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Physico-Chemical Studies on Room Temperature Ionic Liquids

A typical salt such as table salt has usually a very high melting point temperature. Ionic liquids however are salts that have a melting point near or even below room temperature! Furthermore, because ionic liquids are entirely composed of ions, their vapor pressure is essentially zero. (In other words, you essentially can't get the ionic liquids to boil, even when applying vacuum!) These properties of ionic liquids make them strong candidates to replace hazardous volatile solvents in industrial chemical processes. Hence, over the last decade research in the field of ionic liquids has focused on two directions: a) the exploration of (organic) chemical reactions in ionic liquids and b) the development of new ionic liquid compounds. Much less research emphasis has been placed in developing a better physico-chemical understanding of the ionic-liquids as a solvent system. Here is where our research interests enter. How do the cations and anions in an ionic liquid interact with each other and how do they interact with a solute? What are the phase behavior properties of ionic liquids with other solvents, in particular with supercritical carbon dioxide, another "environmental solvent system"? Is it possible to combine these two environmentally benign solvent systems?

Significant findings towards answering some of these types of questions disseminated in the past five years include:

  • The ionic liquid 1-ethyl-3-methylimidazolium bis(trifyl)amide displays ion pairing of extremely long lifetime-stability when dissolved in low-dielectric media (Journal of Solution Chemistry, 2004, Vol. 33, 379-392).
  • The ionic liquid tryhexyltetradecylphosphonium chloride is soluble in dense CO2 to 7% by mass. To the best of our knowledge, this is the first report of an ionic liquid being soluble in CO2 (Green Chemistry, 2005, Vol. 7, 475-478).

During my recent (2007-2008) sabbatical research stay at the Friedrich-Schiller-University in Jena, Germany, I had the opportunity to become acquainted with other experimental techniques, especially in the area of calorimetry. We were investigating how a number of physico-chemical properties for several ionic liquids of interest change upon the addition of water to elucidate if water is tightly bound to the ionic liquid, especially when present only in minute quantities.

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