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| Names | |
|---|---|
| Preferred IUPAC name 2,2,4-Trimethylpentane[1] | |
| Identifiers | |
| |
3D model (JSmol) | |
| 1696876 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
|
| ECHA InfoCard | 100.007.964 |
| EC Number |
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| MeSH | 2,2,4-trimethylpentane |
| RTECS number |
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| UNII | |
| UN number | 1262 |
| |
| |
| 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 |
| logP | 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) | 1.391 |
| Thermochemistry | |
| 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: | |
    | |
| 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 | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
2,2,4-Trimethylpentane, also known asisooctane oriso-octane, is anorganic compound with the formula (CH3)3CCH2CH(CH3)2. It is one of severalisomers ofoctane (C8H18). This particular isomer is the standard 100 point on theoctane rating scale (the zero point isn-heptane). It is an important component ofgasoline, frequently used in relatively large proportions (around 10%) to increase theknock resistance of fuel.[2][3]
Strictly speaking, if the standard meaning of ‘iso’ is followed, the nameisooctane should be reserved for the isomer2-methylheptane. However, 2,2,4-trimethylpentane is by far the most important isomer of octane and historically it has been assigned this name.[4]
Isooctane is produced on a massive scale in thepetroleum industry by alkylation ofisobutene withisobutane. This process is conducted inalkylation units in the presence ofacid catalysts.[5]
It can also be produced fromisobutylene bydimerization using anAmberlystcatalyst to produce a mixture of iso-octenes.Hydrogenation of this mixture produces 2,2,4-trimethylpentane.[6]
Engine knocking is an unwanted process that can occur during high compression ratios ininternal combustion engines. In 1926Graham Edgar added different amounts ofn-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 theoctane rating scale.[7] 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.
In common with all hydrocarbons, 2,2,4-trimethylpentane is flammable.[8]
