Ionic Liquids as Green Solvents: Progress and Prospects

Abstract

Volatile organic solvents (VOS) creating increasing air pollution are common reaction media for many chemical processes. VOS cannot be easily separated from the desired reaction products and difficult to recycle. In view of awareness of the deteriorating environment, researches are directed on developing alternative environmental friendly solvent systems to replace traditional volatile organics. Within this context, the interest of ionic liquids (ILs) as “green” solvents resides in their extremely low vapor pressure and high thermal stability, which offers advantages such as ease of containment, product recovery, and recycling ability. In addition, ILs show considerable variation in their stability to moisture and their miscibility with molecular liquids. Properties such as density, melting point, water and cosolvent miscibility, viscosity, polarity, acid/base character, and coordinating ability can be tailored by the appropriate selection of the cation and/or anion component. ILs have been implemented as solvent systems in chemical reactions, separations, extractions, electroanalytical applications and chemical sensing, among many others. Also, they have high ionic character that enhances the reaction rates to a great extent in many reactions. These features allow ILs to be used as potential alternative solvents to VOS in a wide variety of industrial chemical processes. Furthermore, the use of ILs as industrial solvents can result in economical, social, and ecological impact due to their effect on the human health and environment.