A type of isomerism characteristic of polyhydric alcohols. Isomerism of alcohols

alcohols refers to compounds containing one or more hydroxyl groups directly attached to a hydrocarbon radical.

Alcohol classification

Alcohols are classified according to various structural features.

1. According to the number of hydroxyl groups, alcohols are classified into

o monatomic(one group -OH)

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

o polyatomic(two or more -OH groups).

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

diatomic alcohol -ethylene glycol(ethanediol)

HO–CH 2 –CH 2 –OH

triatomic 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 turn 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 bonded to, alcohols are distinguished

o primary R-CH 2 -OH,

o secondary R 2 CH-OH,

o tertiary R 3 C–OH.

For instance:

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

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

o marginal(for example, CH 3 - CH 2 -OH)

o unlimited(CH 2 \u003d CH-CH 2 -OH)

o aromatic(C 6 H 5 CH 2 -OH)

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

For instance,vinyl alcohol CH 2 \u003d CH–OH turns into acetaldehydeCH 3 -CH \u003d O

Limit monohydric alcohols

1. Definition

LIMITED MONOATOMIC ALCOHOLS - oxygen-containing organic substances, derivatives of saturated hydrocarbons, in which one hydrogen atom is replaced by a functional group (- oh)

2. Homologous series

3. Nomenclature of alcohols

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

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 structural isomerism:

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

· carbon skeleton(starting from C 4);
For example, carbon skeleton isomers forC4H9OH:

· interclass isomerism with ethers
For instance,

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

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:

From the electronic formula it can be seen that the oxygen in the alcohol molecule has two unshared 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 to the more electronegative oxygen atom:

The oxygen atom in alcohols sp 3 hybridization is characteristic. Two 2sp3 atomic orbitals are involved in the formation of its bonds with C and H atoms; the C–O–H bond angle is close to tetrahedral (about 108°). Each of the other two 2 sp 3 oxygen orbitals 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 "sour" in the series of monoatomic saturated alcohols will be methyl (methanol).
The radicals in the alcohol molecule also play a role in the manifestation of acidic properties. Typically, hydrocarbon radicals lower the acidic properties. But if they contain electron-withdrawing groups, then the acidity of alcohols increases markedly. For example, alcohol (CF 3) 3 C-OH becomes so acidic due to fluorine atoms that it is able to displace carbonic acid from its salts.

Municipal budgetary educational institution

"Novoshimkussk secondary school

Yalchik district of the Chuvash Republic

Abstract open lesson in chemistry
in 10th grade

« The structure of limiting 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 , influence of alcohols on a living organism.

Tasks:

educational:

developing:

logical thinking

educational

healthy lifestyle

Equipment and reagents:

egg white

During the classes:

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

3.1. Setting the cognitive task of the lesson.

3.2. The concept of alcohols: the 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. Speech by the student "The effect of ethanol on the human body."

4. Fixing.

5. Reflection.

6. Homework par.20, ex. 5-7, page 88

1. Organizational moment.

2. Repetition of the composition and properties of hydrocarbons.

What hydrocarbons are discussed in riddles?

We are similar in properties to alkenes

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

upper class

And now we will conduct a small chemical dictation.

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

1. The names have a suffix - en. (Alkanes)

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

3. Molecules contain only sigma bonds. (Alkanes, cycloalkanes)

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

5. There must be a cyclic fragment in the molecule. (cycloalkanes)

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

7. The general formula of these hydrocarbons is SpN2p. (Alkenes, cycloalkanes)

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

9. A triple bond is necessarily present in molecules. (Alkynes)

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

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

3. Statement of the cognitive task of the lesson.

Substances we are not simple
And have been known since ancient times.
In medicine are applicable:
Fight back infection.
By properties, we are not so simple,
And we are called ... (alcohols)

So, the topic of our lesson today is

“The structure of limiting 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 can 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 Arabic"intoxicating". It is widely applied in various fields National economy. Has 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 air is 1.59. (The answer is ethanol C2H5OH.)

The general formula for all monohydric alcohols SpH2p + 1OH or ROH. Consider the structure of an alcohol molecule using the example of C2H5OH - ethyl alcohol.

One of the hydrogen atoms is different from the other atoms. (Question to students - Why?) It is connected to the carbon atom through oxygen. Therefore, it can be assumed that it will behave differently. What is this assumption based on? You will answer this question yourself, because you know that oxygen has a higher electronegativity. It will pull the electrons of the hydrogen atom towards itself. O-N connection becomes polar. This is indicated by a directional arrow:

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

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

What remains in an alcohol molecule after the mental removal of a functional group is called a hydrocarbon radical.

Now we can derive the definition of alcohols ... (the students themselves formulate, offer different options for the definition of alcohols)

alcohols called organic matter, the molecules of which contain one or more functional hydroxyl groups connected 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 - These are organic compounds whose molecules 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 is methyl alcohol. (С2Н5ОН, С3Н7ОН - they call them independently.)

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

CH3OH is methanol.

Basic principles of alcohol nomenclature:

The longest carbon chain is selected and numbered from the end of the chain closest to the hydroxo group. Name the substituents in the main carbon chain and indicate their positions with numbers. Name the main chain as alkane and add the suffix -ol. The number indicates the position of the OH group.

(Students complete the assignment on the nomenclature of alcohols, written on the board)

Task on the board: Name the alcohols according to the systematic nomenclature:

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

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

Alcohols are classified differently.

alcohols are: marginal unlimited aromatic

There are alcohols: monatomic diatomic triatomic

3. The nature of the carbon atom. Depending on the valency of the alcohol group alcohols are: primary - contain a monovalent alcohol group -CH2OH (for example, CH3-CH2OH ethanol); secondary - contain a divalent alcohol group \u003d CHOH (for example, CH3-CHOH-CH3 propanol-2); tertiary - contain a trivalent alcohol group \u003d C-OH (for example, 2-methylbutanol-2:

(From the formulas presented earlier, students find alcohols, formulas of 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 is a diagram of the types of isomerism of alcohols, the concepts of “isomers” and “isomerism” are repeated.)

7. Isomerism of alcohols

Alcohols are characterized by the following types of isomerism:

Isomerism of the carbon skeleton

For instance,

Interclass isomerism

For instance,

Exercise:

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

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

4. Fixing.

5. Reflection. What have you learned 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.

C2H5OH is a drug. Under the influence of ethanol, a person's attention is weakened, the reaction is inhibited, and the correlation of movements is disturbed. Prolonged use causes severe damage nervous system, diseases of cardio-vascular system, digestive tract, a serious illness occurs - alcoholism.

Classification of alcohols.

1. By the nature of the hydrocarbon radical alcohols are: marginal - the hydrocarbon radical contains only single bonds (for example, CH3OH methanol, C4H9OH butanol); unlimited - 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 distinguish 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 glycerol or propanetriol-1,2,3).

Isomerism of the carbon skeleton

For instance,

Functional group position isomerism

For instance,

Interclass isomerism: alcohols are isomeric to ethers.

For instance,

(Students complete the task of fixing on separate cards.)

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

Task 3. Write down all possible isomers of the substance C4H9OH.

Obviously, for methane and ethane, in which all hydrogen atoms are equivalent, by replacing one hydrogen with hydroxyl, one can get 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: primary, in which the hydroxyl is bonded to the primary carbon atom (propyl alcohol or propanol-1), and secondary - 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 of a twofold nature - 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 come from two different hydrocarbon chains: from n-butane and isobutane.

For alcohols, all the main types of stereoisomerism are also possible.

13.2. Physical properties of alcohols

From a comparison of the boiling points of alcohols of a similar structure, it can be seen that when moving from one member of the homologous series to another, the increase in the boiling point is approximately 20 ° C. Chain branching, 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 the boiling points, the concept was used hydrogen bond. It can be considered that in alcohols the hydrogen atom of the hydroxyl group serves as a bridge between two electronegative oxygen atoms, and it is connected with one of them 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; their abnormal high temperatures boiling is due to the additional energy required to break hydrogen bonds. For more information on hydrogen bonding, see Chapter 3, Fundamentals of the Theory electronic structure organic molecules.

The essential difference between alcohols and hydrocarbons is that lower alcohols are miscible with water in any ratio. Due to the presence of the OH group, the alcohol molecules are held together by the same intermolecular forces of interaction that exist in water. As a result, mixing of two types of molecules is possible, and the energy required to separate water or alcohol molecules from each other is taken from the formation of similar bonds between water and alcohol molecules. However, this is true only for lower alcohols, in which the OH group makes up a significant part of the molecule. The long aliphatic chain with a small OH group is largely similar to alkanes, and the physical properties of such compounds reflect this. The decrease in solubility in water 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 higher alcohols are even less.

According to the magnitude of the dipole moments (μ=1.6-1.8D), alcohols are polar substances that have weak electron-donor 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* to the electron transition of the lone pair of the oxygen atom.

· IR spectroscopy. In the IR spectrum of alcohols, strong stretching vibrations of ν OH are observed at 3635-3615 cm -1 and 3600-3200 cm -1, respectively, for highly diluted and concentrated solutions with hydrogen bonds. In addition, bending vibrations δ OH appear 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 alcohol, 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 during 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 to form a fragment ion containing a hydroxyl group.

· PMR spectroscopy . In the NMR 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, it is more economical to carry out large-scale production 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: the hydration of alkenes obtained by cracking oil, and the enzymatic hydrolysis of carbohydrates. In addition to these two methods, there are some others that have a more limited application.

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

Only those alcohols that are formed according to the Markovnikov rule can be synthesized in this way: for example, isopropyl, but not propyl; second- butyl, but not n- butyl, tert butyl but not isobutyl. Only one primary alcohol, ethyl alcohol, can be obtained by these methods. Moreover, this method lacks 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 production of secondary and tertiary alcohols. In the laboratory, it has been superseded by another method based on the reaction of hydroxymercuration-demercuration of alkenes. More about it later.

v Enzymatic hydrolysis carbohydrate-containing raw materials (grapes, berries, wheat, potatoes, etc.) are 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 source material in addition to ethyl alcohol are formed 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, pulp and paper industry waste ( hydrolysis alcohol).

§ Interesting is Weizmann reaction- enzymatic hydrolysis of carbohydrates by bacteria Clostridium acetobutylicum, resulting in a mixture n-butyl alcohol (60%), ethyl alcohol (10%) and acetone CH 3 COCH 3 (30%).

v Hydrolysis alkyl halides . The reaction is not significant, because. the halogen 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, a mixture of five isomeric alcohols is obtained, which is used as a solvent. Inaccessible pure pentanol-1 is obtained from it 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 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 initially 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 Alfol process – way to get n-alkanols by ethylene telomerization in the presence of a catalyst based on titanium chloride and triethylaluminum according to Ziegler (for details, see Chapter 8 "Alkenes"), followed by oxidation of telomerization products. In particular, primary alcohols C 12 -C 18 are synthesized by this method.

v Oxidation alkanes. When higher alkanes are oxidized 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 aqueous solution 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:

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

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

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

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

Alkylboranes are not isolated, but 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's rule and without rearrangements.

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

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

§ Mechanism hydroboration reactions can be thought of as a typical electrophilic addition of boron hydride to 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-center intermediate complex.

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

The oxidation reaction of alkylboranes proceeds as follows. At 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 flows quickly and releases heat.

The resulting boric acid ester is easily decomposed under reaction conditions to release 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 easily 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). Methods for obtaining alcohols from alkylboranes were further developed in the works of G. Brown and M. Raschke, who proposed carbon monoxide (II) as an alkylborane acceptor. The reaction proceeds at temperatures of 100-125 °C. In the intermediate complex, successive migration of alkyl groups from the boron atom to the carbon atom occurs.

By this method, depending on the reaction conditions, it is possible to obtain primary, secondary and tertiary alcohols in high yield.

v Hydroxymercuration-demercuration of alkenes leads to the formation of alcohols and is not accompanied by rearrangement. The direction of the reaction corresponds to Markovnikov's rule; it flows into mild conditions, and the yields are close to theoretical.

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

The demercuration of the resulting mercuric alcohols proceeds quantitatively when they are treated with sodium borohydride.

For instance:

Replacing water with an alcohol or carboxylic acid results in ethers or esters. In the laboratory, this method has completely supplanted the hydration reaction 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 quantities of straight chain alcohols containing even number carbon atoms, previously obtained in pure form by sodium reduction in ethyl or butyl alcohol of esters of fatty acids or fats according to Bouvo-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 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 provide stereoselectivity along with reduction selectivity.

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

When the Grignard reagent reacts 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 so it reacts first with the Grignard reagent.

v Receipt alcohols based on oxiranes.

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

§ Epoxides at action lithium aluminum hydride are converted to alcohols. The reaction consists in a nucleophilic attack of the hydride anion at the least substituted (less shielded) carbon atom to form a secondary or tertiary alcohol.

In view of the fact that a-oxides are usually obtained from olefins, this two-stage process can be considered as an alternative to the alkene hydration reaction. 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 side products.

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

Substitution of a halogen atom at secondary asymmetric carbon atoms by hydroxyl is accompanied by a 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 breaking of the C–OH bond and CO–H, due to the fact that alcohols exhibit acid-base properties.

13.5.1. Breaking the C-OH bond

v Substitution of a hydroxyl group by a halogen . There are a large number of reactions of substitution of a hydroxyl group for 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 initial alcohol, the substitution reaction can proceed according to the S N 1 or S N 2 mechanism.

· Reaction of alcohols with hydrogen halides . The success of the reaction, in addition to the conditions of conduct, 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 passing from a tertiary to a primary alcohol. Thus, tertiary alcohol reacts with hydrohalic 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 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 reaction rate zinc chloride is added, which facilitates substitution by the chloride ion.

So, i.e., according to the S N 2 mechanism, methanol and most of the spatially unhindered primary alcohols react. Protonation of alcohols converts the hydroxyl group into a good 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 the 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 a 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 according to 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 mechanism. It is determined by the concentration of alcohol, acid, reaction temperature and the nature of the solvent.

· Test Lucas . Whether the alcohol is primary, secondary, or tertiary can be determined using Lucas tryouts, which is based on the different reactivity of the three classes of alcohols with respect to hydrogen halides. Tertiary alcohols react with Lucas's reagent (a mixture of concentrated HCl with anhydrous ZnCl 2) immediately, as evidenced by the instantaneous turbidity of the reaction mixture, secondary alcohols within 5 minutes, and primary alcohols at room temperature noticeably unresponsive. Tertiary alcohols easily form carbocations, secondary alcohols are slower, and primary ones 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 exceptions are the primary allyl and benzyl alcohols, which form stable carbocations and therefore give a positive reaction.

· Interaction of alcohols with phosphorus and sulfur halides . Compared with hydrogen halides, phosphorus and sulfur halides, as well as acid 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 most probable reaction mechanism is the following. Initially, a trialkyl phosphite is formed and, if the process is carried out in the presence of bases, this compound can be the final product of the reaction.

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

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

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

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

v Application of n-toluenesulfonyl chlorides in the substitution of hydroxyl groups . Alcohols are known to interact with P-toluenesulfochloride (TsCl) in the presence of pyridine to form alkyl- P-toluenesulfonates ( tosylates).

Insofar as P-toluene sulfate ion is a very easy 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 most easily dehydrated, then secondary, and finally primary. The process of dehydration of alcohols is subject to Zaitsev's 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:

The dehydration of alcohols proceeds in two stages. First, the protonation of the OH group occurs, and then the elimination of the water molecule by the E2 mechanism, if we are talking 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 instance, according to the E1 mechanism dehydration occurs tert- butyl alcohol.

Tertiary alcohols dehydrate so easily that it is possible selective dehydration of diol 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, heated to 160 ºС or 60-70% sulfuric acid at a temperature of 90-100 ºС.

§ Alkene formation 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 actually three alkenes are obtained.

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

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

Most of all in the reaction products there will be 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 implementing the E2 mechanism due to steric hindrances.

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

For them, the E2 splitting mechanism is realized. It is not the alcohol itself that enters the reaction, but the alkyl sulfate, and the hydrosulfate anion or water plays the role of the nucleophile.

It is interesting to note that when the reaction is carried out at 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 aluminum oxide as a dehydrating agent. Heterogeneous catalytic dehydration is carried out for primary, secondary and tertiary alcohols.

Along with chamois and phosphoric acids, aluminum oxide for the dehydration of alcohols also use oxalic acid, benzenesulfonic acid, zinc chloride and thorium oxide ThO 2 . It is noteworthy that when secondary alcohols are heated with thorium(IV) oxide, alkenes are obtained 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 acid chlorides are toluenesulfonic acid, methanesulfonic acid and trifluoromethanesulfonic acid:

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

Reactions proceed stereospecifically with configuration reversal.

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 reactants, primary, secondary and tertiary amines, as well as quaternary ammonium salts, can be obtained. The use of alumina as a catalyst at 300°C leads to the same results.

13.5.2. Breaking the O–H bond

v Reactions of alcohols as acids . As you know, the strength of an acid is characterized by its ability to split off a proton. For alcohols, it is determined by the difference in the electronegativity of the oxygen and hydrogen atoms, as well as the nature and number of substituents at the hydroxyl-containing carbon atom. The presence of alkyl substituents, which have a positive inductive effect (+I-effect), reduces the acidity of alcohols. Indeed, the acidity of alcohols decreases in the series:

CH 3 OH > primary > secondary > tertiary.

With the introduction of electron-withdrawing substituents, the acidity of alcohols increases, and, for example, alcohol (СF 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 an ionic or covalent bond 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 the 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 mobile hydrogen atoms. It is known as the Chugaev–Tserevitinov–Terentiev 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, which makes it possible to remove water in the form of an azeotropic mixture.

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

v Oxidation or catalytic dehydrogenation of alcohols. The oxidation of alcohols leads to carbonyl compounds. In this case, primary alcohols are converted into aldehydes, which can then be 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 bichromate, 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 are oxidized through the hydrate form 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 an aldehyde hydrate is impossible, and therefore no carboxylic acid is synthesized.

The 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 reaction.

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

· catalytic oxidation . V Lately primary alcohols began to be oxidized to aldehydes with atmospheric oxygen with a 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 a copper-silver catalyst at 400-500°C.

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

13.6. individual representatives of monohydric alcohols

§ Methyl alcohol get by reaction:

This is the main way to get methanol. Methanol is widely used in engineering for the methylation of aniline, the production of dimethyl sulfoxide and formalin. It is 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 obtained by ethylene hydration or enzymatic hydrolysis of carbohydrates. It is used in the form of 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. Ethanol forms an azeotrope with water, 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 in it is chemically bound, for example, calcium oxide is added before distillation.

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

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

§ Butyl alcohol in large quantities is obtained from a mixture formed during the fermentation of sugars under the influence Bacterium acetobutylicum, where its content is 60%, 30% is acetone and 10% is ethyl alcohol. Moreover, nα-butyl alcohol is produced industrially by the hydroformylation of propylene. It is 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.

§ Alcohols with long chains found in plant waxes, found in insects and some animals. Obtained by hydroformylation and oxidation of aluminum alkyl, as well as hydrogenation of fats.

13.7. Unsaturated alcohols and their esters

Enols

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

For structures bearing a hydroxyl at an unsaturated carbon atom that is not bound to electron-withdrawing groups (>C=O, –NO2, etc.), the Eltekov–Erlenmeyer rule is in full force. Therefore, vinyl alcohol and its homologues do not exist, and when trying to obtain them, they rearrange 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 an unsaturated alcohol - enol, For example:

Isomerism between a carbonyl compound and an unsaturated alcohol-enol formed from it during the movement of one hydrogen atom 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 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 protonated and is created at the second unsaturated carbon atom with its δ– charge comfortable spot to attack a proton.

Alcohols are derivatives of hydrocarbons 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 monoatomic (with one hydroxyl), diatomic (with two hydroxyls), triatomic (with three hydroxyls) and polyhydric.

Like saturated hydrocarbons, monohydric alcohols form a regularly 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 the homological 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 associated with one radical or with a hydrogen atom at methanol (hydroxyl at the primary carbon atom). Secondary alcohols are characterized by a >CHOH group associated with 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 higher functions in the compound, the hydroxyl group is denoted by the prefix hydroxy- (in Russian, the prefix oxy- is often used). As the main chain, the longest unbranched chain of carbon atoms is selected, which includes a carbon atom associated with a hydroxyl group; if the compound is unsaturated, then the 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 named according to the radicals to which the hydroxyl group is connected: (CH 3) 2 CHOH - isopropyl alcohol, (CH 3) 3 COH - tert-butyl alcohol.

The rational nomenclature of 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 through 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 during the transition of molecules to 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.

Alcohols with a low molecular weight are highly soluble in water, which is understandable given 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; no wonder, 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 high molecular weight monohydric alcohols are already very similar to those of the corresponding hydrocarbons.