03.03.2022

Aromatic HC. Benzene

DEFINITION

Benzene(cyclohexatriene - 1,3,5) - an organic substance, the simplest representative of a number of aromatic hydrocarbons.

Formula - C 6 H 6 (structural formula - Fig. 1). Molecular weight - 78, 11.

Rice. 1. Structural and spatial formulas of benzene.

All six carbon atoms in the benzene molecule are in the sp 2 hybrid state. Each carbon atom forms 3σ bonds with two other carbon atoms and one hydrogen atom lying in the same plane. Six carbon atoms form a regular hexagon (σ-skeleton of the benzene molecule). Each carbon atom has one unhybridized p-orbital, which contains one electron. Six p-electrons form a single π-electron cloud (aromatic system), which is depicted as a circle inside a six-membered cycle. The hydrocarbon radical derived from benzene is called C 6 H 5 - - phenyl (Ph-).

Chemical properties of benzene

Benzene is characterized by substitution reactions proceeding according to the electrophilic mechanism:

- halogenation (benzene interacts with chlorine and bromine in the presence of catalysts - anhydrous AlCl 3, FeCl 3, AlBr 3)

C 6 H 6 + Cl 2 \u003d C 6 H 5 -Cl + HCl;

- nitration (benzene easily reacts with a nitrating mixture - a mixture of concentrated nitric and sulfuric acids)

- alkylation with alkenes

C 6 H 6 + CH 2 \u003d CH-CH 3 → C 6 H 5 -CH (CH 3) 2;

Addition reactions to benzene lead to the destruction of the aromatic system and proceed only under harsh conditions:

- hydrogenation (the reaction proceeds when heated, the catalyst is Pt)

- addition of chlorine (occurs under the action of UV radiation with the formation of a solid product - hexachlorocyclohexane (hexachlorane) - C 6 H 6 Cl 6)

Like any organic compound, benzene enters into a combustion reaction with the formation of carbon dioxide and water as reaction products (it burns with a smoky flame):

2C 6 H 6 + 15O 2 → 12CO 2 + 6H 2 O.

Physical properties of benzene

Benzene is a colorless liquid, but has a specific pungent odor. Forms an azeotropic mixture with water, mixes well with ethers, gasoline and various organic solvents. Boiling point - 80.1C, melting point - 5.5C. Toxic, carcinogen (i.e. contributes to the development of cancer).

Obtaining and using benzene

The main methods for obtaining benzene:

— dehydrocyclization of hexane (catalysts - Pt, Cr 3 O 2)

CH 3 -(CH 2) 4 -CH 3 → C 6 H 6 + 4H 2;

- dehydrogenation of cyclohexane (the reaction proceeds when heated, the catalyst is Pt)

C 6 H 12 → C 6 H 6 + 4H 2;

– trimerization of acetylene (the reaction proceeds when heated to 600C, the catalyst is activated carbon)

3HC≡CH → C 6 H 6 .

Benzene serves as a raw material for the production of homologues (ethylbenzene, cumene), cyclohexane, nitrobenzene, chlorobenzene, and other substances. Previously, benzene was used as an additive to gasoline to increase its octane number, however, now, due to its high toxicity, the content of benzene in fuel is strictly regulated. Sometimes benzene is used as a solvent.

Examples of problem solving

EXAMPLE 1

Exercise Write down the equations with which you can carry out the following transformations: CH 4 → C 2 H 2 → C 6 H 6 → C 6 H 5 Cl.
Solution To obtain acetylene from methane, the following reaction is used:

2CH 4 → C 2 H 2 + 3H 2 (t = 1400C).

Obtaining benzene from acetylene is possible by the reaction of trimerization of acetylene, which occurs when heated (t = 600C) and in the presence of activated carbon:

3C 2 H 2 → C 6 H 6 .

The chlorination reaction of benzene to obtain chlorobenzene as a product is carried out in the presence of iron (III) chloride:

C 6 H 6 + Cl 2 → C 6 H 5 Cl + HCl.

EXAMPLE 2

Exercise To 39 g of benzene in the presence of iron (III) chloride was added 1 mol of bromine water. What amount of the substance and how many grams of what products did this result in?
Solution Let us write the equation for the reaction of benzene bromination in the presence of iron (III) chloride:

C 6 H 6 + Br 2 → C 6 H 5 Br + HBr.

The reaction products are bromobenzene and hydrogen bromide. The molar mass of benzene, calculated using the table of chemical elements of D.I. Mendeleev - 78 g/mol. Find the amount of benzene substance:

n(C 6 H 6) = m(C 6 H 6) / M(C 6 H 6);

n(C 6 H 6) = 39/78 = 0.5 mol.

According to the condition of the problem, benzene reacted with 1 mol of bromine. Consequently, benzene is in short supply and further calculations will be made for benzene. According to the reaction equation n (C 6 H 6): n (C 6 H 5 Br) : n (HBr) \u003d 1: 1: 1, therefore n (C 6 H 6) \u003d n (C 6 H 5 Br) \u003d: n(HBr) = 0.5 mol. Then, the masses of bromobenzene and hydrogen bromide will be equal:

m(C 6 H 5 Br) = n(C 6 H 5 Br)×M(C 6 H 5 Br);

m(HBr) = n(HBr)×M(HBr).

Molar masses of bromobenzene and hydrogen bromide, calculated using the table of chemical elements of D.I. Mendeleev - 157 and 81 g/mol, respectively.

m(C 6 H 5 Br) = 0.5×157 = 78.5 g;

m(HBr) = 0.5 x 81 = 40.5 g.
Answer The reaction products are bromobenzene and hydrogen bromide. The masses of bromobenzene and hydrogen bromide are 78.5 and 40.5 g, respectively.

DEFINITION

Benzene- It is a colorless liquid with a characteristic odor; boiling point 80.1 o C, melting point 5.5 o C. Insoluble in water, toxic.

The aromatic properties of benzene, determined by the features of its structure, are expressed in the relative stability of the benzene ring, despite the unsaturation of benzene in composition. Thus, unlike unsaturated compounds with ethylene double bonds, benzene is resistant to oxidizing agents.

Rice. 1. The structure of the benzene molecule according to Kekule.

Getting benzene

The main methods for obtaining benzene are:

– dehydrocyclization of hexane (catalysts - Pt, Cr 3 O 2)

CH 3 -(CH 2) 4 -CH 3 → C 6 H 6 + 4H 2 (t o C, p, kat \u003d Cr 2 O 3);

— dehydrogenation of cyclohexane

C 6 H 12 → C 6 H 6 + 3H 2 (t o C, kat = Pt, Ni);

– trimerization of acetylene (the reaction proceeds when heated to 600 o C, the catalyst is activated carbon)

3HC≡CH → C 6 H 6 (t = 600 o C, kat = C activ).

Chemical properties of benzene

Benzene is characterized by substitution reactions proceeding according to the electrophilic mechanism:

Halogenation (benzene interacts with chlorine and bromine in the presence of catalysts - anhydrous AlCl 3 , FeCl 3 , AlBr 3)

C 6 H 6 + Cl 2 \u003d C 6 H 5 -Cl + HCl;

- nitration (benzene easily reacts with a nitrating mixture - a mixture of concentrated nitric and sulfuric acids)


- alkylation with alkenes

C 6 H 6 + CH 2 \u003d CH-CH 3 → C 6 H 5 -CH (CH 3) 2

Addition reactions to benzene lead to the destruction of the aromatic system and proceed only under harsh conditions:

- hydrogenation (reaction product - cyclohexane)

C 6 H 6 + 3H 2 → C 6 H 12 (t o C, kat = Pt);

- addition of chlorine (occurs under the action of UV radiation with the formation of a solid product - hexachlorocyclohexane (hexachloran) - C 6 H 6 Cl 6)

C 6 H 6 + 6Cl 2 → C 6 H 6 Cl 6.

Application of benzene

Benzene is widely used in industrial organic chemistry. Almost all compounds that have benzene rings in their composition are obtained from benzene, for example, styrene, phenol, aniline, halogen-substituted arenes. Benzene is used for the synthesis of dyes, surfactants, and pharmaceuticals.

Examples of problem solving

EXAMPLE 1

Exercise The vapor density of the substance is 3.482 g/l. Its pyrolysis yielded 6 g of soot and 5.6 liters of hydrogen. Determine the formula for this substance.
Solution Soot is carbon. Let's find the amount of soot substance based on the conditions of the problem (the molar mass of carbon is 12 g/mol):

n(C) = m(C) / M(C);

n(C) \u003d 6 / 12 \u003d 0.5 mol.

Calculate the amount of hydrogen substance:

n(H 2) \u003d V (H 2) / V m;

n (H 2) \u003d 5.6 / 22.4 \u003d 0.25 mol.

So, the amount of substance of one hydrogen atom will be equal to:

n(H) = 2 × 0.25 = 0.5 mol.

Let's denote the number of carbon atoms in the hydrocarbon molecule as "x", and the number of hydrogen atoms as "y", then the ratio of these atoms in the molecule:

x: y \u003d 0.5: 0.5 \u003d 1: 1.

Then the simplest hydrocarbon formula will be expressed by the composition CH. The molecular weight of a molecule of CH composition is:

M(CH) = 13 g/mol

Let's find the molecular weight of the hydrocarbon based on the conditions of the problem:

M (C x H y) = ρ × V m ;

M (C x H y) \u003d 3.482 × 22.4 \u003d 78 g / mol.

Let's define the true formula of hydrocarbon:

k \u003d M (C x H y) / M (CH) \u003d 78/13 \u003d 6,

therefore, the coefficients "x" and "y" must be multiplied by 6 and then the hydrocarbon formula will take the form C 6 H 6. It's benzene.
Answer The desired hydrocarbon has the composition C 6 H 6 . It's benzene.

EXAMPLE 2

Story

For the first time, benzene-containing mixtures resulting from the distillation of coal tar were described by the German chemist Johann Glauber in the book Furni novi philosophici, published in 1651. Benzene as an individual substance was described by Michael Faraday, who isolated this substance in 1825 from the condensate of light gas obtained by coking coal. Soon, in 1833, benzene was obtained - during the dry distillation of the calcium salt of benzoic acid - and the German physical chemist Eilhard Mitscherlich. It was after this preparation that the substance began to be called benzene.

By the 1860s, it was known that the ratio of the number of carbon atoms and hydrogen atoms in a benzene molecule was similar to that of acetylene, and the empirical formula for them is C n H n. The study of benzene was seriously taken up by the German chemist Friedrich August Kekule, who in 1865 managed to propose the correct - cyclic formula of this compound. There is a story that F. Kekule imagined benzene in the form of a snake of six carbon atoms. The idea of ​​​​the cyclical connection came to him in a dream, when an imaginary snake bit its tail. Friedrich Kekule managed at that time to most fully describe the properties of benzene.

Physical properties

Colorless liquid with a peculiar pungent odor. Melting point = 5.5 °C, Boiling point = 80.1 °C, Density = 0.879 g/cm³, Molar mass = 78.11 g/mol. Like unsaturated hydrocarbons, benzene burns with a highly sooty flame. It forms explosive mixtures with air, mixes well with ether, gasoline and other organic solvents, forms an azeotropic mixture with water with a boiling point of 69.25 ° C (91% benzene). Solubility in water 1.79 g/l (at 25 °C).

Chemical properties

Benzene is characterized by substitution reactions - benzene reacts with alkenes, chloroalkanes, halogens, nitric and sulfuric acids. Benzene ring cleavage reactions take place under harsh conditions (temperature, pressure).

  • Interaction with chlorine and bromine in the presence of a catalyst to form chlorobenzene (electrophilic substitution reaction):
\mathsf(C_6H_6 + Cl_2 \xrightarrow(FeCl_3) C_6H_5Cl + HCl)
  • In the absence of a catalyst, when heated or illuminated, a radical addition reaction occurs with the formation of a mixture of hexachlorocyclohexane isomers
\mathsf(C_6H_6 + 3Cl_2 \xrightarrow(T, h\nu) C_6H_6Cl_6)
  • Interaction with halogen derivatives of alkanes (benzene alkylation, Friedel-Crafts reaction) to form alkylbenzenes:
\mathsf(C_6H_6 + C_2H_5Br \xrightarrow(FeBr_3) C_6H_5C_2H_5 + HBr)
  • Sulfonation and nitration reactions (electrophilic substitution):
\mathsf(C_6H_6 + HNO_3 \xrightarrow(H_2SO_4) C_6H_5NO_2 + H_2O)\mathsf(C_6H_6 + H_2SO_4 \rightarrow C_6H_5SO_3H + H_2O)
  • Burning benzene:
\mathsf(2C_6H_6 + 15O_2 \rightarrow 12CO_2 + 6H_2O)

Structure

By composition, benzene belongs to unsaturated hydrocarbons (homologous series C n H2 n−6), but unlike hydrocarbons of the ethylene series, C 2 H 4, exhibits properties inherent in unsaturated hydrocarbons (they are characterized by addition reactions), only under harsh conditions, but benzene is more prone to substitution reactions. This "behavior" of benzene is explained by its special structure: the presence of atoms in the same plane and the presence of a conjugated 6π-electron cloud in the structure. The modern idea of ​​the electronic nature of bonds in benzene is based on the hypothesis of Linus Pauling, who proposed to depict the benzene molecule 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.

Production

To date, there are several fundamentally different methods for the production of benzene.

Application

A significant part of the resulting benzene is used for the synthesis of other products:

  • about 50% of benzene is converted to ethylbenzene (alkylation of benzene with ethylene);
  • about 25% of benzene is converted to cumene (alkylation of benzene with propylene);
  • approximately 10-15% benzene is hydrogenated to cyclohexane;
  • about 10% of benzene is spent on the production of nitrobenzene;
  • 2-3% of benzene is converted into linear alkylbenzenes;
  • approximately 1% of benzene is used to synthesize chlorobenzene.

In much smaller quantities, benzene is used for the synthesis of some other compounds. Occasionally and in extreme cases, due to its high toxicity, benzene is used as a solvent.

In addition, benzene is a constituent of gasoline. In the 1920s - 1930s, benzene was added de into straight-run gasoline to increase its octane rating, but by the 1940s such blends could not compete with high-octane gasolines. Due to the high toxicity, the content of benzene in fuel is limited by modern standards to the introduction of up to 1%.

Biological action

With a short inhalation of benzene vapor, no immediate poisoning occurs, therefore, until recently, the procedure for working with benzene was not particularly regulated.

In large doses, benzene causes nausea and dizziness, and in some severe cases, poisoning can be fatal. Euphoria is often the first sign of benzene poisoning. Benzene vapor can penetrate intact skin. Liquid benzene is quite irritating to the skin. If the human body is exposed to long-term exposure to benzene in small quantities, the consequences can also be very serious.

Benzene and substance abuse

Benzene has an intoxicating effect on a person and can lead to drug addiction.

Acute poisoning

At very high concentrations - almost instantaneous loss of consciousness and death within a few minutes. The color of the face is cyanotic, the mucous membranes are often cherry red. At lower concentrations - excitation, similar to alcohol, then drowsiness, general weakness, dizziness, nausea, vomiting, headache, loss of consciousness. Muscle twitches are also observed, which can turn into tonic convulsions. The pupils are often dilated and unresponsive to light. Breathing is first quickened, then slowed down. Body temperature drops sharply. Pulse quickened, small filling. The blood pressure is lowered. Cases of severe cardiac arrhythmia are known.

After severe poisoning that does not lead directly to death, long-term health disorders are sometimes observed: pleurisy, catarrhs ​​of the upper respiratory tract, diseases of the cornea and retina, liver damage, heart disorders, etc. A case of vasomotor neurosis with swelling of the face and extremities, disorders sensitivity and convulsions shortly after acute benzene vapor poisoning. Sometimes death occurs some time after poisoning.

chronic poisoning

In severe cases, there are: headaches, extreme fatigue, shortness of breath, dizziness, weakness, nervousness, drowsiness or insomnia, indigestion, nausea, sometimes vomiting, lack of appetite, increased urination, menstruation, persistent bleeding from the oral mucosa, especially gums, often develops. , and nose, lasting for hours and even days. Sometimes persistent bleeding occurs after tooth extraction. Numerous small hemorrhages in the skin. Blood in stools, uterine bleeding, retinal hemorrhage. Usually, it is the bleeding, and often the accompanying fever (temperature up to 40 ° and above) that brings the poisoned to the hospital. In such cases, the prognosis is always serious. The cause of death is sometimes secondary infections: there are cases of gangrenous inflammation of the periosteum and necrosis of the jaw, severe ulcerative inflammation of the gums, general sepsis with septic endometritis.

Sometimes, with severe poisoning, symptoms of nervous diseases develop: increased tendon reflexes, bilateral clonus, positive Babinsky symptom, deep sensitivity disorder, pseudo-tabetic disorders with paresthesias, ataxia, paraplegia and motor disorders (signs of damage to the posterior columns of the spinal cord and pyramidal tract).

The most typical changes in the blood. The number of erythrocytes is usually sharply reduced, down to 1-2 million and below. The content of hemoglobin also falls sharply, sometimes up to 10%. The color index in some cases is low, sometimes close to normal, and sometimes high (especially with severe anemia). Anisocytosis and poikilocytosis, basophilic puncture and the appearance of nuclear erythrocytes, an increase in the number of reticulocytes and the volume of erythrocytes are noted. A sharp decrease in the number of leukocytes is more typical. Sometimes initially leukocytosis, quickly followed by leukopenia, accelerated ESR. Changes in the blood do not develop simultaneously. Most often, the leukopoietic system is affected earlier, later thrombocytopenia joins. The defeat of erythroblastic function often occurs even later. In the future, a characteristic picture of severe poisoning may develop - aplastic anemia.

The action of benzene on biomembranes

Benzene is an effective solubilizer of biomembranes; it quickly dissolves non-polar tails of lipids, mainly cholesterol, which is part of membranes. The solubilization process is limited by the concentration of benzene, the more it is, the faster this process proceeds. In this case, a rupture of the double lipid layer occurs, which leads to complete destruction of the membrane and subsequent cell apoptosis (during the destruction of biomembranes, activation of receptors that trigger cell apoptosis occurs).

Action on the skin

With frequent contact of hands with benzene, dry skin, cracks, itching, redness (usually between the fingers), swelling, and millet-like blisters are observed. Sometimes, due to skin lesions, workers are forced to quit their jobs.

The maximum allowable concentration is 5 mg/m 3 .

see also

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Notes

Literature

  • Benzene // Great Soviet Encyclopedia: [in 30 volumes] / ch. ed. A. M. Prokhorov. - 3rd ed. - M. : Soviet encyclopedia, 1969-1978.
  • // Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.
  • Encyclopedic Dictionary of a Young Chemist / Comp. V. A. Kritsman, V. V. Stanzo. - Pedagogy. - M ., 1982. - 368 p.
  • O. S. Gabrielyan, I. G. Ostroumov. Handbook of a chemistry teacher grade 10. - M .: Bustard, 2010.
  • Omelyanenko L. M. and Senkevich N. A. Clinic and prevention of benzene poisoning. - M., 1957.
Exercise Calculate the amount of acetylene required to produce 400 ml of benzene (density 0.8 g/ml).
Solution We write the reaction equation for the production of benzene from acetylene:

Such a compound as benzene, Mrs. Chemistry in her household finally and irrevocably acquired only in 1833. Benzene is a compound that has a quick-tempered, one might say, even explosive character. How did you find out?

Story

Johann Glauber in 1649 turned his attention to a compound that had been successfully formed while the chemist was working on coal tar. But it wished to remain incognito.

After about 170 years, and to be much more precise, in the mid-twenties of the XIX century, by chance, benzene was extracted from the lighting gas, namely from the released condensate. Mankind owes such efforts to Michael Faraday, a scientist from England.

The baton for the acquisition of benzene was intercepted by the German Eilgard Mitscherlich. This happened during the processing of anhydrous calcium salts of benzoic acid. Perhaps that is why the compound was given such a name - benzene. Still, as an option, the scientist called it gasoline. Incense, if translated from Arabic.

Benzene burns beautifully and brightly, in connection with these observations, Auguste Laurent advised to call it "fen" or "benzene". Bright, shining - if translated from Greek.

Based on the opinion of the concept of the nature of the electronic bond, the qualities of benzene, the scientist provided the molecule of the compound in the form of the following image. This is a hexagon. A circle is inscribed in it. The foregoing suggests that benzene has an integral electron cloud, which safely contains six (without exception) carbon atoms of the cycle. There are no fixed binary bonds.

Benzene was previously treated as a solvent. But basically, as they say, he was not a member, did not participate, was not involved. But this is in the 19th century. Significant changes took place in the XX. The properties of benzene express the most valuable qualities that helped him become more popular. The octane number, which turned out to be high, made it possible to use it as a fuel element for refueling cars. This action was the impetus for the extensive withdrawal of benzene, the extraction of which is carried out as a by-product of the coking of steel production.

By the forties, in the chemical field, benzene began to be consumed in the manufacture of substances that explode quickly. The 20th century crowned itself with the fact that the oil refining industry produced so much benzene that it began to supply the chemical industry.

Characterization of benzene

Unsaturated hydrocarbons are very similar to benzene. For example, the hydrocarbon series of ethylene characterizes itself as an unsaturated hydrocarbon. It has an addition reaction. Benzene willingly enters into All this thanks to the atoms that are in the same plane. And as a fact - the conjugated electron cloud.

If there is a benzene ring in the formula, then we can come to the elementary conclusion that this is benzene, the structural formula of which looks exactly like this.

Physical properties

Benzene is a colorless liquid, but has an unfortunate smell. Benzene melts when the temperature reaches 5.52 degrees Celsius. Boils at 80.1. The density is 0.879 g / cm 3, the molar mass is 78.11 g / mol. When burning, it smokes heavily. Forms explosive compounds when air enters. rocks (gasoline, ether and others) are combined with the described substance without problems. An azeotropic compound creates with water. Heating before the start of vaporization occurs at 69.25 degrees (91% benzene). At 25 degrees Celsius, 1.79 g / l can be dissolved in water.

Chemical properties

Benzene reacts with sulfuric and nitric acid. And also with alkenes, halogens, chloroalkanes. The substitution reaction is what is characteristic of him. The pressure temperature affects the breakthrough of the benzene ring, which takes place under rather harsh conditions.

We can consider each benzene reaction equation in more detail.

1. Electrophilic substitution. Bromine, in the presence of a catalyst, interacts with chlorine. The result is chlorobenzene:

С6H6+3Cl2 → C6H5Cl + HCl

2. Friedel-Crafts reaction, or benzene alkylation. The appearance of alkylbenzenes occurs due to the combination with alkanes, which are halogen derivatives:

C6H6 + C2H5Br → C6H5C2H5 + HBr

3. Electrophilic substitution. Here is the reaction of nitration and sulfonation. The benzene equation will look like this:

C6H6 + H2SO4 → C6H5SO3H + H2O

C6H6 + HNO3 → C6H5NO2 + H2O

4. Benzene when burning:

2C6H6 + 15O2 → 12CO2 + 6H2O

Under certain conditions, it exhibits a character characteristic of saturated hydrocarbons. The p-electron cloud, which is in the structure of the substance under consideration, explains these reactions.

Various types of benzene depend on special technology. This is where the labeling of petroleum benzene comes from. For example, purified and higher purification, for synthesis. I would like to separately note the homologues of benzene, and more specifically, their chemical properties. These are alkylbenzenes.

Benzene homologues are much more likely to react. But the above reactions of benzene, namely homologues, take place with some difference.

Halogenation of alkylbenzenes

The form of the equation is as follows:

С6H5-CH3 + Br = C6H5-CH2Br + HBr.

The aspiration of bromine into the benzene ring is not observed. It goes into the chain on the side. But thanks to the Al(+3) salt catalyst, bromine boldly enters the ring.

Nitration of alkylbenzenes

Thanks to sulfuric and nitric acids, benzenes and alkylbenzenes are nitrated. Reactive alkylbenzenes. Two products are obtained from the three presented - these are para- and ortho-isomers. You can write one of the formulas:

C6H5 - CH3 + 3HNO3 → C6H2CH3 (NO2)3.

Oxidation

For benzene, this is unacceptable. But alkylbenzenes react willingly. For example, benzoic acid. The formula is below:

C6H5CH3 + [O] → C6H5COOH.

Alkylbenzene and benzene, their hydrogenation

In the presence of an enhancer, hydrogen begins to react with benzene, resulting in the formation of cyclohexane, as discussed above. Similarly, alkylbenzenes are easily converted to alkylcyclohexanes. To obtain alkylcyclohexane, it is required to subject the desired alkylbenzene to hydrogenation. Basically, it is a necessary procedure for the production of a pure product. And this is not all the reactions of benzene and alkylbenzene.

Benzene production. Industry

The foundation of such production is based on the processing of components: toluene, naphtha, tar, which is released during coal cracking, and others. Therefore, benzene is produced at petrochemical, metallurgical enterprises. It is important to know how to get benzene of varying degrees of purification, because the brand of this substance is directly dependent on the principle of manufacture and purpose.

The lion's share is made by thermocatalytic reforming of the caustobiolite part, boiling off at 65 degrees, having the effect of an extract, distillation with dimethylformamide.

During the production of ethylene and propylene, liquid products are obtained, which are formed during the decomposition of inorganic and organic compounds under the influence of heat. Of these, benzene is isolated. But, unfortunately, there is not so much source material for this benzene production option. Therefore, the substance of interest to us is produced by reforming. By this method, the volume of benzene is increased.

By dealkylation at a temperature of 610-830 degrees with a plus sign, in the presence of steam formed during the boiling of water and hydrogen, benzene is obtained from toluene. There is another option - catalytic. When the presence of zeolites, or, alternatively, oxide catalysts, is observed, subject to a temperature regime of 227-627 degrees.

There is another, older, way to develop benzene. With the help of absorption by organic absorbers, it is isolated from the final result of coal coking. The product is steam-gas and has been pre-cooled. For example, oil is used, the source of which is oil or coal. When the distillation is carried out with steam, the scavenger is separated. Hydrotreating helps to free crude benzene from excess substances.

Coal raw materials

In metallurgy, when coal is used, or, to be more precise, its dry distillation, coke is obtained. During this procedure, the air supply is limited. Do not forget that coal is heated to a temperature of 1200-1500 Celsius.

Coal-chemical benzene needs thorough purification. It is necessary to get rid of methyl cyclohexane and its companion n-heptane without fail. should also be removed. Benzene is to undergo a process of separation, purification, which will be carried out more than once.

The method described above is the oldest, but after time it loses its high position.

Oil fractions

0.3-1.2% - such indicators of the composition of our hero in crude oil. Scanty indicators to invest finances and forces. It is best to use an industrial procedure for processing petroleum fractions. That is catalytic reforming. In the presence of an aluminum-platinum-rhenium amplifier, the percentage of inclusion of aromatic carbohydrates increases, and the indicator that determines the ability of the fuel not to ignite spontaneously during its compression increases.

Pyrolysis resins

If our oil product is extracted from non-solid raw materials, namely by pyrolysis of propylene and ethylene arising in the manufacture, then this approach will be the most acceptable. To be precise, benzene is released from the pyrocondensate. Decomposition of certain fractions requires hydrotreatment. Sulfur and unsaturated mixtures are removed during cleaning. In the initial result, the content of xylene, toluene, benzene was noted. With the help of a distillation, which is extractive, the BTX group is separated and benzene is obtained.

Hydrodealkylation of toluene

The protagonists of the process, a cocktail of hydrogen flow and toluene, are fed heated into the reactor. Toluene passes through the catalyst bed. During this process, the methyl group is separated to form benzene. There is a certain way of purification here. The result is a highly pure substance (for nitration).

Toluene disproportionation

As a result of the rejection of the methyl class, creation to benzene takes place, xylene is oxidized. In this process, transalkylation has been observed. The catalytic action is due to palladium, platinum and neodymium, which are on aluminum oxide.

Toluene and hydrogen are supplied to the reactor with a stable catalyst bed. Its purpose is to keep hydrocarbons from settling onto the catalyst plane. The stream that exits the reactor is cooled, and hydrogen is safely recovered for recycle. What is left is distilled three times. At the initial stage, compounds that are non-aromatic are withdrawn. Benzene is extracted second, and the last step is the extraction of xylenes.

Acetylene trimerization

Thanks to the work of the French physical chemist Marcelin Berthelot, benzene began to be produced from acetylene. But at the same time, a heavy cocktail stood out from many other elements. The question was how to lower the reaction temperature. The answer was received only at the end of the forties of the XX century. V. Reppe found an appropriate catalyst, it turned out to be nickel. Trimerization is the only way to get benzene from acetylene.

The formation of benzene occurs with the help of activated carbon. At high heat rates, acetylene passes over the coal. Benzene is released if the temperature is at least 410 degrees. At the same time, a variety of aromatic hydrocarbons are still born. Therefore, good equipment is needed that is capable of purifying acetylene in a qualitative manner. With such a laborious method as trimerization, a lot of acetylene is consumed. To get 15 ml of benzene, 20 liters of acetylene are taken. You can see how it looks in the reaction will not take long.

3C2H2 → C6H6 (Zelinsky equation).

3CH → CH = (t, kat) = C6H6.

Where is benzene used

Benzene is a fairly popular brainchild of chemistry. Especially often it was noticed how benzene was used in the manufacture of cumene, cyclohexane, ethylbenzene. To create styrene, ethylbenzene is indispensable. The starting material for the production of caprolactam is cyclohexane. When making a thermoplastic resin, it is caprolactam that is used. The described substance is indispensable in the manufacture of various paints and varnishes.

How dangerous is benzene

Benzene is a toxic substance. The manifestation of a feeling of malaise, which is accompanied by nausea and severe dizziness, is a sign of poisoning. Even death is not ruled out. The feeling of indescribable delight is no less disturbing bells in case of benzene poisoning.

Liquid benzene causes skin irritation. Benzene vapors easily penetrate even through intact skin. With the most short-term contact with a substance in a small dose, but on a regular basis, unpleasant consequences will not be long in coming. This may be a lesion of the bone marrow and acute leukemia of various types.

In addition, the substance is addictive in humans. Benzene acts like a dope. Tobacco smoke produces a tar-like product. When they studied it, they came to the conclusion that the content of the latter is not safe for humans. In addition to the presence of nicotine, the presence of aromatic carbohydrates of the benzpyrene type was also found. A distinctive feature of benzpyrene are carcinogens. They have a very harmful effect. For example, they cause cancer.

Despite the foregoing, benzene is a starting material for the production of various drugs, plastics, synthetic rubber and, of course, dyes. This is the most common brainchild of chemistry and aromatic compound.

The molecules of which contain a benzene ring, or core, a cyclic group of carbon atoms with a special nature of bonds.

The simplest representative of arenes is benzene C 6 H 6 . The homologous series of benzene has the general formula C n H2 n-6 .

The first structural formula of benzene was proposed in 1865 by the German chemist F.A. Kekule:

The C atoms in the benzene molecule form a regular flat hexagon, although it is often drawn elongated.

The above formula correctly reflects the equivalence of six C atoms, but does not explain a number of special properties of benzene. For example, despite the unsaturation, it does not show a tendency to addition reactions: it does not decolorize bromine water and potassium permanganate solution, i.e. it is not characterized by qualitative reactions typical of unsaturated compounds.

In the structural formula of Kekule, there are three single and three double alternating carbon-carbon bonds. But such an image does not convey the true structure of the molecule. In fact, the carbon-carbon bonds in benzene are equivalent. This is due to the electronic structure of its molecule.

Each C atom in the benzene molecule is in the state sp 2 - hybridization. It is connected to two neighboring C atoms and an H atom by three α-bonds. As a result, a flat hexagon is formed, where all six C atoms and all C-C and C-H bonds lie in the same plane (the angle between the C-C bonds is 120 o). Third p-orbital of the carbon atom is not involved in hybridization. It has the shape of a dumbbell and is oriented perpendicular to the plane of the benzene ring. Such p-orbitals of neighboring C atoms overlap above and below the plane of the ring. As a result, six p-electrons (all six C atoms) form a common -electron cloud and a single chemical bond for all C atoms.

The electron cloud causes a reduction in the distance between C atoms. In the benzene molecule, they are the same and equal. This means that in the benzene molecule there is no alternation of simple and double bonds, but there is a special bond - “one and a half” - intermediate between a simple and a double, the so-called aromatic connection. To show the uniform distribution of the p-electron cloud in the benzene molecule, it is more correct to depict it as a regular hexagon with a circle inside (the circle symbolizes the equivalence of bonds between C atoms).

However, the Kekule formula is often used with indication of double bonds (II), remembering, however, its shortcomings:

physical properties. Benzene is a colorless, volatile, flammable liquid with a peculiar odor. It is practically insoluble in water, but serves as a good solvent for many organic substances. It burns with a very smoky flame (92.3% of the mass is carbon). Vapors of benzene with air form an explosive mixture. Liquid benzene and benzene vapors are poisonous. The boiling point of benzene is 80.1 °C. When cooled, it easily solidifies into a white crystalline mass with a melting point of 5.5 °C.


Chemical properties. The benzene core has great strength. This explains the propensity of arenes to substitution reactions. They flow more easily than saturated hydrocarbons.

Reaction substitution (ionic mechanism).

1) hydrogenation. Benzene adds hydrogen at low temperature in the presence of a catalyst - nickel or platinum, forming cyclohexane:

2) Halogenation. Benzene, under ultraviolet irradiation, adds chlorine, forming hexachlorocyclohexane (hexachloran):

Reactions oxidation .

1) Benzene is very resistant to oxidizing agents. Unlike unsaturated hydrocarbons, it does not discolor bromine water and KMnO 4 solution.

2) Benzene burns in air with a smoky flame:

2C 6 H 6 + 15O 2 12CO 2 + 6H 2 O.

Arenes, therefore, can enter into both substitution and addition reactions, however, the conditions for these transformations differ significantly from similar transformations of saturated and unsaturated hydrocarbons. These reactions of benzene are outwardly similar to the reactions of alkanes and alkenes, but proceed according to different mechanisms.

toxic, carcinogenic
Data is based on standard conditions (25 °C, 100 kPa) unless otherwise noted.

An excerpt characterizing Benzene

“I don’t know… Your Excellency… There were no people, Your Excellency.”
- You could take it from cover!
That there was no cover, Tushin did not say this, although it was the absolute truth. He was afraid to let the other boss down by this and silently, with fixed eyes, looked straight into Bagration's face, just as a student who has gone astray looks into the examiner's eyes.
The silence was quite long. Prince Bagration, apparently not wanting to be strict, did not have anything to say; the rest did not dare to intervene in the conversation. Prince Andrei looked at Tushin from under his brows, and his fingers moved nervously.
“Your Excellency,” Prince Andrei interrupted the silence with his harsh voice, “you deigned to send me to Captain Tushin’s battery. I was there and found two-thirds of the men and horses killed, two guns mangled, and no cover.
Prince Bagration and Tushin were now equally stubbornly looking at Bolkonsky, who spoke with restraint and excitement.
“And if, Your Excellency, let me express my opinion,” he continued, “the success of the day we owe most of all to the action of this battery and the heroic stamina of Captain Tushin with his company,” said Prince Andrei and, without waiting for an answer, immediately got up and walked away from the table.
Prince Bagration looked at Tushin and, apparently not wanting to show distrust of Bolkonsky's sharp judgment and, at the same time, feeling unable to fully believe him, bowed his head and told Tushin that he could go. Prince Andrew followed him.
“Thank you, you helped me out, my dear,” Tushin told him.
Prince Andrei glanced at Tushin and, without saying anything, walked away from him. Prince Andrei was sad and hard. It was all so strange, so unlike what he had hoped.

"Who are they? Why are they? What do they need? And when will it all end?" thought Rostov, looking at the changing shadows before him. The pain in my arm was getting worse and worse. Sleep became irresistible, red circles jumped in my eyes, and the impression of these voices and these faces and the feeling of loneliness merged with the feeling of pain. It was they, these soldiers, wounded and unwounded, it was they who pressed, and weighed, and twisted the veins, and burned the meat in his broken arm and shoulder. To get rid of them, he closed his eyes.
He forgot himself for one minute, but during this short interval of oblivion he saw countless objects in a dream: he saw his mother and her big white hand, saw Sonya's thin shoulders, Natasha's eyes and laughter, and Denisov with his voice and mustache, and Telyanin , and all his history with Telyanin and Bogdanych. This whole story was one and the same, that this soldier with a sharp voice, and this and that whole story, and this and that soldier so painfully, relentlessly held, crushed, and all in one direction pulled his hand. He tried to move away from them, but they did not let go of his hair, not even for a second on his shoulder. It wouldn't hurt, it would be great if they didn't pull it; but it was impossible to get rid of them.
He opened his eyes and looked up. The black canopy of night hung a yard above the light of the coals. Powders of falling snow flew in this light. Tushin did not return, the doctor did not come. He was alone, only some kind of soldier was now sitting naked on the other side of the fire and warming his thin yellow body.
"No one wants me! thought Rostov. - No one to help or pity. And I was once at home, strong, cheerful, beloved. He sighed and groaned involuntarily.
- What hurts? - asked the soldier, shaking his shirt over the fire, and without waiting for an answer, grunting, added: - You never know they spoiled the people in a day - passion!
Rostov did not listen to the soldier. He looked at the snowflakes fluttering over the fire and recalled the Russian winter with a warm, bright house, a fluffy fur coat, a fast sleigh, a healthy body, and with all the love and care of the family. "And why did I come here!" he thought.
The next day, the French did not resume their attacks, and the remnant of the Bagration detachment joined Kutuzov's army.

Prince Vasily did not consider his plans. He even less thought to do evil to people in order to gain an advantage. He was only a man of the world who had succeeded in the world and made a habit out of this success. Depending on the circumstances, according to his rapprochement with people, he constantly drew up various plans and considerations, in which he himself did not fully realize, but which constituted the whole interest of his life. Not one or two such plans and considerations happened to him in use, but dozens, of which some were just beginning to appear to him, others were achieved, and still others were destroyed. He did not say to himself, for example: “This man is now in power, I must gain his trust and friendship and through him arrange for a lump-sum allowance,” or he did not say to himself: “Here, Pierre is rich, I must lure him to marry his daughter and borrow the 40,000 I need”; but a man in strength met him, and at that very moment instinct told him that this man could be useful, and Prince Vasily approached him and at the first opportunity, without preparation, instinctively, flattered, became familiar, talked about that, about what was needed.
Pierre was at his fingertips in Moscow, and Prince Vasily arranged for him to be appointed to the Junker Chamber, which then equaled the rank of State Councilor, and insisted that the young man go with him to Petersburg and stay at his house. As if absent-mindedly and at the same time with undoubted confidence that this should be so, Prince Vasily did everything that was necessary in order to marry Pierre to his daughter. If Prince Vasily had thought ahead of his plans, he could not have had such naturalness in his manners and such simplicity and familiarity in dealing with all people placed above and below himself. Something constantly attracted him to people stronger or richer than him, and he was gifted with the rare art of seizing precisely that moment when it was necessary and possible to use people.
Pierre, having suddenly become rich and Count Bezukhy, after recent loneliness and carelessness, felt himself surrounded and busy to such an extent that he only managed to remain alone in bed with himself. He had to sign papers, deal with government offices, the meaning of which he did not have a clear idea, ask the general manager about something, go to an estate near Moscow and receive many people who previously did not even want to know about its existence, but now would be offended and upset if he did not want to see them. All these diverse faces - businessmen, relatives, acquaintances - were all equally well, affectionately disposed towards the young heir; all of them, obviously and undoubtedly, were convinced of the high merits of Pierre. Incessantly he heard the words: “With your extraordinary kindness”, or “with your beautiful heart”, or “you yourself are so pure, count ...”, or “if he were as smart as you”, etc., so he he sincerely began to believe in his extraordinary kindness and his extraordinary mind, especially since it always seemed to him, in the depths of his soul, that he was really very kind and very smart. Even people who were previously angry and obviously hostile became tender and loving with him. Such an angry eldest of the princesses, with a long waist, with her hair smoothed like a doll's, came to Pierre's room after the funeral. Lowering her eyes and constantly flashing, she told him that she was very sorry for the misunderstandings that had been between them and that now she did not feel entitled to ask anything, except for permission, after the stroke that had befallen her, to stay for several weeks in the house that she loved so much and where made so many sacrifices. She could not help but cry at these words. Touched by the fact that this statue-like princess could have changed so much, Pierre took her by the hand and asked for forgiveness, without knowing why. From that day on, the princess began to knit a striped scarf for Pierre and completely changed towards him.
“Do it for her, mon cher; all the same, she suffered a lot from the deceased, ”Prince Vasily told him, letting him sign some kind of paper in favor of the princess.
Prince Vasily decided that this bone, a bill of 30 tons, should still be thrown to the poor princess so that it would not occur to her to talk about the participation of Prince Vasily in the case of the mosaic portfolio. Pierre signed the bill, and since then the princess has become even kinder. The younger sisters also became affectionate towards him, especially the youngest, pretty, with a mole, often embarrassed Pierre with her smiles and embarrassment at the sight of him.
It seemed so natural to Pierre that everyone loved him, it would seem so unnatural if someone did not love him, that he could not help but believe in the sincerity of the people around him. Moreover, he did not have time to ask himself about the sincerity or insincerity of these people. He constantly had no time, he constantly felt himself in a state of meek and cheerful intoxication. He felt himself to be the center of some important general movement; felt that something was constantly expected of him; that, if he didn’t do this, he would upset many and deprive them of what they expected, but if he did this and that, everything would be fine - and he did what was demanded of him, but this something good still remained ahead.
More than anyone else in this first time, both Pierre's affairs and himself were mastered by Prince Vasily. Since the death of Count Earless, he has not let go of Pierre. Prince Vasily looked like a man weighed down by deeds, tired, exhausted, but out of compassion he could not finally leave this helpless young man, the son of his friend, apres tout, [in the end] and with such a huge fortune. In those few days that he spent in Moscow after the death of Count Bezukhy, he called Pierre to him or came to him himself and ordered him what needed to be done, in such a tone of fatigue and confidence, as if he always said:
"Vous savez, que je suis accable d" affaires et que ce n "est que par pure charite, que je m" occupe de vous, et puis vous savez bien, que ce que je vous propose est la seule chose faisable. You know, I'm overwhelmed with business; but it would be ruthless to leave you like that; of course, what I'm telling you is the only possible way.]
“Well, my friend, we’re leaving tomorrow, finally,” he once said to him, closing his eyes, running his fingers over his elbow and in such a tone as if what he was saying had been decided a long time ago between them and could not have been decided otherwise.
- Tomorrow we are going, I give you a place in my carriage. I am very happy. Here we have everything important. And I should have for a long time. Here's what I got from the Chancellor. I asked him about you, and you are enlisted in the diplomatic corps and made chamber junker. Now the diplomatic road is open to you.
Despite all the strength of the tone of fatigue and the confidence with which these words were uttered, Pierre, who had been thinking about his career for so long, wanted to object. But Prince Vasily interrupted him in that cooing, bass tone, which excluded the possibility of interrupting his speech and which he used in case of need for extreme persuasion.
- Mais, mon cher, [But, my dear,] I did it for myself, for my conscience, and there is nothing to thank me for. No one ever complained that he was too loved; and then, you are free, even if you quit tomorrow. Here you will see everything yourself in St. Petersburg. And it's time for you to move away from these terrible memories. Prince Vasily sighed. Yes, yes, my soul. And let my valet ride in your carriage. Oh yes, I had forgotten, ”Prince Vasily added,“ you know, mon cher, that we had accounts with the deceased, so I received from Ryazan and will leave it: you don’t need it. We agree with you.
What Prince Vasily called from "Ryazan" was several thousand dues, which Prince Vasily left with himself.
In St. Petersburg, as well as in Moscow, an atmosphere of gentle, loving people surrounded Pierre. He could not refuse the place or, rather, the title (because he did nothing) that Prince Vasily brought him, and there were so many acquaintances, calls and social activities that Pierre, even more than in Moscow, experienced a feeling of haziness, haste and everything that comes, but does not happen any good.
From his former bachelor society, many were not in St. Petersburg. The Guard went on the march. Dolokhov was demoted, Anatole was in the army, in the provinces, Prince Andrei was abroad, and therefore Pierre could neither spend the nights, as he used to like to spend them, nor occasionally take his soul in a friendly conversation with an older respected friend. All the time it was held at dinners, balls, and mainly with Prince Vasily - in the company of the fat princess, his wife, and the beautiful Helen.
Anna Pavlovna Scherer, like others, showed Pierre the change that had taken place in the public view of him.
Previously, Pierre, in the presence of Anna Pavlovna, constantly felt that what he was saying was indecent, tactless, not what was needed; that his speeches, which seem clever to him, while he is preparing them in his imagination, become stupid as soon as he speaks out loud, and that, on the contrary, the most stupid speeches of Hippolytus come out smart and sweet. Now everything he said came out charmant. Even if Anna Pavlovna did not say this, he saw that she wanted to say it, and she only, in respect of his modesty, refrained from doing so.
At the beginning of the winter from 1805 to 1806, Pierre received from Anna Pavlovna the usual pink note with an invitation, in which was added: "Vous trouverez chez moi la belle Helene, qu "on ne se lasse jamais de voir." [I will have a beautiful Helen that you never get tired of admiring.]
Reading this place, Pierre for the first time felt that some kind of connection had formed between him and Helene, recognized by other people, and this thought at the same time frightened him, as if an obligation was imposed on him that he could not keep, and together he liked it, as an amusing assumption.
Anna Pavlovna's evening was the same as the first, only the novelty that Anna Pavlovna treated her guests was now not Mortemar, but a diplomat who had arrived from Berlin and brought the latest details about the stay of Emperor Alexander in Potsdam and how the two highest friend swore there in an inseparable alliance to defend a just cause against the enemy of the human race. Pierre was received by Anna Pavlovna with a touch of sadness, obviously related to the fresh loss that befell the young man, to the death of Count Bezukhy (everyone constantly considered it a duty to assure Pierre that he was very upset by the death of his father, whom he hardly knew) - and sadness exactly the same as that highest sadness that was expressed at the mention of the august Empress Maria Feodorovna. Pierre felt flattered by this. Anna Pavlovna, with her usual art, arranged circles in her drawing room. The large circle, where Prince Vasily and the generals were, used a diplomat. The other circle was at the tea table. Pierre wanted to join the first, but Anna Pavlovna, who was in an irritated state of a commander on the battlefield, when thousands of new brilliant thoughts come that you barely have time to put into practice, Anna Pavlovna, seeing Pierre, touched him on the sleeve.
- Attendez, j "ai des vues sur vous pour ce soir. [I have views of you this evening.] She looked at Helen and smiled at her. - Ma bonne Helene, il faut, que vous soyez charitable pour ma pauvre tante , qui a une adoration pour vous. Allez lui tenir compagnie pour 10 minutes. it was boring, here is a dear count who will not refuse to follow you.
The beauty went to her aunt, but Pierre Anna Pavlovna still kept her beside her, showing a look as if she still had to make the last necessary order.
- Isn't she amazing? - she said to Pierre, pointing to the departing majestic beauty. - Et quelle tenue! [And how she keeps herself!] For such a young girl and such tact, such masterful demeanor! It comes from the heart! Happy will be the one whose it will be! With her, the most non-secular husband will involuntarily occupy the most brilliant place in the world. Is not it? I just wanted to know your opinion, - and Anna Pavlovna let Pierre go.
Pierre sincerely answered Anna Pavlovna in the affirmative to her question about Helen's art of keeping herself. If he ever thought of Helen, he thought precisely of her beauty and of her unusual calm ability to be silently worthy in the world.
Auntie received two young people into her corner, but it seemed she wished to hide her adoration for Helen and wished to express her fear of Anna Pavlovna more. She looked at her niece, as if asking what she should do with these people. Moving away from them, Anna Pavlovna again touched Pierre's sleeve with her finger and said:
- J "espere, que vous ne direz plus qu" on s "ennuie chez moi, [I hope you won't say another time that I'm bored] - and looked at Helen.
Helen smiled with a look that said that she did not allow the possibility that anyone could see her and not be admired. The aunt cleared her throat, swallowed her saliva, and said in French that she was very glad to see Helen; then she turned to Pierre with the same greeting and with the same mine. In the middle of a boring and stumbling conversation, Helen looked back at Pierre and smiled at him with that smile, clear, beautiful, with which she smiled at everyone. Pierre was so accustomed to this smile, it expressed so little for him that he paid no attention to it. Auntie was talking at that time about the collection of snuff boxes that Pierre's late father, Count Bezukhy, had, and showed her snuff box. Princess Helen asked to see the portrait of her aunt's husband, which was made on this snuffbox.
“That’s right, it was done by Vines,” said Pierre, naming a well-known miniaturist, bending down to the table to pick up a snuffbox, and listening to the conversation at another table.
He got up, wanting to go around, but the aunt brought the snuffbox right over Helen, behind her. Helen leaned forward to make room and looked around smiling. She was, as always at the evenings, in a dress that was very open, in the fashion of the time, in front and behind. Her bust, which always seemed marble to Pierre, was at such a close distance from his eyes that with his short-sighted eyes he involuntarily distinguished the lively beauty of her shoulders and neck, and so close to his lips that he had to bend down a little to touch her. He could hear the warmth of her body, the smell of perfume, and the creak of her corset as she moved. He did not see her marble beauty, which was one with her dress, he saw and felt all the charm of her body, which was covered only by clothes. And, having once seen this, he could not see otherwise, how we cannot return to the deceit once explained.

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