Ethylene

Ethylene
Names
Preferred IUPAC name
Ethene
Systematic IUPAC name
Ethene
Other names
Refrigerant R-1150
Identifiers
3D model (JSmol)
1730731
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.742 Edit this at Wikidata
EC Number
  • 200-815-3
214
KEGG
RTECS number
  • KU5340000
UNII
UN number 1962 1038
  • InChI=1S/C2H4/c1-2/h1-2H2 checkY
    Key: VGGSQFUCUMXWEO-UHFFFAOYSA-N checkY
  • InChI=1/C2H4/c1-2/h1-2H2
    Key: VGGSQFUCUMXWEO-UHFFFAOYAE
  • C=C
Properties
C
2H
4
Molar mass 28.054 g·mol−1
Appearance colourless gas
Density 1.178 kg/m3 at 15 °C, gas
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); 2.9 mg/L
Solubility in ethanol 4.22 mg/L
Solubility in diethyl ether good
Acidity (pKa) 44
Conjugate acid Ethenium
−15.30·10−6 cm3/mol
Viscosity 10.28 μPa·s
Structure
D2h
zero
Thermochemistry
219.32 J·K−1·mol−1
+52.47 kJ/mol
Hazards
GHS labelling:
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
Propylene
Supplementary data page
Ethylene (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkYX markN ?)

Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula C2H4 or H2C=CH2. It is a colourless, flammable odorless gas. It is the simplest alkene (a hydrocarbon with carbon–carbon double bonds).

Ethylene is widely used in the chemical industry, and its worldwide production (over 225 million tonnes in 2022) exceeds that of any other organic compound. Much of this production goes toward creating polyethylene, which is a widely used plastic containing polymer chains of ethylene units in various chain lengths.

Ethylene is also an important natural plant hormone and is used in agriculture to induce ripening of fruits. The hydrate of ethylene is ethanol.

Structure and properties

Orbital description of bonding between ethylene and a transition metal

This hydrocarbon has four hydrogen atoms bound to a pair of carbon atoms that are connected by a double bond. All six atoms that comprise ethylene are coplanar. The H-C-H angle is 117.4°, close to the 120° for ideal sp² hybridized carbon. The molecule is also relatively weak: rotation about the C-C bond is a high energy process that requires breaking the π-bond by supplying heat at 50 °C.[citation needed]

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

Being a simple molecule, ethylene is spectroscopically simple. Its UV-Vis spectrum is still used as a test of theoretical methods.

Production

To give a sense of the scale of production, 107 million tonnes were produced in 2005. This technology results in significant greenhouse gas emissions, namely significant amounts of carbon dioxide.

Industrial process

Ethylene is produced by several methods in the petrochemical industry. A primary method is steam cracking (SC) where hydrocarbons and steam are heated to 750–950 °C. This process converts large hydrocarbons into smaller ones and introduces unsaturation. When ethane is the feedstock, ethylene is the product. Ethylene is separated from the resulting mixture by repeated compression and distillation. 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). Other procedures employed for the production of ethylene include Fischer-Tropsch synthesis and methanol-to-olefins (MTO).

Laboratory synthesis

Although of great value industrially, ethylene is rarely synthesized in the laboratory and is ordinarily purchased. It can be produced via dehydration of ethanol with sulfuric acid or in the gas phase with activated alumina.

Biosynthesis

Ethylene is produced biologically through several pathways. In plants, it is synthesized from methionine via S-adenosylmethionine (SAM) and 1-aminocyclopropane-1-carboxylic acid (ACC), its immediate precursor. ACC synthase converts SAM into ACC, which is then converted into ethylene by ACC oxidase. The ACC oxidase reaction requires molecular oxygen, ferrous iron and ascorbate, and releases carbon dioxide and cyanide as coproducts.

Some microorganisms produce ethylene through pathways that do not involve ACC. In the bacterium Pseudomonas syringae, an ethylene-forming enzyme (EFE) catalyses the conversion of 2-oxoglutarate (α-ketoglutarate) into ethylene and carbon dioxide. This reaction requires molecular oxygen, ferrous iron and L-arginine. The enzyme also catalyses a separate reaction involving arginine hydroxylation and the conversion of 2-oxoglutarate into succinate and carbon dioxide.

Another microbial pathway proceeds through 2-keto-4-methylthiobutyric acid (KMBA), a derivative of methionine. Ethylene production through this route has been demonstrated in the yeast Cryptococcus albidus and the fungus Botrytis cinerea.

The EFE pathway has also been investigated for biotechnological ethylene production. Introducing the bacterial EFE gene into cyanobacteria, including Synechocystis sp. PCC 6803, enables photosynthetic ethylene production from carbon dioxide using light as the energy source. Sustained ethylene production for more than four months has been demonstrated using engineered Synechocystis sp. PCC 6803 immobilized in cellulose nanofiber-based films and cultivated in a continuous-flow photobiofilm reactor.

Uses

Diagram of uses of ethene

Major industrial reactions of ethylene include in order of scale: 1) polymerization, 2) oxidation, 3) halogenation and hydrohalogenation, 4) alkylation, 5) hydration, 6) oligomerization, and 7) hydroformylation. In the United States and Europe, approximately 90% of ethylene is used to produce ethylene oxide, ethylene dichloride, ethylbenzene and polyethylene.

Main industrial uses of ethylene. Clockwise from the upper right: its conversions to ethylene oxide, precursor to ethylene glycol; to ethylbenzene, precursor to styrene; to various kinds of polyethylene; to ethylene dichloride, precursor to vinyl chloride.

Polymerization

Polyethylene production uses more than half of the world's ethylene supply. Polyethylene, also called polyethene and polythene, is the world's most widely used plastic. It is primarily used to make films in packaging, carrier bags and trash liners. Linear alpha-olefins, produced by oligomerization (formation of short-chain molecules) are used as precursors, detergents, plasticisers, synthetic lubricants, additives, and also as co-monomers in the production of polyethylenes.

Oxidation

Ethylene is oxidized to produce ethylene oxide, a key raw material in the production of surfactants and ethylene glycol.

Ethylene oxidation in the presence of a palladium catalyst can form acetaldehyde. This conversion once was a major industrial process. The process proceeds via the complexation of ethylene to a Pd(II) center.

Halogenation and hydrohalogenation

The halogenation of ethylene gives ethylene dichloride. The handling of chlorine entails "oxychlorination". Some products derived from this group are polyvinyl chloride, trichloroethylene, perchloroethylene, polyvinylidene chloride, and copolymers.

Alkylation

A major chemical intermediate from alkylation of ethylene is ethylbenzene, precursor to styrene. Styrene is used principally in polystyrene for packaging and insulation, as well as in styrene-butadiene rubber for tires and footwear. Smaller scale intermediates include ethyltoluene and alkylaluminium compounds. Products of these intermediates include polystyrene, unsaturated polyesters and ethylene-propylene terpolymers.

Oxo reaction

Ethylene is a precursor to propionic acid by the hydrocarboxylation using nickel carbonyl as the catalyst:

Hydrocarboxylation of ethene with carbon monoxide and water to form propionic acid in the presence of nickel tetracarbonyl as catalyst

Hydration

Ethylene has long represented the major non-fermentative precursor to ethanol. The original method entailed its conversion to diethyl sulfate, followed by hydrolysis. The main method practiced since the mid-1990s is the direct hydration of ethylene catalyzed by solid acid catalysts:

C2H4 + H2O → CH3CH2OH

Dimerization to butenes

Ethylene is dimerized by hydrovinylation to give n-butenes using processes licensed by Lummus or IFP. The Lummus process produces mixed n-butenes (primarily 2-butenes) while the IFP process produces 1-butene. 1-Butene is used as a comonomer in the production of certain kinds of polyethylene.

Fruit and flowering

Ethylene is a hormone that affects the ripening and flowering of many plants. It is widely used to control freshness in horticulture and fruits. The scrubbing of naturally occurring ethylene delays ripening. Harvested fruit bound for shipping are often stored in oxygen-controlled environments as well as use of absorbents like zeolites to reduce the speed of ripening reaction.

Ligand

Chlorobis(ethylene)rhodium dimer is a well-studied complex of ethylene.

Ethylene is a fundamental ligand in transition metal alkene complexes. One of the first organometallic compounds, Zeise's salt is a complex of ethylene. Useful reagents containing ethylene include Pt(PPh3)2(C2H4) and Rh2Cl2(C2H4)4. The Rh-catalysed hydroformylation of ethylene is conducted on an industrial scale to provide propionaldehyde.

History

Ethylene appears to have been discovered by Johann Joachim Becher, who obtained it by heating ethanol with sulfuric acid; he mentioned the gas in his Physica Subterranea (1669). Joseph Priestley also mentions the gas in his Experiments and observations relating to the various branches of natural philosophy: with a continuation of the observations on air (1779), where he reports that Jan Ingenhousz saw ethylene synthesized in the same way by a Mr. Enée in Amsterdam in 1777 and that Ingenhousz subsequently produced the gas himself. The properties of ethylene were studied in 1795 by four Dutch chemists, Johann Rudolph Deimann, Adrien Paets van Troostwyck, Anthoni Lauwerenburgh and Nicolas Bondt, who found that it differed from hydrogen gas and that it contained both carbon and hydrogen. This group also discovered that ethylene could be combined with chlorine to produce the Dutch oil, 1,2-dichloroethane; this discovery gave ethylene the name used for it at that time, olefiant gas (oil-making gas.) 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
2H
4) was the "daughter of ethyl" (C
2H
5).[citation needed] The name ethylene was used in this sense as early as 1852.

In 1866, the German chemist August Wilhelm von Hofmann 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 alkane. 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.

Following experimentation by Luckhardt, Crocker, and Carter at the University of Chicago, ethylene was used as an anesthetic. It remained in use through the 1940s, even while chloroform was being phased out.

Nomenclature

The 1979 IUPAC nomenclature rules made an exception for retaining the non-systematic name ethylene; however, this decision was reversed in the 1993 rules, and it remains unchanged in the newest 2013 recommendations, so the IUPAC name is now ethene. In the IUPAC system, the name ethylene is reserved for the divalent group -CH2CH2-. Hence, names like ethylene oxide and ethylene dibromide are permitted, but the use of the name ethylene for the two-carbon alkene is not. Nevertheless, use of the name ethylene for H2C=CH2 (and propylene for H2C=CHCH3) is still prevalent among chemists in North America.

Safety

Like all hydrocarbons, ethylene is a combustible asphyxiant. It is listed as an IARC group 3 agent, since there is no current evidence that it causes cancer in humans.

See also

References

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  21. ↑ Martinez, Salette; Fellner, Matthias; Herr, Caitlyn Q.; Ritchie, Anastasia; Hu, Jian; Hausinger, Robert P. (2017). "Structures and Mechanisms of the Non-Heme Fe(II)- and 2-Oxoglutarate-Dependent Ethylene-Forming Enzyme: Substrate Binding Creates a Twist". Journal of the American Chemical Society. 139 (34): 11980–11988. doi:10.1021/jacs.7b06186. PMC 5599930. PMID 28780854.
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    Gregory W (1857). Handbook of organic chemistry (4th American ed.). A.S. Barnes & Co. p. 157.
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