Ionic Liquids Lose their Green Stripes

Despite being heralded as the green alternative to noxious, toxic, inflammable volatile organic compounds, room temperature ionic liquids are slowly losing their green stripes. In a paper published in the journal Green Chemistry (2006, 8, 238-240), Italian researchers report the acute toxicity of these compounds to zebra fish.

Luigi Intorre of the University of Pisa and colleagues, explain that although interest in ionic liquids because of claimed environmental safety is on the increase, these very good non-volatile solvents, could have harmful effects on certain ecosystems nevertheless.

The team has assessed the acute toxicity towards zebrafish of several ionic liquids with different anions and cations and found that toxic effects depended on the specific structure of the ionic liquid. However, the overall effect is potentially fatal harm to the fish’s gills.

This publication comes in the wake of earlier revelations that ionic liquids, although purportedly non-volatile, can indeed be distilled, according to a C&EN report.

Having said all that, ionic liquids still present a potentially “greener” alternative, if handled and disposed of safely, than many of the volatile organic solvents used in industry.

Research Blogging IconPretti, C., Chiappe, C., Pieraccini, D., Gregori, M., Abramo, F., Monni, G., & Intorre, L. (2006). Acute toxicity of ionic liquids to the zebrafish (Danio rerio) Green Chemistry, 8 (3) DOI: 10.1039/b511554j

3 thoughts on “Ionic Liquids Lose their Green Stripes”

  1. The Nature paper cited in the C&EN report on distillable ionic liquids has turned out to be rather popular topping citation index analysis in chemistry recently.

    ‘The distillation and volatility of ionic liquids’ was first published in the renowned science journal Nature in 2006 by scientists from QUILL (Queen’s University’s Ionic Liquids Laboratories) , who were awarded the Queen’s Anniversary Prize in February 2006.

    With a huge rise in scientific interest in room temperature ionic liquids – salts that are liquid below 100°C – in recent years, the ground-breaking paper blew apart a major myth.

    It illustrated that these liquids, previously regarded as involatile, are in fact volatile. The paper also demonstrated that the liquid salts can be vaporised with no decomposition and recovered and purified by fractional distillation.

  2. Indeed, there are always two sides to every story and I’ve certainly been impressed with the various efforts to find alternatives to volatile organic compounds (VOCs), viz supercritical fluids (SCFs) and room temperature ionic liquids (RTILs). One also has to consider the energy, environmental and economic costs of refitting a global industry to be able to handle these new solvents too. It isn’t after all simply a case of swapping out the toluene and using an RTIL instead.

    Additionally, the long-term impact of RTILs on the environment is not known, what if they turn out to be worse than VOCs for some as yet unknown reason. A comment on another post on the site also asked, what should we do with an RTIL once we’re finished using it for a particular reaction, bury it?

  3. While it is possible that ionic liquids are not as “green” as previously thought, another way of looking at it could be on a relative scale instead of on an absolute scale. On an absolute scale, perhaps yes, they are not absolutely “green”. But I’d imagine that they are still much more green that their volatile, toxic, organic counterparts?

    Another way of looking at this could be: what are the alternatives to ionic liquids? Are there better alternatives from whom the cost to ecology/environment is less than that for ionic liquids?

    Just some thoughts

    CO, Plant Oils A-Z

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