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(n-heptane), the hydrocarbon C7H16, a colorless volatile liquid with a slight odor. Boiling point, 98.4° C; density, 0.6838 g/cm3 at 20° C; refractive index (nD20), 1.3876; heat of combustion, 1167.11 kilocalories per mole (25° C); explosion limits in air, 1.10-6.00 volume · percent; flash point, −17° C. Insoluble in water; soluble in ether and other organic solvents.
The dehydrocyclization of heptane to toluene is of great interest, playing an important part in catalytic reforming and the aromatization of petroleum products. Pure heptane can be prepared by the usual methods for synthesis of saturated hydrocarbons; it can also be isolated by fractionation of petroleum or synthetic gasoline. Heptane is used as a primary reference standard in determining the knock rating of carburetor fuels (the octane number of heptane is assumed to be zero). Among the structural isomers of heptane, 2,2,3-trimethylbutane (triptane) is of practical importance, being added to motor fuels.