Xylene isomer mixtures (primarily ortho-, meta-, and para-xylene) are colorless, transparent liquids with a characteristic odor at room temperature. They are insoluble in water but miscible with most organic solvents, are flammable, and their vapors can form explosive mixtures with air. As an alkylbenzene mixture, their chemical properties are similar to toluene: the benzene ring can undergo substitution reactions such as halogenation and nitration, while the methyl groups can be oxidized to corresponding phthalic acids. The boiling points of the three isomers are close, making separation difficult, so they are often used industrially as mixtures. Owing to their excellent solvent power and relatively high boiling point range, their primary applications are as important organic solvents widely used in paints, coatings, inks, pesticides, and adhesives. They are also key chemical raw materials for producing terephthalic acid (used in polyester fibers and plastics), phthalic anhydride (used in plasticizers), isophthalic acid, as well as dyes and pharmaceuticals.