Analytical Sciences

Polyoxometalates in Imidazolim-based Ionic Liquids: Acceptor Number and Polarity Estimated from Their Voltammetric Behaviour

Hiroki ISHIDA,*1 Shinya AZUMA,*1 Naoki YAMASAKI,*1 Hitomi KURITA,*2 Takuya HASEGAWA,*3 Shuhei OGO,*4,*5 and Tadaharu UEDA*4,*5

*1 Graduate School of Integrated Arts and Sciences, Kochi University, Kochi 780-8520, Japan
*2 Department of Applied Science, Faculty of Science, Kochi University, Kochi 780-8520, Japan
*3 Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Sendai, Miyagi 980-8577, Japan
*4 Department of Marine Resource Science, Faculty of Agriculture and Marine Sciences, Kochi University, Nankoku 783-8520, Japan
*5 Center for Advanced Marine Core Research, Kochi University, Nankoku 783-8520, Japan

The selection of an appropriate solvent is essential for achieving high yields and selectivity in chemical reactions. The chemical and physical parameters of organic solvents have been classified into several groups, and solvents can be compared with each other with respect to these properties. The acceptor number (A_N), donor number (D_N) and polarity (E_T^N) have been widely accepted and used for theoretically and quantitatively evaluating the properties of organic solvents. In a similar manner, the A_N, D_N and E_T^N of room temperature ionic liquids (RTILs) have been estimated from spectral changes in solvatochromic compounds. In this paper, the A_N and E_T^N of eight types of imidazolium-based RTILs were estimated from the relationship between the A_N and E_T^N values and the first redox potential obtained from the voltammograms of polyoxometalates (POMs) in various organic solvents. The obtained parameters were compared with those estimated by spectrophotometric methods reported previously by several groups. This new method for estimating the A_N and E_T^N of RTILs using the voltammetric behaviour of POMs with low charge density and high symmetry could provide the other path to obtain more reliable A_N and E_T^N of RTILs.

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