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The chlorine gas which is used is employed in anhydrous form. The reaction of the m-difluoronitro-aromatic compounds with the chlorine must be carried out in the absence of Lewis acids or other chlorinating catalysts. The required temperatures are within the range from 80° to 250° C. preferably 100° to 200° C. The reaction can be carried out in the presence or absence of a fluoride-capturing agent. The necessary chlorodifluorobenzene compound (starting compound) can, for example, be prepared as follows: 1800 g (11.3 mol) of 2,4-difluoronitrobenzene (anhydrous and free of Lewis acids) are initially introduced into a 2 l four-neck flask having a stirrer, gas-entry tube and distillation bridge. The reaction solution is brought to 160° C. A stream of chlorine of 4-6 l/h is then passed through the solution at this temperature. After 1-2 h, brown gases are formed which are absorbed in dilute sodium hydroxide solution. After 28 h, the entry of gas is stopped and the reaction solution is distilled (head temperature 127° C). 675.8 g of 2,4-difluorochlorobenzene are obtained, corresponding to a yield of 91%, based on reacted 2,4-difluoronitrobenzene.

1. customare within the range from 80° to 250° C. preferably 100° to 200° C
2. customThe reaction
3. distillationdistillation bridge
4. customis brought to 160° C
5. custombrown gases are formed which
6. customare absorbed in dilute sodium hydroxide solution
7. waitAfter 28 h
8. distillationthe reaction solution is distilled (head temperature 127° C)