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Title: 2,2,4-Trimethylpentane  
Author: World Heritage Encyclopedia
Language: English
Subject: Octane rating, Octane, Alkane, Antiknock agents, Octane (disambiguation)
Collection: Alkanes, Antiknock Agents
Publisher: World Heritage Encyclopedia


Skeletal formula of 2,2,4-trimethylpentane
Ball and stick model of 2,2,4-trimethylpentane
Spacefill model of 2,2,4-trimethylpentane
IUPAC name
ChemSpider  Y
EC number 208-759-1
Jmol-3D images Image
RTECS number SA3320000
UN number 1262
Molar mass 114.23 g·mol−1
Appearance Colorless liquid
Odor Odorless
Density 0.692 g cm−3
Melting point −107.44 to −107.32 °C; −161.39 to −161.18 °F; 165.71 to 165.83 K
Boiling point 99.1 to 99.5 °C; 210.3 to 211.0 °F; 372.2 to 372.6 K
log P 4.373
Vapor pressure 5.5 kPa (at 21 °C)
3.0 nmol Pa−1 kg−1
UV-vismax) 210 nm
242.49 J K−1 mol−1
328.03 J K−1 mol−1
−260.6 to −258.0 kJ mol−1
−5462.6 to −5460.0 kJ mol−1
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The environment pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
H225, H304, H315, H336, H410
P210, P261, P273, P301+310, P331
Highly Flammable F Harmful Xn Dangerous for the Environment (Nature) N
R-phrases R50/53, R65, R67
S-phrases (S2), S16, S29, S33
NFPA 704
Flash point −12 °C (10 °F; 261 K)
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  (: Y/N?)

2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an 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]

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 ended up with this name.[3]


  • Production 1
  • History 2
  • Safety 3
  • See also 4
  • References 5
  • External links 6


Isooctane is produced on a massive scale in the petroleum industry by distillation of petroleum. It can also be produced from isobutylene by dimerization (a variant of alkylation) using an Amberlyst catalyst to produce a mixture of iso-octenes. Hydrogenation of this mixture produces 2,2,4-trimethylpentane.[4]

Dimerization of isobutylene followed by hydrogenation produces 2,2,4-trimethylpentane


Engine knocking is an unwanted process that can occur during combustion 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 was the origin of the octane rating scale.[5] Test motors, using 2,2,4-trimethylpentane gave a certain performance which 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.


In common with all hydrocarbons, 2,2,4-trimethylpentane is exceedingly flammable in the presence of oxygen, and its vapours readily form explosive mixtures with air.

Also in common with all hydrocarbons, inhalation or ingestion of large quantities of 2,2,4-trimethylpentane is harmful. In rare cases a stronger reaction can occur.[6]

See also


  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 and Klaus Reders "Automotive Fuels" in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim.doi:10.1002/14356007.a16_719.pub2
  3. ^ Clayden, Jonathan (2005). Organic chemistry (Reprinted (with corrections). ed.). Oxford [u.a.]: Oxford Univ. Press. p. 315.  
  4. ^ Dimerization of isobutylene,
  5. ^ Fuels and lubricants handbook, Volume 1, George E. Totten, Steven R. Westbrook, Rajesh J. Shah, page 62
  6. ^ 2,2,4-Trimethylpentane, Integrated Risk Information System, United States Environmental Protection Agency

External links

  • International Chemical Safety Card 0496
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