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Isooctane is a flammable liquid isomer of octane. It is best known for defining the octane number to rate the antiknock quality of gasoline, which is related to engine performance.
Since 1930, many chemical processes, such as alkylation and polymerization, have been developed to increase the production of branched compounds in refi nery operations. High octane numbers in gasoline are those associated with the alkenes (olefins) and aromatics, especially akyl benzene compounds. For example, 2-pentene has a RON of 154. Benzene itself has a RON of 98, but 1,3,5-trimethylbenzene has a RON of 170. The highest octane numbers in gasoline are associated with cyclic alkenes, but these account for only a minute fraction of gasoline.

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2,2,4-Trimethylpentane (isooctane), C8H18, is a colorless liquid naturally found in crude petroleum and in small amounts in natural gas. It is released to the environment by the petroleum industries, by automotive exhausts and emissions, and from hazardous-waste sites, landfills, and emissions from wood combustion.

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Octane is a colorless liquid with a gasoline-like odor. The odor threshold is 4 ppm and 48 ppm (New Jersey Fact Sheet). An odor threshold concentration of 670 ppbv was reported by Nagata and Takeuchi (1990).

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2,2,4-Trimethylpentane is used as a mobile phase in High Performance Liquid Chromatography and Liquid Chromatography coupled with Mass Spectrometry.

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Isooctane is produced from the fractional distillation of petroleum fractions and naphthas. It is also produced from the alkylation of 2-methylpropene with isobutane.

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ChEBI: 2,2,4-Trimethylpentane is an alkane that consists of pentane bearing two methyl substituents at position 2 and a single methyl substituent at position 4.

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A clear colorless liquid with a petroleum-like odor. Flash point 10°F. Less dense than water and insoluble in water. Vapors are heavier than air.

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Highly flammable. Insoluble in water.

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Saturated aliphatic hydrocarbons, such as 2,2,4-Trimethylpentane, may be incompatible with strong oxidizing agents like nitric acid. Charring of the hydrocarbon may occur followed by ignition of unreacted hydrocarbon and other nearby combustibles. In other settings, aliphatic saturated hydrocarbons are mostly unreactive. They are not affected by aqueous solutions of acids, alkalis, most oxidizing agents, and most reducing agents.

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Intermediate, azeotropic distillation entrainer.

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Inhalation or contact with material may irritate or burn skin and eyes. Fire may produce irritating, corrosive and/or toxic gases. Vapors may cause dizziness or suffocation. Runoff from fire control or dilution water may cause pollution.

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Highly flammable liquid; flash point (closed cup) －12.2°C (10°F); autoignition temperature 418°C (784°F) (NFPA 1997); fireextinguishing agent: dry chemical, foam, or CO2; use a water spray to keep fire-exposed containers cool. Isooctane forms explosive mixtures with air within the range 1–4.6% by volume of air.

Safety Profile

Mutation data reported. High concentrations can cause narcosis. A very dangerous fire hazard when exposed to heat, flame, oxidmers. Can react vigorously with reducing materials. Explosive in the form of vapor when exposed to heat or flame. To fight fire, use CO2, dry chemical. When heated to decomposition it emits acrid smoke and irritating fumes. See also ALKANES.

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Octane is used as a solvent; as a fuel; as an intermediate in organic synthesis; and in azeotropicdistillations.

Carcinogenicity

Male and female rats were initiated with 170 ppm N-ethyl-N-hydroxyethylnitrosamine for 2 weeks and subsequently exposed to isooctane for 61 weeks. An increase in atypical cell foci (a preneoplastic lesion) was observed in male but not female rats promoted with the high dose.

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Surface Water. Mackay and Wolkoff (1973) estimated an evaporation half-life of 4.1 sec from a surface water body that is 25 °C and 1 m deep.
Photolytic. The following rate constants were reported for the reaction of 2,2,4-trimethylpentane and OH radicals in the atmosphere: 2.3 x 10^-12 cm³/moleculesec at 300 K (Hendry and Kenley, 1979); 2.83 x 10^-12 cm³/moleculesec at 298 K (Greiner, 1970); 3.73 x 10^-12 cm³/moleculesec at 298–305 K (Darnall et al., 1978); 3.7 x 10^-12 cm³/moleculesec (Atkinson et al., 1979); 3.90 x 10^-12 cm³/moleculesec at 298 K (Atkinson, 1985). Based on a photooxidation rate constant of 3.68 x 10^-12 cm³/moleculesec for the reaction of 2,2,4-trimethylpentane and OH radicals in summer sunlight, the lifetime is 16 h (Altshuller, 1991).
Products identified from the reaction of 2,2,4-trimethylpentane with OH radicals in the presence of nitric oxide included acetone, 2-methypropanal, 4-hydroxy-4-methyl-2-pentanone, and hydroxy nitrates (Tuazon et al., 2002).
Chemical/Physical. Complete combustion in air produces carbon dioxide and water vapor. 2,2,4-Trimethylpentane will not hydrolyze in water.

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UN1262 Octanes, Hazard Class: 3; Labels: 3-Flammable liquid.

Purification Methods

Distil isooctane from sodium, pass it through a column of silica gel or activated alumina (to remove traces of olefins), and again distilled from sodium. Extract repeatedly with conc H2SO4, then agitate it with aqueous KMnO4, wash it with water, dry (CaSO4) and distil it. Purify it also by azeotropic distillation with EtOH, which is subsequently washed out with water, and the trimethylpentane is dried and fractionally distilled. [Forziati et al. J Res Nat Bur Stand 36 126 1946.] [Beilstein 1 IV 439.]

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Reacts with strong oxidizers, causing fire and explosion hazard. Attacks some forms of plastics, rubber and coatings.

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Dissolve or mix the material with a combustible solvent and burn in a chemical incinerator equipped with an after burner and scrubber. All federal, state, and local environmental regulations must be observed.

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