Sedov I A, Magsumov T I, Salikov T M, Solomonov B N
Chemical Institute, Kazan Federal University, Kremlevskaya 18, 420008, Kazan, Russia.
Phys Chem Chem Phys. 2017 Sep 27;19(37):25352-25359. doi: 10.1039/c7cp05249a.
The solvation properties of protic ionic liquids such as alkylammonium salts are still virtually uncharacterized. Both electrostatic interactions between charged particles and hydrogen bond networks in a solvent are known to hinder the solubility of apolar species. Protic ionic liquids can be a priori expected to dissolve hydrocarbons worse than aprotic ionic liquids which do not form hydrogen bonds between the ions. We measured the limiting activity coefficients of several alkanes and alkylbenzenes in propylammonium and butylammonium nitrates at 298 K. Surprisingly, we observed the tendency of higher solubility than for the same compounds in aprotic ionic liquids with a similar molar volume. The calculations of the excess Gibbs free energies using test particle insertions into the snapshots of molecular dynamics trajectories reproduced lower values in protic rather than in aprotic ionic liquids for both methane molecules and hard sphere solutes. This can be explained by the favorable solvation of apolar species in the apolar domain of nanostructured PILs. For the first time, we point out at the essential difference between the solvation properties of two types of ionic liquids and prove that it arises from the cavity formation term.
质子型离子液体（如烷基铵盐）的溶剂化性质实际上仍未得到充分表征。已知溶剂中带电粒子之间的静电相互作用和氢键网络都会阻碍非极性物质的溶解性。与离子之间不形成氢键的非质子型离子液体相比，质子型离子液体预计对烃类的溶解能力更差。我们在298 K下测量了几种烷烃和烷基苯在丙基铵和丁基铵硝酸盐中的极限活度系数。令人惊讶的是，我们观察到与具有相似摩尔体积的非质子型离子液体相比，这些化合物在质子型离子液体中的溶解度更高。使用测试粒子插入分子动力学轨迹快照对过量吉布斯自由能进行的计算表明，对于甲烷分子和硬球溶质，质子型离子液体中的值低于非质子型离子液体。这可以通过非极性物质在纳米结构质子型离子液体的非极性区域中的有利溶剂化来解释。我们首次指出了两种类型离子液体溶剂化性质的本质差异，并证明这种差异源于空穴形成项。
