Pyrrolidinium Ionic Liquids

The pyrrolidinium ionic liquid is an ionic liquid containing a pyrrolidinium cation. The X^- represents different kinds of anions such as NO₃^-, HSO₄^-, HCOO^-, CH₃COO^-, CF₃COO^- or C₇H₁₅COO^- anions.

Figure 1. The structure of pyrrolidinium ionic liquids

Applications

• Electrochemistry: Pyrrolidine ionic liquids have good electrochemical properties. For example, a new polymeric ionic liquid having pyrrolidine cation units exhibits excellent electrochemical performance with the lithium salt. The pyrrolidinium-based polymeric ionic liquids are used as mechanically and electrochemically stable polymer electrolytes. A free standing mechanically stable transparent polymer film exhibiting an ionic conductivity higher than 10^-4 Scm^-1 at room temperature can be obtained. In addition, the electrolytes have a wide electrochemical window, which makes them candidates for all solid state lithium batteries. Another example is the use of an ionic liquid composed of a 1-butyl-1-methylpyrrolidine cation and various anions. A simple change in the anion structure or overall ion composition results in a change in the physical properties of this type of ionic liquid to produce a variety of solvents. These pyrrolidinium ionic liquids can be easily produced and have a broad range of potential applicability. They can be used as fuel cell electrolytes and catalysts, and they can also be used as an alternative to conventional inorganic acids in acid catalyzed reaction environments.

• Organic chemistry: Pyrrolidine ionic liquids are widely used as solvents in organic chemistry. For example, the conversion and stereoselectivity of the endo- and exo-norbornene derivatives in a Diels-Alder reaction of cyclopentadiene with an alkyl acrylate can influenced by the pyrrolidinium ionic liquid. When a reaction is carried out in a pyrrolidine ionic liquid in the presence of a metal chloride and a triflate as a catalyst, shorter reaction and higher dienophile conversion are observed compared to a similar cycloaddition reaction carried out in the presence of conventional organic solvents. And in most cases, endo isomers were found to have higher stereoselectivity.

Figure 2. Diels-Alder reaction of cyclopentadiene with an alkyl acrylate in pyrrolidinium ionic liquids

References

1. Pont, A.-L.; et al. (2009). “Pyrrolidinium-based polymeric ionic liquids as mechanically and electrochemically stable polymer electrolytes.” Journal of Power Sources 188(2), 558–563.
2. Anouti, M.; et al. (2008). “Synthesis and Characterization of New Pyrrolidinium Based Protic Ionic Liquids. Good and Superionic Liquids.” The Journal of Physical Chemistry B 112(42), 13335–13343.