1,4-氯苯

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 180 C, used as a solvent and chemical intermediate for dyes, pigment, agrochemicals and wide range of organic synthesis ; meta- , colorless liquid boiling at 172 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. p-Dichlorobenzene 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 2,5-dichloroaniline, plastics (e.g polyphenylene sulfide resins used for surface coatings and molding resins), dyes, pharmaceuticals, agrochemicals and other organic synthesis.