Towards greener and sustainable ionic liquids using naturally occurring and nature-inspired pyridinium structures

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The present study investigated the ready biodegradability of naturally occurring and nature-inspired pyridinium cations for the design of greener or sustainable ionic liquids (ILs). Our results showed that trigonelline ([C1COOHPy][Cl]) and 1-methylnicotinamide ([C1CONH2Py][I]) were completely mineralizable and non-toxic under the conditions of the Closed Bottle Test (CBT), while [C1CONH2Py][I] was readily biodegradable. In contrast, the nicotinium structures, 1-methylnicotinium and 1,1′-dimethylnicotinium, were biologically persistent but non-toxic to the inoculum, whereas S-nicotine itself was identified as readily biodegradable. The biodegradability of these pyridinium structures was compared with that of the commercial pyridinium ILs [C1Py][PF6] and [C2Py][Br] having short alkyl residues. While [C2Py][Br] demonstrated only partial but not ultimate biodegradation, [C1Py][PF6] was shown to be readily biodegradable in the CBT. HRMS confirmed the biodegradation results. The results also showed the negative influence of short alkyl residues on biodegradability. Based on the results, new highly biodegradable and non-toxic pyridinium ILs can be designed to limit the accumulation of persistent ILs in the aquatic environment. Moreover, since some of our pyridinium structures and all their pyridine precursors can be isolated either from renewable sources or waste materials, ILs based on [C1COOHPy][Cl], [C1CONH2Py][I] and [C1Py][PF6] as cationic scaffolds can also be referred to as sustainable ILs if the anion fulfills the criteria too. Besides their physicochemical and environmental properties, the use of such methylated pyridinium blocks offers the opportunity for biotechnological synthesis using S-adenosyl methionine as the methyl donor catalyzed by N-methyltransferases and therefore the avoidance of commonly used carcinogenic methylating agents such as iodomethane or dimethyl sulfate. Thus, the synthesis of these ILs can be improved towards sustainability and the principles of Green Chemistry (e.g., 3rd less hazardous chemical synthesis, 9th catalysis, and 12th inherently safer chemistry for accident prevention) and an inherently safer pathway to ILs can be created.

Original languageEnglish
Article number25
JournalGreen Chemistry
Issue number1
Pages (from-to)365-374
Number of pages10
Publication statusPublished - 07.01.2023

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