Jennifer Neumann

Biodegradability of 27 pyrrolidinium, morpholinium, piperidinium, imidazolium and pyridinium ionic liquid cations under aerobic conditions

The chemical and thermal stability of ionic liquids (ILs) makes them interesting for a large variety of applications in nearly all areas of the chemical industry. However, this stability is often reflected in their recalcitrance towards biodegradation, which comes with the risk of persistence when they are released into the environment. In this study we carried out a systematic investigation of the biodegradability of pyrrolidinium, morpholinium, piperidinium, imidazolium and pyridinium-based IL cations substituted with different alkyl or functionalised side chains and using halide counterions. We examined their primary degradability by specific analysis and/or their ultimate biodegradability using biochemical oxygen demand tests according to OECD guideline 301F. Biological transformation products were investigated using mass spectrometry. A comparison of the biodegradation potential of these ILs shows that for all five head groups, representatives can be found that are readily or inherently biodegradable, thus permitting the structural design of ILs with a reduced environmental hazard.

Anaerobic biodegradability of ionic liquid cations under denitrifying conditions

Biodegradability and ecotoxicity of ionic liquids (ILs) are key properties for determining the greenness of IL applications, and have been increasingly investigated during the last few years. Former studies on the biodegradability of ILs were solely focused on the aerobic side. Nevertheless, the anaerobic biodegradation of many compounds plays an important role in the environment. Anaerobic respiration, especially nitrogen reduction, is widespread in the environment and is commonly used for waste water treatment. Therefore, we investigated in this study, whether ILs can be biodegraded under nitrogen reducing conditions. The primary anaerobic biodegradability of nine different imidazolium, pyridinium and dimethylaminopyridinium based IL cations was monitored via HPLC-UV over a time period of 11 months. Only for the 1-(8-hydroxyoctyl)-3-methyl-imidazolium cation (IM18OH), and a degradation could be observed and several metabolites were identified using LC-MS. Co-metabolism is sometimes the only way to degrade difficult substances. However, a possible co-metabolism of the substances by using acetate was not observed. All in all, the biodegradability of the tested ILs seems to be even worse under denitrifying conditions compared to aerobic ones. Nevertheless, the present paper aims to fill the gap concerning the biodegradability of ILs in waste water treatment plants. It gives a first insight into the biological degradation of ILs in the absence of oxygen, and provides further data for an appropriate hazard assessment.

Hydrolysis study of fluoroorganic and cyano-based ionic liquid anions – consequences for operational safety and environmental stability

The hydrolytic stability of ionic liquid anions is a key property with regard to their technical applicability and environmental stability. From a technical point of view hydrolytic processes may lead to reduced durability, diminished technical performance and reduced operational safety in that corrosive and/or toxic hydrolysis products are formed. On the other hand, susceptibility to hydrolytic processes is advantageous where environmental stability and persistency are concerned, since hydrolysis is the most important abiotic degradation pathway in the environment. We investigated the hydrolytic stability of the most common ionic liquid anions, dicyanimide [N(CN)2]−, tricyanmethanide [C(CN)3]−, tetracyanidoboranate [B(CN)4]−, bis(trifluoromethylsulphonyl)imide [(CF3SO2)2N]−, trifluorotris(pentafluoroethyl)phosphate [(C2F5)3PF3]− and 1,1,2,2-tetrafluoroethanesulphonic acid [H(C2F4)SO3]−, as a function of pH (1, 7, 9 and 13) and temperature. The results show that there was no difference in hydrolytic stability as recorded for 1-ethyl-3-methylimidazolium (IM12) or for the alkali cations. All the anions were stable under neutral and slightly basic conditions (half-lives at 25 °C ⇒1 year). In strongly acidic and basic solutions, however, B(CN)4−, (CF3SO2)2N−, (C2F5)3PF3− and H(C2F4)SO3− were hydrolytically stable, whereas N(CN)2− and C(CN)3− were not. The kinetics of hydrolysis were recorded and Arrhenius plots were generated for the latter two anions. In addition, their hydrolysis pathways and the resulting products were identified via mass spectrometry. The cytotoxicity of hydrolysed IL solutions towards the mammalian cell line IPC-81 and the identified hydrolysis products (pure compounds) was investigated for a first estimate of their toxicological properties.

Ionic Liquids: Methods of Degradation and Recovery

In recent years ionic liquids (ILs) have attracted considerable attention owing to their potential use in a diversified range of applications. It is believed that ILs can successfully replace volatile organic media in a wide range of chemical processes. They have been studied and applied in organometallic catalysis, organocatalysis and biocatalysis, where they provide unique reaction media offering better selectivity, faster rates and greater catalyst or enzyme stability in comparison to conventional solvents (Buszewski & Studzinska, 2008; Dupont et al., 2002; Liu et al., 2010; Mathews et al., 2000; Minami, 2009; Welton, 1999). The applications of ILs also include areas such as electrochemical transformation, fuel cells, solar cells, sensors and nanochemistry. They are emerging as lubricants, modifiers of mobile and stationary phases in the separation sciences, and are candidates for the dissolution of cellulose, starch and wood (Wassersheid & Welton, 2003). ILs are characterized by properties such as negligible vapour pressure and non-flammability under ambient conditions, high thermal conductivity, a wide electrochemical window and high polarity. They also have the ability to dissolve a wide diversity of materials, including salts, fats, proteins, amino acids, surfactants, sugars, polysaccharides and organic solvents. However, the most important attribute of ILs is the possibility of designing their properties to order. Thanks to the enormous number of cation and anion combinations, ILs can possess a wide spectrum of physical and chemical properties (solubility, polarity, viscosity or solvent miscibility), and they are already recognized by the chemical industry as new, target-oriented reaction media. The properties of ILs can be used for developing new processes that are technologically, environmentally and economically advantageous. Listed benefits include the possibilities of reusing and relatively easily recovering ILs, which effectively reduces the amount of waste generated during technological operations. It is, however, important to remember that ILs are still quite expensive media, and their recycling after regeneration or recovery makes such a technology economically all the more justified. Among available technologies, conventional processes such as distillation, membrane separation and extraction can be

Biodegradability of fluoroorganic and cyano-based ionic liquid anions under aerobic and anaerobic conditions

The present study deals with the primary biodegradability of ionic liquids in order to obtain a greater insight into their fate under different environmental conditions. The focus was thereby on the biodegradation potential of ionic liquid anions when undergoing aerobic and anaerobic biological waste water treatment. Five technologically relevant fluoroorganic and cyano-based ionic liquid anions were investigated as alkaline salts (Li (CF3SO2)2N, K (C2F5)3PF3 and Na N(CN)2, K C(CN)3, K B(CN)4 respectively). Their biodegradability was determined in activated sludge over a period of around 60 days by specific analysis of the anion using ion chromatography. Additionally, the antimicrobial activity of the test compounds towards the activated sludge organisms was tested in inhibition studies. Because of the technologically desirable chemical, thermal and electrochemical stability of these anions, their biodegradability is questioned. The results seem to support the hypothesis: although the concentrations used did not inhibit the inoculum, none of these anions could be biodegraded under either aerobic or denitrifying conditions. The present paper provides information concerning the biodegradability of ionic liquids in waste water treatment plants and gives a first systematic view of the aerobic and anaerobic biodegradability of fluoroorganic and cyano-based ionic liquid anions and therefore supports further hazard assessment.

Ion chromatographic determination of structurally varied ionic liquid cations and anions—a reliable analytical methodology applicable to technical and natural matrices

An ion chromatographic system with conductometric detection was used to analyse a broad structural variety of ionic liquid (IL) cations and anions. The selection of cationic entities covered the chemical space of IL cations as comprehensively as possible and contained the most common head groups substituted with different alkyl- and functionalized side chains. Also investigated was a set of commonly used IL anions showing a relatively wide polarity range, from comparatively hydrophilic species (e.g.dicyanimide and tetrafluoroethanesulfonic acid) to moderately hydrophobic entities (e.g.(CF3SO2)2N− or B(CN)4−) and to the strongly hydrophobic trifluorotris(pentafluoroethyl)phosphate anion (((C2F5)3PF3)−). The separation of these IL constituents from inorganic matrix-forming ions (Li+, Na+, K+, Mg2+, Ca2+ or F−, Cl−, Br−, SO42−, HPO42−) was achieved for all 30 tested IL structures, depending on the eluent used. Activated sludge samples from biodegradation experiments were chosen for a case study in order to illustrate the performance and the usefulness of the methods developed. The separation and quantification of traces of IL ions in the presence of large numbers of inorganic ions and high organic matrix loads were demonstrated. In general, the analytical system and its associated methods appear to be widely applicable to a broad range of IL structures as well as different technical and natural matrices.

Interaction of dodecaborate cluster compounds on hydrophilic column materials in water.

The interaction of a series of dodecaborate cluster compounds B(12)X(12)(2-) and B(12)X(11)Y(2-) (X=H, Cl, Br, I and Y=SH, OH, NR(3)) with hydrophilic column materials (Superdex 200, Sepharose 4B, Sephadex G-50, Sephadex G-100, alumina, silica gel and anion exchange material) was studied. Almost all the dodecaborate cluster compounds were retained strongly on Superdex 200. The halogenated cluster compounds interacted with Sepharose 4B, Sephadex G-50, Sephadex G-100 and alumina; on alumina, also the non-halogenated clusters were retained. Silica gel showed the least interaction with all compounds. The thermodynamic parameters were investigated for a selection of compounds on Superdex 200 and Sephadex G-100. Values for ΔH° were found to be negative on both gels. As the change in entropy ΔS° was also negative, it compensated ΔH° to a large extent. The clusters interacted also strongly with anion exchange material in ion chromatography; the interaction decreased with increasing acetonitrile concentration, implying a large contribution from solvent effects.

Biodegradation potential of cyano-based ionic liquid anions in a culture of Cupriavidus spp. and their in vitro enzymatic hydrolysis by nitrile hydratase.

Biodegradation tests with bacteria from activated sludge revealed the probable persistence of cyano-based ionic liquid anions when these leave waste water treatment plants. A possible biological treatment using bacteria capable of biodegrading similar compounds, namely cyanide and cyano-complexes, was therefore examined. With these bacteria from the genera Cupriavidus, the ionic liquid anions B(CN)4−, C(CN)3−, N(CN)2− combined with alkaline cations were tested in different growth media using ion chromatography for the examination of their primary biodegradability. However, no enhanced biodegradability of the tested cyano-based ionic liquids was observed. Therefore, an in vitro enzymatic hydrolysis test was additionally run showing that all tested ionic liquid (IL) anions can be hydrolysed to their corresponding amides by nitrile hydratase, but not by nitrilase under the experimental conditions. The biological stability of the cyano-based anions is an advantage in technological application, but the occurrence of enzymes that are able to hydrolyse the parent compound gives a new perspective on future cyano-based IL anion treatment.