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Eutectic solvents (ESs) are a relatively new class of solvents that have been arousing a lot of attention due to their easy preparation and great tunability of their thermophysical properties, which has been granting their application in a wide range of areas. The aim of this work is to present a new ES based on the mixture of an organic sodium salt, sodium hexanoate and dodecanoate, and a long alkyl chain carboxylic acid, octanoic, nonanoic, and decanoic acids, and to infer about the effect of introducing a sodium atom. The solid–liquid phase diagrams of these new sodium salt-based ES were determined to evaluate the liquid window where they can be confidently used as solvents. Other important properties of solvents have also been studied, and in particular, density and viscosity, at atmospheric pressure and in the temperature range between 293.15 and 353.15 K, were measured. In addition, the polarity of these new sodium salt-based deep eutectic solvents (DESs) was evaluated in terms of the Kamlet–Taft α, β, and π* and ETN parameters. The obtained results were compared with those of other commonly used hydrophilic and hydrophobic DESs and conclusions were taken.

In the last couple of years, deep eutectic solvents (DESs) have been raising a lot of attention mainly due to their versatility and their easy and speedy preparation without the need of further purification. Moreover, the vast array of very different compounds that can be selected for their preparation has led to the full tailoring of their relevant properties as solvents. We herein leave our opinion on the current challenges and opportunities in this blossoming field, which are curiously aligned with the scope of today's major concerns, where DESs are called to make a valuable contribution to important areas such as clean water, clean energy, and biotechnology.