Switchable Solvents: A Combination of Reaction & Separations

Abstract

A switchable solvent is a solvent capable of reversing its properties between a non-ionic liquid to an ionic liquid which is highly polar and viscous. Switchable solvents have applications for the Heck reaction, which is the chemical reaction of an unsaturated halide with an alkene in the presence of a palladium catalyst to form a substituted alkene. The objective of this research was to apply a switchable solvent system to the Heck reaction in order to optimize reaction and separations by eliminating multiple reaction steps. Switchable solvents reduce the need to add and remove multiple solvents because they are capable of switching properties and dissolving both the inorganic and organic components of the reaction. This reversal of chemical properties by a switchable solvent provides for easier separation of the product, minimizes the cost by eliminating the need for multiple solvents, and reduces the overall environmental impact of the industrial process. Specifically, the cost is lowered by the ability of the catalyst and solvent to be recycled from the system. In addition, the "switch" that initiates the formation of the ionic liquid switchable solvent is carbon dioxide, which is cheap and nontoxic. In conclusion, we were able to use a switchable solvent system to obtain good product yields of E-Stilbene, the desired product of the Heck reaction, and recycle the remaining catalyst + solvent which also produced good product yields at a lower economic and environmental cost.