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Performance and Synthesis of Ionic Liquid

Ionic Liquids

Ionic liquids (ILs) are compounds that consist entirely out of ions. In contrast to molten salts, ILs are defined by a melting point below 100 °C. While NaCl is a high melting solid (mp = 803 °C) which is quite corrosive in the liquid state, ionic liquids consists of ions with a high degree of charge delocalization and a low degree of symmetry resulting in much lower melting points (some candidates down to -20 °C).

Left: Crystal structure of NaCl (yellow: Na+, red: Cl-); Right: crystal structure of 1-ethyl-3-methyl imidazolium bis(trifluoromethylsulfonylimide) ([EMIM][NTf2]) (yellow: sulfur atoms, red: oxygen, blue: nitrogen, green: fluorine, grey: carbon).

Ionic liquids are considered as green alternatives to volatile organic solvents due to their extremely low vapor pressures (in the range of metals). More relevant is however the fact that ILs represent a class of liquid materials with unique property profiles, such as combinations of wide liquidus range, electric conductivity, good electrochemical and thermal stability, excellent tribological properties as well as special solubility and coordination properties. For our group, the ability of ionic liquids to dissolve homogeneous transition metal catalysts, to stabilize catalytic nanoparticles or to modify the surface of classical heterogeneous catalysts is of special relevance.

Cations (top) and anions (bottom) found frequently in ionic liquids.

The development of ionic liquids dates back to the early years of the 20th century with the discovery of liquid ethylammonium acetate by Walden (1918) and the development of organic chloroaluminate salts by Hurley und Wier (1948). Since the early 1990th ionic liquids are applied in multiphase catalysis (Chauvin) and since the mid 1990th a large number of hydrolytical stable ionic liquids are available (Grätzel). Since 2000 ionic liquids are produced commercially, today in multi-ton scale for a large variety of applications.

SciFinder search results for “ionic liquid” and “ionic liquids” 1997-2007.

Our institute deals with ionic liquid research in many different aspects. We run research projects ranging from synthesizing new IL structures and investigating fundamental physico-chemical properties to ionic liquid applications in catalysis, material science, electrochemistry and engineering applications (e.g. lubrication, separation or absorption cooling). We are also active in the up-scaling of ionic liquid syntheses for industrial IL production.

Prof. Wasserscheid is the coordinator of SPP 1191, a priority programme sponsored by the German Science Foundation focussing on the better physico-chemical understanding of ionic liquid materials. More information about the SPP 1191 is found on the webpage of the priority programme.