Catalytic reactions in ionic liquids

The chemical industry is under considerable pressure to replace many of the volatile organic compounds (VOCs) that are currently used as solvents in o rganic synthesis. The toxic and/or hazardous properties of many solvents, n otably chlorinated hydrocarbons, combined with serious environmental issues , such as atmospheric emissions and contamination of aqueous effluents is m aking their use prohibitive. This is an important driving force in the ques t for novel reaction media. Curzons and coworkers,(1) for example, recently noted that rigorous management of solvent use is likely to result in the g reatest improvement towards greener processes for the manufacture of pharma ceutical intermediates. The current emphasis on novel reaction media is als o motivated by the need for efficient methods for recycling homogeneous cat alysts. The key to waste minimisation in chemicals manufacture is the wides pread substitution of classical 'stoichiometric' syntheses by atom efficien t, catalytic alternatives.(2) In the context of homogeneous catalysis, effi cient recycling of the catalyst is a conditio sine qua non for economically and environmentally attractive processes. Motivated by one or both of the above issues much attention has been devoted to homogeneous catalysis in aq ueous biphasic(3,4) and fluorous biphasic(5) systems as well as in supercri tical carbon dioxide.(6) Similarly, the use of ionic liquids as novel react ion media may offer a convenient solution to both the solvent emission and the catalyst recycling problem.(7,8).