Ionic liquid
An ionic liquid is a liquid that contains only ions. In the broad sense, this term includes all the molten salts, for instance, sodium chloride whose temperature is higher than 800 ° C. In the narrow sense, however, the term 'ionic liquid' indicates the salts whose melting point is relatively low. In particular, the salts that melt at room temperature are called 'room-temperature ionic liquids'. Usually, ionic liquids (in the narrow sense below) consist of bulky organic cations such as 1-alkyl-3-methylimidazolium ion and 1-alkylpyridinium ion and inorganic anions such as tetrafluoroborate ion, hexafluorophosphate ion, and halogen ions. For example, the melting point of 1-buthyl-3-methylimidazolium tetrafluoroborate is about -80 ° C, and it is a colorless liquid with high viscosity at room temperature. The notable characteristics of ionic liquids are their non-measurable vapor pressure, non-flammability, thermal stability, wide range of temperatures as liquids, and solvating properties with diverse kinds of materials. It is known that, as in conventional organic solvents, many kinds of chemical reactions such as Diels-Alder reactions and Friedel-Crafts reactions occur in ionic liquids. Another important feature of ionic liquids is their designability; the cation and the anion can be functionalized for various purposes. Because of their properties, ionic liquids attract great attention from chemists in many fields, including organic chemistry, electrochemistry, and physical chemisty. In addition, their non-volatility results in low impact on the environment and human health, and they are recognized as solvents for green chemistry.