Alkanes occur as such in natural gas and petroleum and accordingly are the cheapest raw materials for chemicals. They are the feedstocks for cracking (Sections 2.2.1, 2.2.2) and catalytic reforming (Section 2.2.3). Methane is the main source for synthesis gas (Section 10.4) via steam reforming. The higher alkanes can be subjected to the same process if desired, or the steam reforming process can be redirected to give methane. An important process is pyrolysis of hydrocarbons to carbon black, which is discussed at the end of this chapter.
Apart from pyrolysis, these reactions are endothermic. They are all unselective and take place at high temperatures. There are few examples of alkane functionalization, that is, of the use of alkanes directly for downstream chemicals. The most important are the conversion of n-butane to maleic anhydride (Section 5.4), the oxidation of n-butane or naphtha to acetic acid (Section 10.5.2.2), the oxidation of isobutane to tert-butyl hydroperoxide (Section 4.11), the oxidation of ethylbenzene to ethylbenzene hydroperoxide (Section 4.11) and the chlorination of methane (Section 10.2). Lesser volume uses involve ammoxidation of methane to hydrocyanic acid (Section 10.1), conversion of methane to acetylene (Section 10.3), and nitration of propane. These have largely been discussed.
Any alkane may be nitrated. In practice, only propane is used as feed and from its nitration result nitromethane, nitroethane, and 1-and 2-nitropropane. The nitration takes place at 420ยฐC, and the products are separated by distillation. They are used as additives for gasoline for racing cars, as solvents especially for polycyanoacrylates,