Magnetic ionic liquids as catalysts in organic reactions

The present review summarizes the application of magnetic ionic liquids (MILs) as efficient magnetically recoverable catalysts in different organic transformations. They are supported mainly on magnetite coated silica gel preventing agglomeration of the magnetic nanoparticles (MNPs) and are protected from acidic solutions. Depending on the functionalization they are used as catalysts in multicomponent reactions allowing the easy synthesis of pyrans, pyridines, pyrimidines, quinazolines and their derivatives. Other heterocyclic compounds such as thiazolidinones, furanones, pyrazoles, imidazoles and triazoles are synthesized also by three-component reactions. These multicomponent processes are applied to the preparation of 1-amidoalkyl-2-naphthols and propargylamines by an A3-coupling. Condensation reactions of carbon dioxide gives cyclic carbonates, benzimidazolones and quinazolinedione and other reactions involving amines gives amides, oxazolidinones and pyrroles. Condensation of aldehydes with different compounds provides benzoxazoles and thiazoles as well as Knoevenagel reactions. Esterification and transesterification reactions of fatty acids have been applied for biodiesel production. Oxidation of alcohols and sulfur compounds, as well as epoxidation of alkenes, are easily achieved under mild reaction conditions. Cross-coupling reactions are performed with Pd NPs immobilized on MILs and hydrogenation of alkynes and enals with Pt NPs with low metal leaching. Other reactions involve diazotation-iodination of anilines, sodium azide ring opening of epoxides, etherification of 5-hydroxymethylfurfural, aza-Michael additions and Friedel-Crafts alkylation and sulfonylation of aromatic compounds.