Studying of the Basicity of Ionic Liquids by Potentiometric Titration

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 acid-dissociation constant pK(b) values of a series of basic ionic liquids synthesized were determined by potentiometric titration method. Then, the basicity of these ionic liquids was characterized by comparison of their pK(b) 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 amino-functionalized imidazolium ionic liquid is weaker than that of triethylamine due to the strong electron withdrawing effect of the positively charged imidazolium ring.