Hexane

Not to be confused with hexene or hexyne.
Hexane
Names
IUPAC name
Hexane[1]
Identifiers
110-54-3 YesY
1730733
ChEBI CHEBI:29021 YesY
ChEMBL ChEMBL15939 YesY
ChemSpider 7767 YesY
DrugBank DB02764 YesY
EC Number 203-777-6
1985
Jmol interactive 3D Image
KEGG C11271 YesY
MeSH n-hexane
PubChem 8058
RTECS number MN9275000
UNII 2DDG612ED8 YesY
UN number 1208
Properties
C6H14
Molar mass 86.18 g·mol−1
Appearance Colorless liquid
Odor Petrolic
Density 0.6548 g mL−1
Melting point −96 to −94 °C; −141 to −137 °F; 177 to 179 K
Boiling point 68.5 to 69.1 °C; 155.2 to 156.3 °F; 341.6 to 342.2 K
9.5 mg L−1
log P 3.764
Vapor pressure 17.60 kPa (at 20.0 °C)
7.6 nmol Pa−1 kg−1
UV-vis (λmax) 200 nm
1.375
Viscosity 0.3 mPa · s
Thermochemistry
265.2 J K−1 mol−1
296.06 J K−1 mol−1
−199.4–−198.0 kJ mol−1
−4180–−4140 kJ mol−1
Hazards
Safety data sheet See: data page
GHS pictograms
GHS signal word DANGER
H225, H304, H315, H336, H373, H411
P210, P261, P273, P281, P301+310, P331
F Xn N
R-phrases R11, R38, R48/20, R51/53, R62, R65, R67
S-phrases (S2), S16, S29, S33, S36/37
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
3
2
0
Flash point −26.0 °C (−14.8 °F; 247.2 K)
234.0 °C (453.2 °F; 507.1 K)
Explosive limits 1.2–7.7%
Lethal dose or concentration (LD, LC):
25 g kg−1 (oral, rat)
28710 mg/kg (rat, oral)[2]
56137 mg/kg (rat, oral)[2]
US health exposure limits (NIOSH):
TWA 500 ppm (1800 mg/m3)[3]
TWA 50 ppm (180 mg/m3)[3]
1100 ppm[3]
Related compounds
Related alkanes
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
YesY verify (what is YesYN ?)
Infobox references

Hexane /ˈhɛkseɪn/ is an alkane of six carbon atoms, with the chemical formula C6H14.

The term may refer to any of the five structural isomers with that formula, or to a mixture of them.[4] In IUPAC nomenclature, however, hexane is the unbranched isomer (n-hexane); the other four structures are named as methylated derivatives of pentane and butane. IUPAC also uses the term as the root of many compounds with a linear six-carbon backbone, such as 2-methylhexane (C7H16), which is also called "isoheptane".

Hexanes are significant constituents of gasoline. They are all colorless liquids at room temperature, odorless when pure, with boiling points between 50 and 70 °C. They are widely used as cheap, relatively safe, largely unreactive, and easily evaporated non-polar solvents.

Isomers

Common name IUPAC name Text formula Skeletal formula
normal hexane
n-hexane		 hexane CH3(CH2)4CH3
isohexane 2-methylpentane (CH3)2CH(CH2)2CH3
3-methylpentane CH3CH2CH(CH3)CH2CH3
2,3-dimethylbutane CH3CH(CH3)CH(CH3)CH3
neohexane 2,2-dimethylbutane CH3C(CH3)2CH2CH3

Uses

In industry, hexanes are used in the formulation of glues for shoes, leather products, and roofing. They are also used to extract cooking oils (such as canola oil or soy oil) from seeds, for cleansing and degreasing a variety of items, and in textile manufacturing. It is commonly used in food based soybean oil extraction in the United States, and it is a contaminant potentially present in all soy food products using the technique, which is controversially not regulated by the FDA.[5][6]

A typical laboratory use of hexanes is to extract oil and grease contaminants from water and soil for analysis.[7] Since hexane cannot be easily deprotonated, it is used in the laboratory for reactions that involve very strong bases, such as the preparation of organolithiums. For example, butyllithiums are typically supplied as a hexane solution.

Hexanes are commonly used in chromatography 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 an oil and the alkanes may interfere with analysis.

In many applications (especially pharmaceutical), the use of n-hexane is being phased out due to its long term toxicity. It is often replaced by n-heptane, which will not form the toxic metabolite hexane-2,5-dione.[8]

Production

Hexanes are chiefly obtained by the refining of crude oil. The exact composition of the fraction depends largely on the source of the oil (crude or reformed) and the constraints of the refining. The industrial product (usually around 50% by weight of the straight-chain isomer) is the fraction boiling at 65–70 °C.

Physical properties

All alkanes are colorless.[9][10] 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.[11]

Isomer M.P. (°C) B.P. (°C)
n-hexane −95.3 68.7
3-methylpentane −118.0 63.3
2-methylpentane (isohexane) −153.7 60.3
2,3-dimethylbutane −128.6 58.0
2,2-dimethylbutane (neohexane) −99.8 49.7

Hexane has considerable vapor pressure at room temperature:[12]

Temperature (°C) Vapor pressure (mmHg)
−40 3.36
−30 7.12
−20 14.01
−10 25.91
0 45.37
10 75.74
20 121.26
25 151.28
30 187.11
40 279.42
50 405.31
60 572.76

Safety

Acute exposure to n-hexane usually occurs by inhalation, but it may be absorbed orally and transdermally. Minor exposures may occur when people fill their automobile fuel tanks with gasoline. Recent research suggests that certain fungi may be able to produce n-hexane.[13]

The acute toxicity of n-hexane is rather low. However, it has been reported to be the most highly toxic member of the alkanes. When n-hexane is ingested, it causes nausea, vertigo, bronchial irritation, intestinal irritation and CNS effects. It has been reported that ~50 g of n-hexane may be fatal to humans. Furthermore, n-hexane is biotransformed to 2-hexanol and further to 2,5-hexanediol by cytochrome P450 mixed function oxidases by omega oxidation. 2,5-Hexanediol may be further oxidized to 2,5-hexanedione, which is neurotoxic and produces a polyneuropathy.[13]

Products with low viscosity such as hexane and other volatile hydrocarbons (petroleum ether) present an extreme aspiration risk. Even small amounts of a low-viscosity material, once aspirated, can involve a significant portion of the lung and produce a chemical pneumonitis. Hydrocarbon pneumonia is an acute hemorrhagic necrotizing disease that can develop within 24 h after the ingestion. Pneumonia may require several weeks for complete resolution. Therefore, gastric lavage is not indicated for hydrocarbon ingestion because of the risk of aspiration if the patient vomits around the lavage tube.[14]

n-Hexane is also used as a solvent in the extraction of oil from seeds (soybean, cottonseed, flaxseed, safflower seed, and others). It is sometimes used as a denaturant for alcohol, and as a cleaning agent in the textile, furniture, and leather industries. It is slowly being replaced with other less toxic solvents.[13]

A peer reviewed study found that inhalation of n-hexane at 5000 ppm for 10 minutes produces marked vertigo; 2500-1000 ppm for 12 hours produces drowsiness, fatigue, loss of appetite, and paresthesia in the distal extremities; 2500-5000 ppm produces muscle weakness, cold pulsation in the extremities, blurred vision, headache and anorexia.[15] The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) for hexane isomers (not n-hexane) of 100 ppm (350 mg/m3) over an 8-hour workday.[16]

Occupational hexane poisoning has occurred with Japanese sandal workers, Italian shoe workers,[17] Taiwan press proofing workers, and others.[18] Analysis of Taiwanese workers has shown occupational exposure to substances including n-hexane.[19] In 2010-2011, Chinese workers manufacturing iPhones were reported as having suffered hexane poisoning.[20][21]

References

  1. ↑ "n-hexane – Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 31 December 2011.
  2. 1 2 "n-Hexane". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
  3. 1 2 3 "NIOSH Pocket Guide to Chemical Hazards #0322". National Institute for Occupational Safety and Health (NIOSH).
  4. ↑ "C5 and C6 alkanes". A and B Scott Organic Chemistry. Retrieved 30 October 2007.
  5. ↑ "The Tofurky Company : Our Ingredients". Tofurky.com. Retrieved 2015-03-17.
  6. ↑ Palmer, Brian (2010-04-26). "A study found hexane in soy protein. Should you stop eating veggie burgers?". Slate.com. Retrieved 2015-03-17.
  7. ↑ Archived 5 April 2013 at the Wayback Machine
  8. ↑ 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". Adv Exp Med Biol 387: 411–427. PMID 8794236.
  9. ↑ "Organic Chemistry-I" (PDF). Nsdl.niscair.res.in. Retrieved 2014-02-17.
  10. ↑ "13. Hydrocarbons | Textbooks". Textbook.s-anand.net. Retrieved 2014-02-17.
  11. ↑ William D. McCain (1990). The properties of petroleum fluids. PennWell. ISBN 0-87814-335-1.
  12. ↑
  13. 1 2 3 Stephen R Clough; Leyna Mulholland (2005), "Hexane", Encyclopedia of Toxicology 2 (2nd ed.), Elsevier, pp. 522–525
  14. ↑ Shayne C Gad (2005), "Petroleum Hydrocarbons", Encyclopedia of Toxicology 3 (2nd ed.), Elsevier, pp. 377–379
  15. ↑ "N-HEXANE". Toxicology data network Hazardous Substances Data Bank. National Library of Medicine.
  16. ↑ "CDC - NIOSH Pocket Guide to Chemical Hazards - Hexane isomers (excluding n-Hexane)". www.cdc.gov. Retrieved 2015-11-03. line feed character in |title= at position 47 (help)
  17. ↑ 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. PMID 6249607.
  18. ↑ n-Hexane, Environmental Health Criteria (122), World Health Organization, 1991
  19. ↑ Liu, C. H.; Huang, C. Y.; Huang, C. C. (2012). "Occupational Neurotoxic Diseases in Taiwan". Safety and Health at Work 3 (4): 257–67. doi:10.5491/SHAW.2012.3.4.257. PMC 3521924. PMID 23251841.
  20. ↑ "Workers poisoned while making iPhones - ABC News (Australian Broadcasting Corporation)". Abc.net.au. 2010-10-26. Retrieved 2015-03-17.
  21. ↑ David Barboza (February 22, 2011). "Workers Sickened at Apple Supplier in China". The New York Times. Retrieved 2015-03-17.

External links

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