Room temperature molten salts: neoteric "green" solvents for chemical reactions and processes

Journal of the Brazilian Chemical Society

Consorti, Crestina S.¹  Dupont, Jaírton¹  Spencer, John¹  Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil¹  Thrombosis Research Institute, London¹ 

关键词: solvents;    catalysis;    molten salts;    ionic liquids;    clean technologies;   

DOI  :  10.1590/S0103-50532000000400002

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

With many chemical transformations taking place in solution, the role of solvents in chemistry is vital. Although, in principle, any liquid could be employed as a solvent, polar organic solvents have been extensively used for both synthetic chemistry and extraction technologies and have largely superseded water, which was widely employed historically. However, the ever-increasing awareness of the detrimental health and environmental effects of some organic solvents has given chemists the impetus to search for 'green' technologies1.The obviously ideal situation for a chemical process, from an ecological point of view, involves no solvent2. Although many reactions can be performed without solvent, chemistry remains dominated by processes taking place in solution. Note that most of solvents have a significant solubility in the water phase, and therefore must be stripped from the water before it leaves the process, both for economic and environmental reasons. Moreover, if the solvent cannot be effectively recovered for recycle back to the system (reactor, extractor, etc.) then the process will not be economically viable3. Nowadays, there are several alternatives under investigation as solvents including the resurgence of water4, perfluorinated hydrocarbons5 and supercritical fluids, in particular CO2 6.Room temperature molten salts (ionic liquids) have been known since the beginning of this century7 and are emerging as an attractive, alternative, 'green' technology in both organic and organometallic chemistry. This review covers the main achievements on the use of room temperature ionic liquids (RTILs) in the area of green chemistry with special emphasis on the results disclosed over the last two years. The synthesis and physical-chemical properties of molten salts, in particular halo-aluminates derivatives, have been extensively studied and a series of books on this subject is available8. The use of ionic liquids as solvents for catalysis and organic synthesis has been recently reviewed9. Molten Salts (Ionic Liquids)Molten salts, or ionic liquids, can be described as liquid compounds that display ionic-covalent crystalline structures. This definition involves pure inorganic compounds (sodium chloride, mp=801 oC), organic compounds (tetrabutylphosphonium chloride, mp=80 oC) or even eutectic mixtures of inorganic salts (such as lithium chloride/potassium chloride, 6/4, mp=352 oC) or organo-mineral combinations (triethylammonium chloride/cooper chloride, 1/1, mp=25 oC).Organo-chloroaluminate ionic liquids, especially those resulting from the combination of N-alkylpyridinium chloride or 1,3-dialkylimidazolium chloride and aluminium chloride (Scheme 1), have a broad range of liquid phase down to -88 oC 8.

【 授权许可】

Unknown