Non-Ideality in Thymol + Menthol Type V Deep Eutectic Solvents
Nicolas Schaeffer, Dinis O. Abranches, Liliana P. Silva, Mónia A. R. Martins, Pedro J. Carvalho, Olga Russina, Alessandro Triolo, Laurent Paccou, Yannick Guinet, Alain Hédoux, João A. P. Coutinho
Abstract
The nonionic Type V deep eutectic solvent (DESs) thymol + menthol is experimentally and computationally studied aiming to clarify the relation between its liquid phase structure and its thermodynamic nonideality. 1H NMR, Raman, and X-ray scattering analysis of the thymol + menthol system, supported by molecular dynamics simulations, show complex intermolecular interactions dominated by sterically hindered H-bonded clusters. For temperatures greater than or equal to room temperature, a quasi-linear evolution of the eutectic system properties between the pure compounds is observed, suggesting the absence of a magic stoichiometric composition in the eutectic solvent. However, temperature dependent Raman spectroscopy indicates a notable increase in thymol–menthol H-bonding as temperatures approach the eutectic point. This study shows that nonionic Type V DESs present an important temperature-dependent nonideality originating from the change in the intermolecular H-bonding with temperature. These findings have significant implications for the design and growing application of Type V DESs.