Thymol plus l-menthol eutectic mixtures: Thermophysical properties and possible applications as decontaminants

The substitution of conventional organic solvents for others with less environmental impact is one of the basic premises of green chemistry. To carry this out optimally, tools based on the similarity of thermo-physical behaviour are being developed. Thus, the characterization of new solvents is a key step in any field of application. In this work, we studied the eutectic hydrophobic thymol + l-menthol system. The solid-liquid equilibrium of the system and several properties of three of its mixtures close to eutectic composition were measured and discussed. Calculations and correlations were performed to obtain prop-erties of interest such as the internal pressure, critical temperature, and solubility parameter, among others. To predict the system behaviour under any operating conditions, the PC-SAFT equation of state was validated. Considering the problem of the presence of drugs as micro pollutants in the environment, the ability of this eutectic system to both dissolve drugs and remove them from contaminated water was also analysed. The results showed a strong thymol-l-menthol interaction, and a higher thymol ratio made the liquid more compact and structured but less polar and viscous. The difference in densities with respect to that of water and the moderate viscosity values indicated that this system can be an adequate solvent in liquid-liquid extraction processes. The solubilities of quercetin (Q), nitrofurantoin (NF) and tetracycline (TC) were enhanced in the eutectic mixtures; for Q, the solubility was 10000-fold higher than that in water. Finally, this system could be used to remove traces of Q and NF from the water, with an efficiency of up to 81 %.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).