Ethylene(IUPACname:ethene) is ahydrocarbonwhich has the formulaC2H4orH2C=CH2.It is a colourless,flammablegas with a faint "sweet andmusky"odour when pure.[7]It is the simplestalkene(a hydrocarbon withcarbon–carbondouble bonds).

Ethylene
Names
Preferred IUPAC name
Ethene[1]
Systematic IUPAC name
Ethene
Other names
Refrigerant R-1150
Identifiers
3D model (JSmol)
1730731
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.742Edit this at Wikidata
EC Number
  • 200-815-3
214
KEGG
RTECS number
  • KU5340000
UNII
UN number 1962 1038
  • InChI=1S/C2H4/c1-2/h1-2H2checkY
    Key: VGGSQFUCUMXWEO-UHFFFAOYSA-NcheckY
  • InChI=1/C2H4/c1-2/h1-2H2
    Key: VGGSQFUCUMXWEO-UHFFFAOYAE
  • C=C
Properties
C
2
H
4
Molar mass 28.054g·mol−1
Appearance colourless gas
Density 1.178 kg/m3at 15 °C, gas[2]
Melting point −169.2 °C (−272.6 °F; 104.0 K)
Boiling point −103.7 °C (−154.7 °F; 169.5 K)
131 mg/L (25 °C);[3]2.9 mg/L[4]
Solubilityinethanol 4.22 mg/L[4]
Solubilityindiethyl ether good[4]
Acidity(pKa) 44
Conjugate acid Ethenium
-15.30·10−6cm3/mol
Viscosity 10.28 μPa·s[5]
Structure
D2h
zero
Thermochemistry
219.32 J·K−1·mol−1
+52.47 kJ/mol
Hazards
GHSlabelling:
GHS02: FlammableGHS07: Exclamation mark
Danger
H220,H336
P210,P261,P271,P304+P340,P312,P377,P381,P403,P403+P233,P405,P501
NFPA 704(fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
2
4
2
Flash point −136 °C (−213 °F; 137 K)
542.8 °C (1,009.0 °F; 815.9 K)
Safety data sheet(SDS) ICSC 0475
Related compounds
Related compounds
Ethane
Acetylene
Propene
Supplementary data page
Ethylene (data page)
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).

Ethylene is widely used in the chemical industry, and its worldwide production (over 150 milliontonnesin 2016[8]) exceeds that of any otherorganic compound.[9][10]Much of this production goes toward creatingpolythene,which is a widely usedplasticcontainingpolymerchains of ethylene units in various chain lengths. Productionemits greenhouse gases,includingmethanefromfeedstockproduction andcarbon dioxidefrom any non-sustainable energyused.

Ethylene is also an important naturalplant hormoneand is used in agriculture to induceripeningoffruits.[11]Thehydrateof ethylene isethanol.

Structure and properties

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Orbital description of bonding between ethylene and a transition metal

Thishydrocarbonhas fourhydrogenatomsbound to a pair ofcarbonatoms that are connected by adouble bond.All six atoms that comprise ethylene arecoplanar.The H-C-Hangleis 117.4°, close to the 120° for ideal sp²hybridizedcarbon. The molecule is also relatively weak: rotation about the C-C bond is a very low energy process that requires breaking theπ-bondby supplying heat at 50 °C.[citation needed]

Theπ-bondin the ethylene molecule is responsible for its useful reactivity. The double bond is a region of highelectron density,thus it is susceptible to attack byelectrophiles.Many reactions of ethylene are catalyzed by transition metals, which bind transiently to the ethylene using both the π and π* orbitals.[citation needed]

Being a simple molecule, ethylene is spectroscopically simple. Its UV-visspectrumis still used as a test of theoretical methods.[12]

Uses

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Diagram of uses of ethene

Major industrial reactions of ethylene include in order of scale: 1)polymerization,2)oxidation,3)halogenationandhydrohalogenation,4)alkylation,5)hydration,6)oligomerization,and 7)hydroformylation.In theUnited StatesandEurope,approximately 90% of ethylene is used to produceethylene oxide,ethylene dichloride,ethylbenzeneandpolyethylene.[13]Most of the reactions with ethylene areelectrophilic addition.[citation needed]

Main industrial uses of ethylene. Clockwise from the upper right: its conversions toethylene oxide,precursor toethylene glycol;toethylbenzene,precursor tostyrene;to various kinds ofpolyethylene;toethylene dichloride,precursor tovinyl chloride.

Polymerization

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Polyethylene production uses more than half of the world's ethylene supply. Polyethylene, also calledpolyetheneandpolythene,is the world's most widely used plastic. It is primarily used to make films inpackaging,carrier bagsand trashliners.LinearAlpha -olefins,produced byoligomerization(formation of short-chain molecules) are used asprecursors,detergents,plasticisers,synthetic lubricants,additives, and also as co-monomers in the production of polyethylenes.[13]

Oxidation

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Ethylene isoxidizedto produceethylene oxide,a key raw material in the production ofsurfactantsanddetergentsbyethoxylation.Ethylene oxide is also hydrolyzed to produceethylene glycol,widely used as an automotive antifreeze as well as higher molecular weight glycols,glycol ethers,andpolyethylene terephthalate.[14][15]

Ethylene oxidation in the presence of a palladium catalyst can formacetaldehyde.This conversion remains a major industrial process (10M kg/y).[16]The process proceeds via the initial complexation of ethylene to a Pd(II) center.[citation needed]

Halogenation and hydrohalogenation

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Major intermediates from thehalogenationandhydrohalogenationof ethylene includeethylene dichloride,ethyl chloride,andethylene dibromide.The addition of chlorine entails "oxychlorination",i.e. chlorine itself is not used. Some products derived from this group arepolyvinyl chloride,trichloroethylene,perchloroethylene,methyl chloroform,polyvinylidene chlorideandcopolymers,andethyl bromide.[17]

Alkylation

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Major chemical intermediates from thealkylationwith ethylene isethylbenzene,precursor tostyrene.Styrene is used principally inpolystyrenefor packaging and insulation, as well as instyrene-butadienerubber for tires and footwear. On a smaller scale,ethyltoluene,ethylanilines, 1,4-hexadiene, andaluminiumalkyls. Products of these intermediates includepolystyrene,unsaturatedpolyestersand ethylene-propyleneterpolymers.[17]

Oxo reaction

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Thehydroformylation(oxo reaction) of ethylene results inpropionaldehyde,a precursor topropionic acidandn-propyl alcohol.[17]

Hydration

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Ethylene has long represented the major nonfermentative precursor toethanol.The original method entailed its conversion todiethyl sulfate,followed by hydrolysis. The main method practiced since the mid-1990s is the direct hydration of ethylene catalyzed bysolid acid catalysts:[18]

C2H4+ H2O → CH3CH2OH

Dimerization to butenes

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Ethylene isdimerizedbyhydrovinylationto given-butenes using processes licensed by Lummus orIFP.The Lummus process produces mixedn-butenes (primarily2-butenes) while the IFP process produces1-butene.1-Butene is used as acomonomerin the production of certain kinds ofpolyethylene.[19]

Fruit and flowering

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Ethylene is a hormone that affects the ripening and flowering of many plants. It is widely used to control freshness inhorticultureandfruits.[20]The scrubbing of naturally occurring ethylene delays ripening.[21]Adsorption of ethylene by nets coated intitanium dioxidegel has also been shown to be effective.[22]

Niche uses

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An example of a niche use is as ananesthetic agent(in an 85% ethylene/15% oxygen ratio).[23]Another use is as a welding gas.[13][24]It is also used as a refrigerant gas for low temperature applications under the name R-1150.[25]

Production

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Global ethylene production was 107 million tonnes in 2005,[9]109 million tonnes in 2006,[26]138 million tonnes in 2010, and 141 million tonnes in 2011.[27]By 2013, ethylene was produced by at least 117 companies in 32 countries. To meet the ever-increasing demand for ethylene, sharp increases in production facilities are added globally, particularly in theMideastand inChina.[28]Productionemits greenhouse gas,namely significant amounts of carbon dioxide.[29]

Industrial process

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Ethylene is produced by several methods in thepetrochemical industry.A primary method issteam cracking(SC) where hydrocarbons and steam are heated to 750–950 °C. This process converts large hydrocarbons into smaller ones and introduces unsaturation. Whenethaneis the feedstock, ethylene is the product. Ethylene is separated from the resulting mixture by repeatedcompressionanddistillation.[17]In Europe and Asia, ethylene is obtained mainly from cracking naphtha, gasoil and condensates with the coproduction of propylene, C4 olefins and aromatics (pyrolysis gasoline).[30]Other technologies employed for the production of ethylene includeFischer-Tropsch synthesisandmethanol-to-olefins(MTO).[31]

Laboratory synthesis

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Although of great value industrially, ethylene is rarely synthesized in the laboratory and is ordinarily purchased.[32]It can be produced via dehydration ofethanolwithsulfuric acidor in the gas phase withaluminium oxideoractivated alumina.[33]

Biosynthesis

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Ethylene is produced frommethioninein nature. The immediate precursor is1-aminocyclopropane-1-carboxylic acid.[34]

Ligand

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Chlorobis(ethylene)rhodium dimeris a well-studied complex of ethylene.[35]

Ethylene is a fundamentalligandintransition metal alkene complexes.One of the first organometallic compounds,Zeise's saltis a complex of ethylene. Useful reagents containing ethylene include Pt(PPh3)2(C2H4) and Rh2Cl2(C2H4)4.The Rh-catalysedhydroformylationof ethylene is conducted on an industrial scale to providepropionaldehyde.[36]

History

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Some geologists and scholars believe that the famous Greek Oracle atDelphi(thePythia) went into her trance-like state as an effect of ethylene rising from ground faults.[37]

Ethylene appears to have been discovered byJohann Joachim Becher,who obtained it by heatingethanolwith sulfuric acid;[38]he mentioned the gas in hisPhysica Subterranea(1669).[39]Joseph Priestleyalso mentions the gas in hisExperiments and observations relating to the various branches of natural philosophy: with a continuation of the observations on air(1779), where he reports thatJan Ingenhouszsaw ethylene synthesized in the same way by a Mr. Enée in Amsterdam in 1777 and that Ingenhousz subsequently produced the gas himself.[40]The properties of ethylene were studied in 1795 by fourDutchchemists, Johann Rudolph Deimann, Adrien Paets van Troostwyck, Anthoni Lauwerenburgh and Nicolas Bondt, who found that it differed fromhydrogengas and that it contained both carbon and hydrogen.[41]This group also discovered that ethylene could be combined withchlorineto produce theDutch oil,1,2-dichloroethane;this discovery gave ethylene the name used for it at that time,olefiant gas(oil-making gas.)[42]The term olefiant gas is in turn the etymological origin of the modern word "olefin", the class of hydrocarbons in which ethylene is the first member.[citation needed]

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
2
H
4
) was the "daughter ofethyl"(C
2
H
5
). The name ethylene was used in this sense as early as 1852.[43]

In 1866, theGermanchemistAugust Wilhelm von Hofmannproposed 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 parentalkane.[44]In this system, ethylene becameethene.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 theIUPACnomenclature. However, by that time, the name ethylene was deeply entrenched, and it remains in wide use today, especially in the chemical industry.

Following experimentation by Luckhardt, Crocker, and Carter at the University of Chicago,[45]ethylene was used as an anesthetic.[46][7]It remained in use through the 1940s use even while chloroform was being phased out. Its pungent odor and its explosive nature limit its use today.[47]

Nomenclature

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The 1979 IUPAC nomenclature rules made an exception for retaining the non-systematic nameethylene;[48]however, this decision was reversed in the 1993 rules,[49]and it remains unchanged in the newest 2013 recommendations,[50]so the IUPAC name is nowethene.In the IUPAC system, the nameethyleneis reserved for thedivalentgroup -CH2CH2-. Hence, names likeethylene oxideandethylene dibromideare permitted, but the use of the nameethylenefor the two-carbon alkene is not. Nevertheless, use of the nameethylenefor H2C=CH2(and propylene for H2C=CHCH3) is still prevalent among chemists in North America.[51]

Greenhouse gas emissions

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"A key factor affecting petrochemicals life-cycle emissions is the methane intensity of feedstocks, especially in the production segment."[52]Emissions from cracking of naptha and natural gas (common in the US as gas is cheap there) depend a lot on the source of energy (for example gas burnt to provide high temperatures[53]) but that from naptha is certainly more per kg of feedstock.[54]Both steam cracking and production from natural gas via ethane are estimated to emit 1.8 to 2kg of CO2 per kg ethylene produced,[55]totalling over 260 million tonnes a year.[56]This is more than all other manufactured chemicals except cement and ammonia.[57]According to a 2022 report using renewable or nuclear energy could cut emissions by almost half.[54]

Safety

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Like all hydrocarbons, ethylene is a combustibleasphyxiant.It is listed as anIARCgroup 3 agent,since there is no current evidence that it causes cancer in humans.[58]

See also

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  • RediRipe,an ethylene detector for fruits.

References

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