Solvent Effects on Metal Complexation with Crown Ethers from Liquid to Supercritical Fluids (DE-FG07-98ER 149 13)

The purpose of this project is to study the salvation effects of metal-crown ether complexation in different solvents. It has been suggested in the literature that supercritical fluid carbon dioxide (SF-CO2) is a tunable solvent because its salvation environment can be varied with the fluid density. In this project, spectroscopic techniques including nuclear magnetic resonance (NMR) and Fourier Transform Infrared (FTIR) were used to evaluate salvation effects of metal crown complexation in organic solvents and in SF-CO2. In most solvent extraction systems, water is often involved in the extraction processes. We have carried out extensive studies of water-crown ether interactions in different solvents and in SF-CO2 using NMR and FTIR techniques. Water molecules can be attached to crown ethers through hydrogen bonding of H-0-H to the oxygen atoms of crown ether cavities. This type of interaction is like a Lewis acid-Lewis base complexation. During the course of this project, we noticed that some CO2 soluble Lewis base such as tri-n-butyl-phosphate (TBP) can also form such Lewis acid-Lewis base complexes with water and other inorganic acids including nitric acid and hydrochloric acid. Inorganic acids (e.g. nitric acid) are normally not soluble in SF-CO2. However, because TBP is highly soluble in SF-CO2, an inorganic acid bound to TBP via hydrogen bonding becomes CO2 soluble. This Lewis acid-Lewis base complex approach provides a method of introducing inorganic acids into supercritical fluid CO2 for chemical reactions