Annegret Stark

Progress in evaluation of risk potential of ionic liquids—basis for an eco-design of sustainable products

Motivated by the prevailing need for a sustainable development and taking the principles of Green Chemistry as a starting point, the present paper describes new and updated findings regarding a sustainable product design for ionic liquids. The focus is on environmental risk. Nevertheless, cytotoxicity testing and first indicative results from a genotoxicity study extend present knowledge also with regard to possible effects on humans. The structural variability of commercially available ionic liquids as well as the abundance of theoretically accessible ionic liquids is illustrated and the consequences for an integrated risk assessment accompanying the development process are discussed. The side chain effect on toxicity for imidazolium type ionic liquids was confounded by more complex biological testing. Also, an influence of an anion on cytotoxicity is shown for the first time. Testing of presumed metabolites of the imidazolium type cations showed a significantly lower biological activity in cytotoxicity studies than their parent compounds. The importance of a purity assessment for ionic liquids is pointed out and a collection of methods that is believed to be adequate is presented. In addition to risk analysis, the use of life cycle analysis for the multi-objective problem of designing ionic liquids is sketched and an eco-design scheme for ionic liquids is proposed. In conclusion, the paper illustrates the complex nature of the development processes ionic liquids are currently undergoing and provides guidance on which aspects have to be kept in mind.

Ionic liquids in the biorefinery: a critical assessment of their potential

The combination of the concept of an integrated biorefinery with ionic liquid technology is critically assessed, and potentials for further research and development are identified.

Purity specification methods for ionic liquids

In the last decade, ionic liquids have shown great promise in a plethora of applications. However, little attention has been paid to the characterisation of the purity of these fluids, which has ultimately led to non-reproducible data in the literature. In order to facilitate specification of ionic liquids, a number of analytical protocols with their limits of detection (where available) have been compiled, including methods of other authors. In particular, quantitative methods have been developed and summarised for the determination of the total ionic liquid content, residual unreacted ionic liquid starting material and by-products (amines, alkylating agents, inorganic halides), solvents from extraction procedures and water, in addition to decomposition products and total volatiles.

Energetic, environmental and economic balances : Spice up your ionic liquid research efficiency

The energy requirement, environmental impact and material costs of the synthesis of ionic liquids, and of their subsequent use as reaction media in the metathesis of 1-octene, are compared to conventional solvents. This preliminary study lays the foundation for an ecological and strategic experimental design. Energetic, environmental and economic assessments over all life-cycle stages allow for the identification of both, disadvantages and opportunities of individual process steps, at an early R&D level. Thus, this approach helps to find new and improved solutions, which comply with the concepts of “Green Chemistry”, that cannot be determined by experimental work alone. The potential of innovative methods can be quantitatively compared to current technologies by means of the energy efficiency factor EEF. Interestingly, this study demonstrates that under certain circumstances, a solvent-free reaction mode may not necessarily be ecologically advantageous. Also, the presumption that, due to facile recycling, a bi-phasic reaction mode is always superior to a homogeneous one is questioned: compared to the energy required for the manufacture of a solvent which results in a biphasic reaction mode (e.g. an ionic liquid), the energy needed for the separation of a homogeneous reaction mixture by distillation is comparatively small. Thus, efficient recycling of such a solvent must be guaranteed.

Significant Cation Effects in Carbon Dioxide–Ionic Liquid Systems

Carbon dioxide–ionic liquid systems are of great current interest, and significant efforts have been made lately to understand the intermolecular interactions in these systems. In general, all the experimental and theoretical studies have concluded so far that the main solute–solvent interaction takes effect through the anion, and the cation has no, or only a secondary role in solvation. In this theoretical approach it is shown that this view is unfounded, and evidence is provided that, similarly to the benzene–CO2 system, dispersion interactions are present between the solute and the cation. Therefore, this defines a novel site for tailoring solvents to tune CO2 solubility.

Making diazomethane accessible for R&D and industry: generation and direct conversion in a continuous micro-reactor set-up

Micro-reaction technology offers a safe way to deliver diazomethane on demand both on the R&D and the industrially relevant scale, including in situ conversion to the desired product to avoid handling and storage of explosive diazomethane solutions, thus making this potent compound accessible for the pharmaceutical and fine chemical sector.

Ionic Liquid Structure-Induced Effects on Organic Reactions

Understanding the ways in which the constituents of ionic liquids, i.e. the type of cation, its substitution, and the type of anion chosen, interact with reactants is prerequisite to deliberately designing an ionic liquid solvent with optimum performance. Several approaches, including physico-chemical and spectroscopic measurements and computational studies of binary ionic liquid-substrate mixtures have been presented that investigate the strength of interactions.The qualitative order of the basicity (hydrogen bond acceptor potential) of anions as most prominent force is already reasonably well understood, and reliably determined using, e.g. selective solvatochromic dyes. In certain reactions, the relative order of basicity correlates well with the reactivity of substrates. However, the determination of a relative order for the cations is still in its infancy. Owing to the fact that potential cation-derived interactions may not solely be due to hydrogen bond interactions, but also to ion pair interactions (electron pair donor/acceptor properties), the relative magnitudes of interactions between the anion and cation vary considerably - even in the absence of solutes - depending on the experimental method. In addition, it appears that the basicity of the anion superimposes in many instances on the effects exhibited by the cation and/or the cations substituent. Hence, understanding the effect of the cation on the activation of substrates is still a challenge.This chapter aims at summarising the trends observed for binary model systems in experimental and computational investigations, and drawing conclusions about ionic liquid structure-induced effects relevant to organic reactions, in particular nucleophilic substitution reactions.

On the nature of interactions between ionic liquids and small amino-acid-based biomolecules.

During the last decade, ionic liquids (ILs) have revealed promising properties and applications in many research fields, including biotechnology and biological sciences. The focus of this contribution is to give a critical review of the phenomena observed and current knowledge of the interactions occurring on a molecular basis. As opposed to the huge advances made in understanding the properties of proteins in ILs, complementary investigations dealing with interactions between ILs and peptides or oligopeptides are underrepresented and are mostly only of phenomenological nature. However, the field has received more attention in the last few years. This Review features a meta-analysis of the available data and findings and should, therefore, provide a basis for a scientifically profound understanding of the nature and mechanisms of interactions between ILs and structured or nonstructured peptides. Fundamental aspects of the interactions between different peptides/oligopeptides and ILs are complemented by sections on the experimental (spectroscopy, structural biology) and theoretical (computational chemistry) possibilities to explain the phenomena reported so far in the literature. In effect, this should lead to the development of novel applications and support the understanding of IL-solute interactions in general.

Ionic Liquid Applications in Peptide Chemistry: Synthesis, Purification and Analytical Characterization Processes

This review aims to provide a comprehensive overview of the recent advances made in the field of ionic liquids in peptide chemistry and peptide analytics.

Triphilic Ionic-Liquid Mixtures: Fluorinated and Non-fluorinated Aprotic Ionic-Liquid Mixtures

We present here the possibility of forming triphilic mixtures from alkyl- and fluoroalkylimidazolium ionic liquids, thus, macroscopically homogeneous mixtures for which instead of the often observed two domains—polar and nonpolar—three stable microphases are present: polar, lipophilic, and fluorous ones. The fluorinated side chains of the cations indeed self-associate and form domains that are segregated from those of the polar and alkyl domains. To enable miscibility, despite the generally preferred macroscopic separation between fluorous and alkyl moieties, the importance of strong hydrogen bonding is shown. As the long-range structure in the alkyl and fluoroalkyl domains is dependent on the composition of the liquid, we propose that the heterogeneous, triphilic structure can be easily tuned by the molar ratio of the components. We believe that further development may allow the design of switchable, smart liquids that change their properties in a predictable way according to their composition or even their environment.