This substance is produced by vapor phase oxidation of n-butane. The overall process converts methyl groups to carboxylates and dehydrogenates the main chain. The selectivity of this process shows the strength of maleic anhydride by the double and conjugated bond system. Traditionally, maleic anhydride was produced by the oxidation of benzene or other aromatic compounds As of 2006, only a few smaller plants still use benzene.