Poole Colin F
Department of Chemistry, Room 183, Wayne State University, Detroit, MI 48202, USA.
J Chromatogr A. 2004 May 28;1037(1-2):49-82. doi: 10.1016/j.chroma.2003.10.127.
Room temperature ionic liquids are novel solvents with favorable environmental and technical features. Synthetic routes to over 200 room temperature ionic liquids are known but for most ionic liquids physicochemical data are generally lacking or incomplete. Chromatographic and spectroscopic methods afford suitable tools for the study of solvation properties under conditions that approximate infinite dilution. Gas-liquid chromatography is suitable for the determination of gas-liquid partition coefficients and activity coefficients as well as thermodynamic constants derived from either of these parameters and their variation with temperature. The solvation parameter model can be used to define the contribution from individual intermolecular interactions to the gas-liquid partition coefficient. Application of chemometric procedures to a large database of system constants for ionic liquids indicates their unique solvent properties: low cohesion for ionic liquids with weakly associated ions compared with non-ionic liquids of similar polarity; greater hydrogen-bond basicity than typical polar non-ionic solvents; and a range of dipolarity/polarizability that encompasses the same range as occupied by the most polar non-ionic liquids. These properties can be crudely related to ion structures but further work is required to develop a comprehensive approach for the design of ionic liquids for specific applications. Data for liquid-liquid partition coefficients is scarce by comparison with gas-liquid partition coefficients. Preliminary studies indicate the possibility of using the solvation parameter model for interpretation of liquid-liquid partition coefficients determined by shake-flask procedures as well as the feasibility of using liquid-liquid chromatography for the convenient and rapid determination of liquid-liquid partition coefficients. Spectroscopic measurements of solvatochromic and fluorescent probe molecules in room temperature ionic liquids provide insights into solvent intermolecular interactions although interpretation of the different and generally uncorrelated "polarity" scales is sometimes ambiguous. All evidence points to the ionic liquids as a unique class of polar solvents suitable for technical development. In terms of designer solvents, however, further work is needed to fill the gaps in our knowledge of the relationship between ion structures and physicochemical properties.
室温离子液体是具有良好环境和技术特性的新型溶剂。已知有超过200种室温离子液体的合成路线，但对于大多数离子液体而言，其物理化学数据通常缺乏或不完整。色谱法和光谱法为在接近无限稀释的条件下研究溶剂化性质提供了合适的工具。气液色谱法适用于测定气液分配系数和活度系数，以及从这些参数中的任何一个及其随温度的变化导出的热力学常数。溶剂化参数模型可用于定义各个分子间相互作用对气液分配系数的贡献。将化学计量学程序应用于离子液体系统常数的大型数据库表明了它们独特的溶剂性质：与具有相似极性的非离子液体相比，具有弱缔合离子的离子液体内聚能较低；氢键碱性比典型的极性非离子溶剂更强；以及一系列偶极矩/极化率，其范围与最极性非离子液体所占据的范围相同。这些性质可以粗略地与离子结构相关，但需要进一步开展工作以开发一种用于特定应用的离子液体设计的综合方法。与气液分配系数相比，液液分配系数的数据很少。初步研究表明，使用溶剂化参数模型解释通过摇瓶法测定的液液分配系数是可能的，以及使用液液色谱法方便快捷地测定液液分配系数也是可行的。对室温离子液体中溶剂化显色和荧光探针分子的光谱测量提供了对溶剂分子间相互作用的深入了解，尽管对不同且通常不相关的“极性”标度的解释有时并不明确。所有证据都表明离子液体是一类适合技术开发的独特极性溶剂。然而，就定制溶剂而言，还需要进一步开展工作以填补我们在离子结构与物理化学性质之间关系的知识空白。
