Task-Specific Ionic Liquid for Solubilizing Metal Oxides

Protonated betaine bis(trifluoromethylsulfonyl)imide is an ionic liquid with the ability to dissolve large quantities
of metal oxides. This metal-solubilizing power is selective. Soluble are oxides of the trivalent rare earths,
uranium(VI) oxide, zinc(II) oxide, cadmium(II) oxide, mercury(II) oxide, nickel(II) oxide, copper(II) oxide,
palladium(II) oxide, lead(II) oxide, manganese(II) oxide, and silver(I) oxide. Insoluble or very poorly soluble
are iron(III), manganese(IV), and cobalt oxides, as well as aluminum oxide and silicon dioxide. The metals
can be stripped from the ionic liquid by treatment of the ionic liquid with an acidic aqueous solution. After
transfer of the metal ions to the aqueous phase, the ionic liquid can be recycled for reuse. Betainium bis(trifluoromethylsulfonyl)imide forms one phase with water at high temperatures, whereas phase separation
occurs below 55.5 °C (temperature switch behavior). The mixtures of the ionic liquid with water also show
a pH-dependent phase behavior:  two phases occur at low pH, whereas one phase is present under neutral or
alkaline conditions. The structures, the energetics, and the charge distribution of the betaine cation and the
bis(trifluoromethylsulfonyl)imide anion, as well as the cation−anion pairs, were studied by density functional
theory calculations.

质子化的甜菜碱双(三氟甲磺酰)亚胺是一种具有溶解大量金属氧化物能力的离子液体。此金属溶解化能力具有选择性。可溶解的三价稀土氧化物、铀(VI)氧化物、锌(II)氧化物、镉(II)氧化物、汞(II)氧化物、镍(II)氧化物、铜(II)氧化物、钯(II)氧化物、铅(II)氧化物、锰(II)氧化物及银(I)氧化物。铁(III)氧化物、锰(IV)氧化物、钴氧化物，以及氧化铝和二氧化硅则不溶或溶解度极低。通过使用酸性水溶液处理离子液体，可以将其中的金属提取出来。金属离子转移到水相之后，该离子液体可被回收再利用。在高温下，甜菜碱双(三氟甲磺酰)亚胺与水形成单一相，而在55.5°C以下则会发生相分离（温度切换行为）。离子液体与水的混合物也显示出pH依赖的相行为：在低pH值时出现两相，而在中性或碱性条件下则呈现为一相。通过密度泛函理论计算研究了甜菜碱阳离子和双(三氟甲磺酰)亚胺阴离子的结构、能量学以及电荷分布，以及阳离子-阴离子对的性质。