Acid-functionalized Ionic Liquid Multi-component Reactions

Multi-component reaction (MCR) processes, in which three or more reactants were combined in a single chemical step to products that incorporate substantial portions of all the components, naturally comply with stringent requirement for ideal organic synthesis. The attractive features of MCRs are simple procedure, high resource utilization and excellent atom economy.Ionic liquids, new green media and "soft" functional materials, have been developing rapidly in recent years. Because of its dissolution and catalytic properties, ionic liquids are widely used in organic reactions and gradually expand to actual production application.The paper mainly studied on multi-component reactions catalyzed by acidic ionic liquids, including:(1) An efficient one-pot synthesis of amidoalkyl naphthols was described. This involved the three-component Ritter-type reaction of P-naphthol, aromatic aldehyde and amide or urea catalyzed by sulfonic ionic liquid, 1-methyl-3-propanesulfonic acid immidazolium hydrogen sulfate [MIMPS][HSO4]. The results show that, under solvent-free conditions at 125℃and n(β-naphthol):n(aromatic aldehyde):n(amide or urea):n([MIMPS [HSO4])=1:1:1.3:0.1, for 5-40 min, the yield of amidoalkyl naphthols was 85% -97%. The product could be separated simply by filtration after the reaction. The ionic liquid was recycled four times without apparent decrease in catalytic activity.(2) 7-hydroxy-4-methyl coumarin was prepared by Pechmann condensation with resorcinol and ethyl acetoacetate in the presence of [MIMPS][HS04] and under solvent-free condition. Effects of reaction temperature, mole ratio of resorcinol to ethyl acetoacetate, catalyst dosage and reaction time on yield were investigated. The optimum conditions were as follows:reaction temperature 110℃, reaction time 30 min, n(resorcinol):n(ethyl acetoacetate):n([MIMPS][HSO4])=1:1:0.15, the yield to 7-hydroxy-4-methyl coumarin was 93.8%.(3) Sulfonic ionic liquids were used as a Bronstedacid catalyst for the three-component synthesis ofα-aminophosphates via aromatic aldehydes, aromatic amines and triethyl phosphate at room temperature in water. Under conditions of n(aldehydes):n(amines):n(triethyl phosphate):n([MIMPS][HSO4])=1:1:1:0.1, for 30-150 min, the yield ofα-aminophosphates was 51%～96%.The results show that sulfonic ionic liquid, 1-methyl-3-propanesulfonic acid immidazolium hydrogen sulfate [MIMPS][HSO4] is an efficient, novel and green catalyst. The reactions were carried out under solvent-free conditions or in water meida. It proved that it is an efficient and green method to reduce time, increase yields and improve selectivity, which offers several advantages such as mild conditions, environment friendly, easy workup procedure. The catalyst could be recycled. All the compounds were confirmed by melting point, IR,1H NMR and MS spectra. Meanwhile, the factors which influenced the multi-component reactions were discussed including the structures of reactants. The possible mechanism was postulated as well.