Deep Eutectic Solvents: Alternative reaction media for organic oxidation reactions

Deep Eutectic Solvents (DESs) have emerged an alternative to Ionic Liquids (ILs). DESs share with ILs some appealing features, such as low vapor pressure, capability to dissolve reagents insoluble in common organic solvents, and the possibility to tune the overall pH of the medium by replacing one of the constituents of the mixture. Furthermore, DESs can be prepared combining molecules that come from natural sources (i.e., glycerol, glucose), making them biodegradable. DESs have already been used for a variety of reactions and protocols, since they were reported for the first time by Abbott in 2003, and among the reactions studied, organic oxidations have recently gained much attention. In particular, the recyclability of these ionic compounds makes it possible to achieve anchoring of organic oxidants, such as TEMPO and peroxydisulfate, directly onto one species of the DES mixture component. In addition, their solubility properties play a crucial role in organic oxidations since DESs have the ability to dissolve both organic lipophilic and hydrophilic species, making the oxidation of organic compounds mediated by hydrogen peroxide more efficient. Herein we report the state-of-the-art of this developing field, focusing on the benefits of substituting common organic solvents with DESs, especially in terms of sustainability, enhancement of reactivity, and recyclability.