Aromatic Hydrocarbons—Benzene and Other Alkylbenzenes

Abstract Benzene and its alkyl derivatives are monocyclic aromatic compounds (arenes). The compounds are of considerable economic importance as industrial raw materials, solvents, and components of innumerable commercial and consumer products, and as precursors in the production of drugs, plastics, synthetic rubber, and dyes. The aromatics differ vastly in chemical, physical, and biological characteristics from the aliphatic and alicyclic hydrocarbons. The aromatics are typically more toxic to humans and other mammals than are the aliphatic and alicyclic hydrocarbons; toxic effects of prime importance are the toxicity of benzene to the hematopoietic system resulting in aplastic anemia, myelodysplastic syndromes (MDS), and acute myeloid leukemias (AML) as a result of chronic exposures, and central nervous system effects with acute exposures for the class. The simplest single‐ring aromatic hydrocarbon compound is benzene, the nonsubstituted ring system. When one methyl group is attached to the ring, methylbenzene or toluene is formed, and with two attached methyl groups, dimethylbenzene or xylene is formed. Xylene occurs in three isomeric forms: ortho (1,2)‐, meta (1,3)‐, and para (1,4)‐dimethylbenzene. Other important substituted benzenes are phenol (hydroxy‐) and aniline (amino‐). The hemimellitenes and mesitylenes possess three methyl groups, durene four, and the penta and hexamethylbenzenes, five and six methyl groups, respectively. Other industrially important compounds are ethylbenzene and isopropylbenzene or cumene.