Extraction of polar materials such as sugars, proteins and nucleotides from water is known as a difficult issue since organic solvents which are immiscible with water are basically apolar. On the other hand, ionic liquids (ILs), salts which are liquid below 100 °C, are very interesting solvents because some ILs are immiscible with water despite their high polarity. If the miscibility of the ILs with water can be controlled by pH or CO2/N2 bubbling of solution, it will be a quite useful system. It is known that hydrophobicity of ILs is sensitive to the structures of ILs. On the other hand, zwitterions, salts whose cation and anion are tethered by a covalent bond, are known to show a higher hydrophobicity. We developed a new IL which can reversibly switch to zwitterion. To develop such IL/zwitterion molecules, we designed an IL which has dynamic covalent bond, a covalent bond is formed or broken reversibly by pH change. When 20 wt% of the IL (zwitterion form) was added, it was immiscible to water and clear biphasic system was constructed. After CO2 bubbling, IL turned miscible with water. After N2 bubbling, the IL returned immiscible and a clear biphasic system was confirmed. This behavior change was repeatable. We investigated the ratio of the IL- and zwitterion forms by 1H NMR during CO2/N2 bubbling. The ratio of IL form was 27 mol% in the IL phase of the biphasic system. After bubbling CO2, it was confirmed that the ratio of IL form increased to 62 mol%. After N2 bubbling, the ratio of the IL form decreased to 40 mol% in the IL phase. It was confirmed that the phase behavior occurred based on the change of the ratio of the IL- and zwitterion forms. This research was promoted by COI program “Construction of next-generation infrastructure using innovative materials—Realization of a safe and secure society that can coexist with the earth for centuries” supported by MEXT and JST.

New design of a polar ionic liquid switchable in miscibility with water by CO2/N2

254th National Meeting (2017)

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