Chapter 2 Liquefied mixtures of solids can extract natural products : application of ionic liquids and deep eutectic solvents to natural product research

Mixtures of solid chemicals may become liquids under certain conditions. The liquids are characterized by formation of strong ionic (ionic liquids) or hydrogen bonds (deep eutectic solvents). Due to their extremely low vapor pressure, these liquids are now widely used in polymer chemistry and synthetic organic chemistry, yet little attention has been paid to the extraction capacity of ionic liquids or deep eutectic solvents for natural products. This review summarizes the preparation of ionic liquids and deep eutectic solvents with natural product components, and recent progress in their application to the extractions and analysis of natural products, covering both primary and secondary metabolites, and enzymatic reactions alternative to conventional organic solvents. Additionally, the various factors affecting extraction features of ionic liquids and deep eutectic solvents, as well as potential technologies including microwave and supercritical fluid extraction to increase the extraction efficiency are discussed.