Ionic Liquids
Authors: Meindersma G. Wytze , Maase Matthias , De Haan André B. 
Published: August 2007

The article contains sections titled:1.Introduction2Physical and Chemical Properties2.1.Introduction2.2.Melting Point2.3.Density2.4.Viscosity2.5.Thermal Stability2.6.Electrochemical Window3Synthesis/Production3.1.Introduction3.2.Synthesis3.2.1.Lewis Acid‐Based ILs3.2.2.Anion Metathesis3.2.3.Synthesis of Chloride Free ILs3.2.4.Preparation with Microwaves3.3.Producers of Ionic Liquids4Applications4.1Potential Applications4.1.1.Solvents for Synthesis and Catalysis4.1.1.2Solvents for Catalysis4.1.1.3Polymer Synthesis4.1.1.4Biocatalysis4.1.2.Electrochemical Applications4.1.3.Analytical Applications4.1.4.Separations4.1.4.1Liquid Separations4.1.4.2Gas Separations4.1.5.Fluid Applications: Thermal Fluids and Lubricants4.2.Applications in Pilot Plants and Industry4.2.1.Reactions4.2.1.1.Acid Scavenging4.2.1.2.Production of 2,5‐dihydrofuran4.2.1.3.Chlorination of Alcohols/Cleavage of Ethers4.2.1.4.Hydrosilylation4.2.1.5.Fluorination4.2.1.6.Dimerization and Oligomerization of Olefins4.2.2.Separations4.2.2.1Extractive Distillation4.2.2.2.Extraction of Aromatic Hydrocarbons4.2.3.Electroplating/Polishing4.2.4.ILs as Performance Chemicals4.2.4.1Compatibilizers for Pigment Pastes4.2.4.2.Antistatic Additives for Cleaning Fluids4.2.5.ILs in Gas Processing4.2.5.1.Storage of Gases4.2.5.2.Ionic Compressor5Analysis6Toxicology and Occupational Health6.1.(Eco)toxicology6.2.Mutagenicity6.3.Safety and Corrosion7References

The common definition of an ionic liquid (IL), or a room temperature ionic liquid (RTIL), is that it is a liquid composed entirely of ions, which is fluid below 100 °C. Ionic liquids are generally much denser (ρ = 1 − 1.6 g/cm3) and more viscous (η = 10 − 500 mPa · s) than conventional solvents. Ionic liquids can be stable up to temperatures of 500 °C. They can easily be synthesized and the variability of the cation and anion may be used to adjust the properties of the ionic liquids. Therefore, the possibility arises to optimize an ionic liquid for a specific application by stepwise tuning the relevant solvent properties. For this reason ionic liquids have been referred to as “designer solvents”.

The potential to use ionic liquids as novel solvents or fluids for a diverse range of applications has become increasingly apparent. The intrinsic nonvolatile nature of ILs provides an opportunity to reduce, or even completely eliminate, hazardous and toxic emissions to the atmosphere, thus providing the promise for significant environmental benefits. In synthesis and catalysis, ILs have been used as solvents (or solvents and catalysts), with the greatest current effort on using the ILs as alternatives to volatile organic compounds (VOCs). Electrochemical studies have utilized the fact that ILs are liquids rather than solids to provide liquid electrolytes without needing to add an additional solvent. Ionic liquids are also used in separations, replacing volatile solvents. The number of applications on pilot‐plant and commercial scale is still limited, but growing.

Although ionic liquids are also known as “green solvents”, this is not always true. They can be corrosive, flammable, or toxic. Due to their nonvolatile nature, ionic liquids are generally considered as having a low impact on the environment and human health, and thus recognized as solvents for green chemistry. However, the impact of ionic liquids on aquatic ecosystems is important given their mild to high solubility in water. Before ionic liquids will be widely used in industry, the effects of ILs on the aquatic environment must be known.