GB835750A - Manufacture of polychlorobenzenes - Google Patents

Abstract

Catalysts for the preparation of polychlorobenzenes by the chlorination of benzene hexachloride (see Group IV (b)) comprise a mixture of gas adsorption carbon and a metal chlorination catalyst prepared for example by treating gas adsorption carbon with an aqueous solution of aluminium chloride, ferric chloride, chromic chloride or an aluminium chloride-cupric chloride mixture and heating. A mixture of active carbon and active alumina may also be used.ALSO:Polychlorobenzenes are made by reacting hexachlorocyclohexane and chlorine in the gas phase using as catalyst a mixture of a gas-adsorbing substance, for example gas-adsorbing carbon, and a substantially non-volatile metalliferous chlorination catalyst, preferably an oxide of an element, the halides of which act as Friedel-Crafts catalysts, either singly or in admixture with one or more other metal compounds of similar volatility. The reaction is suitably carried out by causing the reaction mixture to react first in contact with a catalyst of lower activity, for example one of the components of the mixed catalyst such as alumina, and then bringing the partially reacted mixture into contact with the mixed catalyst. The preferred catalysts comprise a mixture of gas-adsorption carbon and alumina or ferric oxide, made, for example, by saturating the carbon with a solution of Al2O3.6H2O and heating to convert the aluminium chloride with aluminium oxide. Examples describe the conversion of benzene hexachloride to hexachlorobenzene according to the invention using as a catalyst gas adsorption carbon saturated with aqueous solutions of (a) aluminium chloride, (b) ferric chloride; (c) a mixture of aluminium chloride and cupric chloride and (d) chromic chloride, and converted to the oxide by heating, and also using as catalyst a 1 : 1 mixture of alumina and active carbon. Tetrachlorobenzene may also be formed.