pentane

{{Expand section|date=January 2025}}

Normal pentane was discovered in 1862 by Carl Schorlemmer, who, while analyzing pyrolysis products of the cannel coal mined in Wigan, identified, separated by fractional distillation and studied a series of liquid hydrocarbons inert to nitric and sulfuric acids. The lightest of them, which he called hydride of amyl, had an empirical formula of C₅H₁₂, density of 0.636 at 17 °C and boiled between 39 and 40 °C.{{Cite journal |last=Schorlemmer |first=C. |date=1862 |title=On the hydrides of the alcohol-radicles existing in the products of the destructive distillation of cannel coal |url=https://books.google.com/books?id=51fYFmBb7_kC&pg=PA419 |journal=Journal of the Chemical Society |language=en |volume=15 |pages=419–427 |doi=10.1039/JS8621500419 |issn=0368-1769}} In the next year he identified the same compound in the Pennsylvanian oil.{{Cite book |last= |first= |url=https://books.google.com/books?id=fTw9AQAAMAAJ&pg=RA1-PA81 |title=Proceedings of the Literary and Philosophical Society of Manchester |date=1864 |language=en}} By 1872 he switched his nomenclature to the modern one.{{Cite journal |last=Schorlemmer |first=Carl |date=1872 |title=On the normal paraffins |url=https://books.google.com/books?id=Sow5AQAAMAAJ&pg=PA113 |journal=Philosophical Transactions of the Royal Society of London |volume=162 |pages=111–123 |doi=10.1098/rstl.1872.0007|url-access=subscription }}

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Pentanes are some of the primary blowing agents used in the production of polystyrene foam and other foams. Usually, a mixture of n-, i-, and increasingly cyclopentane is used for this purpose.

Acid-catalyzed isomerization gives isopentane, which is used in producing high-octane fuels.{{cite encyclopedia |author=Karl Griesbaum |author2=Arno Behr |author3=Dieter Biedenkapp |author4=Heinz-Werner Voges |author5=Dorothea Garbe |author6=Christian Paetz |author7=Gerd Collin |author8=Dieter Mayer |author9=Hartmut Höke |chapter=Hydrocarbons|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|year=2002|publisher=Wiley-VCH|place=Weinheim|doi=10.1002/14356007.a13_227|isbn=978-3-527-30673-2}}

Because of their low boiling points, low cost, and relative safety, pentanes are used as a working medium in geothermal power stations and organic Rankine cycles. It is also used in some blended refrigerants.

Pentanes are solvents in many ordinary products, e.g. in some pesticides.{{cite book|editor-last=Milne|editor-first=G. W. A.|title=Gardner's Commercially Important Chemicals: Synonyms, Trade Names, and Properties|date=2005|publisher=John Wiley & Sons, Inc|location=Hoboken, New Jersey|isbn=978-0-471-73518-2|page=477}}

Pentanes are relatively inexpensive and are the most volatile liquid alkanes at room temperature, so they are often used in the laboratory as solvents that can be conveniently and rapidly evaporated. However, because of their nonpolarity and lack of functionality, they dissolve only nonpolar and alkyl-rich compounds. Pentanes are miscible with most common nonpolar solvents such as chlorocarbons, aromatics, and ethers.

They are often used in liquid chromatography.

The boiling points of the pentane isomers range from about 9 to 36 °C. As is the case for other alkanes, the more thickly branched isomers tend to have lower boiling points.

The same tends to be true for the melting points of alkane isomers, and that of isopentane is 30 °C lower than that of n-pentane. However, the melting point of neopentane, the most heavily branched of the three, is 100 °C higher than that of isopentane. The anomalously high melting point of neopentane has been attributed to the tetrahedral molecules packing more closely in solid form; this explanation is contradicted by the fact that neopentane has a lower density than the other two isomers,{{cite journal | last=Wei | first=James | title=Molecular Symmetry, Rotational Entropy, and Elevated Melting Points | journal=Industrial & Engineering Chemistry Research | publisher=American Chemical Society (ACS) | volume=38 | issue=12 | year=1999 | issn=0888-5885 | doi=10.1021/ie990588m | pages=5019–5027}} and the high melting point is actually caused by neopentane's significantly lower entropy of fusion.

The branched isomers are more stable (have lower heat of formation and heat of combustion) than n-pentane. The difference is 1.8 kcal/mol for isopentane, and 5 kcal/mol for neopentane.From the values listed at Standard enthalpy change of formation (data table).{{cite journal | last=Good | first=W.D | title=The enthalpies of combustion and formation of the isomeric pentanes | journal=The Journal of Chemical Thermodynamics | publisher=Elsevier BV | volume=2 | issue=2 | year=1970 | issn=0021-9614 | doi=10.1016/0021-9614(70)90088-1 | pages=237–244}}

Rotation about two central single C-C bonds of n-pentane produces four different conformations.{{cite journal |journal=J. Phys. Chem. A |volume = 113 |issue = 6 |pages = 1012–9 |doi=10.1021/jp809639s |title=Enthalpy Difference between Conformations of Normal Alkanes: Raman Spectroscopy Study of n-Pentane and n-Butane |year=2009 |author=Roman M. Balabin |pmid=19152252|bibcode = 2009JPCA..113.1012B |author-link = Roman Balabin }}

Like other alkanes, pentanes are largely unreactive at standard room temperature and conditions - however, with sufficient activation energy (e.g., an open flame), they readily oxidize to form carbon dioxide and water:

:C₅H₁₂ + 8 O₂ → 5 CO₂ + 6 H₂O + heat/energy

Like other alkanes, pentanes undergo free radical chlorination:

:C₅H₁₂ + Cl₂ → C₅H₁₁Cl + HCl

Without zeolite catalysts, such reactions are unselective, so with n-pentane, the result is a mixture of the 1-, 2-, and 3-chloropentanes, as well as more highly chlorinated derivatives. Other radical halogenations can also occur.

Pentane is produced by fractional distillation of petroleum and purified by rectification (successive distillations).{{Cite web|title=Pentane|url=https://pubchem.ncbi.nlm.nih.gov/compound/Pentane|access-date=2023-06-29|website=PubChem}}

It occurs in alcoholic beverages and in hop oil. It is a component of exhaled breath for some individuals. A degradation product of unsaturated fatty acids, its presence is associated with some diseases and cancers.{{cite journal|doi=10.1016/S0378-4347(99)00127-9|pmid=10410929|title=Variation in volatile organic compounds in the breath of normal humans|journal=Journal of Chromatography B: Biomedical Sciences and Applications|volume=729|issue=1–2|pages=75–88|year=1999|last1=Phillips|first1=Michael|last2=Herrera|first2=Jolanta|last3=Krishnan|first3=Sunithi|last4=Zain|first4=Mooena|last5=Greenberg|first5=Joel|last6=Cataneo|first6=Renee N.}}

Pentane is a relatively minor component of automobile gasoline, with its share varying within 1–6% in 1990s Sweden,{{Cite journal |last1=Östermark |first1=Ulf |last2=Petersson |first2=Göran |date=1992-09-01 |title=Assessment of hydrocarbons in vapours of conventional and alkylate-based petrol |url=https://publications.lib.chalmers.se/records/fulltext/local_72590.pdf |journal=Chemosphere |volume=25 |issue=6 |pages=763–768 |doi=10.1016/0045-6535(92)90066-Z |issn=0045-6535}} 2–13% in 1990s US{{Cite journal |last1=Doskey |first1=Paul V. |last2=Porter |first2=Joseph A. |last3=Scheff |first3=Peter A. |date=November 1992 |title=Source Fingerprints for Volatile Non-Methane Hydrocarbons |url=https://www.tandfonline.com/doi/full/10.1080/10473289.1992.10467090 |journal=Journal of the Air & Waste Management Association |language=en |volume=42 |issue=11 |pages=1437–1445 |doi=10.1080/10473289.1992.10467090 |issn=1047-3289}} and 1–3% in the US in 2011.{{cite web |date=2011 |title=Hydrocarbon Composition of Gasoline Vapor Emissions from Enclosed Fuel Tanks |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100GPED.TXT |website=nepis.epa.gov |publisher=United States Environmental Protection Agency}} At 62, its octane number (both RON and MON) is quite low.{{Cite book |last=Scherzer |first=Julius |url=https://books.google.com/books?id=0R2qSCsVT3cC&pg=PA9 |title=Octane-Enhancing Zeolitic FCC Catalysts: Scientific and Technical Aspects |date=1990 |publisher=CRC Press |isbn=978-0-8247-8399-0 |pages=9 |language=en}}

{{Reflist}}

• [https://www.inchem.org/documents/icsc/icsc/eics0534.htm International Chemical Safety Card 0534] at ILO.org
• [https://www.cdc.gov/niosh/npg/npgd0486.html NIOSH Pocket Guide to Chemical Hazards] at CDC.gov
• [https://web.archive.org/web/20150923173922/http://www.ars-grin.gov/cgi-bin/duke/chemical.pl?PENTANE Phytochemical data for pentane] at Ars-grin.gov

{{Alkanes}}

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Category:Alkanes

Category:Hydrocarbon solvents