Xylene

Xylene is a collective term for three isomeric dimethylbenzenes: ortho-xylene, meta-xylene, and para-xylene, with the chemical formula C8H10. In industry, xylene often denotes mixtures containing all three isomers (mixed xylene). The isomers are colorless, highly flammable liquids with a characteristic sweet odor.

Xylene occurs naturally in coal tar and is produced commercially during petroleum refining and chemical processing, primarily via catalytic reforming and toluene disproportionation. Mixed xylene is a common solvent and a chemical feedstock. It is typically separated into individual isomers, which are further used or oxidized in chemical synthesis.

Physical properties include volatility and low water solubility. The boiling range of xylene mixtures is about 138–144°C. The isomers have similar chemical behavior, though their exact melting points vary. Xylene is widely used as a solvent in paints, coatings, inks, adhesives, and degreasing formulations. It also serves as a feedstock for the production of important consumer plastics.

For chemical production, p-xylene is oxidized to terephthalic acid, a key monomer for polyethylene terephthalate (PET). The m- and o- isomers can be oxidized to isophthalic and phthalic acids, respectively, which are used in the manufacture of polyesters and related products.

Safety and environmental notes: Xylene is flammable and can be harmful if inhaled, absorbed through the skin, or ingested. Prolonged exposure may affect the nervous system, liver, or kidneys. It requires good ventilation, proper containment, and personal protective equipment. It is a volatile organic compound and can contribute to outdoor air pollution and groundwater contamination in spills.