Aquatic Toxicology of Ionic Liquids (ILs)

Toward the Proactive Design of Sustainable Chemicals: Ionic Liquids as a Prime Example

“…In accordance with the structure–toxicity trends outlined above, its short alkyl chains and hydroxylation made the choline cation a promising candidate for ILs with low ecotoxicity, confirmed in numerous studies using model organisms representing several trophic levels. ,,, Nevertheless, even though choline Cl and choline PF 6 were found to be practically harmless toward A. fischeri , D. magna , L. minor , and D. rerio , their toxicity toward R. subcapitata was far from negligible, with EC 50 values of 72.5 mg/L for the chloride and 37.7 mg/L for the PF 6 – salt. , Furthermore, some well-established structure–toxicity relationships for other ILs do not hold true for choline ILs. For example, the introduction of additional polar hydroxyethyl groups into this cation head group surprisingly correlates with increased toxicity toward A. fischeri , which was interpreted as being an indication of a different toxic mode of action for those ILs . Low toxicity toward several bacteria and fungi was reported for IL cations based on amino acids .…”

“…A substantial trend in the design of less (eco)­toxic ILs is the use of bioderived precursors , such as choline, amino acids, carbohydrates, glycine betaine, lignin-derived aldehydes, and naturally occurring organic acids . Structural elements of ILs cations (head groups and side chains) and anions increasing and decreasing (eco)­toxicity are shown in Figure .…”

“…Since the toxicity of such bioderived cations is rather low, the impact of the anion on overall IL toxicity plays an important role in this case. , In particular, choline ILs with anions with long aliphatic side chains exhibit dramatically increased toxicities that easily exceed the toxicity of conventional organic solvents. ,, Therefore, the principle idea of exploiting natural precursors was extended to the anion component through the use of amino acids, , carbohydrates, , and other naturally occurring organic acids . Amino acid-based IL anions are a very promising approach; however, overall toxicity again depends strongly on the anion structure.…”

“…This was mainly due to the impact of the Tf 2 N − precursors methanesulfonyl fluoride and lithium nitride. 51 Due to the high environmental impact of IL synthesis from fossil fuels, interest in bioderived precursors, such as amino acids, 48,62,63 choline, 63 carbohydrates, 64 glycine betaine, 65 lignin-derived aldehydes (e.g. 5-hydroxymethylfurfural), 66,67 and naturally occurring organic acids, 68 has been growing.…”

“…Because of its pronounced hydrophobicity, stable ion pairing is assumed to be responsible for the effect, and reassociation of the Tf 2 N anion with IL cations within biomembranes was reported. 199 A substantial trend in the design of less (eco)toxic ILs is the use of bioderived precursors 69,71 such as choline, 63 amino acids, 63 carbohydrates, 64 glycine betaine, 65 lignin-derived aldehydes, 67 and naturally occurring organic acids. 68 Structural elements of ILs cations (head groups and side chains) and anions increasing and decreasing (eco)toxicity are shown in Figure 8.…”