Acylation and related reactions under microwaves. 4. Sulfonylation reactions of aromatics

Solvent-free sulfonylation of benzene and its activated or deactivated deri vatives were carried out under microwave (MW) irradiation and a catalytic a mount of iron(III) chloride, which, under these conditions, is more active than other metallic salts. With more reactive and/or nonvolatile reagents ( anisole, xylenes, mesitylene) expeditious conditions (short reaction time a t constant MW power without control of the temperature) were used. With les s reactive and/or low-boiling reagents (benzene, toluene, halobenzenes), th e rise in temperature and the increase of reaction time were controlled eit her by sequential MW irradiation or by a temperature order. It was shown th at MWs cause preferential interactions with polar species present in the re action, especially the aryl sulfone and its FeCl3-complexed form. A MW nont hermal effect was not observed when identical temperature gradients were pr oduced by classical heating and MW irradiation, and if reaction temperature was strictly controlled.