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Fabrication and Functionalization of Ionic Liquids
Published in Vineet Kumar, Praveen Guleria, Nandita Dasgupta, Shivendu Ranjan, Functionalized Nanomaterials I, 2020
In 1914, the first attempt was made to synthesize room-temperature ionic liquids by the reaction of ethylammonium nitrate, which is the neutralization reaction of ethyl amine using concentrated nitric acid with the synthesized ionic liquid melting at 12 oC (Walden, 2019). Ionic liquids did not gain any interest until the development of binary ionic liquids derived from mixing 1,3-dialkylimidazolium chloride or N alkylpyridinium and aluminum chloride (Chum et al., 1975; Wilkes, 2002). These ionic liquids have been classified into two categories, i.e., simple salts made up of a single cation and anion, while the binary ionic liquids where equilibrium exists between cations and anions, e.g. ethylammonium nitrate, are simple ionic liquids. On the other hand, the ionic liquids synthesized from 1,3-dialkylimidazolium chlorides and aluminum chloride are the binary ionic liquids that carry various ionic species with different melting points and other properties such as viscosity, stability, etc., depending on the mole fractions of cations and anions used. (Figure 15.1). Different routes for the fabrication of ionic liquids.
Special Issue on Progress Using Ionic Liquids in Liquid-Liquid Extraction
Published in Solvent Extraction and Ion Exchange, 2018
More than a century ago in 1914, Paul Walden reported the first room-temperature ionic liquid, ethylammonium nitrate, which has melting point of 13–14°C, in sharp contrast to that of the inorganic salts which melt at very high temperatures (for example, NaCl melts at 801°C). This has opened up the area of electrochemical studies in ionic melts at significantly low temperatures. Organic ionic compounds such as substituted pyridinium chlorides were synthesized in the 1932 and used as solvents for cellulose. Subsequently, a mixture of these salts with AlCl3 was used for a variety of electrochemical applications in a narrow composition range. After no significant development for nearly half a century, methylimidazolium (mim) based ionic liquids were synthesized in the 1980s and were used along with AlCl3 as the [mim]+[AlCl4]– type ionic liquids which had limited applications to chemical reactions involving aqueous solutions due to their moisture sensitivity. However, these compounds were reported to have lesser viscosity and wider electrochemical window compared with their pyridinium counterparts. In 1992, Wilkes and Zaworotko reported 2-ethyl-1-methyl imidazolium salts with a host of counter anions, which were found to be immune to degradation in the presence of water, resulting in many applications. By the late 1990s, many hydrophobic room-temperature ionic liquids were known and were found to be attractive solvents for myriad applications in organic synthesis, catalysis, electrochemistry, solvent extraction, etc.