Synthesis and Evaluation of Novel Bio-Based Solvents and Solubilizers

The field of green chemistry rapidly gained interest in recent years due to the increasing visibility of present environmental problems. In particular, the replacement of conventional organic solvents is considered urgently important in view of the fact that they are often volatile compounds, obtained from petroleum resource and highly abundant in chemical processes and industry. The idea of this thesis was to develop new approaches towards the development of green, alternative solvents and solubilization concepts. Several substance classes accessed by means of different strategies were studied to reach this aim. Firstly, the naturally originating L-carnitine was found to be a valuable starting material for the development of ionic liquids, cationic hydrotropes and surfactants. Starting from the zwitterionic natural molecule, cationic carnitine ester species were synthesized and the greenness of the employed reaction pathways was evaluated. The properties of the resulting pure substances and aqueous solutions were determined next to their applicability in terms of solubilization. In a second approach, the rather new solvent class of deep eutectic solvents was studied by extending the so far investigated range of members of this class. Mixtures consisting of betaine or carnitine in combination with carboxylic acids were found to exhibit a certain ionic liquid character. Furthermore, the suitability of biologically relevant substances, such as antioxidants was assessed for the formation of functional deep eutectic solvents. Natural hormones, in particular sodium salts of dehydroepiandrosterone sulphate, indole-3-acetic acid and indole-3-butyric acid were found to feature hydrotropic character. This allowed for the consideration of hormones being relevant for mechanisms in the organism beyond their primary function as hormones. The presented work has shown that numerous approaches relying on the utilization of well-known natural substances or modified derivatives thereof hold promise for their use as solvents or solubilizers in green chemistry