电位滴定法研究离子液体的碱性

Studying of the Basicity of Ionic Liquids by Potentiometric Titration

近年来碱性离子液体的设计、合成及应用获得广泛关注.离子液体碱性表征对于碱性离子液体的应用具有重要意义.然而,关于碱性离子液体碱性表征深入研究的报道还比较少.我们合成了系列碱性离子液体,利用电位滴定法测定了碱性离子液体的pKb值,通过相应pKb值来表征离子液体的碱性强度,最后考察了离子液体碱性与其结构之间的关联关系.结果表明,羧酸根碱性离子液体的碱性主要由阴离子决定,但不同的阳离子也会影响到其碱性强度,从而对离子液体的碱性进行微调;对于胺基功能化的咪唑型离子液体,由于离子液体结构中咪唑阳离子具有较强的吸电子诱导效应,相对于对应的三乙胺其碱性显著下降.

Design, synthesis and application of basic ionic liquids have attracted much extensive interest in recent years. The determination of the basic strength is of crucial significance for the utilization of basic ionic liquids. However, studies on the basicity characterization were rarely reported for basic ionic liquids to the best of our knowledge. In this paper, the aciddissociation constant pKb values of a series of basic ionic liquids synthesized were determined by potentiometric titration method. Then, the basicity of these ionic liq- uids was characterized by comparison of their pKb values. Finally, the relationship between the basicity and structure of these ionic liquids was discussed. The results show that the basicity of carboxylate ionic liquids is determined mainly by their anions, whereas the different cation is able to have its basicity finely tuned. The results also show that the basicity of aminofunctionalized imidazolium ionic liquid is weaker than that of triethylamine due to the strong electron withdrawing effect of the positively charged imidazolium ring.