Study on the synthesis of dual-chain ionic liquids and their application in the extraction of flavonoids

Ionic liquids, as tuneable, highly soluble, non-flammable, non-volatile and reusable extractants, have attracted extensive attention in the extraction of flavonoids from plants. In the present work, novel dual-chain imidazolium-derived ionic liquids were synthesized by a simple and efficient method and characterized (NMR spectroscopy, thermal stability, viscosity, conductivity, and polarity). Then, the imidazolium ionic liquids with different cation were used in the microwave-assisted extraction of flavonoids from Pinus massoniana Lamb. The results showed that the ionic liquid [Bmbim]Br, with a relatively low viscosity, conductivity and π* as well as a relatively large β, offered the best extraction efficiency and selectivity for flavonoids. Subsequently, the parameters of the extraction procedure for flavonoids were optimized as follows: extraction temperature of 80 °C, extraction time of 60 min, microwave power of 300 W, solid-liquid ratio of 1:20, and [Bmbim]Br solution concentration of 1.0 mol/L. The extraction yield of total flavonoids was 41.07 mg/g. Finally, a recovery method of the ionic liquid had been demonstrated, and the recovery rate of ionic liquid was 73.14%.