aromatic compounds are important in industry. key aromatic hydrocarbons of commercial interest are benzene, toluene, "ortho"-xylene and "para"-xylene. about 35 million tonnes are produced worldwide every year. they are extracted from complex mixtures obtained by the refining of oil or by distillation of coal tar. they are used to produce a range of important chemicals and polymers, including styrene, phenol, aniline, polyester and nylon.