Bayer Aktiengesellschaft

Kai Rohlk

Helmut Fiege

Hans-Josef Buysch

Karlfried Wedemeyer

Lothar Puppe

Rolf Grosser

Franz-Josef Mais

Ursula Pentling

Michael Pies

Sigurd Hartung

Helmut Lahr

Hans-Ingolf Paul

In a particularly advantageous process for isolating m-dichlorobenzene from mixtures of dichlorobenzene isomers by crystallization as eutectic crystals using a processing aid, the processing aid used is a compound of the formula (I) ##STR1## in which R.sup.1 to R.sup.6 are, independently of one another, hydrogen, halogen, C.sub.1 -C.sub.4 -alkyl, hydroxyl, NH.sub.2 or R--CO-- having R=C.sub.1 -C.sub.4 -alkyl, with 1-bromo-4-chlorobenzene and 1,4-dibromobenzene being excepted.

Process for isolating M-dichlorobenzene from mixtures of dichlorobenzene

Mixtures of m- and p-dichlorobenzene can be separated by treating such mixtures in the liquid phase with a pentasil zeolite at from 20.degree. to 250.degree. C., a filtrate enriched in m-dichlorobenzene being removed and the p-dichlorobenzene being obtained by desorption of the pentasil zeolite. The pentasil zeolites may contain, as exchangeable cations, protons, cations of the first or second main group of the Mendeleev Periodic System, cations of the rare earth metals or a mixture of a plurality thereof. In order to prepare the liquid phase a solvent is used that belongs to the group of cyclic saturated hydrocarbons having 5 to 15 carbon atoms, alkyl-substituted aromatic hydrocarbons having 8 to 12 carbon atoms, and halogen-substituted aromatic hydrocarbons having 6 to 10 carbon atoms and 1 to 3 halogen atoms. The solvents ethylbenzene, chlorobenzene, p-xylene, p-chlorotoluene and dichlorobenzene are excepted. A mixture of a plurality of these solvents may also be used.

Process for separating mixtures of m- and p-dichlorobenzene

Mixtures containing alkylaromatrics chlorinated in the side chain are worked up by blowing them out with an inert gas before distillation at elevated temperature and carrying out the distillation in the presence of amines and/or chlorinated amines.

Process for stripping and distilling mixtures containing alkylaromatics

Aromatic hydrocarbons are chlorinated in the nucleus in the presence of Friedel-Crafts catalysts and in the presence of co-catalysts in the liquid phase by using thiazepines as co-catalysts.

Process for nucleus-chlorination of aromatic hydrocarbons

The invention relates to a process for the removal of m-dichlorobenzene from dichlorobenzene mixtures by chlorination in the liquid phase at elevated temperature in the presence of Friedel-Crafts catalysts, the chlorination being carried out with addition of sulphur, sulphur compounds, iodine and/or iodine compounds and the chlorination mixture then being worked up in the usual way.

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Bergisch Gladbach, Germany

Kai Rohlk