C6HCl5

C6HCl5, commonly known as pentachlorobenzene, is an organochlorine compound consisting of a benzene ring in which five hydrogen atoms are replaced by chlorine atoms, leaving a single hydrogen on the ring. The five chlorine substituents occupy five ring positions, and due to the symmetry of the benzene ring there is essentially one structural isomer of pentachlorobenzene.

Production and occurrence: Pentachlorobenzene can be formed as a byproduct or intermediate in chlorination processes and in the manufacture of other chlorinated hydrocarbons. It may also be detected as a trace impurity in certain chlorinated pesticides and wood-preservative formulations. Environmental monitoring sometimes includes it among persistent chlorinated aromatics due to its stability and potential for long-term persistence.

Physical and chemical properties: Pentachlorobenzene appears as a colorless to pale yellow solid at ambient conditions. It has low water solubility and is more soluble in organic solvents. The compound is relatively nonpolar, chemically stable, and exhibits low reactivity toward hydrolysis. It has a higher melting and boiling point relative to many non-halogenated aromatics because of its chlorination.

Applications and safety: Today, pentachlorobenzene has limited direct use and is mainly encountered in the context of synthesis, analytical standards, or environmental studies. It is considered persistent in the environment and can bioaccumulate. Potential health and ecological risks have led to regulatory attention in some regions, with emphasis on minimizing exposure and controlling discharges containing chlorinated aromatics.

See also: pentachlorobenzene isomerism; chlorinated benzenes; environmental fate of organochlorines.