Within the last 25 years ionic liquids have written a tremendous success story, which is documented in a nearly uncountable amount of original research papers, reviews, and numerous applications in research and industry. These days, ionic liquids can be considered as a mature class of compounds for many different applications. Frequently, they are used as neoteric solvents for chemical tansformations, and the number of reviews on this field of research is huge. In this focused review, though, we are trying to evaluate the state of the art of ionic liquid chemistry beyond using them simply as solvents for chemical transformations. It is not meant to be a comprehensive overview on the topic; the choice of emphasis and examples rather refects the authors’ personal view on the field. We are especially highlighting fields in which we believe the most fundamental developments within the next five years will take place: biomass processing, (chiral) ionic liquids from natural sources, biotransformations, and organic synthesis.
19F,1H HOESY experiments with three ionic liquids ([bmim]BF4, [bmim]PF6 and [emim]BF4) were run in two different solvents and neat. The results give preferred probabilities of presence and enable us to systematically study interactions between the cations and the anions in the ionic liquid phase by NMR spectroscopy. The influence of different solvents and of the presence or absence of air (i.e. oxygen) is discussed. This enabled us to substantially speed up the NMR experiments and to develop a more precise method for the investigation of liquid-phase structures in ionic liquids.
In recent years, ionic liquids have attracted the attention of many chemists as a result of their unique properties as solvents for chemical transformations. The focus of this Minireview is on applications of so-called “task-specific” ionic liquids, whereby the role of the ionic liquid goes beyond that of a solvent. Such ionic liquids find application in a wide range of areas, including catalysis, synthesis, gas absorption, and analysis.
Seit einigen Jahren haben ionische Flüssigkeiten (ionic liquids, ILs) wegen ihrer einzigartigen Eigenschaften als Lösungsmittel für chemische Transformationen die Aufmerksamkeit vieler Chemiker erregt. Dieser Kurzaufsatz konzentriert sich auf den Einsatz von so genannten “task-specific”, also anwendungsorientierten ionischen Flüssigkeiten, deren Rolle über die eines Lösungsmittels hinaus geht. Vielfältige Anwendungsmöglichkeiten finden sich z. B. in den Bereichen der Katalyse, der Synthese, der Gasabsorption oder der Analytik.
We are reporting the first synthesis of the new chiral Brønsted acid BINBAM [(R)-1,1′-binaphthyl-2,2′-bis(sulfon)amide, 2], which can be obtained in four steps from commercially available BINOL (5). The compound is expected to be an alternative for established catalysts like phosphoric acids of BINOL 4 or TRIP and to show stronger Brønsted acidity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Economic, transition-metal-free syntheses of partially or completely deuterated imidazolium ionic liquids (ILs) were developed. Double alkylation starting from imidazole afforded side-chain deuterated imidazolium ionic liquids, which subsequently were fully deuterated by H/D-exchange on the cation ring. Isotopic exchange was studied for a range of ionic liquids, solvents and bases. Here, the presence of small amounts of basic impurities was found to significantly affect the exchange behaviour.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Anhydrous neodymium(III) iodide and erbium(III) iodide were dissolved in carefully dried batches of the ionic liquid 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C12mim][Tf2N]. Provided that the ionic liquid had a low water content, intense near-infrared emission could be observed for both the neodymium(III) ion and for the erbium(III) ion. Luminescence lifetimes have been measured, and the quantum yield of the neodymium(III) sample has been measured. Exposure of the hygroscopic samples to atmospheric moisture conditions caused a rapid decrease of the luminescence intensities.
The enantioselective hydrogenation of trimethylindolenine (1) has been carried out in a variety of ionic liquids using an Ir-XYLIPHOS catalyst. Compared to the reaction in conventional organic media, slightly higher temperatures (50 °C) are required, which is mainly due to the higher viscosities of the ionic media. Under these conditions we were able to identify three reaction media that gave ees comparable to the conventional process in toluene with greatly reduced reaction time (15 h as opposed to 23 h for 100% conversion; 91% conversion after 8 h). The sensitivity of the reaction system towards oxygen was also reduced significantly.
