Deep eutectic solvents: alternative reaction media for organic oxidation reactions

Deep eutectic solvents (DESs) have emerged as 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 by 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 A. P. Abbott, G. Capper, D. L. Davies, R. K. Rasheed and V. Tambyrajah, Chem. Commun., 2003, 70, and among the reactions studied, organic oxidation has 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 components. In addition, their solubility properties play a crucial role in organic oxidation 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.