Date of Award
Master of Science in Chemical Sciences (MSCB)
Mohammad A. Halim
Deep eutectic solvent (DES) is the alternative and greener solvent in which two compounds, usually a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD), are used. Two components form a complex network with strong intermolecular forces and show a lower melting point than those of the constituent compounds. DESs have many characteristics that are similar to those of ionic liquids (ILs), yet DESs are nontoxic, biodegradable, and have the potential for biological applications. Traditional solvents are homogeneous, having only one component, and their chemistry is relatively simple. However, DESs comprise two components, so their synthesis, characterization, and interaction chemistry between HBA: HBD in DESs are complicated. In this work, we introduce a greener approach to synthesizing DES and combine multi-techniques approaches including spectroscopic, statistical, thermal, and mass spectrometry to characterize various types of DESs. The mechanochemical approach is employed as a synthesis method for preparing DESs, and results are compared with the thermochemical approach. Three types of DES including (i) Type III (Ionic: HBD, Choline Chloride: Urea); (ii) emerging Type V (Non-ionic DES, Menthol-Octanoic acid, Menthol-Thymol, Menthol-Camphor, and Thymol-Camphor); and (iii) Type VI (Therapeutic DES, Ibuprofen-Menthol) were synthesized using mechanochemical and thermochemical methods. The spectroscopic (FT-IR) investigation confirmed the formation of DES from both methods. Principal Component Analysis (PCA) of the FTIR spectra data showed that both methods produced similar results for all the DESs synthesized. Thermal analysis of the DESs was performed with Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The results revealed that the DESs made from both methods exhibited closely similar thermal behavior. Although various techniques are used to characterize DES, mass spectrometry (MS) experiments are rarely implemented. Along with other techniques, MS experiments were employed to detect the gas phase stoichiometry, cluster formation, and interaction network between two components of DESs. The MS results showed that ionic DESs could form small and large series of clusters. Non-ionic and therapeutics DES typically exhibited small and random clusters. Most importantly MS experiments revealed that DESs not only form hetero clusters between the components they also form very stable homo clusters of HBA: HBA and HBD: HBD.
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