How green are ionic liquids? - A multicriteria decision analysis approach

Area of Science:

• Green Chemistry
• Environmental Science
• Chemical Safety

Background:

• Ionic liquids (ILs) possess desirable physicochemical properties, leading to their increasing popularity and consideration as green solvents.
• However, environmental, health, and safety (EHS) assessments have cast doubt on the actual benignness and greenness of ILs.
• The current greenness status of ILs remains unclear, necessitating a thorough evaluation.

Purpose of the Study:

• To conduct a comprehensive assessment of the greenness of over 300 commercially available ionic liquids.
• To clarify the ambiguous greenness status of ILs by applying a robust evaluation methodology.
• To establish a comparative ranking of ILs against well-characterized organic solvents.

Main Methods:

• Utilized multicriteria decision analysis (MCDA) to rank ionic liquids based on multiple criteria.
• Evaluated criteria including toxicity towards various organisms, biodegradability, hazard statements, and handling precautions.
• Incorporated organic solvents as reference points due to their established greenness profiles.

Main Results:

• When considering all criteria, ionic liquids were ranked between recommended polar solvents and problematic/undesirable non-polar organic solvents.
• Exclusion of toxicity data, due to unavailability of endpoints, resulted in an assessment of ILs as greener than most organic solvents.
• The comprehensive assessment highlights the variability in IL greenness depending on the specific compound and evaluation criteria.

Conclusions:

• The greenness of ionic liquids is not absolute and requires careful, criterion-based assessment.
• Toxicity data is crucial for an accurate EHS evaluation of ILs; its absence can lead to an overestimation of their greenness.
• ILs present a complex profile, necessitating a nuanced understanding beyond simple categorization as "green" solvents.