chlorobenzene,  a colourless, mobile liquid with a penetrating
almondlike odour; it belongs to the family of organic halogen
compounds and is used as a solvent and starting material for the
manufacture of other organic compounds.  Chlorobenzene was first
prepared in 1851 by the reaction of phenol and phosphorus
pentachloride; its formation by the chlorination of benzene was
observed in 1868. It has been manufactured on a large industrial
scale in Europe and the United States since the early 20th
century by the reaction of benzene with chlorine in the presence
of catalysts, usually the trichloride of a metal such as iron,
antimony, or aluminum.  Chlorobenzene reacts readily with
chlorine, nitric acid, or sulfuric acid, forming
dichlorobenzenes, chloronitrobenzenes, or chlorobenzenesulfonic
acids, respectively, and with chloral in the presence of
sulfuric acid to form DDT, an insecticide. Under high pressure
and at high temperature, chlorobenzene reacts with water or with
ammonia, which displace the chlorine at