2,2,4-Trimethylpentane
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| Names | |
|---|---|
| Preferred IUPAC name
2,2,4-Trimethylpentane[1] | |
| Identifiers | |
3D model (JSmol)
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| 1696876 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.007.964 |
| EC Number |
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| MeSH | 2,2,4-trimethylpentane |
PubChem CID
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| RTECS number |
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| UNII | |
| UN number | 1262 |
CompTox Dashboard (EPA)
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| Properties | |
| C8H18 | |
| Molar mass | 114.232 g·mol−1 |
| Appearance | Colorless liquid |
| Odor | petroleum-like |
| Density | 0.692 g cm−3 |
| Melting point | −107.38 °C; −161.28 °F; 165.77 K |
| Boiling point | 99.30 °C; 210.74 °F; 372.45 K |
| log P | 4.373 |
| Vapor pressure | 5.5 kPa (at 21 °C) |
Henry's law
constant (kH) |
3.0 nmol Pa−1 kg−1 |
| UV-vis (λmax) | 210 nm |
| −98.34·10−6 cm3/mol | |
Refractive index (nD)
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1.391 |
| Thermochemistry | |
Heat capacity (C)
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242.49 J K−1 mol−1 |
Std molar
entropy (S⦵298) |
328.03 J K−1 mol−1 |
Std enthalpy of
formation (ΔfH⦵298) |
−260.6 to −258.0 kJ mol−1 |
Std enthalpy of
combustion (ΔcH⦵298) |
−5462.6 to −5460.0 kJ mol−1 |
| Hazards | |
| GHS labelling: | |
   
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| Danger | |
| H225, H304, H315, H336, H410 | |
| P210, P261, P273, P301+P310, P331 | |
| NFPA 704 (fire diamond) | |
| Flash point | −12 °C (10 °F; 261 K) |
| 396 °C (745 °F; 669 K) | |
| Explosive limits | 1.1–6.0% |
| Related compounds | |
Related alkanes
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula (CH3)3CCH2CH(CH3)2. It is one of several isomers of octane (C8H18). This particular isomer is the standard 100 point on the octane rating scale (the zero point is n-heptane). It is an important component of gasoline, frequently used in relatively large proportions (around 10%) to increase the knock resistance of fuel.[2][3]
Strictly speaking, if the standard meaning of "iso" is followed, the name isooctane should be reserved for the isomer 2-methylheptane. However, 2,2,4-trimethylpentane is by far the most important isomer of octane and historically it has been assigned this name.[4]
Production
[edit]Isooctane is produced on a massive scale in the petroleum industry by alkylation of isobutene with isobutane. This process is conducted in alkylation units in the presence of acid catalysts.[5]
It can also be produced from isobutylene by dimerization using an Amberlyst catalyst to produce a mixture of iso-octenes. Hydrogenation of this mixture produces 2,2,4-trimethylpentane.[6]
History
[edit]Engine knocking is an unwanted process that can occur during high compression ratios in internal combustion engines. During the 1920s different measurement methods of knock were proposed but laboratories struggled to reproduce them reliably.
In 1926 Ethyl Corporation's Graham Edgar selected two specific hydrocarbons, n-heptane (commercially available in high purity from Jeffrey pine) and 2,2,4-trimethylpentane, itself first synthesized from tert-butyl alcohol via diisobutene by J. W. McKinney at the same laboratory in the same year, as primary standards. Compared to various chemicals and natural gasolines proposed before that, these two compounds had extremely close boiling points, ensuring the vapor mixture in the cylinder would be the same regardless of the carburetor, and didn't depend on the composition of particular crudes.[7]
This method became known as the octane rating scale. Test motors using 2,2,4-trimethylpentane gave a certain performance that was standardized as 100 octane. The same test motors, run in the same fashion, using heptane, gave a performance which was standardized as 0 octane. All other fuels were then graded against mixtures of these two chemicals and assigned octane numbers.[8][9]
Safety
[edit]In common with all hydrocarbons, 2,2,4-trimethylpentane is flammable.[10]
See also
[edit]References
[edit]- ^ "2,2,4-trimethylpentane - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Identification and Related Records. Retrieved 11 March 2012.
- ^ Werner Dabelstein; Arno Reglitzky; Andrea Schütze; Klaus Reders (2007). "Automotive Fuels". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16_719.pub2. ISBN 978-3527306732.
- ^ Richardson, KA; Wilmer, JL; Smith-Simpson, D; Skopek, TR (February 1986). "Assessment of the genotoxic potential of unleaded gasoline and 2,2,4-trimethylpentane in human lymphoblasts in vitro". Toxicology and Applied Pharmacology. 82 (2): 316–22. Bibcode:1986ToxAP..82..316R. doi:10.1016/0041-008x(86)90207-3. PMID 3945956.
- ^ Clayden, Jonathan (2005). Organic chemistry (Reprinted (with corrections). ed.). Oxford [u.a.]: Oxford Univ. Press. pp. 315. ISBN 978-0-19-850346-0.
- ^ Bipin V. Vora; Joseph A. Kocal; Paul T. Barger; Robert J. Schmidt; James A. Johnson (2003). "Alkylation". Kirk-Othmer Encyclopedia of Chemical Technology. doi:10.1002/0471238961.0112112508011313.a01.pub2. ISBN 0471238961.
- ^ Dimerization of isobutylene, Amberlyst.com
- ^ "Measurement of Knock Characteristics of Gasoline in Terms of a Standard Fuel1". ACS Publications. 1927-01-01. doi:10.1021/ie50205a049. Retrieved 2026-04-26.
- ^ Brooks, Donald B. (1946). "Development of REFERENCE FUEL SCALES for KNOCK RATING". SAE Transactions. 54: 394–403. ISSN 0096-736X.
- ^ Fuels and lubricants handbook, Volume 1, George E. Totten, Steven R. Westbrook, Rajesh J. Shah, page 62
- ^ 2,2,4-Trimethylpentane, Integrated Risk Information System, United States Environmental Protection Agency
External links
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