The increasing amount of papers published on ionic liquids generates an extensive quantity of data. The thermal stability data of divergent ionic liquids are collected in this paper with attention to the experimental set-up. The influence and importance of the latter parameters are broadly addressed. Both ramped temperature and isothermal thermogravimetric analysis are discussed, along with state-of-the-art methods, such as TGA-MS and pyrolysis-GC. The strengths and weaknesses of the different methodologies known to date demonstrate that analysis methods should be in line with the application. The combination of data from advanced analysis methods allows us to obtain in-depth information on the degradation processes. Aided with computational methods, the kinetics and thermodynamics of thermal degradation are revealed piece by piece. The better understanding of the behaviour of ionic liquids at high temperature allows selective and application driven design, as well as mathematical prediction for engineering purposes.

The stability of ionic liquids is of paramount importance in selecting the appropriate ionic liquid for a well‐defined application. This Review provides an overview of stability issues, both chemical and electrochemical, and the underlying degradation mechanisms that are known. The influence of various functionalities on the stability of the ionic liquid, influencing both the cationic as the anionic parts of the ionic liquid, still requires several careful studies.

Biological properties of ionic liquids (ILs) have been usually tested with the help of standard biodegradation or ecotoxicity tests. So far, several articles on the identification of intermediate metabolites of microbiological decay of ILs have been published. Simultaneously, the number of novel ILs with unrecognized characteristics regarding biodegradability and effect on organisms and environment is still increasing. In this work, seven imidazolium ionic liquids of different chemical structure were studied. Three of them are 1-alkyl-3-methyl-imidazolium bromides, while the other four are tetra- or completely substituted imidazolium iodides. This study focused on the identification of intermediate metabolites of the aforementioned ionic liquids subjected to biodegradation in a laboratory activated sludge system. Both fully substituted ionic liquids and 1-ethyl-3-methyl-imidazolium bromide were barely biodegradable. In the case of two of them, no biotransformation products were detected. The elongation of the alkyl side chain made the IL more susceptible for microbiological decomposition. 1-Decyl-3-methyl-imidazolium bromide was biotransformed most easily. Its primary biodegradation up to 100 % could be achieved. Nevertheless, the cleavage of the imidazolium ring has not been observed.Electronic supplementary materialThe online version of this article (doi:10.1007/s10532-015-9747-0) contains supplementary material, which is available to authorized users.

BACKGROUND Ionic liquids are regarded as potential substitutes for volatile organic solvents. Thus, gaining knowledge about their biological properties is an important task. The main aim of this work was to estimate the biodegradability of newly synthesized tetra‐ and completely substituted imidazolium ionic liquids. Additionally, the kinetic parameters for the biological treatment of wastewater containing one of these ionic liquids were determined. RESULTS The results of OECD tests showed that none of the ionic liquids studied can be classified as readily or inherently biodegradable. The tetra‐substituted ionic liquid with the longest alkyl side chain consisting of six carbon atoms was more susceptible to biodegradation than the other ionic liquids tested. The values of Monod kinetic parameters estimated for the biological treatment of wastewater containing one of these ionic liquids were usually in the range of the values determined for municipal wastewater. CONCLUSION Newly synthesized tetra‐ and completely substituted imidazolium ionic liquids are not susceptible to microbial decomposition. At the same time their presence in wastewater neither reduces the growth rate of activated sludge biomass nor decreases the affinity of substrate to biomass. © 2013 Society of Chemical Industry

A versatile and efficient method to synthesize tetrasubstituted imidazoles via a one-pot modified Debus-Radziszewski reaction and their subsequent transformation into the corresponding imidazolium ionic liquids is reported. The tetrasubstituted imidazoles were also synthesized by means of a continuous flow process. This straightforward synthetic procedure allows for a fast and selective synthesis of tetrasubstituted imidazoles on a large scale. The completely substituted imidazolium dicyanamide and bis(trifluoromethylsulfonyl)imide salts were obtained via a metathesis reaction of the imidazolium iodide salts. The melting points and viscosities are of the same order of magnitude as for their non-substituted analogues. In addition to the superior chemical stability of these novel ionic liquids, which allows them to be applied in strong alkaline media, the improved thermal and electrochemical stabilities of these compounds compared with conventional imidazolium ionic liquids is also demonstrated by thermogravimetrical analysis (TGA) and cyclic voltammetry (CV). Although increased substitution of the ionic liquids does not further increase thermal stability, a definite increase in cathodic stability is observable.