Practical application of ethylene. The use of ethylene and acetylene gases for fruit ripening
Physical Properties
Ethan at n. y.- colorless gas, odorless. Molar mass - 30.07. Melting point -182.81 °C, boiling point -88.63 °C. . Density ρ gas. \u003d 0.001342 g / cm³ or 1.342 kg / m³ (n.a.), ρ fl. \u003d 0.561 g / cm³ (T \u003d -100 ° C). Dissociation constant 42 (in water, acc.) [ a source?] . Vapor pressure at 0 ° C - 2.379 MPa.
Chemical properties
Chemical formula C 2 H 6 (rational CH 3 CH 3). The most characteristic reactions are the substitution of hydrogen by halogens, which proceed according to the free radical mechanism. Thermal dehydrogenation of ethane at 550-650 °C leads to ketene, at temperatures above 800 °C - to catacetylene (benzolysis is also formed). Direct chlorination at 300-450 ° C - to ethyl chloride, nitration in the gas phase gives a mixture (3: 1) of nitroethane-nitromethane.
Receipt
In industry
In industry, it is obtained from petroleum and natural gases, where it is up to 10% by volume. In Russia, the content of ethane in petroleum gases is very low. In the USA and Canada (where its content in oil and natural gases is high) it serves as the main raw material for the production of ethene.
In vitro
Obtained from iodomethane by the Wurtz reaction, from sodium acetate by electrolysis by the Kolbe reaction, by fusing sodium propionate with alkali, from ethyl bromide by the Grignard reaction, by hydrogenation of ethene (over Pd) or acetylene (in the presence of Raney nickel).
Application
The main use of ethane in industry is the production of ethylene.
Butane(C 4 H 10) - class organic compound alkanes. In chemistry, the name is mainly used to refer to n-butane. The same name has a mixture of n-butane and its isomer isobutane CH(CH3)3. The name comes from the root "but-" (English name butyric acid - butyric acid) and the suffix "-an" (belonging to alkanes). In high concentrations, it is poisonous; inhalation of butane causes dysfunction of the pulmonary-respiratory apparatus. Contained in natural gas, is formed when cracking oil products, when separating the associated petroleum gas, "fatty" natural gas. As a representative of hydrocarbon gases, it is flammable and explosive, has low toxicity, has a specific characteristic odor, and has narcotic properties. According to the degree of impact on the body, the gas belongs to substances of the 4th hazard class (low-hazardous) according to GOST 12.1.007-76. Harmfully affects the nervous system .
isomerism
Bhutan has two isomer:
Physical Properties
Butane is a colorless combustible gas, with a specific odor, easily liquefied (below 0 °C and normal pressure, or at elevated pressure and normal temperature - a highly volatile liquid). Freezing point -138°C (at normal pressure). Solubility in water - 6.1 mg in 100 ml of water (for n-butane, at 20 ° C, it dissolves much better in organic solvents ). Can form azeotropic mixture with water at a temperature of about 100 °C and a pressure of 10 atm.
Finding and receiving
Contained in gas condensate and petroleum gas (up to 12%). It is a product of catalytic and hydrocatalytic cracking oil fractions. In the laboratory can be obtained from wurtz reactions.
2 C 2 H 5 Br + 2Na → CH 3 -CH 2 -CH 2 -CH 3 + 2NaBr
Desulfurization (demercaptanization) of butane fraction
The straight-run butane fraction must be purified from sulfur compounds, which are mainly represented by methyl and ethyl mercaptans. The method of cleaning the butane fraction from mercaptans consists in alkaline extraction of mercaptans from the hydrocarbon fraction and subsequent regeneration of alkali in the presence of homogeneous or heterogeneous catalysts with atmospheric oxygen with the release of disulfide oil.
Applications and reactions
With free radical chlorination, it forms a mixture of 1-chloro- and 2-chlorobutane. Their ratio is well explained by the difference in the strength of C-H bonds in positions 1 and 2 (425 and 411 kJ/mol). Complete combustion in air forms carbon dioxide and water. Butane is used in combination with propane in lighters, in gas cylinders in a liquefied state, where it has an odor, as it contains specially added odorants. In this case, "winter" and "summer" mixtures with different compositions are used. The calorific value of 1 kg is 45.7 MJ (12.72 kWh).
2C 4 H 10 + 13 O 2 → 8 CO 2 + 10 H 2 O
In the absence of oxygen, it forms soot or carbon monoxide or both together.
2C 4 H 10 + 5 O 2 → 8 C + 10 H 2 O
2C 4 H 10 + 9 O 2 → 8 CO + 10 H 2 O
firm dupont developed a method for obtaining maleic anhydride from n-butane during catalytic oxidation.
2 CH 3 CH 2 CH 2 CH 3 + 7 O 2 → 2 C 2 H 2 (CO) 2 O + 8 H 2 O
n-Butane - raw material for production butene, 1,3-butadiene, a component of high octane gasolines. High purity butane and especially isobutane can be used as a refrigerant in refrigeration applications. The performance of such systems is slightly lower than freon ones. Butane is environmentally friendly, unlike freon refrigerants.
In the food industry, butane is registered as food additive E943a, and isobutane - E943b, How propellant, for example, in deodorants.
Ethylene(on IUPAC: ethene) - organic chemical compound, described by the formula C 2 H 4 . Is the simplest alkene (olefin). Ethylene is practically not found in nature. It is a colorless flammable gas with a slight odor. Partially soluble in water (25.6 ml in 100 ml of water at 0°C), ethanol (359 ml under the same conditions). It dissolves well in diethyl ether and hydrocarbons. Contains a double bond and is therefore classified as unsaturated or unsaturated hydrocarbons. Plays an extremely important role in the industry, and is also phytohormone. Ethylene is the most produced organic compound in the world ; total world production of ethylene in 2008 amounted to 113 million tons and continues to grow by 2-3% per year .
Application
Ethylene is the leading product basic organic synthesis and is used to obtain the following compounds (listed in alphabetical order):
Vinyl acetate;
Dichloroethane / vinyl chloride(3rd place, 12% of the total volume);
Ethylene oxide(2nd place, 14-15% of the total volume);
Polyethylene(1st place, up to 60% of the total volume);
Styrene;
Acetic acid;
Ethylbenzene;
ethylene glycol;
Ethanol.
Ethylene mixed with oxygen has been used in medicine for anesthesia up to the mid-1980s in the USSR and the Middle East. Ethylene is phytohormone almost all plants , among others responsible for the fall of needles in conifers.
Basic chemical properties
Ethylene is a chemically active substance. Since there is a double bond between carbon atoms in the molecule, one of them, less strong, is easily broken, and at the place of the bond break, the molecules are joined, oxidized, and polymerized.
Halogenation:
CH 2 \u003d CH 2 + Cl 2 → CH 2 Cl-CH 2 Cl
Bromine water becomes decolorized. This is a qualitative reaction to unsaturated compounds.
Hydrogenation:
CH 2 \u003d CH 2 + H - H → CH 3 - CH 3 (under the action of Ni)
Hydrohalogenation:
CH 2 \u003d CH 2 + HBr → CH 3 - CH 2 Br
Hydration:
CH 2 \u003d CH 2 + HOH → CH 3 CH 2 OH (under the action of a catalyst)
This reaction was discovered by A.M. Butlerov, and it is used for the industrial production of ethyl alcohol.
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.
Ethylene oxide is a fragile substance, the oxygen bridge breaks and water joins, resulting in the formation of ethylene glycol:
C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O
Polymerization:
nCH 2 \u003d CH 2 → (-CH 2 -CH 2 -) n
Isoprene CH 2 \u003d C (CH 3) -CH \u003d CH 2, 2-methylbutadiene-1,3 - unsaturated hydrocarbon diene series (C n H 2n−2 ) . Under normal conditions, a colorless liquid. He is monomer for natural rubber and a structural unit for many molecules of other natural compounds - isoprenoids, or terpenoids. . Soluble in alcohol. Isoprene polymerizes to give isoprene rubbers. Isoprene also reacts polymerization with vinyl connections.
Finding and receiving
Natural rubber is a polymer of isoprene - most commonly cis-1,4-polyisoprene with a molecular weight of 100,000 to 1,000,000. It contains a few percent of other materials as impurities, such as squirrels, fatty acid, resin and inorganic substances. Some sources of natural rubber are called gutta-percha and consists of trans-1,4-polyisoprene, structural isomer, which has similar but not identical properties. Isoprene is produced and released into the atmosphere by many types of trees (the main one is oak) The annual production of isoprene by vegetation is about 600 million tons, half of which is produced by tropical broadleaf trees, the rest is produced by shrubs. After exposure to the atmosphere, isoprene is converted by free radicals (such as the hydroxyl (OH) radical) and, to a lesser extent, ozone into various substances such as aldehydes, hydroxyperoxides, organic nitrates and epoxies, which mix with water droplets to form aerosols or haze. Trees use this mechanism not only to avoid overheating of the leaves by the Sun, but also to protect against free radicals, especially ozone. Isoprene was first obtained by heat treatment of natural rubber. Most commercially available as a product of thermal cracking naphtha or oils, as well as a by-product in the production ethylene. Approximately 20,000 tons per year are produced. About 95% of isoprene production is used to produce cis-1,4-polyisoprene, a synthetic version of natural rubber.
Butadiene-1,3(divinyl) CH 2 \u003d CH-CH \u003d CH 2 - unsaturated hydrocarbon, the simplest representative diene hydrocarbons.
Physical Properties
Butadiene - colorless gas with a characteristic odor boiling temperature-4.5°C the melting temperature-108.9°C, flash point-40°C maximum allowable concentration in air (MAC) 0.1 g/m³, density 0.650 g/cm³ at -6 °C.
We will slightly dissolve in water, we will well dissolve in alcohol, kerosene with air in an amount of 1.6-10.8%.
Chemical properties
Butadiene tends to polymerization, easily oxidized air with education peroxide compounds that accelerate polymerization.
Receipt
Butadiene is obtained by the reaction Lebedev transmission ethyl alcohol across catalyst:
2CH 3 CH 2 OH → C 4 H 6 + 2H 2 O + H 2
Or dehydrogenation of normal butylene:
CH 2 \u003d CH-CH 2 -CH 3 → CH 2 \u003d CH-CH \u003d CH 2 + H 2
Application
The polymerization of butadiene produces a synthetic rubber. Copolymerization with acrylonitrile and styrene receive ABS plastic.
Benzene (C 6 H 6 , Ph H) - organic chemical compound, colorless liquid with a pleasant sweetness smell. Protozoa aromatic hydrocarbon. Benzene is part of gasoline, widely used in industry, is the raw material for the production medicines, various plastics, synthetic rubber, dyes. Although benzene is part of crude oil, on an industrial scale, it is synthesized from its other components. toxic, carcinogenic.
Physical Properties
Colorless liquid with a peculiar pungent odor. Melting point = 5.5 °C, Boiling point = 80.1 °C, Density = 0.879 g/cm³, Molar mass = 78.11 g/mol. Like all hydrocarbons, benzene burns and forms a lot of soot. Forms explosive mixtures with air, mixes well with ethers, gasoline and other organic solvents, with water forms an azeotropic mixture with a boiling point of 69.25 ° C (91% benzene). Solubility in water 1.79 g/l (at 25 °C).
Chemical properties
Substitution reactions are characteristic of benzene - benzene reacts with alkenes, chlorine alkanes, halogens, nitric and sulfuric acid. Benzene ring cleavage reactions take place under harsh conditions (temperature, pressure).
Interaction with chlorine in the presence of a catalyst:
C 6 H 6 + Cl 2 -(FeCl 3) → C 6 H 5 Cl + HCl forms chlorobenzene
Catalysts promote the creation of an active electrophilic species by polarization between halogen atoms.
Cl-Cl + FeCl 3 → Cl ઠ - ઠ +
C 6 H 6 + Cl ઠ - -Cl ઠ + + FeCl 3 → [C 6 H 5 Cl + FeCl 4] → C 6 H 5 Cl + FeCl 3 + HCl
In the absence of a catalyst, when heated or illuminated, a radical substitution reaction occurs.
C 6 H 6 + 3Cl 2 - (lighting) → C 6 H 6 Cl 6 a mixture of hexachlorocyclohexane isomers is formed video
Interaction with bromine (pure):
Interaction with halogen derivatives of alkanes ( Friedel-Crafts reaction):
C 6 H 6 + C 2 H 5 Cl -(AlCl 3) → C 6 H 5 C 2 H 5 + HCl ethylbenzene is formed
C 6 H 6 + HNO 3 -(H 2 SO 4) → C 6 H 5 NO 2 + H 2 O
Structure
Benzene is classified as unsaturated hydrocarbons(homologous series C n H 2n-6), but unlike hydrocarbons of the series ethylene C 2 H 4 exhibits properties inherent in unsaturated hydrocarbons (they are characterized by addition reactions) only under harsh conditions, but benzene is more prone to substitution reactions. This "behavior" of benzene is explained by its special structure: the location of all bonds and molecules on the same plane and the presence of a conjugated 6π-electron cloud in the structure. The modern idea of the electronic nature of bonds in benzene is based on the hypothesis Linus Pauling, who proposed to depict the benzene molecule as a hexagon with an inscribed circle, thereby emphasizing the absence of fixed double bonds and the presence of a single electron cloud covering all six carbon atoms of the cycle.
Production
To date, there are three fundamentally different methods for the production of benzene.
Coking coal. This process was historically the first and served as the main source of benzene until World War II. At present, the proportion of benzene obtained by this method is less than 1%. It should be added that benzene obtained from coal tar contains a significant amount of thiophene, which makes such benzene a raw material unsuitable for a number of technological processes.
catalytic reforming(aromaizing) gasoline fractions of oil. This process is the main source of benzene in the US. In Western Europe, Russia and Japan, 40-60% of the total amount of the substance is obtained in this way. In this process, in addition to benzene, toluene and xylenes. Due to the fact that toluene is produced in quantities exceeding the demand for it, it is also partially processed into:
benzene - by hydrodealkylation method;
a mixture of benzene and xylenes - by disproportionation;
Pyrolysis gasoline and heavier oil fractions. Up to 50% of benzene is produced by this method. Along with benzene, toluene and xylenes are formed. In some cases, this entire fraction is sent to the dealkylation stage, where both toluene and xylenes are converted to benzene.
Application
Benzene is one of the ten most important substances in the chemical industry. [ source not specified 232 days ] Most of the resulting benzene is used for the synthesis of other products:
about 50% of benzene is converted into ethylbenzene (alkylation benzene ethylene);
about 25% of benzene is converted into cumene (alkylation benzene propylene);
about 10-15% benzene hydrogenate in cyclohexane;
about 10% of benzene is used for production nitrobenzene;
2-3% benzene is converted into linear alkylbenzenes;
approximately 1% benzene is used for synthesis chlorobenzene.
In much smaller quantities, benzene is used for the synthesis of some other compounds. Occasionally and in extreme cases, due to its high toxicity, benzene is used as a solvent. In addition, benzene is gasoline. Due to its high toxicity, its content is limited by new standards to the introduction of up to 1%.
Toluene(from Spanish Tolu, tolu balsam) - methylbenzene, a colorless liquid with a characteristic odor, belongs to arenas.
Toluene was first obtained by P. Peltier in 1835 during the distillation of pine resin. In 1838, it was isolated by A. Deville from a balm brought from the city of Tolú in Colombia, after which it received its name.
general characteristics
Colorless mobile volatile liquid with a pungent odor, exhibits a weak narcotic effect. Miscible to an unlimited extent with hydrocarbons, many alcohols and ethers, not miscible with water. Refractive index light 1.4969 at 20 °C. Combustible, burns with a smoky flame.
Chemical properties
Toluene is characterized by reactions of electrophilic substitution in the aromatic ring and substitution in the methyl group by a radical mechanism.
Electrophilic substitution in the aromatic ring it goes predominantly in the ortho and para positions relative to the methyl group.
In addition to substitution reactions, toluene enters into addition reactions (hydrogenation), ozonolysis. Some oxidizing agents (an alkaline solution of potassium permanganate, dilute nitric acid) oxidize the methyl group to a carboxyl group. Auto-ignition temperature 535 °C. Concentration limit of flame propagation, %vol. Temperature limit of flame propagation, °C. Flash point 4 °C.
Interaction with potassium permanganate in an acidic environment:
5С 6 H 5 СH 3 + 6KMnO 4 + 9H 2 SO 4 → 5С 6 H 5 COOH + 6MnSO 4 + 3K 2 SO 4 + 14H 2 O formation of benzoic acid
Receiving and cleaning
Product catalytic reforming gasoline factions oil. It is isolated by selective extraction and subsequent rectification.Good yields are also achieved with catalytic dehydrogenation heptane across methylcyclohexane. Purify toluene in the same way. benzene, only if applied concentrated sulfuric acid we must not forget that toluene sulfonated lighter than benzene, which means that it is necessary to maintain a lower temperature reaction mixture(less than 30 °C). Toluene also forms an azeotropic mixture with water. .
Toluene can be obtained from benzene Friedel-Crafts reactions:
Application
Raw materials for production benzene, benzoic acid, nitrotoluenes(including trinitrotoluene), toluene diisocyanates(via dinitrotoluene and toluene diamine) benzyl chloride and other organic substances.
Is an solvent for many polymers, is a component of various commercial solvents for varnishes and colors. Included in solvents: R-40, R-4, 645, 646 , 647 , 648. Used as a solvent in chemical synthesis.
Naphthalene- C 10 H 8 solid crystalline substance with a characteristic smell. It does not dissolve in water, but it is good - in benzene, broadcast, alcohol, chloroform.
Chemical properties
Naphthalene is chemically similar to benzene: easy nitrated, sulfonated, interacts with halogens. It differs from benzene in that it reacts even more easily.
Physical Properties
Density 1.14 g/cm³, melting point 80.26 °C, boiling point 218 °C, solubility in water about 30 mg/l, flash point 79 - 87 °C, autoignition point 525 °C, molar mass 128.17052 g/mol.
Receipt
Get naphthalene from coal tar. Also, naphthalene can be isolated from heavy pyrolysis tar (quenching oil), which is used in the pyrolysis process in ethylene plants.
Termites also produce naphthalene. Coptotermes formosanus to protect their nests from ants, fungi and nematodes .
Application
Important raw material of the chemical industry: used for the synthesis phthalic anhydride, tetralin, decalina, various derivatives of naphthalene.
Naphthalene derivatives are used to obtain dyes and explosives, in medicine, How insecticide.
The inhabitants of the British Isles are known to be addicted people. Having once put half the world under their control, they did not forget about the simple joys of life. About apples, for example. In the mid-to-late 19th century and early 20th, apple breeding reached its peak, but for the connoisseur, selection and varieties are not the only variety. To be a connoisseur is not only to crunch your favorite variety and know a couple of others, but for each variety to observe the development of the taste and texture of an apple during its ripening and storage. We often do not think that a fruit is a living organism with complex biochemistry and with its own hormones. Even the fruit is already plucked from the plant. One of the simplest hormones in structure, one of the most important and therefore the most studied, is the plant maturation hormone ethylene (C 2 H 4). Ethylene is the main assistant of all fruit distribution. You collect bananas while they are still firm and easily transportable, but green, astringent and inedible when raw, and ship them ten thousand kilometers to anywhere in the world. Then you either wait until they ripen, become soft and fragrant, under the influence of a naturally secreted ripening hormone, or if you need to sell them right now, you create an artificial ethylene atmosphere.
Ethylene, in fact, is a plant hormone with a wide range of effects, it regulates plant growth, leaf fall, flower opening. But it is interesting for us precisely as a fruit ripening hormone.
Fruit is the only food that nature intended as food. This is the plant's way of spreading its seeds over a wide area. But only on condition that the fruit is eaten by the distributors at the moment when the seeds are ready to germinate. And the plant regulates this with the help of maturation. The biochemistry of this process is complex, but evident. Color change due to the breakdown of chlorophyll to color pigments anthocyanins and carotenoids, breakdown of tasteless polysaccharides to sweet sugars, accumulation of aromatic compounds, breakdown of cell wall pectins with observed softening of the fruit.
In a wide group of plants, these processes can occur in the fruit even after it has been plucked from the plant and nutrient access has ceased. These fruits have already accumulated enough initial substances to start ripening. And this maturation is caused by the hormone ethylene. In the scientific literature, such fruits are called menopausal, these are apples, bananas, tomatoes, etc.
For another group of fruits, ripening is possible only on a branch with access to plant nutrients. This group includes pineapples, citrus fruits. After being harvested, they no longer ripen.
Ethylene is a gas, invisible, with a very slight odor of its own, so at home the ripening processes look a little mystical - you put a banana on the shelf and wait a week until it ripens, put it in a closed bag and you need to wait less. This is because ethylene works on the principle of positive feedback - it is released by the fruit itself and acts as a hormone on the same fruit, bananas release a lot of ethylene, in this they are almost champions. With damage, lack of water and other stresses, the release of ethylene increases. It is said that this fact was known in ancient Egypt, when several fruits were cut on branches to ripen figs.
By chemical structure, ethylene is the simplest alkene and one of the most common chemicals produced in the world in general, competing with sulfuric acid. Of course, not for the sake of fruit ripening. For example, as a monomer of polyethylene.
With a friend double bond.
1. Physical properties
Ethylene is a colorless gas with a slight pleasant odour. It is slightly lighter than air. Slightly soluble in water, but soluble in alcohol and other organic solvents.
2. Structure
Molecular formula C 2 H 4. Structural and electronic formulas:
3. Chemical properties
Unlike methane, ethylene is chemically quite active. It is characterized by addition reactions at the site of a double bond, polymerization reactions and oxidation reactions. In this case, one of the double bonds is broken and a simple single bond remains in its place, and due to the dismissed valences, other atoms or atomic groups are attached. Let's look at some examples of reactions. When ethylene is passed into bromine water (an aqueous solution of bromine), the latter becomes colorless as a result of the interaction of ethylene with bromine to form dibromoethane (ethylene bromide) C 2 H 4 Br 2:
As can be seen from the scheme of this reaction, it is not the replacement of hydrogen atoms by halogen atoms, as in saturated hydrocarbons, but the addition of bromine atoms at the site of the double bond. Ethylene also easily discolors the violet color of an aqueous solution with potassium manganate KMnO 4 even at ordinary temperature. At the same time, ethylene itself is oxidized to ethylene glycol C 2 H 4 (OH) 2. This process can be represented by the following equation:
- 2KMnO 4 -> K 2 MnO 4 + MnO 2 + 2O
Reactions between ethylene and bromine and potassium manganate serve to discover unsaturated hydrocarbons. Methane and other saturated hydrocarbons, as already noted, do not interact with potassium manganate.
Ethylene reacts with hydrogen. So, when a mixture of ethylene and hydrogen is heated in the presence of a catalyst (nickel, platinum or palladium powder), they combine to form ethane:
Reactions in which hydrogen is added to a substance are called hydrogenation or hydrogenation reactions. Hydrogenation reactions are of great practical importance. they are quite often used in industry. Unlike methane, ethylene burns in air with a swirling flame, since it contains more carbon than methane. Therefore, not all carbon burns out immediately and its particles become very hot and glow. These carbon particles are then burned in the outer part of the flame:
- C 2 H 4 + 3O 2 \u003d 2CO 2 + 2H 2 O
Ethylene, like methane, forms explosive mixtures with air.
4. Receipt
Ethylene does not occur naturally, except for minor impurities in natural gas. Under laboratory conditions, ethylene is usually obtained by the action of concentrated sulfuric acid on ethyl alcohol when heated. This process can be represented by the following summary equation:
During the reaction, water elements are subtracted from the alcohol molecule, and the two valences saturate each other with the formation of a double bond between carbon atoms. For industrial purposes, ethylene is obtained in large quantities from petroleum cracking gases.
5. Application
In modern industry, ethylene is widely used for the synthesis of ethyl alcohol and the production of important polymeric materials (polyethylene, etc.), as well as for the synthesis of other organic substances. A very interesting property of ethylene is to accelerate the ripening of many garden and garden fruits (tomatoes, melons, pears, lemons, etc.). Using this, fruits can be transported while still green, and then brought to a ripe state already at the place of consumption, introducing small amounts of ethylene into the air of storage rooms.
Ethylene is used to produce vinyl chloride and polyvinyl chloride, butadiene and synthetic rubbers, ethylene oxide and polymers based on it, ethylene glycol, etc.
Notes
Sources
- F. A. Derkach "Chemistry" L. 1968
|
||||||||
| ||||||||
The industrial method of obtaining cracking alkan alkan alkan + alken with a longer with a longer carbon carbon carbon carbon carbon carbon with a chain chain with a chain chain example: t = C T = C 10 H 22 C 5 H 12 + C 5 H 10 C 10 H 22 C 5 H 12 + C 5 H 10 decane pentane pentene decane pentane pentene
LABORATORY METHOD OF OBTAINING DEHYDROHALOGENATION REMOVE HYDROGEN HALOGEN ACTION REMOVE HYDROGEN HALOGEN ACTION EXAMPLE: alcohol alcohol H H solution H H solution H-C-C-H + KOHH 2 C=CH 2 +KCl+H 2 O H Cl ethene H Cl ethene chloroethane (ethylene) chloroethane (ethylene)
POLYMERIZATION REACTION This is the process of combining identical molecules into larger ones. EXAMPLE: n CH 2 \u003d CH 2 (-CH 2 -CH 2 -) n ethylene polyethylene (monomer) (polymer) n - degree of polymerization, shows the number of molecules that have reacted -CH 2 -CH 2 - structural unit
Ethylene application Property Application Example 1. Polymerization Production of polyethylene, plastics 2. Halogenation Solvent production 3. Hydrohalogenation For: local anesthesia, solvent production, in agriculture for decontamination of granaries
Property Application Example 4. Hydration Production of ethyl alcohol used as a solvent, anti-septic agent in medicine, in the production of synthetic rubber 5. Oxidation with KMnO 4 solution Production of antifreeze, brake fluids, in the production of plastics 6. Special property of ethylene: Ethylene accelerates the ripening of fruits
Unsaturated hydrocarbons with a double chemical bond in molecules belong to the group of alkenes. The first representative of the 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. 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. 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 weight is 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 the laboratory. Another way is the splitting off of hydrogen atoms from alkane molecules. By acting with caustic sodium or potassium on halogen-substituted compounds of 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, an aqueous solution of red-brown bromine becomes colorless, 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 goes with the formation of 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. Rigid 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 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 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, 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.
