1. Ionic liquids in low dielectric media (.pdf file)
2. Physicochemical and reaction studies of surfactant systems
There is a good possibility that external funding (funding requests are currently pending) would be available to fund summer research students for the surfactant research described below.
Surfactant (surface activating agent) molecules are amphiphiles, which means they can dissolve in both water and non polar solvents. They are typically used as additives in many common products such as cleaning agents, paints, etc. Although not limited to NMR spectroscopy, prior projects have been utilizing primarily this spectroscopic tool to study aggregation size and dynamics of surfactants in water as well as in other solvents.
Lately, our focus has shifted on systems that are rich in surfactant and/or exclude water as one of the present components because we have realized that liquid nonionic surfactants could actually serve as a novel solvent for chemistry. Specifically, given that many liquid nonionic surfactants posses a negligibly low vapor pressure, may dissolve a wide variety of substances because of their amphiphilic structure, are of little toxic concern because they are already widely used in household products, and are biodegradable, why not exploiting them as a possible new class of "green solvents" for chemical synthesis? So far we have accomplished proof of concept for a particular Diels-Alder reaction and have some promising results for epoxide rearrangement reactions. (Further work on this particular reaction study would be in collaboration with Dr. Godleski.) We have also noted some considerable solubility of simple inorganic salts such as KCl in the (dry!) surfactant medium, and continuing solubility measurements are needed.
3. Phase Behavior of Ionic Liquids with Supercritical Carbon Dioxide
Ionic liquids are salts that are liquid at room temperature conditions. A liquid salt is an unusual medium for chemistry because this solvent is entirely composed of charged species, cations and anions. You might recall from general chemistry that salts like table salt dissolve easily in water but have little tendency to "dissolve in air". Their vapor pressure is so small that it is nearly immeasurable. The same is true for ionic liquids, i.e., liquid salts. Thus, unlike traditional organic solvents such as acetone or ether, ionic liquids don't smell, are nonflammable and are inherently safer to use because one does not get exposed to the ionic liquid solvent through inhalation. Because of these benign properties, ionic liquids have been included on the list of "green solvents". Supercritical carbon dioxide (scCO2) also belongs to the list of "green solvents" because it is non-flammable, incombustible, and non-toxic. ScCO2 is compressed carbon dioxide at temperatures above 31oC where it cannot be liquefied anymore. Variation in pressure will gradually change the density of this compressed solvent without undergoing a phase transition.
While ionic liquids are generally speaking good solvents for polar solutes, scCO2 is more appropriate as a solvent for non-polar solutes. In chemical synthesis, one often encounters the difficulty of dissolving polar and non-polar reactants in the same solvent. A mixed solvent system of ionic liquid and scCO2 would therefore be an attractive medium for such reactions between disparate reactants because both components, ionic liquid and scCO2, are considered green solvents. Of course, one first needs to find a suitable ionic liquid that is able to dissolve in scCO2. That is the motivation and goal or this research that investigates the phase behavior of various ionic liquids with scCO2. Recently, we discovered that the particular ionic liquid trihexyltetradecylphosphonium chloride dissolves in liquid and sc CO2 up to 8 mass%. In a follow-up study on a similar ionic liquid (different anion but same cation) we observed that also this ionic liquid dissolves into the CO2 phase but the amount was to miniscule to reliable determine the conditions of the phase transition. However, we observed that the presence of the ionic liquid caused an enormous collapse of the CO2 volume requirement in absence of the ionic liquid. In other words the partial molar volume of the ionic liquid would actually be negative. This initial observation needs further careful investigations, which would be the subject of the summer research activities.
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