Diaryl sulfones were synthesised using a variety of Lewis acid catalysts under microwave activation. Catalysts were used both homogeneously and heterogeneously (K10 montmorillonite clay). The most effective catalyst in terms of yield was found to be iron(III) chloride with a yield of 89% supported iron(III) chloride gave a yield of 77%. The highest selectivity to the 4,4' isomer was obtained using Supported bismuth(III) chloride. A series of other diaryl sulfones were synthesised using microwave-assisted Lewis acid catalysis in good yield. The energy used in the reactions was Measured and the quantity of carbon dioxide generated per mole Of product Was compared using microwave and traditional thermal activation (oil bath) methods. Where yields were comparable, microwave-assisted synthesis was shown to produce substantially less carbon dioxide per mole of product. (C) 2009 Elsevier B.V. All rights reserved.