Deep Eutectic Solvents: Green Applications

Abstract

Recently, ionic liquids (ILs) have attracted considerable attention in scientific research as greensolvents. Owing to their low vapor pressure, ILs were qualified as green solvents. However, the ”greenaffiliation” of ILs is now contested by many research groups. The hazardous toxicity and the very poorbiodegradability of many ILs have been reported in the literature. Additionally, their synthesis generallyrequires a large amount of salts and solvents. These drawbacks and the high price of common ILs delayedtheir industrial applications. To overcome these drawbacks, a new generation of solvents, named DeepEutectic Solvents (DESs), has emerged. DESs can be formed by mixing, at moderate temperature, two ormore components that can be chosen to be cheap, renewable and biodegradable. These compounds arecapable of forming a eutectic mixture with a melting point lower than that of the individual component.DESs are generally liquid at temperatures lower than 100 C.Many DESs have similar physical-chemical properties to those of ILs, while being much cheaper andenvironmentally friendlier. Owing to these advantages, there is growing interest in DESs in many fields ofresearch. DESs are chemically tailorable solvents since they can be designed by properly combining variousquaternary ammonium or phosphonium salts with different hydrogen bond donors (HBD) or complexingagents. Hence, task-specific DESs with different physical-chemical properties can be prepared.In this work, we discuss the important contributions of DESs in diverse applications, e.g. electrochemicalprocesses, catalysis, synthesis, absorption of CO2, desulfurization of fuels, separation, and dissolution andextraction processes.