Acylation and Related Reactions under Microwaves. 4. Sulfonylation Reactions of Aromatics

Abstract

Solvent-free sulfonylation of benzene and its activated or deactivated derivatives were carried out under microwave (MW) irradiation and a catalytic amount 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 at constant MW power without control of the temperature) were used. With less reactive and/or low-boiling reagents (benzene, toluene, halobenzenes), the rise in temperature and the increase of reaction time were controlled either by sequential MW irradiation or by a temperature order. It was shown that MWs cause preferential interactions with polar species present in the reaction, especially the aryl sulfone and its FeCl3-complexed form. A MW nonthermal effect was not observed when identical temperature gradients were produced by classical heating and MW irradiation, and if reaction temperature was strictly controlled.

Nonthermal Effects of Microwaves in Organic Synthesis

“…This conclusion is also in agreement with the results obtained for the sulfonylation of mesitylene in the presence of metallic catalysts such as FeCl 3 [102] (5 %) (Eq. 50).…”

Microwave‐Heated Transition Metal‐Catalyzed Coupling Reactions

“…Dubac and co-workers found a practical method using high-temperature microwave conditions where only 5-10 mol% of FeCl 3 (relative to the sulfonyl chloride) sufficed for complete reactions to occur [201]. A number of arenes including alkylbenzenes, anisole, and halobenzenes were sulfonylated using a number of different arylsulfonyl chlorides.…”

Regioselective Electrophilic Aromatic Substitution Reactions over Reusable Zeolites

“…Recently, several new catalytic systems have been developed for such sulfonylation reactions. These systems include use of cation-exchanged zeolites (ZSM-5, Y, β) [125], Fe(III)-exchanged montmorillonite clay [126,127], Bi(III) triflate [128], triflic acid (TfOH)-Bi(III) halide [129] and microwave irradiation in the presence of a small quantity of certain metal salts [130][131][132].…”