Some Aspects of Ionic Liquids as Diverse and Versatile Sustainable Solvents

Abstract

In this mini review several particular cases of ionic liquid solution behavior are discussed, namely solutions of ionic liquids with aliphatic alcohols, polyalcohols, arenes, chloromethanes and poly(ethyleneglycol) as well as salting-out and salting-in effects. The presented cases clearly expose ionic liquids as being diverse and versatile sustainable solvents that exhibit flexible phase behavior and, consequently, variable phase diagrams. These can be tuned either by changing the length of the alkyl chain(s) of the ionic liquid’s cation (and/or sometimes the anion), or by introducing a different aliphatic nature to the other solution constituent (e.g., by varying polymer chain length or the number of carbon atoms in chloromethanes). Sometimes, the evolution of the phase diagrams is fine and continuous, showing several consecutive stages, revealing both qualitative and quantitative changes. Finally, the diversity and versatility of ionic liquids are viewed as important features that contribute to their efficiency as tunable solvents or salting media.

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Abbreviations

UCST:

Upper-critical-solution-temperature

LCST:

Lower-critical-solution-temperature

[C2mim][PF6]:

1-Ethyl-3-methylimidazolium hexafluorophosphate

[C4mim][PF6]:

1-Butyl-3-methylimidazolium hexafluorophosphate

[C4mim][NTf2]:

1-Butyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}amide

[C2mim][NTf2]:

1-Ethyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}amide

[C2mim][OTf]:

1-Ethyl-3-methylimidazolium triflate

[C2OHmim][PF6]:

1-Hydroxyethyl-3-methylimidazolium hexafluorophosphate

[C2OHmim][BF4]:

1-Hydroxyethyl-3-methylimidazolium tetrafluoroborate

[C2mim][EtSO4]:

1-Ethyl-3-methylimidazolium ethylsulfate or ECOENG212®

[C4mim]Cl:

1-Butyl-3-methylimidazolium chloride

[C8mim]Cl:

1-Octyl-3-methylimidazolium chloride

[C10mim]Cl:

1-Decyl-3-methylimidazolium chloride

[C4mim][MeSO4]:

1-Butyl-3-methylimidazolium methyl sulfate

[C4C1mim]Cl:

1-Butyl-2,3-dimethylimidazolium chloride

[C n mim][NTf2]:

1-Alkyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}amide

[C n mim][OTf]:

1-Alkyl-3-methylimidazolium triflate

[C n mim]Cl:

1-Alkyl-3-methylimidazolium chloride

[BF4] :

Tetrafluoroborate anion

[PF6] :

Hexafluorophosphate anion

[MeSO4] :

Methyl sulfate anion

[NTf2] :

Bis{(trifluoromethyl) sulfonyl}amide (or bistriflamide) anion

[CF3SO3] or [OTf] :

Triflate anion

[C1mim]+ :

1-Methyl-3-methylimidazolium cation

[C6mim]+ :

1-Hexyl-3-methylimidazolium cation

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Acknowledgments

This work was sponsored by the projects PEst-OE/QUI/UIO100/2011 and PTDC/EQU-EPR/103505/2008, both financed by the Portuguese Foundation for Science and Technology (FC&T).

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Correspondence to Zoran P. Visak.

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Visak, Z.P. Some Aspects of Ionic Liquids as Diverse and Versatile Sustainable Solvents. J Solution Chem 41, 1673–1695 (2012). https://doi.org/10.1007/s10953-012-9899-z

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Keywords

  • Ionic liquids
  • Sustainable solvents
  • Phase diagrams
  • Phase equilibria
  • Anions
  • Cations