Ethylene (IUPAC name:
ethene) is the
chemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula C
2H
4. It is the simplest
alkeneIn organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
. Because it contains a carbon-carbon double bond, ethylene is called an
unsaturated hydrocarbon or an
olefin. It is extremely important in industry and also has a role in biology as a
hormoneA hormone is a chemical released by one or more cells that affects cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. It is essentially a chemical messenger that transports a signal from one cell to another. All multicellular organisms...
. Ethylene is the most produced
organic compoundAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
in the world; global production of ethylene exceeded 107 million metric tonnes in 2005. To meet the ever increasing demand for ethylene, sharp increases in production facilities have been added globally, particularly in the
Gulf countriesThe Arab Gulf States, also known as Arab states of the Persian Gulf or Gulf Arab states or Gulf states, are usually reserved for the six Arab monarchical states joined since 1981 in the Cooperation Council for the Arab States of the Gulf, or Gulf Cooperation Council : Bahrain, Saudi Arabia, the...
.
Structure
This
hydrocarbonIn organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon and hydrogen are referred to as "pure"...
has four
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
atomThe atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s bound to a pair of
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atoms that are connected by a
double bondA double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...
. All six atoms that comprise ethylene are coplanar. The H-C-H
angleIn geometry and trigonometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle...
is 119°, close to the 120° for ideal sp² hybridized carbon. The molecule is also relatively rigid: rotation about the C-C bond is a high energy process that requires breaking the π-bond, while retaining the σ-bond between the carbon atoms.
The double bond is a region of high
electron densityElectron density is the measure of the probability of an electron being present at a specific location.In molecules, regions of electron density are usually found around the atom, and its bonds...
, and most reactions occur at this double bond position.
History
Ethylene was first synthesized in 1795 by a collaboration of four
DutchThe Netherlands is a country in Northwestern Europe, constituting the major portion of the Kingdom of the Netherlands. It is a parliamentary democratic constitutional monarchy. The Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east...
chemists. Following its discovery, it was referred as the
olefiant gas (oil-making gas), because it could be combined with
chlorineChlorine Chlorine Chlorine ( , from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and...
to produce the
oil of the Dutch (
1,2-dichloroethaneThe chemical compound 1,2-dichloroethane, commonly known by its old name of ethylene dichloride , is a chlorinated hydrocarbon, mainly used to produce vinyl chloride monomer , the major precursor for PVC production. It is a colourless liquid with a chloroform-like odour...
).
In the mid-19th century, the suffix
-ene (an Ancient Greek root added to the end of female names meaning "daughter of") was widely used to refer to a molecule or part thereof that contained one fewer hydrogen atoms than the molecule being modified. Thus,
ethylene (C
2H
4) was the "daughter of
ethylIn chemistry, an ethyl group is an alkyl functional group derived from ethane . It has the formula -C
2H
5 and is very often abbreviated -Et....
" (C
2H
5). The name ethylene was used in this sense as early as 1852.
In 1866, the
GermanGermany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium,...
chemist
August Wilhelm von Hofmann-Biography:Hofmann was born at Gießen, Grand Duchy of Hesse. Not intending originally to devote himself to physical science, he first took up the study of law and philology at Göttingen. But he then turned to chemistry, and studied under Justus von Liebig at University of Giessen...
proposed a system of hydrocarbon nomenclature in which the suffixes -ane, -ene, -ine, -one, and -une were used to denote the hydrocarbons with 0, 2, 4, 6, and 8 fewer hydrogens than their parent
alkaneAlkanes, also known as paraffins, are chemical compounds that consist only of the elements carbon and hydrogen , wherein these atoms are linked together exclusively by single bonds without any cyclic structure...
. In this system, ethylene became
ethene. Hofmann's system eventually became the basis for the Geneva nomenclature approved by the International Congress of Chemists in 1892, which remains at the core of the IUPAC nomenclature. However, by that time, the name ethylene was deeply entrenched, and it remains in wide use today, especially in the chemical industry.
The 1979 IUPAC nomenclature rules made an exception for retaining the non-systematic name ethylene, however, this decision was reversed in the 1993 rules so the correct name is now
ethene.
Uses
Approximately 80% of ethylene used in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
and
EuropeEurope is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains , and the Black Sea to the southeast...
is used to create
ethylene oxideEthylene oxide, also called oxirane, is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. It is commonly handled and shipped as a...
, ethylene dichloride, and
polyethylenePolyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons. Its primary use is within packaging .- Description :Polyethylene is a thermoplastic polymer consisting of long chains of the monomer ethylene...
. In smaller quantities, ethylene is used as an anesthetic agent (in an 85% ethylene/15% oxygen ratio), to hasten fruit ripening, as well as a welding gas.
Polyethylenes of various density and melt flow account for more than 50% of world ethylene demand. The primary use of polyethylene is in film applications for packaging, carrier bags and trash liners. Other applications include
injection mouldingInjection molding is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the mold cavity...
, pipe extrusion, wire and cable sheathing and
insulationAn insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate...
, as well as extrusion coating of paper and cardboard.
Ethylene derivatives include:
ethylene oxideEthylene oxide, also called oxirane, is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. It is commonly handled and shipped as a...
,
styreneStyrene, also known as vinyl benzene as well as many other names , is an organic compound with the chemical formula C
6H
5CH=CH
2. This aromatic hydrocarbon is a colorless oily liquid that evaporates easily and has a sweet smell, although high concentrations confer a...
monomer (via ethyl benzene) and linear higher olefins.
Ethylene oxideEthylene oxide, also called oxirane, is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. It is commonly handled and shipped as a...
is a key raw material in the production of
surfactantSurfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids.- Etymology :The term surfactant is a blend of surface active agent...
s and
detergentA detergent is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning...
s. It is also used to manufacture
ethylene glycolEthylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet tasting liquid....
(widely used as an automotive antifreeze), higher molecular weight glycols, and
glycol ethersGlycol ethers are a group of solvents based on alkyl ethers of ethylene glycol commonly used in paints. These solvents typically have higher boiling point, together with the favorable solvent properties of lower molecular weight ethers and alcohols...
.
StyreneStyrene, also known as vinyl benzene as well as many other names , is an organic compound with the chemical formula C
6H
5CH=CH
2. This aromatic hydrocarbon is a colorless oily liquid that evaporates easily and has a sweet smell, although high concentrations confer a...
monomer is used principally in
polystyrenePolystyrene , sometimes abbreviated PS, is an aromatic polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry...
for packaging and insulation, as well as in styrene butadiene rubber for tires and footwear.
Linear higher olefins are used as base materials for the manufacture of detergents, plasticisers, synthetic lubricants and additives, but also as co-monomers in the production of polyethylenes.
Ethylene is a key component in Levinstein sulfur mustard, a chemical weapon agent.
Production
Ethylene is produced in the
petrochemicalPetrochemicals are chemical products made from raw materials of petroleum or other hydrocarbon origin. Although some of the chemical compounds that originate from petroleum may also be derived from coal and natural gas, petroleum is the major source...
industry by steam cracking. In this process, gaseous or light liquid hydrocarbons are heated to 750–950 °C, inducing numerous free radical
reactionsA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
followed by immediate
quenchA quench refers to a rapid cooling. In polymer chemistry and materials science, quenching is used to prevent low-temperature processes such as phase transformations from occurring by only providing a narrow window of time in which the reaction is both thermodynamically favorable and kinetically...
to freeze the reactions. This process converts large hydrocarbons into smaller ones and introduces unsaturation. Ethylene is separated from the resulting complex mixture by repeated
compressionPhysical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. The opposite of compression is rarefraction tension.- Explanation :...
and
distillationDistillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
. In a related process used in oil refineries, high molecular weight hydrocarbons are cracked over
zeoliteZeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
catalysts. Heavier feedstocks, such as naphtha and gas oils require at least two "quench towers" downstream of the cracking furnaces to recirculate pyrolysis-derived gasoline and process water. When cracking a mixture of ethane and propane, only one water quench tower is required.
The areas of an ethylene plant are:
- steam cracking furnaces:
- primary and secondary heat recovery with quench;
- a dilution steam recycle system between the furnaces and the quench system;
- primary compression of the cracked gas (3 stages of compression);
- hydrogen sulfide and carbon dioxide removal (acid gas removal);
- secondary compression (1 or 2 stages);
- drying of the cracked gas;
- cryogenic treatment;
- all of the cold cracked gas stream goes to the demethanizer tower. The overhead stream from the demethanizer tower consists of all the hydrogen and methane that was in the cracked gas stream. Different methods of cryogenically treating this overhead stream results in the separation of the hydrogen and the methane. This usually involves liquid methane at a temperature around . Complete recovery of all the methane is critical to the economical operation of an ethylene plant. Often one or two Turboexpander
A turboexpander, also referred to as a turbo-expander or an expansion turbine, is a centrifugal or axial flow turbine through which a high pressure gas is expanded to produce work that is often used to drive a compressor....
s are used for MethaneMethane is a chemical compound with the chemical formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees. Burning methane in the presence of oxygen produces carbon dioxide and water. The relative abundance of methane and its clean...
recovery from the demethanizer overhead stream.
- the bottom stream from the demethanizer tower goes to the deethanizer tower. The overhead stream from the deethanizer tower consists of all the C2,'s that were in the cracked gas stream. The C2's then go to a C2 splitter. The product ethylene is taken from the overhead of the tower and the ethane coming from the bottom of the splitter is recycled to the furnaces to be cracked again;
- the bottom stream from the deethanizer tower goes to the depropanizer tower. The overhead stream from the depropanizer tower consists of all the C3's that were in the cracked gas stream. Prior to sending the C3's to the C3 splitter this stream is hydrogenated in order to react out the methylacetylene and propadiene. Then this stream is sent to the C3 splitter. The overhead stream from the C3 splitter is product propylene and the bottom stream from the C3 splitter is propane which can be sent back to the furnaces for cracking or used as fuel.
- The bottom stream from the depropanizer tower is fed to the debutanizer tower. The overhead stream from the debutanizer is all of the C4's that was in the cracked gas stream. The bottom stream from the debutanizer consists of everything in the cracked gas stream that is C5 or heavier. This could be called a light pyrolysis gasoline.
Since the production of ethylene is energy intensive, much effort has been dedicated to recovering heat from the gas leaving the furnaces. Most of the energy recovered from the cracked gas is used to make high pressure (1200 psig) steam. This steam is in turn used to drive the turbines for compressing cracked gas, the propylene refrigeration compressor, and the ethylene refrigeration compressor. An ethylene plant, once running, does not need to import any steam to drive its steam turbines. A typical world scale ethylene plant (about 1.5 billion pounds of ethylene per year) uses a cracked gas compressor, a propylene compressor, and a ethylene compressor.
When starting an ethylene plant it is important to start the cooling systems in the proper order. The cooling systems consist of Cooling Tower Water (CTW); propylene refrigeration with four or five different levels or stages. Each level corresponds to a particular pressure and temperature; and three or four stages of ethylene regfrigeration. The CTW must be started first because the propylene system needs it to condense propylene and the ethylene refrigeration systems needs it to desuperheat high pressure ethylene. The propylene system must start next because the ethylene system needs high pressure propylene for desuperheating the high pressure ethylene stage and the low pressure propylene stage for condensing the high pressure ethylene. While the ethylene plant is running, the plant can continue to run for a time if the ethylene refrigeration compressor shuts down. However, if the propylene compressor shuts down the whole plant must be shut down immediately.
Laboratory preparation
Ethylene can be conveniently produced in the laboratory by distilling absolute
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
with an excess of concentrated
sulfuric acidSulfuric acid, , is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion...
and washing the distillate vapor stream in an aqueous solution of
sodium hydroxideSodium hydroxide , also known as lye and caustic soda, is a caustic metallic base. It is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Worldwide production in 1998 was around...
to remove the
sulfur dioxideSulfur dioxide is the chemical compound with the formula SO
2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide...
contaminant.
Peculiarity of spectrum
Although ethylene is a relatively simple molecule, its
spectrumSpectroscopy was originally the study of the interaction between radiation and matter as a function of wavelength . In fact, historically, spectroscopy referred to the use of visible light dispersed according to its wavelength, e.g. by a prism. Later the concept was expanded greatly to comprise...
is considered to be one of the most difficult to explain adequately from both a theoretical and practical perspective. For this reason, it is often used as a test case in
computational chemistryComputational chemistry is a branch of chemistry that uses computers to assist in solving chemical problems. It uses the results of theoretical chemistry, incorporated into efficient computer programs, to calculate the structures and properties of molecules and solids...
. Of particular note is the difficulty in characterizing the ultraviolet absorption of the molecule. Interest in the subtleties and details of the ethylene spectrum can be dated back to at least the 1950s.
Chemical reactions
Ethylene is an extremely important building block in the petrochemical industry. It can undergo many types of reactions which leads to a plethora of major chemical products. A list of some major types of reactions includes, 1)
polymerizationIn polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
, 2) oxidation, 3)
halogenationHalogenation is a chemical reaction that incorporates a halogen atom into a molecule. More specific descriptions exist that specify the type of halogen: fluorination, chlorination, bromination, and iodination....
and
hydrohalogenationA hydrohalogenation reaction is the electrophilic addition of hydrohalic acids like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes ....
, 4)
alkylationAlkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene . Alkylating agents are widely used in chemistry because the alkyl group is probably the most common group encountered in...
, 5)
hydrationHydration may refer to:* Hydration reaction, a chemical addition reaction where a hydroxyl group and proton are added to a compound* Mineral hydration, an inorganic chemical reaction where water is added to the crystal structure of a mineral...
, 6) oligomerization, 7)
hydroformylationHydroformylation, also known as oxo synthesis, is an important industrial process for the production of aldehydes from alkenes. This chemical reaction entails the addition of a formyl group and a hydrogen atom to a carbon-carbon double bond...
, and 8) a ripening agent for fruits and vegetables (see Physiological responses of plants).
Additions to double bond
Like most alkenes, ethylene reacts with
halogenThe halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine, ; chlorine, ; bromine, ; iodine, ; and astatine,...
s to produce halogenated hydrocarbons1,2-C
2H
4X
2. It can also react with water to produce
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
, but the rate at which this happens is very slow unless a suitable catalyst, such as
phosphoricPhosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more...
or
sulfuric acidSulfuric acid, , is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion...
, is used. Under high pressure, and, in the presence of a catalytic metal (
platinumPlatinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements...
,
rhodiumRhodium is a chemical element that is a rare, silvery-white, hard transition metal and a member of the platinum group. Rhodium is found in platinum ores and is used in alloys with platinum and as a catalyst. It is abbreviated to Rh and has atomic number 45...
,
nickelNickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements at about room temperature, other three being iron, cobalt and gadolinium...
),
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
will react with ethylene to form
ethaneEthane is a chemical compound with chemical formula C
2H
6. It is the only two-carbon alkane that is an aliphatic hydrocarbon. At standard temperature and pressure, ethane is a colorless, odorless gas....
.
Ethylene is used primarily as an intermediate in the manufacture of other chemicals in the synthesis of monomers. Ethylene can be
chlorinatedChlorine Chlorine Chlorine ( , from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and...
to produce
1,2-dichloroethaneThe chemical compound 1,2-dichloroethane, commonly known by its old name of ethylene dichloride , is a chlorinated hydrocarbon, mainly used to produce vinyl chloride monomer , the major precursor for PVC production. It is a colourless liquid with a chloroform-like odour...
(ethylene dichloride). This can be converted to
vinyl chlorideVinyl chloride is the organochloride with the formula CH2:CHCl. It is also called vinyl chloride monomer, or VCM. This colourless compound is an important industrial chemical chiefly used to produce the polymer polyvinyl chloride . At ambient pressure and temperature, vinyl chloride is...
, the monomer precursor to plastic
polyvinyl chloridePolyvinyl chloride, commonly abbreviated PVC, is the third most widely used thermoplastic polymer after polyethylene and polypropylene. In terms of revenue generated, it is one of the most valuable products of the chemical industry. Around the world, over 50% of PVC manufactured is used in...
, or combined with
benzeneBenzene, or benzol, is an organic chemical compound with the molecular formula C6H6. It is sometimes abbreviated Ph–H. Benzene is a colorless and highly flammable liquid with a sweet smell and a relatively high melting point...
to produce
ethylbenzeneEthylbenzene is an organic compound with the formula C
6H
5CH
2CH
3. This aromatic hydrocarbon is important in the petrochemical industry as an intermediate in the production of styrene, which in turn is used for making polystyrene, a commonly used plastic...
, which is used in the manufacture of
polystyrenePolystyrene , sometimes abbreviated PS, is an aromatic polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry...
, another important plastic.
Ethylene is more reactive than alkanes because of two reasons:
1. It has a double bond, one called the π-bond(pi) and one called the σ-bond (sigma), where the π-bond is weak and the σ-bond is strong. The presence of the π-bond makes it a high energy molecule. Thus bromine water decolourises readily when it is added to ethylene.
2. High electron density at the double bond makes it react readily. It is broken in an
addition reactionAn addition reaction, in organic chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one.There are two main types of polar addition reactions:* Electrophilic addition* Nucleophilic addition...
to produce many useful products.
Polymerization
Ethylene
polymerA polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties.Due to the extraordinary...
izes to produce
polyethylenePolyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons. Its primary use is within packaging .- Description :Polyethylene is a thermoplastic polymer consisting of long chains of the monomer ethylene...
, also called
polyethene or
polythene, the world's most widely-used plastic.
Major polyethylene product groups are low density polyethylene, high density polyethylene, polyethylene copolymers, as well as ethylene-propylene co- & terpolymers.
Oxidation
Ethylene is oxidized to produce
ethylene oxideEthylene oxide, also called oxirane, is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. It is commonly handled and shipped as a...
, which is
hydrolysedHydrolysis is a chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions, which may go on to participate in further reactions. It is the type of reaction that is used to break down certain polymers, especially those made by step-growth polymerization...
to
ethylene glycolEthylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet tasting liquid....
. It is also a precursor to
vinyl acetateVinyl acetate is an organic compound with the formula CH3COOCH=CH2. A colorless liquid with a pungent odor, it is the precursor to polyvinyl acetate, an important polymer in industry.-Preparation:...
.
Ethylene undergoes oxidation by palladium to give
acetaldehydeAcetaldehyde is an organic chemical compound with the formula CH3CHO or MeCHO. It is a flammable liquid. Acetaldehyde occurs naturally in ripe fruit, coffee, and bread, and is produced by plants as part of their normal metabolism...
. This conversion was at one time a major industrial process. The process proceeds via the initial complexation of ethylene to a Pd(II) center.
Major intermediates of the oxidation of Ethylene are
ethylene oxideEthylene oxide, also called oxirane, is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. It is commonly handled and shipped as a...
,
acetaldehydeAcetaldehyde is an organic chemical compound with the formula CH3CHO or MeCHO. It is a flammable liquid. Acetaldehyde occurs naturally in ripe fruit, coffee, and bread, and is produced by plants as part of their normal metabolism...
,
vinyl acetateVinyl acetate is an organic compound with the formula CH3COOCH=CH2. A colorless liquid with a pungent odor, it is the precursor to polyvinyl acetate, an important polymer in industry.-Preparation:...
and
ethylene glycolEthylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet tasting liquid....
. The list of products made from these intermediates is long. Some of them are: polyesters,
polyurethaneA polyurethane, IUPAC abbreviation PUR, but commonly abbreviated PU, is any polymer consisting of a chain of organic units joined by urethane links...
,
morpholineMorpholine is an organic chemical compound having the chemical formula O
2NH. This heterocycle, pictured at right, features both amine and ether functional groups. Because of the amine, morpholine is a base; its conjugate acid is called morpholinium...
, ethanolamines,
aspirinAspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication....
and
glycol ethersGlycol ethers are a group of solvents based on alkyl ethers of ethylene glycol commonly used in paints. These solvents typically have higher boiling point, together with the favorable solvent properties of lower molecular weight ethers and alcohols...
.
Halogenation and hydrohalogenation
Major intermediates from the
halogenationHalogenation is a chemical reaction that incorporates a halogen atom into a molecule. More specific descriptions exist that specify the type of halogen: fluorination, chlorination, bromination, and iodination....
and
hydrohalogenationA hydrohalogenation reaction is the electrophilic addition of hydrohalic acids like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes ....
of ethylene include: ethylene dichloride, ethyl chloride and ethylene dibromide. Some products in this group are:
polyvinyl chloridePolyvinyl chloride, commonly abbreviated PVC, is the third most widely used thermoplastic polymer after polyethylene and polypropylene. In terms of revenue generated, it is one of the most valuable products of the chemical industry. Around the world, over 50% of PVC manufactured is used in...
,
trichloroethyleneThe chemical compound trichloroethylene is a chlorinated hydrocarbon commonly used as an industrial solvent. It is a clear non-flammable liquid with a sweet smell....
, perchloroethylene, methyl chloroform, polyvinylidiene chloride and copolymers, and ethyl bromide.
Alkylation
Major chemical intermediates from the
alkylationAlkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene . Alkylating agents are widely used in chemistry because the alkyl group is probably the most common group encountered in...
of ethylene include:
ethylbenzeneEthylbenzene is an organic compound with the formula C
6H
5CH
2CH
3. This aromatic hydrocarbon is important in the petrochemical industry as an intermediate in the production of styrene, which in turn is used for making polystyrene, a commonly used plastic...
, ethyl
tolueneToluene, also known as methylbenzene, or Toluol, is a clear water-insoluble liquid with the typical smell of paint thinners, reminiscent of the related compound benzene. It is an aromatic hydrocarbon that is widely used as an industrial feedstock and as a solvent...
, ethyl anilines, 1,4-hexadiene and
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
alkyls. Products of these intermediates include
polystyrenePolystyrene , sometimes abbreviated PS, is an aromatic polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry...
, unsaturated polyesters and ethylene-propylene terpolymers.
Hydration
EthanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
is the primary intermediate of the
hydrationHydration may refer to:* Hydration reaction, a chemical addition reaction where a hydroxyl group and proton are added to a compound* Mineral hydration, an inorganic chemical reaction where water is added to the crystal structure of a mineral...
of ethylene. Important products from ethanol are: ethylamines,
acetaldehydeAcetaldehyde is an organic chemical compound with the formula CH3CHO or MeCHO. It is a flammable liquid. Acetaldehyde occurs naturally in ripe fruit, coffee, and bread, and is produced by plants as part of their normal metabolism...
, and
ethyl acetateEthyl acetate is the organic compound with the formula CH3COOCH2CH3. This colorless liquid has a characteristic sweet smell like certain glues or nail polish removers, in which it is used...
.
Oligomerization
The primary products of the Oligomerization of ethylene are alpha-olefins and linear primary alcohols. These are used as plasticizers and surfactants.
Oxo-reaction
The hydroformylation (
Oxo-reactionHydroformylation, also known as oxo synthesis, is an important industrial process for the production of aldehydes from alkenes. This chemical reaction entails the addition of a formyl group and a hydrogen atom to a carbon-carbon double bond...
) of ethylene results in
propionaldehydePropionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is a saturate 3-carbon aldehyde and is a structural isomer of acetone...
with its primary products of
propionic acidPropionic acid is a naturally-occurring carboxylic acid with chemical formula CH3CH2COOH. It is a clear liquid with a pungent odor...
and n-propyl alcohol.
In the synthesis of fine chemicals
Ethylene is useful in
organic synthesisOrganic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
. Representative reactions include Diels-Alder additions,
ene reactionThe Ene reaction is a chemical reaction between an alkene with an allylic hydrogen and a multiple bond . It is a group transfer reaction...
, and arene alkylation.
Miscellaneous
Ethylene is found in many lip gloss products.
Production of ethylene in
mineral oilMineral oil or liquid petroleum is a by-product in the distillation of petroleum to produce gasoline and other petroleum based products from crude oil. It is a transparent, colorless oil composed mainly of alkanes and cyclic paraffins, related to petroleum jelly . It has a density of around 0.8...
-filled transformers is a key indicator of severe localized overheating (>750 °C).
Ethylene as a plant hormone
Ethylene acts physiologically as a
hormonePlant hormones are chemicals that regulate plant growth, which, in the UK, are termed 'plant growth substances'. Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations. Hormones regulate cellular processes in targeted cells locally and when moved...
in
plantPlants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
s. It exists as a gas and acts at trace levels throughout the life of the plant by stimulating or regulating the
ripeningRipening is a process in fruits that causes them to become more edible. In general, a fruit becomes sweeter, less green, and softer as it ripens. However the acidity as well as sweetness rises during ripening, but the fruit still tastes sweeter regardless...
of
fruitThe term fruit has different meanings dependent on context, and the term is not synonymous in food preparation and biology. Fruits are the means by which flowering plants disseminate seeds, and the presence of seeds indicates that a structure is most likely a fruit, though not all seeds come from...
, the opening of
flowerA flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to mediate the union of male sperm with female ovum in order to produce seeds...
s, and the
abscissionAbscission is the shedding of a body part. It most commonly refers to the process by which a plant intentionally drops one or more of its parts, such as a leaf, fruit, flower or seed, though the term is also used to describe the shedding of a claw by an animal, and is also the word used to...
(or shedding) of
leavesLeaves are an Icelandic five-piece alternative rock band who formed in 2001. Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times. They came to prominence in 2002 with their debut album, Breathe, drawing comparisons to groups such as The Verve and Doves...
. Its biosynthesis starts from
methionineMethionine is an α-amino acid with the chemical formula HO
2CCHCH
2CH
2SCH
3. This essential amino acid is classified as nonpolar.-Function:...
with
1-aminocyclopropane-1-carboxylic acid1-Aminocyclopropane-1-carboxylic acid is a disubstituted cyclic alpha-amino acid in which a three-membered cyclopropane ring is fuzed to the C-atom of the amino acid....
(ACC) as a key intermediate.
History of ethylene in plant biology
Ethylene has been used in practice since the ancient Egyptians, who would gash figs in order to stimulate ripening (wounding stimulates ethylene production by plant tissues). The ancient Chinese would burn
incenseIncense is composed of aromatic biotic materials, which release fragrant smoke when burned. The term incense refers to the substance itself, rather than to the odor that it produces....
in closed rooms to enhance the ripening of pears. In 1864, it was discovered that gas leaks from street lights led to stunting of growth, twisting of plants, and abnormal thickening of stems (Arteca, 1996; Salisbury and Ross, 1992). In 1901, a Russian scientist named Dimitry Neljubow showed that the active component was ethylene . Doubt discovered that ethylene stimulated
abscissionAbscission is the shedding of a body part. It most commonly refers to the process by which a plant intentionally drops one or more of its parts, such as a leaf, fruit, flower or seed, though the term is also used to describe the shedding of a claw by an animal, and is also the word used to...
in 1917. It wasn't until 1934 that Gane reported that plants synthesize ethylene. In 1935, Crocker proposed that ethylene was the plant hormone responsible for fruit ripening as well as senescence of vegetative tissues (Crocker, 1935).
Ethylene biosynthesis in plants
It has been shown that ethylene is produced from essentially all parts of higher plants, including leaves, stems, roots, flowers, fruits, tubers, and seedlings.
"Ethylene production is regulated by a variety of developmental and environmental factors. During the life of the plant, ethylene production is induced during certain stages of growth such as germination, ripening of fruits, abscission of leaves, and senescence of flowers. Ethylene production can also be induced by a variety of external aspects such as mechanical wounding, environmental stresses, and certain chemicals including auxin and other regulators"
The biosynsthesis of the hormone starts with conversion of the amino acid methionine to
S-adenosyl-L-methionineS-Adenosyl methionine is a common co-substrate involved in methyl group transfers. SAM-e was first discovered in Italy by G. L. Cantoni in 1912. It is made from adenosine triphosphate and methionine by methionine adenosyltransferase . Transmethylation, transsulfuration, and aminopropylation are...
(SAM, also called Adomet) by the enzyme Met Adenosyltransferase. SAM is then converted to 1-aminocyclopropane-1-carboxylic-acid (ACC) by the enzyme ACC synthase (ACS); the activity of ACS is the rate-limiting step in ethylene production, therefore regulation of this enzyme is key for the ethylene biosynthesis. The final step requires oxygen and involves the action of the enzyme ACC-oxidase (ACO), formerly known as the Ethylene Forming Enzyme (EFE).
Ethylene biosynthesis can be induced by endogenous or exogenous ethylene. ACC synthesis increases with high levels of auxins, specially Indole Acetic Acid (IAA), and cytokinins. ACC synthase is inhibited by abscisic acid.
Ethylene perception in plants
Ethylene could be perceived by a transmembrane protein
dimerA dimer is a chemical or biological entity consisting of two structurally similar subunits called monomers, which are joined by bonds, which can be strong or weak.- Organic chemistry :...
complex. The first gene encoding an ethylene receptor was first cloned from
Arabidopsis thalianaArabidopsis thaliana , is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, Arabidopsis is popular as a model organism in plant biology and genetics...
by Caren Chang, Elliot Meyerowitz and colleagues at the
California Institute of TechnologyThe California Institute of Technology is a private research university located in Pasadena, California, United States. The Institute maintains a strong emphasis on the natural sciences and engineering, and operates and manages NASA's neighboring Jet Propulsion Laboratory...
and then in
tomatoThe tomato is a herbaceous, usually sprawling plant in the Solanaceae or nightshade family that is typically cultivated for the purpose of harvesting its fruit for human consumption...
by Jack Wilkinson, Harry Klee and colleagues at the Monsanto Company. Ethylene receptors are encoded by multiple genes in the Arabidopsis and tomato genomes. The
gene familyA gene family is a set of genes with a known homology. They are generally biochemically similar. Genes are categorized this way into families, depending on shared nucleotide or protein sequences....
is comprised of five receptors in Arabidopsis and at least six in tomato, most of which have been shown to bind ethylene.
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
sequences for ethylene receptors have also been identified in many other plant species and an ethylene binding protein has even been identified in
CyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
Environmental and biological triggers of ethylene
Environmental cues can induce the biosynthesis of the plant hormone. Flooding, drought, chilling, wounding, and pathogen attack can induce ethylene formation in the plant.
In flooding, root suffers from lack of oxygen, or
anoxiaHypoxia or oxygen depletion is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point detrimental to aquatic organisms living in the system...
, which leads to the synthesis of
1-Aminocyclopropane-1-carboxylic acid1-Aminocyclopropane-1-carboxylic acid is a disubstituted cyclic alpha-amino acid in which a three-membered cyclopropane ring is fuzed to the C-atom of the amino acid....
(ACC). ACC is transported upwards in the plant and then oxidized in leaves. The product, the ethylene causes epinasty of the leaves.
One speculation recently put forth for epinasty is the downard pointing leaves may act as pump handles in the wind. The ethylene may or may not additionally induce the growth of a valve in the
xylemIn vascular plants, xylem is one of the two types of transport tissue, phloem being the other. The word "xylem" is derived from classical Greek ξυλον , "wood", and indeed the best-known xylem tissue is wood, though it is found throughout the plant...
, but the idea would be that the plant would harness the power of the wind to pump out more water from the roots of the plants than would normally happen with
transpirationTranspiration is the evaporation of water from the aerial parts of plants, especially leaves but also stems, flowers and roots. Leaf surfaces are dotted with openings called stoma that are bordered by guard cells. Collectively the structures are called stomata...
.
Physiological responses of plants
Like the other plant hormones, ethylene is considered to have pleiotropic effects. This essentially means that it is thought that at least some of the effects of the hormone are unrelated. What is actually caused by the gas may depend on the tissue affected as well as environmental conditions. In the evolution of plants, ethylene would simply be a message that was coopted for unrelated uses by plants during different periods of the evolutionary development.
List of plant responses to ethylene
- Seedling triple response, thickening and shortening of hypocotyl with pronounced apical hook. This is thought to be a seedling's reaction to an obstacle in the soil such a stone, allowing it to push past the obstruction.
- In pollination
Pollination is the process by which pollen is transferred in plants, thereby enabling fertilization and sexual reproduction. Pollen grains, which contain the male gametes to where the female gamete are contained within the carpel; in gymnosperms the pollen is directly applied to the ovule itself...
, when the pollen reaches the stigma, the precursor of the ethylene, ACC1-Aminocyclopropane-1-carboxylic acid is a disubstituted cyclic alpha-amino acid in which a three-membered cyclopropane ring is fuzed to the C-atom of the amino acid....
, is secreted to the petal, the ACC releases ethylene with ACC oxidase.
- Stimulates leaf and flower senescence
Senescence refers to the biological changes which take place in organisms as they age. It encompasses all of the biological processes of a living organism's approaching an advanced age...
- Stimulates senescence of mature xylem
In vascular plants, xylem is one of the two types of transport tissue, phloem being the other. The word "xylem" is derived from classical Greek ξυλον , "wood", and indeed the best-known xylem tissue is wood, though it is found throughout the plant...
cells in preparation for plant use
- Inhibits shoot growth except in some habitually flooded plants like rice
Rice is the seed of a monocot plant Oryza sativa, of the grass family . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East, South, Southeast Asia, the Middle East, Latin America, and the West Indies...
- Induces leaf abscission
Abscission is the shedding of a body part. It most commonly refers to the process by which a plant intentionally drops one or more of its parts, such as a leaf, fruit, flower or seed, though the term is also used to describe the shedding of a claw by an animal, and is also the word used to...
- Induces seed germination
Germination is the process in which a seed or spore emerges from a period of dormancy. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However, the growth of a sporeling from a spore, for example the growth of hyphae from fungal...
- Induces root hair
A root hair is a tubular outgrowth of root epidermal cells of vascular plants. They are found only in the region of maturation of the root. Root hairs are a specialized form of rhizoid....
growth – increasing the efficiency of water and mineral absorption
- Induces the growth of adventitious roots during flooding
- Stimulates epinasty – leaf petiole
In botany, the petiole is the small stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly...
grows out, leaf hangs down and curls into itself
- Stimulates fruit ripening
- Induces a climacteric
The climacteric is a stage of fruit ripening associated with ethylene production and cell respiration rise. Apples, bananas, melons, apricots, tomatoes are climacteric fruit. Citrus, grapes, strawberries are non-climacteric...
rise in respiration in some fruit which causes a release of additional ethylene. This can be the one bad apple in a barrel spoiling the rest phenomenon.
- Affects neighboring individuals
- Affects gravitropism
- Stimulates nutational bending
- Disease/wounding resistance
- Inhibits stem growth outside of seedling stage
- Stimulates stem and cell broadening and lateral branch growth also outside of seedling stage
- Synthesis is stimulated by auxin
Auxins are a class of plant growth substance and morphogens . Auxins have an essential role in coordination of many growth and behavioral processes in the plant life cycle...
and maybe cytokininCytokinins are a class of plant growth substances that promote cell division. They are primarily involved in cell growth, differentiation, and other physiological processes. Their effects were first discovered through the use of coconut milk in the 1940s by a scientist at the University of...
as well
- Ethylene levels are decreased by light
- The flooding of roots stimulates the production of ACC which travels through the xylem
In vascular plants, xylem is one of the two types of transport tissue, phloem being the other. The word "xylem" is derived from classical Greek ξυλον , "wood", and indeed the best-known xylem tissue is wood, though it is found throughout the plant...
to the stem and leaves where it is converted to the gas
- Interference with auxin
Auxins are a class of plant growth substance and morphogens . Auxins have an essential role in coordination of many growth and behavioral processes in the plant life cycle...
transport (with high auxin concentrations)
- Inhibits stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is formed by a pair of specialized parenchyma cells known as guard cells which are responsible for regulating the size of the opening...
tal closing except in some water plants or habitually flooded ones such as some rice varieties, where the opposite occurs (conserving CO2 and O2)
- Where ethylene induces stomatal closing, it also induces stem elongation
- Induces flowering in pineapple
Pineapple is the common name for an edible tropical plant and also its fruit. It is native to the southern part of Brazil, and Paraguay. Pineapple is eaten fresh or canned and is available as a juice or in juice combinations. It is used in desserts, salads, as a complement to meat dishes and in...
s
Commercial Issues
Ethylene shortens the shelf life of many fruits by hastening fruit ripening and floral senescence.
TomatoThe tomato is a herbaceous, usually sprawling plant in the Solanaceae or nightshade family that is typically cultivated for the purpose of harvesting its fruit for human consumption...
es,
bananaBanana is the common name for a herbaceous plants of the genus Musa, and the commonly eaten fruit it produces. They are native to the tropical region of Southeast Asia, and are likely to have been first domesticated in Papua New Guinea. Today, they are cultivated throughout the tropics.Banana...
s and
appleThe apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family Rosaceae. It is one of the most widely cultivated tree fruits...
s will ripen faster in the presence of ethylene. Bananas placed next to other fruits will produce enough ethylene to cause accelerated fruit ripening.
Ethylene will shorten the shelf life of cut flowers and potted plants by accelerating floral senescence and floral
abscissionAbscission is the shedding of a body part. It most commonly refers to the process by which a plant intentionally drops one or more of its parts, such as a leaf, fruit, flower or seed, though the term is also used to describe the shedding of a claw by an animal, and is also the word used to...
. Flowers and plants which are subjected to stress during shipping, handling, or storage produce ethylene causing a significant reduction in floral display. Flowers affected by ethylene include
carnationDianthus caryophyllus is a species of Dianthus. It is probably native to the Mediterranean region but its exact range is unknown due to extensive cultivation for the last 2,000 years. It is the wild ancestor of the garden Carnation.It is a herbaceous perennial plant growing to 80 cm tall...
,
geraniumPelargonium is a genus of flowering plants which includes about 200 species of perennials, succulents, and shrubs, commonly known as geraniums or storksbills. Confusingly, Geranium is the correct botanical name of a separate genus of related plants often called Cranesbills. Both genera are in...
,
petuniaPetunia is a trumpet shaped, widely-cultivated genus of flowering plants of South American origin, in the family Solanaceae. The popular flower derived its name from French, which took the word petun 'tobacco' from a Tupi-Guarani language. Most of the varieties seen in gardens are hybrids...
,
roseA rose is a perennial flower shrub or vine of the genus Rosa, within the family Rosaceae, that contains over 100 species and comes in a variety of colours. The species form a group of erect shrubs, and climbing or trailing plants, with stems that are often armed with sharp prickles...
, and many others.
Ethylene can cause significant economic losses for florists, markets, suppliers, and growers. Researchers have come up with several ways to inhibit ethylene, including inhibiting ethylene synthesis and inhibiting ethylene perception. Aminoethoxyvinylglycine (AVG), Aminooxyacetic acid (AOA), and silver ions are ethylene inhibitors. Inhibiting ethylene synthesis is less effective for reducing post-harvest losses since ethylene from other sources can still have an effect. By inhibiting ethylene perception, fruits, plants and flowers don't respond to ethylene produced endogenously or from exogenous sources. Inhibitors of ethylene perception include compounds that have a similar shape to ethylene, but do not elicit the ethylene response. One example of an ethylene perception inhibitor is
1-methylcyclopropene1-Methylcyclopropene is a cyclopropene derivative used as a synthetic plant growth regulator. It is structurally related to the natural plant hormone ethylene and it is used commercially to slow down the ripening of fruit and to help maintain the freshness of cut flowers.-Chemical...
(1-MCP).
Commercial growers of bromeliads, including
pineapplePineapple is the common name for an edible tropical plant and also its fruit. It is native to the southern part of Brazil, and Paraguay. Pineapple is eaten fresh or canned and is available as a juice or in juice combinations. It is used in desserts, salads, as a complement to meat dishes and in...
plants, use ethylene to induce flowering. Plants can be induced to flower either by treatment with the gas in a chamber, or by placing a
bananaBanana is the common name for a herbaceous plants of the genus Musa, and the commonly eaten fruit it produces. They are native to the tropical region of Southeast Asia, and are likely to have been first domesticated in Papua New Guinea. Today, they are cultivated throughout the tropics.Banana...
peel next to the plant in an enclosed area.
Effects upon humans
Depending on the concentration, ethylene gas can cause a pleasant odor, euphoria,
nauseaNausea is the sensation of unease and discomfort in the stomach with an urge to vomit.-Causes:...
,
hyperglycemiaHyperglycemia, hyperglycaemia, or high blood sugar is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a blood glucose level of 10+ mmol/L , but symptoms may not start to become noticeable until later numbers such as 15-20+ mmol/L or...
, a variety of psychological effects,
blood pressureBlood pressure is the pressure exerted by circulating blood on the walls of blood vessels, and is one of the principal vital signs. During each heartbeat, BP varies between a maximum and a minimum pressure...
changes,
hypoxiaHypoxia is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
, loss of consciousness, or death.
Symptoms
Ethylene has a pleasant sweet faint odor, and has a slightly sweet taste, and as it enhances fruit ripening, assists in the development of odour-active aroma volatiles (especially
esterEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s), which are responsible for the specific smell of each kind of flower or fruit.
In mild doses, ethylene produces states of euphoria, associated with stimulus to the pleasure centers of the human brain.
Exposure at 37.5% for 15 minutes may result in marked memory disturbances. Humans exposed to as much as 50% ethylene in air, whereby the oxygen availability is decreased to 10%, experience a complete loss of consciousness and may subsequently die due to
hypoxiaHypoxia is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
.
Symptoms of ethylene exposure include the following.
Mild exposure in air
- Percent of O2 saturation at 90%
- Night vision decreased
- Mild euphoria reported.
Moderate exposure in air
- Percent of O2 saturation at 82 to 90%
- Respiratory rate has compensatory increase
- Pulse, also a compensatory increase
- Night vision is decreased further, focus is simplified
- Performance ability is somewhat reduced, mild distortion to speech, utterances increasingly ambiguous.
- General alertness level is somewhat reduced to anything but central concerns
- Symptoms may begin in those patients with pre-existing significant cardiac, pulmonary, or hematologic diseases.
- Euphoria
High concentration in air
- Percent of O2 saturation at 64 to 82%
- Compensatory mechanisms increasingly become inadequate
- Air hunger, gasping for breath
- Fatigue, lassitude, inability to maintain balance
- Tunnel vision, out-of-body experiences
- Dizziness
- Mild to persistent headache
- Belligerence, certainty of truth
- Extreme euphoria, belief in capacities of the self enhanced
- Visual acuity is reduced, dreamlike seeing of visions
- Numbness and tingling of extremities
- Hyperventilation
- Distortions of judgement, abnormal or illogical inferences drawn
- Memory loss after event
- Increased cyanosis
- Decreased ability for escape from toxic environment
Very high concentration in air
- Percent of O2 saturation at 60 to 70% or less
- Further deterioration in judgment and coordination may occur in 3 to 5 minutes or less
Severe oxygen deprivation
- Loss of consciousness results when the air contains about 11% of oxygen.
- Death occurs quickly when the oxygen content falls to 8% or less.
Very high concentrations in oxygen
- Prolonged inhalation of about 85% in oxygen is slightly toxic, resulting in a slow fall in blood pressure
Blood pressure is the pressure exerted by circulating blood on the walls of blood vessels, and is one of the principal vital signs. During each heartbeat, BP varies between a maximum and a minimum pressure...
.
- At about 94% in oxygen, ethylene is acutely fatal.
Medical Use
Ethylene has long been in use as an inhalatory anaesthetic. When used as a surgical anaesthetic, it is always administered with oxygen with an increased risk of fire. In such cases, however, it acts as a simple, rapid anaesthetic having a quick recovery.
Historical Significance
Many geologists and scholars believe that the famous Greek Oracle at
DelphiDelphi is both an archaeological site and a modern town in Greece on the south-western spur of Mount Parnassus in the valley of Phocis...
(the
PythiaThe Pythia was the priestess presiding over the Oracle of Apollo at Delphi, located on the slopes of Mount Parnassus. The Pythia was widely credited with giving prophecies inspired by Apollo, giving her a prominence unusual for a woman in male-dominated ancient Greece. The Delphic oracle was...
) went into her trance-like state as an effect of ethylene rising from ground faults.
Safety
There is no evidence to indicate that prolonged exposure to
low concentrations of ethylene can result in chronic effects. Prolonged exposure to high concentrations may cause permanent effects because of oxygen deprivation. Prolonged inhalation of about 85% in oxygen (a relatively high concentration) is also slightly toxic, resulting in a slow fall in
blood pressureBlood pressure is the pressure exerted by circulating blood on the walls of blood vessels, and is one of the principal vital signs. During each heartbeat, BP varies between a maximum and a minimum pressure...
. At about 94% in oxygen, ethylene is acutely fatal.
It shows little or no carcinogenic or mutagenic properties. Although there may be moderate hyperglycemia, post operative nausea - while higher than nitrous oxide - is less than in the use of
cyclopropaneCyclopropane is a cycloalkane molecule with the molecular formula C
3H
6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms....
. During the induction and early phases, blood pressure may rise a little, but this effect may be due to patient anxiety, as blood pressure quickly returns to normal. Cardiac arrythmias are infrequent and cardio-vascular effects are benign.
See also
Further reading
Ethylene hormone receptor action in Arabidopsis. Chang C, Stadler R. Bioessays. 2001 Jul;23(7):619-27. Review. PMID: 11462215
Differential petiole growth in Arabidopsis thaliana: photocontrol and hormonal regulation. Millenaar FF, van Zanten M, Cox MC, Pierik R, Voesenek LA, Peeters AJ. New Phytol. 2009 Jun 24. [Epub ahead of print] PMID: 19558423
External links