(6ar) Designing for Sustainability with CO2-Tunable Solvents

Developing greener, more efficient, and less energy-intensive processes will lead the chemical industry into a more sustainable future. The utilization of alternative solvents to displace or reduce the use of traditional organic solvents is an important part of this effort. Gas-expanded liquids (GXLs) form a unique class of environmentally benign and tunable solvents that can be used in a variety of applications. GXLs reduce the need for organic solvents, operate at more moderate pressures than supercritical fluids, and facilitate less energy-intensive separations through depressurization to recover products and catalysts. We have recently employed GXLs in the recovery of fine chemicals from renewable resources, and in biomass pretreatment. A more complete understanding of the interactions between the gas, the organic liquid, and solutes at the molecular level will enable the full exploitation of GXLs.

We have used two kinetic probes, the Diels-Alder reaction of anthracene with 4-phenyl-1,2,4-triazoline-3,5-dione and the Menschutkin reaction of tributylamine with methyl p-nitrobenzenesulfonate to examine the local solvent structure of CO₂-expanded acetonitrile. We have correlated our kinetic results with solvatochromic probes including the Kamlet-Taft parameters and Kosower's Z to develop comprehensive models explaining the intermolecular phenomena involving the GXL and the solutes. The results of this research can be used to guide future applications of GXLs as green reaction solvents.