As in the case of benzene and toluene, xylenes are used as solvents.
Hydrocarbons are composed only of carbon and hydrogen and can be divided into two types: aliphatic hydrocarbons and aromatic hydrocarbons. The latter have multiple bonds plus a special type of stabilization called aromaticity, which modifies the way they interact chemically. Toluene and xylene are aromatic hydrocarbons, derived from benzene, with the chemical formula C 6 H 6 . The skeletal carbon atoms in benzene form what resembles a Ferris wheel, with the six hydrogen atoms corresponding to automobiles. Benzene is transformed into toluene and xylene by replacing the hydrogen atoms with methyl groups (CH 3 -).
Maternal exposure to toluene has been linked to attention deficit disorders in children.
Toluene and xylene differ in their degree of methyl substitution. Only one hydrogen atom is replaced by a methyl in toluene, which has the chemical formula C 6 H 5 CH 3 . Although there are six carbon atoms in a benzene ring, they are all the same chemically, as the symmetry suggests. For this reason, it does not matter which carbon the methyl group is attached to, since the result is the same in each case. It is not necessary to number the carbon atoms of the toluene ring as all toluene molecules are identical, which simplifies processing as there are no isomers to separate.
Xylene is disubstituted benzene, which has two methyl groups replacing two hydrogen atoms. There are actually three different types or isomers of xylene. Atoms in the benzene ring part of the structure are labeled one through six. Starting with the top ring carbon and proceeding clockwise, the three varieties are ortho-xylene or 1,2-dimethylbenzene; meta-xylene or 1,3-dimethylbenzene; and para-xylene or 1,4-dimethylbenzene. The benzene ring portion of each structure is written C 6 H 4 .
Benzene has excellent solvent properties for many applications. Unfortunately, benzene impairs the body’s ability to fight infection and is closely linked to the development of leukemia in workers. Toluene and xylene are especially important as replacement solvents for benzene. These substances are not only used as solvents; As the familiar letters “TNT” indicate, toluene is used in the manufacture of the powerful explosive trinitrotoluene. Another useful toluene derivative is produced simply by oxidizing its methyl group to benzoic acid, a commercially important preservative.
The xylenes can be used together, as “xylene” or “mixed xylenes”, or they can be used individually. As in the case of benzene and toluene, xylenes are used as solvents. Briefly, the ortho and para isomers of xylene can oxidize their methyl side chains to form the important dicarboxylic acids, terephthalic acid and orthophthalic acid. Phthalic acids are used in the manufacture of polyesters, alkyd resins, and plasticizers. They are also used in the manufacture of specialty chemicals such as anthraquinone and phenolphthalein.