2,2,4-Trimethylpentane

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 to increase the knock resistance of the fuel.[2]

For other isomers of octane, see Octane § Isomers.
2,2,4-Trimethylpentane
Names
IUPAC name
2,2,4-Trimethylpentane[1]
Identifiers
CAS Number
3D model (JSmol)
Beilstein Reference
 1696876
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.007.964
EC Number
  • 208-759-1
MeSH 2,2,4-trimethylpentane
PubChem CID
RTECS number
  • SA3320000
UNII
UN number 1262
CompTox Dashboard (EPA)
Properties
Chemical formula
 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
Magnetic susceptibility (χ)
 -98.34·10−6 cm3/mol
Refractive index (nD)
 1.391
Thermochemistry
Heat capacity (C)
 242.49 J K−1 mol−1
Std molar
entropy (So298)
 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 pictograms
GHS Signal word Danger
GHS hazard statements
 H225, H304, H315, H336, H410
GHS precautionary statements
 P210, P261, P273, P301+310, P331
NFPA 704 (fire diamond)
3
1
0
Flash point −12 °C (10 °F; 261 K)
Autoignition
temperature
 396 °C (745 °F; 669 K)
Explosive limits 1.1–6.0%
Related compounds
Related alkanes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

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 so, historically, it has been assigned this name.[3]

Production

Isooctane is produced on a massive scale in the petroleum industry by alkylation of isobutene with isobutane. The process is conducted in alkylation units in the presence of acid catalysts.[4]

Route to 2,2,4-trimethylpentane from isobutene and isobutane

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.[5]

History

Engine knocking is an unwanted process that can occur during high compression ratios in internal combustion engines. Graham Edgar in 1926 added different amounts of n-heptane and 2,2,4-trimethylpentane to gasoline, and discovered that the knocking stopped when 2,2,4-trimethylpentane was added. This work was the origin of the octane rating scale.[6] 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 compounds and blends of compounds then were graded against these two standards and assigned octane numbers.

Safety

In common with all hydrocarbons, 2,2,4-trimethylpentane is flammable.[7]

See also
  • Oil refinery
  • Antiknock agents

References
  1. "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.
  2. 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.
  3. Clayden, Jonathan (2005). Organic chemistry (Reprinted (with corrections). ed.). Oxford [u.a.]: Oxford Univ. Press. pp. 315. ISBN 978-0-19-850346-0.
  4. 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.
  5. Dimerization of isobutylene, Amberlyst.com
  6. Fuels and lubricants handbook, Volume 1, George E. Totten, Steven R. Westbrook, Rajesh J. Shah, page 62
  7. 2,2,4-Trimethylpentane, Integrated Risk Information System, United States Environmental Protection Agency
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