Novel Ionic Liquids Composed of Only Heterocycles

Since delocalized charge considerably helps to lower the melting point (Tm) of the salts, -conjugated cations were frequently used. Similarly, introduction of halogens such as fluoride and chloride are used to lower the negative charge density. Therefore, most of general ionic liquids contain halogenated counter anions. Some halogen-free anions were also used to form salts with relatively low Tm, there were a few reports about the ionic liquids based on these anions. It is important to design halogen free ionic liquids from the viewpoint of green chemistry. We had prepared novel ionic liquids by using sulfur-based anion such as thiol or dithiocarboxylic acid expecting small surface charge density of sulfur. For this purpose, we prepared new ionic liquids composed of heterocycles having sulfur-based anion having heterocycle. Negative charge should be delocalized in the heterocycles like imidazolium cation in which positive charge was delocalized. These heterocyclic anions were characterized to have only C, H, and N atoms.