Benzene is used as a solvent in many commercial, industrial, and research operations. It has long been of interest as a fuel because of its high octane number. Some manufacturers, particularly in Europe, have used it as a gasoline additive to increase engine efficiency and to improve starting qualities.
By far the most important use of benzene, however, is in the production of other aromatic compounds. The word aromatic was originally applied to benzene because of its distinctive odor, but it later took on a broader meaning, referring to any compound whose molecular structure includes one or more benzene rings. The largest volume of compounds made from benzene goes toward the production of commercially valuable polymers, such as polystyrene, nylon, and synthetic rubber.
The benzene derivative produced in largest quantity is ethylbenzene (C6H5C2H5). Ethylbenzene is converted to styrene (C6H5CH=CH2) which, in turn, is polymerized to form polystyrene. Nearly half of all benzene used in chemical synthesis is used for this process.
In another example, benzene is treated with propylene to form cumene (C6H5CH[CH3]2). The cumene thus formed is then oxidized to produce phenol. Phenol is the starting point for a large number of polymers known as phenolic resins.
Synthetic fibers are produced by yet a third kind of benzene substitution sequence. The addition of hydrogen to benzene converts it to cyclohexane (C6H12), which is then oxidized to adipic acid (COOH[CH2]4-COOH) The acid can then be treated with hexamethylene diamine to form nylon.