Preparation of aromatic sulfohalides

A process for the preparation of an aromatic sulfohalide by reacting an aqueous solution, containing a hydrogen halide, of an aromatic diazonium halide with sulfur dioxide, which process comprises:

• (a) reacting
• (1) an aqueous solution which does not dissolve sulfur dioxide, said solution essentially containing the hydrogen halide HX of a diazonium salt which is derived from the corresponding aromatic amine and the halogen X of the desired sulfohalide, with
• (2) sulfur dioxide in the presence of an inert organic solvent which dissolves the sulfur dioxide but which is immiscible or only partially miscible with water;
• (b) decomposing the diazonium salt, simultaneously or subsequently, by means of a catalyst for diazonium salt decomposition;
• and
• (c) treating the resulting reaction mixture, or the organic phase thereof after removal of the aqueous phase, with an oxidizing agent.