Phosphonium-based ionic liquids PILs

The present review is aimed at describing the state-of-the-art, for the period January-December 2014, of two pillar classes of phosphorus-containing compounds, the phosphonium salts and ylides. The importance of these derivatives is revealed by the very high number of references cited herein. For the Reader s convenience, topics are organized to offer an introductory survey on the methods of preparation and characterisation of both types of compounds, followed by an analysis of applicative and curiosity driven research. A special section is devoted to phosphonium-based ionic liquids (PILs). 

Phosphonium-based ionic liquids (PILs) have elicited a phenomenal interest due to their low viscosity and high thermal and electrochemical stability, especially when compared with ammonium analogues. To evaluate possible applications of PILs, several studies investigated the physico-chemical properties of such compounds, while, at the same time, computational methods were developed to predict the viscosities, densities, etc. of PILs. 

In the drive towards expanding the range of useful ionic liquids (ILs), with suitably low viscosities, sufficient stability, and conductivity for electrochemical uses, phosphonium-based ionic liquids (PILs) are exceptionally promising compounds. Due to the high thermal and electrochemical stabilities of PILs compared to ammonium-based ILs (allq l-ammonium, imidazolium, pyridinium, pyrrolidinium, and piperidinium compounds), phosphonium salts have been especially considered for applications as electrolytes. Their properties (both thermal and electrochemical stabilities) are in fact crucial to improve safety, durability, power and energy densities of electrochemical devices such as electric double layer capacitors. 

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