Oxidation of alkenes with hydrogen peroxide. Alkenes II. Oxidative cleavage of alkenes

18. Redox reactions (continued 2)

18.9. OVR involving organic substances

in OVR organic matter with inorganic organic substances are most often reducing agents. So, when organic matter burns in excess of oxygen, carbon dioxide and water are always formed. Reactions are more difficult when less active oxidizing agents are used. In this section, only the reactions of representatives of the most important classes of organic substances with some inorganic oxidizing agents are considered.

Alkenes. With mild oxidation, alkenes are converted to glycols (dihydric alcohols). The reducing atoms in these reactions are carbon atoms linked by a double bond.

The reaction with a solution of potassium permanganate proceeds in a neutral or slightly alkaline medium as follows:

C 2 H 4 + 2KMnO 4 + 2H 2 O CH 2 OH–CH 2 OH + 2MnO 2 + 2KOH (cooling)

Under more severe conditions, oxidation leads to the breaking of the carbon chain at the double bond and the formation of two acids (in a strongly alkaline medium, two salts) or an acid and carbon dioxide (in a strongly alkaline medium, a salt and a carbonate):

1) 5CH 3 CH=CHCH 2 CH 3 + 8KMnO 4 + 12H 2 SO 4 5CH 3 COOH + 5C 2 H 5 COOH + 8MnSO 4 + 4K 2 SO 4 + 17H 2 O (heating)

2) 5CH 3 CH=CH 2 + 10KMnO 4 + 15H 2 SO 4 5CH 3 COOH + 5CO 2 + 10MnSO 4 + 5K 2 SO 4 + 20H 2 O (heating)

3) CH 3 CH \u003d CHCH 2 CH 3 + 6KMnO 4 + 10KOH CH 3 COOK + C 2 H 5 COOK + 6H 2 O + 6K 2 MnO 4 (heating)

4) CH 3 CH \u003d CH 2 + 10KMnO 4 + 13KOH CH 3 COOK + K 2 CO 3 + 8H 2 O + 10K 2 MnO 4 (heating)

Potassium dichromate in a sulfuric acid medium oxidizes alkenes similarly to reactions 1 and 2.

Alkynes. Alkynes begin to oxidize under slightly more severe conditions than alkenes, so they usually oxidize with the triple bond breaking the carbon chain. As in the case of alkanes, the reducing atoms here are carbon atoms linked in this case by a triple bond. As a result of the reactions, acids and carbon dioxide are formed. Oxidation can be carried out with permanganate or potassium dichromate in an acidic environment, for example:

5CH 3 C CH + 8KMnO 4 + 12H 2 SO 4 5CH 3 COOH + 5CO 2 + 8MnSO 4 + 4K 2 SO 4 + 12H 2 O (heating)

Sometimes it is possible to isolate intermediate oxidation products. Depending on the position of the triple bond in the molecule, these are either diketones (R 1 –CO–CO–R 2) or aldoketones (R–CO–CHO).

Acetylene can be oxidized with potassium permanganate in a slightly alkaline medium to potassium oxalate:

3C 2 H 2 + 8KMnO 4 \u003d 3K 2 C 2 O 4 + 2H 2 O + 8MnO 2 + 2KOH

In an acidic environment, oxidation goes to carbon dioxide:

C 2 H 2 + 2KMnO 4 + 3H 2 SO 4 \u003d 2CO 2 + 2MnSO 4 + 4H 2 O + K 2 SO 4

Benzene homologues. Benzene homologues can be oxidized with a solution of potassium permanganate in a neutral medium to potassium benzoate:

C 6 H 5 CH 3 + 2KMnO 4 \u003d C 6 H 5 COOK + 2MnO 2 + KOH + H 2 O (at boiling)

C 6 H 5 CH 2 CH 3 + 4KMnO 4 \u003d C 6 H 5 COOK + K 2 CO 3 + 2H 2 O + 4MnO 2 + KOH (when heated)

Oxidation of these substances with dichromate or potassium permanganate in an acidic environment leads to the formation of benzoic acid.

Alcohols. The direct products of the oxidation of primary alcohols are aldehydes, while those of secondary alcohols are ketones.

The aldehydes formed during the oxidation of alcohols are easily oxidized to acids; therefore, aldehydes from primary alcohols are obtained by oxidation with potassium dichromate in an acid medium at the boiling point of the aldehyde. Evaporating, aldehydes do not have time to oxidize.

3C 2 H 5 OH + K 2 Cr 2 O 7 + 4H 2 SO 4 \u003d 3CH 3 CHO + K 2 SO 4 + Cr 2 (SO 4) 3 + 7H 2 O (heating)

With an excess of an oxidizing agent (KMnO 4, K 2 Cr 2 O 7) in any environment, primary alcohols are oxidized to carboxylic acids or their salts, and secondary - to ketones. Tertiary alcohols are not oxidized under these conditions, but methyl alcohol is oxidized to carbon dioxide. All reactions take place when heated.

Dihydric alcohol, ethylene glycol HOCH 2 -CH 2 OH, when heated in an acid medium with a solution of KMnO 4 or K 2 Cr 2 O 7, is easily oxidized to carbon dioxide and water, but sometimes it is possible to isolate intermediate products (HOCH 2 -COOH, HOOC- COOH, etc.).

Aldehydes. Aldehydes are rather strong reducing agents, and therefore are easily oxidized by various oxidizing agents, for example: KMnO 4, K 2 Cr 2 O 7, OH. All reactions take place when heated:

3CH 3 CHO + 2KMnO 4 \u003d CH 3 COOH + 2CH 3 COOK + 2MnO 2 + H 2 O
3CH 3 CHO + K 2 Cr 2 O 7 + 4H 2 SO 4 = 3CH 3 COOH + Cr 2 (SO 4) 3 + 7H 2 O
CH 3 CHO + 2OH \u003d CH 3 COONH 4 + 2Ag + H 2 O + 3NH 3

Formaldehyde with an excess of oxidizing agent is oxidized to carbon dioxide.

18.10. Comparison of the redox activity of various substances

From the definitions of the concepts "oxidizing atom" and "reducing atom" it follows that atoms in the highest oxidation state have only oxidizing properties. On the contrary, only restorative properties have atoms in the lowest oxidation state. Atoms in intermediate oxidation states can be both oxidizing and reducing agents.

However, based only on the degree of oxidation, it is impossible to unambiguously assess the redox properties of substances. As an example, consider the connections of the elements of the VA group. Nitrogen(V) and antimony(V) compounds are more or less strong oxidizers, bismuth(V) compounds are very strong oxidizers, and phosphorus(V) compounds have practically no oxidizing properties. In this and other similar cases, it matters how given degree oxidation is characteristic of a given element, that is, how stable are compounds containing atoms of a given element in this oxidation state.

Any OVR proceeds in the direction of the formation of a weaker oxidizing agent and a weaker reducing agent. In the general case, the possibility of any OVR, as well as any other reaction, can be determined by the sign of the change in the Gibbs energy. In addition, to quantify the redox activity of substances, the electrochemical characteristics of oxidizing agents and reducing agents (standard potentials of redox pairs) are used. Based on these quantitative characteristics, it is possible to build series of redox activity of various substances. The series of metal stresses known to you is built in this way. This series makes it possible to compare the reduction properties of metals in aqueous solutions under standard conditions ( With= 1 mol/l, T= 298.15 K), as well as the oxidizing properties of simple aquacations. If ions (oxidizing agents) are placed in the top line of this series, and metal atoms (reducing agents) are placed in the bottom line, then the left side of this series (up to hydrogen) will look like this:

In this series, the oxidizing properties of ions (top line) increase from left to right, while the reducing properties of metals (bottom line), on the contrary, increase from right to left.

Taking into account the differences in redox activity in different media, it is possible to construct similar series for oxidizing agents. So, for reactions in an acidic medium (pH = 0), a "continuation" of a series of metal activity is obtained in the direction of enhancing the oxidizing properties

As in the activity series of metals, in this series the oxidizing properties of oxidizing agents (top row) increase from left to right. But, using this series, it is possible to compare the reducing activity of reducing agents (bottom line) only if their oxidized form coincides with that given in the top line; in this case it amplifies from right to left.

Let's look at a few examples. To find out if this redox is possible, we will use the general rule that determines the direction of the redox reactions (reactions proceed in the direction of the formation of a weaker oxidizing agent and a weaker reducing agent).

1. Can magnesium reduce cobalt from a CoSO 4 solution?
Magnesium is a stronger reducing agent than cobalt, and Co 2 ions are stronger oxidizing agents than Mg 2 ions, therefore, it is possible.
2. Can a solution of FeCl 3 oxidize copper to CuCl 2 in an acidic environment?
Since Fe 3B ions are stronger oxidizing agents than Cu 2 ions, and copper is a stronger reducing agent than Fe 2 ions, it is possible.
3. Is it possible, by blowing oxygen through a solution of FeCl 2 acidified with hydrochloric acid, to obtain a solution of FeCl 3?
It would seem not, since in our series oxygen is to the left of Fe 3 ions and is a weaker oxidizing agent than these ions. But in an aqueous solution, oxygen is almost never reduced to H 2 O 2, in this case it is reduced to H 2 O and occupies a place between Br 2 and MnO 2. Therefore, such a reaction is possible, however, it proceeds rather slowly (why?).
4. Is it possible to oxidize H 2 O 2 in an acidic environment with potassium permanganate?
In this case, H 2 O 2 is a reducing agent and the reducing agent is stronger than Mn 2B ions, and MnO 4 ions are oxidizing agents stronger than oxygen formed from peroxide. Therefore, it is possible.

A similar series constructed for OVR in an alkaline medium looks like this:

Unlike the "acid" series, this series cannot be used in conjunction with the metal activity series.

Electron-ion balance method (half-reaction method), intermolecular OVR, intramolecular OVR, OVR dismutation (disproportionation, self-oxidation-self-healing), OVR switching, passivation.

Using the method of electron-ion balance, make up the equations of the reactions that occur when a solution of a) H 2 S (S, more precisely, S 8 ) is added to a solution of potassium permanganate acidified with sulfuric acid; b) KHS; c) K 2 S; d) H 2 SO 3; e) KHSO 3 ; e) K 2 SO 3 ; g) HNO 2 ; g) KNO 2 ; i) KI (I 2 ); j) FeSO 4 ; k) C 2 H 5 OH (CH 3 COOH); l) CH 3 CHO; m) (COOH) 2 (CO 2 ); n) K 2 C 2 O 4 . Here and below, where necessary, oxidation products are indicated in curly brackets.
Make up the equations of the reactions that occur when the following gases are passed through a solution of potassium permanganate acidified with sulfuric acid: a) C 2 H 2 (CO 2 ); b) C 2 H 4 (CO 2 ); c) C 3 H 4 (propyne) (CO 2 and CH 3 COOH); d) C 3 H 6 ; e) CH 4 ; e) HCHO.
The same, but the reducing agent solution is added to the neutral potassium permanganate solution: a) KHS; b) K 2 S; c) KHSO 3 ; d) K 2 SO 3; e) KNO 2 ; e) KI.
The same, but potassium hydroxide solution was previously added to the potassium permanganate solution: a) K 2 S (K 2 SO 4 ); b) K 2 SO 3; c) KNO 2 ; d) KI (KIO 3 ).
Make equations for the following reactions occurring in solution: a) KMnO 4 + H 2 S ...;
b) KMnO 4 + HCl ...;
c) KMnO 4 + HBr ...;
d) KMnO 4 + HI...
Write the following OVR equations for manganese dioxide:
Solutions of the following substances are added to a solution of potassium dichromate acidified with sulfuric acid: a) KHS; b) K 2 S; c) HNO 2 ; d) KNO 2 ; e) KI; e) FeSO 4 ; g) CH 3 CH 2 CHO; i) H 2 SO 3 ; j) KHSO 3 ; k) K 2 SO 3. Write the equations for the ongoing reactions.
The same, but the following gases are passed through the solution: a) H 2 S; b) SO2.
Solutions of a) K 2 S (K 2 SO 4 ) are added to a potassium chromate solution containing potassium hydroxide; b) K 2 SO 3; c) KNO 2 ; d) KI (KIO 3 ). Write the equations for the ongoing reactions.
A solution of potassium hydroxide was added to a solution of chromium(III) chloride until the initially formed precipitate was dissolved, and then bromine water was added. Write the equations for the ongoing reactions.
The same, but at the last stage, a solution of potassium persulfate K 2 S 2 O 8 was added, which was reduced during the reaction to sulfate.
Write the equations for the reactions taking place in the solution:

a) CrCl 2 + FeCl 3; b) CrSO 4 + FeCl 3; c) CrSO 4 + H 2 SO 4 + O 2;

d) CrSO 4 + H 2 SO 4 + MnO 2; e) CrSO 4 + H 2 SO 4 + KMnO 4.

Write equations for the reactions that take place between solid chromium trioxide and the following substances: a) C; b) CO; c) S (SO 2 ); d) H 2 S; e) NH 3 ; e) C 2 H 5 OH (CO 2 and H 2 O); g) CH 3 COCH 3 .
Make up the equations of the reactions that occur when the following substances are added to concentrated nitric acid: a) S (H 2 SO 4 ); b) P 4 ((HPO 3) 4 ); c) graphite; d) Se; e) I 2 (HIO 3 ); e) Ag; g) Cu; i) Pb; j) KF; k) FeO; l) FeS; m) MgO; o) MgS; p) Fe(OH) 2 ; c) P 2 O 3 ; m) As 2 O 3 (H 3 AsO 4 ); y) As 2 S 3; f) Fe(NO 3) 2; x) P 4 O 10 ; c) Cu 2 S.
The same, but with the passage of the following gases: a) CO; b) H 2 S; c) N 2 O; d) NH3; e) NO; e) H 2 Se; g) HI.
The reactions will proceed in the same way or differently in the following cases: a) a piece of magnesium was placed in a high test tube two-thirds filled with concentrated nitric acid; b) a drop of concentrated nitric acid was placed on the surface of a magnesium plate? Write reaction equations.
What is the difference between the reaction of concentrated nitric acid with hydrosulfide acid and with gaseous hydrogen sulfide? Write reaction equations.
Will OVR proceed in the same way when anhydrous crystalline sodium sulfide and its 0.1 M solution are added to a concentrated solution of nitric acid?
A mixture of the following substances was treated with concentrated nitric acid: Cu, Fe, Zn, Si and Cr. Write the equations for the ongoing reactions.
Make up the equations of the reactions that occur when the following substances are added to dilute nitric acid: a) I 2 ; b) Mg; c) Al; d) Fe; e) FeO; f) FeS; g) Fe (OH) 2; i) Fe(OH) 3 ; j) MnS; k) Cu 2 S; l) CuS; m) CuO; n) Na 2 S cr; p) Na 2 S p; c) P 4 O 10 .
What processes will take place when a) ammonia, b) hydrogen sulfide, c) carbon dioxide is passed through a dilute solution of nitric acid?
Write the equations for the reactions that occur when added to concentrated sulfuric acid the following substances: a) Ag; b) Cu; c) graphite; d) HCOOH; e) C 6 H 12 O 6; f) NaCl cr; g) C 2 H 5 OH.
When hydrogen sulfide is passed through cold concentrated sulfuric acid, S and SO 2 are formed, hot concentrated H 2 SO 4 oxidizes sulfur to SO 2. Write reaction equations. How will the reaction proceed between hot concentrated H 2 SO 4 and hydrogen sulfide?
Why is hydrogen chloride obtained by treating crystalline sodium chloride with concentrated sulfuric acid, while hydrogen bromide and hydrogen iodine are not obtained in this way?
Make up the equations of the reactions that take place during the interaction of dilute sulfuric acid with a) Zn, b) Al, c) Fe, d) chromium in the absence of oxygen, e) chromium in air.
Make up the reaction equations that characterize the redox properties of hydrogen peroxide:

In which of these reactions is hydrogen peroxide an oxidizing agent and in which is it a reducing agent?

What reactions occur when the following substances are heated: a) (NH 4) 2 CrO 4; b) NaNO 3 ; c) CaCO 3 ; d) Al(NO 3) 3; e) Pb(NO 3) 3 ; f) AgNO 3 ; g) Hg (NO 3) 2; i) Cu(NO 3) 2 ; j) CuO; l) NaClO 4 ; l) Ca(ClO 4) 2; m) Fe(NO 3) 2; n) PCl 5 ; p) MnCl 4 ; c) H 2 C 2 O 4 ; m) LiNO 3 ; s) HgO; f) Ca(NO 3) 2; x) Fe(OH) 3 ; c) CuCl 2 ; h) KClO 3 ; w) KClO 2 ; w) CrO 3 ?
When hot solutions of ammonium chloride and potassium nitrate are drained, a reaction occurs, accompanied by gas evolution. Write an equation for this reaction.
Make up the equations of the reactions that occur when a) chlorine is passed through a cold solution of sodium hydroxide, b) bromine vapor. The same, but through a hot solution.
When interacting with a hot concentrated solution of potassium hydroxide, selenium undergoes dismutation to the nearest stable oxidation states (–II and +IV). Write an equation for this OVR.
Under the same conditions, sulfur undergoes a similar dismutation, but the excess sulfur reacts with sulfite ions to form thiosulfate ions S 2 O 3 2 . Write the equations for the ongoing reactions. ;
Make up the equations for the electrolysis reactions of a) a copper nitrate solution with a silver anode, b) a lead nitrate solution with a copper anode.

Experience 1. Oxidizing properties of potassium permanganate in an acidic environment. To 3-4 drops of a solution of potassium permanganate add an equal volume of a dilute solution of sulfuric acid, and then a solution of sodium sulfite until discoloration. Write an equation for the reaction.

Experience 2.Oxidizing properties potassium permanganate in a neutral medium. Add 5-6 drops of sodium sulfite solution to 3-4 drops of potassium permanganate solution. What substance was isolated in the form of a precipitate?

Experience 3. Oxidizing properties of potassium permanganate in an alkaline medium. Add 10 drops of concentrated sodium hydroxide solution and 2 drops of sodium sulfite solution to 3-4 drops of potassium permanganate solution. The solution should turn green.

Experience 4. Oxidizing properties of potassium dichromate in an acidic environment. Acidify 6 drops of potassium dichromate solution with 4 drops of dilute sulfuric acid solution and add sodium sulfite solution until the color of the mixture changes.

Experience 5. Oxidizing properties of dilute sulfuric acid. Place a zinc granule in one test tube, and a piece of copper tape in the other. Add 8-10 drops of dilute sulfuric acid solution to both tubes. Compare what is happening. EXPERIENCE IN A FAN CABINET!

Experience 6. Oxidizing properties of concentrated sulfuric acid. Similar to experiment 5, but add concentrated sulfuric acid solution. A minute after the start of the release of gaseous reaction products, insert strips of filter paper moistened with solutions of potassium permanganate and copper sulfate into the test tubes. Explain what is happening. EXPERIENCE IN A FAN CABINET!

Experience 7. Oxidizing properties of dilute nitric acid. Similar to experiment 5, but add a dilute nitric acid solution. Observe the color change of the gaseous reaction products. EXPERIENCE IN A FAN CABINET!

Experience 8. Oxidizing properties of concentrated nitric acid. Place a piece of copper tape in a test tube and add 10 drops of concentrated nitric acid solution. Gently heat until the metal is completely dissolved. EXPERIENCE IN A FAN CABINET!

Experience 9. Oxidizing properties of potassium nitrite. To 5-6 drops of a solution of potassium nitrite add an equal volume of a dilute solution of sulfuric acid and 5 drops of a solution of potassium iodide. What substances are formed?

Experience 10. Reducing properties of potassium nitrite. To 5-6 drops of a solution of potassium permanganate add an equal volume of a dilute solution of sulfuric acid and a solution of potassium nitrite until the mixture is completely discolored.

Experience 11.Thermal decomposition of copper nitrate. Place one microspatula of copper nitrate trihydrate in a test tube, fix it in a rack and gently heat it with an open flame. Observe dehydration and subsequent salt decomposition. EXPERIENCE IN A FAN CABINET!

Experience 12.Thermal decomposition of lead nitrate. Carry out similarly to experiment 11, placing lead nitrate in a test tube. EXPERIENCE IN A FAN CABINET! What is the difference between the processes occurring during the decomposition of these salts?

Select the main carbon chain in the molecule. First, it must be the longest. Secondly, if there are two or more chains of the same length, then the most branched one is selected from them. For example, in a molecule there are 2 chains with the same number (7) of C atoms (highlighted in color):

In case (a), the chain has 1 substituent, and in case (b), it has 2. Therefore, option (b) should be chosen.

1. Number the carbon atoms in the main chain so that the C atoms associated with the substituents receive the lowest possible numbers. Therefore, the numbering starts from the end of the chain closest to the branch. For example:

Name all radicals (substituents), indicating in front the numbers indicating their location in the main chain. If there are several identical substituents, then for each of them a number (location) is written separated by a comma, and their number is indicated by prefixes di-, three-, tetra-, penta- etc. (For example, 2,2-dimethyl or 2,3,3,5-tetramethyl).

The names of all substituents are arranged in alphabetical order (as established by the latest IUPAC rules).

Name the main chain of carbon atoms, i.e. the corresponding normal alkane.

Thus, in the name of a branched alkane, the root + suffix is the name of a normal alkane (Greek numeral + suffix "an"), prefixes are numbers and names of hydrocarbon radicals. Name construction example:

Chem. St. alkanesCracking of alkanes. Cracking is a process of thermal decomposition of hydrocarbons, which is based on the reactions of splitting the carbon chain of large molecules with the formation of compounds with a shorter chain. Isomerization of alkanes Alkanes of normal structure under the influence of catalysts and when heated are able to turn into branched alkanes without changing the composition of the molecules, i.e. enter into isomerization reactions. These reactions involve alkanes whose molecules contain at least 4 carbon atoms. For example, the isomerization of n-pentane to isopentane (2-methylbutane) occurs at 100°C in the presence of an aluminum chloride catalyst:

The starting material and the product of the isomerization reaction have the same molecular formulas and are structural isomers (carbon skeleton isomerism).

Dehydrogenation of alkanes

When alkanes are heated in the presence of catalysts (Pt, Pd, Ni, Fe, Cr 2 O 3 , Fe 2 O 3 , ZnO), their catalytic dehydrogenation– splitting off of hydrogen atoms due to the breaking of C-H bonds.

The structure of the dehydrogenation products depends on the reaction conditions and the length of the main chain in the starting alkane molecule.

1. Lower alkanes containing from 2 to 4 carbon atoms in the chain, when heated over a Ni catalyst, split off hydrogen from neighboring carbon atoms and turn into alkenes:

Along with butene-2 this reaction produces butene-1 CH 2 \u003d CH-CH 2 -CH 3. In the presence of a Cr 2 O 3 /Al 2 O 3 catalyst at 450-650 С from n-butane is also received butadiene-1,3 CH 2 =CH-CH=CH 2 .

2. Alkanes containing more than 4 carbon atoms in the main chain are used to obtain cyclical connections. At the same time, it happens dehydrocyclization- dehydrogenation reaction, which leads to the closure of the chain into a stable cycle.

If the main chain of an alkane molecule contains 5 (but not more) carbon atoms ( n-pentane and its alkyl derivatives), then when heated over a Pt catalyst, hydrogen atoms are split off from the terminal atoms of the carbon chain, and a five-membered cycle is formed (cyclopentane or its derivatives):

Alkanes with a main chain of 6 or more carbon atoms also enter into the dehydrocyclization reaction, but always form a 6-membered cycle (cyclohexane and its derivatives). Under the reaction conditions, this cycle undergoes further dehydrogenation and turns into an energetically more stable benzene cycle of an aromatic hydrocarbon (arene). For example:

These reactions underlie the process reforming– processing of petroleum products in order to obtain arenes ( aromatization saturated hydrocarbons) and hydrogen. transformation n- alkanes in arenas leads to improved knock resistance of gasoline.

Alkynes with a non-terminal triple bond serve as a potential source for the synthesis of 1,2-diketones under the action of a suitable oxidizing agent. However, no universal reagent has yet been found that causes the oxidation of a triple carbon–carbon bond to a 1,2-dicarbonyl group. RuO 4 proposed for this purpose, ruthenium (VIII) oxide, is too expensive and often causes further oxidative degradation of 1,2-diketones to carboxylic acids. When disubstituted acetylenes react with such strong oxidizing agents as potassium permanganate, only in a completely neutral medium at pH 7–8 at 0 С can oxidation be stopped at the stage of formation of -diketone. So, for example, stearolic acid at pH 7.5 is oxidized to α-diketone. In most cases, oxidation is accompanied by the cleavage of the triple bond with the formation of carboxylic acids:

The yield of products of oxidative degradation of alkynes is low, and this reaction does not play a significant role in organic synthesis. It is used solely to prove the structure of the natural acetylenic acid contained in the leaves of tropical plants in Central America. During its oxidative destruction, two acids were isolated - lauric and adipic. This means that the original acid is 6-octadecic acid with a normal carbon skeleton of seventeen carbons:

Much more important is the oxidative coupling of alkynes-1 catalyzed by copper salts (the Glaser–Eglinton reaction). In 1870, Glaser discovered that a suspension of copper (I) acetylenide in alcohol is oxidized by atmospheric oxygen to form 1,3-diynes:

For the oxidation of copper (I) acetylenides, potassium hexacyanoferrate (III) K 3 in DME or DMF is more effective as an oxidizing agent. In 1959, Eglinton proposed a much more convenient modification of the oxidative condensation of alkynes. Alkyne is oxidized with copper(II) acetate in a solution of pyridine at 60–70°C. Eglinton's modification proved to be extremely useful for the synthesis of macrocyclic polyynes from ,-diynes. As an illustration, we present the synthesis of two cyclopolyines during the oxidative condensation of hexadiine-1,5 (F. Sondheimer, 1960):

One of the polyins is a product of cyclotrimerization, the other is a product of cyclotetramerization of the starting gesadiin-1,5. The trimer serves as the initial reagent for the synthesis of aromatic -annulenes (for more details on annules, see Chapter 12). Similarly, under the same conditions of nonadiine-1,8, its dimer is obtained - 1,3,10,12-cyclooctadecatetraene along with trimer, tetramer and pentamer:

To obtain unsymmetrical diynes, condensation of haloacetylenes with alkyne-1 (terminal alkyne) in the presence of copper (I) salts and a primary amine is used (coupling according to Kadio–Chodkevich, 1957):

The initial bromalkynes are obtained by the action of sodium hypobromite on alkynes-1 or from lithium and bromine acetylides:

The organocopper derivative of terminal alkyne is generated directly in the reaction mixture of Cu 2 Cl 2 and alkyne-1.

6.3.4. Triple bond electrophilic addition reactions

Electrophilic addition reactions to the triple bond are among the most typical and important reactions of alkynes. In contrast to the electrophilic addition to alkenes, the synthetic application of this large group of reactions was far ahead of the development of theoretical ideas about its mechanism. However, over the past twenty years, the situation has changed significantly and at present this is one of the rapidly developing areas of physical organic chemistry. The HOMO of the alkyne is located lower than the HOMO of the alkene (Sec. 2), and this circumstance in the vast majority of cases predetermines the lower rate of addition of the electrophilic agent to the alkyne compared to the alkene. Another factor that determines the difference in the reactivity of alkynes and alkenes in electrophilic addition reactions is the relative stability of the intermediates that arise when an electrophilic species is added to triple and double bonds. When an electrophilic particle H + or E + is attached to a double bond, a cyclic or open carbocation is formed (Ch. 5). The addition of H + or E + to a triple bond leads to the formation of an open or cyclic vinyl cation. In a linear open vinyl cation, the central carbon atom is in sp-hybrid state, while vacant R-orbital is orthogonal to the -bond. Because the sp-hybrid carbon atom of the vinyl cation has a higher electronegativity compared to sp 2-hybrid atom of the alkyl cation, the vinyl cation should be less stable compared to the alkyl cation:

The data of quantum mechanical calculations, as well as thermodynamic data for the gas phase, obtained using high-pressure mass spectrometry and cyclotron resonance spectroscopy, are in full agreement with these considerations. In table. 6.3 shows thermodynamic data for the formation of a number of carbocations and hydrocarbons, related to the gas phase at 25 С.

Carbocation	Δ H f ˚ kcal/mol

From the data presented in Tal. 6.3, it follows that the vinyl cation is 47 kcal/mol less stable than the ethyl cation containing the same number of atoms. The same conclusion can be drawn from the ionization enthalpy in the gas phase CH 3 CH 2 Cl and CH 2 =CHCl:

It is easy to see that the combination of both factors - the higher energy of the vinyl cation and the low HOMO of the alkyne - represents the lower reactivity of alkynes compared to alkenes in electrophilic addition reactions. In table. 6.4 contains comparative data on the addition of halogens, sulfene and selenyl chlorides, trifluoroacetic acid and water to various alkenes and alkynes that do not contain any activating or deactivating functional group.

Table 6.4

Comparative characteristics of alkynes and alkenes

in electrophilic addition reactions

	substrates	K alkene / K alkyne
Bromination in acetic acid	CH 2 CH 2 /HCCH C 4 H 9 CH \u003d CH 2 / C 4 H 9 C  CH C 6 H 5 CH \u003d CH 2 / C 6 H 5 C  CH
Chlorination in acetic acid	C 6 H 5 CH \u003d CH 2 / C 6 H 5 C  CH C 4 H 9 CH \u003d CH 2 / C 6 H 5 C  CH C 2 H 5 C \u003d SNS 2 H 5 / C 2 H 5 C  SS 2 H 5
Addition of 4-chlorophenylsulfen chloride P-ClС 6 H 4 SeCl	CH 2 \u003d CH 2 / HC  CH C 4 H 9 CH \u003d CH 2 / C 4 H 9 C  CH C 6 H 5 CH \u003d CH 2 / C 6 H 5 C  CH
Addition of phenylselene chloride C 6 H 5 SeCl	CH 2 \u003d CH 2 / HC  CH C 4 H 9 CH \u003d CH 2 / C 4 H 9 C  CH C 6 H 5 CH \u003d CH 2 / C 6 H 5 C  CH
Addition of trifluoroacetic acid	C 4 H 9 CH \u003d CH 2 / C 4 H 9 C  CH C 6 H 5 CH \u003d CH 2 / C 6 H 5 C  CH C 2 H 5 CH \u003d CH 2 / C 2 H 5 C  CH
Acid catalyzed hydration	C 4 H 9 CH \u003d CH 2 / C 4 H 9 C  CH C 2 H 5 CH \u003d SNS 2 H 5 / C 2 H 5 C  SS 2 H 5 C 6 H 5 CH \u003d CH 2 / C 6 H 5 C  CH

It follows from these data that only the addition of acidic agents and water to triple and double bonds occurs at similar rates. The addition of halogens, sulfenchlorides and a number of other reagents to alkenes proceeds 10 2 - 10 5 times faster than to alkynes. This means that hydrocarbons containing non-conjugated triple and double bonds selectively add these reactants at the double bond, for example:

Data on the comparative hydration of alkynes and alkenes should be treated with caution, since the hydration of alkynes requires catalysis by mercury (II) ions, which is inefficient for the addition of water to the double bond. Therefore, the data on the hydration of the triple and double bonds, strictly speaking, are not comparable.

The addition of halogens, hydrogen halides, sulfen chlorides and other electrophilic agents can be carried out in steps, which can be easily illustrated using the following examples:

In redox reactions, organic substances more often exhibit the properties of reducing agents, while they themselves are oxidized. Ease of oxidation organic compounds depends on the availability of electrons when interacting with an oxidizing agent. All known factors that cause an increase in the electron density in the molecules of organic compounds (for example, positive inductive and mesomeric effects) will increase their ability to oxidize and vice versa.

The tendency of organic compounds to oxidize increases with the growth of their nucleophilicity, which corresponds to the following rows:

The growth of nucleophilicity in the series

Consider redox reactions representatives of the most important classes organic matter with some inorganic oxidizing agents.

Alkene oxidation

With mild oxidation, alkenes are converted to glycols (dihydric alcohols). The reducing atoms in these reactions are carbon atoms linked by a double bond.

The reaction with a solution of potassium permanganate proceeds in a neutral or slightly alkaline medium as follows:

3C 2 H 4 + 2KMnO 4 + 4H 2 O → 3CH 2 OH–CH 2 OH + 2MnO 2 + 2KOH

1) 5CH 3 CH=CHCH 2 CH 3 + 8KMnO 4 + 12H 2 SO 4 → 5CH 3 COOH + 5C 2 H 5 COOH + 8MnSO 4 + 4K 2 SO 4 + 17H 2 O

2) 5CH 3 CH=CH 2 + 10KMnO 4 + 15H 2 SO 4 → 5CH 3 COOH + 5CO 2 + 10MnSO 4 + 5K 2 SO 4 + 20H 2 O

3) CH 3 CH=CHCH 2 CH 3 + 8KMnO 4 + 10KOH → CH 3 COOK + C 2 H 5 COOK + 6H 2 O + 8K 2 MnO 4

4) CH 3 CH \u003d CH 2 + 10KMnO 4 + 13KOH → CH 3 COOK + K 2 CO 3 + 8H 2 O + 10K 2 MnO 4

Potassium dichromate in a sulfuric acid medium oxidizes alkenes similarly to reactions 1 and 2.

During the oxidation of alkenes, in which carbon atoms in the double bond contain two carbon radicals, two ketones are formed:

Alkyne oxidation

Alkynes oxidize under slightly more severe conditions than alkenes, so they usually oxidize with the triple bond breaking the carbon chain. As in the case of alkenes, the reducing atoms here are carbon atoms linked by a multiple bond. As a result of the reactions, acids and carbon dioxide are formed. Oxidation can be carried out with permanganate or potassium dichromate in an acidic environment, for example:

5CH 3 C≡CH + 8KMnO 4 + 12H 2 SO 4 → 5CH 3 COOH + 5CO 2 + 8MnSO 4 + 4K 2 SO 4 + 12H 2 O

Acetylene can be oxidized with potassium permanganate in a neutral medium to potassium oxalate:

3CH≡CH +8KMnO 4 → 3KOOC –COOK +8MnO 2 +2KOH +2H 2 O

In an acidic environment, oxidation goes to oxalic acid or carbon dioxide:

5CH≡CH + 8KMnO 4 + 12H 2 SO 4 → 5HOOC -COOH + 8MnSO 4 + 4K 2 SO 4 + 12H 2 O
CH≡CH + 2KMnO 4 + 3H 2 SO 4 → 2CO 2 + 2MnSO 4 + 4H 2 O + K 2 SO 4

Oxidation of benzene homologues

Benzene does not oxidize even under fairly harsh conditions. Benzene homologues can be oxidized with a solution of potassium permanganate in a neutral medium to potassium benzoate:

C 6 H 5 CH 3 + 2KMnO 4 → C 6 H 5 COOK + 2MnO 2 + KOH + H 2 O

C 6 H 5 CH 2 CH 3 + 4KMnO 4 → C 6 H 5 COOK + K 2 CO 3 + 2H 2 O + 4MnO 2 + KOH

Oxidation of benzene homologues with dichromate or potassium permanganate in an acid medium leads to the formation of benzoic acid.

5C 6 H 5 CH 3 + 6KMnO 4 +9 H 2 SO 4 → 5C 6 H 5 COOH + 6MnSO 4 + 3K 2 SO 4 + 14H 2 O

5C 6 H 5 –C 2 H 5 + 12KMnO 4 + 18H 2 SO 4 → 5C 6 H 5 COOH + 5CO 2 + 12MnSO 4 + 6K 2 SO 4 + 28H 2 O

Alcohol oxidation

The direct products of the oxidation of primary alcohols are aldehydes, while those of secondary alcohols are ketones.

3C 2 H 5 OH + K 2 Cr 2 O 7 + 4H 2 SO 4 → 3CH 3 CHO + K 2 SO 4 + Cr 2 (SO 4) 3 + 7H 2 O

With an excess of an oxidizing agent (KMnO 4, K 2 Cr 2 O 7) in any medium, primary alcohols are oxidized to carboxylic acids or their salts, and secondary alcohols to ketones.

5C 2 H 5 OH + 4KMnO 4 + 6H 2 SO 4 → 5CH 3 COOH + 4MnSO 4 + 2K 2 SO 4 + 11H 2 O

3CH 3 -CH 2 OH + 2K 2 Cr 2 O 7 + 8H 2 SO 4 → 3CH 3 -COOH + 2K 2 SO 4 + 2Cr 2 (SO 4) 3 + 11H 2 O

Tertiary alcohols are not oxidized under these conditions, but methyl alcohol is oxidized to carbon dioxide.

Dihydric alcohol, ethylene glycol HOCH 2 -CH 2 OH, when heated in an acidic medium with a solution of KMnO 4 or K 2 Cr 2 O 7, is easily oxidized to oxalic acid, and in neutral to potassium oxalate.

5CH 2 (OH) - CH 2 (OH) + 8KMnO 4 + 12H 2 SO 4 → 5HOOC -COOH + 8MnSO 4 + 4K 2 SO 4 + 22H 2 O

3CH 2 (OH) - CH 2 (OH) + 8KMnO 4 → 3KOOC -COOK + 8MnO 2 + 2KOH + 8H 2 O

Oxidation of aldehydes and ketones

Aldehydes are rather strong reducing agents, and therefore are easily oxidized by various oxidizing agents, for example: KMnO 4, K 2 Cr 2 O 7, OH, Cu (OH) 2. All reactions take place when heated:

3CH 3 CHO + 2KMnO 4 → CH 3 COOH + 2CH 3 COOK + 2MnO 2 + H 2 O

3CH 3 CHO + K 2 Cr 2 O 7 + 4H 2 SO 4 → 3CH 3 COOH + Cr 2 (SO 4) 3 + 7H 2 O

CH 3 CHO + 2KMnO 4 + 3KOH → CH 3 COOK + 2K 2 MnO 4 + 2H 2 O

5CH 3 CHO + 2KMnO 4 + 3H 2 SO 4 → 5CH 3 COOH + 2MnSO 4 + K 2 SO 4 + 3H 2 O

CH 3 CHO + Br 2 + 3NaOH → CH 3 COONa + 2NaBr + 2H 2 O

silver mirror reaction

With an ammonia solution of silver oxide, aldehydes are oxidized to carboxylic acids, which give ammonium salts in an ammonia solution (“silver mirror” reaction):

CH 3 CH \u003d O + 2OH → CH 3 COONH 4 + 2Ag + H 2 O + 3NH 3

CH 3 -CH \u003d O + 2Cu (OH) 2 → CH 3 COOH + Cu 2 O + 2H 2 O

Formic aldehyde (formaldehyde) is oxidized, as a rule, to carbon dioxide:

5HCOH + 4KMnO 4 (hut) + 6H 2 SO 4 → 4MnSO 4 + 2K 2 SO 4 + 5CO 2 + 11H 2 O

3CH 2 O + 2K 2 Cr 2 O 7 + 8H 2 SO 4 → 3CO 2 + 2K 2 SO 4 + 2Cr 2 (SO 4) 3 + 11H 2 O

HCHO + 4OH → (NH 4) 2 CO 3 + 4Ag↓ + 2H 2 O + 6NH 3

HCOH + 4Cu(OH) 2 → CO 2 + 2Cu 2 O↓+ 5H 2 O

Ketones are oxidized under severe conditions by strong oxidizing agents with a gap C-C connections and give mixtures of acids:

carboxylic acids. Among the acids, formic and oxalic acids have strong reducing properties, which are oxidized to carbon dioxide.

HCOOH + HgCl 2 \u003d CO 2 + Hg + 2HCl

HCOOH + Cl 2 \u003d CO 2 + 2HCl

HOOC-COOH + Cl 2 \u003d 2CO 2 + 2HCl

Formic acid, in addition to acidic properties, also exhibits some properties of aldehydes, in particular, reducing. It is then oxidized to carbon dioxide. For example:

2KMnO4 + 5HCOOH + 3H2SO4 → K2SO4 + 2MnSO4 + 5CO2 + 8H2O

When heated with strong dehydrating agents (H2SO4 (conc.) or P4O10) it decomposes:

HCOOH →(t)CO + H2O

Catalytic oxidation of alkanes:

Catalytic oxidation of alkenes:

Phenol oxidation:

Alkenes - These are hydrocarbons in the molecules of which there is ONE double C \u003d C bond.

Alkene nomenclature: suffix appears in the name -EN.

The first member of the homologous series is C2H4 (ethene).

For the simplest alkenes, historically established names are also used:

ethylene (ethene)

propylene (propene),

The following monovalent alkene radicals are often used in the nomenclature:

CH2-CH=CH2

Types of isomerism of alkenes:

1. Isomerism of the carbon skeleton:(starting from C4H8 - butene and 2-methylpropene)

2. Multiple bond position isomerism:(starting with C4H8): butene-1 and butene-2.

3. Interclass isomerism: With cycloalkanes(starting with propene):

C4H8 - butene and cyclobutane.

4. Spatial isomerism of alkenes:

Due to the fact that free rotation around the double bond is impossible, it becomes possible cis-trans- isomerism.

Alkenes having two carbon atoms at each double bond various substitutes, can exist in the form of two isomers that differ in the arrangement of substituents relative to the π-bond plane:

Chemical properties of alkenes.

Alkenes are characterized by:

· double bond addition reactions,

· oxidation reactions,

· substitution reactions in the "side chain".

1. Double bond addition reactions: the weaker π-bond is broken, a saturated compound is formed.

These are electrophilic addition reactions - AE.

1) Hydrogenation:

CH3-CH=CH2 + H2 à CH3-CH2-CH3

2) Halogenation:

CH3-CH=CH2 + Br2 (solution)à CH3-CHBr-CH2Br

Discoloration of bromine water is a qualitative reaction to a double bond.

3) Hydrohalogenation:

CH3-CH=CH2 + HBr à CH3-CHBr-CH3

(MARKOVNIKOV'S RULE: hydrogen is attached to the most hydrogenated carbon atom).

4) Hydration - water connection:

CH3-CH=CH2 + HOH à CH3-CH-CH3

(attachment also occurs according to Markovnikov's rule)

2. Addition of hydrogen bromide to presence of peroxides (Harash effect) - this is a radical addition - AR

CH3-CH=CH2 + HBr -(H2O2)à CH3-CH2-CH2Br

(reaction with hydrogen bromide in the presence of peroxide proceeds against Markovnikov's rule )

3. Combustion- complete oxidation of alkenes with oxygen to carbon dioxide and water.

С2Н4 + 3О2 = 2СО2 + 2Н2О

4. Soft oxidation of alkenes - Wagner reaction : reaction with a cold aqueous solution of potassium permanganate.

3CH3- CH=CH2+ 2KMnO4 + 4H2O à 2MnO2 + 2KOH + 3 CH3 - CH - CH2

Oh Oh

( a diol is formed)

Discoloration of an aqueous solution of potassium permanganate with alkenes is a qualitative reaction for alkenes.

5. Hard oxidation of alkenes- hot neutral or acidic potassium permanganate solution. Comes with a break in the C=C double bond.

1. Under the action of potassium permanganate in an acidic environment, depending on the structure of the alkene skeleton, the following is formed:

Fragment of the carbon chain at the double bond	What does it turn into

= CH -R	R– COOHcarboxylic acid
= C – R	ketoneR – C – R

CH3-C-1 H=C-2Н2 +2 KMn+7O4 + 3H2SO4 a

CH3-C+3 Oh + C+4 O2 + 2Mn+2SO4 + K2SO4 + 4H2O

2. If the reaction proceeds in a neutral environment when heated, then, accordingly, potassium salt:

Fragment of a chain near a double bond	What does it turn into
	K2CO3
= CH -R	R– COOTO- carboxylic acid salt
= C – R	ketoneR – C – R

3CH3C-1H=WITH-2Н2 +10 K MnO4 - ta 3 CH3 C+3OO K + + 3K 2C+4O3 + 10MnO2 +4Н2О+ K Oh

6. Oxidation ethylene oxygen in the presence of palladium salts.

CH2=CH2 + O2 –(kat)à CH3CHO

(acetaldehyde)

7. Chlorination and bromination to the side chain: if the reaction with chlorine is carried out in the light or at high temperature- Hydrogen is being replaced in the side chain.

CH3-CH=CH2 + Cl2 – (light)à CH2-CH=CH2 + HCl

8. Polymerization:

n CH3-CH=CH2 а(-CH–CH2-)n

propylene ô polypropylene

ALKENES PRODUCTION

I . Cracking alkanes:	С7Н16 –(t)а CH3-CH=CH2 + C4H10 alkene alkane
II. Dehydrohalogenation of haloalkanes under the action of an alcohol solution of alkali - the reaction ELIMINATING.	Zaitsev's rule: The elimination of a hydrogen atom in elimination reactions occurs predominantly from the least hydrogenated carbon atom.
III. Dehydration of alcohols at an elevated temperature (above 140°C) in the presence of depriving reagents - aluminum oxide or concentrated sulfuric acid - the elimination reaction.	CH3- CH-CH2-CH3 – (H2SO4,t>140o)à à H2O+CH3- CH=CH-CH3 (also obeys the Zaitsev rule)
IV. Dehalogenation of dihaloalkanes having halogen atoms at neighboring carbon atoms, under the action of active metals.	CH2 Br-CH Br-CH3+ mg aCH2=CH-CH3+ MgBr2 Zinc may also be used.
V. Dehydrogenation of alkanes at 500°С:
VI. Incomplete hydrogenation of dienes and alkynes	С2Н2 + Н2 (deficiency) –(kat)à С2Н4

ALKADIENES.

These are hydrocarbons containing two double bonds. The first member of the series is C3H4 (propadiene or allene). The suffix appears in the name - DIEN .

Types of double bonds in dienes:

1.Insulateddouble bonds separated in chain by two or more σ-bonds:

CH2=CH–CH2–CH=CH2. Dienes of this type exhibit properties characteristic of alkenes.

2. Cumulativedouble bonds located on one carbon atom: CH2=C=CH2(allen)

Such dienes (allenes) belong to a rather rare and unstable type of compounds.

3.Paireddouble bonds separated by one σ-bond: CH2=CH–CH=CH2

Conjugated dienes are characterized by characteristic properties due to the electronic structure of the molecules, namely, a continuous sequence of four sp2 carbon atoms.

Diene isomerism

1. Isomerism double bond positions:

2. Isomerism carbon skeleton:

3. Interclass isomerism with alkynes And cycloalkenes . For example, the following compounds correspond to the formula C4H6:

4. Spatial isomerism

Dienes having various substituents at carbon atoms at double bonds, like alkenes, exhibit cis-trans isomerism.

(1) Cis isomer (2) Trans isomer

Electronic structure of conjugated dienes.

Molecule of butadiene-1,3 CH2=CH-CH=CH2 contains four carbon atoms sp2 - hybridized state and has a flat structure.

π-electrons of double bonds form a single π-electron cloud (adjoint system ) and are delocalized between all carbon atoms.

The multiplicity of bonds (the number of common electron pairs) between carbon atoms has an intermediate value: there are no purely single and purely double bonds. The structure of butadiene is more accurately reflected by the formula with delocalized "one and a half" bonds.

CHEMICAL PROPERTIES OF CONJUGATED ALKADIENES.

REACTIONS OF ADDITION TO CONJUGATED DIENES.

The addition of halogens, hydrogen halides, water and other polar reagents occurs by an electrophilic mechanism (as in alkenes).

In addition to addition at one of the two double bonds (1,2-addition), conjugated dienes are characterized by the so-called 1,4-addition, when the entire delocalized system of two double bonds participates in the reaction:

The ratio of 1,2- and 1,4-addition products depends on the reaction conditions (with an increase in temperature, the probability of 1,4-addition usually increases).

1. Hydrogenation.

CH3-CH2-CH=CH2 (1,2 product)

CH2=CH-CH=CH2 + H2

CH3-CH=CH-CH3 (1,4 product)

In the presence of a Ni catalyst, a complete hydrogenation product is obtained:

CH2=CH-CH=CH2 + 2 H2 –(Ni, t)à CH3-CH2-CH2-CH3

2. Halogenation, hydrohalogenation and hydration

1,4-attachment.

1,2-attachment.

With an excess of bromine, one more of its molecule is added at the site of the remaining double bond to form 1,2,3,4-tetrabromobutane.

3. polymerization reaction.

The reaction proceeds predominantly by the 1,4-mechanism, with the formation of a polymer with multiple bonds, called rubber :

nCH2=CH-CH=CH2 à (-CH2-CH=CH-CH2-)n

polymerization of isoprene:

nCH2=C–CH=CH2 à(–CH2 –C =CH –CH2 –)n

CH3 CH3 (polyisoprene)

OXIDATION REACTIONS - soft, hard, as well as burning.

They proceed in the same way as in the case of alkenes - mild oxidation leads to a polyhydric alcohol, and hard oxidation leads to a mixture of various products depending on the structure of the diene:

CH2=CH –CH=CH2 + KMnO4 + H2O à CH2 – CH – CH – CH2 + MnO2 + KOH

Alkadienes are burning to carbon dioxide and water. C4H6 + 5.5O2 à 4CO2 + 3H2O

OBTAINING ALKADIENES.

1. catalytic dehydrogenation alkanes (through the stage of formation of alkenes). In this way, divinyl is obtained in industry from butane contained in oil refining gases and associated gases:

Isoprene is obtained by catalytic dehydrogenation of isopentane (2-methylbutane):

2. Lebedev's synthesis:

(catalyst - a mixture of oxides Al2O3, MgO, ZnO

2 C2H5OH –(Al2O3,MgO, ZnO, 450˚C)à CH2=CH-CH=CH2 + 2H2O + H2

3. Dehydration of dihydric alcohols:

4. Action of an alcoholic solution of alkali on dihaloalkanes (dehydrohalogenation):