Abstract: A method of producing chlorobenzenes from benzene sulphonyl chlorides by a thermal chlorinating decomposition of aromatic sulphonyl chlorides of the general formula ##SPC1##WhereinX = hydrogen, halogen, alkyl group with 1-4 carbon atoms, or alkoxy group with 1-4 carbon atoms, andn = an integer of from 1 to 5,In the presence of a catalyst including a combination of active carbon and compounds selected from the group consisting of phosphorus chlorides, phosphorus bromides, and organic azo compounds capable of yielding free radicals when degrading.