A bit of history...



  • Past
  • Ionic liquids are not new; some of them have been known for many years. For instance [EtNH3[NO3], which has a melting point of 12°C, was first described in 1914!3
    Among imidazolium salts, one of the first 1,3-dialkylimidazolium room temperature ionic liquids (RTIL) - obtained through the mixing of 1-ethyl-3-methylimidzolium chloride with aluminum trichloride - was reported more that a half of century ago. However, these organo-aluminate ionic liquids are unstable to air and water and they are not inert towards various organic compounds, which has most probably limited their range of applications.6

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...Some figures2

The most widely used ionic liquids are probably N,N-dialkylimidazolium salts.
Figures from the RSC, ACS and Elsevier publications databases support this assertion. To illustrate, of eighty-three RSC publications in 2002 dealing with ionic liquids, seventy-four involved imidazolium salts. The percentages from ACS and Elsevier imprint journals for 2002 are similar.

  • Present
  • Soon after the first reports on the syntheses and applications in organometallic catalysis of the air stable room temperature ionic liquids (RTILs) 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF4), hexafluorophosphate (BMI.PF6) and their analogues, in the middle of the 1990s a renaissance of the rich chemistry of molten salts has begun and continues to flourish.6
    Until 2001 the halogenoaluminate (III) (in particular [emim]AlCl4, which contains the cation 1-ethyl-3-methylimidazolium and the smaller anion tetrachloroaluminate) and the closely related alkylhalogenoaluminate (III) ionic liquids have been by far the most widely studied3: nowadays 1,3-dialkyl imidazolium salts are the most popular and investigated classes of room temperature ionic liquids.2,6

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