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Purpose of the lesson: to deepen and systematize students’ knowledge on the topic of the arena, to bring them to the realization that properties, signs and knowledge are necessary in order to build order out of chaos.

Tasks:

• Educational: consolidate the idea of ​​aromatic hydrocarbons. Consider the cause and effect relationship between composition, properties and use, study the physical and chemical properties of benzene, and show its toxic effect.
• Developmental: develop skills in writing equations chemical reactions, express and prove your opinion, present the material briefly and coherently, contribute to the continued development of sustainable interest in chemical science.
• Educational: to cultivate a desire to increase personal knowledge, develop innovative thinking, show the importance of chemical knowledge for modern people.

Lesson type: meta-subject lesson learning new material.

Equipment: computer, screen, multimedia projector, signal cards, cards with formulas, presentation for the lesson made in PowerPoint, reference notes.

Methods: conversation, independent work in pairs, problem presentation.

Lesson progress

1. Org. Moment.

Hello guys! Sit down.

2. Teacher's word conversation .

We have a chemistry lesson with two topics. The first theme is chaos and order. From your point of view, what is chaos?

Student answers.

That is, chaos is a violation of order. Then what is order?

Student answers.

A root is a row, something arranged in a row. Is chaos good or bad?

Student answers.

Remember this.

3. Repetition.

Guys, what kind of chemistry have we started studying?

Student answers.

What is this chemistry and what does it study?

Student answers.

How many hydrocarbons are known?

Student answers.

What hydrocarbons have we studied?

Student answers.

You have cards with hydrocarbon formulas scattered chaotically on your tables:

CH 4, C 3 H 8, C 8 H 18, C 2 H 4, C 2 H 2, C 3 H 4, C 6 H 6, C 6 H 5 CH 3, C 6 H 5 (CH 3) 2

Now, working in pairs, put things in order in the given formulas, and explain how you did it and on what basis.

Student work Substances are divided into three groups: saturated. Unsaturated and aromatic.

And what we get is that we have one chaos, but many orders. And chemistry is a world of order. And today in our lesson we will build order in the chemical properties of benzene and its homologues. To what class do benzene and its homologues belong?

Student answers.

What are arenas?

Student answers.

Write the formulas of benzene, toluene and xylene on the board.

Students write formulas at the blackboard.

4. Learning new material

Physical properties. Benzene– colorless, volatile, flammable liquid with an unpleasant odor. It is lighter than water (=0.88 g/cm3) and does not mix with it, but it is soluble in organic solvents, and itself dissolves many substances well. Benzene boils at 80.1 C; when cooled, it easily solidifies into a white crystalline mass. Benzene and its vapors are poisonous. Benzene vapors with air form an explosive mixture. Under normal conditions, most aromatic hydrocarbons are also colorless liquids, insoluble in water, with a characteristic odor.

Benzene is a highly toxic substance. Inhaling its vapors causes dizziness and headaches. At high concentrations of benzene, cases of loss of consciousness are possible. Its vapors irritate the eyes and mucous membranes.

Liquid benzene easily penetrates the body through the skin, which can lead to poisoning. Therefore, working with benzene and its homologues requires special care.

Studies of a tar-like substance obtained from tobacco smoke have shown that, in addition to nicotine, it contains aromatic hydrocarbons such as benzopyrene,

having strong carcinogenic properties, i.e. these substances act as cancer causative agents. Tobacco tar, when it comes into contact with the skin and lungs, causes the formation of cancerous tumors. Smokers are more likely to develop cancer of the lip, tongue, larynx, and esophagus. They are much more likely to suffer from angina pectoris and myocardial infarction.

Let's consider the chemical properties of benzene. What is the formula of benzene?

Student answers.

Do you think it is saturated or unsaturated?

Student answers.

Then it should decolorize the potassium permanganate solution and bromine water. Let's watch the video experience.

What can be concluded?

Student answers.

The chemical properties of benzene and other aromatic hydrocarbons differ from saturated and unsaturated hydrocarbons.

Most characteristic of them substitution reactions hydrogen atoms of the benzene ring. They proceed more easily than with saturated hydrocarbons.

What can hydrogen be replaced with?

Student answers.

Benzene undergoes halogenation reactions in the presence of a catalyst. If it reacts with bromine, then the catalyst is iron (III) bromide, if with chlorine, then iron (III) chloride. Let's write the reaction:

Bromobenzene is a colorless liquid, insoluble in water.

But if toluene reacts, then the substitution occurs at position 2,4,6 and 2,4,6 - tribromotoluene is formed.

If benzene is treated with a mixture of concentrated nitric and sulfuric acids (nitrating mixture), then the hydrogen atom is replaced by a nitro group - NO 2: watch the video experiment and write the reaction equation:

This benzene nitration reaction . Nitrobenzene is a pale yellow oily liquid with the smell of bitter almonds, insoluble in water, used as a solvent.

But if toluene, rather than benzene, is nitrated, then substitution occurs at position 2,4,6 and 2,4,6 is formed - trinitrotoluene or TNT, let's write the equation of the chemical reaction:

C 6 H 5 CH 3 +3 HONO 2 -> C 6 H 2 (NO 2) 3 CH 3

Guys, is there a different way to show the benzene ring or nucleus?

Student answers.

This means that benzene is unsaturated and can undergo addition reactions.

Addition reactions to benzene occur with great difficulty. For their occurrence, special conditions are required: increased temperature and pressure, selection of a catalyst, light irradiation, etc. Thus, in the presence of a catalyst - nickel or platinum - benzene is hydrogenated, i.e. adds hydrogen to form cyclohexane:

Cyclohexane is a colorless volatile liquid with the smell of gasoline and is insoluble in water.

Under ultraviolet irradiation, benzene adds chlorine: watch the video experiment

Hexachlorocyclohexane, or hexachlorane, is a crystalline substance used as a powerful insect killer.

Well, the last chemical property of benzene, characteristic of all hydrocarbons, regardless of class, is combustion. Let's watch the video experiment and write down the equation of the chemical reaction ourselves:

2C 6 H 6 + 15O2 = 12CO 2 + 6H 2 O

We looked at the chemical properties of benzene and what conclusion can we draw?

Student answers.

Guys, the use of benzene and its homologues is widespread. In the textbook on page 65, Figure 23 shows the applications of benzene

Application conclusion:

Guys, what did we look at today?

Student answers.

Let's consolidate what we've learned

1. Which of the following properties characterize benzene: 1) colorless liquid, 2) colorless gas, 3) crystalline substance, 4) odorless, 5) has a characteristic odor, 6) unlimitedly soluble in water, 7) insoluble in water, 8 ) lighter than water, 9) heavier than water, 10) burns with a highly smoky flame, 11) burns with a colorless flame, 12) is it a good solvent?

1, 5, 7, 8, 10, 12

2. Nitration of benzene is carried out:

1. concentrated nitric acid
2. melted sodium nitrate
3. a mixture of concentrated sulfuric and nitric acids
4. nitric oxide (IV)

3. Which formula is unacceptable to use to depict a benzene molecule?

4. Which of the reactions of benzene is a substitution reaction?

1. Nitration
2. Combustion
3. Hydrogenation
4. Interaction with chlorine under UV irradiation

5. To hydrogenate 1 mol of benzene to cyclohexane, hydrogen will be required in the amount of:

1. 1 mole
2. 2 mol
3. 3 mol
4. 4 mol

Guys, on your tables the cards are white on one side and green on the other side. Now I will make a couple of statements, if you agree, raise the green one, if not, then the white one:

1. Benzene is an aromatic hydrocarbon.
2. Benzene and toluene are isomers.
3. Benzene does not undergo substitution reactions.
4. Benzene undergoes addition reactions.
5. Benzene is neither saturated nor unsaturated.

5. Homework:

1. Paragraph 15 exercise 12 (a,b) page 67
2. Come up with a problem on the properties of benzene and its homologues and solve it;

7. Reflection.

Let's return to the first topic: chaos and order.

Based on the structure of the benzene molecule, we built order in its chemical properties. Chaos alone. And there can be many orders.

We can probably say that chaos is an order of things that we cannot understand.

No, disruption is not always a bad thing. Today we had an unusual lesson. We have a lot of guests. This is a violation of order. But I can’t say that this is bad. I had a tremendous pleasure working with you. Thanks for the lesson!

Lesson topic: Properties and applications of arenas.

Target: Give students an idea of ​​the properties and applications of arenas.

Tasks:

Educational:

To form students’ knowledge about the properties and applications (using a computer presentation on the topic: “Properties and applications of arenes”), using the example of toluene to give an idea of ​​the mutual influence of atoms and groups of atoms in the molecules of organic substances.

Continue developing skills to solve calculation problems various types.

Educational:

Develop observation and memory (when watching a computer presentation, when studying the properties and use of arenas).

Develop the ability to compare (for example, comparing the properties of arene homologues).

Teach students to generalize and draw conclusions.

Educational:

Continue the formation of a dialectical-materialistic worldview based on ideas about the use of aromatic hydrocarbons.

Lesson teaching methods:

Verbal (conversation, explanation, story).

Visual (computer presentation, poster on the structure of aromatic hydrocarbons).

Practical (demonstration of video experiments, drawing up models of molecules)

Lesson type: Combined.

Lesson progress

I . Organizational moment. (there is 1 presentation slide on the screen with the name of the lesson topic)

Communicate the purpose and objectives of the lesson. Planned learning outcomes.

II. Updating knowledge, skills and abilities:

Conversation on questions:

Teacher: What are aromatic hydrocarbons? What types of aromatic hydrocarbons can be distinguished?

(Arenes are hydrocarbons with the general formula CnH2n-6, the molecules of which contain at least one benzene ring. There are several main types of arenes: 1. Monocyclic arenes, 2. Arenes containing two or more isolated rings, 3. Arenes with conjugated rings (conjugate and condensed))

Next, I introduce students to the origin of the term “aromatic compounds.” I inform you that this name arose in the initial period of the development of chemistry. It was noticed that benzene compounds are obtained by distillation of some pleasant-smelling (aromatic) substances - natural resins and balms. However, most aromatic compounds are odorless or smell unpleasant. But this term has been preserved in chemistry. Teacher: Yes, you are right (slide 2, 3)

Teacher: What is the structure of benzene?

The student comes to the board and talks about the structure of benzene (Demonstration of a poster on the structure of benzene). A student talks about the structure of benzene using a poster (slide 4)

I call 3 students to the board.

Exercise:

assemble models of molecules:

A) benzene

B) methylbenzene (toluene)

B) 1.4 dimethylbenzene (p-xylene)

What substances are called homologues benzene? (slide5)

I call 2 students to solve problems about benzene homologues.

1.What is the mass of an aromatic hydrocarbon containing 12 hydrogen atoms? Propose two different structural formulas for this arena and name them.

2. Determine the molecular formula of an aromatic hydrocarbon whose molecular weight is 134. Propose two different structural formulas for this arene and name them.

At this time, I invite class students to solve problems in their notebooks. (slide 6)

Exercise :

(Determine the amount of substance

1, 2-dimethylbenzene, the mass of which is 212 g (answer: 2 mol)

Determine the mass of ethylbenzene, the amount of substance of which is 0.5 mol. (answer: 53g)

We check the completion of tasks.

Solving calculation problems to receive arenas (3 students)

What volume of acetylene (at standard conditions) will be required to obtain 156 g of benzene?

(Ans.: 134.4l)

What mass of benzene can be obtained as a result of the dehydrogenation of cyclohexane weighing 336 g? (Answer: 312 g)

What mass of benzene can be obtained as a result of dehydrogenation of hexane with a mass of

172 g? (answer: 156g)

Let's remember now ways to get arenas(slides 7-11)

Let me summarize the results of the survey.

III. Learning new material:

Physical properties of arenas.(slide 12)

(Demonstration of samples of aromatic hydrocarbons: benzene, toluene, xylene, styrene, naphthalene)

Teacher: A story about the physical properties of arenas. Under normal conditions, lower arenas are colorless liquids with a characteristic odor. They are insoluble in water, but highly soluble in non-polar solvents: ether, carbon tetrachloride, ligroin.

I draw students' attention to the fact that benzene is highly toxic substance. Inhaling its vapors causes dizziness and headaches. At high concentrations of benzene, cases of loss of consciousness are possible. Its vapors irritate the eyes and mucous membranes.

Liquid benzene easily penetrates the body through the skin, which can lead to poisoning. Therefore, working with benzene and its homologues requires special care.

I talk about the dangers of smoking. Studies of a tar-like substance obtained from tobacco smoke have shown that, in addition to nicotine, it contains aromatic hydrocarbons such as benzpyrene, which have strong carcinogenic properties. They are called carcinogens chemicals, the impact of which significantly increases the incidence of tumors or shortens the period of their development in humans or animals, i.e., these substances act as causative agents of cancer. It has been shown that about 90% of lung cancer cases are a consequence of excessive smoking. Tobacco tar, when it comes into contact with the skin and lungs, causes the formation of cancerous tumors. Smokers are more likely to develop cancer of the lip, tongue, larynx, and esophagus. They are much more likely to suffer from angina pectoris and myocardial infarction. I note that a smoker releases about 50% of toxic substances into the surrounding space, creating around himself a ring of “passive smokers” who quickly develop headaches, nausea, general malaise, and then may develop chronic diseases.

In addition, benzene and its homologues can themselves act as solvents.

Video demonstration “Physical properties of benzene”

Chemical properties of arenes (slide 13)

Teacher: Now let’s look at what chemical properties are characteristic of substances of the “Arena” class. (The teacher poses a problem to the students: remembering the structure of arenes, make an assumption about their reactivity. Students, based on the structure of benzene, assume what properties are characteristic of the class of arenes).

Teacher: To break the aromatic system of arenes, it is necessary to expend a lot of energy, so arenes enter into addition reactions only under severe conditions: with a significant increase in temperature or in the presence of very active reagents. In this regard, the most characteristic reactions for them will be the substitution reactions of hydrogen atoms, occurring with the preservation of the aromatic system.

Students write down in a notebook all the reactions characteristic of benzene and its homologues.

Demonstration of slides 14 and 15 of the presentation. “Reaction of benzene bromination”

Watch the video “Benzene Bromination”

Demonstration of slide 16 of the presentation “Reaction of benzene nitration”

Watch the video “Nitration of benzene”

Demonstration of slide 17 of the presentation “Nitration of Toluene”.

We are discussing the question: why, during the nitration of benzene, only one hydrogen atom is replaced by a nitro group, and during the nitration of toluene, three hydrogen atoms are replaced by nitro groups? (This is explained by the influence of the methyl radical on the benzene ring. The methyl group shifts the bond density away from itself. As a result of the shift in electron density from the methyl group towards the benzene ring in positions 2.4, 6, the electron density in the benzene ring increases and hydrogen atoms are easier to react with substitution)

Addition reactions (slide 18).

Addition reactions in aromatic hydrocarbons take place under more severe conditions than in unsaturated hydrocarbons.

Demonstration of slide 18 of the presentation “Benzene hydrogenation”

Demonstration of slide 19 of the presentation “Chlorination of benzene”

Oxidation reactions (slide 20)

Benzene is resistant to oxidizing agents; under normal conditions it does not discolor the potassium permanganate solution.

Demonstration of 21 slides of the presentation “Combustion of benzene”

Watch the video “Combustion of benzene”

Demonstration of the presentation slide “Oxidation of Toluene” Discussion of the question: why, unlike benzene, is toluene oxidized by potassium permanganate?

In this case, the benzene ring already affects the methyl radical. That in it, in comparison with, for example, CH 4, the electron bond density decreases and under the influence of such a strong oxidizing agent as potassium permanganate, the methyl group is oxidized and converted into the carboxyl group COOH)

Thus, we see that not only the methyl group can affect the benzene ring, but the benzene ring also affects the methyl group, i.e. groups of atoms in a molecule exert mutual influence on each other.

Application of arenas.

The student receives an advanced task in the previous lesson and talks about the use of benzene using a presentation (slide 25)

Summarizing new material.

Teacher: So, we have examined the class of aromatic hydrocarbons, learned about their characteristics, their preparation, properties and applications.

V. Homework (slide 26)

Learn paragraph 5.3

to “3” exercise 14, 15 page 132. (standard level)

If you want to get a higher grade, then choose which problem you will solve at home (algorithmic or heuristic level). I offer students problems in envelopes of different colors, they themselves determine the problem of what level of difficulty they will solve at home: “4” or “5”

IV. Reinforcing the material learned

Teacher: Well, you worked very well today, now let’s remember once again everything that we talked about. And tests will help us with this. Students receive tests.

Aromatic hydrocarbons

Option I

1. Indicate the name of the cycloalkane from which benzene can be obtained by dehydrogenation reaction:

1) cyclopentane

2) methylcyclopentane

3) methylcyclohexane

4) cyclohexane

2. Are the judgments about benzene and its homologues correct?

A. Benzene is not oxidized by a solution of potassium permanganate.

B. When potassium permanganate acts on toluene, the methyl radical, and not the benzene ring, undergoes oxidation.

3. For benzeneNot characteristic reaction:

1) hydrogenation 3) isomerization

2) substitution 4) nitration

4. Unlike benzene, toluene reacts with:

1) halogens 3) nitric acid

2) oxygen 4) potassium permanganate

5. Match the reactants and reaction products:

Reactants: reaction products:

A) C 6 H 5 CH 3 +HNO 3 ⟶ 1. C 6 H 12

B) C 6 H 6 +Br 2 ⟶ 2. C 6 H 2 (NO 2 ) 3 CH 3 +3H 2 O

B) C 6 H 5 CH 3 + [O] ⟶ 3. C 6 H 5 Br + HBr

D) C 6 H 6 + H 2 ⟶ 4. C 6 H 5 COOH

5. CO 2 + H 2 O

Aromatic hydrocarbons.

Option 2.

1. Indicate the name of the cycloalkane from which toluene can be obtained by dehydrogenation reaction:

1) cyclohexane;

2) methylcyclopentane;

3) methylcyclohexane;

4) ethylcyclohexane.

2. Are the following statements about benzene and its homologues true?

A) Benzene is characterized by addition reactions

B) Substitution reactions in toluene occur much more easily than in benzene.

1) only A is true. 3) both judgments are true.

2) only B is true. 4) both judgments are incorrect.

3. BenzeneNot interacts with:

1) bromine 3) nitric acid

2) water 4) hydrogen

4. Benzene interacts with each substance of the pair:

1) HNO 3, H 2 O 3) H 2, C 2 H 5 O H

2) Br 2, HNO 3 4) Br 2, KMnO 4

5. Establish a correspondence between the left side of the reaction equation and the type of reaction and to which it belongs:

Left side of the reaction equation: reaction type:

A) C 6 H 6 + HNO 3 ⟶ 1. substitution
B) C 6 H 6 + 3H 2 ⟶ 2. isomerization
B) C 6 H 5 CH 3 + ⟶ 3. trimerization
D) 3C 2 H 2 ⟶ 4. accession

5. oxidation

Mutual verification of tests. (slide 27)

Answers to the test on the topic “Aromatic hydrocarbons”

1 option	Option 2
5. A-2 B- 3 C- 4 D- 1	5. A-1 B-4 C-5 D-3

At this time, 3 students at the board solve level problems.

(Students choose the level of difficulty of the task independently)

We check the results of the work.

VI. Summing up

Teacher: So, guys, our lesson is coming to an end. You did a very good job in class today (grades are given). Well done!

CHEMISTRY AND BIOLOGY TEACHER

MKOU BUTURLINOVSKAYA secondary school No. 4

BLACK T.M.,

2014

ARENAS. BENZENE AND ITS HOMOLOGUES

CHEMISTRY, 10TH GRADE

DICTIONARY

Aromatic compounds (from Greek ároma - incense), a class of organic cyclic compounds, all atoms of which participate in the formation of a single conjugate system; The p-electrons of such a system form a stable, i.e., closed, electron shell.

The name “Aromatic compounds” was stuck due to the fact that the first discovered and studied representatives of this class of substances had a pleasant odor.

General formula of aromatic hydrocarbons

C n H 2 n -6. ( n at least 6)

Nomenclature

Benzene homologues – compounds formed by replacing one or more hydrogen atoms in a benzene molecule with hydrocarbon radicals ( R ):

WITH 6 N 5  R (alkylbenzene), R  WITH 6 N 4  R (dialkylbenzene), etc.

Nomenclature. Widely used trivial names(toluene, xylene, cumene, etc.). Systematic names built from the name of the hydrocarbon radical (prefix) and the word benzene

WITH 6 N 5  WITH H 3 WITH 6 N 5  WITH 2 H 5 WITH 6 N 5  WITH 3 H 7

methylbenzene ethylbenzene propylbenzene

History of discovery

Benzene was first described by a German chemist Johann Glauber , who obtained this compound in 1649 by distilling coal tar. But the substance did not receive a name, nor was its composition known.

Johann

Glauber

Benzene received its rebirth thanks to the work of Faraday. Benzene was discovered in 1825 year English physicist Michael Faraday , who isolated it from the liquid condensate of illuminating gas .

Michael Faraday

IN 1833 German physicist and chemist Eilhard Mitscherlich obtained benzene by dry distillation of the calcium salt of benzoic acid (this is where the name benzene comes from)

Eilhard Mitscherlich

Structural formula of benzene

It was proposed by the German scientist A. Kekule in 1865

Benzene doesn't interact With bromine water And

solution potassium permanganate!

A.Kekule

H0

against!

Kekule's formula and its inconsistency

for!

The structure of benzene

At one time there was

a lot has been proposed

structural options

benzene formulas, but neither

one of them couldn't

satisfactorily

explain his special

properties.

Cyclicity of the structure

benzene is confirmed

by the fact that it

monosubstituted

derivatives have no

isomers.

N

N

N

WITH 6

N

N

N

• 1)Type of hybridization - s r 2
• 2) sigma bonds are formed between carbon and carbon and hydrogen atoms, lying in the same plane.
• 3) bond angle – 120 degrees
• 4) length S-S connections 0.140nm

Scheme of formation of pi bonds in a benzene molecule

Due to non-hybrid

p – electronic clouds in a benzene molecule perpendicular to the plane of formation of sigma bonds, a single

p-electron I system consisting of 6 p – electrons and common to all carbon atoms.

• The modern understanding of the electronic nature of bonds in benzene is based on the hypothesis of an American physicist and chemist, two-time Nobel Prize winner L. Pauling.

• It was at his suggestion that the benzene molecule began to be depicted as a hexagon with an inscribed circle, thereby emphasizing the absence of fixed double bonds and the presence of a single electron cloud covering all six carbon atoms of the cycle.

• The combination of six sigma connections with a single n system is called aromatic bond
• A ring of six carbon atoms linked by an aromatic bond is called benzene ring or benzene ring.

Substitution reactions.

1) Halogenation

When benzene reacts with a halogen (in this case, chlorine), the hydrogen atom of the nucleus is replaced by a halogen.

Substitution reactions.

In case benzene homologues the reaction of radical substitution of hydrogen atoms in the side chain occurs more easily

Substitution reactions.

2) Nitration. When benzene is exposed to a nitrating mixture, the hydrogen atom is replaced by a nitro group (the nitrating mixture is a mixture of concentrated nitric and sulfuric acids in a ratio of 1:2, respectively).

Substitution reactions.

3 ) Sulfonation carried out with concentrated sulfuric acid or oleum. During the reaction, the hydrogen atom is replaced by a sulfo group.

C 6 H 6 +H 2 SO 4 - SO 3  C 6 H 5 – SO 3 H+H 2 O

(benzenesulfonic acid)

Substitution reactions.

4 ) Alkylation

The replacement of a hydrogen atom in the benzene ring with an alkyl group (alkylation) occurs under the action of alkyl halides (Friedel-Crafts reaction) or alkenes in the presence of catalysts AlCl 3 , AlBr 3 , FeCl 3 (Lewis acids).

Substitution reactions

with benzene homologues

Benzene homologues (alkylbenzenes) C 6 N 5 – R are more active in substitution reactions compared to benzene.

For example, during the nitration of toluene C 6 N 5 CH 3 (70  C) replacement of not one, but three hydrogen atoms occurs with the formation of 2,4,6-trinitrotoluene:

CH 3  WITH 6 N 5 + 3 HNO 3  CH 3  WITH 6 N 2 ( NO 2 ) 3 + 3 H 2 O

2,4,6-trinitrotoluene

TNT, tol)

When toluene is brominated, three hydrogen atoms are also replaced:

AlBr 3

CH 3  WITH 6 N 5 + 3 Br 2  CH 3  WITH 6 N 2 Br 3 + 3 HBr

2,4,6-tribromotoluene

Despite the tendency of benzene to undergo substitution reactions, under harsh conditions it also enters addition reactions.

5) Hydrogenation.

Hydrogen addition occurs only in the presence catalysts and at elevated temperature . Benzene is hydrogenated to form cyclohexane, and benzene derivatives give cyclohexane derivatives.

6) Halogenation. Radical chlorination In conditions of radical reactions (ultraviolet light, elevated temperature) addition of halogens to aromatic compounds is possible. By radical chlorination of benzene, “hexachlorane” (a means of combating harmful insects) was obtained.

Remember

If a benzene molecule contains one of the hydrogen atoms replaced by a hydrocarbon radical , then in the future first of all atoms will be replaced hydrogen at the second, fourth and sixth carbon atoms .

Oxidation reactions

7) Oxidation reactions.

Toluene, unlike methane, is oxidized to mild conditions (discolors acidified KMnO solution 4 when heated):

In toluene, it is not the benzene ring that is oxidized, but the methyl radical.

8) Combustion.

2 C 6 H 6 + 15 O 2  12 CO 2 + 6 H 2 O (smoking flame).

Receipt

1) Catalytic dehydrocyclization of alkanes, i.e. elimination of hydrogen with simultaneous cyclization (method of B.A. Kazansky and A.F. Plate). The reaction occurs at elevated temperature using a catalyst such as chromium oxide

C 7 H 16 ––500 °C → C 6 H 5 – CH 3 + 4H 2

2) Catalytic dehydrogenation of cyclohexane and its derivatives (N.D. Zelinsky). The catalyst used is palladium black or platinum at 300 °C.

C 6 H 12 ––300 °C , Pd → C 6 H 6 + 3H 2

3) Cyclic trimerization of acetylene and its homologues over activated carbon at 600 °C (N.D. Zelinsky).

3C 2 H 2 ––600 °C → C 6 H 6

4) Fusion of salts of aromatic acids with alkali or soda lime.

C 6 H 5 -COONa + NaOH ––t° → C 6 H 6 +Na 2 CO 3

5) Alkylation of benzene itself halogen derivatives (Friedel-Crafts reaction) or olefins.

C 6 H 6 +CH 3 C l ––AlCl 3 → C 6 H 5 – CH 3 +HCl

C 6 H6+CH 2 = CH 2 ––H 3 P.O. 4 → C 6 H 5 –CH 2 –CH 3

Benzene C 6 N 6 used as a starting product for the production of various aromatic compounds – nitrobenzene, chlorobenzene, aniline, phenol, styrene etc., used in production drugs, plastics, dyes, pesticides and many other organic substances.

• Toluene C 6 N 5 -CH 3 used in the production of dyes, medicinal substances and explosives (TNT, tol).
• Xylenes C 6 N 4 (SN 3 ) 2 in the form of a mixture of three isomers (ortho-, meta- and para-xylenes) - technical xylene - is used as a solvent and starting product for the synthesis of many organic compounds.
• Isopropylbenzene (cumene) C 6 N 4 -CH(CH 3 ) 2 – starting material to obtain phenol and acetone.
• Vinylbenzene (styrene) C 6 H 5 -CH=CH 2 used to produce valuable polymer material polystyrene.

1 of 20

Presentation on the topic: Aromatic hydrocarbons

Slide no. 1

Slide description:

Slide no. 2

Slide description:

Arenas Aromatic hydrocarbons (arenes) are substances whose molecules contain one or more benzene rings - cyclic groups of carbon atoms with a special nature of bonds. The concept of “benzene ring” requires decoding. To do this, it is necessary to consider the structure of the benzene molecule. The first structure of benzene was proposed in 1865. German scientist A. Kekule:

Slide no. 3

Slide description:

This formula correctly reflects the equivalence of six carbon atoms, but does not explain a number of special properties of benzene. For example, despite its unsaturation, benzene does not show a tendency to addition reactions: it does not discolor bromine water and a solution of potassium permanganate, i.e., it does not give qualitative reactions typical of unsaturated compounds. The structural features and properties of benzene were fully explained only after the development of the modern quantum mechanical theory of chemical bonds. According to modern concepts, all six carbon atoms in the benzene molecule are in the sp2 hybrid state. Each carbon atom forms s-bonds with two other carbon atoms and one hydrogen atom, lying in the same plane. The bond angles between the three s-bonds are 120°. Thus, all six carbon atoms lie in the same plane, forming a regular hexagon (s-skeleton of the benzene molecule).

Slide no. 4

Slide description:

Each carbon atom has one unhybridized p orbital. Six such orbitals are located perpendicular to the flat s-skeleton and parallel to each other (see Fig. a). All six electrons interact with each other, forming p-bonds, not localized in pairs as in the formation of double bonds, but combined into a single p-electron cloud. Thus, circular conjugation occurs in the benzene molecule. The highest p-electron density in this conjugated system is located above and below the s-skeleton plane (see Fig. b).

Slide no. 5

Slide description:

As a result, all bonds between carbon atoms in benzene are aligned and have a length of 0.139 nm. This value is intermediate between the length of a single bond in alkanes (0.154 nm) and the length of a double bond in alkenes (0.133 nm). The equivalence of connections is usually depicted with a circle inside the cycle (see Fig. c). Circular conjugation gives an energy gain of 150 kJ/mol. This value constitutes the conjugation energy - the amount of energy that must be expended to disrupt the aromatic system of benzene. This electronic structure explains all the features of benzene. In particular, it is clear why benzene is difficult to enter into addition reactions - this would lead to a violation of conjugation. Such reactions are only possible under very harsh conditions.

Slide no. 6

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Nomenclature and isomerism. Conventionally, the arenas can be divided into two rows. The first includes benzene derivatives (for example, toluene or biphenyl), the second includes condensed (polynuclear) arenes (the simplest of them is naphthalene): The homologous series of benzene corresponds to the general formula C6H2n-6.where n>=6

Slide no. 7

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Structural isomerism in the homologous series of benzene is due to the mutual arrangement of substituents in the nucleus. Monosubstituted benzene derivatives do not have positional isomers, since all atoms in the benzene ring are equivalent. Disubstituted derivatives exist in the form of three isomers, differing in the relative arrangement of substituents. The position of the substituents is indicated by numbers or prefixes: ortho- (o-), meta- (m-), para- (p-). The C6H5 radical is called phenyl.

Slide no. 8

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Physical properties. The first members of the homologous series of benzene (for example, toluene, ethylbenzene, etc.) are colorless liquids with a specific odor. They are lighter than water and insoluble in it. They dissolve well in organic solvents. Benzene and its homologues are themselves good solvents for many organic substances. All arenas burn with a smoky flame due to the high carbon content in their molecules.

Slide no. 9

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Methods of obtaining. 1. Preparation from aliphatic hydrocarbons. When straight-chain alkanes with at least six carbon atoms per molecule are passed over heated platinum or chromium oxide, dehydrocyclization occurs - the formation of an arene with the release of hydrogen:

Slide no. 10

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2. Dehydrogenation of cycloalkanes. The reaction occurs by passing vapors of cyclohexane and its homologues over heated platinum: 3. Preparation of benzene by trimerization of acetylene. 4. Preparation of benzene homologues using the Friedel-Crafts reaction (see below). 5. Fusion of salts of aromatic acids with alkali:

Slide no. 11

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Chemical properties. Possessing a mobile six p-electrons, the aromatic nucleus is a convenient object for attack by electrophilic reagents. This is also facilitated by the spatial arrangement of the p-electron cloud on both sides of the flat s-skeleton of the molecule (see Fig. b). The most typical reactions for arenes are those that proceed through the electrophilic substitution mechanism, designated by the symbol SE (from the English substitution electrophilic).

Slide no. 12

Slide description:

The mechanism of electrophilic substitution can be represented as follows. The electrophilic reagent XY (X is an electrophile) attacks the electron cloud and, due to weak electrostatic interaction, an unstable p-complex is formed. The aromatic system is not yet disrupted. This stage proceeds quickly. In the second, slower stage, a covalent bond is formed between electrophile X and one of the carbon atoms of the ring due to two p-electrons of the ring. This carbon atom goes from sp2- to sp3-hybrid state. In this case, the aroma of the system is disrupted. The four remaining p-electrons are distributed among five other carbon atoms, and the benzene molecule forms a carbocation, or s-complex. Breaking aromaticity is energetically unfavorable, so the s-complex structure is less stable than the aromatic structure. To restore aromaticity, a proton is removed from the carbon atom bound to the electrophile (third stage). In this case, two electrons return to the p-system and thereby restore aromaticity: Electrophilic substitution reactions are widely used for the synthesis of many benzene derivatives.

“Aromatic hydrocarbons” - Toluene is used as a raw material for the production of an explosive - trinitrotoluene. A white rock composed of calcium carbonate. 24. Nomenclature. 15. Raw materials for the production of phosphate fertilizers. 16. Addition and oxidation reactions are possible. Red brass. 17. Conclusion: Amide. 12. Ruby. 27. All aromatic compounds are solid or liquid substances.

“Hydrocarbons” - Lesson summary. Phenacetin. Chambers for coking coal. Ammonia. Ethanol. Coke oven diagram. Petrol. 2 – refifcation column. Mineral deposits. Solvents. Test tube No. 1. Coke. Coal processing products. Artificial ripening of fruits. Aniline. Great scientists. Coal tar.

"Properties of aromatic hydrocarbons" - Great value have synthetic methods of production. Physical properties. Receipt. Preparation of aromatic hydrocarbons. Application. The main sources of aromatic hydrocarbons are coal tar, oil and petroleum products. Chemical properties. Vinylbenzene (styrene) is used to produce a polymer material - polystyrene.

“Benzene and its properties” - History. Along with benzene, toluene and xylenes are formed. Coking of coal. Benzene vapor can penetrate intact skin. Solubility in water 1.79 g/l (at 25 °C). Strong carcinogen. Benzene (C6H6, PhH) is an organic chemical compound, a colorless liquid with a pleasant sweetish odor.

"Chemistry Hydrocarbons" - Problem. Plan. The vapor density of the substance in air is 2.966. Specify reaction conditions. 4. Drawing up a table: “Classes of hydrocarbons.” Determine the formula. Resources. When 8.6 g of saturated hydrocarbon was burned, 26.4 g were obtained carbon dioxide and 12.6 g of water. Compose isomers. Generalization of the topic “Hydrocarbons”.

“Use of hydrocarbons” - Test yourself!!! It is of great importance in medicine, perfumery and cosmetics. Objectives: The importance of alkanes in modern world huge. Alkane compounds are used as refrigerants in home refrigerators. Methane: production of tires, paint. Used in medicine, perfumery and cosmetics. Cyclohexane is also widely used as a solvent and for the synthesis of polymers (nylon, nylon).

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