Thermo-solvatochromism in binary mixtures of water and ionic liquids: on the relative importance of solvophobic interactions
作者:Bruno M. Sato、Carolina G. de Oliveira、Clarissa T. Martins、Omar A. El Seoud
DOI:10.1039/b921391k
日期:——
The thermo-solvatochromism of 2,6-dibromo-4-[(E)-2-(1-methylpyridinium-4-yl)ethenyl] phenolate, MePMBr2, has been studied in mixtures of water, W, with ionic liquids, ILs, in the temperature range of 10 to 60 °C, where feasible. The objectives of the study were to test the applicability of a recently introduced solvation model, and to assess the relative importance of solute–solvent solvophobic interactions. The ILs were 1-allyl-3-alkylimidazolium chlorides, where the alkyl groups are methyl, 1-butyl, and 1-hexyl, respectively. The equilibrium constants for the interaction of W and the ILs were calculated from density data; they were found to be linearly dependent on NC, the number of carbon atoms of the alkyl group; van’t Hoff equation (log K versus 1/T) applied satisfactorily. Plots of the empirical solvent polarities, ET (MePMBr2) in kcal mol−1, versus the mole fraction of water in the binary mixture, χw, showed non-linear, i.e., non-ideal behavior. The dependence of ET (MePMBr2) on χw, has been conveniently quantified in terms of solvation by W, IL, and the “complex” solvent IL-W. The non-ideal behavior is due to preferential solvation by the IL and, more efficiently, by IL-W. The deviation from linearity increases as a function of increasing NC of the IL, and is stronger than that observed for solvation of MePMBr2 by aqueous 1-propanol, a solvent whose lipophilicity is 12.8 to 52.1 times larger than those of the ILs investigated. The dependence on NC is attributed to solute–solvent solvophobic interactions, whose relative contribution to solvation are presumably greater than that in mixtures of water and 1-propanol.
2,6-二溴-4-[(E)-2-(1-甲基吡啶-4-基)乙烯基]酚,MePMBr2的热溶剂效应已在水(W)和离子液体(IL)混合物中研究,温度范围为10至60°C。研究的目的在于测试最近提出的溶剂化模型的适用性,并评估溶质-溶剂之间的溶剂疏水相互作用的重要性。所用的IL是1-烯丙基-3-烷基咪唑盐氯化物,其中烷基群分别为甲基、1-丁基和1-己基。W与IL之间的相互作用的平衡常数是根据密度数据计算得出的,发现它们与烷基组的碳原子数(NC)呈线性相关;van't Hoff方程(log K与1/T的关系)适用性良好。经验性溶剂极性ET(MePMBr2,以kcal mol−1为单位)与二元混合物中水的摩尔分数χw的关系图显示了非线性,即非理想行为。ET(MePMBr2)对χw的依赖关系已方便地用水、IL和“复合”溶剂IL-W的溶剂化量化。非理想行为是由于IL的优先溶剂化,更有效的是IL-W。随着IL的NC增加,偏离线性的程度也随之增加,这种程度强于MePMBr2与水和1-丙醇的溶剂化,后者的亲脂性比所研究的IL高出12.8到52.1倍。对NC的依赖被归因于溶质-溶剂的疏水相互作用,其对溶剂化的相对贡献大于水和1-丙醇混合物中的贡献。