Ionicity of room temperature ionic liquids: A parameter controlling the physicochemical properties

I&EC 111

Hiroyuki Tokuda, htokuda@ynu.ac.jp and Masayoshi Watanabe. Department of Chemistry and Biotechnology, Yokohama National University and CREST-JST, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501, Japan
To obtain a principle for ionic design of room temperature ionic liquids (RTILs) with desirable physical and chemical properties, typical RTILs were prepared with changing their cationic and anionic structures. To evaluate the ionicity of the RTILs, the molar conductivity ratio (ΛimpNMR), calculated from the molar conductivity measured by electrochemical impedance method (Λimp) and that estimated by PGSE-NMR ionic self-diffusion coefficients and the Nernst-Einstein relation (ΛNMR), was introduced. The ΛimpNMR well illustrates degree of formation of cation-anion aggregates in each ionic liquid under chemical equilibria, from the basis on experimental correlation of the ΛimpNMR with anionic donor and cationic acceptor abilities estimated by solvatochromic UV-visible measurement. As a measure of electrostatic interaction of the RTILs, effective ionic concentration (Ceff) was introduced as a product of the ΛimpNMR and molar concentration. Reduction of the Ceff for each RTIL well correlates with a decrease of reported cohesive energies and normal boiling points.