Description
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.
Chemical Properties
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.
Physical properties
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).
Uses
In determining octane numbers of fuels; in spectrophotometric analysis; as solvent and thinner.
Uses
Isooctane is a petroleum product, producedby the refining of petroleum. It is used as thestandard in determining the octane numbersof fuels (its antiknock octane number is 100)and as a solvent in chemical analysis.
Uses
2,2,4-Trimethylpentane is used as a mobile phase in High Performance Liquid Chromatography and Liquid Chromatography coupled with Mass Spectrometry.
Production Methods
Isooctane is produced from the fractional distillation of
petroleum fractions and naphthas. It is also produced from
the alkylation of 2-methylpropene with isobutane.
Definition
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.
General Description
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.
Air & Water Reactions
Highly flammable. Insoluble in water.
Reactivity Profile
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.
Hazard
Intermediate, azeotropic distillation entrainer.
Health Hazard
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.
Health Hazard
The acute toxicity of isooctane is very lowand is similar to n-octane. Exposure tohigh concentrations may produce irritationof respiratory tract. Exposure to 30,000 ppmfor an hour may be lethal to mice. There isno report of any other adverse effects fromexposure to isooctane.
Fire Hazard
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.
Flammability and Explosibility
Flammable
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.
Potential Exposure
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.
Source
Schauer et al. (1999) reported 2,2,4-trimethylpentane in a diesel-powered medium-duty
truck exhaust at an emission rate of 1,240 μg/km.
A constituent in gasoline. Harley et al. (2000) analyzed the headspace vapors of three grades of
unleaded gasoline where ethanol was added to replace methyl tert-butyl ether. The gasoline vapor
concentrations of 2,2,4-trimethylpentane in the headspace were 2.7 wt % for regular grade, 2.8 wt
% for mid-grade, and 3.3 wt % for premium grade.
California Phase II reformulated gasoline contained 2,2,4-trimethylpentane at a concentration of
34.6 g/kg. Gas-phase tailpipe emission rates from gasoline-powered automobiles with and without
catalytic converters were 8.20 and 1,080 mg/km, respectively (Schauer et al., 2002).
Environmental Fate
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 cm
3/molecule?sec at 300 K (Hendry and
Kenley, 1979); 2.83 x 10
-12 cm
3/molecule?sec at 298 K (Greiner, 1970); 3.73 x 10
-12
cm
3/molecule?sec at 298–305 K (Darnall et al., 1978); 3.7 x 10
-12 cm
3/molecule?sec (Atkinson et
al., 1979); 3.90 x 10
-12 cm
3/molecule?sec at 298 K (Atkinson, 1985). Based on a photooxidation
rate constant of 3.68 x 10
-12 cm
3/molecule?sec 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.
Shipping
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.]
Incompatibilities
Reacts with strong oxidizers, causing fire
and explosion hazard. Attacks some forms of plastics, rubber
and coatings.
Waste Disposal
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.
