Stability of Ionic Liquids in Application Conditions

Ionic liquids have a large variety of applications in nearly all areas of the chemical industries. They are used for example as lubricants, plasticizers, solvents and catalysts for synthesis, matrices for mass spectroscopy, solvents for extraction and in the manufacture of nano-materials, and as electrolytes. There are numerous studies in the corresponding literature concerning the unique properties, preparation methods, and different applications of ionic liquids. Nowadays, researchers try to answer questions concerning the stability of ionic liquids within practical applications. In this review, a general description of the stability and - degradation products of ionic liquids formed under different physicochemical conditions such as high temperature, irradiation, varying electrical current density, oxidizing agents are discussed. The main focus of this paper is on how the structure of ionic liquid cations and anions as well as impurities (e.g. water) influence the stability of ionic liquids in application and in utilization conditions. Additionally, it is also very important to consider the stability of ionic liquids with respect to environmental issues and for the hazard assessment of those compounds. These aspects, as well the possibility to use strongly oxidizing conditions (advanced oxidation processes) to remove ionic liquid structures from wastewaters are discussed within this review.