Green Solvents

Last week we discussed surfactants and other compounds that would better for the environment than VOCs, this got me thinking maybe we should look more closely at these alternative solvents. I found an article that discusses an ionic liquid (IL). Ionic liquids have been used in industry and are being studied to see their usefulness in science and synthesis. Ionic liquids are believed to be better solvents since they can be used in an exact amount and can also be used as catalysts. However this research group describes some negative aspects of ILs, since there is little to no data on their toxicity and/or stability.
The study used 1-butyl-3-methylimidazolium hexafluorophosphate as the IL and studied how it reacts. It was shown that it produces the [PF6] anion which has been shown t0 produce volatiles including HF in the presence of moisture. The article also discusses using ILs that do not produce [PF6] anions and using salt rather than an acid for metathesis may be a good idea, but then disposal of ILs has to be taken into consideration. When considering disposal for a "green" solvent it has to have functionalities and elements that can either go through biodegradation and/ or incineration
Overall the researchers state the use of GRAS (generally regarded as safe) or non-toxic ions used in pharmaceuticals should be used as guidelines to develop new ILs that are low in hazard to humans and the environment. And until this is possible ILs containing [PF6] anions, should be looked at as solvent that still has some negative effects to the environment and society.

http://www.rsc.org/ej/GC/2003/b304400a.pdf
Swatloski, R.P. ; Holbrey, J.D.; Rogers, R.D., Ionic liquids are not always green: hydrolysis of 1-butyl-3-methylimidazolium hexafluorophosphate, Green Chemistry, 2003, 5, 361-363.