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 atom and form phenol or aniline. Pure chlorobenzene freezes at -45.6 C (-50.1 F) and boils at 132 C (270 F); it is denser than water and practically insoluble in it, but it dissolves in a number of organic solvents.