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{{Short description|Organic compound (H<sub>3</sub>C–CH<sub>3</sub>)}}
{{Short description|Organic compound (H<sub>3</sub>C–CH<sub>3</sub>)}}
{{About|the chemical compound|the emergency service protocol|ETHANE}}
{{About|the chemical compound|the emergency service protocol|ETHANE}}
{{Distinguish|Ethene|Ethyne|Methane}}
{{distinguish|ethene|ethyne}}
{{Chembox
{{Chembox
| Watchedfields = changed
| Watchedfields = changed
| verifiedrevid = 477168309
| verifiedrevid = 477168309
| ImageFile1 = Ethane-staggered-CRC-MW-dimensions-2D.png
| ImageFile1 = Ethane-staggered-CRC-MW-dimensions-2D.png
| ImageFile1_Ref = {{chemboximage|correct|??}}
| ImageFile1_Ref = {{chemboximage|correct|??}}
| ImageName1 = Skeletal formula of ethane with all hydrogens and carbons shown
| ImageName1 = Skeletal formula of ethane with all hydrogens and carbons shown
| ImageCaption1 = [[Molecular geometry]] of ethane based on [[rotational spectroscopy]].
| ImageCaption1 = [[Molecular geometry]] of ethane based on [[rotational spectroscopy]].
| ImageFile2 = Ethan Skelett.svg
| ImageFile2 = Ethan Skelett.svg
| ImageFile2_Ref = {{chemboximage|correct|??}}
| ImageFile2_Ref = {{chemboximage|correct|??}}
| ImageName2 = Skeletal formula of ethane with all implicit carbons shown, and all explicit hydrogens added
| ImageName2 = Skeletal formula of ethane with all implicit carbons shown, and all explicit hydrogens added
| ImageFileL2 = Ethane-A-3D-balls.png
| ImageFileL2 = Ethane-A-3D-balls.png
| ImageFileL2_Ref = {{chemboximage|correct|??}}
| ImageFileL2_Ref = {{chemboximage|correct|??}}
| ImageNameL2 = Ball and stick model of ethane
| ImageNameL2 = Ball and stick model of ethane
| ImageFileR2 = Ethane-3D-vdW.png
| ImageFileR2 = Ethane-3D-vdW.png
| ImageFileR2_Ref = {{chemboximage|correct|??}}
| ImageFileR2_Ref = {{chemboximage|correct|??}}
| ImageNameR2 = Spacefill model of ethane
| ImageNameR2 = Spacefill model of ethane
| OtherNames = {{Unbulleted list|Dimethyl ({{chem2|CH3CH3}}, {{chem2|Me2}} or {{chem2|(CH3)2}})|Ethyl hydride}}
| PIN = Ethane<ref>{{Cite book|author=[[International Union of Pure and Applied Chemistry]]|date=2014|title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013|publisher=[[Royal Society of Chemistry|The Royal Society of Chemistry]]|page=133|doi=10.1039/9781849733069|isbn=978-0-85404-182-4|quote=The saturated unbranched acyclic hydrocarbons C<sub>2</sub>H<sub>6</sub>, C<sub>3</sub>H<sub>8</sub>, and C<sub>4</sub>H<sub>10</sub> have the retained names ethane, propane, and butane, respectively.|ref={{sfnref|IUPAC|2014}}}}</ref>
| PIN = Ethane<ref>{{Cite book|author=[[International Union of Pure and Applied Chemistry]]|date=2014|title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013|publisher=[[Royal Society of Chemistry|The Royal Society of Chemistry]]|page=133|doi=10.1039/9781849733069|isbn=978-0-85404-182-4|quote=The saturated unbranched acyclic hydrocarbons C<sub>2</sub>H<sub>6</sub>, C<sub>3</sub>H<sub>8</sub>, and C<sub>4</sub>H<sub>10</sub> have the retained names ethane, propane, and butane, respectively.|ref={{sfnref|IUPAC|2014}}}}</ref>
| SystematicName = Dicarbane (never recommended{{sfn|IUPAC|2014|p=4|ps=. "Similarly, the retained names 'ethane', 'propane', and 'butane' were never replaced by systematic names 'dicarbane', 'tricarbane', and 'tetracarbane' as recommended for analogues of silane, 'disilane'; phosphane, 'triphosphane'; and sulfane, 'tetrasulfane'."}})
| SystematicName = Dicarbane (never recommended{{sfn|IUPAC|2014|p=4|ps=. "Similarly, the retained names 'ethane', 'propane', and 'butane' were never replaced by systematic names 'dicarbane', 'tricarbane', and 'tetracarbane' as recommended for analogues of silane, 'disilane'; phosphane, 'triphosphane'; and sulfane, 'tetrasulfane'."}})
|Section1={{Chembox Identifiers
| Section1 = {{Chembox Identifiers
| CASNo = 74-84-0
| CASNo = 74-84-0
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo_Ref = {{cascite|correct|CAS}}
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| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
}}
}}
|Section2={{Chembox Properties
| Section2 = {{Chembox Properties
| C=2 | H=6
| C=2 | H=6
| Appearance = Colorless gas
| Appearance = Colorless gas
| Odor = Odorless
| Odor = Odorless
| Density = {{Unbulleted list| 1.3562{{nbsp}}kg/m<sup>3</sup> (gas at 0&nbsp;°C)<ref name=pubchem>{{cite web|title=Ethane – Compound Summary|url=https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=6324&loc=ec_rcs|work=PubChem Compound|publisher=National Center for Biotechnology Information|access-date=7 December 2011|location=USA|date=16 September 2004}}</ref>}}<br />
| Density = {{Unbulleted list| 1.3562{{nbsp}}kg/m<sup>3</sup> (gas at 0&nbsp;°C)<ref name=pubchem>{{cite web|title=Ethane – Compound Summary|url=https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=6324&loc=ec_rcs|work=PubChem Compound|publisher=National Center for Biotechnology Information|access-date=7 December 2011|location=US|date=16 September 2004}}</ref>}}<br />
544.0&nbsp;kg/m<sup>3</sup> (liquid at -88,5&nbsp;°C)<br />
544.0&nbsp;kg/m<sup>3</sup> (liquid at -88,5&nbsp;°C)<br />
206&nbsp;kg/m<sup>3</sup> (at critical point 305.322&nbsp;K)
206&nbsp;kg/m<sup>3</sup> (at critical point 305.322&nbsp;K)
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| BoilingPtK = 184.6
| BoilingPtK = 184.6
| CriticalTP = {{convert|305.32 |K}} {{convert|48.714|bar}}
| CriticalTP = {{convert|305.32 |K}} {{convert|48.714|bar}}
| Solubility = 56.8 mg L<sup>−1</sup><ref>{{RubberBible86th|page=8.88}}</ref>
| Solubility = 56.8 mg/L<ref>{{RubberBible86th|page=8.88}}</ref>
| VaporPressure = 3.8453 MPa (at 21.1&nbsp;°C)
| VaporPressure = 3.8453 MPa (at 21.1&nbsp;°C)
| HenryConstant = 19 nmol Pa<sup>−1</sup> kg<sup>−1</sup>
| HenryConstant = 19 nmol Pa<sup>−1</sup> kg<sup>−1</sup>
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| MagSus = -37.37·10<sup>−6</sup> cm<sup>3</sup>/mol
| MagSus = -37.37·10<sup>−6</sup> cm<sup>3</sup>/mol
}}
}}
|Section3={{Chembox Thermochemistry
| Section3 = {{Chembox Thermochemistry
| DeltaHf = −84 kJ mol<sup>−1</sup>
| DeltaHf = −84 kJ mol<sup>−1</sup>
| DeltaHc = −1561.0–−1560.4 kJ mol<sup>−1</sup>
| DeltaHc = −1561.0–−1560.4 kJ mol<sup>−1</sup>
| HeatCapacity = 52.14{{Plusminus|0.39}} J K<sup>−1</sup> mol<sup>−1</sup> at 298 Kelvin<ref>{{Cite web |url=https://webbook.nist.gov/cgi/cbook.cgi?ID=C74840&Mask=1 |title=Ethane |access-date=2024-05-16 |website=webbook.nist.gov |agency=[[National Institute of Standards and Technology]]}}</ref>
| HeatCapacity = 52.49 J K<sup>−1</sup> mol<sup>−1</sup>
}}
}}
|Section4={{Chembox Hazards
| Section4 = {{Chembox Hazards
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0266.htm inchem.org]
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0266.htm inchem.org]
| GHSPictograms = {{GHS flame}}
| GHSPictograms = {{GHS flame}}
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| ExploLimits = 2.9–13%
| ExploLimits = 2.9–13%
}}
}}
|Section5={{Chembox Related
| Section5 = {{Chembox Related
| OtherFunction_label = alkanes
| OtherFunction_label = alkanes
| OtherFunction = {{Unbulleted list|[[Methane]]|[[Methyl iodide]]|[[Diiodomethane]]|[[Iodoform]]|[[Carbon tetraiodide]]|[[Ethyl iodide]]|[[Propane]]|[[n-Propyl iodide|''n''-Propyl iodide]]|[[Isopropyl iodide]]}}
| OtherFunction = {{Unbulleted list|[[Methane]]|[[Propane]]|[[Butane]]}}
| OtherCompounds = {{Unbulleted list|[[Disilane]]|[[Digermane]]}}
| OtherCompounds = {{Unbulleted list|[[Disilane]]|[[Digermane]]}}
}}
}}
}}
}}


'''Ethane''' ({{IPAc-en|US|ˈ|ɛ|θ|eɪ|n}} {{Respell|ETH|ayn}}, {{IPAc-en|UK|ˈ|iː|-}} {{Respell|EE|-}}) is an [[Organic compound|organic]] [[chemical compound]] with [[chemical formula]] {{chem|C|2|H|6}}. At [[Standard conditions for temperature and pressure|standard temperature and pressure]], ethane is a colorless, odorless [[gas]]. Like many [[hydrocarbon]]s, ethane is [[List of purification methods in chemistry|isolated]] on an industrial scale from [[natural gas]] and as a [[petrochemical]] by-product of [[oil refinery|petroleum refining]]. Its chief use is as [[feedstock]] for [[ethylene]] production.
'''Ethane''' ({{IPAc-en|US|ˈ|ɛ|θ|eɪ|n}} {{Respell|ETH|ayn}}, {{IPAc-en|UK|ˈ|iː|-}} {{Respell|EE|-}}) is a naturally occurring [[Organic compound|organic]] [[chemical compound]] with [[chemical formula]] {{chem|C|2|H|6}}. At [[standard temperature and pressure]], ethane is a colorless, odorless [[gas]]. Like many [[hydrocarbon]]s, ethane is [[List of purification methods in chemistry|isolated]] on an industrial scale from [[natural gas]] and as a [[petrochemical]] by-product of [[oil refinery|petroleum refining]]. Its chief use is as [[feedstock]] for [[ethylene]] production. The [[ethyl group]] is formally, although rarely practically, derived from ethane.

Related compounds may be formed by replacing a hydrogen atom with another [[functional group]]; the ethane [[moiety (chemistry)|moiety]] is called an [[ethyl group]]. For example, an ethyl group linked to a [[hydroxyl]] group yields [[ethanol]], the alcohol in beverages.


== History ==
== History ==
Ethane was first synthesised in 1834 by [[Michael Faraday]], applying [[electrolysis]] of a [[potassium acetate]] solution. He mistook the hydrocarbon product of this reaction for [[methane]] and did not investigate it further.<ref name=Faraday/>
Ethane was first synthesised in 1834 by [[Michael Faraday]], applying [[electrolysis]] of a [[potassium acetate]] solution. He mistook the hydrocarbon product of this reaction for [[methane]] and did not investigate it further.<ref name=Faraday/> The process is now called [[Kolbe electrolysis]]:
: [[acetate|CH<sub>3</sub>COO<sup></sup>]] CH<sub>3</sub> + [[carbon dioxide|CO<sub>2</sub>]] + [[electron|e<sup></sup>]]
: CH<sub>3</sub>• + •CH<sub>3</sub> → C<sub>2</sub>H<sub>6</sub>


During the period 1847–1849, in an effort to vindicate the [[radical theory]] of [[organic chemistry]], [[Hermann Kolbe]] and [[Edward Frankland]] produced ethane by the reductions of [[propionitrile]] ([[ethyl cyanide]])<ref name=Kolbe/> and [[ethyl iodide]]<ref name=Frankland/> with [[potassium]] metal, and, as did Faraday, by the electrolysis of [[Aqueous solution|aqueous]] acetates. They mistook the product of these reactions for the [[methyl radical]] ({{Chem2|CH3}}), of which ethane ({{Chem2|C2H6}}) is a [[Dimer (chemistry)|dimer]].
During the period 1847–1849, in an effort to vindicate the [[radical theory]] of [[organic chemistry]], [[Hermann Kolbe]] and [[Edward Frankland]] produced ethane by the reductions of [[propionitrile]] ([[ethyl cyanide]])<ref name=Kolbe/> and [[ethyl iodide]]<ref name=Frankland/> with [[potassium]] metal, and, as did Faraday, by the electrolysis of [[Aqueous solution|aqueous]] acetates. They mistook the product of these reactions for the [[methyl radical]] ({{Chem2|CH3}}), of which ethane ({{Chem2|C2H6}}) is a [[Dimer (chemistry)|dimer]].
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==Properties==
==Properties==
At standard temperature and pressure, ethane is a colorless, odorless gas. It has a boiling point of {{cvt|-88.5|°C|F}} and melting point of {{cvt|-182.8|°C|F}}. Solid ethane exists in several modifications.<ref name="Nes">{{cite journal |doi= 10.1107/S0567740878007037 |title= Single-crystal structures and electron density distributions of ethane, ethylene and acetylene. I. Single-crystal X-ray structure determinations of two modifications of ethane |journal= Acta Crystallographica Section B |volume=34 |issue=6 |page= 1947 |year= 1978 |last1= Van Nes |first1= G.J.H. |last2= Vos |first2= A. |s2cid= 55183235 |url= http://www.rug.nl/research/portal/files/3440910/c3.pdf}}</ref> On cooling under normal pressure, the first modification to appear is a [[plastic crystal]], crystallizing in the cubic system. In this form, the positions of the hydrogen atoms are not fixed; the molecules may rotate freely around the long axis. Cooling this ethane below ca. {{convert|89.9|K|C F}} changes it to monoclinic metastable ethane II ([[space group]] P 21/n).<ref>{{cite web |url= https://log-web.de/chemie/Start.htm?name=ethaneCryst&lang=en |title= Ethane as a solid |access-date= 2019-12-10}}</ref> Ethane is only very sparingly soluble in water.
At standard temperature and pressure, ethane is a colorless, odorless gas. It has a boiling point of {{cvt|-88.5|°C|F}} and melting point of {{cvt|-182.8|°C|F}}. Solid ethane exists in several modifications.<ref name="Nes">{{cite journal |doi= 10.1107/S0567740878007037 |title= Single-crystal structures and electron density distributions of ethane, ethylene and acetylene. I. Single-crystal X-ray structure determinations of two modifications of ethane |journal= Acta Crystallographica Section B |volume=34 |issue=6 |page= 1947 |year= 1978 |last1= Van Nes |first1= G.J.H. |last2= Vos |first2= A. |bibcode= 1978AcCrB..34.1947V |s2cid= 55183235 |url= http://www.rug.nl/research/portal/files/3440910/c3.pdf}}</ref> On cooling under normal pressure, the first modification to appear is a [[plastic crystal]], crystallizing in the cubic system. In this form, the positions of the hydrogen atoms are not fixed; the molecules may rotate freely around the long axis. Cooling this ethane below ca. {{convert|89.9|K|C F}} changes it to monoclinic metastable ethane II ([[space group]] P 21/n).<ref>{{cite web |url= https://log-web.de/chemie/Start.htm?name=ethaneCryst&lang=en |title= Ethane as a solid |access-date= 2019-12-10}}</ref> Ethane is only very sparingly soluble in water.


The bond parameters of ethane have been measured to high precision by microwave spectroscopy and electron diffraction: ''r''<sub>C−C</sub> = 1.528(3) Å, ''r''<sub>C−H</sub> = 1.088(5) Å, and ∠CCH = 111.6(5)° by microwave and ''r''<sub>C−C</sub> = 1.524(3) Å, ''r''<sub>C−H</sub> = 1.089(5) Å, and ∠CCH = 111.9(5)° by electron diffraction (the numbers in parentheses represents the uncertainties in the final digits).<ref>{{Cite journal|last=Harmony|first=Marlin D.|date=1990-11-15|title=The equilibrium carbon–carbon single‐bond length in ethane|journal=The Journal of Chemical Physics|language=en|volume=93|issue=10|pages=7522–7523|doi=10.1063/1.459380|issn=0021-9606|bibcode=1990JChPh..93.7522H}}</ref>
The bond parameters of ethane have been measured to high precision by microwave spectroscopy and electron diffraction: ''r''<sub>C−C</sub> = 1.528(3) Å, ''r''<sub>C−H</sub> = 1.088(5) Å, and ∠CCH = 111.6(5)° by microwave and ''r''<sub>C−C</sub> = 1.524(3) Å, ''r''<sub>C−H</sub> = 1.089(5) Å, and ∠CCH = 111.9(5)° by electron diffraction (the numbers in parentheses represents the uncertainties in the final digits).<ref>{{Cite journal|last=Harmony|first=Marlin D.|date=1990-11-15|title=The equilibrium carbon–carbon single-bond length in ethane|journal=The Journal of Chemical Physics|language=en|volume=93|issue=10|pages=7522–7523|doi=10.1063/1.459380|issn=0021-9606|bibcode=1990JChPh..93.7522H}}</ref>

[[File:Ethane conformations and relative energies.svg|left|thumb|300px|Ethane (shown in [[Newman projection]]) barrier to rotation about the carbon-carbon bond. The curve is potential energy as a function of rotational angle. [[Activation energy|Energy barrier]] is 12 [[kJ/mol]] or about 2.9 [[kcal/mol]].<ref>{{Cite book|title=Organic chemistry|last=J|first=McMurry|date=2012|publisher=Brooks|isbn=9780840054449|edition=8|location=Belmont, CA|pages=95}}</ref>]]
Rotating a molecular substructure about a twistable bond usually requires energy. The minimum energy to produce a 360° bond rotation is called the [[rotational barrier]].

Ethane gives a classic, simple example of such a rotational barrier, sometimes called the "ethane barrier". Among the earliest experimental evidence of this barrier (see diagram at left) was obtained by modelling the entropy of ethane.<ref>{{cite journal |doi= 10.1021/ja01281a014 |title= The Entropy of Ethane and the Third Law of Thermodynamics. Hindered Rotation of Methyl Groups |journal= Journal of the American Chemical Society |volume=59 |issue=2 |pages=276 |year=1937 |last1=Kemp |first1=J. D. |last2=Pitzer |first2= Kenneth S.}}
</ref> The three hydrogens at each end are free to pinwheel about the central carbon–carbon bond when provided with sufficient energy to overcome the barrier. The physical origin of the barrier is still not completely settled,<ref>{{cite journal |doi= 10.1021/ed082p1703 |title= Determination of the Rotational Barrier in Ethane by Vibrational Spectroscopy and Statistical Thermodynamics |year=2005 |last1= Ercolani |first1=G. |journal= J. Chem. Educ. |volume=82 |issue=11 |pages= 1703–1708 |bibcode = 2005JChEd..82.1703E }}</ref> although the overlap (exchange) repulsion<ref>{{cite journal |doi= 10.1021/ar00090a004 |title= The Barrier to Internal Rotation in Ethane |year=1983 |last1= Pitzer |first1= R.M. |journal= Acc. Chem. Res. |volume=16 |issue=6 |pages= 207–210}}</ref> between the hydrogen atoms on opposing ends of the molecule is perhaps the strongest candidate, with the stabilizing effect of [[hyperconjugation]] on the staggered conformation contributing to the phenomenon.<ref>{{cite journal|doi=10.1002/anie.200352931|title=The Magnitude of Hyperconjugation in Ethane: A Perspective from Ab Initio Valence Bond Theory|year=2004|last1=Mo|first1=Y.|last2=Wu|first2=W.|last3=Song|first3=L.|last4=Lin|first4=M.|last5=Zhang|first5=Q.|last6=Gao|first6=J.|journal=Angew. Chem. Int. Ed.|volume=43|issue=15|pages=1986–1990|pmid=15065281}}</ref> Theoretical methods that use an appropriate starting point (orthogonal orbitals) find that hyperconjugation is the most important factor in the origin of the ethane rotation barrier.<ref>{{cite journal |author1= Pophristic, V. |author2=Goodman, L. |title= Hyperconjugation not steric repulsion leads to the staggered structure of ethane |journal= Nature |volume= 411 |issue= 6837 |pages= 565–8 |doi= 10.1038/35079036 |pmid= 11385566 |year=2001|bibcode=2001Natur.411..565P |s2cid=205017635 }}</ref><ref>{{cite journal |author= Schreiner, P. R. |title= Teaching the right reasons: Lessons from the mistaken origin of the rotational barrier in ethane |journal= Angewandte Chemie International Edition |volume=41 |issue=19 |pages=3579–81, 3513 |pmid= 12370897 |year= 2002 |doi= 10.1002/1521-3773(20021004)41:19<3579::AID-ANIE3579>3.0.CO;2-S}}
</ref>

As far back as 1890–1891, chemists suggested that ethane molecules preferred the staggered conformation with the two ends of the molecule askew from each other.<ref>{{cite journal |author= Bischoff, CA |title= Ueber die Aufhebung der freien Drehbarkeit von einfach verbundenen Kohlenstoffatomen |year=1890 |journal= Chem. Ber. |volume=23 |page= 623 |doi= 10.1002/cber.18900230197|url= https://zenodo.org/record/1425584 }}</ref><ref>{{cite journal |author= Bischoff, CA |title= Theoretische Ergebnisse der Studien in der Bernsteinsäuregruppe |year= 1891 |journal= Chem. Ber. |volume=24 |pages= 1074–1085 |doi= 10.1002/cber.189102401195|url= https://zenodo.org/record/1425620 }}</ref><ref>{{cite journal |author= Bischoff, CA |title= Die dynamische Hypothese in ihrer Anwendung auf die Bernsteinsäuregruppe |year= 1891 |journal= Chem. Ber. |volume=24 |pages=1085–1095 |doi= 10.1002/cber.189102401196 |url= https://zenodo.org/record/1425622 }}</ref><ref>{{cite journal |year=1893 |volume=26 |issue=2 |page= 1452 |doi= 10.1002/cber.18930260254 |title= Die Anwendung der dynamischen Hypothese auf Ketonsäurederivate |journal= Berichte der Deutschen Chemischen Gesellschaft |last1= Bischoff |first1=C.A. |last2= Walden |first2= P.|url=https://zenodo.org/record/1425708 }}</ref>


===Atmospheric and extraterrestrial===
===Atmospheric and extraterrestrial===
[[File:Titan North Pole Lakes PIA08630.jpg|right|thumb|250px|A photograph of [[Titan (moon)|Titan]]'s northern latitudes. The dark features are hydrocarbon lakes containing ethane]]
[[File:Titan North Pole Lakes PIA08630.jpg|right|thumb|250px|A photograph of [[Titan (moon)|Titan]]'s northern latitudes. The dark features are hydrocarbon lakes containing ethane]]


Ethane occurs as a trace gas in the [[Earth's atmosphere]], currently having a concentration at [[sea level]] of 0.5 [[parts per billion|ppb]],<ref>[https://web.archive.org/web/20081222061502/http://www.atmosphere.mpg.de/enid/3tg.html Trace gases] (archived). Atmosphere.mpg.de. Retrieved on 2011-12-08.</ref> though its preindustrial concentration is likely to have been only around 0.25 part per billion since a significant proportion of the ethane in today's atmosphere may have originated as [[fossil fuel]]s. Global ethane quantities have varied over time, likely due to [[Gas flare|flaring]] at [[natural gas field]]s.<ref name="SimpsonSulbaek Andersen2012">{{cite journal|last1=Simpson|first1=Isobel J.|last2=Sulbaek Andersen|first2=Mads P.|last3=Meinardi|first3=Simone|last4=Bruhwiler|first4=Lori|last5=Blake|first5=Nicola J.|last6=Helmig|first6=Detlev|last7=Rowland|first7=F. Sherwood|last8=Blake|first8=Donald R.|title=Long-term decline of global atmospheric ethane concentrations and implications for methane|journal=Nature|volume=488|issue=7412|year=2012|pages=490–494|doi=10.1038/nature11342|pmid=22914166|url=https://zenodo.org/record/898122|bibcode=2012Natur.488..490S|s2cid=4373714}}</ref> Global ethane emission rates declined from 1984 to 2010,<ref name="SimpsonSulbaek Andersen2012"/> though increased [[shale gas]] production at the [[Bakken Formation]] in the U.S. has arrested the decline by half.<ref name="KortSmith2016">{{cite journal|last1=Kort|first1=E. A.|last2=Smith|first2=M. L.|last3=Murray|first3=L. T.|last4=Gvakharia|first4=A.|last5=Brandt|first5=A. R.|last6=Peischl|first6=J.|last7=Ryerson|first7=T. B.|last8=Sweeney|first8=C.|last9=Travis|first9=K.|title=Fugitive emissions from the Bakken shale illustrate role of shale production in global ethane shift|journal=Geophysical Research Letters|year=2016|doi=10.1002/2016GL068703|volume=43|issue=9|pages=4617–4623|bibcode=2016GeoRL..43.4617K|doi-access=free}}</ref>
Ethane occurs as a trace gas in the [[Earth's atmosphere]], currently having a concentration at [[sea level]] of 0.5 [[parts per billion|ppb]].<ref>{{cite web|url=http://www.atmosphere.mpg.de/enid/3tg.html|title=Trace gases (archived)|website=Atmosphere.mpg.de|archive-url=https://web.archive.org/web/20081222061502/http://www.atmosphere.mpg.de/enid/3tg.html |access-date=2011-12-08|archive-date=2008-12-22 }}</ref> Global ethane quantities have varied over time, likely due to [[Gas flare|flaring]] at [[natural gas field]]s.<ref name="SimpsonSulbaek Andersen2012">{{cite journal|last1=Simpson|first1=Isobel J.|last2=Sulbaek Andersen|first2=Mads P.|last3=Meinardi|first3=Simone|last4=Bruhwiler|first4=Lori|last5=Blake|first5=Nicola J.|last6=Helmig|first6=Detlev|last7=Rowland|first7=F. Sherwood|last8=Blake|first8=Donald R.|title=Long-term decline of global atmospheric ethane concentrations and implications for methane|journal=Nature|volume=488|issue=7412|year=2012|pages=490–494|doi=10.1038/nature11342|pmid=22914166|url=https://zenodo.org/record/898122|bibcode=2012Natur.488..490S|s2cid=4373714}}</ref> Global ethane emission rates declined from 1984 to 2010,<ref name="SimpsonSulbaek Andersen2012"/> though increased [[shale gas]] production at the [[Bakken Formation]] in the U.S. has arrested the decline by half.<ref name="KortSmith2016">{{cite journal|last1=Kort|first1=E. A.|last2=Smith|first2=M. L.|last3=Murray|first3=L. T.|last4=Gvakharia|first4=A.|last5=Brandt|first5=A. R.|last6=Peischl|first6=J.|last7=Ryerson|first7=T. B.|last8=Sweeney|first8=C.|last9=Travis|first9=K.|title=Fugitive emissions from the Bakken shale illustrate role of shale production in global ethane shift|journal=Geophysical Research Letters|year=2016|doi=10.1002/2016GL068703|volume=43|issue=9|pages=4617–4623|bibcode=2016GeoRL..43.4617K|doi-access=free|hdl=2027.42/142509|hdl-access=free}}</ref><ref>{{cite web|url=http://ns.umich.edu/new/multimedia/videos/23735-one-oil-field-a-key-culprit-in-global-ethane-gas-increase|title=One oil field a key culprit in global ethane gas increase|date=April 26, 2016|publisher=University of Michigan}}</ref>
<ref>{{cite web|url=http://ns.umich.edu/new/multimedia/videos/23735-one-oil-field-a-key-culprit-in-global-ethane-gas-increase|title=One oil field a key culprit in global ethane gas increase|date=April 26, 2016|publisher=University of Michigan}}</ref>


Although ethane is a [[greenhouse gas]], it is much less abundant than methane, has a lifetime of only a few months compared to over a decade,<ref name="Feasibility">Aydin, Kamil Murat; Williams, M.B. and Saltzman, E.S.; ‘Feasibility of reconstructing paleoatmospheric records of selected alkanes, methyl halides, and sulfur gases from Greenland ice cores’; ''Journal of Geophysical Research''; volume 112, D07312</ref> and is also less efficient at absorbing radiation relative to mass. In fact, ethane's [[global warming potential]] largely results from its conversion in the atmosphere to methane.<ref>Hodnebrog, Øivind; Dalsøren, Stig B. and Myrhe, Gunnar; ‘Lifetimes, direct and indirect radiative forcing, and globalwarming potentials of ethane (C<sub>2</sub>H<sub>6</sub>), propane (C<sub>3</sub>H<sub>8</sub>),and butane (C<sub>4</sub>H<sub>10</sub>)’; ''Atmospheric Science Letters''; 2018;19:e804</ref> It has been detected as a trace component in the atmospheres of all four [[giant planet]]s, and in the atmosphere of [[Saturn]]'s moon [[Titan (moon)|Titan]].<ref>{{cite web|first =Bob|last = Brown| year =2008|url = http://www.jpl.nasa.gov/news/news.cfm?release=2008-152|title = NASA Confirms Liquid Lake on Saturn Moon|display-authors=et al|publisher=NASA Jet Propulsion Laboratory}}</ref>
Although ethane is a [[greenhouse gas]], it is much less abundant than methane, has a lifetime of only a few months compared to over a decade,<ref name="Feasibility">{{cite journal|last1=Aydin|first1=Kamil Murat|last2=Williams|first2=M.B.|last3=Saltzman|first3=E.S.|title=Feasibility of reconstructing paleoatmospheric records of selected alkanes, methyl halides, and sulfur gases from Greenland ice cores|journal=Journal of Geophysical Research|volume=112|date=April 2007|issue=D7 |doi=10.1029/2006JD008027 |bibcode=2007JGRD..112.7312A }}</ref> and is also less efficient at absorbing radiation relative to mass. In fact, ethane's [[global warming potential]] largely results from its conversion in the atmosphere to methane.<ref>{{cite journal|last1=Hodnebrog|first1=Øivind|last2=Dalsøren|first2=Stig B.|last3=Myrhe|first3=Gunnar|title=Lifetimes, direct and indirect radiative forcing, and global warming potentials of ethane (C<sub>2</sub>H<sub>6</sub>), propane (C<sub>3</sub>H<sub>8</sub>), and butane (C<sub>4</sub>H<sub>10</sub>)|journal=Atmospheric Science Letters|year=2018|volume=19 |issue=2 |doi=10.1002/asl.804|doi-access=free|bibcode=2018AtScL..19E.804H }}</ref> It has been detected as a trace component in the atmospheres of all four [[giant planet]]s, and in the atmosphere of [[Saturn]]'s moon [[Titan (moon)|Titan]].<ref>{{cite web|first = Bob|last = Brown|year = 2008|url = http://www.jpl.nasa.gov/news/news.cfm?release=2008-152|title = NASA Confirms Liquid Lake on Saturn Moon|display-authors = et al|publisher = NASA Jet Propulsion Laboratory|access-date = 2008-07-30|archive-date = 2011-06-05|archive-url = https://web.archive.org/web/20110605031218/http://www.jpl.nasa.gov/news/news.cfm?release=2008-152|url-status = dead}}</ref>


Atmospheric ethane results from the Sun's [[photochemistry|photochemical]] action on methane gas, also present in these atmospheres: [[ultraviolet]] photons of shorter [[wavelength]]s than 160 [[nanometer|nm]] can photo-dissociate the methane molecule into a [[methyl]] radical and a [[hydrogen]] atom. When two methyl radicals recombine, the result is ethane:
Atmospheric ethane results from the Sun's [[photochemistry|photochemical]] action on methane gas, also present in these atmospheres: [[ultraviolet]] photons of shorter [[wavelength]]s than 160 [[nanometer|nm]] can photo-dissociate the methane molecule into a [[methyl]] radical and a [[hydrogen]] atom. When two methyl radicals recombine, the result is ethane:


: CH<sub>4</sub> → CH<sub>3</sub>• + •H
: CH<sub>4</sub> &nbsp;&nbsp; CH<sub>3</sub>• + •H
: CH<sub>3</sub>• + •CH<sub>3</sub> → C<sub>2</sub>H<sub>6</sub>
: CH<sub>3</sub>• + •CH<sub>3</sub> &nbsp;&nbsp; C<sub>2</sub>H<sub>6</sub>


In Earth's atmosphere, [[Hydroxyl radical|hydroxyl radicals]] convert ethane to [[methanol]] vapor with a half-life of around three months.<ref name="Feasibility"/>
In Earth's atmosphere, [[hydroxyl radical]]s convert ethane to [[methanol]] vapor with a half-life of around three months.<ref name="Feasibility"/>


It is suspected that ethane produced in this fashion on Titan rains back onto the moon's surface, and over time has accumulated into hydrocarbon seas covering much of the moon's polar regions. In December 2007 the [[Cassini probe]] found at least one lake at Titan's south pole, now called [[Ontario Lacus]] because of the lake's similar area to [[Lake Ontario]] on Earth (approximately 20,000&nbsp;km<sup>2</sup>). Further analysis of infrared spectroscopic data presented in July 2008<ref>{{cite journal|doi=10.1038/nature07100|title=The identification of liquid ethane in Titan's Ontario Lacus|year=2008|last1=Brown|first1=R. H.|last2=Soderblom|first2=L. A.|last3=Soderblom|first3=J. M.|last4=Clark|first4=R. N.|last5=Jaumann|first5=R.|last6=Barnes|first6=J. W.|last7=Sotin|first7=C.|last8=Buratti|first8=B.|last9=Baines|first9=K. H.|last10=Nicholson|first10=P. D.|journal=Nature|volume=454|issue=7204|pages=607–10|pmid=18668101|bibcode = 2008Natur.454..607B |s2cid=4398324|display-authors=8}}</ref> provided additional evidence for the presence of liquid ethane in Ontario Lacus. Several significantly larger hydrocarbon lakes, [[Ligeia Mare]] and [[Kraken Mare]] being the two largest, were discovered near Titan's north pole using radar data gathered by Cassini. These lakes are believed to be filled primarily by a mixture of liquid ethane and methane.
It is suspected that ethane produced in this fashion on Titan rains back onto the moon's surface, and over time has accumulated into hydrocarbon seas covering much of the moon's polar regions. In mid-2005, the ''[[Cassini-Huygens|Cassini]]'' orbiter discovered [[Ontario Lacus]] in Titan's south polar regions. Further analysis of infrared spectroscopic data presented in July 2008<ref>{{cite journal|doi=10.1038/nature07100|title=The identification of liquid ethane in Titan's Ontario Lacus|year=2008|last1=Brown|first1=R. H.|last2=Soderblom|first2=L. A.|last3=Soderblom|first3=J. M.|last4=Clark|first4=R. N.|last5=Jaumann|first5=R.|last6=Barnes|first6=J. W.|last7=Sotin|first7=C.|last8=Buratti|first8=B.|last9=Baines|first9=K. H.|last10=Nicholson|first10=P. D.|journal=Nature|volume=454|issue=7204|pages=607–10|pmid=18668101|bibcode = 2008Natur.454..607B |s2cid=4398324|display-authors=8}}</ref> provided additional evidence for the presence of liquid ethane in Ontario Lacus. Several significantly larger hydrocarbon lakes, [[Ligeia Mare]] and [[Kraken Mare]] being the two largest, were discovered near Titan's north pole using radar data gathered by Cassini. These lakes are believed to be filled primarily by a mixture of liquid ethane and methane.


In 1996, ethane was detected in [[Comet Hyakutake]],<ref name= Mumma/> and it has since been detected in some other [[comets]]. The existence of ethane in these distant solar system bodies may implicate ethane as a primordial component of the [[solar nebula]] from which the sun and planets are believed to have formed.
In 1996, ethane was detected in [[Comet Hyakutake]],<ref name= Mumma/> and it has since been detected in some other [[comets]]. The existence of ethane in these distant solar system bodies may implicate ethane as a primordial component of the [[solar nebula]] from which the sun and planets are believed to have formed.


In 2006, Dale Cruikshank of NASA/Ames Research Center (a [[New Horizons]] co-investigator) and his colleagues announced the spectroscopic discovery of ethane on [[Pluto]]'s surface.<ref>{{cite web
In 2006, Dale Cruikshank of NASA/Ames Research Center (a ''[[New Horizons]]'' co-investigator) and his colleagues announced the spectroscopic discovery of ethane on [[Pluto]]'s surface.<ref>{{Cite web |last=Stern |first= A. |author-link=Alan Stern |date=November 1, 2006 |title=Making Old Horizons New |url=http://pluto.jhuapl.edu/overview/piPerspectives/piPerspective_11_1_2006.php |url-status=dead |archive-url=https://web.archive.org/web/20080828012339/http://pluto.jhuapl.edu/overview/piPerspectives/piPerspective_11_1_2006.php |archive-date=August 28, 2008 |access-date=2007-02-12 |website=The PI's Perspective |publisher=Johns Hopkins University Applied Physics Laboratory}}</ref>
|author = Stern, A.
|author-link = Alan Stern
|date = November 1, 2006
|url = http://pluto.jhuapl.edu/overview/piPerspectives/piPerspective_11_1_2006.php
|title = Making Old Horizons New
|work = The PI's Perspective
|publisher = Johns Hopkins University Applied Physics Laboratory
|access-date = 2007-02-12
|url-status = dead
|archive-url = https://web.archive.org/web/20080828012339/http://pluto.jhuapl.edu/overview/piPerspectives/piPerspective_11_1_2006.php
|archive-date = August 28, 2008
}}</ref>


==Chemistry==
==Chemistry==
The reactions of ethane involve chiefly [[free radical reaction]]s. Ethane can react with the [[halogen]]s, especially [[chlorine]] and [[bromine]], by [[free-radical halogenation]]. This reaction proceeds through the propagation of the [[ethyl group|ethyl]] radical:<ref>{{cite book |doi=10.1002/14356007.o06_o01 |chapter=Chlorethanes and Chloroethylenes |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2011 |last1=Dreher |first1=Eberhard-Ludwig |last2=Torkelson |first2=Theodore R. |last3=Beutel |first3=Klaus K. |isbn=978-3-527-30385-4 }}</ref>
: Cl<sub>2</sub> &nbsp;→&nbsp; 2 Cl•
: C<sub>2</sub>H<sub>6</sub> + Cl• &nbsp;&nbsp; C<sub>2</sub>H<sub>5</sub> + HCl
: C<sub>2</sub>H<sub>5</sub>• + Cl<sub>2</sub> &nbsp;&nbsp; C<sub>2</sub>H<sub>5</sub>Cl + Cl•
: Cl• + C<sub>2</sub>H<sub>6</sub> &nbsp;&nbsp; C<sub>2</sub>H<sub>5</sub>• + HCl


The [[combustion]] of ethane releases 1559.7 kJ/mol, or 51.9 kJ/g, of heat, and produces [[carbon dioxide]] and [[water]] according to the [[chemical equation]]:
Ethane can be viewed as two [[methyl group]]s joined, that is, a [[dimer (chemistry)|dimer]] of methyl groups. In the laboratory, ethane may be conveniently synthesised by [[Kolbe electrolysis]]. In this technique, an aqueous solution of an [[acetate]] salt is [[electrolysis|electrolysed]]. At the [[anode]], acetate is oxidized to produce [[carbon dioxide]] and [[methyl]] radicals, and the highly reactive methyl radicals combine to produce ethane:
: [[acetate|CH<sub>3</sub>COO<sup></sup>]] CH<sub>3</sub> + [[carbon dioxide|CO<sub>2</sub>]] + [[electron|e<sup></sup>]]
: 2 C<sub>2</sub>H<sub>6</sub> + 7 [[oxygen|O<sub>2</sub>]] &nbsp;→&nbsp; 4 [[carbon dioxide|CO<sub>2</sub>]] + 6 [[water|H<sub>2</sub>O]] + 3120 kJ
: CH<sub>3</sub>• + •CH<sub>3</sub> → C<sub>2</sub>H<sub>6</sub>


Combustion may also occur without an excess of oxygen, yielding [[carbon monoxide]], [[acetaldehyde]], [[methane]], [[methanol]], and [[ethanol]]. At higher temperatures, especially in the range {{cvt|600|-|900|°C|F}}, [[ethylene]] is a significant product:
Synthesis by oxidation of [[acetic anhydride]] by [[peroxide]]s, is conceptually similar.
: {{chem2|2 C2H6 + O2 → 2 C2H4 + 2 H2O}}

Such oxidative dehydrogenation reactions are relevant to the production of [[ethylene]].<ref>{{cite journal |doi=10.1039/D0CS01518K |title=Oxidative dehydrogenation of ethane: Catalytic and mechanistic aspects and future trends |date=2021 |last1=Najari |first1=Sara |last2=Saeidi |first2=Samrand |last3=Concepcion |first3=Patricia |last4=Dionysiou |first4=Dionysios D. |last5=Bhargava |first5=Suresh K. |last6=Lee |first6=Adam F. |last7=Wilson |first7=Karen |journal=Chemical Society Reviews |volume=50 |issue=7 |pages=4564–4605 |pmid=33595011 |s2cid=231946397 }}</ref>
The chemistry of ethane involves chiefly [[free radical reaction]]s. Ethane can react with the [[halogen]]s, especially [[chlorine]] and [[bromine]], by [[free-radical halogenation]]. This reaction proceeds through the propagation of the [[ethyl group|ethyl]] radical:

: C<sub>2</sub>H<sub>5</sub>• + [[chlorine|Cl<sub>2</sub>]] → [[chloroethane|C<sub>2</sub>H<sub>5</sub>Cl]] + Cl•
: Cl• + C<sub>2</sub>H<sub>6</sub> → C<sub>2</sub>H<sub>5</sub>• + [[hydrochloric acid|HCl]]

Because halogenated ethanes can undergo further free radical halogenation, this process results in a mixture of several halogenated products. In the chemical industry, more selective chemical reactions are used for the production of any particular two-carbon haloalkane.

===Combustion===
The complete [[combustion]] of ethane releases 1559.7 kJ/mol, or 51.9 kJ/g, of heat, and produces [[carbon dioxide]] and [[water]] according to the [[chemical equation]]:

: 2 C<sub>2</sub>H<sub>6</sub> + 7 [[oxygen|O<sub>2</sub>]] → 4 [[carbon dioxide|CO<sub>2</sub>]] + 6 [[water|H<sub>2</sub>O]] + 3120 kJ

Combustion may also occur without an excess of oxygen, forming a mix of amorphous carbon and [[carbon monoxide]].

: 2 C<sub>2</sub>H<sub>6</sub> + 3 [[oxygen|O<sub>2</sub>]] → 4 C + 6 [[water|H<sub>2</sub>O]] + energy
: 2 C<sub>2</sub>H<sub>6</sub> + 5 [[oxygen|O<sub>2</sub>]] → 4 CO + 6 [[water|H<sub>2</sub>O]] + energy
: 2 C<sub>2</sub>H<sub>6</sub> + 4 [[oxygen|O<sub>2</sub>]] → 2 C + 2 CO + 6 [[water|H<sub>2</sub>O]] + energy etc.

Combustion occurs by a complex series of free-radical reactions. [[Computer simulation]]s of the [[chemical kinetics]] of ethane combustion have included hundreds of reactions. An important series of reaction in ethane combustion is the combination of an ethyl radical with [[oxygen]], and the subsequent breakup of the resulting [[peroxide]] into ethoxy and hydroxyl radicals.

: C<sub>2</sub>H<sub>5</sub>• + O<sub>2</sub> → C<sub>2</sub>H<sub>5</sub>OO•
: C<sub>2</sub>H<sub>5</sub>OO• + HR → C<sub>2</sub>H<sub>5</sub>OOH + •R
: C<sub>2</sub>H<sub>5</sub>OOH → C<sub>2</sub>H<sub>5</sub>O• + •OH

The principal carbon-containing products of incomplete ethane combustion are single-carbon compounds such as [[carbon monoxide]] and [[formaldehyde]]. One important route by which the [[carbon-carbon bond|carbon–carbon bond]] in ethane is broken, to yield these single-carbon products, is the decomposition of the [[ethoxy]] radical into a [[methyl]] radical and [[formaldehyde]], which can in turn undergo further oxidation.

: C<sub>2</sub>H<sub>5</sub>O• → CH<sub>3</sub>• + CH<sub>2</sub>O

Some minor products in the incomplete combustion of ethane include [[acetaldehyde]], [[methane]], [[methanol]], and [[ethanol]]. At higher temperatures, especially in the range {{cvt|600|-|900|°C|F}}, [[ethylene]] is a significant product. It arises through reactions such as this:

: C<sub>2</sub>H<sub>5</sub>• + [[oxygen|O<sub>2</sub>]] → [[ethylene|C<sub>2</sub>H<sub>4</sub>]] + •OOH

Similar reactions (with agents other than oxygen as the hydrogen abstractor) are involved in the production of ethylene from ethane in [[steam cracking]].

===Barrier===
[[File:Ethane conformations and relative energies.svg|left|thumb|300px|Ethane (shown in [[Newman projection]]) barrier to rotation about the carbon-carbon bond. The curve is potential energy as a function of rotational angle. [[Activation energy|Energy barrier]] is 12 [[kJ/mol]] or about 2.9 [[kcal/mol]].<ref>{{Cite book|title=Organic chemistry|last=J|first=McMurry|date=2012|publisher=Brooks|isbn=9780840054449|edition=8|location=Belmont, CA|pages=95}}</ref>]]
Rotating a molecular substructure about a twistable bond usually requires energy. The minimum energy to produce a 360° bond rotation is called the [[rotational barrier]].

Ethane gives a classic, simple example of such a rotational barrier, sometimes called the "ethane barrier". Among the earliest experimental evidence of this barrier (see diagram at left) was obtained by modelling the entropy of ethane.<ref>{{cite journal |doi= 10.1021/ja01281a014 |title= The Entropy of Ethane and the Third Law of Thermodynamics. Hindered Rotation of Methyl Groups |journal= Journal of the American Chemical Society |volume=59 |issue=2 |pages=276 |year=1937 |last1=Kemp |first1=J. D. |last2=Pitzer |first2= Kenneth S.}}
</ref> The three hydrogens at each end are free to pinwheel about the central carbon–carbon bond when provided with sufficient energy to overcome the barrier. The physical origin of the barrier is still not completely settled,<ref>{{cite journal |doi= 10.1021/ed082p1703 |title= Determination of the Rotational Barrier in Ethane by Vibrational Spectroscopy and Statistical Thermodynamics |year=2005 |last1= Ercolani |first1=G. |journal= J. Chem. Educ. |volume=82 |issue=11 |pages= 1703–1708 |bibcode = 2005JChEd..82.1703E }}</ref> although the overlap (exchange) repulsion<ref>{{cite journal |doi= 10.1021/ar00090a004 |title= The Barrier to Internal Rotation in Ethane |year=1983 |last1= Pitzer |first1= R.M. |journal= Acc. Chem. Res. |volume=16 |issue=6 |pages= 207–210}}</ref> between the hydrogen atoms on opposing ends of the molecule is perhaps the strongest candidate, with the stabilizing effect of [[hyperconjugation]] on the staggered conformation contributing to the phenomenon.<ref>{{cite journal|doi=10.1002/anie.200352931|title=The Magnitude of Hyperconjugation in Ethane: A Perspective from Ab Initio Valence Bond Theory|year=2004|last1=Mo|first1=Y.|last2=Wu|first2=W.|last3=Song|first3=L.|last4=Lin|first4=M.|last5=Zhang|first5=Q.|last6=Gao|first6=J.|journal=Angew. Chem. Int. Ed.|volume=43|issue=15|pages=1986–1990|pmid=15065281}}</ref> Theoretical methods that use an appropriate starting point (orthogonal orbitals) find that hyperconjugation is the most important factor in the origin of the ethane rotation barrier.<ref>{{cite journal |author1= Pophristic, V. |author2=Goodman, L. |title= Hyperconjugation not steric repulsion leads to the staggered structure of ethane |journal= Nature |volume= 411 |issue= 6837 |pages= 565–8 |doi= 10.1038/35079036 |pmid= 11385566 |year=2001|bibcode=2001Natur.411..565P |s2cid=205017635 }}</ref><ref>{{cite journal |author= Schreiner, P. R. |title= Teaching the right reasons: Lessons from the mistaken origin of the rotational barrier in ethane |journal= Angewandte Chemie International Edition |volume=41 |issue=19 |pages=3579–81, 3513 |pmid= 12370897 |year= 2002 |doi= 10.1002/1521-3773(20021004)41:19<3579::AID-ANIE3579>3.0.CO;2-S}}
</ref>

As far back as 1890–1891, chemists suggested that ethane molecules preferred the staggered conformation with the two ends of the molecule askew from each other.<ref>{{cite journal |author= Bischoff, CA |title= Ueber die Aufhebung der freien Drehbarkeit von einfach verbundenen Kohlenstoffatomen |year=1890 |journal= Chem. Ber. |volume=23 |page= 623 |doi= 10.1002/cber.18900230197|url= https://zenodo.org/record/1425584 }}</ref><ref>{{cite journal |author= Bischoff, CA |title= Theoretische Ergebnisse der Studien in der Bernsteinsäuregruppe |year= 1891 |journal= Chem. Ber. |volume=24 |pages= 1074–1085 |doi= 10.1002/cber.189102401195|url= https://zenodo.org/record/1425620 }}</ref><ref>{{cite journal |author= Bischoff, CA |title= Die dynamische Hypothese in ihrer Anwendung auf die Bernsteinsäuregruppe |year= 1891 |journal= Chem. Ber. |volume=24 |pages=1085–1095 |doi= 10.1002/cber.189102401196 |url= https://zenodo.org/record/1425622 }}</ref><ref>{{cite journal |year=1893 |volume=26 |issue=2 |page= 1452 |doi= 10.1002/cber.18930260254 |title= Die Anwendung der dynamischen Hypothese auf Ketonsäurederivate |journal= Berichte der Deutschen Chemischen Gesellschaft |last1= Bischoff |first1=C.A. |last2= Walden |first2= P.|url=https://zenodo.org/record/1425708 }}</ref>


==Production==
==Production==
Line 195: Line 154:


==Usage==
==Usage==
The chief use of ethane is the production of [[ethylene]] (ethene) by [[steam cracking]]. When diluted with steam and briefly heated to very high temperatures (900&nbsp;°C or more), heavy hydrocarbons break down into lighter hydrocarbons, and [[saturated hydrocarbon]]s become [[unsaturated (hydrocarbon)|unsaturated]]. Ethane is favored for ethylene production because the steam cracking of ethane is fairly selective for ethylene, while the steam cracking of heavier hydrocarbons yields a product mixture poorer in ethylene and richer in heavier [[alkene|alkenes (olefins)]], such as [[propene|propene (propylene)]] and [[butadiene]], and in [[aromatic hydrocarbon]]s.
The chief use of ethane is the production of [[ethylene]] (ethene) by [[steam cracking]]. Steam cracking of ethane is fairly selective for ethylene, while the steam cracking of heavier hydrocarbons yields a product mixture poorer in ethylene and richer in heavier [[alkene|alkenes (olefins)]], such as [[propene|propene (propylene)]] and [[butadiene]], and in [[aromatic hydrocarbon]]s.


Experimentally, ethane is under investigation as a feedstock for other commodity chemicals. [[Oxidative]] chlorination of ethane has long appeared to be a potentially more economical route to [[vinyl chloride]] than ethylene chlorination. Many processes for producing this reaction have been [[patent]]ed, but poor selectivity for [[vinyl chloride]] and [[Corrosion|corrosive]] reaction conditions (specifically, a reaction mixture containing [[hydrochloric acid]] at temperatures greater than 500&nbsp;°C) have discouraged the commercialization of most of them. Presently, [[INEOS]] operates a 1000 t/a ([[tonnes]] per [[annum]]) ethane-to-vinyl chloride pilot plant at [[Wilhelmshaven]] in [[Germany]].
Ehane has been investigated as a feedstock for other commodity chemicals. [[Oxidative]] chlorination of ethane has long appeared to be a potentially more economical route to [[vinyl chloride]] than ethylene chlorination. Many patent exist on this theme, but poor selectivity for [[vinyl chloride]] and [[Corrosion|corrosive]] reaction conditions have discouraged the commercialization of most of them. Presently, [[INEOS]] operates a 1000 t/a ([[tonnes]] per [[annum]]) ethane-to-vinyl chloride pilot plant at [[Wilhelmshaven]] in [[Germany]].


Similarly, the [[Saudi Arabia]]n firm [[SABIC]] has announced construction of a 30,000 t/a plant to produce [[acetic acid]] by ethane oxidation at [[Yanbu]]. The economic viability of this process may rely on the low cost of ethane near Saudi oil fields, and it may not be competitive with [[methanol carbonylation]] elsewhere in the world.
[[SABIC]] operates a 34,000 t/a plant at [[Yanbu]] to produce [[acetic acid]] by ethane oxidation.<ref name="SABIC-plant-launch">{{Cite web |title = SABIC's Acetic Acid Plant Comes on Stream |last = Ramkumar |first=K.S. |work = Arab News |date = 26 May 2005 |access-date = 4 July 2024 |url = https://www.arabnews.com/node/267532 |archive-url=http://web.archive.org/web/20130609063705/http://arabnews.com/node/267532 |archive-date=9 June 2013}}</ref> The economic viability of this process may rely on the low cost of ethane near Saudi oil fields, and it may not be competitive with [[methanol carbonylation]] elsewhere in the world.<ref name="Mizuno2009">{{cite book |editor-last=Mizuno |editor-first=Noritaka |last1=Cavani |first1=Fabrizio |last2=Ballarini |first2=Nicola |title=Modern Heterogeneous Oxidation Catalysis |publisher=Wiley |year=2009 |isbn=978-3-527-62755-4 |url=https://books.google.com/books?id=66k5iyn9xmIC |access-date=4 July 2024 |page=291}}</ref>


Ethane can be used as a refrigerant in cryogenic refrigeration systems.
Ethane can be used as a refrigerant in cryogenic refrigeration systems. On a much smaller scale, in scientific research, liquid ethane is used to [[Cryopreservation#Vitrification|vitrify]] water-rich samples for [[cryo-electron microscopy]]. A thin film of water quickly immersed in liquid ethane at −150&nbsp;°C or colder freezes too quickly for water to crystallize. Slower freezing methods can generate cubic ice crystals, which can disrupt [[soft materials|soft structures]] by damaging the samples and reduce image quality by scattering the electron beam before it can reach the detector.


===In the laboratory===
[[MAN Energy Solutions]] currently manufactures two-stroke dual fuel engines (B&W ME-GIE) which can run on both [[Marine diesel oil]] and ethane.
On a much smaller scale, in scientific research, liquid ethane is used to [[Cryopreservation#Vitrification|vitrify]] water-rich samples for [[cryo-electron microscopy]]. A thin film of water quickly immersed in liquid ethane at −150&nbsp;°C or colder freezes too quickly for water to crystallize. Slower freezing methods can generate cubic ice crystals, which can disrupt [[soft materials|soft structures]] by damaging the samples and reduce image quality by scattering the electron beam before it can reach the detector.


==Health and safety==
==Health and safety==
At room temperature, ethane is an extremely flammable gas. When mixed with air at 3.0%–12.5% by volume, it forms an [[explosion|explosive]] mixture.
At room temperature, ethane is an extremely flammable gas. When mixed with air at 3.0%–12.5% by volume, it forms an [[explosion|explosive]] mixture.


Ethane is not a [[carcinogen]].<ref>{{Cite book | title = Environmental Biotechnology: A Biosystems Approach | author = Vallero, Daniel |doi=10.1016/B978-0-12-375089-1.10014-5|chapter=Cancer Slope Factors| publisher = Academic Press | date = June 7, 2010 | page = 641| isbn = 9780123750891 }}</ref>
Some additional precautions are necessary where ethane is stored as a cryogenic liquid. Direct contact with liquid ethane can result in severe [[frostbite]]. Until they warm to room temperature, the vapors from liquid ethane are heavier than air and can flow along the floor or ground, gathering in low places; if the vapors encounter an ignition source, the chemical reaction can flash back to the source of ethane from which they evaporated.

Ethane can displace [[oxygen]] and become an [[asphyxiation]] hazard. Ethane poses no known acute or chronic [[Toxicology|toxicological]] risk. It is not a [[carcinogen]].<ref>{{Cite book | title = Environmental Biotechnology: A Biosystems Approach | author = Vallero, Daniel |doi=10.1016/B978-0-12-375089-1.10014-5|chapter=Cancer Slope Factors| publisher = Academic Press | date = June 7, 2010 | page = 641| isbn = 9780123750891 }}</ref>


==See also==
==See also==
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==External links==
==External links==
{{commons|Ethane|Ethane}}
{{commons}}
*[http://www.inchem.org/documents/icsc/icsc/eics0266.htm International Chemical Safety Card 0266]
*[http://www.inchem.org/documents/icsc/icsc/eics0266.htm International Chemical Safety Card 0266]
*[http://www.aet.com/gtip1.htm Market-Driven Evolution of Gas Processing Technologies for NGLs]
*[http://www.aet.com/gtip1.htm Market-Driven Evolution of Gas Processing Technologies for NGLs]
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[[Category:Alkanes]]
[[Category:Alkanes]]
[[Category:Industrial gases]]
[[Category:Industrial gases]]
[[Category:Greenhouse gases]]

Latest revision as of 00:52, 22 November 2024

Ethane
Skeletal formula of ethane with all hydrogens and carbons shown
Skeletal formula of ethane with all implicit carbons shown, and all explicit hydrogens added
Ball and stick model of ethane
Ball and stick model of ethane
Spacefill model of ethane
Spacefill model of ethane
Names
Preferred IUPAC name
Ethane[1]
Systematic IUPAC name
Dicarbane (never recommended[2])
Other names
  • Dimethyl (CH3CH3, Me2 or (CH3)2)
  • Ethyl hydride
Identifiers
3D model (JSmol)
1730716
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.741 Edit this at Wikidata
EC Number
  • 200-814-8
212
MeSH Ethane
RTECS number
  • KH3800000
UNII
UN number 1035
  • InChI=1S/C2H6/c1-2/h1-2H3 checkY
    Key: OTMSDBZUPAUEDD-UHFFFAOYSA-N checkY
  • CC
Properties
C2H6
Molar mass 30.070 g·mol−1
Appearance Colorless gas
Odor Odorless
Density
  • 1.3562 kg/m3 (gas at 0 °C)[3]

544.0 kg/m3 (liquid at -88,5 °C)
206 kg/m3 (at critical point 305.322 K)

Melting point −182.8 °C; −296.9 °F; 90.4 K
Boiling point −88.5 °C; −127.4 °F; 184.6 K
Critical point (T, P) 305.32 K (32.17 °C; 89.91 °F) 48.714 bars (4,871.4 kPa)
56.8 mg/L[4]
Vapor pressure 3.8453 MPa (at 21.1 °C)
19 nmol Pa−1 kg−1
Acidity (pKa) 50
Basicity (pKb) −36
Conjugate acid Ethanium
-37.37·10−6 cm3/mol
Thermochemistry
52.14± 0.39 J K−1 mol−1 at 298 Kelvin[5]
−84 kJ mol−1
−1561.0–−1560.4 kJ mol−1
Hazards
GHS labelling:
GHS02: Flammable
Danger
H220, H280
P210, P410+P403
NFPA 704 (fire diamond)
Flash point −135 °C (−211 °F; 138 K)
472 °C (882 °F; 745 K)
Explosive limits 2.9–13%
Safety data sheet (SDS) inchem.org
Related compounds
Related alkanes
Related compounds
Supplementary data page
Ethane (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 checkY☒N ?)

Ethane (US: /ˈɛθn/ ETH-ayn, UK: /ˈ-/ EE-) is a naturally occurring organic chemical compound with chemical formula C
2
H
6
. At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petrochemical by-product of petroleum refining. Its chief use is as feedstock for ethylene production. The ethyl group is formally, although rarely practically, derived from ethane.

History

[edit]

Ethane was first synthesised in 1834 by Michael Faraday, applying electrolysis of a potassium acetate solution. He mistook the hydrocarbon product of this reaction for methane and did not investigate it further.[6] The process is now called Kolbe electrolysis:

CH3COO → CH3• + CO2 + e
CH3• + •CH3 → C2H6

During the period 1847–1849, in an effort to vindicate the radical theory of organic chemistry, Hermann Kolbe and Edward Frankland produced ethane by the reductions of propionitrile (ethyl cyanide)[7] and ethyl iodide[8] with potassium metal, and, as did Faraday, by the electrolysis of aqueous acetates. They mistook the product of these reactions for the methyl radical (CH3), of which ethane (C2H6) is a dimer.

This error was corrected in 1864 by Carl Schorlemmer, who showed that the product of all these reactions was in fact ethane.[9] Ethane was discovered dissolved in Pennsylvanian light crude oil by Edmund Ronalds in 1864.[10][11]

Properties

[edit]

At standard temperature and pressure, ethane is a colorless, odorless gas. It has a boiling point of −88.5 °C (−127.3 °F) and melting point of −182.8 °C (−297.0 °F). Solid ethane exists in several modifications.[12] On cooling under normal pressure, the first modification to appear is a plastic crystal, crystallizing in the cubic system. In this form, the positions of the hydrogen atoms are not fixed; the molecules may rotate freely around the long axis. Cooling this ethane below ca. 89.9 K (−183.2 °C; −297.8 °F) changes it to monoclinic metastable ethane II (space group P 21/n).[13] Ethane is only very sparingly soluble in water.

The bond parameters of ethane have been measured to high precision by microwave spectroscopy and electron diffraction: rC−C = 1.528(3) Å, rC−H = 1.088(5) Å, and ∠CCH = 111.6(5)° by microwave and rC−C = 1.524(3) Å, rC−H = 1.089(5) Å, and ∠CCH = 111.9(5)° by electron diffraction (the numbers in parentheses represents the uncertainties in the final digits).[14]

Ethane (shown in Newman projection) barrier to rotation about the carbon-carbon bond. The curve is potential energy as a function of rotational angle. Energy barrier is 12 kJ/mol or about 2.9 kcal/mol.[15]

Rotating a molecular substructure about a twistable bond usually requires energy. The minimum energy to produce a 360° bond rotation is called the rotational barrier.

Ethane gives a classic, simple example of such a rotational barrier, sometimes called the "ethane barrier". Among the earliest experimental evidence of this barrier (see diagram at left) was obtained by modelling the entropy of ethane.[16] The three hydrogens at each end are free to pinwheel about the central carbon–carbon bond when provided with sufficient energy to overcome the barrier. The physical origin of the barrier is still not completely settled,[17] although the overlap (exchange) repulsion[18] between the hydrogen atoms on opposing ends of the molecule is perhaps the strongest candidate, with the stabilizing effect of hyperconjugation on the staggered conformation contributing to the phenomenon.[19] Theoretical methods that use an appropriate starting point (orthogonal orbitals) find that hyperconjugation is the most important factor in the origin of the ethane rotation barrier.[20][21]

As far back as 1890–1891, chemists suggested that ethane molecules preferred the staggered conformation with the two ends of the molecule askew from each other.[22][23][24][25]

Atmospheric and extraterrestrial

[edit]
A photograph of Titan's northern latitudes. The dark features are hydrocarbon lakes containing ethane

Ethane occurs as a trace gas in the Earth's atmosphere, currently having a concentration at sea level of 0.5 ppb.[26] Global ethane quantities have varied over time, likely due to flaring at natural gas fields.[27] Global ethane emission rates declined from 1984 to 2010,[27] though increased shale gas production at the Bakken Formation in the U.S. has arrested the decline by half.[28][29]

Although ethane is a greenhouse gas, it is much less abundant than methane, has a lifetime of only a few months compared to over a decade,[30] and is also less efficient at absorbing radiation relative to mass. In fact, ethane's global warming potential largely results from its conversion in the atmosphere to methane.[31] It has been detected as a trace component in the atmospheres of all four giant planets, and in the atmosphere of Saturn's moon Titan.[32]

Atmospheric ethane results from the Sun's photochemical action on methane gas, also present in these atmospheres: ultraviolet photons of shorter wavelengths than 160 nm can photo-dissociate the methane molecule into a methyl radical and a hydrogen atom. When two methyl radicals recombine, the result is ethane:

CH4  →  CH3• + •H
CH3• + •CH3  →  C2H6

In Earth's atmosphere, hydroxyl radicals convert ethane to methanol vapor with a half-life of around three months.[30]

It is suspected that ethane produced in this fashion on Titan rains back onto the moon's surface, and over time has accumulated into hydrocarbon seas covering much of the moon's polar regions. In mid-2005, the Cassini orbiter discovered Ontario Lacus in Titan's south polar regions. Further analysis of infrared spectroscopic data presented in July 2008[33] provided additional evidence for the presence of liquid ethane in Ontario Lacus. Several significantly larger hydrocarbon lakes, Ligeia Mare and Kraken Mare being the two largest, were discovered near Titan's north pole using radar data gathered by Cassini. These lakes are believed to be filled primarily by a mixture of liquid ethane and methane.

In 1996, ethane was detected in Comet Hyakutake,[34] and it has since been detected in some other comets. The existence of ethane in these distant solar system bodies may implicate ethane as a primordial component of the solar nebula from which the sun and planets are believed to have formed.

In 2006, Dale Cruikshank of NASA/Ames Research Center (a New Horizons co-investigator) and his colleagues announced the spectroscopic discovery of ethane on Pluto's surface.[35]

Chemistry

[edit]

The reactions of ethane involve chiefly free radical reactions. Ethane can react with the halogens, especially chlorine and bromine, by free-radical halogenation. This reaction proceeds through the propagation of the ethyl radical:[36]

Cl2  →  2 Cl•
C2H6• + Cl•  →  C2H5• + HCl
C2H5• + Cl2  →  C2H5Cl + Cl•
Cl• + C2H6  →  C2H5• + HCl

The combustion of ethane releases 1559.7 kJ/mol, or 51.9 kJ/g, of heat, and produces carbon dioxide and water according to the chemical equation:

2 C2H6 + 7 O2  →  4 CO2 + 6 H2O + 3120 kJ

Combustion may also occur without an excess of oxygen, yielding carbon monoxide, acetaldehyde, methane, methanol, and ethanol. At higher temperatures, especially in the range 600–900 °C (1,112–1,652 °F), ethylene is a significant product:

2 C2H6 + O2 → 2 C2H4 + 2 H2O

Such oxidative dehydrogenation reactions are relevant to the production of ethylene.[37]

Production

[edit]

After methane, ethane is the second-largest component of natural gas. Natural gas from different gas fields varies in ethane content from less than 1% to more than 6% by volume. Prior to the 1960s, ethane and larger molecules were typically not separated from the methane component of natural gas, but simply burnt along with the methane as a fuel. Today, ethane is an important petrochemical feedstock and is separated from the other components of natural gas in most well-developed gas fields. Ethane can also be separated from petroleum gas, a mixture of gaseous hydrocarbons produced as a byproduct of petroleum refining.

Ethane is most efficiently separated from methane by liquefying it at cryogenic temperatures. Various refrigeration strategies exist: the most economical process presently in wide use employs a turboexpander, and can recover more than 90% of the ethane in natural gas. In this process, chilled gas is expanded through a turbine, reducing the temperature to approximately −100 °C (−148 °F). At this low temperature, gaseous methane can be separated from the liquefied ethane and heavier hydrocarbons by distillation. Further distillation then separates ethane from the propane and heavier hydrocarbons.

Usage

[edit]

The chief use of ethane is the production of ethylene (ethene) by steam cracking. Steam cracking of ethane is fairly selective for ethylene, while the steam cracking of heavier hydrocarbons yields a product mixture poorer in ethylene and richer in heavier alkenes (olefins), such as propene (propylene) and butadiene, and in aromatic hydrocarbons.

Ehane has been investigated as a feedstock for other commodity chemicals. Oxidative chlorination of ethane has long appeared to be a potentially more economical route to vinyl chloride than ethylene chlorination. Many patent exist on this theme, but poor selectivity for vinyl chloride and corrosive reaction conditions have discouraged the commercialization of most of them. Presently, INEOS operates a 1000 t/a (tonnes per annum) ethane-to-vinyl chloride pilot plant at Wilhelmshaven in Germany.

SABIC operates a 34,000 t/a plant at Yanbu to produce acetic acid by ethane oxidation.[38] The economic viability of this process may rely on the low cost of ethane near Saudi oil fields, and it may not be competitive with methanol carbonylation elsewhere in the world.[39]

Ethane can be used as a refrigerant in cryogenic refrigeration systems.

In the laboratory

[edit]

On a much smaller scale, in scientific research, liquid ethane is used to vitrify water-rich samples for cryo-electron microscopy. A thin film of water quickly immersed in liquid ethane at −150 °C or colder freezes too quickly for water to crystallize. Slower freezing methods can generate cubic ice crystals, which can disrupt soft structures by damaging the samples and reduce image quality by scattering the electron beam before it can reach the detector.

Health and safety

[edit]

At room temperature, ethane is an extremely flammable gas. When mixed with air at 3.0%–12.5% by volume, it forms an explosive mixture.

Ethane is not a carcinogen.[40]

See also

[edit]

References

[edit]
  1. ^ International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 133. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4. The saturated unbranched acyclic hydrocarbons C2H6, C3H8, and C4H10 have the retained names ethane, propane, and butane, respectively.
  2. ^ IUPAC 2014, p. 4. "Similarly, the retained names 'ethane', 'propane', and 'butane' were never replaced by systematic names 'dicarbane', 'tricarbane', and 'tetracarbane' as recommended for analogues of silane, 'disilane'; phosphane, 'triphosphane'; and sulfane, 'tetrasulfane'."
  3. ^ "Ethane – Compound Summary". PubChem Compound. US: National Center for Biotechnology Information. 16 September 2004. Retrieved 7 December 2011.
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  7. ^ Kolbe, Hermann; Frankland, Edward (1849). "On the products of the action of potassium on cyanide of ethyl". Journal of the Chemical Society. 1: 60–74. doi:10.1039/QJ8490100060.
  8. ^ Frankland, Edward (1850). "On the isolation of the organic radicals". Journal of the Chemical Society. 2 (3): 263–296. doi:10.1039/QJ8500200263.
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  28. ^ Kort, E. A.; Smith, M. L.; Murray, L. T.; Gvakharia, A.; Brandt, A. R.; Peischl, J.; Ryerson, T. B.; Sweeney, C.; Travis, K. (2016). "Fugitive emissions from the Bakken shale illustrate role of shale production in global ethane shift". Geophysical Research Letters. 43 (9): 4617–4623. Bibcode:2016GeoRL..43.4617K. doi:10.1002/2016GL068703. hdl:2027.42/142509.
  29. ^ "One oil field a key culprit in global ethane gas increase". University of Michigan. April 26, 2016.
  30. ^ a b Aydin, Kamil Murat; Williams, M.B.; Saltzman, E.S. (April 2007). "Feasibility of reconstructing paleoatmospheric records of selected alkanes, methyl halides, and sulfur gases from Greenland ice cores". Journal of Geophysical Research. 112 (D7). Bibcode:2007JGRD..112.7312A. doi:10.1029/2006JD008027.
  31. ^ Hodnebrog, Øivind; Dalsøren, Stig B.; Myrhe, Gunnar (2018). "Lifetimes, direct and indirect radiative forcing, and global warming potentials of ethane (C2H6), propane (C3H8), and butane (C4H10)". Atmospheric Science Letters. 19 (2). Bibcode:2018AtScL..19E.804H. doi:10.1002/asl.804.
  32. ^ Brown, Bob; et al. (2008). "NASA Confirms Liquid Lake on Saturn Moon". NASA Jet Propulsion Laboratory. Archived from the original on 2011-06-05. Retrieved 2008-07-30.
  33. ^ Brown, R. H.; Soderblom, L. A.; Soderblom, J. M.; Clark, R. N.; Jaumann, R.; Barnes, J. W.; Sotin, C.; Buratti, B.; et al. (2008). "The identification of liquid ethane in Titan's Ontario Lacus". Nature. 454 (7204): 607–10. Bibcode:2008Natur.454..607B. doi:10.1038/nature07100. PMID 18668101. S2CID 4398324.
  34. ^ Mumma, Michael J.; et al. (1996). "Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin". Science. 272 (5266): 1310–1314. Bibcode:1996Sci...272.1310M. doi:10.1126/science.272.5266.1310. PMID 8650540. S2CID 27362518.
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