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Iso-octane

2,2,4-Trimethylpentane
Skeletal formula of 2,2,4-trimethylpentane
Ball and stick model of 2,2,4-trimethylpentane
Spacefill model of 2,2,4-trimethylpentane
Names
IUPAC name
2,2,4-Trimethylpentane
Identifiers
540-84-1 YesY
3D model (Jmol) Interactive image
1696876
ChEBI CHEBI:62805 N
ChEMBL ChEMBL1797261 N
ChemSpider 10445 YesY
ECHA InfoCard 100.007.964
EC Number 208-759-1
MeSH 2,2,4-trimethylpentane
PubChem 10907
RTECS number SA3320000
UN number 1262
Properties
C8H18
Molar mass 114.23 g·mol−1
Appearance Colorless liquid
Odor Odorless
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)
3.0 nmol Pa−1 kg−1
UV-vis (λmax) 210 nm
-98.34·10−6 cm3/mol
1.391
Thermochemistry
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
Hazards
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 R11, R38, R50/53, R65, R67
S-phrases (S2), S16, S29, S33
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 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine 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
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  (what is YesYN ?)
Infobox references

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.

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.

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.

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. 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.


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