Aqueous Process Chemistry: The Preparation of Aryl Sulfonyl Chlorides

The use of aqueous acidic conditions for the preparation of arylsulfonyl chlorides from diazonium salts in the presence of copper salts, preferably CuCl, together with thionyl chloride as the sulfur dioxide source, has considerable advantages over recommended literature procedures, whereby reactions are carried out in acetic acid with minimisation of water content of the solvent. The method has been shown to be successful for a wide range of electron-deficient and electron-neutral aryl substrates. The sulfonyl chlorides are protected from hydrolysis by their low solubility in water, which results in their direct precipitation from the reaction mixture in good yields (> 70%) and high strength (> 98% w/w). The aqueous process, which is additionally safer and more robust, can be readily scaled up and has significant environmental benefits.