On the way to greener ionic liquids: identification of a fully mineralizable phenylalanine-based ionic liquid

Abstract

Over the past few decades ionic liquids (ILs) are increasingly seen as an important building block of green chemistry because of their specific properties as solvents, such as their potential for high recyclability, low volatility, low flammability, low toxicity, and their potential for synthesis from renewable resources. However, avoiding persistent or toxic cation/anion fragments is also urgently needed. In the best case they should be fully mineralizable by microorganisms after their release into the aquatic environment. The fragments fostering this can be determined by biodegradation studies, and the employment of identified readily biodegradable building blocks presents an innovation in the targeted design of green environmentally friendly ILs. The aim of this study was to improve the data-platform for the design of completely mineralizable ILs. Therefore the ready biodegradability of seven phenylalanine-based ILs and three nonionic related compounds was investigated with a modified Closed Bottle test based on OECD guideline 301D. Liquid chromatography combined with high-resolution mass spectrometry (LC-HRMS) analysis was used to identify the chemical structures of products resulting from incomplete biodegradation and transformation. Two kinds of degradation pathways were observed: the hydrolysis of an ethyl ester group or the hydrolysis of an amide bond and biodegradation of the released phenylalanine ethyl ester. Both degradation pathways resulted in persistent transformation products (TPs) with the exception of IL (4), a pyridinium substituted phenylalanine derived IL and the non-ionic deanol derivative (2a). IL (4) was ultimately biodegraded in the CBT after 42 days without leaving any TP. The biodegradation of compound (2a) was 78% after 42 days but resulted in a TP, which was readily biodegradable in a further CBT after a lag phase of 3 weeks, respectively. Even if both compounds were not "readily biodegradable" in the sense of the OECD guideline, particularly IL (4) can be proposed as a basic structure for sustainable and green ILs (benign by design) with the aim of optimizing its degradation rate further. † Electronic supplementary information (ESI) available. See

Synthesis of a series of amino acid derived ionic liquids and tertiary amines: green chemistry metrics including microbial toxicity and preliminary biodegradation data analysis

“…To answer these questions a detailed biodegradation assessment, including transformation product identification and analysis of the transformation products oxygen demand is required, and is published in the accompanying paper. 39 Based on the data presented in Table 9 we cannot state with absolute certainty that a general trend is biodegradation of all ester groups occurs for 4-24.…”

Environmental Impact of Ionic Liquids: Recent Advances in (Eco)toxicology and (Bio)degradability

“…ILs with other head groups have been synthesized in the last years, andtheir toxicity and biodegradability have been assessed in their early phase of developmentt od etermine their hazard potential before their indiscriminate use. For example, phenylalanine ethyl ester derived ILs of four different types (i.e.,p rolinium, choline,i midazolium, pyridinium) haveb een produced by Haiß et al [70] and their biodegradabilityh as been evaluated by the closed-bottle test, with only thesec ompounds reaching the 60 %b iodegradation level under the tested conditions (14-63%). Twod egradation pathways have been identified for the tested compounds;f or some com-pounds, only the ester group is hydrolyzed, which results in the formation of an amino acid, whereas the remaining compounds are cleaved at the amide bond.…”

Mandelic acid derived ionic liquids: synthesis, toxicity and biodegradability

“…Fig. 5 Percentage biodegradation results for fully mineralisable pyridinium IL (27) synthesised by Jordan et al 35 and Haib et al 37 Biodegradation values assessed by the CBT OECD 301D. can be rationalised as biodegradation of the ester/amide groups (side chain) of the ILs.…”

“…Our strategy regarding toxicity screening of chemicals as part of a tandem toxicity and biodegradation assessment has been previously published. [34][35][36][37] One reason a compound can fail a biodegradation test is due to high toxicity to critical microorganisms in the inoculum required for breakdown. For instance, previous studies have shown that high toxicity to bacteria, e.g.…”

“…34 The assumption was that the aromatic ring of the phenylalanine moiety was converted to CO 2 , although no transformation product analysis was performed in that study to conrm this breakdown. More recently Jordan et al 35 and Haib et al 37 have further shown that a fully mineralisable IL can be produced from an amino acid (phenylalanine) IL containing an aromatic side chain. Although, the introduction of a phenyl group in the form of phenylalanine did not lead to a signicant increase in biodegradation in all cases.…”