Spectroscopic, Thermal and Mass Spectrometry Investigations of Mechanochemically Synthesized Deep Eutectic Solvents

Abstract

Deep eutectic solvents (DESs) are sustainable mixtures of hydrogen bond donors and acceptors that interact strongly to form liquids with melting points lower than their individual components. Various methods are employed to synthesize DESs; the most common one is the thermochemical approach which uses heat assisted with stirring to obtain the eutectic point of the DESs. However, this technique produces byproducts and/or impurities with side reactions or establishing covalent bonds between the molecules. In this study, the mechanochemical strategy is used to synthesize Type V DES which consists of non-ionic molecules. Some well-studied (type V) DES systems including menthol-octanoic acid, menthol-thymol, menthol-camphor, and thymol-camphor were selected for this study. A comprehensive suite of spectroscopic and thermoanalytical techniques, such as ATR-FTIR, PCA, 1NMR, DSC, and TGA were employed to elucidate the structural, compositional, and physicochemical characteristics of the eutectic mixtures synthesized via mechanochemical and conventional thermal approaches. The ATR-FTIR spectra confirmed DES formation through characteristic band shifts in the synthesized eutectic systems relative to those of the individual precursor components. The PCA of the FTIR spectra data demonstrated that both approaches yielded comparable outcomes for all the synthesized DESs. 1H NMR was used to understand chemical integrity. Moreover, TGA demonstrated the thermal robustness and decomposition behavior of the DES systems, while DSC confirmed eutectic formation and phase-transition characteristics through depressed melting events and altered thermal profiles. Additionally, the GC-MS analysis was used to detect byproducts or impurities of the studied eutectic mixtures. Physical measurements such as PH, Density were measured to understand the applicability of DES.