Stepping away from serendipity in Deep Eutectic Solvent formation: prediction from precursors ratio

Deep Eutectic Solvents (DES) are a class of environment friendly and cheap solvents that are effectively employed in many different fields; nevertheless, a thorough elucidation of their structure is still lacking and the unambiguous categorization of a mixture as a DES is challenging. Throughout this paper, we develop a procedure based on computational tools (supported by experimental data) that could help in making a priori predictions of DESs formation. After validating the approach with X-ray scattering data, a series of aromatic molecules (as Hydrogen Bond Donor, HBD) was investigated to corroborate the method that could be potentially extended to other DESs. The computational findings evidenced a remarkable and unprecedented predictive power. Furthermore, as a bridge between computed and experimental data, a linear correlation between the calculated chloride-HBD coordination number and the decrease of the freezing temperature of the mixtures is found, being 0.7 a threshold value to obtain a liquid eutectic mixture at room temperature as further validated by experimental Raman spectra. This approach has been preliminary tested also with DESs based on alternative HBDs (i.e., aliphatic alcohols, amines, and carboxylic acids), confirming the flexibility and the generality of the method.