What Is Isooctane?
Isooctane is one of the branched compounds of the eight-carbon saturated hydrocarbons.
In the fuel industry, it is called 2,2,4-trimethylpentane. Because of its stable combustion, it is used as a standard for octane rating (octane rating or octane number). Under the Fire Service Act, it is classified as a Class 4 Hazardous Substance, Petroleum No. 1.
| Chemical Formula | C8H18 |
| English Name | Isooctane |
| Molecular Weight | 114.23 |
Uses of Isooctane
Isooctane is used as a standard fuel (octane number 100) to measure octane number. It can also be used as a blending material for the production of high-octane gasoline. High-octane fuels have low anti-knock properties and are therefore suitable for running automobile engines.
Other applications include use as “solvents,” “extraction solvents,” “solvents for organic synthesis,” “aerosol solvents,” “agents for correction fluids,” “metal cleaners,” “inks,” “paints,” and “adhesives. Furthermore, it can be used as a “solvent for analysis” such as in high-performance liquid chromatography.
Properties of Isooctane
Isooctane has a melting point of -107°C and a boiling point of 99°C. It is a colorless liquid at room temperature and pressure and is found in trace amounts in petroleum.
It is insoluble in water but will mix with hydrocarbon solvents in any proportion.
Structure of Isooctane
Isooctane’s molecular formula is C8H18, its molecular weight is 114.23, and its density is 0.69 g/cm3. It has a branched structure with three methyl groups attached to pentane. The specific formula is CH3C(CH3)2CH2CH(CH3)2.
There are 18 different structural isomers. However, if stereoisomers are also considered, there are 24 isomers.
Other Information on Isooctane
1. Synthesis of Isooctane
Isooctane can be produced by alkylation of isobutane with isobutylene. It can also be obtained by dimerizing isobutylene with sulfuric acid and phosphoric acid and hydrogenating the resulting diisobutylene.
2. Isooctane in Octane Number
The octane number is a numerical value that expresses the resistance of gasoline to auto-ignition and knocking in the engine. The higher the octane number, the higher the knock resistance and anti-knock properties.
The octane number of isooctane, which has relatively high knock resistance among gasoline components, is 100, and that of n-heptane, which has low knock resistance, is 0. In other words, the octane number of a sample is the volume ratio of isooctane in a mixture of isooctane and n-heptane. In general, saturated hydrocarbons with more branches have higher knock resistance.
3. Structural Isomers of Isooctane
Main Chain: C8, C7
Octane, with 8 carbons in the main chain, is a structural isomer of isooctane. The structural isomers with 7 carbons in the main chain include 2-methylheptane, 3-methylheptane, and 4-methylheptane, which have one side chain.
Main Chain: C6
The structural isomer of isooctane with 6 carbons in the main chain includes 3-ethylhexane, which has one side chain. There are also 2,2-dimethylhexane, 2,3-dimethylhexane, 2,4-dimethylhexane, 2,5-dimethylhexane, 3,3-dimethylhexane and 3,4-dimethylhexane with two side chains.
Main Chain: C5, C4
Structural isomers of isooctane with 5 carbons in the main chain include 3-ethyl-2-methylpentane and 3-ethyl-3-methylpentane, which have two side chains, and 2,2,3-trimethylpentane, 2,3,3-trimethylpentane, and 2,3,4-trimethylpentane, which have three side chains.
Additionally, there is 2,2,3,3-tetramethylbutane, which has four side chains, as a structural isomer with four carbons in the main chain.