A Comparative Study on Mechanochemically and Thermally Prepared Deep Eutectic Solvents

Recent developments in mechanochemistry have enabled the preparation of deep eutectic solvents (DESs) that can be a greener and viable alternative to the traditional thermal DESs. Since the mechanochemical method can be performed under ambient conditions, the mechanical energy generated during the grinding process can be sufficient to dissolve the solid HBA and HBD components and create a homogeneous mixture of DES. As thermally prepared DESs involve heating their components, often an extended duration of heating may alter their functionality through byproduct or covalent bond formation. In contrast, the mechanochemical preparation of DES requires no heating. This significantly reduces energy consumption and reduces the chance of the formation of any covalent bonds. In this study, we prepared three classes of DES using thermal and mechano-assisted rotary tumbler ball milling techniques without the application of any heat and analyzed them using multitechnique approaches, including physical, spectroscopic, statistical, and thermal analysis. Spectroscopic FT-IR and ¹H NMR investigations were used to confirm the formation of DESs and to detect the presence of any impurities or byproducts in both methods. Principal component analysis (PCA) of the FTIR spectra data showed that both methods produced similar results for all of the DESs prepared. Thermal analysis of the DESs was performed by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The physical properties of DES were measured for all three types of DESs. The results revealed that in all cases, even and almost for more challenging DESs, the mechanochemical-assisted rotary tumbler ball milling method showed unique advantages in comparison with traditional preparation processes, in terms of energy, performance, security, functionality, operating time, economics, and thus industrial-scale reality. This method can reveal the pathway to meet the industry's new expectations for DES production and the future development of this green solvent-based process in different fields.