Preparation and properties of ethylene. Chemical properties of ethylene. Ethylene formula. Characteristics and physical properties of ethene

DEFINITION

Ethylene (ethene)- the first representative of a series of alkenes - unsaturated hydrocarbons with one double bond.

Formula – C 2 H 4 (CH 2 = CH 2). Molecular weight (mass of one mole) – 28 g/mol.

The hydrocarbon radical formed from ethylene is called vinyl (-CH = CH 2). The carbon atoms in the ethylene molecule are in sp 2 hybridization.

Chemical properties of ethylene

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

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.

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.

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.

During oxidation reactions ethylene, the formation of various products is possible, and the composition is determined by the conditions of oxidation. Thus, during the oxidation of ethylene in mild conditions(oxidizing agent - potassium permanganate) the π-bond is broken and a dihydric alcohol - 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.

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.

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 -.

Physical properties of ethylene

Ethylene is a colorless gas with a faint odor, slightly soluble in water, soluble in alcohol, and highly soluble in diethyl ether. Forms an explosive mixture when mixed with air

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 dihalogen derivatives of 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.

Applications of ethylene

Ethylene is one of the most important compounds produced on a huge industrial scale. It is used as a raw material for the production of a whole range of various organic compounds (ethanol, ethylene glycol, acetic acid, etc.). Ethylene serves as a feedstock for the production of polymers (polyethylene, etc.). It is used as a substance that accelerates the growth and ripening of vegetables and fruits.

Examples of problem solving

EXAMPLE 1

Exercise

Carry out a series of transformations ethane → ethene (ethylene) → ethanol → ethene → chloroethane → butane.

Solution

To obtain ethene (ethylene) from ethane, it is necessary to use the ethane dehydrogenation reaction, which occurs in the presence of a catalyst (Ni, Pd, Pt) and upon heating: C 2 H 6 →C 2 H 4 + H 2 . Ethanol is produced from ethene by a hydration reaction with water in the presence of mineral acids (sulfuric, phosphoric): C 2 H 4 + H 2 O = C 2 H 5 OH. To obtain ethene from ethanol, a dehydration reaction is used: The production of chloroethane from ethene is carried out by the hydrohalogenation reaction: C 2 H 4 + HCl → C 2 H 5 Cl. To obtain butane from chloroethane, the Wurtz reaction is used: 2C 2 H 5 Cl + 2Na → C 4 H 10 + 2NaCl.

EXAMPLE 2

Exercise	Calculate how many liters and grams of ethylene can be obtained from 160 ml of ethanol, the density of which is 0.8 g/ml.
Solution	Ethylene can be obtained from ethanol by a dehydration reaction, the condition for which is the presence of mineral acids (sulfuric, phosphoric). Let us write the reaction equation for producing ethylene from ethanol: C 2 H 5 OH → (t, H2SO4) → C 2 H 4 + H 2 O. Let's find the mass of ethanol: m(C 2 H 5 OH) = V(C 2 H 5 OH) × ρ (C 2 H 5 OH); m(C 2 H 5 OH) = 160 × 0.8 = 128 g. Molar mass (molecular weight of one mole) of ethanol, calculated using the table of chemical elements by D.I. Mendeleev – 46 g/mol. Let's find the amount of ethanol: v(C 2 H 5 OH) = m(C 2 H 5 OH)/M(C 2 H 5 OH); v(C 2 H 5 OH) = 128/46 = 2.78 mol. According to the reaction equation v(C 2 H 5 OH): v(C 2 H 4) = 1:1, therefore, v(C 2 H 4) = v(C 2 H 5 OH) = 2.78 mol. Molar mass (molecular weight of one mole) of ethylene, calculated using the table of chemical elements by D.I. Mendeleev – 28 g/mol. Let's find the mass and volume of ethylene: m(C 2 H 4) = v(C 2 H 4) × M(C 2 H 4); V(C 2 H 4) = v(C 2 H 4) ×V m; m(C 2 H 4) = 2.78 × 28 = 77.84 g; V(C 2 H 4) = 2.78 × 22.4 = 62.272 l.
Answer	The mass of ethylene is 77.84 g, the volume of ethylene is 62.272 liters.

January 18, 2018

Unsaturated hydrocarbons with a double chemical bond in their molecules belong to the group of alkenes. The first representative of the homologous series is ethene, or ethylene, the formula of which is: C 2 H 4. Alkenes are often called olefins. The name is historical and arose in the 18th century, after obtaining the product of the reaction of ethylene with chlorine - ethyl chloride, which looks like an oily liquid. Then ethene was called oil gas. In our article we will study its chemical properties, as well as its production and use in industry.

The relationship between the structure of the molecule and the properties of the substance

According to the theory of the structure of organic substances proposed by M. Butlerov, the characteristics of a compound completely depend on the structural formula and type of bonds of its molecule. The chemical properties of ethylene are also determined by the spatial configuration of atoms, the hybridization of electron clouds and the presence of a pi bond in its molecule. The two unhybridized p-electrons of the carbon atoms overlap in a plane perpendicular to the plane of the molecule itself. A double bond is formed, the rupture of which determines the ability of alkenes to undergo addition and polymerization reactions.

Physical properties

Ethene is a gaseous substance with a subtle, peculiar odor. It is poorly soluble in water, but soluble in benzene, carbon tetrachloride, gasoline and other organic solvents. Based on the formula of ethylene C 2 H 4, its molecular weight is 28, that is, ethene is slightly lighter than air. In the homologous series of alkenes, with an increase in their mass, the state of aggregation of substances changes according to the scheme: gas - liquid - solid compound.

Gas production in the laboratory and industry

By heating ethyl alcohol to 140 °C in the presence of concentrated sulfuric acid, ethylene can be obtained in the laboratory. Another method is the abstraction of hydrogen atoms from alkane molecules. By acting with caustic sodium or potassium on halogen-substituted compounds of saturated hydrocarbons, for example, chloroethane, ethylene is produced. In industry, the most promising way to obtain it is the processing of natural gas, as well as pyrolysis and cracking of oil. All chemical properties of ethylene - reactions of hydration, polymerization, addition, oxidation - are explained by the presence of a double bond in its molecule.

Interaction of olefins with elements of the main subgroup of the seventh group

All members of the homologous series of ethene attach halogen atoms at the site of pi-bond cleavage in their molecule. Thus, an aqueous solution of red-brown bromine becomes discolored, resulting in the formation of the equation ethylene - dibromoethane:

C 2 H 4 + Br 2 = C 2 H 4 Br 2

The reaction with chlorine and iodine proceeds similarly, in which the addition of halogen atoms also occurs at the site of destruction of the double bond. All olefin compounds can interact with hydrogen halides: hydrogen chloride, hydrogen fluoride, etc. As a result of the addition reaction, which proceeds according to the ionic mechanism, substances are formed - halogen derivatives of saturated hydrocarbons: chloroethane, fluoroethane.

Industrial ethanol production

The chemical properties of ethylene are often used to obtain important substances widely used in industry and everyday life. For example, heating ethene with water in the presence of orthophosphoric or sulfuric acids, under the influence of a catalyst, a hydration process occurs. It goes with the formation of ethyl alcohol - a large-scale product obtained at chemical plants of organic synthesis. The mechanism of the hydration reaction proceeds by analogy with other addition reactions. In addition, the interaction of ethylene with water also occurs as a result of the cleavage of the pi bond. The free valences of the carbon atoms of ethene are joined by hydrogen atoms and the hydroxo group that are part of the water molecule.

Hydrogenation and combustion of ethylene

Despite all of the above, the hydrogen compound reaction is not of great practical importance. However, it shows the genetic relationship between different classes of organic compounds, in this case alkanes and olefins. By adding hydrogen, ethene turns into ethane. The opposite process - the elimination of hydrogen atoms from saturated hydrocarbons leads to the formation of a representative of alkenes - ethene. The severe oxidation of olefins, called combustion, is accompanied by the release of a large amount of heat; the reaction is exothermic. Combustion products are the same for substances of all classes of hydrocarbons: alkanes, unsaturated compounds of the ethylene and acetylene series, aromatic substances. These include carbon dioxide and water. Air reacts with ethylene to form an explosive mixture.

Oxidation reactions

Ethene can be oxidized with a solution of potassium permanganate. This is one of the qualitative reactions with the help of which the presence of a double bond in the composition of the substance being determined is proven. The violet color of the solution disappears due to the cleavage of the double bond and the formation of a dihydric saturated alcohol - ethylene glycol. The reaction product has a wide range of industrial uses as a raw material for the production of synthetic fibers, such as lavsan, explosives and antifreeze. As you can see, the chemical properties of ethylene are used to obtain valuable compounds and materials.

Polymerization of olefins

Increasing temperature, increasing pressure and the use of catalysts are necessary conditions for the polymerization process. Its mechanism is different from addition or oxidation reactions. It represents the sequential binding of many ethylene molecules at the sites where double bonds are broken. The reaction product is polyethylene, the physical characteristics of which depend on the value of n - the degree of polymerization. If it is small, then the substance is in a liquid state of aggregation. If the indicator approaches 1000 links, then polyethylene film and flexible hoses are made from such a polymer. If the degree of polymerization exceeds 1500 links in the chain, then the material is a white solid, greasy to the touch.

It is used for the production of solid cast products and plastic pipes. A halogen derivative of ethylene, Teflon has non-stick properties and is a widely used polymer, in demand in the manufacture of multicookers, frying pans, and frying pans. Its high ability to resist abrasion is used in the production of lubricants for automobile engines, and its low toxicity and tolerance to the tissues of the human body have made it possible to use Teflon prostheses in surgery.

In our article, we examined such chemical properties of olefins as ethylene combustion, addition reactions, oxidation and polymerization.

Receipt

Ethylene began to be widely used as a monomer before World War II due to the need to obtain a high-quality insulating material that could replace polyvinyl chloride. After developing a method for polymerizing ethylene under high pressure and studying the dielectric properties of the resulting polyethylene, its production began, first in the UK, and later in other countries.

The main industrial method for producing ethylene is the pyrolysis of liquid petroleum distillates or lower saturated hydrocarbons. The reaction is carried out in tube furnaces at +800-950 °C and a pressure of 0.3 MPa. When straight-run gasoline is used as a raw material, the ethylene yield is approximately 30%. Simultaneously with ethylene, a significant amount of liquid hydrocarbons, including aromatic ones, are also formed. When pyrolyzing gas oil, the yield of ethylene is approximately 15-25%. The highest ethylene yield - up to 50% - is achieved when using saturated hydrocarbons as raw materials: ethane, propane and butane. Their pyrolysis is carried out in the presence of water vapor.

When leaving production, during commodity accounting operations, when checking it for compliance with regulatory and technical documentation, ethylene samples are taken according to the procedure described in GOST 24975.0-89 “Ethylene and propylene. Sampling methods." Ethylene samples can be taken in both gaseous and liquefied forms using special samplers in accordance with GOST 14921.

Ethylene produced industrially in Russia must meet the requirements set out in GOST 25070-2013 “Ethylene. Technical conditions".

Production structure

Currently, in the structure of ethylene production, 64% comes from large-scale pyrolysis units, ~17% from small-scale gas pyrolysis units, ~11% from gasoline pyrolysis and 8% from ethane pyrolysis.

Application

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

• 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);

Ethylene mixed with oxygen was used in medicine for anesthesia until the mid-1980s in the USSR and the Middle East. Ethylene is a phytohormone in almost all plants; among other things, it is responsible for the fall of needles in conifers.

Electronic and spatial structure of the molecule

The carbon atoms are in the second valence state (sp 2 hybridization). As a result, three hybrid clouds are formed on a plane at an angle of 120°, which form three σ bonds with carbon and two hydrogen atoms; The p-electron, which did not participate in hybridization, forms a π-bond in the perpendicular plane with the p-electron of the neighboring carbon atom. This forms a double bond between carbon atoms. The molecule has a planar structure.

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:

C H 2 = C H 2 + B r 2 → C H 2 B r - C H 2 B r + D (\displaystyle (\mathsf (CH_(2)(\text(=))CH_(2)+Br_(2)\rightarrow CH_(2)Br(\text(-))CH_(2)Br+D))) Bromine water becomes discolored. This is a qualitative reaction to unsaturated compounds.

• Hydrogenation:

C H 2 = C H 2 + H 2 → N i C H 3 - C H 3 (\displaystyle (\mathsf (CH_(2)(\text(=))CH_(2)+H_(2)(\xrightarrow[()] (Ni))CH_(3)(\text(-))CH_(3))))

• Hydrohalogenation:

C H 2 = C H 2 + H B r → C H 3 C H 2 B r (\displaystyle (\mathsf (CH_(2)(\text(=))CH_(2)+HBr\rightarrow CH_(3)CH_(2)Br )))

• Hydration:

C H 2 = C H 2 + H 2 O → H + C H 3 C H 2 O H (\displaystyle (\mathsf (CH_(2)(\text(=))CH_(2)+H_(2)O(\xrightarrow[( )](H^(+)))CH_(3)CH_(2)OH))) 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. The result is ethylene glycol. Reaction equation: 3 C H 2 = C H 2 + 2 K M n O 4 + 4 H 2 O → C H 2 O H - C H 2 O H + 2 M n O 2 + 2 K O H (\displaystyle (\mathsf (3CH_(2)(\text(= ))CH_(2)+2KMnO_(4)+4H_(2)O\rightarrow CH_(2)OH(\text(-))CH_(2)OH+2MnO_(2)+2KOH)))

• Combustion:

C H 2 = C H 2 + 3 O 2 → 2 C O 2 + 2 H 2 O (\displaystyle (\mathsf (CH_(2)(\text(=))CH_(2)+3O_(2)\rightarrow 2CO_(2 )+2H_(2)O)))

• Polymerization (production of polyethylene):

n C H 2 = C H 2 → (- C H 2 - C H 2 -) n (\displaystyle (\mathsf (nCH_(2)(\text(=))CH_(2)\rightarrow ((\text(-))CH_ (2)(\text(-))CH_(2)(\text(-)))_(n)))) 2 C H 2 = C H 2 → C H 2 = C H - C H 2 - C H 3 (\displaystyle (\mathsf (2CH_(2)(\text(=))CH_(2)\rightarrow CH_(2)(\text(= ))CH(\text(-))CH_(2)(\text(-))CH_(3))))

Biological role

Among the most well-known functions of ethylene is the development of the so-called triple response in etiolated (grown in the dark) seedlings when treated with this hormone. The triple response includes three reactions: shortening and thickening of the hypocotyl, shortening of the root, and strengthening of the apical hook (sharp bending of the upper part of the hypocotyl). The response of seedlings to ethylene is extremely important in the first stages of their development, as it promotes the penetration of seedlings towards the light.

Commercial harvesting of fruits and fruits uses special rooms or chambers for fruit ripening, into the atmosphere of which ethylene is injected from special catalytic generators that produce ethylene gas from liquid ethanol. Typically, to stimulate fruit ripening, a concentration of ethylene gas in the chamber atmosphere of 500 to 2000 ppm is used for 24-48 hours. At higher air temperatures and higher concentrations of ethylene in the air, fruit ripening occurs faster. It is important, however, to ensure control of the carbon dioxide content in the atmosphere of the chamber, since high-temperature ripening (at temperatures above 20 degrees Celsius) or ripening with a high concentration of ethylene in the air of the chamber leads to a sharp increase in the release of carbon dioxide by quickly ripening fruits, sometimes up to 10%. carbon dioxide in the air 24 hours after the start of ripening, which can lead to carbon dioxide poisoning of both workers harvesting already ripened fruits and the fruits themselves.

Ethylene has been used to stimulate fruit ripening since ancient Egypt. The ancient Egyptians deliberately scratched or lightly crushed dates, figs and other fruits to stimulate their ripening (tissue damage stimulates the production of ethylene by plant tissues). The ancient Chinese burned wooden incense sticks or scented candles indoors to stimulate the ripening of peaches (when candles or wood burn, not only carbon dioxide is released, but also under-oxidized intermediate combustion products, including ethylene). In 1864, it was discovered that leaking natural gas from street lamps caused nearby plants to stunt their growth in length, twist them, abnormally thicken their stems and roots, and accelerate the ripening of fruits. In 1901, the Russian scientist Dmitry Nelyubov showed that the active component of natural gas that causes these changes is not its main component, methane, but ethylene present in small quantities. Later in 1917, Sarah Dubt proved that ethylene stimulates premature leaf drop. However, it was not until 1934 that Hein discovered that plants themselves synthesize endogenous ethylene. . In 1935, Crocker proposed that ethylene is a plant hormone responsible for the physiological regulation of fruit ripening, as well as senescence of plant vegetative tissues, leaf drop, and growth inhibition.

Young cycle

The ethylene biosynthesis cycle begins with the conversion of the amino acid methionine to S-adenosyl-methionine (SAMe) by the enzyme methionine adenosyltransferase. S-adenosyl-methionine is then converted to 1-aminocyclopropane-1-carboxylic acid (ACC, ACC) using the enzyme 1-aminocyclopropane-1-carboxylate synthetase (ACC synthetase). The activity of ACC synthetase limits the rate of the entire cycle, therefore the regulation of the activity of this enzyme is key in the regulation of ethylene biosynthesis in plants. The last stage of ethylene biosynthesis requires the presence of oxygen and occurs through the action of the enzyme aminocyclopropane carboxylate oxidase (ACC oxidase), formerly known as the ethylene-forming enzyme. Ethylene biosynthesis in plants is induced by both exogenous and endogenous ethylene (positive feedback). The activity of ACC synthetase and, accordingly, the formation of ethylene also increases at high levels of auxins, especially indoleacetic acid, and cytokinins.

The ethylene signal in plants is perceived by at least five different families of transmembrane receptors, which are protein dimers. In particular, the ethylene receptor ETR 1 is known in Arabidopsis ( Arabidopsis). Genes encoding receptors for ethylene have been cloned from Arabidopsis and then from tomato. Ethylene receptors are encoded by multiple genes in both the Arabidopsis and tomato genomes. Mutations in any of the gene family, which consists of five types of ethylene receptors in Arabidopsis and at least six types of receptors in tomato, can lead to plant insensitivity to ethylene and disturbances in plant maturation, growth and wilting. DNA sequences characteristic of ethylene receptor genes have also been found in many other plant species. Moreover, ethylene-binding protein has even been found in cyanobacteria.

Unfavorable external factors, such as insufficient oxygen in the atmosphere, flood, drought, frost, mechanical damage (wound) to the plant, attack by pathogenic microorganisms, fungi or insects, can cause increased formation of ethylene in plant tissues. For example, during flooding, plant roots suffer from excess water and lack of oxygen (hypoxia), which leads to the biosynthesis of 1-aminocyclopropane-1-carboxylic acid in them. ACC is then transported along pathways in the stems up to the leaves, and in the leaves it is oxidized to ethylene. The resulting ethylene promotes epinastic movements, leading to mechanical shaking of water from the leaves, as well as withering and falling of leaves, flower petals and fruits, which allows the plant to simultaneously get rid of excess water in the body and reduce the need for oxygen by reducing the total mass of tissues.

Small amounts of endogenous ethylene are also produced in animal cells, including humans, during lipid peroxidation. Some endogenous ethylene is then oxidized to ethylene oxide, which has the ability to alkylate DNA and proteins, including hemoglobin (forming a specific adduct with the N-terminal valine of hemoglobin - N-hydroxyethyl-valine). Endogenous ethylene oxide can also alkylate guanine bases of DNA, which leads to the formation of a 7-(2-hydroxyethyl)-guanine adduct, and is one of the reasons for the inherent risk of endogenous carcinogenesis in all living things. Endogenous ethylene oxide is also a mutagen. On the other hand, there is a hypothesis that if it were not for the formation of small amounts of endogenous ethylene and, accordingly, ethylene oxide in the body, the rate of spontaneous mutations and, accordingly, the rate of evolution would be much lower.

Notes

1. Devanny Michael T. Ethylene(English) (unavailable link). SRI Consulting (September 2009). Archived from the original on July 18, 2010.
2. Ethylene(English) (unavailable link). WP Report. SRI Consulting (January 2010). Archived from the original on August 31, 2010.
3. Gas chromatographic measurement of mass concentrations of hydrocarbons: methane, ethane, ethylene, propane, propylene, butane, alpha-butylene, isopentane in the air of the working area. Methodical instructions. MUK 4.1.1306-03 (Approved by the Chief State Sanitary Doctor of the Russian Federation on March 30, 2003)
4. “Growth and development of plants” V. V. Chub (undefined) (unavailable link). Retrieved January 21, 2007. Archived January 20, 2007.
5. "Delaying Christmas tree needle loss"
6. Khomchenko G.P. §16.6. Ethylene and its homologues// Chemistry for those entering universities. - 2nd ed. - M.: Higher School, 1993. - P. 345. - 447 p. - ISBN 5-06-002965-4.
7. V. Sh. Feldblum. Dimerization and disproportionation of olefins. M.: Chemistry, 1978
8. Lin, Z.; Zhong, S.; Grierson, D. (2009). “Recent advances in ethylene research.” J. Exp. Bot. 60 (12): 3311-36. DOI:10.1093/jxb/erp204. PMID.
9. Ethylene and Fruit Ripening / J Plant Growth Regul (2007) 26:143–159 doi:10.1007/s00344-007-9002-y (English)
10. Lutova L.A. Genetics of plant development / ed. S.G. Inge-Vechtomov. - 2nd ed. - St. Petersburg: N-L, 2010. - P. 432.
11. . ne-postharvest.com Archived September 14, 2010 on the Wayback Machine
12. Nelyubov D. N. (1901). “On horizontal nutation in Pisum sativum and some other plants.” Proceedings of the St. Petersburg Society of Natural History. 31 (1). , also Beihefte zum “Bot. Centralblatt", vol. X, 1901

Unsaturated hydrocarbons with a double chemical bond in their molecules belong to the group of alkenes. The first representative of the homologous series is ethene, or ethylene, the formula of which is: C 2 H 4. Alkenes are often called olefins. The name is historical and arose in the 18th century, after obtaining the product of the reaction of ethylene with chlorine - ethyl chloride, which looks like an oily liquid. Then ethene was called oil gas. In our article we will study its chemical properties, as well as its production and use in industry.

The relationship between the structure of the molecule and the properties of the substance

According to the theory of the structure of organic substances proposed by M. Butlerov, the characteristics of a compound completely depend on the structural formula and type of bonds of its molecule. The chemical properties of ethylene are also determined by the spatial configuration of atoms, the hybridization of electron clouds and the presence of a pi bond in its molecule. The two unhybridized p-electrons of the carbon atoms overlap in a plane perpendicular to the plane of the molecule itself. A double bond is formed, the rupture of which determines the ability of alkenes to undergo addition and polymerization reactions.

Physical properties

Ethene is a gaseous substance with a subtle, peculiar odor. It is poorly soluble in water, but soluble in benzene, carbon tetrachloride, gasoline and other organic solvents. Based on the formula of ethylene C 2 H 4, its molecular weight is 28, that is, ethene is slightly lighter than air. In the homologous series of alkenes, with an increase in their mass, the state of aggregation of substances changes according to the scheme: gas - liquid - solid compound.

Gas production in the laboratory and industry

By heating ethyl alcohol to 140 °C in the presence of concentrated sulfuric acid, ethylene can be obtained in the laboratory. Another method is the abstraction of hydrogen atoms from alkane molecules. By acting with caustic sodium or potassium on halogen-substituted compounds of saturated hydrocarbons, for example, chloroethane, ethylene is produced. In industry, the most promising way to obtain it is the processing of natural gas, as well as pyrolysis and cracking of oil. All chemical properties of ethylene - reactions of hydration, polymerization, addition, oxidation - are explained by the presence of a double bond in its molecule.

Interaction of olefins with elements of the main subgroup of the seventh group

All members of the homologous series of ethene attach halogen atoms at the site of pi-bond cleavage in their molecule. Thus, an aqueous solution of red-brown bromine becomes discolored, resulting in the formation of the equation ethylene - dibromoethane:

C 2 H 4 + Br 2 = C 2 H 4 Br 2

The reaction with chlorine and iodine proceeds similarly, in which the addition of halogen atoms also occurs at the site of destruction of the double bond. All olefin compounds can interact with hydrogen halides: hydrogen chloride, hydrogen fluoride, etc. As a result of the addition reaction, which proceeds according to the ionic mechanism, substances are formed - halogen derivatives of saturated hydrocarbons: chloroethane, fluoroethane.

Industrial ethanol production

The chemical properties of ethylene are often used to obtain important substances widely used in industry and everyday life. For example, heating ethene with water in the presence of orthophosphoric or sulfuric acids, under the influence of a catalyst, a hydration process occurs. It goes with the formation of ethyl alcohol - a large-scale product obtained at chemical plants of organic synthesis. The mechanism of the hydration reaction proceeds by analogy with other addition reactions. In addition, the interaction of ethylene with water also occurs as a result of the cleavage of the pi bond. The free valences of the carbon atoms of ethene are joined by hydrogen atoms and the hydroxo group that are part of the water molecule.

Hydrogenation and combustion of ethylene

Despite all of the above, the hydrogen compound reaction is not of great practical importance. However, it shows the genetic relationship between different classes of organic compounds, in this case alkanes and olefins. By adding hydrogen, ethene turns into ethane. The opposite process - the elimination of hydrogen atoms from saturated hydrocarbons leads to the formation of a representative of alkenes - ethene. The severe oxidation of olefins, called combustion, is accompanied by the release of a large amount of heat; the reaction is exothermic. Combustion products are the same for substances of all classes of hydrocarbons: alkanes, unsaturated compounds of the ethylene and acetylene series, aromatic substances. These include carbon dioxide and water. Air reacts with ethylene to form an explosive mixture.

Oxidation reactions

Ethene can be oxidized with a solution of potassium permanganate. This is one of the qualitative reactions with the help of which the presence of a double bond in the composition of the substance being determined is proven. The violet color of the solution disappears due to the cleavage of the double bond and the formation of a dihydric saturated alcohol - ethylene glycol. The reaction product has a wide range of industrial uses as a raw material for the production of synthetic fibers, such as lavsan, explosives and antifreeze. As you can see, the chemical properties of ethylene are used to obtain valuable compounds and materials.

Polymerization of olefins

Increasing temperature, increasing pressure and the use of catalysts are necessary conditions for the polymerization process. Its mechanism is different from addition or oxidation reactions. It represents the sequential binding of many ethylene molecules at the sites where double bonds are broken. The reaction product is polyethylene, the physical characteristics of which depend on the value of n - the degree of polymerization. If it is small, then the substance is in a liquid state of aggregation. If the indicator approaches 1000 links, then polyethylene film and flexible hoses are made from such a polymer. If the degree of polymerization exceeds 1500 links in the chain, then the material is a white solid, greasy to the touch.

It is used for the production of solid cast products and plastic pipes. A halogen derivative of ethylene, Teflon has non-stick properties and is a widely used polymer, in demand in the manufacture of multicookers, frying pans, and frying pans. Its high ability to resist abrasion is used in the production of lubricants for automobile engines, and its low toxicity and tolerance to the tissues of the human body have made it possible to use Teflon prostheses in surgery.

In our article, we examined such chemical properties of olefins as ethylene combustion, addition reactions, oxidation and polymerization.

Encyclopedic YouTube

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  Ethylene began to be widely used as a monomer before World War II due to the need to obtain a high-quality insulating material that could replace polyvinyl chloride. After developing a method for polymerizing ethylene under high pressure and studying the dielectric properties of the resulting polyethylene, its production began, first in the UK, and later in other countries.

  The main industrial method for producing ethylene is the pyrolysis of liquid petroleum distillates or lower saturated hydrocarbons. The reaction is carried out in tube furnaces at +800-950 °C and a pressure of 0.3 MPa. When straight-run gasoline is used as a raw material, the ethylene yield is approximately 30%. Simultaneously with ethylene, a significant amount of liquid hydrocarbons, including aromatic ones, are also formed. When pyrolyzing gas oil, the yield of ethylene is approximately 15-25%. The highest ethylene yield - up to 50% - is achieved when using saturated hydrocarbons as raw materials: ethane, propane and butane. Their pyrolysis is carried out in the presence of water vapor.

  When leaving production, during commodity accounting operations, when checking it for compliance with regulatory and technical documentation, ethylene samples are taken according to the procedure described in GOST 24975.0-89 “Ethylene and propylene. Sampling methods." Ethylene samples can be taken in both gaseous and liquefied forms using special samplers in accordance with GOST 14921.

  Ethylene produced industrially in Russia must meet the requirements set out in GOST 25070-2013 “Ethylene. Technical conditions".

  Production structure

  Currently, in the structure of ethylene production, 64% comes from large-scale pyrolysis units, ~17% from small-scale gas pyrolysis units, ~11% from gasoline pyrolysis and 8% from ethane pyrolysis.

  Application

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

  • 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);

  Ethylene mixed with oxygen was used in medicine for anesthesia until the mid-1980s in the USSR and the Middle East. Ethylene is a phytohormone in almost all plants; among other things, it is responsible for the fall of needles in conifers.

  Electronic and spatial structure of the molecule

  Carbon atoms are in the second valence state (sp 2 hybridization). As a result, three hybrid clouds are formed on a plane at an angle of 120°, which form three σ bonds with carbon and two hydrogen atoms; The p-electron, which did not participate in hybridization, forms a π-bond in the perpendicular plane with the p-electron of the neighboring carbon atom. This forms a double bond between carbon atoms. The molecule has a planar structure.

  CH 2 =CH 2

  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 + Br 2 → CH 2 Br-CH 2 Br 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. The result is ethylene glycol. Reaction equation: 3CH 2 =CH 2 + 2KMnO 4 + 4H 2 O → 3HOH 2 C - CH 2 OH + 2MnO 2 + 2KOH
  • Combustion:
  C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O
  • Polymerization (production of polyethylene):
  nCH 2 =CH 2 → (-CH 2 -CH 2 -) n
  • Dimerization (V. Sh. Feldblyum. Dimerization and disproportionation of olefins. M.: Khimiya, 1978)
  2CH 2 =CH 2 →CH 2 =CH-CH 2 -CH 3

  Biological role

  Ethylene is the first gaseous plant hormone discovered and has a very wide range of biological effects. Ethylene performs a variety of functions in the life cycle of plants, including control of seedling development, fruit ripening (in particular, fruits), bud opening (flowering process), aging and falling of leaves and flowers. Ethylene is also called a stress hormone, since it is involved in the response of plants to biotic and abiotic stress, and its synthesis in plant organs increases in response to various types of damage. In addition, being a volatile gaseous substance, ethylene carries out rapid communication between different plant organs and between plants in a population, which is important. in particular, with the development of stress resistance.

  Among the most well-known functions of ethylene is the development of the so-called triple response in etiolated (grown in the dark) seedlings when treated with this hormone. The triple response includes three reactions: shortening and thickening of the hypocotyl, shortening of the root, and strengthening of the apical hook (sharp bending of the upper part of the hypocotyl). The response of seedlings to ethylene is extremely important in the first stages of their development, as it promotes the penetration of seedlings towards the light.

  In commercial harvesting of fruits and vegetables, special rooms or chambers are used for ripening fruits, into the atmosphere of which ethylene is injected from special catalytic generators that produce ethylene gas from liquid ethanol. Typically, to stimulate fruit ripening, a concentration of ethylene gas in the chamber atmosphere of 500 to 2000 ppm is used for 24-48 hours. At higher air temperatures and higher concentrations of ethylene in the air, fruit ripening occurs faster. It is important, however, to ensure control of the carbon dioxide content in the atmosphere of the chamber, since high-temperature ripening (at temperatures above 20 degrees Celsius) or ripening with a high concentration of ethylene in the air of the chamber leads to a sharp increase in the release of carbon dioxide by quickly ripening fruits, sometimes up to 10%. carbon dioxide in the air 24 hours after the start of ripening, which can lead to carbon dioxide poisoning of both workers harvesting already ripened fruits and the fruits themselves.

  Ethylene has been used to stimulate fruit ripening since ancient Egypt. The ancient Egyptians deliberately scratched or lightly crushed dates, figs and other fruits to stimulate their ripening (tissue damage stimulates the production of ethylene by plant tissues). The ancient Chinese burned wooden incense sticks or scented candles indoors to stimulate the ripening of peaches (when candles or wood burn, not only carbon dioxide is released, but also under-oxidized intermediate combustion products, including ethylene). In 1864, it was discovered that leaking natural gas from street lamps caused nearby plants to stunt their growth in length, twist them, abnormally thicken their stems and roots, and accelerate the ripening of fruits. In 1901, Russian scientist Dmitry Nelyubov showed that the active component of natural gas that causes these changes is not its main component, methane, but ethylene present in small quantities. Later in 1917, Sarah Dubt proved that ethylene stimulates premature leaf loss. However, it was not until 1934 that Hein discovered that plants themselves synthesize endogenous ethylene. In 1935, Crocker proposed that ethylene is a plant hormone responsible for the physiological regulation of fruit ripening, as well as aging of plant vegetative tissues, leaf drop and growth inhibition.

  The ethylene biosynthesis cycle begins with the conversion of the amino acid methionine to S-adenosyl-methionine (SAMe) by the enzyme methionine adenosyltransferase. S-adenosyl-methionine is then converted to 1-aminocyclopropane-1-carboxylic acid (ACC, ACC) using the enzyme 1-aminocyclopropane-1-carboxylate synthetase (ACC synthetase). The activity of ACC synthetase limits the rate of the entire cycle, therefore the regulation of the activity of this enzyme is key in the regulation of ethylene biosynthesis in plants. The last stage of ethylene biosynthesis requires the presence of oxygen and occurs through the action of the enzyme aminocyclopropane carboxylate oxidase (ACC oxidase), formerly known as the ethylene-forming enzyme. Ethylene biosynthesis in plants is induced by both exogenous and endogenous ethylene (positive feedback). The activity of ACC synthetase and, accordingly, the formation of ethylene also increases at high levels of auxins, especially indoleacetic acid, and cytokinins.

  The ethylene signal in plants is perceived by at least five different families of transmembrane receptors, which are protein dimers. In particular, the ethylene receptor ETR 1 is known in Arabidopsis ( Arabidopsis). Genes encoding receptors for ethylene were cloned from Arabidopsis and then from tomato. Ethylene receptors are encoded by multiple genes in both the Arabidopsis and tomato genomes. Mutations in any of the gene family, which consists of five types of ethylene receptors in Arabidopsis and at least six types of receptors in tomato, can lead to plant insensitivity to ethylene and disturbances in the processes of maturation, growth and wilting. DNA sequences characteristic of ethylene receptor genes have also been found in many other plant species. Moreover, ethylene-binding protein has even been found in cyanobacteria.

  Unfavorable external factors, such as insufficient oxygen in the atmosphere, flood, drought, frost, mechanical damage (wound) to the plant, attack by pathogenic microorganisms, fungi or insects, can cause increased formation of ethylene in plant tissues. For example, during flooding, plant roots suffer from excess water and lack of oxygen (hypoxia), which leads to the biosynthesis of 1-aminocyclopropane-1-carboxylic acid in them. ACC is then transported along pathways in the stems up to the leaves, and in the leaves it is oxidized to ethylene. The resulting ethylene promotes epinastic movements, leading to mechanical shaking of water from the leaves, as well as withering and falling of leaves, flower petals and fruits, which allows the plant to simultaneously get rid of excess water in the body and reduce the need for oxygen by reducing the total mass of tissues.

  Small amounts of endogenous ethylene are also produced in animal cells, including humans, during lipid peroxidation. Some endogenous ethylene is then oxidized to ethylene oxide, which has the ability to alkylate DNA and proteins, including hemoglobin (forming a specific adduct with the N-terminal valine of hemoglobin - N-hydroxyethyl-valine). Endogenous ethylene oxide can also alkylate guanine bases of DNA, which leads to the formation of a 7-(2-hydroxyethyl)-guanine adduct, and is one of the reasons for the inherent risk of endogenous carcinogenesis in all living beings. Endogenous ethylene oxide is also a mutagen. On the other hand, there is a hypothesis that if it were not for the formation of small amounts of endogenous ethylene and, accordingly, ethylene oxide in the body, the rate of spontaneous mutations and, accordingly, the rate of evolution would be much lower.

  Notes

  1. Devanny Michael T. Ethylene(English) . SRI Consulting (September 2009). Archived from the original on August 21, 2011.
  2. Ethylene(English) . WP Report. SRI Consulting (January 2010). Archived from the original on August 21, 2011.
  3. Gas chromatographic measurement of mass concentrations of hydrocarbons: methane, ethane, ethylene, propane, propylene, butane, alpha-butylene, isopentane in the air of the working area. Methodical instructions. MUK 4.1.1306-03 (Approved by the Chief State Sanitary Doctor of the RF 03/30/2003)
  4. “Growth and development of plants” V.V. Chub
  5. "Delaying Christmas tree needle loss"
  6. Khomchenko G.P. §16.6. Ethylene and its homologues// Chemistry for those entering universities. - 2nd ed. - M.: Higher School, 1993. - P. 345. - 447 p. - ISBN 5-06-002965-4.
  7. Lin, Z.; Zhong, S.; Grierson, D. (2009). “Recent advances in ethylene research.” J. Exp. Bot. 60 (12): 3311-36. DOI:10.1093/jxb/erp204. PMID.
  8. Ethylene and Fruit Ripening / J Plant Growth Regul (2007) 26:143–159 doi:10.1007/s00344-007-9002-y (English)
  9. Lutova L.A. Genetics of plant development / ed. S.G. Inge-Vechtomov. - 2nd ed. - St. Petersburg: N-L, 2010. - P. 432.
  10. . ne-postharvest.com (unavailable link since 06-06-2015)
  11. Nelyubov D. N. (1901). “On horizontal nutation in Pisum sativum and some other plants.” Proceedings of the St. Petersburg Society of Natural History. 31 (1). , also Beihefte zum “Bot. Centralblatt", vol. X, 1901