Unsaturated hydrocarbons with double chemical bond in molecules belong to the group of alkenes. First Representative homologous series is ethene, or ethylene, whose formula is: C 2 H 4 . Alkenes are often referred to as olefins. The name is historical and originated in the 18th century, after obtaining the product of the interaction of ethylene with chlorine - ethyl chloride, which looks like an oily liquid. Then ethene was called oil-producing gas. In our article, we will study its chemical properties, as well as its production and application 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 characteristic of a compound depends entirely on the structural formula and the type of bonds of its molecule. Chemical properties ethylene is also determined by the spatial configuration of atoms, the hybridization of electron clouds, and the presence of a pi bond in its molecule. Two unhybridized p-electrons of 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 smell. It is poorly soluble in water, but readily soluble in benzene, carbon tetrachloride, gasoline and other organic solvents. Based on the formula of ethylene C 2 H 4, its molecular mass equal to 28, that is, ethene is slightly lighter than air. In the homologous series of alkenes, with an increase in their mass, the aggregate state of substances changes according to the scheme: gas - liquid - solid compound.
Gas production in laboratory and industry
By heating ethyl alcohol to 140 ° C in the presence of concentrated sulfuric acid, ethylene can be obtained in laboratory conditions. Another way is the splitting off of hydrogen atoms from alkane molecules. Acting with caustic sodium or potassium on halogen-substituted compounds saturated hydrocarbons, for example, on chloroethane, ethylene is produced. In industry, the most promising way to obtain it is the processing of natural gas, as well as the 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 ethene homologous series attach halogen atoms at the site of the pi-bond break in their molecule. So, water solution red-brown bromine is decolorized, resulting in the formation of the equation ethylene - dibromoethane:
C 2 H 4 + Br 2 \u003d 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 the destruction of the double bond. All compounds - olefins can interact with hydrogen halides: hydrogen chloride, hydrogen fluoride, etc. As a result of the addition reaction proceeding according to the ionic mechanism, substances are formed - halogen derivatives of saturated hydrocarbons: chloroethane, fluoroethane.
Industrial production of ethanol
The chemical properties of ethylene are often used to obtain important substances widely used in industry and everyday life. For example, by heating ethene with water in the presence of phosphoric or sulfuric acids, a hydration process occurs under the action of a catalyst. It comes with education ethyl alcohol- a large-tonnage product obtained at chemical enterprises 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 breaking the pi bond. Hydrogen atoms and a hydroxo group, which are part of the water molecule, are added to the free valences of the carbon atoms of ethene.
Hydrogenation and combustion of ethylene
Despite all of the above, the hydrogen compound reaction is of little practical importance. However, it shows the genetic relationship between different classes of organic compounds, in this case alkanes and olefins. By adding hydrogen, ethene is converted to ethane. The opposite process - the splitting off 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 number 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 potassium permanganate solution. This is one of the qualitative reactions, with the help of which they prove the presence of a double bond in the composition of the analyte. The violet color of the solution disappears due to the rupture of the double bond and the formation of a dihydric saturated alcohol - ethylene glycol. The reaction product has a wide range of applications in industry 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.
Olefin polymerization
An increase in temperature, an increase in pressure and the use of catalysts are necessary conditions for carrying out the polymerization process. Its mechanism is different from addition or oxidation reactions. It represents the sequential binding of many ethylene molecules at the sites of double bond breakage. 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 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 solid white color oily to the touch.
It goes to the manufacture of solid products and plastic pipes. Teflon, a halogenated compound of ethylene, has non-stick properties and is a widely used polymer that is in demand in the manufacture of multicookers, frying pans, and braziers. Its high ability to resist abrasion is used in the production of lubricants for automobile engines, and its low toxicity and tolerance to human tissues have made it possible to use Teflon prostheses in surgery.
In our article, we considered such chemical properties of olefins as ethylene combustion, addition reactions, oxidation and polymerization.
Contains a double bond and therefore refers to unsaturated or unsaturated hydrocarbons. It plays an extremely important role in industry and is also a phytohormone. Ethylene is the most produced organic compound in the world ; the total world production of ethylene in 2008 amounted to 113 million tons and continues to grow by 2-3% per year. Ethylene has a narcotic effect. Hazard class - fourth.
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 the development of a method for the polymerization of ethylene under high pressure and the study of 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, is also formed. During the pyrolysis of gas oil, the yield of ethylene is approximately 15-25%. The highest yield of ethylene - up to 50% - is achieved when saturated hydrocarbons are used as raw materials: ethane, propane and butane. Their pyrolysis is carried out in the presence of steam.
When released from 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 sampling can be carried out both in gaseous and liquefied form in special samplers in accordance with GOST 14921.
Ethylene produced industrially in Russia must comply with the requirements set forth in GOST 25070-2013 “Ethylene. Specifications".
Production structure
Currently, in the structure of ethylene production, 64% falls on large-tonnage pyrolysis plants, ~17% - on small-tonnage gas pyrolysis plants, ~11% is gasoline pyrolysis, and 8% falls on 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 the plane at an angle of 120°, which form three σ-bonds with carbon and two hydrogen atoms; p-electron, which did not participate in hybridization, forms a π-bond with the p-electron of the neighboring carbon atom in the perpendicular plane. 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, less strong, is easily broken, and at the place of the bond breaking, the molecules are joined, oxidized, and polymerized.
- Halogenation:
- Hydrogenation:
- Hydrohalogenation:
- Hydration:
- Oxidation:
- Combustion:
- Polymerization (obtaining polyethylene):
Biological role
Among the best known functions of ethylene is the development of the so-called triple response in etiolated (grown in the dark) seedlings upon treatment 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 (a sharp bend in the upper part of the hypocotyl). The response of seedlings to ethylene is extremely important at the first stages of their development, as it contributes to the penetration of seedlings towards the light.
Commercial fruit and fruit picking uses special rooms or chambers for fruit ripening, into which ethylene is injected from special catalytic generators that produce gaseous ethylene from liquid ethanol. Usually, to stimulate fruit ripening, the concentration of gaseous ethylene in the atmosphere of the chamber is from 500 to 2000 ppm for 24-48 hours. At a higher air temperature and a higher concentration of ethylene in the air, fruit ripening is faster. It is important, however, to maintain control over the content carbon dioxide in the atmosphere of the chamber, since high-temperature ripening (at temperatures above 20 degrees Celsius) or ripening at a high concentration of ethylene in the air of the chamber leads to a sharp increase in the release of carbon dioxide by rapidly ripening fruits, sometimes up to 10% carbon dioxide in the air after 24 hours from the start of ripening, which can lead to carbon dioxide poisoning of both workers who harvest already ripened fruits, and the fruits themselves.
Ethylene has been used to stimulate fruit ripening since Ancient Egypt. The ancient Egyptians intentionally scratched or slightly crushed, beat off dates, figs and other fruits in order to stimulate their ripening (tissue damage stimulates the formation of ethylene by plant tissues). The ancient Chinese burned wooden incense sticks or scented candles indoors to stimulate the ripening of peaches (when burning candles or wood, not only carbon dioxide is released, but also incompletely oxidized intermediate combustion products, including ethylene). In 1864, it was discovered that natural gas leaking from street lamps caused growth inhibition in the length of nearby plants, their twisting, abnormal thickening of stems and roots, and accelerated fruit ripening. 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 the ethylene present in it in small quantities. Later in 1917, Sarah Dubt proved that ethylene stimulated premature leaf drop. However, it was not until 1934 that Gein 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 the plant's vegetative tissues, leaf fall, and growth inhibition.
The ethylene biosynthetic cycle begins with the conversion of the amino acid methionine to S-adenosyl methionine (SAMe) by the enzyme methionine adenosyl transferase. Then S-adenosyl-methionine is converted to 1-aminocyclopropane-1-carboxylic acid (ACA, 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 step in ethylene biosynthesis requires 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 is also increased 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. Known, in particular, the ethylene receptor ETR 1 in Arabidopsis ( Arabidopsis). The genes encoding ethylene receptors have been cloned in Arabidopsis and then in tomato. Ethylene receptors are encoded by multiple genes in both 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 disruption of 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 content in the atmosphere, flood, drought, frost, mechanical damage (injury) to the plant, attack by pathogenic microorganisms, fungi or insects, can cause advanced education ethylene in plant tissues. So, for example, during a flood, the roots of a plant suffer from an excess of water and a 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 oxidized to ethylene in the leaves. The resulting ethylene promotes epinastic movements, leading to mechanical shaking of water from the leaves, as well as wilting 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 formed 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 the guanine bases of DNA, which leads to the formation of the 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, then the rate of spontaneous mutations and, accordingly, the rate of evolution would be much lower.
Notes
- DevanneyMichael T. Ethylene(English) (unavailable link). SRI Consulting (September 2009). Archived from the original on July 18, 2010.
- Ethylene(English) (unavailable link). WP Report. SRI Consulting (January 2010). Archived from the original on August 31, 2010.
- 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)
- "Growth and development of plants" V. V. Chub (indefinite) (unavailable link). Retrieved January 21, 2007. Archived from the original on January 20, 2007.
- "Delaying Christmas Tree Needle Loss"
- Khomchenko G.P. §16.6. Ethylene and its homologues// Chemistry for applicants to universities. - 2nd ed. - M.: Higher School, 1993. - S. 345. - 447 p. - ISBN 5-06-002965-4.
- V. Sh. Feldblum. Dimerization and disproportionation of olefins. Moscow: Chemistry, 1978
- 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.
- Ethylene and Fruit Ripening / J Plant Growth Regul (2007) 26:143-159 doi:10.1007/s00344-007-9002-y
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Ethylene began to be widely used as a monomer before the Second World War due to the need to obtain a high-quality insulating material that could replace polyvinyl chloride. After the development of a method for the polymerization of ethylene under high pressure and the study of 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, is also formed. During the pyrolysis of gas oil, the yield of ethylene is approximately 15-25%. The highest yield of ethylene - up to 50% - is achieved when saturated hydrocarbons are used as raw materials: ethane, propane and butane. Their pyrolysis is carried out in the presence of steam.
When released from 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 sampling can be carried out both in gaseous and liquefied form in special samplers in accordance with GOST 14921.
Ethylene produced industrially in Russia must comply with the requirements set forth in GOST 25070-2013 “Ethylene. Specifications".
Production structure
Currently, in the structure of ethylene production, 64% falls on large-tonnage pyrolysis plants, ~17% - on small-tonnage gas pyrolysis plants, ~11% is gasoline pyrolysis, and 8% falls on ethane pyrolysis.
Application
Ethylene is the leading product of the main 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 the plane at an angle of 120°, which form three σ-bonds with carbon and two hydrogen atoms; p-electron, which did not participate in hybridization, forms a π-bond with the p-electron of the neighboring carbon atom in the perpendicular plane. This forms a double bond between carbon atoms. The molecule has a planar structure.
CH 2 \u003d 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, less strong, is easily broken, and at the place of the bond breaking, the molecules are joined, oxidized, and polymerized.
- Halogenation:
- Hydrogenation:
- Hydrohalogenation:
- Hydration:
- Oxidation:
- Combustion:
- Polymerization (obtaining polyethylene):
- Dimerization (V. Sh. Feldblum. Dimerization and disproportionation of olefins. M.: Chemistry, 1978)
Biological role
Ethylene is the first gaseous plant hormone discovered, with a very wide range of biological effects. Ethylene performs a variety of functions in the life cycle of plants, including control of seedling development, ripening of fruits (in particular, fruits), blooming of buds (flowering process), aging and falling of leaves and flowers. Ethylene is also called the stress hormone, since it is involved in the response of plants to biotic and abiotic stress, and its synthesis in plant organs is enhanced in response to various types of damage. In addition, being a volatile gaseous substance, ethylene provides 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 best known functions of ethylene is the development of the so-called triple response in etiolated (grown in the dark) seedlings upon treatment 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 (a sharp bend in the upper part of the hypocotyl). The response of seedlings to ethylene is extremely important at the first stages of their development, as it facilitates the penetration of seedlings towards the light.
In the commercial harvesting of fruits and fruits, special rooms or chambers are used for ripening fruits, into the atmosphere of which ethylene is injected from special catalytic generators that produce gaseous ethylene from liquid ethanol. Usually, to stimulate fruit ripening, the concentration of gaseous ethylene in the atmosphere of the chamber is from 500 to 2000 ppm for 24-48 hours. At a higher air temperature and a higher concentration of ethylene in the air, fruit ripening is faster. It is important, however, to ensure control of the carbon dioxide content in the chamber atmosphere, since high-temperature ripening (at temperatures above 20 degrees Celsius) or ripening at a high concentration of ethylene in the chamber air leads to a sharp increase in carbon dioxide emissions from rapidly ripening fruits, sometimes up to 10%. carbon dioxide in the air after 24 hours from the start of ripening, which can lead to carbon dioxide poisoning of both workers who harvest already ripened fruits, and the fruits themselves.
Ethylene has been used to stimulate fruit ripening since ancient Egypt. The ancient Egyptians intentionally scratched or slightly crushed, beat off dates, figs and other fruits in order to stimulate their ripening (tissue damage stimulates the formation of ethylene by plant tissues). The ancient Chinese burned wooden incense sticks or scented candles indoors to stimulate the ripening of peaches (when burning candles or wood, not only carbon dioxide is released, but also incompletely oxidized intermediate combustion products, including ethylene). In 1864, it was discovered that natural gas leaking from street lamps caused growth inhibition in the length of nearby plants, their twisting, abnormal thickening of stems and roots, and accelerated fruit ripening. 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 the ethylene present in it in small quantities. Later in 1917, Sarah Dubt proved that ethylene stimulates premature leaf fall. However, it was not until 1934 that Gein discovered that plants themselves synthesize endogenous ethylene. In 1935, Crocker suggested that ethylene is a plant hormone responsible for the physiological regulation of fruit ripening, as well as for the aging of plant vegetative tissues, leaf drop, and growth inhibition.
The ethylene biosynthetic cycle begins with the conversion of the amino acid methionine to S-adenosyl methionine (SAMe) by the enzyme methionine adenosyl transferase. Then S-adenosyl-methionine is converted to 1-aminocyclopropane-1-carboxylic acid (ACA, 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 step in ethylene biosynthesis requires 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 is also increased 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. Known, in particular, the ethylene receptor ETR 1 in Arabidopsis ( Arabidopsis). The genes encoding ethylene receptors have been cloned in Arabidopsis and then in tomato. Ethylene receptors are encoded by multiple genes in both 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 disruption of 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 content in the atmosphere, flood, drought, frost, mechanical damage (injury) of the plant, attack by pathogenic microorganisms, fungi or insects, can cause increased production of ethylene in plant tissues. So, for example, during a flood, the roots of a plant suffer from an excess of water and a 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 oxidized to ethylene in the leaves. The resulting ethylene promotes epinastic movements, leading to mechanical shaking of water from the leaves, as well as wilting and falling of leaves, petals of flowers 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 formed 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 hemoglobin's N-terminal valine, N-hydroxyethyl-valine). Endogenous ethylene oxide can also alkylate the guanine bases of DNA, which leads to the formation of the 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, then the rate of spontaneous mutations and, accordingly, the rate of evolution would be much lower.
Notes
- DevanneyMichael T. Ethylene(English) . SRI Consulting (September 2009). Archived from the original on August 21, 2011.
- Ethylene(English) . WP Report. SRI Consulting (January 2010). Archived from the original on August 21, 2011.
- Gas chromatographic measurement of mass concentrations of hydrocarbons: methane, ethane, ethylene, propane, propylene, butane, alpha-butylene, isopentane in the air of the working area. Methodological instructions. MUK 4.1.1306-03 (Approved by the chief state sanitary doctor of the Russian Federation on March 30, 2003)
- "Growth and development of plants" V. V. Chub
- "Delaying Christmas tree needle loss"
- Khomchenko G.P. §16.6. Ethylene and its homologues// Chemistry for applicants to universities. - 2nd ed. - M.: Higher school, 1993. - S. 345. - 447 p. - ISBN 5-06-002965-4.
- 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.
- Ethylene and Fruit Ripening / J Plant Growth Regul (2007) 26:143-159 doi:10.1007/s00344-007-9002-y
- Lutova L.A. Genetics of plant development / ed. S.G. Inge-Vechtomov. - 2nd ed. - St. Petersburg: N-L, 2010. - S. 432.
- . ne-postharvest.com (unavailable link since 06-06-2015 )
- Nelyubov D. N. (1901). "On horizontal nutation in Pisum sativum and some other plants". Proceedings of the St. Petersburg Society of Natural History. 31 (one). , also Beihefte zum "Bot. Centralblatt, vol. X, 1901
The history of the discovery of ethylene
Ethylene was first obtained by the German chemist Johann Becher in 1680 by the action of vitriol oil (H 2 SO 4) on wine (ethyl) alcohol (C 2 H 5 OH).
CH 3 -CH 2 -OH + H 2 SO 4 → CH 2 \u003d CH 2 + H 2 O
Initially, it was identified with "combustible air", i.e., with hydrogen. Later, in 1795, the Dutch chemists Deiman, Pots-van-Trusvik, Bond and Lauerenburg similarly obtained ethylene and described it under the name "oxygen gas", as they discovered the ability of ethylene to attach chlorine to form an oily liquid - ethylene chloride ("oil of Dutch chemists"), (Prokhorov, 1978).
The study of the properties of ethylene, its derivatives and homologues began in the middle of the 19th century. The beginning of the practical use of these compounds was laid by the classical studies of A.M. Butlerov and his students in the field of unsaturated compounds and especially the creation of Butlerov's theory chemical structure. In 1860, he obtained 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 seedlings, in which the top was bent with a hook and did not bend. In the greenhouse and in the open air, the seedlings were even, tall, and the top in the light quickly straightened the hook. Nelyubov suggested that the factor causing the physiological effect is in the laboratory air.
At that time, the premises were lit with gas. The same gas burned in street lamps, and it has long been noticed that in the event of an accident in a gas pipeline, trees standing near the site of a gas leak turn yellow prematurely and shed their leaves.
The lighting gas contained a variety of organic matter. To remove the admixture of gas, Nelyubov passed it through a heated tube with copper oxide. Pea seedlings developed normally in "purified" air. In order to find out exactly which substance causes the response of seedlings, Nelyubov added various components of the lighting gas in turn, and found that the addition of ethylene causes:
1) slow growth in length and thickening of the seedling,
2) "non-bending" apical loop,
3) Changing the orientation of the seedling in space.
This physiological reaction of seedlings has been called the triple response to ethylene. Peas were so sensitive to ethylene that they began to use them in bioassays to detect 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 capable of synthesizing ethylene; ethylene is a phytohormone (Petushkova, 1986).
Physical Properties ethylene
Ethylene- 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), and its inhalation has a narcotic effect on humans. Ethylene is soluble in ether and acetone, much less in water and alcohol. Forms an explosive mixture when mixed with air
Solidifies at -169.5°C, 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 a weak soot. The rounded molar mass of the substance is 28 g/mol. The third and fourth representatives of the ethene homologous series are also gaseous substances. The physical properties of the fifth and following alkenes are different, they are liquids and solids.
Ethylene production
The main methods for producing ethylene:
Dehydrohalogenation of halogen derivatives of alkanes under the action 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 action of active metals
Cl-CH 2 -CH 2 -Cl + Zn → ZnCl 2 + CH 2 = CH 2;
Ethylene dehydration when it is heated with sulfuric acid (t>150˚ C) or when its vapor is passed over a catalyst
CH 3 -CH 2 -OH → CH 2 = CH 2 + H 2 O;
Dehydrogenation of ethane on heating (500C) in the presence of a catalyst (Ni, Pt, Pd)
CH 3 -CH 3 → CH 2 \u003d CH 2 + H 2.
Chemical properties of ethylene
Ethylene is characterized by reactions proceeding by the mechanism of electrophilic, addition, radical substitution reactions, oxidation, reduction, and polymerization.
1. Halogenation(electrophilic addition) - the interaction of ethylene with halogens, for example, with bromine, in which bromine water becomes decolorized:
CH 2 \u003d CH 2 + Br 2 \u003d Br-CH 2 -CH 2 Br.
Ethylene halogenation 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 \u003d CH 2 + Cl 2 → CH 2 \u003d CH-Cl + HCl.
2. Hydrohalogenation- interaction of ethylene with hydrogen halides (HCl, HBr) with the formation of halogenated alkanes:
CH 2 \u003d CH 2 + HCl → CH 3 -CH 2 -Cl.
3. Hydration- interaction of ethylene with water in the presence of mineral acids (sulphuric, phosphoric) with the formation of saturated monohydric alcohol - ethanol:
CH 2 \u003d CH 2 + H 2 O → CH 3 -CH 2 -OH.
Among the reactions of electrophilic addition, addition is distinguished hypochlorous acid(1), reactions hydroxy- And alkoxymercuration(2, 3) (obtaining organomercury compounds) and hydroboration (4):
CH 2 \u003d CH 2 + HClO → CH 2 (OH) -CH 2 -Cl (1);
CH 2 \u003d 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 \u003d CH 2 + BH 3 → CH 3 -CH 2 -BH 2 (4).
Nucleophilic addition reactions are characteristic of ethylene derivatives containing electron-withdrawing substituents. Among the nucleophilic addition reactions, a special place is occupied by the addition reactions of hydrocyanic acid, ammonia, and ethanol. For example,
2 ON-CH \u003d CH 2 + HCN → 2 ON-CH 2 -CH 2 -CN.
4. oxidation. Ethylene is easily oxidized. If ethylene is passed through a solution of potassium permanganate, it will become colorless. This reaction is used to distinguish between saturated and unsaturated compounds. The result is ethylene glycol.
3CH 2 \u003d CH 2 + 2KMnO 4 + 4H 2 O \u003d 3CH 2 (OH) -CH 2 (OH) + 2MnO 2 + 2KOH.
At hard oxidation ethylene with a boiling solution of potassium permanganate in an acidic medium, a complete cleavage 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 \u003d CH 2 + 1 / 2O 2 \u003d CH 3 -CH \u003d O.
5. hydrogenation. At recovery ethylene is the formation of 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 proceed is the presence of catalysts (Ni, Pd, Pt), as well as heating the reaction mixture:
CH 2 \u003d CH 2 + H 2 \u003d CH 3 -CH 3.
6. Ethylene enters into polymerization reaction. Polymerization - the process of formation of a high molecular weight compound - a polymer - by combining with each other using the main valences of the molecules of the original low molecular weight substance - a monomer. Ethylene polymerization occurs under the action of acids (cationic mechanism) or radicals (radical mechanism):
n CH 2 \u003d CH 2 \u003d - (-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 \u003d CH 2 → CH 2 \u003d 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 repeated combinations of many small ethylene molecules into larger ones. This process takes place at high pressures and temperatures. The applications for ethylene are numerous. Polyethylene is a polymer that is used especially in large quantities in the production of packaging films, wire coatings 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 ( industrial alcohol), ethylene oxide ( antifreeze, polyester fibers and films), acetaldehyde and vinyl chloride. In addition to these compounds, ethylene with benzene forms 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 (containing carbon and hydrogen) materials. Single ethylene molecules can be joined together to make polyethylene (which means many ethylene molecules). Polyethylene is used to make plastics. Moreover, it can be used to make detergents and synthetic lubricants, which represent chemical substances used to reduce friction. The use of ethylene to obtain styrenes is relevant in the process of creating rubber and protective packaging. In addition, it is used in the shoe 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 on a global scale.
Ethylene is used in glass production special purpose for the automotive industry.
Characteristics and physical properties of ethene
DEFINITION
Ethene (ethylene)- a colorless combustible gas (the structure of the molecule is shown in Fig. 1), which has a slight odor. Slightly soluble in water.
Ethene (ethylene) is a colorless combustible gas (the structure of the molecule is shown in Fig. 1), which has a slight odor. Slightly soluble in water. It dissolves well in diethyl ether and hydrocarbons.
Rice. 1. The structure of the ethylene molecule.
Table 1. Physical properties of ethene.
Getting ethene
In industrial volumes, ethene is obtained during oil refining: by cracking and dehydrogenation of ethane. Laboratory methods for producing ethylene are presented
– ethanol dehydration
CH 3 -CH 2 -OH → CH 2 \u003d CH 2 + H 2 O (H 2 SO 4 (conc), t o \u003d 170).
— dehydrohalogenation of monohaloethane
CH 3 -CH 2 -Br + NaOH alcohol →CH 2 \u003d CH 2 + NaBr + H 2 O (t o).
— dehalogenation of dihaloethane
Cl-CH 2 -CH 2 -Cl + Zn(Mg) →CH 2 =CH 2 + ZnCl 2 (MgCl 2);
- incomplete hydrogenation of acetylene
CH≡CH + H 2 →CH 2 \u003d CH 2 (Pd, t o).
Chemical properties of ethene
Ethene is a highly reactive compound. All chemical transformations of ethylene proceed with splitting:
- p-bonds С-С (addition, polymerization and oxidation)
- hydrogenation
CH 2 \u003d CH 2 + H 2 → CH 3 -CH 3 (kat \u003d Pt).
- halogenation
CH 2 \u003d CH 2 + Br 2 → BrCH-CHBr.
- hydrohalogenation
CH 2 \u003d CH 2 + H-Cl → H 2 C-CHCl.
- hydration
CH 2 \u003d CH 2 + H-OH → CH 3 -CH 2 -OH (H +, t o).
- polymerization
nCH 2 \u003d CH 2 → -[-CH 2 -CH 2 -] - n (kat, t o).
- oxidation
CH 2 \u003d CH 2 + 2KMnO 4 + 2KOH → HO-CH 2 -CH 2 -OH + 2K 2 MnO 4;
2CH 2 \u003d CH 2 + O 2 → 2C 2 OH 4 (epoxide) (kat \u003d Ag,t o);
2CH 2 \u003d CH 2 + O 2 → 2CH 3 -C (O) H (kat \u003d PdCl 2, CuCl).
- bonds With sp 3 -H (in the allyl position)
CH 2 \u003d CH 2 + Cl 2 → CH 2 \u003d CH-Cl + HCl (t o \u003d 400).
- Breaking all ties
C 2 H 4 + 2O 2 → 2CO 2 + 2H 2 O.
Application of ethene
The main use of ethylene is industrial organic synthesis such compounds as halogen derivatives, alcohols (ethanol, ethylene glycol), acetaldehyde, acetic acid, etc. In addition, this compound is used in the production of polymers.
Examples of problem solving
EXAMPLE 1
The task As a result of the addition of iodine to ethylene, 98.7 g of the iodo derivative were obtained. Calculate the mass and amount of the ethylene substance taken for the reaction. Solution We write the reaction equation for the addition of iodine to ethylene: H 2 C \u003d CH 2 + I 2 → IH 2 C - CH 2 I.
As a result of the reaction, an iodo derivative, diiodoethane, was formed. Calculate its amount of substance (molar mass is - 282 g / mol):
n(C 2 H 4 I 2) \u003d m (C 2 H 4 I 2) / M (C 2 H 4 I 2);
n (C 2 H 4 I 2) \u003d 98.7 / 282 \u003d 0.35 mol.
According to the reaction equation n(C 2 H 4 I 2): n(C 2 H 4) = 1:1, i.e. n (C 2 H 4 I 2) \u003d n (C 2 H 4) \u003d 0.35 mol. Then the mass of ethylene will be equal to (molar mass - 28 g / mol):
m(C 2 H 4) = n (C 2 H 4) ×M (C 2 H 4);
m(C 2 H 4) \u003d 0.35 × 28 \u003d 9.8 g.
Answer The mass of ethylene is 9.8 g, the amount of ethylene substance is 0.35 mol. EXAMPLE 2
The task Calculate the volume of ethylene, reduced to normal conditions, that can be obtained from technical ethyl alcohol C 2 H 5 OH weighing 300 g. Note that technical alcohol contains impurities, the mass fraction of which is 8%. Solution We write the reaction equation for the production of ethylene from ethyl alcohol: C 2 H 5 OH (H 2 SO 4) → C 2 H 4 + H 2 O.
Find the mass of pure (without impurities) ethyl alcohol. To do this, we first calculate mass fraction:
ω pure (C 2 H 5 OH) \u003d ω impure (C 2 H 5 OH) - ω impurity;
ω pure (C 2 H 5 OH) = 100% - 8% = 92%.
m pure (C 2 H 5 OH) \u003d m impure (C 2 H 5 OH) ×ω pure (C 2 H 5 OH) / 100%;
m pure (C 2 H 5 OH) = 300 × 92 / 100% = 276 g.
Let's determine the amount of ethyl alcohol substance (molar mass - 46 g / mol):
n(C 2 H 5 OH) \u003d m (C 2 H 5 OH) / M (C 2 H 5 OH);
n(C 2 H 5 OH) = 276/46 = 3.83 mol.
According to the reaction equation n(C 2 H 5 OH): n(C 2 H 4) = 1:1, i.e. n (C 2 H 5 OH) \u003d n (C 2 H 4) \u003d 3.83 mol. Then the volume of ethylene will be equal to:
V(C 2 H 4) = n(C 2 H 4) × V m ;
V (C 2 H 4) \u003d 3.83 × 22.4 \u003d 85.792 liters.
Answer The volume of ethylene is 85.792 liters.
