Trichlorobenzenes

Trichlorobenzenes are a family of chlorinated benzenes in which three hydrogen atoms on a benzene ring have been replaced by chlorine atoms, giving the molecular formula C6H3Cl3. Four constitutional isomers exist: 1,2,3-trichlorobenzene; 1,2,4-trichlorobenzene; 1,3,4-trichlorobenzene; and 1,3,5-trichlorobenzene. The isomers differ in the arrangement of chlorine substituents and can have distinct physical and chemical properties.

Production and occurrence: Industrially, trichlorobenzenes are produced by controlled chlorination of benzene or of lower chlorobenzenes, followed by separation and purification to yield the individual isomers. They may be encountered as components in technical mixtures produced during chlorination processes and can be isolated for specific applications.

Physical and chemical properties: Trichlorobenzenes are relatively nonpolar and exhibit low water solubility. They are typically colorless to pale yellow solids or liquids with high boiling points and limited volatility at room temperature, making them more susceptible to accumulation in organic phases and in the environment than lighter hydrocarbons.

Applications: They are used as solvents and as intermediates in the synthesis of dyes, pigments, pharmaceuticals, and agrochemicals. Some isomers, notably certain 1,2,4- and 1,3,5-trichlorobenzenes, have found use as heat transfer fluids in specialized industrial applications due to their stability and high boiling points.

Safety and regulatory notes: Chlorinated benzenes can be toxic and persistent in the environment; exposure or improper disposal poses health and ecological risks. They are subject to regulatory controls and require appropriate handling, containment, and disposal procedures.