Ionic liquids and their heating behaviour during microwave

Ionic liquids and their heating behaviour during microwave irradiation -a state of the art report and challenge to assessment Graduate Student: D. N. Guo Advisor: M. C. Hsiao

content • Introduction • Experimental • Resluts and discussion • Conclusions

Introduction • The application of ionic liquids as alternative reaction media was frequently reported in literature during recent years. • Properties of ionic liquids such as solubility, solvation strength, acidity, and coordination were selectively varied and in most cases successfully validated.

Introduction • However, extended reaction times of some syntheses lead to the question of whether higher temperatures and thus shorter reaction times would result in higher product yields and selectivities. • Microwave-assisted reactions are known for their short reaction times. This advantage results from the way in which substances are heated in the microwave field.

Introduction • Microwaves directly excite polar molecules (dipole relaxation) and ions (ionic conduction). Therefore, the presence of ions and/or polar molecules is necessary for substances to be heated in the microwave field. • Due to their broad application spectrum, a series of 1, 3 -dialkylimidazolium compounds was synthesised and their heating behaviour was studied under multi-mode microwave conditions.

Experimental selected mixtures of aforementioned ionic liquids with toluene or cyclohexane were prepared and temperature-timecurves were registered.

Experimental Microwave heating experiments The temperature was recorded with a fibre optic sensor for different microwave power settings in an ETHOS® 1600 microwave furnace (MLS Gmb. H, Leutkirch, Germany). Furthermore, selected mixtures of aforementioned ionic liquids with toluene or cyclohexane were prepared and temperature–time-curves were registered.

Results and discussion

Results and discussion

Results and discussion

Results and discussion

Results and discussion

Conclusion 1. Only small amounts of ionic liquids are necessary in order to significantly reduce the heating time of toluene or cyclohexane under microwave conditions. 2. An increase in the microwave power further amplifies this reduction in heating time. 3. Ionic liquids of the 1, 3 - alkylimidazoliumtype can be advantageously employed as solvents and cosolvents in synthesis as well as separations.