(566f) Gas Expanded Liquids for Tailoring Chemical and Physical Properties

Gas expanded liquids (GXL) are a class of solvents that combine the properties of common organic solvents with supercritical fluids.  They arise from dissolution of a gas, most often CO₂, into an organic solvent, causing a volume expansion of the system.  The physical and chemical properties of the solvents can be controlled by modifying processing parameters such as pressure and temperature.  Local composition enhancements have shown to be important when tuning the solvent properties. This tunabilty can be exploited for carrying reactions under controlled chemical environments while facilitating separations for post-reaction processing.  Additionally employing CO₂ involves a series of environmental advantages such as low toxicity, reduced flammability, high availability and recyclability. At the same time, the amount of organic solvent used is significantly reduced. GXLs technologies can be utilized for sustainable processes that take advantage of in situ, reversible protection and/or activation strategies. An example of activation is the reversible formation of alkylcarbonic acid from alcohols and CO₂.  Alkylcarbonic acids can be used as reversible, or self-neutralizing, acids for acid-catalyzed processes for applications including the formation of ketals or diazonium intermediates toward the synthesis of dyes, and the hydrolysis of b-pinene. Additionally, reversible activation and protection can synergistically contribute to higher reaction performances, easy separation and recycling strategies. This presentation will highlight the benefits of employing GXL for chemical processing by tuning the chemical environment of the solvent system.  Specific examples of in situ protection and substrate activation will be discussed, coupling efficient reaction with facile down-stream processing.  The results will be analyzed in light of specific interactions occurring in GXL systems for specific reactions of interest.