Centro de Química Estrutural, Faculdade de Ciências, Universidade de Lisboa, Lisboa 1749-016, Portugal.
School of Science and Technology, NOVA University of Lisbon, Caparica 2829-516, Portugal.
J Phys Chem B. 2021 Oct 21;125(41):11491-11497. doi: 10.1021/acs.jpcb.1c06133. Epub 2021 Oct 12.
The knowledge of water solubility in ionic liquids (ILs) is an important property with an impact on the design of many physical and chemical processes, like the purification of organic compounds or the establishment of decontamination procedures. The development of methods to predict or establish solubility trends in ILs is, therefore, extremely relevant, as it may avoid expensive and time-consuming experimental procedures. In this work, we compare results of water solubility in ILs predicted by a quantitative structure-property relationship (QSPR) model with trends found using aggregation studies in molecular dynamics (MD) simulation results. This study was performed for ILs combining the cations 1-butyl-1-methylpyrrolidinium and 1-butyl-1-methylmorpholinium, with the anions bis(pentafluoroethylsulfonyl)imide (BETI), trifluoromethanesulfonate (TF), and tetrafluoroborate (BF). Both methods indicated that, at 298.15 K, the water solubility in ILs was almost independent of the investigated cations. However, if the IL is composed of a hydrophobic anion, a slight increase in the mixability of the IL with water may be observed if the cation can form H-bonds. The QSPR model indicated that the hydrophobic BETI anion leads to solubilities ( ∼ 0.33), approximately half of those predicted when the cations are combined with TF and BF anions ( ∼ 0.60). The MD results suggested that this difference is essentially related to the ability of the water molecules to interact with the anion. This interaction involves the formation of networks of molecules, where HO is completely solvated by anions. These structures make the formation of interactions between water molecules difficult, which are responsible for their segregation from solution and, therefore, to liquid-liquid phase separation. For the investigated ILs, the MD data also suggest that the solubility trends are inversely proportional to the number of "isolated" anions relative to ···AN-HO-AN-HO··· networks.
水在离子液体（ILs）中的溶解度是一个重要的性质，它对许多物理和化学过程的设计都有影响，例如有机化合物的纯化或去污程序的建立。因此，开发预测或建立 ILs 中溶解度趋势的方法非常重要，因为它可以避免昂贵和耗时的实验程序。在这项工作中，我们将通过定量构效关系（QSPR）模型预测的 IL 中溶解度的结果与通过分子动力学（MD）模拟结果中的聚集研究发现的趋势进行比较。这项研究是针对结合 1-丁基-1-甲基吡咯烷鎓和 1-丁基-1-甲基吗啉鎓阳离子的 IL 进行的，阴离子为双（五氟乙基磺酰基）亚胺（BETI）、三氟甲磺酸根（TF）和四氟硼酸根（BF）。这两种方法都表明，在 298.15 K 时，IL 中的水溶解度几乎与所研究的阳离子无关。然而，如果 IL 由疏水性阴离子组成，如果阳离子能够形成氢键，则 IL 与水的混合能力可能会略有增加。QSPR 模型表明，疏水性 BETI 阴离子导致溶解度（∼0.33），大约是与 TF 和 BF 阴离子结合的阳离子时预测值（∼0.60）的一半。MD 结果表明，这种差异主要与水分子与阴离子相互作用的能力有关。这种相互作用涉及到分子网络的形成，其中 HO 完全被阴离子溶剂化。这些结构使得水分子之间形成相互作用变得困难，这是它们从溶液中分离出来的原因，从而导致液-液分相。对于所研究的 ILs，MD 数据还表明，溶解度趋势与“孤立”阴离子的数量成反比，而与···AN-HO-AN-HO···网络成正比。
