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CHEMISTRY
Research into ionic liquids is booming. The first industrial process involving ionic liquids was announced in March 2003, and the potential of ionic liquids for new chemical technologies is beginning to be recognized. The burgeoning interest in the field was obvious at the recent American Chemical Society (ACS) meeting in New York, where ionic liquids were the focus of 10 sessions (1).
Ionic liquids are composed entirely of ions. For example, molten sodium chloride is an ionic liquid; in contrast, a solution of sodium chloride in water (a molecular solvent) is an ionic solution. The term "ionic liquids" has replaced the older phrase "molten salts" (or "melts"), which suggests that they are high-temperature, corrosive, viscous media (like molten minerals). The reality is that ionic liquids can be liquid at temperatures as low as -96[degrees]C. Furthermore, room-temperature ionic liquids are frequently colorless, fluid, and easy to handle. In the patent and academic literature, the term "ionic liquids" now refers to liquids composed entirely of ions that are fluid around or below 100[degrees]C.
One of the primary driving forces behind research into ionic liquids is the perceived benefit of substituting traditional industrial solvents, most of which are volatile organic compounds (VOCs), with nonvolatile ionic liquids. Replacement of conventional solvents by ionic liquids would prevent the emission of VOCs, a major source of environmental pollution. Ionic liquids are not intrinsically "green"-some are extremelv toxic-but they can be designed to be environmentally benign, with large potential benefits for sustainable chemistry (2).
There are four principal strategies to avoid using conventional organic solvents: No solvent (heterogeneous catalysis), water, supercritical fluids, and ionic liquids. The solventless option is the best established, and is central to the petrochemical industry, the least polluting chemical sector. The use of water can also be advantageous, but...