Hexane is a colorless liquid, odorless when pure, and with a boiling point of approximately 69 °C (156 °F). It is widely used as a cheap, relatively safe, largely unreactive, and easily evaporatednon-polar solvent, and moderngasoline blends contain about 3% hexane.[8]
The termhexanes refers to amixture, composed largely (>60%) ofn-hexane, with varying amounts of theisomeric compounds2-methylpentane and3-methylpentane, and possibly, smaller amounts of nonisomeric C5, C6, and C7 (cyclo)alkanes. These "hexanes" mixtures are cheaper than pure hexane, and are often used in large-scale operations that don't require a singleisomer (e.g., as cleaning solvent or forchromatography).
A typical laboratory use of hexanes is to extractoil andgrease contaminants from water and soil for analysis.[9] Since hexane cannot be easilydeprotonated, it is used in the laboratory for reactions that involve very strong bases, such as the preparation oforganolithiums. For example, butyllithiums are typically supplied as a hexane solution.[10]
Hexanes are commonly used inchromatography as a non-polar solvent. Higher alkanes present as impurities in hexanes have similar retention times as the solvent, meaning that fractions containing hexane will also contain these impurities. In preparative chromatography, concentration of a large volume of hexanes can result in a sample that is appreciably contaminated by alkanes. This may result in a solid compound being obtained as anoil and the alkanes may interfere with analysis.
As aninternal combustion engine fuel,n-hexane has lowoctane numbers; aresearch octane number of 24.8 and amotor octane number of 26.[11] In 1983 its share in Japanese gasoline varied around 6%,[12] in 1992 it was present in American gas between 1 and 3%,[13] and in Swedish automobile fuel in the same year the share was consistently under 2%, often below 1%.[14] By 2011 its share in US gas stood between 1 and 7%.[15]
Hexane is chiefly obtained byrefiningcrude oil. The exact composition of the fraction depends largely on the source of the oil (crude or reformed) and the constraints of the refining.[16] The industrial product (usually around 50% by weight of the straight-chain isomer) is the fraction boiling at 65–70 °C (149–158 °F).
All alkanes are colorless.[17][18] The boiling points of the various hexanes are somewhat similar and, as for other alkanes, are generally lower for the more branched forms. The melting points are quite different and the trend is not apparent.[19]
Like most alkanes, hexanes typically exhibit low reactivity and are suitablesolvents for reactive compounds. Commercial samples ofn-hexane however often containsmethylcyclopentane, which features tertiaryC-H bonds, which are incompatible with someradical reactions.[20]
Inhalation ofn-hexane at 5000 ppm for 10 minutes produces marked vertigo; 2500-1000 ppm for 12 hours producesdrowsiness,fatigue, loss of appetite, andparesthesia in the distal extremities; 2500–5000 ppm produces muscle weakness, cold pulsation in the extremities, blurred vision,headache, andanorexia.[21] Chronic occupational exposure to elevated levels ofn-hexane has been demonstrated to be associated withperipheral neuropathy inauto mechanics in the US, andneurotoxicity in workers in printing presses, and shoe and furniture factories in Asia, Europe, and North America.[22]
Hexane and other volatile hydrocarbons (petroleum ether) present anaspiration risk.[26]n-Hexane is sometimes used as adenaturant for alcohol, and as a cleaning agent in thetextile,furniture, and leather industries. It is slowly being replaced with other solvents.[27]
Like gasoline, hexane is highly volatile and is an explosion risk.
The 1981Louisville sewer explosions, which destroyed over 13 mi (21 km) of sewer lines and streets in the Kentucky city, were caused by ignition of hexane vapors which had been illegally discharged from asoybean processing plant owned byRalston-Purina.
Hexane was attributed as the cause of an explosion that occurred in theNational University of Río Cuarto, Argentina on 5 December 2007, due to a hexane spill near a heat-producing machine that exploded, producing a fire that killed one student and injured 24 more.
Occupational hexane poisoning has occurred with Japanese sandal workers, Italian shoe workers,[28] Taiwan press proofing workers, and others.[29] Analysis ofTaiwanese workers has shown occupational exposure to substances includingn-hexane.[30] In 2010–2011, Chinese workers manufacturingiPhones were reported to have suffered hexane poisoning.[31][32]
^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.
^"n-hexane – Compound Summary".PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records.Archived from the original on 8 March 2012. Retrieved31 December 2011.
^Centers for Disease Control and Prevention (CDC) (16 November 2001). "n-Hexane-related peripheral neuropathy among automotive technicians--California, 1999-2000".MMWR. Morbidity and Mortality Weekly Report.50 (45):1011–1013.ISSN0149-2195.PMID11724159.
^Gad, Shayne C (2005), "Petroleum Hydrocarbons",Encyclopedia of Toxicology, vol. 3 (2nd ed.), Elsevier, pp. 377–379
^abClough, Stephen R; Mulholland, Leyna (2005). "Hexane".Encyclopedia of Toxicology. Vol. 2 (2nd ed.). Elsevier. pp. 522–525.
^Rizzuto, N; De Grandis, D; Di Trapani, G; Pasinato, E (1980). "N-hexane polyneuropathy. An occupational disease of shoemakers".European Neurology.19 (5):308–15.doi:10.1159/000115166.PMID6249607.
^Filser JG, Csanády GA, Dietz W, Kessler W, Kreuzer PE, Richter M, Störmer A (1996). "Comparative Estimation of the Neurotoxic Risks of N-Hexane and N-Heptane in Rats and Humans Based on the Formation of the Metabolites 2,5-Hexanedione and 2,5-Heptanedione".Biological Reactive Intermediates V. Advances in Experimental Medicine and Biology. Vol. 387. pp. 411–427.doi:10.1007/978-1-4757-9480-9_50.ISBN978-1-4757-9482-3.PMID8794236.
