(334a) Unique CO2-Philic Neutral Open-Chain Crown Ether Analogues as Selective Ligands for Metal Ions Separation by Supercritical Carbon Dioxide

It remains a big challenge for chemists to design and synthesize more CO2-philic and selective ligands without fluorination for supercritical carbon dioxide extraction (SFE) of metal ions from solid matrices and liquids. The novel ligands of neutral open-chain crown ether analogues: R1O(R2O)P(O)(OCH2CH2)4OP(O)(OR2)OR1, (R1=methyl, R2=octyl, ethylhexyl, 2-(2-methoxypropoxy)propyl) have been synthesized directly with the simple chemical reagents, and the structures were confirmed by IR, 1HNMR, 13CNMR, APCI mass spectroscopy and elemental analysis. The solubilities of these ligands in the supercritical carbon dioxide (scCO2) were measured at temperatures (313~333K) and pressures (12~22Mpa). They all exhibited advantageous affinity to CO2 , whose solubilities were more than 2×10-3 (in molar fraction). The calculated results by a semiempirical model showed satisfactory agreement with the experimental solubilities data. The five metal ions ( La3+, Nd3+, Yb3+, Sr2+ and Ni2+) spiked in the filter paper as the simulated matrix were extracted by the static mode with the SFE condition (333K, 20MPa). All the novel ligands showed beneficially higher extractability and selectivity for lanthanoids. Furthermore, the extraction efficiency of Nd3+ was the highest. This selective behavior was similar with calixarenes or crown ethers, which indicated that the EO bridge rendered the preorganized conformations of the flexible ligands pseudocyclic. In terms of efficiency and selectivity, unexpectedly, the ligand with R2= ethylhexyl was the best but not the one with R2=2-(2-methoxypropoxy)propyl.