Richard P. Swatloski

Room temperature ionic liquids as novel media for ‘clean’ liquid–liquid extraction

The partitioning of simple, substituted-benzene derivatives between water and the room temperature ionic liquid, butylmethylimidazolium hexafluorophosphate, is based on the solutes’ charged state or relative hydrophobicity; room temperature ionic liquids thus may be suitable candidates for replacement of volatile organic solvents in liquid–liquid extraction processes.

Ionic liquids are not always green: hydrolysis of 1-butyl-3-methylimidazolium hexafluorophosphate

1-Butyl-3-methylimidazolium fluoride hydrate has been identified crystallographically as a decomposition product created during purification of the hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate. This highlights the need to treat ionic liquids much as one would any other research chemical with potentially hazardous properties, unknown toxicity and/or stability, particularly when searching for ‘green solvents’.

Can ionic liquids dissolve wood? Processing and analysis of lignocellulosic materials with 1-n-butyl-3-methylimidazolium chloride

The bulk of the cellulose currently employed by industry is isolated from wood through Kraft pulping, a process which traditionally involves a barrage of environmentally detrimental chemicals and is undeniably ‘non-green.’ In this report we present a simple and novel alternative approach for the processing of lignocellulosic materials that relies on their solubility in solvent systems based on the ionic liquid (IL) 1-n-butyl-3-methylimidazolium chloride ([C4mim]Cl). Dissolution profiles for woods of different hardness are presented, making emphasis on the direct analysis of the cellulosic material and lignin content in the resulting liquors by means of conventional 13C NMR techniques. We also show that cellulose can be readily reconstituted from the IL-based wood liquors in fair yields by the addition of a variety of precipitating solvents. Spectroscopic and thermogravimetric studies indicate that the polysaccharide obtained in this manner is virtually free of lignin and hemicellulose and has characteristics that are comparable to those of pure cellulose samples subjected to similar processing conditions.

The third evolution of ionic liquids: active pharmaceutical ingredients

A modular, ionic liquid (IL)-based strategy allows compartmentalized molecular level design of a wide range of new materials with tunable biological, as well as the well known physical and chemical, properties of ILs, which thus deserve consideration as ‘tunable’ active pharmaceutical ingredients (APIs) with novel performance enhancement and delivery options. IL strategies can take advantage of the dual nature (discrete ions) of ILs to realize enhancements which may include controlled solubility (e.g., both hydrophilic and hydrophobic ILs are possible), bioavailability or bioactivity, stability, elimination of polymorphism, new delivery options (e.g., slow release or the IL-API as ‘solvent’), or even customized pharmaceutical cocktails. Here we exemplify this approach with, among others, lidocaine docusate (LD), a hydrophobic room temperature IL which, when compared to lidocaine hydrochloride, exhibits modified solubility, increased thermal stability, and a significant enhancement in the efficacy of topical analgesia in two different models of mouse antinociception. Studies of the suppression of nerve growth factor mediated neuronal differentiation in rat pheochromocytoma (PC12) cells suggests potential differences between LD and lidocaine hydrochloride at the cellular level indicating an entirely different mechanism of action. Taken together these results suggest that the unique physiochemical properties of ILs in general, may confer a novel effect for the bioactivity of an API due to (at least) slow-release properties in addition to novel delivery mechanisms.

Mechanism of cellulose dissolution in the ionic liquid 1-n-butyl-3-methylimidazolium chloride: a 13C and 35/37Cl NMR relaxation study on model systems

13C and 35/37Cl NMR relaxation measurements on several model systems demonstrate that the solvation of cellulose by the ionic liquid (IL) 1-n-butyl-3-methylimidazolium chloride ([C4mim]Cl) involves hydrogen-bonding between the carbohydrate hydroxyl protons and the IL chloride ions in a 1 ratio 1 stoichiometry.

Task-specific ionic liquids for the extraction of metal ions from aqueous solutions

Imidazolium cations, such as those commonly used in preparing ionic liquids (ILs) can easily be derivatized to include task-specific functionality, such as metal ligating groups that when used as part of the solvent or doped into less expensive ILs, dramatically enhance the partitioning of targeted metal ions into the IL phase from water; the strategy of preparing task-specific ILs is applicable to a wide range of designer solvent needs.

LIQUID/LIQUID EXTRACTION OF METAL IONS IN ROOM TEMPERATURE IONIC LIQUIDS

The search for more environmentally-friendly reaction media has prompted the development of a wide array of alternative systems that will sustain biphasic separations with aqueous solutions without the use of volatile organic compounds (VOCs). We have begun to employ Room Temperature Ionic Liquids (RTIL), specifically 1-alkyl-3-methylimidazolium hexafluorophosphate ([Cnmim][PF6]), as VOC replacements in liquid/liquid separations of metal ions from aqueous solutions. Here we show that the partitioning of metal ions in these novel biphasic systems is consistent with traditional liquid/liquid separations: the metal ion affinity for the hydrophobic phase necessitates the presence of an extractant. In this report we explore the application of wellknown organic (1-(pyridylazo)-2-napthol, PAN, and (1-thiazolylazo)- 2-napthol, TAN) and inorganic (CN−, OCN−, SCN−, and halides) extractants for partitioning a variety of metal cations between [C4mim][PF6] or [C6mim][PF6] and an aqueous phase. PAN and TAN show pH dependent extraction of CD2+, Co+ Ni2+ and Fe3+ where their partitioning to the RTIL increases at least 2 orders of magnitude from pH 1 to 13. The effect of the halides on the partitioning of Hg2+ complexes increases F− < Cl− < Br− < I−. Pseudohalides, especially SCN−, had the greatest effect on enhancing the partitioning of Hg2+to the RTIL, whereas CN− and OCN− provided little benefit for the extraction of any of the metal ions examined.

Optimal and Direct-Current Vector Control of Direct-Driven PMSG Wind Turbines

With the advances of power electronic technology, direct-driven permanent magnet synchronous generators (PMSGs) have increasingly drawn the interest of wind turbine manufacturers. At the present time, a commercial PMSG wind turbine primarily makes use of a passive rectifier followed by an insulated gate bipolar transistor (IGBT) inverter. Although a PMSG wind turbine with two back-to-back voltage source IGBT converters is considered more efficient, it has not been widely adopted by the wind power industry. This paper investigates both the conventional and a novel vector control mechanism for a PMSG wind turbine that has two side-by-side voltage source pulsewidth modulation converters. The proposed approach is based on a direct-current vector control mechanism for control of both machine- and grid-side converters of a PMSG wind turbine. Then, an optimal control strategy is developed for integrated control of PMSG maximum power extraction, reactive power, and grid voltage support controls. A transient system simulation using SimPowerSystem is built to investigate the performance of the conventional and proposed control techniques for the PMSG wind turbine under steady and gusty wind conditions. This paper shows that when using the direct-current vector control structure, a PMSG system has excellent performance in various aspects.

High-resolution 13C NMR studies of cellulose and cellulose oligomers in ionic liquid solutions

High-resolution 13C NMR studies of cellulose and cellulose oligomers dissolved in the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) show that the beta-(1-->4)-linked glucose oligomers are disordered in this medium and have a conformational behavior which parallels the one observed in water, and thus, reveal that the polymer is disordered in IL solution as well.

Mercury(ii) partitioning from aqueous solutions with a new, hydrophobic ethylene-glycol functionalized bis-imidazolium ionic liquidThis work was presented at the Green Solvents for Catalysis Meeting held in Bruchsal, Germany, 13–16th October 2002.

A room temperature ionic liquid containing a bis-imidazolium cation incorporating a short ethylene-glycol spacer, 1,1′-[1,2-ethanediylbis(oxy-1,2-ethanediyl)] bis[3-methyl-1H-imidazolium-1-yl]bis(trifluoromethanesulfonyl)imide, has been prepared from the corresponding chloride salt, and the X-ray crystal structure of the low-melting hexafluorophosphate salt has been determined. The crystal structure reveals the ether linkage to be quite flexible and to participate in strong C2–H⋯O hydrogen bonds leading to asymmetry. The crystal structure of the bis-imidazolium salt incorporating a decyl-spacer, 1,1′-[1,10-decyl]bis[3-methyl-1H-imidazolium-1-yl] hexafluorophosphate, has also been determined and displays an all-trans (symmetric) conformation except at the beta carbon positions where a characteristic kink is observed. Introducing the ethylene-glycol functionality dramatically increases the distribution ratio of mercury ions, but not caesium, from aqueous solution to the hydrophobic ionic liquid, and from basic solution. This is the first example of pH dependent partitioning and stripping of mercury from ionic liquid/aqueous two-phase systems. The crystal structure of the related mercury(II) carbene complex, obtained from the reaction of mercury(II) acetate with 1,1′-[oxybis(2,1-ethanediyloxy-2,1-ethanediyl)]bis[3-methyl-1H-imidazolium-1-yl] tosylate, containing a three-ether spacer, in acetonitrile, reveals the possibility of a carbene extraction mechanism.