Current Organic Chemistry - Volume 15, Issue 12, 2011

Ionic liquids (ILs) are low melting point salts considered to be a new class of alternative solvents that represent ideal non-volatile media for a variety of industrial processes such as organic synthesis and biocatalysis, alternative electrolytes, phases and phase modifications in separation techniques, and alternative lubricants. Today's definition of ILs is based solely on their melting point, which is arbitrarily chosen to be below 100oC. ILs already in common use typically involve nitrogen- or phosphorus-containing organic cations such as alkylimidazolium, alkylpyridinium, alkylpyrrolidinium or alkylphosphonium, and anions like bis(trifluoromethanesulfonyl)imide, hexafluorophosphate and alkylsulfate. Although these cations and anions and their various combinations have already been studied extensively for their potential applications in numerous chemical and physical processes, every year more and more cations and anions forming liquid salts at room temperature are reported. One of the most attractive characteristics of ILs (apart from their negligible vapor pressure) is their potential to be “designed to order”. Properties such as density, moisture stability, viscosity or miscibility with other chemicals can be tailored by the appropriate selection of cation and anion; a very rough estimate indicates that such combinations can be numbered in the millions. It is therefore possible that we are dealing with a momentous breakthrough in modern chemistry and technology. This almost limitless potential to make new ionic liquids tailored to novel or existing applications is an exciting, visionary prospect. On the other hand, we have to be aware that in this field we will soon be facing a huge number of new chemicals, about which we actually know very little. In particular, data relating to hazard assessment are usually incomplete or even non-existent, because these chemicals are not yet being produced on an industrial scale. Once the large-scale implementation of ILs begins, however, it will not be long before they become permanent constituents of industrial effluents. In view of their great stability, they could slip through classical treatment systems to become persistent components of the environment, where the long-term consequences of their presence are still unknown. An understanding of their physicochemical parameters, toxicity and ecotoxicity, mobility and distribution in soils and sediments is therefore crucial for an accurate prediction of their fate in the environment.....

Room-temperature ionic liquids (RTILs) salts with melting points below 100 °C have been intensively studied in recent years. Their unique properties make RTILs efficient alternatives to volatile organic solvents as environmentally benign media in many industrially important chemical processes. ILs will soon be produced on an industrial scale and it will be necessary to develop reliable analytical procedures for their analysis and control. Nowadays, reversed-phase liquid chromatography (RPLC) is widely used for separations of various imidazolium cations on alkyl-bonded stationary phases, phenyl-bonded stationary phases or on silica packing functionalized with mixed polar and apolar functions. Ion chromatography (IC), ion-pair chromatography, capillary electrophoresis and isotachophoresis are also being developed. The primary aim of this review is to outline current developments in chromatographic and electrophoretic methods applied to the analysis of routinely used ionic liquid cations and anions.

In this review an overview on the biological effects of ILs towards microorganisms is presented. Microorganisms are ideal indicators for investigating ILs' toxic effects towards organisms because of their large environmental, ecological and industrial relevance, and their short generation times and quick growth, useful for developing fast and easy toxicity assays. Herein the achievements in the development of ILs as biocides are described by taking into account the antimicrobic activity towards pathogenic microbes; the evaluation of ILs' environmental risk is dealt with the main results obtained by using model eukaryotic and prokaryotic microorganisms; and the current status on the use of ILs as biocompatible solvents for bioprocesses is outlined.

This review aims at summarizing the state of the art knowledge on the effects different ionic liquids and their substructural elements cationic head group, side chain attached to the head group and the anion species can exert in mammalian cell cultures. Special emphasis is given on the following questions when analyzing the available data: (i) What are ionic liquids, which species are we dealing with and which features make them unique from a technological but - even more important - from a toxicological point of view? (ii) which and how much information do we need aiming at a sound hazard and risk assessment of ionic liquids and at a sustainable design of these substances? (iii) what can we learn from the existing cytotoxicity studies with respect to the latter question and what we cannot? and finally (iv) what needs to be done in the field of ionic liquids' toxicology? Analyzing the existing cytotoxicity data guiding principles for a sustainable design of inherently safer ionic liquids are derived and the advantages and limitations of mammalian cell lines in deriving them are presented. Furthermore, modes of toxic action as well as mixture effects and the prediction of these effects using quantitative structure-activity relationships (QSAR) approaches are discussed. Finally, the future needs in ionic liquids' toxicology are discussed with respect to regulatory frameworks and the general hazard assessment of these substances.

Aquatic environments are being contaminated with a myriad of anthropogenic chemicals, a problem likely to continue due to both unintentional and intentional releases. To protect valuable natural resources, novel chemicals should be shown to be environmentally safe prior to use and potential release into the environment. Such proactive assessment is currently being applied to room-temperature ionic liquids (ILs). Because most ILs are water-soluble, their effects are likely to manifest in aquatic ecosystems. Information on the impacts of ILs on numerous aquatic organisms, focused primarily on acute LC50 and EC50 endpoints, is now available, and trends in toxicity are emerging. Cation structure tends to influence IL toxicity more so than anion structure, and within a cation class, the length of alkyl chain substituents is positively correlated with toxicity. While the effects of ILs on several aquatic organisms have been studied, the challenge for aquatic toxicology is now to predict the effects of ILs in complex natural environments that often include diverse mixtures of organisms, abiotic conditions, and additional stressors. To make robust predictions about ILs will require coupling of ecologically realistic laboratory and field experiments with standard toxicity bioassays and models. Such assessments would likely discourage the development of especially toxic ILs while shifting focus to those that are more environmentally benign. Understanding the broader ecological effects of emerging chemicals, incorporating that information into predictive models, and conveying the conclusions to those who develop, regulate, and use those chemicals, should help avoid future environmental degradation.

The fate of ionic liquids in soils and sediments is significant for the sustainable application of ILs in industry. We are obliged to understand how these compounds are transformed in (bio-) chemical processes and how long they will persist in the environment. In addition, we must understand how ionic liquids interact in complex systems. This review analyzes and summarizes the results obtained to date by a significant number of research groups on solution and surface interactions of ionic liquids. Due to the structural similarity of ionic liquids with surfactants, it is possible to determine the interaction mechanism of the ionic liquids, with soils and sediments. It was found that highly lipophilic ILs possessing long alkyl substituents or large organic anions are expected to interact with soils/sediments organic matter thus being rather immobile. Conversely, the weak lipophilic ILs probably be the most mobile in the soil and water, due to their high water solubility as well as their lower affinity to organic matter. For this reason they are thought to present the greatest threat for ground water contamination.

The idea of green or sustainable chemistry is to develop highly efficient technical processes and applications using chemicals with a reduced or zero hazard potential for man and the environment. This approach is perfectly applicable to ionic liquids (ILs). These substances have potential applications in different fields (economic interests), and so far millions of possible structures have been designed, thousands of which have actually been produced, providing a broad base for the structural design of ILs with optimal technological properties and at the same time posing a reduced hazard to humans and the environment. In parallel with the rapidly growing (eco)toxicological knowledge regarding ILs, the available data regarding their biodegradability are also increasing. The following sections introduce the reader to biodegradation test procedures and present an overview of existing aerobic and anaerobic biodegradation data concerning ILs. Besides pure biodegradation kinetics, this discussion covers data on biological degradation products (metabolites) and abiotic degradation processes. Throughout this review special emphasis will be placed on structure-biodegradability relationships and the question whether the 10th principle of Green Chemistry, namely, Design chemicals and products to degrade after use: design chemical products to break down to innocuous substances after use so that they do not accumulate in the environment, is or is not fulfilled for some IL structures. The discussion of this data should help to improve the future design of inherently safer ILs, thereby reducing the risks they may pose to humans and the environment.

Ionic liquids have a large variety of applications in nearly all areas of the chemical industries. They are used for example as lubricants, plasticizers, solvents and catalysts for synthesis, matrices for mass spectroscopy, solvents for extraction and in the manufacture of nano-materials, and as electrolytes. There are numerous studies in the corresponding literature concerning the unique properties, preparation methods, and different applications of ionic liquids. Nowadays, researchers try to answer questions concerning the stability of ionic liquids within practical applications. In this review, a general description of the stability and - degradation products of ionic liquids formed under different physicochemical conditions such as high temperature, irradiation, varying electrical current density, oxidizing agents are discussed. The main focus of this paper is on how the structure of ionic liquid cations and anions as well as impurities (e.g. water) influence the stability of ionic liquids in application and in utilization conditions. Additionally, it is also very important to consider the stability of ionic liquids with respect to environmental issues and for the hazard assessment of those compounds. These aspects, as well the possibility to use strongly oxidizing conditions (advanced oxidation processes) to remove ionic liquid structures from wastewaters are discussed within this review.

Much attention has been paid to ionic liquids related environmental aspects, like toxicity, (eco)toxicity and biodegradability. However, the main efforts are still concentrated on the synthesis of new ionic liquids, the measurement of their properties and the quest for new application fields, while the technical aspects regarding the extent of the ionic liquid lifetime have been neglected. Nevertheless, some experiences have already been reported in the study areas of regeneration, recovery and removal of ionic liquids, for both commercial and potential applications; and in this review it is intended to present them in a useful way. Based on the waste hierarchy, contained in European and other countries regulations, and classifying the experiences according to the separation mechanism used, it was possible to cover the whole spectrum of alternatives known up to now. Last but not least, strategic approaches for the regeneration and recovery of ionic liquids were developed and presented, as a contribution to produce authentic “green” ionic liquids. Insofar, an encouraging pathway is waiting to be explored, and it will be possible to take advantage of a variety of opportunities for further research and development in the areas covered by this review.

This review presents a comprehensive account of methods which are commonly applied for the synthesis of α- aminophosphonic acids. In the following order, protocols based on the methodologies listed below are discussed: a) simultaneous formation of P-CN systems; b) nucleophilic substitution with phosphoroorganic nucleophiles; c) additions of the P-H functions to multiple C-N bonds; d) α-amination of phosphonates and functionalized alkylphosphonates; e) modifications of the side chain of aminoalkylphosphonates; f) modifications of phosphorus functions and h) modifications of functions containing nitrogen.

Aromatic interactions are essential for stabilizing the conformation and crystal packing of molecules. They also play a vital role in drug chemistry by mediating drug-receptor interactions. In the present review, we discuss the various fields in which aromatic interactions are important and the role of such interactions.