How green is “green”?
Ionic liquids are made of cations and anions
Oeiras, 29.11.10
Before a compound is determined safe, a number of tests are required. But what if that compound has over a million variants? ITQB researchers (labs of Molecular Thermodynamics and Applied and Environmental Mycology) and collaborators have analysed the literature available for environmental, health and safety impact of ionic liquids, traditionally considered as “green”. Based on this survey and their own work they have realised that generalizations are extremely misleading. They suggest that the impact of each ionic liquid ought to be analysed on its own. This critical review is published this week in Chemical Society Reviews – the leading impact-factor journal of the Royal Society of Chemistry.
Ionic liquids are best described as salts, most of them liquid at room temperature. Just as ordinary salt is exclusively made up of ions (sodium and chloride), ionic liquids are composed of cations and anions. The large number of possible ions, and thus the immense number of pair combinations, results in a family of compounds with different properties, labelled as ionic liquids. Their generic properties, such as being non-volatile, non-flammable, and having outstanding potential for dissolving almost anything are the basis for their classification as ‘‘green’’ solvents. Yet, true ‘‘greenness’’ should incorporate a sustainable synthesis, low toxicity, and limited environmental persistence and these have still to be comprehensively considered for the majority of ionic liquids.
Research on ionic liquids has enabled rapid advances in numerous applications, including some extant processes at an industrial scale, such as aluminium plating, cellulose dissolution, paint and lubricant additives, batteries and solar cells. Ionic liquids have also provided opportunities at the interface of chemistry with the life sciences, e.g. acting as solvents in enzymatic and whole-cell biocatalysis and as protein stabilisation agents. In addition, their potential use as active pharmaceutical ingredients, though still rather exploratory, further highlights their potential in biochemical studies. While ionic liquids conceptually fulfil the requirements of environmental sustainability, the authors highlight the need for more and more detailed studies.
In summary, ionic liquids must be classified on a one to one basis. “With well over one million simple ionic liquids, arguing from the specific to the generic is both misguided and intellectually dishonest” the authors argue.
Original Article
Chem. Soc. Rev., 2011, Advance Article
Ionic liquids: a pathway to environmental acceptability
Marija Petkovic, Kenneth R. Seddon, Luís Paulo N. Rebelo and Cristina Silva Pereira
