Pentane is anorganic compound with theformula C5H12—that is, analkane with fivecarbon atoms. The term may refer to any of threestructural isomers, or to a mixture of them: in theIUPAC nomenclature, however,pentane means exclusively then-pentane isomer, in which casepentanes refers to a mixture of them; the other two are calledisopentane (methylbutane) andneopentane (dimethylpropane).Cyclopentane is not an isomer of pentane because it has only 10hydrogen atoms where pentane has 12.
Pentanes are components of some fuels and are employed as specialtysolvents in thelaboratory. Their properties are very similar to those ofbutanes andhexanes.
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Normal pentane was discovered in 1862 byCarl Schorlemmer, who, while analyzing pyrolysis products of thecannel coal mined inWigan, identified, separated byfractional distillation and studied a series of liquid hydrocarbons inert tonitric andsulfuric acids. The lightest of them, which he calledhydride of amyl, had anempirical formula of C5H12, density of 0.636 at 17 °C and boiled between 39 and 40 °C.[6] In the next year he identified the same compound in thePennsylvanian oil.[7] By 1872 he switched his nomenclature to the modern one.[8]
Pentanes are some of the primaryblowing agents used in the production ofpolystyrene 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.[10]
Pentanes are relatively inexpensive and are the mostvolatile liquid alkanes at room temperature, so they are often used in the laboratory assolvents that can be conveniently and rapidly evaporated. However, because of theirnonpolarity and lack offunctionality, they dissolve only nonpolar and alkyl-rich compounds. Pentanes aremiscible with most common nonpolar solvents such aschlorocarbons,aromatics, andethers.
Theboiling 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 themelting points of alkane isomers, and that of isopentane is 30 °C lower than that ofn-pentane. However, the melting point ofneopentane, the most heavily branched of the three, is 100 °Chigher than that of isopentane. The anomalously high melting point of neopentane has been attributed to thetetrahedralmolecules packing more closely in solid form; this explanation is contradicted by the fact that neopentane has a lower density than the other two isomers,[12] and the high melting point is actually caused by neopentane's significantly lowerentropy of fusion.
Like otheralkanes, pentanes are largely unreactive at standard room temperature and conditions - however, with sufficientactivation energy (e.g., an open flame), they readilyoxidize to formcarbon dioxide and water:
Without zeolite catalysts, such reactions are unselective, so withn-pentane, the result is a mixture of the 1-, 2-, and 3-chloropentanes, as well as more highly chlorinated derivatives. Other radicalhalogenations can also occur.
It occurs in alcoholic beverages and inhop oil.[16] 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.[17]
Pentane is a relatively minor component of automobilegasoline, with its share varying within 1–6% in 1990s Sweden,[18] 2–13% in 1990s US[19] and 1–3% in the US in 2011.[20] At 62, its octane number (both RON and MON) is quite low.[21]
^Hofmann, August Wilhelm Von (1 January 1867). "I. On the action of trichloride of phosphorus on the salts of the aromatic monamines".Proceedings of the Royal Society of London.15:54–62.doi:10.1098/rspl.1866.0018.S2CID98496840.
^abcWei, James (1999). "Molecular Symmetry, Rotational Entropy, and Elevated Melting Points".Industrial & Engineering Chemistry Research.38 (12):5019–5027.doi:10.1021/ie990588m.
^Karl Griesbaum; Arno Behr; Dieter Biedenkapp; Heinz-Werner Voges; Dorothea Garbe; Christian Paetz; Gerd Collin; Dieter Mayer; Hartmut Höke (2002). "Hydrocarbons".Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH.doi:10.1002/14356007.a13_227.ISBN978-3-527-30673-2.
^Milne, G. W. A., ed. (2005).Gardner's Commercially Important Chemicals: Synonyms, Trade Names, and Properties. Hoboken, New Jersey: John Wiley & Sons, Inc. p. 477.ISBN978-0-471-73518-2.
^Wei, James (1999). "Molecular Symmetry, Rotational Entropy, and Elevated Melting Points".Industrial & Engineering Chemistry Research.38 (12). American Chemical Society (ACS):5019–5027.doi:10.1021/ie990588m.ISSN0888-5885.
^Good, W.D (1970). "The enthalpies of combustion and formation of the isomeric pentanes".The Journal of Chemical Thermodynamics.2 (2). Elsevier BV:237–244.doi:10.1016/0021-9614(70)90088-1.ISSN0021-9614.
^Phillips, Michael; Herrera, Jolanta; Krishnan, Sunithi; Zain, Mooena; Greenberg, Joel; Cataneo, Renee N. (1999). "Variation in volatile organic compounds in the breath of normal humans".Journal of Chromatography B: Biomedical Sciences and Applications.729 (1–2):75–88.doi:10.1016/S0378-4347(99)00127-9.PMID10410929.
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