Chlorobenzene

Chlorobenzene is an aromatic organic compound with the chemical formula C₆H₅Cl. This a colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals.

Uses

Chlorobenzene once was used in the manufacture of certain pesticides, most notably DDT by reaction with chloral (trichloroacetaldehyde), but this application has declined with the diminished use of DDT. At one time, chlorobenzene was the main precursor for the manufacture of phenol:

C₆H₅Cl + NaOH → C₆H₅OH + NaCl

As of 2005, the major use of chlorobenzene is as an intermediate in the production of commodities such as herbicides, dyestuffs, and rubber. Chlorobenzene is also used as a high-boiling solvent in many industrial applications as well as in the laboratory. More specifically, the chlorobenzene is nitrated on a large scale to give nitrochlorobenzene, which is converted to related phenol, anisole, and aniline derivatives.

Synthesis

Chlorobenzene was first described in 1851, when it was prepared by reacting phenol and phosphorus pentachloride. Presently it is manufactured by chlorination of benzene in the presence of a catalytic amount of Lewis acid such as ferric chloride: The catalyst enhances the electrophilicity of the chlorine. Because chlorine is electronegative, C₆H₅Cl exhibits decreased susceptibility to attack by other electrophiles. For this reason, the chlorination process produces only small amounts of dichloro- and trichlorobenzenes.

Safety

Chlorobenzene exhibits "low to moderate" toxicity as indicated by its LD50 of 2.9 g/kg.

References