Thiazolium-based ionic liquids: Synthesis, characterization and physicochemical properties

Thiazolium salts are structurally analogous to the most common imidazolium-based ionic liquids (ILs), and are supposed to be a new class of ILs. However, there are up to now only a few reports and absence of systematic study on thiazolium ILs. In this work, several thiazolium-based ILs were prepared, characterized and comparatively studied. Most of the thiazolium ILs are liquid at room temperature, with melting points below 43.0 °C. Good thermal stability was observed for thiazolium ILs, resulting in thermal decomposition temperatures up to 264 ∼ 358 °C. In comparison with the conventional imidazolium ILs, thiazolium ILs exhibit moderate density, refractive index and surface tension, which all generally decrease with temperature. According to the temperature-dependent viscosity and conductivity, thiazolium ILs follow fractional Walden’s rule, indicating strong ion-ion coupling. Besides, thiazolium ILs display relatively narrow electrochemical window (3.1 ∼ 4.0 V).