H-1, C-13, and F-19 NMR Studies on Molecular Interactions of CO2 with beta-Diketones and UO2(beta-diketonato)(2)DMSO Complexes in Supercritical CO2

摘要

The relationship between solubility of beta-diketones and uranyl beta-diketonato complexes (UO2(beta-diketonato)(2)DMSO) in supercritical carbon dioxide (scCO(2)) and their molecular interactions has been studied by measuring H-1, C-13, and F-19 NMR chemical shifts at 40 degrees C in the pressure range of 7-25 MPa (density; 0.2 < rho (g cm(-3)) < 0.9). The H-1 and F-19 NMR spectra showed that beta-diketones exist mainly as enol form in scCO2 and that UO2(beta-dikefortanato)(2)DMSO in scCO(2) have the same structures as those in nonaqueous solvents with low dielectric constants. It was found that scCO(2) forms the van der Waals interactions with both proton and fluorine groups in beta-diketones and UO2(beta-diketonato)(2)DMSO and that such interactions of scCO(2) with fluorine are much stronger than those with proton. However, the C-13 NMR chemical shifts (C-13-delta s) of scCO(2) containing solutes such as beta-diketones showed a quite different tendency from H-1 and F-19 NMR chemical shifts, The C-13-delta s moved entirely to lower field direction in parallel with those of neat scCO(2), whereas those of scCO(2) containing UO2(beta-diketonato)(2)DMSO did not show such parallel shifts. The magnitude of parallel shifts (Delta delta(C)) of scCO(2) was found to be dependent on the properties of solutes in scCO(2) and to decrease in order of fluorinated beta-diketone > non-fluorinated beta-diketone > organic solvents having C=O groups and hydrogen-bonding OH groups > UO2(beta-diketonato)(2)DMSO. This order was quite consistent with the magnitude of solubility of corresponding compounds in scCO(2). These results indicate that the differences of Delta delta(C) values are mainly attributable to the strength of solute-CO2 interactions through the Lewis acid-Lewis base (LA-LB) interactions and can be used as measure for evaluating the CO2-philicity of solutes, in scCO2. It can be concluded that the solubility of UO2(beta-diketonato)(2)DMSO and beta-diketones in scCO(2) is mainly controlled by the balance among the van der Waals interactions, LA-LB interactions, CH center dot center dot center dot O interactions between CH3 protons and CO2 oxygen atoms, and steric configuration between CO2 and the solutes.