Toluene, colorless hydrocarbon, occurring in coal tar, specific gravity 0.86, boiling point 110.6° C (231.1° F). Toluene is sometimes called toluol or methylbenzene. The name toluene reflects the way in which it was once prepared, through destructive distillation of balsam of tolu. A great deal of industrial toluene is prepared in oil refineries by the alkylation of benzene. It is used as a solvent and as a source of synthetic compounds, for example, in the production of trinitrotoluene. Prolonged breathing of toluene vapor is harmful and should be avoided.