Chemical properties of ethylene. Ethylene formula

Ethylene(other name - ethene) is a chemical compound described by the formula C 2 H 4 . Ethylene practically does not occur in nature. It is a colorless, flammable gas with a faint odor. Partially soluble in water(25.6 ml in 100 ml water at 0°C), ethanol (359 ml in the same conditions). It is highly soluble in diethyl ether and hydrocarbons.

Ethylene is the simplest alkene(olefin). Contains a double bond and is therefore classified as an unsaturated compound. It plays an extremely important role in industry and is also a phytohormone.

Raw materials for polyethylene and more

Ethylene is the most produced organic compound in the world; total global ethylene production in 2005 was 107 million tons and continues to grow at 4–6% per year. The source of industrial production of ethylene is the pyrolysis of various hydrocarbon raw materials, for example, ethane, propane, butane contained in associated gases from oil production; from liquid hydrocarbons - low-octane fractions of direct distillation of oil. Ethylene yield is about 30%. At the same time, propylene and a number of liquid products (including aromatic hydrocarbons) are formed.

When ethylene is chlorinated, 1,2-dichloroethane is obtained, hydration leads to ethyl alcohol, and interaction with HCl leads to ethyl chloride. When ethylene is oxidized with atmospheric oxygen in the presence of a catalyst, ethylene oxide is formed. During liquid-phase catalytic oxidation with oxygen, acetaldehyde is obtained, and under the same conditions in the presence of acetic acid, vinyl acetate is obtained. Ethylene is an alkylating agent, for example, under Friedel-Crafts reaction conditions it is capable of alkylating benzene and other aromatic compounds. Ethylene is capable of polymerizing in the presence of catalysts either independently or acting as a comonomer, forming a wide range of polymers with different properties.

Application

Ethylene is one of the basic products of industrial chemistry and is at the base of a number of synthesis chains. The main use of ethylene is as a monomer in the production of polyethylene(the most large-tonnage polymer in global production). Depending on the polymerization conditions, low-density polyethylenes and high-density polyethylenes are obtained.

Polyethylene is also used for production of a number of copolymers, including propylene, styrene, vinyl acetate and others. Ethylene is the raw material for the production of ethylene oxide; as an alkylating agent - in the production of ethylbenzene, diethylbenzene, triethylbenzene.

Ethylene is used as a starting material for production of acetaldehyde and synthetic ethyl alcohol. It is also used for the synthesis of ethyl acetate, styrene, vinyl acetate, vinyl chloride; in the production of 1,2-dichloroethane, ethyl chloride.

Ethylene is used for accelerating fruit ripening- for example, tomatoes, melons, oranges, tangerines, lemons, bananas; defoliation of plants, reduction of pre-harvest fruit drop, to reduce the strength of attachment of fruits to mother plants, which facilitates mechanized harvesting.

In high concentrations, ethylene affects humans and animals narcotic effect.

About a thousand years ago, as one eastern legend tells, an old gardener lived at the court of the khan. The fruits and flowers that he grew in his master’s garden were famous far beyond the borders of the country. There were many strange plants in the garden. And among them is a small pear tree, which the khan received as a gift from the Indian Maharajah.

One day the khan said to the old man: “This fall, the fruits of the pear tree should decorate my table.” Otherwise, your head won't be blown off.

The gardener's heart sank. Pear fruits ripened only in very hot summers. And this year it was windy and cold. The old man did not leave the tree day and night: he insulated it, fed it. But a fierce hurricane swept over the garden and knocked the still unripe pears off the tree.

Now only a miracle could save the gardener. He collected the fruits and brought them to his cramped hut. Then he took a censer with hot coals, put fragrant incense on top and began to pray to the gods to help him.

The incense burner was “smoked” for three days in a row. For three days the sweet smoke of incense flowed in the hut. And a miracle happened: the pears turned amber yellow and ripened.

Centuries passed, and someone decided to check: could this happen?

The fragrant smoke of incense really had a magical effect on the unripe fruits. But many more years passed before they found out why this was happening.

It turned out that the “culprit” of the miracle was a colorless gas with a sweetish odor, which was found in incense smoke: ethylene. By this time they had learned to obtain it from oil and natural gas. And then converted into polyethylene. “The King of Plastics” is what chemists called the material.

Polyethylene is used to make lightweight and durable water pipes, furniture coverings, unbreakable dishes, and perfume bottles. What about plastic film? Perhaps you can't think of better packaging material.

If you wrap bread in film, it will remain just as fresh a week later. Or you can turn the film into a bag that looks like a huge sausage. It will replace the bulky barge. A tugboat can easily drag along such “sausages” with cargo, for example, oil. You can build greenhouses and greenhouses from film. You can make a shelter for grain. It is impossible to list all the uses that material produced by gas with a sweetish odor is used for.

Here's why ethylene gas It has been discovered relatively recently that it has such a miraculous effect on fruits.

It turned out that a colorless gas is formed in the pulp of the fruit. There is a lot of it in ripe fruits and vegetables. In green - not enough. Fumigating them with ethylene means saturating them with the substance necessary for ripening.

An old gardener brought the fruits of one tree to ripeness. Nowadays, this is done with many tons of fruits and vegetables. The khan's servant laid out the fruits in his hut. Now they are placed in a special ethylene chamber. Sometimes they are placed directly on the shelves. Sometimes they are brought into boxes with holes.

The gardener fumigates the fruits with incense smoke. Pure ethylene is injected into the chamber once a day. Lemons, apples, pears, and tomatoes ripen two or even five times faster, absorbing gas with a sweetish odor.

History of the discovery of ethylene

Ethylene was first obtained by the German chemist Johann Becher in 1680 by the action of oil of vitriol (H 2 SO 4) on wine (ethyl) alcohol (C 2 H 5 OH).

CH 3 -CH 2 -OH+H 2 SO 4 →CH 2 =CH 2 +H 2 O

At first it was identified with “flammable air,” i.e., hydrogen. Later, in 1795, ethylene was obtained in a similar way by the Dutch chemists Deyman, Potts van Truswyk, Bond and Lauerenburg and described it under the name “oil gas”, since they discovered the ability of ethylene to add chlorine to form an oily liquid - ethylene chloride (“Dutch oil chemists") (Prokhorov, 1978).

The study of the properties of ethylene, its derivatives and homologues began in the mid-19th century. The practical use of these compounds began with the classical studies of A.M. Butlerov and his students in the field of unsaturated compounds and especially Butlerov’s creation of the theory of chemical structure. In 1860, he prepared ethylene by the action of copper on methylene iodide, establishing the structure of ethylene.

In 1901, Dmitry Nikolaevich Nelyubov grew peas in a laboratory in St. Petersburg, but the seeds produced twisted, shortened sprouts, the top of which was bent with a hook and did not bend. In the greenhouse and in the fresh air, the seedlings were even, tall, and the top quickly straightened the hook in the light. Nelyubov proposed that the factor causing the physiological effect was in the air of the laboratory.

At that time, the premises were lit with gas. The same gas burned in the street lamps, and it had long been noticed that in the event of a gas pipeline accident, the trees standing next to the gas leak prematurely turned yellow and shed their leaves.

The illuminating gas contained a variety of organic substances. To remove gas impurities, Nelyubov passed it through a heated tube with copper oxide. In the “purified” air, the pea seedlings developed normally. In order to find out which substance causes the response of the seedlings, Nelyubov added various components of the illuminating gas in turn, and discovered that the addition of ethylene causes:

1) slower growth in length and thickening of the seedling,

2) “non-bending” apical loop,

3) Changing the orientation of the seedling in space.

This physiological response of seedlings was called the triple response to ethylene. Peas turned out to be so sensitive to ethylene that they began to be used in biotests to determine low concentrations of this gas. It was soon discovered that ethylene also causes other effects: leaf fall, fruit ripening, etc. It turned out that plants themselves are able to synthesize ethylene, i.e. ethylene is a phytohormone (Petushkova, 1986).

Physical properties of ethylene

Ethylene- an organic chemical compound described by the formula C 2 H 4. It is the simplest alkene ( olefin).

Ethylene is a colorless gas with a faint sweet odor with a density of 1.178 kg/m³ (lighter than air), its inhalation has a narcotic effect on humans. Ethylene dissolves in ether and acetone, much less in water and alcohol. Forms an explosive mixture when mixed with air

It hardens at –169.5°C and melts under the same temperature conditions. Ethene boils at –103.8°C. Ignites when heated to 540°C. The gas burns well, the flame is luminous, with weak soot. The rounded molar mass of the substance is 28 g/mol. The third and fourth representatives of the homologous series of ethene are also gaseous substances. The physical properties of the fifth and subsequent alkenes are different; they are liquids and solids.

Ethylene production

The main methods for producing ethylene:

Dehydrohalogenation of halogenated alkanes under the influence of alcoholic solutions of alkalis

CH 3 -CH 2 -Br + KOH → CH 2 = CH 2 + KBr + H 2 O;

Dehalogenation of dihalogenated alkanes under the influence of active metals

Cl-CH 2 -CH 2 -Cl + Zn → ZnCl 2 + CH 2 = CH 2;

Dehydration of ethylene by heating it with sulfuric acid (t >150˚ C) or passing its vapor over a catalyst

CH 3 -CH 2 -OH → CH 2 = CH 2 + H 2 O;

Dehydrogenation of ethane by heating (500C) in the presence of a catalyst (Ni, Pt, Pd)

CH 3 -CH 3 → CH 2 = CH 2 + H 2.

Chemical properties of ethylene

Ethylene is characterized by reactions that proceed through the mechanism of electrophilic addition, radical substitution, oxidation, reduction, and polymerization.

1. Halogenation(electrophilic addition) - the interaction of ethylene with halogens, for example, with bromine, in which bromine water becomes discolored:

CH 2 = CH 2 + Br 2 = Br-CH 2 -CH 2 Br.

Halogenation of ethylene is also possible when heated (300C), in this case the double bond does not break - the reaction proceeds according to the radical substitution mechanism:

CH 2 = CH 2 + Cl 2 → CH 2 = CH-Cl + HCl.

2. Hydrohalogenation- interaction of ethylene with hydrogen halides (HCl, HBr) with the formation of halogenated alkanes:

CH 2 = CH 2 + HCl → CH 3 -CH 2 -Cl.

3. Hydration- interaction of ethylene with water in the presence of mineral acids (sulfuric, phosphoric) with the formation of saturated monohydric alcohol - ethanol:

CH 2 = CH 2 + H 2 O → CH 3 -CH 2 -OH.

Among the electrophilic addition reactions, addition is distinguished hypochlorous acid(1), reactions hydroxy- And alkoxymercuration(2, 3) (production of organomercury compounds) and hydroboration (4):

CH 2 = CH 2 + HClO → CH 2 (OH)-CH 2 -Cl (1);

CH 2 = CH 2 + (CH 3 COO) 2 Hg + H 2 O → CH 2 (OH)-CH 2 -Hg-OCOCH 3 + CH 3 COOH (2);

CH 2 = CH 2 + (CH 3 COO) 2 Hg + R-OH → R-CH 2 (OCH 3)-CH 2 -Hg-OCOCH 3 + CH 3 COOH (3);

CH 2 = CH 2 + BH 3 → CH 3 -CH 2 -BH 2 (4).

Nucleophilic addition reactions are typical for ethylene derivatives containing electron-withdrawing substituents. Among nucleophilic addition reactions, a special place is occupied by the addition reactions of hydrocyanic acid, ammonia, and ethanol. For example,

2 ON-CH = CH 2 + HCN → 2 ON-CH 2 -CH 2 -CN.

4. oxidation. Ethylene oxidizes easily. If ethylene is passed through a solution of potassium permanganate, it will become discolored. This reaction is used to distinguish between saturated and unsaturated compounds. As a result, ethylene glycol is formed

3CH 2 = CH 2 + 2KMnO 4 +4H 2 O = 3CH 2 (OH)-CH 2 (OH) +2MnO 2 + 2KOH.

At severe oxidation ethylene with a boiling solution of potassium permanganate in an acidic environment, a complete rupture of the bond (σ-bond) occurs with the formation of formic acid and carbon dioxide:

Oxidation ethylene oxygen at 200C in the presence of CuCl 2 and PdCl 2 leads to the formation of acetaldehyde:

CH 2 = CH 2 +1/2O 2 = CH 3 -CH = O.

5. hydrogenation. At restoration Ethylene produces ethane, a representative of the class of alkanes. The reduction reaction (hydrogenation reaction) of ethylene proceeds by a radical mechanism. The condition for the reaction to occur is the presence of catalysts (Ni, Pd, Pt), as well as heating of the reaction mixture:

CH 2 = CH 2 + H 2 = CH 3 -CH 3.

6. Ethylene enters polymerization reaction. Polymerization is the process of forming a high-molecular compound - a polymer - by combining with each other using the main valences of the molecules of the original low-molecular substance - the monomer. Polymerization of ethylene occurs under the action of acids (cationic mechanism) or radicals (radical mechanism):

n CH 2 = CH 2 = -(-CH 2 -CH 2 -) n -.

7. Combustion:

C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O

8. Dimerization. Dimerization- the process of formation of a new substance by combining two structural elements (molecules, including proteins, or particles) into a complex (dimer) stabilized by weak and/or covalent bonds.

2CH 2 =CH 2 →CH 2 =CH-CH 2 -CH 3

Application

Ethylene is used in two main categories: as a monomer from which large carbon chains are built, and as a starting material for other two-carbon compounds. Polymerizations are the repeated combinations of many small ethylene molecules into larger ones. This process occurs at high pressures and temperatures. The areas of application of ethylene are numerous. Polyethylene is a polymer that is used especially in large quantities in the production of packaging films, wire coverings and plastic bottles. Another use of ethylene as a monomer concerns the formation of linear α-olefins. Ethylene is the starting material for the preparation of a number of two-carbon compounds such as ethanol ( technical alcohol), ethylene oxide ( antifreeze, polyester fibers and films), acetaldehyde and vinyl chloride. In addition to these compounds, ethylene and benzene form ethylbenzene, which is used in the production of plastics and synthetic rubber. The substance in question is one of the simplest hydrocarbons. However, the properties of ethylene make it biologically and economically significant.

The properties of ethylene provide a good commercial basis for a large number of organic (carbon and hydrogen containing) materials. Single ethylene molecules can be joined together to make polyethylene (which means many ethylene molecules). Polyethylene is used to make plastics. In addition, it can be used to make detergents and synthetic lubricants, which are chemicals used to reduce friction. The use of ethylene to produce styrene is important in the process of creating rubber and protective packaging. In addition, it is used in the footwear industry, especially sports shoes, as well as in the production of car tires. The use of ethylene is commercially important, and the gas itself is one of the most commonly produced hydrocarbons globally.

Ethylene is used in the production of specialty glass for the automotive industry.

Among vegetable growers who are engaged in the cultivation and supply of agricultural crops professionally, it is customary to collect fruits that have not passed the ripening stage. This approach allows you to preserve vegetables and fruits longer and transport them over long distances without problems. Since green bananas or, for example, tomatoes are unlikely to be in serious demand among the average consumer, and natural ripening can take a long time, gases are used to speed up the process ethylene And acetylene. At first glance, this approach may cause bewilderment, but delving into the physiology of the process, it becomes clear why modern vegetable growers actively use such technology.

Gas ripening hormone for vegetables and fruits

The influence of specific gases on the rate of ripening of crops was first noticed by the Russian botanist Dmitry Nelyubov, who at the beginning of the 20th century. determined a certain dependence of the “ripeness” of lemons on the atmosphere in the room. It turned out that in warehouses with an old heating system, which was not highly airtight and allowed steam to escape into the atmosphere, lemons ripened much faster. Through a simple analysis, it was found that this effect was achieved thanks to ethylene and acetylene, which were contained in the steam emanating from the pipes.

At first, such a discovery was deprived of due attention from entrepreneurs; only rare innovators tried to saturate their storage facilities with ethylene gas to improve productivity. Only in the middle of the 20th century. The “gas hormone” for vegetables and fruits has been adopted by fairly large enterprises.

To implement the technology, cylinders are usually used, the valve system of which allows you to accurately adjust the gas output and achieve the required concentration in the room. It is very important that in this case ordinary air, which contains oxygen, the main oxidizing agent for agricultural products, is displaced from the storage facility. By the way, the technology of replacing oxygen with another substance is actively used to increase the shelf life of not only fruits, but also other food products - meat, fish, cheeses, etc. Nitrogen and carbon dioxide are used for this purpose, as discussed in detail.

Why is ethylene gas called "banana" gas?

So, the ethylene environment allows you to speed up the ripening process of vegetables and fruits. But why is this happening? The fact is that during the ripening process, many crops release a special substance, which is ethylene, which, when released into the environment, affects not only the source of the release itself, but also its neighbors.

this is how apples help with ripening

Each type of fruit produces different amounts of ripening hormone. The biggest differences in this regard are:

apples;
pears;
apricots;
bananas.

The latter enter our country over a considerable distance, so they are not transported in ripe form. In order for banana peels to acquire their natural bright yellow color, many entrepreneurs place them in a special chamber that is filled with ethylene. The cycle of such treatment is on average 24 hours, after which bananas receive a kind of impetus to accelerated ripening. It is interesting that without such a procedure, the favorite fruit of many children and adults will remain in a semi-ripe state for a very long time. Therefore, “banana” gas is simply necessary in this case.

sent for ripening

Methods for creating the required gas concentration in the fruit storage chamber

It was already noted above that to ensure the required concentration of ethylene/acetylene in the storage room for vegetables and fruits, gas cylinders are usually used. In order to save money, some vegetable growers sometimes resort to another method. In the room with the fruits, a piece of calcium carbide is placed, onto which water drips at intervals of 2-3 drops/hour. As a result of the chemical reaction, acetylene is released, gradually filling the internal atmosphere.

This “old-fashioned” method, although attractive in its simplicity, is more typical for private households, since it does not allow achieving the exact concentration of gas in the room. Therefore, in medium and large enterprises, where it is important to calculate the required amount of “gas hormone” for each crop, balloon installations are often used.

The correct formation of the gas environment during the storage and production of food products plays a huge role, making it possible to improve the appearance of the product, its taste and increase its shelf life. Read more about methods of packaging and storing products in a series of articles about food gas mixtures, and you can order these products by selecting the required gas and, if desired, receiving advice on its proper use.

Physical properties

Ethan under n. y is a colorless, odorless gas. Molar mass - 30.07. Melting point -182.81 °C, boiling point -88.63 °C. . Density ρ gas. =0.001342 g/cm³ or 1.342 kg/m³ (no.), ρ liquid. =0.561 g/cm³ (T=-100 °C). Dissociation constant 42 (in water, standard) [ source?] . Vapor pressure at 0 °C - 2.379 MPa.

Chemical properties

Chemical formula C 2 H 6 (rational CH 3 CH 3). The most typical reactions are the replacement of hydrogen with halogens, which occur via a free radical mechanism. Thermal dehydrogenation of ethane at 550-650 °C leads to ketene, at temperatures above 800 °C - cacetylene (benzolysate is also formed). Direct chlorination at 300-450 °C - ethyl chloride, nitration in the gas phase gives a mixture (3:1) of nitroethane and tromethane.

Receipt

In industry

In industry it is obtained from petroleum and natural gases, where it accounts for up to 10% by volume. In Russia, the ethane content in oil gases is very low. In the USA and Canada (where its content in oil and natural gases is high) it serves as the main raw material for the production of ethene.

In laboratory conditions

Obtained from iodomethane by the Wurtz reaction, from sodium acetate by electrolysis by the Kolbe reaction, by fusion of sodium propionate with alkali, from ethyl bromide by the Grignard reaction, by hydrogenation of ethene (over Pd) or acetylene (in the presence of Raney Nickel).

Application

The main use of ethane in industry is the production of ethylene.

Butane(C 4 H 10) - organic compound of the class alkanes. In chemistry, the name is used primarily to refer to n-butane. The mixture of n-butane and its isomer isobutane CH(CH 3) 3 . The name comes from the root "but-" (English name butyric acid - butyric acid) and the suffix “-an” (belonging to alkanes). In high concentrations it is poisonous; inhalation of butane causes dysfunction of the pulmonary-respiratory system. Contained in natural gas, is formed when cracking petroleum products, when dividing the associated oil gas, "fat" natural gas. As a representative of hydrocarbon gases, it is fire and explosive, low-toxic, has a specific characteristic odor, and has narcotic properties. In terms of the degree of impact on the body, the gas belongs to substances of the 4th hazard class (low-hazard) according to GOST 12.1.007-76. Harmful effects on the nervous system .

Isomerism

Butane has two isomer:

Physical properties

Butane is a colorless flammable gas, with a specific odor, easily liquefied (below 0 °C and normal pressure or at elevated pressure and normal temperature - a highly volatile liquid). Freezing point -138°C (at normal pressure). Solubility in water - 6.1 mg in 100 ml of water (for n-butane, at 20 °C, much better soluble in organic solvents ). Can form azeotropic mixture with water at a temperature of about 100 °C and a pressure of 10 atm.

Finding and receiving

Contained in gas condensate and petroleum gas (up to 12%). It is a product of catalytic and hydrocatalytic cracking oil fractions. Can be obtained in the laboratory by Wurtz reactions.

2 C 2 H 5 Br + 2Na → CH 3 -CH 2 -CH 2 -CH 3 + 2NaBr

Desulphurization (demercaptanization) of butane fraction

The straight-run butane fraction must be purified from sulfur compounds, which are mainly represented by methyl and ethyl mercaptans. The method for purifying the butane fraction from mercaptans consists of alkaline extraction of mercaptans from the hydrocarbon fraction and subsequent regeneration of the alkali in the presence of homogeneous or heterogeneous catalysts with atmospheric oxygen with the release of disulfide oil.

Applications and reactions

During free radical chlorination it forms a mixture of 1-chloro- and 2-chlorobutane. Their ratio is well explained by the difference in the strength of C-H bonds in positions 1 and 2 (425 and 411 kJ/mol). Upon complete combustion in air it forms carbon dioxide and water. Butane is used in a mixture with propane in lighters, in gas cylinders in a liquefied state, where it has an odor, as it contains specially added odorants. In this case, “winter” and “summer” mixtures with different compositions are used. Heat of combustion 1 kg - 45.7 MJ (12.72 kWh).

2C 4 H 10 + 13 O 2 → 8 CO 2 + 10 H 2 O

When there is a lack of oxygen, it forms soot or carbon monoxide or both together.

2C 4 H 10 + 5 O 2 → 8 C + 10 H 2 O

2C 4 H 10 + 9 O 2 → 8 CO + 10 H 2 O

By company DuPont a method has been developed for obtaining maleic anhydride from n-butane by catalytic oxidation.

2 CH 3 CH 2 CH 2 CH 3 + 7 O 2 → 2 C 2 H 2 (CO) 2 O + 8 H 2 O

n-Butane - raw material for production butene, 1,3-butadiene, a component of high octane gasolines. High purity butane and especially isobutane can be used as a refrigerant in refrigeration units. The performance of such systems is slightly lower than that of freon systems. Butane is environmentally friendly, unlike freon refrigerants.

In the food industry, butane is registered as food additives E943a, and isobutane - E943b, How propellant, for example, in deodorants.

Ethylene(By IUPAC: ethene) - organic chemical compound, described by the formula C 2 H 4. Is the simplest alkene (olefin). Ethylene practically does not occur in nature. It is a colorless, flammable gas with a faint odor. Partially soluble in water (25.6 ml in 100 ml of water at 0°C), ethanol (359 ml in the same conditions). It is highly soluble in diethyl ether and hydrocarbons. Contains a double bond and is therefore classified as unsaturated or unsaturated hydrocarbons. Plays an extremely important role in industry and is also phytohormone. Ethylene is the most produced organic compound in the world ; total world ethylene production in 2008 amounted to 113 million tons and continues to grow by 2-3% per year .

Application

Ethylene is the leading product basic organic synthesis and is used to produce the following compounds (listed in alphabetical order):

Vinyl acetate;

Dichloroethane / vinyl chloride(3rd place, 12% of the total volume);

Ethylene oxide(2nd place, 14-15% of the total volume);

Polyethylene(1st place, up to 60% of the total volume);

Styrene;

Acetic acid;

Ethylbenzene;

Ethylene glycol;

Ethanol.

Ethylene mixed with oxygen has been used in medicine for anesthesia until the mid-80s of the twentieth century in the USSR and the Middle East. Ethylene is phytohormone in almost all plants , among other things is responsible for the fall of needles in conifers.

Basic chemical properties

Ethylene is a chemically active substance. Since there is a double bond between the carbon atoms in the molecule, one of them, which is less strong, is easily broken, and at the site of the bond break the attachment, oxidation, and polymerization of molecules occurs.

Halogenation:

CH 2 =CH 2 + Cl 2 → CH 2 Cl-CH 2 Cl

Bromine water becomes discolored. This is a qualitative reaction to unsaturated compounds.

Hydrogenation:

CH 2 =CH 2 + H - H → CH 3 - CH 3 (under the influence of Ni)

Hydrohalogenation:

CH 2 =CH 2 + HBr → CH 3 - CH 2 Br

Hydration:

CH 2 =CH 2 + HOH → CH 3 CH 2 OH (under the influence of a catalyst)

This reaction was discovered by A.M. Butlerov, and it is used for the industrial production of ethyl alcohol.

Oxidation:

Ethylene oxidizes easily. If ethylene is passed through a solution of potassium permanganate, it will become discolored. This reaction is used to distinguish between saturated and unsaturated compounds.

Ethylene oxide is a fragile substance; the oxygen bridge breaks and water joins, resulting in the formation ethylene glycol:

C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O

Polymerization:

nCH 2 =CH 2 → (-CH 2 -CH 2 -) n

Isoprene CH 2 =C(CH3)-CH=CH2, 2-methylbutadiene-1,3 - unsaturated hydrocarbon diene series (C n H 2n−2 ) . Under normal conditions, colorless liquid. He is monomer For natural rubber and a structural unit for many molecules of other natural compounds - isoprenoids, or terpenoids. . Soluble in alcohol. Isoprene polymerizes to give isoprene rubbers. Isoprene also reacts polymerization with vinyl compounds.

Finding and receiving

Natural rubber is a polymer of isoprene - most commonly cis-1,4-polyisoprene with a molecular weight of 100,000 to 1,000,000. Contains several percent of other materials as impurities, such as squirrels, fatty acid, resins and inorganic substances. Some sources of natural rubber are called gutta-percha and consists of trans-1,4-polyisoprene, structural isomer, which has similar but not identical properties. Isoprene is produced and released into the atmosphere by many types of trees (the main one is oak) Annual production of isoprene by vegetation is about 600 million tons, with half produced by tropical broadleaf trees, the rest produced by shrubs. Once released into the atmosphere, isoprene is converted by free radicals (such as hydroxyl (OH) radicals) and, to a lesser extent, by ozone into various substances such as aldehydes, hydroxyperoxides, organic nitrates and epoxides, which mix with water droplets to form aerosols or haze. Trees use this mechanism not only to avoid overheating of the leaves by the Sun, but also to protect against free radicals, especially ozone. Isoprene was first obtained by heat treatment of natural rubber. Most industrially available as a thermal product cracking naphtha or oils, and also as a by-product in the production ethylene. Produced around 20,000 tons per year. About 95% of isoprene production is used to make cis-1,4-polyisoprene, a synthetic version of natural rubber.

Butadiene-1.3(divinyl) CH 2 =CH-CH=CH2 - unsaturated hydrocarbon, the simplest representative diene hydrocarbons.

Physical properties

Butadiene - colorless gas with a characteristic odor, boiling temperature−4.5 °C, melting temperature−108.9 °C, flash point−40 °C, maximum permissible concentration in air (maximum permissible concentration) 0.1 g/m³, density 0.650 g/cm³ at −6 °C.

Slightly soluble in water, highly soluble in alcohol, kerosene with air in an amount of 1.6-10.8%.

Chemical properties

Butadiene is prone to polymerization, easily oxidizes air with education peroxide compounds that accelerate polymerization.

Receipt

Butadiene is produced by the reaction Lebedeva transmission ethyl alcohol through catalyst:

2CH 3 CH 2 OH → C 4 H 6 + 2H 2 O + H 2

Or dehydrogenation of normal butylene:

CH 2 =CH-CH 2 -CH 3 → CH 2 =CH-CH=CH 2 + H 2

Application

The polymerization of butadiene produces synthetic rubber. Copolymerization with acrylonitrile And styrene get ABS plastic.

Benzene (C 6 H 6 , Ph H) - organic chemical compound, colorless liquid with a pleasant sweetish smell. simplest aromatic hydrocarbon. Benzene is included in gasoline, widely used in industry, is the raw material for production medications, various plastics, synthetic rubber, dyes. Although benzene is included crude oil, on an industrial scale it is synthesized from its other components. Toxic, carcinogenic.

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 all hydrocarbons, benzene burns and produces a lot of soot. Forms explosive mixtures with air, mixes well with ethers, 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, chlorine alkanes, halogens, nitrogen And sulfuric acids. Reactions of cleavage of the benzene ring take place under harsh conditions (temperature, pressure).

Interaction with chlorine in the presence of a catalyst:

From 6 H 6 + Cl 2 -(FeCl 3) → From 6 H 5 Cl + HCl chlorobenzene is formed

Catalysts promote the creation of an active electrophilic species by polarization between halogen atoms.

Cl-Cl + FeCl 3 → Cl ઠ - ઠ +

C 6 H 6 + Cl ઠ - -Cl ઠ + + FeCl 3 → [C 6 H 5 Cl + FeCl 4 ] → C 6 H 5 Cl + FeCl 3 + HCl

In the absence of a catalyst, a radical substitution reaction occurs when heated or illuminated.

With 6 H 6 + 3Cl 2 - (lighting) → C 6 H 6 Cl 6 a mixture of hexachlorocyclohexane isomers is formed video

Reaction with bromine (pure):

Interaction with halogen derivatives of alkanes ( Friedel-Crafts reaction):

C 6 H 6 + C 2 H 5 Cl -(AlCl 3) → C 6 H 5 C 2 H 5 + HCl ethylbenzene is formed

C 6 H 6 + HNO 3 -(H 2 SO 4) → C 6 H 5 NO 2 + H 2 O

Structure

Benzene is unsaturated in composition. hydrocarbons(homologous series C n H 2n-6), but unlike hydrocarbons of the series ethylene C 2 H 4 exhibits properties inherent to 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 location of all bonds and molecules on the same plane and the presence of a conjugated 6π-electron cloud in the structure. The modern understanding of the electronic nature of bonds in benzene is based on the hypothesis 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

Today, there are three fundamentally different methods for producing benzene.

Coking coal. This process was historically the first and served as the main source of benzene until World War II. Currently, the share of benzene produced by this method is less than 1%.

It should be added that benzene obtained from coal tar contains a significant amount of thiophene, which makes such benzene a raw material unsuitable for a number of technological processes. Catalytic reforming (aromaizing) gasoline fractions of oil. This process is the main source of benzene in the United States. In Western Europe, Russia and Japan, 40-60% of the total amount of the substance is obtained using this method. In this process, in addition to benzene, toluene And

xylenes

Due to the fact that toluene is produced in quantities exceeding the demand for it, it is also partially processed into: benzene - by hydrodealkylation method;

Application

a mixture of benzene and xylenes - by disproportionation method; [ Pyrolysis ] gasoline and heavier petroleum fractions. Up to 50% of benzene is produced by this method. Along with benzene, toluene and xylenes are formed. In some cases, this entire fraction is sent to the dealkylation stage, where both toluene and xylenes are converted to benzene.

Benzene is one of the ten most important substances in the chemical industry. source not specified 232 days (Most of the benzene produced is used for the synthesis of other products: about 50% of benzene is converted into ethylbenzene);
alkylation benzene (Most of the benzene produced is used for the synthesis of other products: about 50% of benzene is converted into ethylene);
about 25% of benzene is converted into cumene propylene approximately 10-15% benzene;
hydrogenate V;
cyclohexane about 10% of benzene is spent on production;
nitrobenzene chlorobenzene.

Benzene is used in significantly smaller quantities for the synthesis of some other compounds. Occasionally and in extreme cases, due to its high toxicity, benzene is used as solvent. In addition, benzene is part of gasoline. Due to its high toxicity, its content is limited by new standards to 1%.

Toluene(from Spanish Tolu, Tolu balsam) - methylbenzene, a colorless liquid with a characteristic odor, belongs to the arenes.

Toluene was first obtained by P. Peltier in 1835 during the distillation of pine resin. In 1838, A. Deville isolated it from a balsam brought from the city of Tolu in Colombia, after which it received its name.

general characteristics

A colorless, mobile, volatile liquid with a pungent odor, exhibits a weak narcotic effect. Miscible within unlimited limits with hydrocarbons, many alcohols And ethers, does not mix with water. Refractive index light 1.4969 at 20 °C. It is flammable and burns with a smoky flame.

Chemical properties

Toluene is characterized by electrophilic substitution reactions in the aromatic ring and substitution in the methyl group according to the radical mechanism.

Electrophilic substitution in the aromatic ring it occurs predominantly in the ortho- and para-positions relative to the methyl group.

In addition to substitution reactions, toluene undergoes addition reactions (hydrogenation) and ozonolysis. Some oxidizing agents (alkaline solution of potassium permanganate, dilute nitric acid) oxidize the methyl group to a carboxyl group. Self-ignition temperature 535 °C. Concentration limit of flame propagation, %vol. Temperature limit of flame propagation, °C. Flash point 4 °C.

Interaction with potassium permanganate in an acidic environment:

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

Receipt and purification

Product catalytic reforming gasoline factions oil. Isolated by selective extraction and subsequent rectification.Also good yields are achieved with catalytic dehydrogenation heptane through methylcyclohexane. Toluene is purified in the same way benzene, only if used concentrated sulfuric acid We must not forget that toluene sulfonated lighter than benzene, which means it is necessary to maintain a lower temperature reaction mixture(less than 30 °C). Toluene also forms an azeotrope with water .

Toluene can be obtained from benzene by Friedel-Crafts reactions:

Application

Raw materials for production benzene, benzoic acid, nitrotoluenes(including trinitrotoluene), toluene diisocyanates(via dinitrotoluene and toluene diamine) benzyl chloride and other organic substances.

Is solvent for many polymers, is included in various commercial solvents for varnishes And paints. Included in solvents: R-40, R-4, 645, 646 , 647 , 648. Used as a solvent in chemical synthesis.

Naphthalene- C 10 H 8 solid crystalline substance with characteristic smell. It does not dissolve in water, but it does well in benzene, on air, alcohol, chloroform.

Chemical properties

Naphthalene is similar in chemical properties to benzene: easily nitrates, sulfonated, interacts with halogens. It differs from benzene in that it reacts even more easily.

Physical properties

Density 1.14 g/cm³, melting point 80.26 °C, boiling point 218 °C, solubility in water approximately 30 mg/l, flash point 79 - 87 °C, auto-ignition temperature 525 °C, molar mass 128.17052 g/mol.

Receipt

Naphthalene is obtained from coal tar. Naphthalene can also be isolated from heavy pyrolysis resin (quenching oil), which is used in the pyrolysis process in ethylene plants.

Termites also produce naphthalene. Coptotermes formosanus to protect their nests from ants, fungi and nematodes .

Application

Important raw material of the chemical industry: used for synthesis phthalic anhydride, tetralin, decalin, various naphthalene derivatives.

Naphthalene derivatives are used to produce dyes And explosives, V medicine, How insecticide.