Dichlorobenzenes
belong to the group of organic halogen compounds replacing two
hydrogen atoms in benzene by chlorine atoms. There are three
isomers; ortho-dichlorobenzene, colorless liquid boiling at **0 C,
used as a solvent and chemical intermediate for dyes, pigment,
agrochemicals and wide range of organic synthesis ; meta- ,
colorless liquid boiling at **2 C, used as a solvent and chemical
intermediate; para- , white solid with a with a characteristic
penetrating odor. It is used mainly as an insecticidal fumigant
against moths, as a space deodorizer, as a general insecticide and
fungicide on crops, and as a chemical intermediate for plastics,
dyes, pharmaceuticals and other organic compounds. All they are
insoluble in water and denser than water. They are prepared by the
chlorination reaction of benzene in the presence of iron(III)
chloride. (the chlorination under strong illumination and without
iron(III) chloride leads to benzene hexachloride instead of mono or
polychlorobenzenes). The chlorination reaction leads to similar
ratio of ortho- and para-dichlorobenzene, but small amount of the
meta isomer is performed. The ortho and para isomers are separated
by fractional freezing. While the para isomer crystallizes, the
ortho isomer remains liquid. The meta-dichlorobenzene is prepared
by heating and pressure with aluminum chloride. m-Dichlorobenzene
is used as a solvent. It is also an chemical intermediate to
manufacture dyes, agrochemicals, pharmaceuticals and other organic
synthesis.
