 are unstable and, splitting off water, immediately transform into aldehydes R – CH = O. Alcohols R – C (OH) 3 do not exist.

2. Depending on which carbon atom (primary, secondary or tertiary) the hydroxy group is attached to, alcohols are distinguished

o primary R – CH 2 –OH,

o secondary R 2 CH – OH,

o tertiary R 3 C – OH.

For example:

In polyhydric alcohols, primary, secondary and tertiary alcohol groups are distinguished. For example, a molecule of a trihydric alcohol glycerol contains two primary alcohols (HO – CH2 -) and one secondary alcohol (–CH (OH) -) group.

3. According to the structure of the radicals associated with the oxygen atom, alcohols are subdivided into

o limit(for example, CH 3 - CH 2 –OH)

o unsaturated(CH 2 = CH – CH 2 –OH)

o aromatic(C 6 H 5 CH 2 –OH)

Unsaturated alcohols with an OH group at a carbon atom bonded to another double bond are very unstable and are immediately isomerized to aldehydes or ketones.

For example,vinyl alcohol CH 2 = CH – OH converts to acetaldehydeCH 3 –CH = O

Saturated monohydric alcohols

1. Definition

ULTIMATE SINGLE ATOMIC ALCOHOLS - oxygen-containing organic substances, derivatives of saturated hydrocarbons, in which one hydrogen atom is replaced by a functional group (- OH)

2. Homological series

3. Nomenclature of alcohols

Systematic names are given by the name of the hydrocarbon with the addition of a suffix -ol and a number indicating the position of the hydroxy group (if necessary). For example:

The numbering is carried out from the end of the chain closest to the OH-group.

The number reflecting the location of the OH-group in Russian is usually placed after the suffix "ol".

According to another method (radical-functional nomenclature), the names of alcohols are derived from the names of radicals with the addition of the word " alcohol". In accordance with this method, the above compounds are called: methyl alcohol, ethyl alcohol, n-propyl alcohol CH 3 -CH 2 -CH 2 -OH, isopropyl alcohol CH 3 -CH (OH) -CH 3.

4. Isomerism of alcohols

Alcohols are characterized by structural isomerism:

· isomerism of the OH-group position(starting from C 3);
For example:

· carbon skeleton(starting from C 4);
For example, carbon skeleton isomers forC 4 H 9 OH:

· interclass isomerism with ethers
For example,

ethanol CH 3 CH 2 –OH and dimethyl ether CH 3 –O – CH 3

It is also possible spatial isomerism- optical.

For example, butanol-2 CH 3 C H (OH) CH 2 CH 3, in the molecule of which the second carbon atom (highlighted in color) is bonded to four different substituents, exists in the form of two optical isomers.

5. The structure of alcohols

The structure of the simplest alcohol - methyl (methanol) - can be represented by the formulas:

It can be seen from the electronic formula that oxygen in the alcohol molecule has two lone electron pairs.

The properties of alcohols and phenols are determined by the structure of the hydroxyl group, the nature of its chemical bonds, the structure of hydrocarbon radicals and their mutual influence.

O – H and C – O bonds are polar covalent. This follows from the differences in the electronegativity of oxygen (3.5), hydrogen (2.1) and carbon (2.4). The electron density of both bonds is shifted towards the more electronegative oxygen atom:

The oxygen atom in alcohols sp 3 -hybridization is inherent. Two 2sp 3 -atomic orbitals are involved in the formation of its bonds with the C and H atoms; the C – O – H bond angle is close to tetrahedral (about 108 °). Each of the other two 2 sp 3 orbitals of oxygen is occupied by a lone pair of electrons.

The mobility of the hydrogen atom in the hydroxyl group of alcohol is somewhat less than in water. More "acidic" in the series of monohydric saturated alcohols will be methyl (methanol).
The radicals in the alcohol molecule also play a role in the manifestation of acidic properties. Usually, hydrocarbon radicals reduce the acidic properties. But if they contain electron-withdrawing groups, then the acidity of alcohols increases markedly. For example, alcohol (CF 3) 3 С-ОН due to fluorine atoms becomes so acidic that it is able to displace carbonic acid from its salts.

Obviously, for methane and ethane, in which all hydrogen atoms are equivalent, by replacing one hydrogen with hydroxyl, one can obtain from a single alcohol: these are methyl CH 3 OH and ethyl CH 3 CH 2 OH alcohols. Propane already has two possibilities - the substitution of hydroxyl for one of the hydrogens of the methyl groups and one of the hydrogens of the methylene group. And, indeed, there are two propyl alcohols: the primary one, in which the hydroxyl is bonded to the primary carbon atom (propyl alcohol or propanol-1), and the secondary one, with the hydroxyl at the secondary carbon atom (isopropyl alcohol or propanol-2).

Thus, the isomerism of alcohols, as well as the isomerism of substituted hydrocarbons in general, is twofold: the isomerism of the hydrocarbon skeleton, already familiar to us from alkanes, and the isomerism of the position of the hydroxyl function in this skeleton. Indeed, for the fourth member of the homologous series of alkanes - butane - alcohols originate from two different hydrocarbon chains: from n-butane and isobutane.

All basic types of stereoisomerism are possible for alcohols.

13.2. Physical properties of alcohols

Comparison of the boiling points of alcohols with a similar structure shows that, when passing from one member of the homologous series to another, the increase in the boiling point is about 20 ° C. The branching of the chain, as in hydrocarbons, increases the melting point (especially strongly for tertiary alcohols, in which the “branched” carbon atom is adjacent to the functional group) and lowers the boiling point. Compared to hydrocarbons, alcohols boil at a much higher temperature.

To explain the anomalies in boiling points, the concept was used hydrogen bond... It can be assumed that in alcohols the hydrogen atom of the hydroxyl group serves as a bridge between two electronegative oxygen atoms, and with one of them it is bound by a covalent bond, and with the other by electrostatic forces of attraction. The hydrogen bond energy in alcohols is about 20 kJ / mol (for most covalent bonds it is 210-420 kJ / mol).

Molecules that are held together by hydrogen bonds are called associated; them abnormally high temperatures boiling is due to the additional energy required to break hydrogen bonds. For more information on hydrogen bonds, see Chapter 3 "Fundamentals of the theory of the electronic structure of organic molecules".

The essential difference between alcohols and hydrocarbons is that lower alcohols are mixed with water in any ratio. Due to the presence of the OH group, alcohol molecules are held together by the same intermolecular interaction forces that exist in water. As a result, it is possible to mix two types of molecules, and the energy required to detach water or alcohol molecules from each other is taken due to the formation of similar bonds between water and alcohol molecules. However, this is true only for lower alcohols, in which the OH group constitutes a significant part of the molecule. A long aliphatic chain with a small OH group is very similar to alkanes, and the physical properties of such compounds reflect this. The decrease in water solubility with an increase in the number of carbon atoms occurs gradually: the first three primary alcohols are infinitely miscible with water; solubility n-butyl alcohol is 8 g per 100 g of water, n- pentyl - 2 g, n-hexyl - 1 g, and even less higher alcohols.

According to the magnitude of the dipole moments (μ = 1.6-1.8D), alcohols are polar substances that have weak electron-donating or nucleophilic properties due to the presence of a lone pair of electrons of the oxygen atom.

13.2.1. Spectroscopy of alcohols

· UV spectroscopy . Alcohols practically do not absorb in the UV range. The available weak band with l max 180-185 nm corresponds to n→ σ * transition of an electron of a lone pair of an oxygen atom.

· IR spectroscopy. In the IR spectrum of alcohols, strong stretching vibrations ν ОН are observed at 3635-3615 cm -1 and 3600-3200 cm -1, respectively, for highly diluted solutions and solutions concentrated with hydrogen bonds. In addition, bending vibrations δ OH appears at 1410-1250 cm -1, and stretching vibrations ν C-O at 1150-1050 cm -1, depending on the structure of alcohols.

· Mass spectrometry . Alcohols, starting with butyl alcohols, are characterized by a low intensity of the molecular ion peak. It decreases with an increase in the molecular weight of alcohols, as well as with the transition from primary to secondary alcohol. For tertiary alcohols, the molecular ion peak is practically absent. For primary and secondary alcohols, the main fragmentation begins with the elimination of a water molecule. In the case of tertiary alcohols, the longest carbon radical is initially cleaved off under electron impact with the formation of a fragment ion containing a hydroxyl group.

· PMR spectroscopy . In the PMR spectra, the hydroxyl proton signal appears in the range from 1.0 to 5.5 ppm, depending on the concentration and nature of the solvent.

13.3. Obtaining monohydric alcohols in industry

The requirements for industrial syntheses are different from those for laboratory methods. In particular, large-scale production is more economical to carry out in a continuous way with multiple recirculation of large masses of reactants. Therefore, for such industries, gas-phase processes are preferable.

For the industrial production of alcohols, two main methods are most widely used: hydration of alkenes obtained by cracking oil, and enzymatic hydrolysis of carbohydrates. In addition to these two methods, there are some others that have more limited application.

v Alkenes hydration . It is known that alkenes containing up to five carbon atoms can be isolated from a mixture obtained by cracking oil. These alkenes are easily converted to alcohols as a result of either direct addition of water or addition of sulfuric acid, followed by hydrolysis of the formed alkyl sulfates. See Chapter 8 Alkenes for details.

In this way, only those alcohols can be synthesized that are formed according to Markovnikov's rule: for example, isopropyl, but not propyl; sec-butyl, but not n-butyl, rubs-butyl, but not isobutyl. Only one primary alcohol, ethyl alcohol, can be obtained by these methods. In addition, this method is devoid of stereospecificity, and rearrangements are possible during hydration. These problems can be circumvented by a two-stage synthesis of alcohols through oxirane, which ultimately leads to anti-hydration(see below) .

In industry, acid-catalyzed hydration of alkenes underlies the production of ethanol from ethylene and propanol-2 from propene:

For the preparation of other alcohols, this method has a very limited area of application, since the hydration of alkenes is often accompanied by isomerization of the carbon skeleton due to rearrangements of carbocations. This circumstance greatly narrows the synthetic possibilities at first glance. easy way obtaining secondary and tertiary alcohols. In the laboratory, it was superseded by another method based on the reaction of hydroxymercuration-demercuration of alkenes. More about him later.

v Enzymatic hydrolysis carbohydrate-containing raw materials (grapes, berries, wheat, potatoes, etc.) is of great practical importance, especially for the production of ethyl alcohol:

C 6 H 12 O 6 → 2C 2 H 5 OH + 2CO 2

Most of it goes to the preparation of alcoholic beverages. Hence the name “wine or food alcohol”. When starch is used as a starting material, in addition to ethyl alcohol, fusel oils, which are a mixture of pentyl alcohols, as well as propyl and isobutyl alcohols, which have a toxic effect.

For industrial purposes, ethanol is used, obtained by hydrolysis and fermentation of wood, waste from the pulp and paper industry ( hydrolysis alcohol).

§ Interesting is Weizmann reaction- enzymatic hydrolysis of carbohydrates by bacteria Clostridium acetobutylicum, as a result of which a mixture is formed n-butyl alcohol (60%), ethyl alcohol (10%) and acetone СН 3 СОСН 3 (30%).

v Hydrolysis alkyl halides ... The reaction is not significant, because the halogenated derivatives of alkanes themselves are more often obtained from alcohols. However, in the industry, chlorination of the mixture n-pentane and isopentane and subsequent hydrolysis of haloalkanes to obtain a mixture of five isomeric alcohols, which is used as a solvent. From it, the inaccessible pure pentanol-1 is obtained by distillation.

v Oxosynthesis ... Heating a mixture of carbon monoxide (II) and hydrogen over catalysts gives various alcohols, the composition of which depends both on the reaction conditions and the ratio of the reactants, for example:

§ Carbonylation of alcohols allows you to lengthen the carbon chain.

· Hydroformylation of alkenes . The addition of carbon monoxide (II) and hydrogen to alkenes in the presence of a catalyst gives aldehydes and ketones, which can be reduced to alcohols.

Oxosynthesis, discovered in the USA (T. Roylen, 1938) and originally developed in Germany, is now becoming increasingly important in the chemical industry. For example, to get n-butyl alcohol from propylene and n-propyl alcohol from ethylene.

v Alfol process . The main competitor to the previous method is the alpha-process – method of obtaining n-alkanols by telomerization of ethylene in the presence of a catalyst based on titanium chloride and triethylaluminum according to Ziegler (for more details, see Chapter 8 "Alkenes"), followed by oxidation of telomerization products. In particular, this method is used to synthesize primary alcohols C 12 -C 18.

v Oxidation alkanes. In the oxidation of higher alkanes with molecular oxygen, secondary alcohols C 12 -C 20 are mainly obtained, which are used to obtain surfactants. The reaction is catalyzed by salts or complexes of transition metals: cobalt, copper, iron, manganese and proceeds through the decomposition of hydroperoxides. See chapter 7 "Alkanes" for details.

13.4. Methods for the synthesis of monohydric alcohols in the laboratory

v Hydrolysis alkyl halides ... Usually, alcohols are obtained by hydrolysis of chloroalkanes by heating with water or an aqueous solution of alkalis. In the first case, the reaction is reversible, and in the second it is often accompanied by the elimination of hydrogen halides, for example:

To avoid side processes, it is preferable to initially synthesize esters from chloroalkanes, which are then saponified to alcohols.

For better homogenization of the reaction mixture, a certain amount of a water-miscible solvent, such as dioxane, is added.

v Hydroboration-oxidation of alkenes . Alkenes react with diborane (BH 3) 2, initially forming alkylboranes, which are converted to alcohols upon oxidation.

The reaction is carried out in tetrahydrofuran. Diborane is prepared by a reaction between two commercial reagents: sodium borohydride and boron fluoride, often in situ(in a reaction mixture in the presence of alkene) or reduce boron (III) chloride with hydrogen.

Alkylboranes are not isolated, but are treated in the same reaction vessel with an alkaline solution of hydrogen peroxide. As can be seen from the above reactions, they proceed against the classical Markovnikov rule and without rearrangements.

It should be noted that it is not diborane that participates in the reaction, but its monomer formed in the solution:

Along with diborane in organic synthesis, a borane complex in tetrahydrofuran is used.

§ Mechanism hydroboration reactions can be represented as a typical electrophilic addition of boron hydride at the double bond, in which the boron atom is the electrophile. From a modern point of view, this reaction is considered as a process proceeding through four-centered intermediate complex.

Apparently, the reaction of hydroboration of alkenes begins with an electrophilic attack of the boron atom. In the resulting p-complex on the boron atom, the negative charge increases with a tendency to form a secondary carbocation. However, the latter is not formed, because a boron atom acquiring a negative charge easily loses a hydrogen atom in the form of a hydride ion with the simultaneous formation of a product cis-connection.

The oxidation reaction of alkylboranes proceeds as follows. In the first stage, the hydroperoxide anion attacks the electron-deficient boron atom.

The resulting intermediate rearranges due to the migration of the alkyl group with its electrons to the oxygen atom according to a scheme similar to the rearrangement of carbocations.

Interaction with hydroperoxide in alkaline environment proceeds quickly and with the release of heat.

The resulting boric acid ester readily decomposes under the reaction conditions with the release of alcohol.

To prevent further oxidation of the reaction products to aldehydes and acids, the process is carried out in a nitrogen atmosphere in the presence of boric acid (A. Bashkirov), which forms oxidation-resistant esters of boric acid B (OR) 3 with alcohols. The latter are then readily hydrolyzed by alkalis. In this way, in industry, in particular, cetyl alcohol C 16 H 33 OH is obtained.

The hydroboration reaction is simple and convenient, the yields are very high, and it can be used to synthesize compounds that are difficult to obtain from alkenes in any other way. For acyclic, mono- and disubstituted alkenes, hydroboration – oxidation provides a unique opportunity for the synthesis of primary alcohols with a total yield of 80–95%.

v Alkylboration of carbon monoxide (II). Further development of methods for obtaining alcohols from alkylboranes was obtained in the works of G. Brown and M. Raschke, who proposed carbon monoxide (II) as an acceptor of alkylborane. This reaction takes place at temperatures of 100-125 ° C. In the intermediate complex, there is a sequential migration of alkyl groups from a boron atom to a carbon atom.

This method, depending on the reaction conditions, can be used to obtain primary, secondary and tertiary alcohols in high yields.

v Hydroxymercuration-demercurization of alkenes leads to the formation of alcohols and is not accompanied by rearrangement. The direction of the reaction corresponds to the Markovnikov rule; it flows in soft conditions, and the outputs are close to theoretical.

The mechanism of this reaction can be represented as follows. Initially, the dissociation of mercury (II) acetate occurs with the formation of the CH 3 COOHg + ion. The acetoxymercurate cation reacts with the C = C double bond of the alkene like a proton. Then the carbocation reacts with water to form an alkyl mercury salt.

The demercurization of the resulting mercury alcohols proceeds quantitatively when they are treated with sodium borohydride.

For example:

Replacing water with alcohol or carboxylic acid results in ethers or esters. In the laboratory, this method has completely replaced the reaction of hydration of alkenes.

v Recovery esters and carboxylic acids leads to primary alcohols.

§ Catalytic hydrogenation esters are usually carried out over platinum catalysts, Raney nickel or copper chromite catalyst.

§ In laboratory conditions, as a reducing agent, it is much more often used lithium aluminum hydride.

§ Large amounts of straight-chain alcohols containing even number carbon atoms, previously obtained in pure form by reduction with sodium in ethyl or butyl alcohol of esters of fatty acids or fats according to the Bouveau-Blanc method.

v Recovery oxo compounds to alcohols can be carried out with hydrogen in the presence of catalysts such as Raney nickel or platinum, as well as lithium aluminum hydride or sodium borohydride. In this case, primary alcohols are obtained from aldehydes, and secondary alcohols are obtained from ketones.

It should be noted that sodium borohydride, unlike lithium aluminum hydride, does not reduce the carboxyl and ester groups, which makes it possible to reduce the carbonyl group in their presence.

Alkyl- and aryl-substituted borohydrides, along with the selectivity of reduction, also provide stereoselectivity.

v Syntheses based on Grignard reagent. Grignard reagents easily interact with carbonyl compounds. In this case, formaldehyde forms a primary alcohol, the remaining aldehydes are secondary, and ketones are tertiary alcohols.

When the Grignard reagent interacts with esters, tertiary alcohols are obtained, with the exception of formic acid esters, which give secondary alcohols.

The resulting ketone is more reactive than the ester and therefore reacts primarily with the Grignard reagent.

v Receiving oxirane-based alcohols.

§ Organic a-oxides (oxiranes or epoxides) also enter into reactions with alkylmagnesium halides forming primary alcohols.

§ Epoxies in action lithium aluminum hydride turn into alcohols. The reaction consists in a nucleophilic attack of the hydride anion at the least substituted (less screened) carbon atom with the formation of a secondary or tertiary alcohol.

Since a-oxides are usually obtained from olefins, such a two-stage process can be considered as an alternative to the hydration reaction of alkenes. In contrast to the latter reaction, the reduction of epoxides proceeds regio- and stereospecifically. In systems for which free rotation around s-bonds is impossible, the hydroxyl group and the hydrogen atom have anti-configuration, hence the name of this process - anti-hydration.

v Interaction primary amines with nitrous acid leads to the formation of alcohols .

C n H 2n + 1 NH 2 + HONO → C n H 2n + 1 OH + N 2 + H 2 O

The reaction has no real synthetic significance, since it is accompanied by the formation of a large number of by-products.

v Interaction haloalkanes with potassium superoxide - one of the most modern methods synthesis of alcohols.

The replacement of the halogen atom at the secondary asymmetric carbon atoms by hydroxyl is accompanied by complete reversal of the configuration.

13.5. Chemical properties of monohydric alcohols

The reactions of alcohols can be divided into two types: proceeding with the cleavage of the C – OH and CO – H bonds, due to the fact that alcohols exhibit acid-base properties.

13.5.1. Breaking the C – OH bond

v Substitution of a hydroxyl group for a halogen . There are a large number of reactions for replacing a hydroxyl group with a halogen. The most famous of them is the interaction of alcohols with hydrohalic acids, as well as phosphorus and sulfur halides. Depending on the structure of the starting alcohol, the substitution reaction can proceed according to the S N 1 or S N 2 mechanism.

· Interaction of alcohols with hydrogen halides ... The success of the reaction, in addition to the conditions, is determined by the nature of the alcohol and the acidity of the hydrogen halide. The reactivity of the latter decreases in the series HI> HBr> HCl >> HF, and in the series of alcohols, the rate of substitution of the OH group sharply decreases upon going from tertiary alcohol to primary alcohol. So, tertiary alcohol reacts with halogen acids, with the exception of hydrogen fluoride, already in the cold. Primary and secondary alcohols are converted to haloalkanes when heated with a mixture of hydrohalic and sulfuric acids for several hours.

Sometimes hydrohalic acids are obtained in the reaction mixture from their sodium and potassium salts the action of concentrated sulfuric acid.

§ It should be noted that the chloride ion is a very weak nucleophile due to its high solvation in aquatic environments. To increase the speed of reaction zinc chloride is added, which facilitates the substitution for chloride ion.

So, that is, according to the S N 2 mechanism, methanol and most spatially unhindered primary alcohols react. Protonation of alcohols converts the hydroxyl group to a well leaving group.

In S N 2 reactions, the reactivity of primary alcohols R - CH 2 OH is lower than for methanol itself. This is due to an increase in steric hindrance for the attack of the protonated alcohol by the halide ion.

§ Tertiary and partially secondary alcohols react according to the S N 1 mechanism, when a protonated alcohol easily and quickly ejects a water molecule, forming a carbocation. Its further stabilization is determined by the attack by a stronger nucleophile, a halide anion, than water.

§ It should be borne in mind that the carbocation formed from secondary alcohols is capable of 1,2-hydride or alkyl shift turn into tertiary, for example:

The last stage is complicated by the side reaction E1 - the elimination of a proton with the formation of an alkene.

§ Some hindered primary alcohols can react by the S N 1 mechanism, for example, neopentyl alcohol. The resulting primary carbocation quickly rearranges into a tertiary carbocation due to a 1,2-methyl shift:

Secondary alcohols can react both according to the S N 1 and S N 2 mechanisms. It is determined by the concentration of alcohol, acid, reaction temperature and the nature of the solvent.

· Lucas test ... Whether the alcohol is primary, secondary or tertiary can be determined using Lucas samples, which is based on the different reactivity of the three classes of alcohols in relation to hydrogen halides. Tertiary alcohols react with Lucas's reagent (a mixture of concentrated HCl with anhydrous ZnCl 2) immediately, as evidenced by the instant turbidity of the reaction mixture, secondary alcohols - within 5 minutes, and primary alcohols - do not noticeably react at room temperature. Tertiary alcohols easily form carbocations, secondary alcohols more slowly, and primary alcohols do not react. Since alcohols are soluble in concentrated hydrochloric acid in the presence of zinc chloride, and the halides formed from them are not, then, accordingly, turbidity is observed. The exception is primary allyl and benzyl alcohols, which form stable carbocations and therefore give a positive reaction.

· Interaction of alcohols with phosphorus and sulfur halides . Compared to hydrogen halides, more convenient reagents for producing haloalkanes from alcohols are phosphorus and sulfur halides, as well as halides of some inorganic acids, for example, SOCl 2, PCl 3, PCl 5, POCl 3, COCl 2.

R-OH + PCl 5 → R-Cl + POCl 3 + HCl

3 R-OH + PBr 3 → 3 R-Br + H 3 PO 3

6 CH 3 OH + 2 P + 3 I 2 → 6 CH 3 I + H 3 PO 3 (P + 3 I 2 → 2PI 3)

§ For reactions with phosphorus trihalides the following reaction mechanism is most probable. Trialkyl phosphite is initially formed and, if the process is carried out in the presence of bases, this compound can be the final product of the reaction.

If the hydrogen bromide is not neutralized, the trialkyl phosphite intermediate is readily protonated and the alkyl groups are converted to haloalkanes.

§ Reactions of alcohols with phosphorus pentahalides usually not accompanied by rearrangements and lead to a change in the configuration of the asymmetric carbon atom bound to the hydroxyl group.

§ In reactions of alcohols with thionyl chloride the chlorosulfite ester is first formed.

In the case when the solvent does not take part in the reaction, the attack of the chloride anion of the chlorosulfite ether molecule proceeds from the rear with the reversal of the configuration of the reaction product.

v The use of n-toluenesulfochlorides in the substitution of hydroxy groups . It is known that alcohols interact with NS-toluenesulfochloride (TsCl) in the presence of pyridine to form alkyl- NS-toluenesulfonates ( tosylates).

Insofar as NS-toluenesulfate ion is a very easily leaving group, it can be easily substituted without rearrangements in reactions with nucleophiles, including halide ions.

v Dehydration alcohols with the help of acids such as sulfuric, phosphoric and oxalic leads to the formation of alkenes.

As mentioned earlier, tertiary alcohols are the easiest to dehydrate, followed by secondary and finally primary alcohols. The dehydration process of alcohols obeys the Zaitsev rule, according to which a hydrogen atom is split off from the least hydrogenated carbon atom, which is in the b-position to the OH-group, for example:

Dehydration of alcohols takes place in two stages. First, the protonation of the OH group occurs, and then the elimination of the water molecule by the E2 mechanism, if it comes about primary alcohols, or according to the E1 mechanism, if the alcohols are tertiary. Secondary alcohols, depending on the reaction conditions, can be dehydrated by the E2 or E1 mechanism.

§ For example, by the E1 mechanism dehydration occurs rubs-butyl alcohol.

Tertiary alcohols dehydrate so easily that it is possible selective diol dehydration containing primary and tertiary hydroxyl groups.

Dehydration of tertiary alcohols can be carried out already in 20-50% sulfuric acid at 85-100 ºС. Secondary alcohols undergo dehydration under more severe conditions: 85% phosphoric acid, heating up to 160 ºС or 60-70% sulfuric acid at a temperature of 90-100 ºС.

§ Alkene formation is determined by the stability of the intermediate carbocation and the thermodynamic stability of the branched alkene. For example, for isoamyl alcohol, according to Zaitsev's rule, only 3-methylbutene-1 should be formed, but in reality, three alkenes are obtained.

The primary carbocation formed at first is the least stable; therefore, as a result of the 1,2-hydride shift, it transforms into a more stable secondary carbocation.

In turn, the secondary carbocation is easily converted to tertiary as the most stable one.

Most of the reaction products will contain 2-methylbutene-2 as the most branched alkene.

It should be noted that isoamyl alcohol belongs to primary alcohols; nevertheless, its dehydration proceeds according to the E1 mechanism, which is explained by the impossibility of realizing the E2 mechanism due to steric hindrances.

§ Primary alcohols dehydrated in concentrated sulfuric acid in the temperature range 170-190 ° C.

For them, the E2 cleavage mechanism is implemented. It is not the alcohol itself that enters into the reaction, but the alkyl sulfate, and the hydrogen sulfate anion or water plays the role of the nucleophile.

It is interesting to note that when the reaction is carried out at a low temperature, the process can be stopped at the alkyl sulfate stage.

§ For dehydration of alcohols in industry instead of sulfuric acid, it is more convenient to use alumina as a dehydrating agent. Heterogeneous catalytic dehydration is carried out for primary, secondary and tertiary alcohols.

Along with sulfuric and phosphoric acids, aluminum oxide, oxalic acid, benzenesulfonic acid, zinc chloride and thorium oxide ThO 2 are also used for the dehydration of alcohols. It is noteworthy that when secondary alcohols are heated with thorium (IV) oxide, alkenes with terminal(terminal) double bond.

Along with the formation of alkenes, depending on the reaction conditions (temperature and acid concentration), alcohols can be converted into ethers, which will be discussed in the corresponding chapter.

v Synthesis of esters of sulfonic acids. Alcohols react with sulfochlorides to form esters:

The most commonly used chlorides of toluenesulfonic acid, methanesulfonic acid and trifluoromethanesulfonic acid:

Esters of sulfonic acids are suitable compounds for various nucleophilic reactions, since the sulfonate group easily, often at room temperature, undergoes substitution, especially for the "triflates" R — O — SO 2 CF 3.

The reactions proceed stereospecifically with reversal of the configuration.

v Synthesis of amines from alcohols . Alkylation of ammonia or amines with alcohols is carried out by heating the reagents in an acidic medium.

Depending on the ratio of the reactants, primary, secondary and tertiary amines, as well as quaternary ammonium salts, can be obtained. The use of aluminum oxide as a catalyst at 300 ºС leads to the same results.

13.5.2. Breaking the O – N bond

v Reactions of alcohols as acids . As you know, the strength of an acid is characterized by its ability to remove a proton. For alcohols, it is determined by the difference in the electronegativities of oxygen and hydrogen atoms, as well as by the nature and number of substituents on the hydroxyl-containing carbon atom. The presence of alkyl substituents with a positive induction effect (+ I-effect) reduces the acidity of alcohols. Indeed, the acidity of alcohols decreases in the following order:

CH 3 OH> primary> secondary> tertiary.

With the introduction of electron-withdrawing substituents, the acidity of alcohols increases, and, for example, alcohol (CF 3) 3 СОН is comparable in acidity with carboxylic acids.

§ Alcohols as weak acids react with alkali, alkaline earth metals, aluminum, gallium, thallium to form alcoholates with ionic or covalent bonds and are able to act as strong bases and good nucleophiles.

§ Alcoholates can also be obtained by the action of sodium and potassium hydrides or amides on alcohols with Grignard reagent.

CH 3 CH 2 OH + NaNH 2 → CH 3 CH 2 ONa + NH 3

CH 3 OH + CH 3 MgI → CH 3 OMgI + CH 4

The latter reaction is used to quantify the mobile hydrogen atoms. It is known as the Chugaev-Tserevitinov-Terent'ev reaction.

Alcohols are significantly inferior in acidity to water, therefore, even under the action of concentrated alkalis, the equilibrium is shifted to the left.

Nevertheless, this reaction is sometimes used in industry to obtain alcoholates of the simplest alcohols. For this purpose, benzene is added to the reaction mixture, allowing water to be removed in the form of an azeotropic mixture.

Among the alcoholates of alcohols, isopropylate ( i- PrO) 3 Al and rubs-butylate ( t‑ BuO) 3 Al aluminum, which serve as reagents for oxidation according to Oppenauer and reduction according to Meyerwein – Ponndorf.

v Oxidation or catalytic dehydrogenation of alcohols. Oxidation of alcohols leads to carbonyl compounds. In this case, primary alcohols are converted into aldehydes, which can be further oxidized to carboxylic acids. Secondary alcohols are oxidized to ketones. Tertiary alcohols in normal conditions do not oxidize.

The oxidation of primary and secondary alcohols to aldehydes or ketones is carried out using the following reagents: KMnO 4, K 2 Cr 2 O 7, CrO 3, MnO 2, Ag 2 O, Ag 2 CO 3, etc. With potassium dichromate, the reaction proceeds according to the equation:

The following reaction mechanism has been established:

While the oxidation of secondary alcohols stops at the stage of obtaining ketones, primary alcohols under these conditions are converted into aldehydes, which, through the hydration form, are oxidized to carboxylic acids:

If there is a need to stop the reaction at the aldehyde stage, then the process is carried out in anhydrous methylene chloride. In this case, the formation of aldehyde hydrate is impossible, and therefore, carboxylic acid is not synthesized.

Oxidation of alcohols with potassium dichromate is accompanied by a change in the yellow color of the chromium solution (Cr 6+) to green (Cr 3+) and can serve as a control over the course of the reaction.

Tertiary alcohols are not oxidized under normal conditions, however, in an acidic medium, they can undergo dehydration to alkenes, which are then oxidized with the destruction of the carbon chain.

· Catalytic oxidation ... Recently, primary alcohols began to be oxidized to aldehydes with atmospheric oxygen in good yield over a mixed catalyst:

· Catalytic dehydrogenation ... Dehydrogenation of primary and secondary alcohols is carried out by passing them over a copper wire or copper-silver catalyst at 400-500 ° C.

· Iodoform reaction. The presence in alcohol of the structural fragment CH 3 -CH-OH can be judged by iodoform reaction... For this, the alcohol is treated with iodine and sodium hydroxide. The latter, when merged, form sodium hypoiodite NaOI; alcohols having the mentioned structural fragment give a yellow precipitate CHI 3.

13.6. some representatives of monohydric alcohols

§ Methyl alcohol get by the reaction:

This is the main route for producing methanol. Methanol is widely used in technology for the methylation of aniline, the production of dimethyl sulfoxide and formalin. Used as a solvent for varnishes. It should be noted that even small amounts of methanol, when ingested, cause severe poisoning of the body. The lethal dose for humans is 25 ml. methanol.

§ Ethanol is obtained by hydration of ethylene or enzymatic hydrolysis of carbohydrates. It is used as a 96% solution. Used in the production of diethyl ether, ethyl acetate and acetaldehyde. In contrast to methanol, ethyl alcohol is not large quantities Acts on the body exciting, and in large causes poisoning. It is found in beer, wine, vodka and other spirits. With water, ethanol forms an azeotrope consisting of 96% alcohol and 4% water. Therefore, it is impossible to obtain 100% ("absolute") alcohol by ordinary distillation. To obtain pure alcohol, the water contained in it is chemically bound, for example, calcium oxide is added before distillation.

§ n-Propyl alcohol is formed during alcoholic fermentation of carbohydrates.

§ Isopropyl alcohol is synthesized by hydration of propylene. Propyl alcohols are used as a substitute for ethyl alcohol and for the production of acetone.

§ Butyl alcohol in large quantities is obtained from the mixture formed during the fermentation of sugars under the influence of Bacterium acetobutylicum, where its content is 60%, 30% is acetone and 10% ethyl alcohol. Besides, n-butyl alcohol is industrially obtained by hydroformylation of propylene. They are used in the production of butyl acetate, herbicides, and also as a solvent in the production of varnishes and paints.

§ sec-butyl alcohol is synthesized by hydration of butylene.

§ Isobutyl alcohol is obtained from water gas in the presence of cobalt salts. It is used to prepare fruit esters or essences.

§ tert-butyl alcohol is obtained by hydration of isobutylene formed during the cracking of oil. Used as an alkylating agent and solvent.

§ Long chain alcohols found in plant waxes, found in insects and some animals. Obtained by hydroformylation and oxidation of alkyl aluminum, as well as by hydrogenation of fats.

13.7. Unsaturated alcohols and their esters

Enols

It is known that olefins cannot carry hydroxyl at the carbon atom in sp 2-hybrid state, therefore structures (1) are unstable and isomerized in (2), according to Eltekov-Erlenmeyer rule.

For structures carrying hydroxyl at an unsaturated carbon atom that is not bound to electron-acceptor groups (> C = O, –NO2, etc.), the Eltekov – Erlenmeyer rule is fully valid. Therefore, vinyl alcohol and its homologues do not exist, and when trying to obtain them, they are rearranged into acetaldehyde or, accordingly, its homologues.

Currently, many compounds are known, however, usually more complex or containing several oxygen atoms, which are stable and can be isolated not only in the carbonyl form, but also in the form of unsaturated alcohol - enola, for example:

Isomerism between a carbonyl compound and the one formed from it by the movement of one hydrogen atom with unsaturated alcohol-enol refers to the phenomena tautomerism, or desmotropia... Liquid mixtures of tautomeric forms in which both isomers are in equilibrium are called allelotropic mixtures. For more information on tautomerism, see Chapter 5, Isomerism.

The reason for the rearrangement is the manifestation, as in the case of vinyl chloride, of the mesomeric effect, but in this case reaching the end.

Due to the mesomeric effect, the hydrogen atom of the hydroxyl group is protonized and is created at the second unsaturated carbon atom with its δ– charge comfortable spot to attack the proton.

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 regularly constructed series of homologues:

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

2. Depending on the carbon atom at which the hydroxyl is located, primary, secondary and tertiary alcohols are distinguished. The molecules of primary alcohols contain a -CH 2 OH group bound to one radical or to the hydrogen atom of methanol (hydroxyl at the primary carbon atom). Secondary alcohols are characterized by the> 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 form:

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 there are more senior functions in the compound, the hydroxyl group is indicated by the prefix hydroxy- (in Russian, the prefix oxy- is often used). The longest unbranched chain of carbon atoms is selected as the main chain, which includes a carbon atom bonded to a hydroxyl group; 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 the numbering, the hydroxyl function usually takes precedence over halogen, double bond and alkyl, therefore, the numbering starts from the end of the chain, closer to which the hydroxyl group is located:

The simplest alcohols are called according to the radicals with which the hydroxyl group is connected: (CH 3) 2 CHOH - isopropyl alcohol, (CH 3) 3 СОН - tert-butyl alcohol.

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

This system is convenient when 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 through hydrogen bonds:

Thus, the higher boiling points of alcohols in comparison with the boiling points of the corresponding hydrocarbons are due to the need to break hydrogen bonds during the transition of molecules into the gas phase, which requires additional energy. On the other hand, this type of association leads, as it were, to an increase in molecular weight, which naturally leads to a decrease in volatility.

Low molecular weight alcohols are readily soluble in water, which is understandable if we take into account the possibility of hydrogen bonding 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 effect of the hydroxyl group on the properties of alcohols decreases, respectively, 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.