(redirected from C8h18)
Also found in: Dictionary, Thesaurus, Medical.


a liquid alkane hydrocarbon found in petroleum and existing in 18 isomeric forms, esp the isomer n-octane. Formula: C8H18



n-octane, a saturated hydrocarbon, C6H18; a colorless liquid with a characteristic odor. Melting point, –56.8°C; boiling point, 125.67°C; density, 0.7025 g/cm3 at 20°C; octane number, 17–19. Along with isooctane and other isomers, octane is found in petroleum and straight-run gasoline (up to 10 percent); large quantities of octane are present in synthetic gasoline prepared from CO and H2.

Octane is extracted commercially by rectification, then refined with urea or by means of molecular sieves. At 500°C and a pressure of 1–2 meganewtons per sq m, or 10–20 kilograms-force per sq cm, octane converts into a mixture of aromatic hydrocarbons (o-xylene and ethylbenzene) when passed over an aluminum-molybdenum or aluminum-chromium catalyst in the presence of hydrogen. This dehydrocyclization reaction is one of the main processes used in catalytic reforming.