Study On The Synthesis Of Ionic Liquids And Their Application In The Extraction Of Flavonoids

Ionic liquids have good solubility,high thermal stability,non-volatile,designability and reusability,therefore they have attracted extensive attention in the extraction of flavonoids from plants.In this paper,novel dual-chain imidazolium ionic liquids were synthesized by a simple and efficient method.Then,the imidazolium ionic liquids with different alkyl substituents were used in the microwave-assisted extraction of flavonoids from Pinus massoniana Lamb,and the extraction mechanism was studied.The main research contents are as follows:(1)Studied on the synthesis of ionic liquids: A series of novel dual-chain imidazolium ionic liquids were synthesized by screening the synthesis process and optimizing the synthesis conditions.The chemical structure of the synthesized ionic liquid was characterized by NMR,which proved to be in accordance with the theoretical expectation.At the same time,the physicochemical properties such as water content,solubility,thermal stability,viscosity,conductivity and polarity of the synthesized ionic liquid were measured,and the law of the influence of ionic liquid structure on the properties was explored.(2)Studied on the extraction technology of flavonoids from Pinus massoniana Lamb: The content of total flavonoids was used as the evaluation index to screen different solvents,the cation structure of different imidazolium ionic liquids,and different conditions in the microwave-assisted extraction process too.The results showed that ionic liquids had absolute advantage in extracting flavonoids,especially the ionic liquid [Bmbim]Br offered the best extraction efficiency and selectivity for flavonoids.Finally,the parameters of the extraction procedure for flavonoids were optimized to the following: [Bmbim]Br solution concentration of 1.0 mol/L,extraction temperature of 86 ?,extraction time of 60 min,microwave power of 400 W and solidliquid ratio of 1:20 g/m L.The extraction yield of total flavonoids was 45.97 mg/g.Then comparing with other extraction techniques,microwave assisted extraction had an advantage than extraction at room temperature and hot reflux extraction.(3)Studied on the extraction mechanism: By FT-IR and SEM analysis of the chemical structure and microstructure of pine needles samples before and after extraction,it can be seen that the ionic liquids would destroy the cell wall of plants during the extraction process,which was mainly caused by the dissolving of cellulose in ionic liquids.However,ionic liquids with different structures made different degrees of damage to the cell wall structure,which result that ionic liquids with different structures shown the selectivity for the extraction of flavonoids in cells.Compared with single chain ionic liquids,double chain ionic liquids can show higher extraction yield in the process of flavonoids extraction.