Special Issue "Ionic Liquids"

Abstract: The behavior of 1-butyl-3-methylimidazolium chloride has been investigated byRaman spectroscopy as a function of hydrostatic pressure. Under ambient pressure tworotational isomers (GA and AA forms) of the 1-butyl-3-methylimidazolium cation coexist inthe ionic liquid state. As the supercooled liquid was compressed from ambient to 0.9 GPa,the contribution of the GA conformer decreases in intensity as the pressure was elevated. Anew high pressure phase is formed above the pressure of 1.5 GPa. This new high pressurephase of 1-butyl-3-methylimidazolium chloride arises from perturbed GA conformer, i.e.,distorted Crystal 2. Crystal 1 form (AA form) is known as a thermodynamically stable formunder ambient pressure. Nevertheless, crystal 1 form is switched to a metastable state underthe condition of high pressure.

Abstract: Several ionic liquids were applied as catalysts for the synthesis of cyclicurethanes from amino alcohols and pressurized CO2 in the presence of alkali metalcompounds as promoters. A comparative study was made for the catalytic performanceusing different ionic liquids, substrates, promoters, and pressures. The optimum catalyticsystem was BMIM-Br promoted by K₂CO₃, which, for 1-amino-2-propanol, produced cyclicurethane in 40% yield with a smaller yield of substituted cyclic urea and no oligomericbyproducts. For other amino alcohols, cyclic urethanes, cyclic ureas, and/or undesiredbyproducts were produced in different yields depending on the substrates used. Possiblereaction mechanisms are proposed.

Abstract: Interest in ionic liquids for their potential in different chemical processes isconstantly increasing, as they are claimed to be environmentally benign – excellent, non-volatile solvents for a wide range of applications. The wide applicability of thesecompounds also demands reliable, relatively simple and reproducible analytical techniques.These methods must be applicable not only to different technical or natural matrices but alsoto the very low concentrations that are likely to be present in biological and environmentalsystems. In this review, therefore, methods for separating and analysing imidazolium- andpyridinium-type ionic liquids in aqueous matrices using high performance liquidchromatography (HPLC) and capillary electrophoresis (CE) are examined. The techniquesfor identifying ionic liquids are meant primarily to track the concentrations of ionic liquidsas residues not only in products and wastes but also in biological or environmental samples.The application of hyphenated techniques in this field is intended to selectively separate thequaternary entity from other cationic and non-ionic species present in the matrix, and toenable its fine-scale quantification. Nowadays, methods developed for cation analysis arebased mostly on reversed-phase high-performance liquid chromatography, ionchromatography, ion-pair chromatography and capillary electrophoresis, where variousbuffered mobile phases are used.

Abstract: Photochemical properties of the ionic liquid (RTIL) 1-butyl-3-methylimidazoliumhexafluorophosphate [bmim][PF₆] and its binary mixed solutions with organic solvent(DMF and MeCN) were investigated by laser photolysis at an excitation wavelength of 355nm, using anthraquinone (AQ) as a probe molecule. It was indicated that the triplet excitedstate of AQ (³AQ*) can abstract hydrogen from [bmim][PF₆]. Moreover, along with thechange of the ratio of RTIL and organic solvent, the reaction rate constant changes regularly.Critical points were observed at volume fraction V_RTIL = 0.2 for RTIL/MeCN and V_RTIL =0.05 for RTIL/DMF. For both systems, before the critical point, the rate constant increasesrapidly with increasing V_RTIL; however, it decreases obviously with VRTIL after the criticalpoint. We conclude that the concentration dependence is dominant at lower V_RTIL, while theviscosity and phase transformation are dominant at higher V_RTIL for the effect of ionic liquidon the decay of rate constant.

Abstract: One of the room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazoliumchloride ([BMIM]Cl) was chosen to prepare the concentrated solutions of Polyacrylonitrile(PAN). The rheological behaviors of the solutions were measured with rotational rheometryunder different conditions, including temperatures, concentration, and molecular weight ofPAN. The solutions exhibited shear-thinning behaviors, similar to that of PAN/DMFsolutions. The viscosities decreased with the increasing of shear rates. However, theviscosity decreased sharply at high shear rates when the concentration was up to 16wt%. Thedependence of the viscosity on temperature was analyzed through the determination of theapparent activation energy. Unusually, the viscosity of solutions of higher concentration islower than that of lower concentration. Similarly, the viscosity of low molecular weightPAN was higher than high molecular weight PAN at high shear rates. The dynamicrheological measurement indicates the loss modulus is much higher than storage modulus.The trend of complex viscosity is similar with the result of static rheological measurement.The interaction between PAN and ionic liquid [BMIM]Cl was discussed.

Abstract: A series of sulfonium halides bearing allyl groups have been prepared andcharacterized. Anion metathesis with Li[Tf₂N] and Ag[N(CN)₂] resulted in sulfonium-basedionic liquids which exhibit low viscosities at room temperature. The solid state structure ofone of the halide salts was determined by single crystal X-ray diffraction.

Abstract: The combinations of 1-butyl-3-methylimidazolium chloride with NbCl₅ yieldedionic mixtures with different melting point temperatures and acidity depending on theniobium molar fraction. The mixtures were characterized by thermal (DSC) andspectroscopic (FT-IR and ¹H NMR) analysis. The Pechmann reactions of different phenolswith ethylacetoacetate, producing coumarins, was used as model to evaluate the catalyticbehavior of these mixtures as acid Lewis catalyst. These reactions were carried out usingacidic mixtures of 60 mol%.

Abstract: Hydrolysis of the ionic liquid Et3NHCl-2AlCl3 and a process for recycling thetriethylamine were studied. When the hydrolysis was carried out at a relatively hightemperature, the released HCl could be absorbed more easily. With addition of sodiumhydroxide to the aqueous hydrolysis solution, a feasible process for recycling triethylaminewas developed, involving first distillation of triethylamine, followed by filtration of thealuminium hydroxide. The yield of recovered triethylamine was about 95%. Thetriethylhydrogenammonium chloride prepared from the recycled triethylamine was of goodpurity and could be reused to synthesize new chloroaluminate ionic liquids.

Abstract: The selective oxidation of alcohols with molecular oxygen was efficientlycompleted in high conversion and selectivity using copper-bisisoquinoline-based catalystsunder mild reaction condition. The effects of various parameters such as reactiontemperature, reaction time, oxidant, ligands, etc, were studied. Solvent effect has been aswell studied in ionic liquids [bmim]PF₆, [omim]BF₄ and [hmim]BF₄, comparing totraditional volatile organic solvent. The use of ionic liquids was found to enhance thecatalytic properties of the catalysts used.

Abstract: The room temperature ionic liquid [bmim][PF₆] was employed as the reactionmedium in the asymmetric glyoxylate-ene reaction of α-methyl styrene (4a) with ethylglyoxylate using chiral palladium(II) complexes as the catalysts. [Pd(S-BINAP)(3,5-CF₃-PhCN)₂](SbF₆)₂ (1b) showed the highest catalytic activity. Under the reaction conditionsof 40 oC, 0.5 h, and 1b/4a molar ratio of 0.05, ethyl α-hydroxy-4-phenyl-4-pentenoate wasobtained in excellent chemical yield (94 %) with high enantioselectivity (70 %). Otherα-hydroxy esters can also be obtained in high chemical yields and enantioselectitiesthrough the glyoxylate-ene reactions of alkenes with glyoxylates catalyzed by 1b in[bmim][PF₆]. Moreover, the ionic liquid [bmim][PF₆] which contained the palladium(II)complex could be recycled and reused several times without significant loss of the catalyticactivity.

Abstract: The liquid-liquid equilibrium for the ternary system formed by n-octane andaromatic (alkylbenzenes) and heteroaromatic compounds (nitrogen and sulfur containingheterocyles) and 1-alkyl-3-methylimidazolium ionic liquids (ILs) associated with variousanions has been investigated. The selectivity on the extraction of a specific aromaticcompound is influenced by anion volume, hydrogen bond strength between the anion andthe imidazolium cation and the length of the 1-methyl-3-alkylimidazolium alkyl side chain.The interaction of alkylbenzenes and sulfur heterocyles with the IL is preferentially throughCH-π hydrogen bonds and the quantity of these aromatics in the IL phase decreases withthe increase of the steric hindrance imposed by the substituents on the aromatic nucleus. Inthe case of nitrogen heterocycles the interaction occurs preferentially throughN(heteroaromatic)-H(imidazolium) hydrogen bonds and the extraction process is largelycontrolled by the nitrogen heterocycle pKa. Competitive extraction experiments suggestthat benzene, pyridine and dibenzothiophene do not compete for the same hydrogen bondsites of the IL.

Abstract: A process to produce fibers from Poly(m-phenyleneisophthalamide)(PMIA)solution in an ionic liquid via wet-spinning technology are described. The spinning processwas investigated on a small laboratory scale. Ionic liquid spinning solutions were firstprepared for PMIA fibers, followed by wet spinning. In the course of this research, thephysical properties of the PMIA fibers were estimated. We studied the dependence of themechanical properties of the obtained PMIA fibers on the composition of the coagulationbath, and on the choice of solvent in spinning solution. The morphology of the fibers fromionic liquid and traditional DMAc solvents via wet-spinning process were observed byscanning electrical microscopy(SEM). The differences of morphologies and properties ofthe PMIA fibers obtained from two different solvents are discussed.

Abstract: The salting-out effect produced by the addition of potassium phosphate, K₃PO₄to aqueous solutions of water-miscible ionic liquids, viz. 1-ethyl-3-methylimidazoliumethyl sulfate, 1-butyl-3-methylimidazolium methyl sulfate, or 1-alkyl-3-methylimidazolium chloride (alkyl = butyl, octyl or decyl) is investigated. The effects areanalyzed using both the corresponding temperature–composition pseudo-binary andcomposition ternary phase diagrams. Different regions of liquid-liquid and solid-liquidphase demixing are mapped. The phase behavior is interpreted taking into account thecomplex and competing nature of the interactions between the ionic liquid, the inorganicsalt and water. In the case of solutions containing 1-octyl- or 1-decyl-3-methylimidazoliumchloride, the smaller magnitude of the salting-out effects is explained in terms of thepossibility of self-aggregation of the ionic liquid.

Abstract: Within the recently launched the spectral-structure activity relationship (S-SAR)analysis, the vectorial anionic-cationic model of a generic ionic liquid is proposed, alongwith the associated algebraic correlation factor in terms of the measured and predictedactivity norms. The reliability of the present scheme is tested by assessing the Hanschfactors, i.e. lipophylicity, polarizability and total energy, to predict the ecotoxicityendpoints of wide types of ionic liquids with ammonium, pyridinium, phosphonium,choline and imidazolium cations on the aquatic bacteria Vibrio fischeri. The results, whileconfirming the cationic dominant influence when only lipophylicity is considered,demonstrate that the anionic effect dominates all other more specific interactions. It wasalso proved that the S-SAR vectorial model predicts considerably higher activity for theionic liquids than for its anionic and cationic subsystems separately, in all consideredcases. Moreover, through applying the least norm-correlation path principle, the completetoxicological hierarchies are presented, unfolding the ecological rules of combined cationicand anionic influences in ionic liquid toxicity.

Abstract: Inspired by the concept of ionic liquids (ILs), this study modified the original Mukaiyama’s reagent, 2-chloro-1-methylpyridinium iodide (m.p. 200-dec), from ionic solid into liquids by changing its anion. The esterification of N-acetyl-L-phenylalanine was investigated as a model reaction. The microwave irradiation was more effective in esterifying N-acetyl-L-phenylalanine than the conventional reflux method. The original Mukaiyama’s reagent was modified into ILs through manipulating its anion. However, only non-nucleophilic anions (such as EtSO₄^- and Tf₂N^-) were favorable since nucleophilic ones (such as CF₃COO^- and CH₃COO^-) could exchange with chlorine resulting in non-reactive coupling reagents. Two modified Mukaiyama’s compounds (i.e. hydrophilic [2- ClMePy][EtSO_4] and hydrophobic [2-ClMePy][Tf₂N]) have been identified as the best ILtype coupling reagents. The esterification reaction was greatly enhanced by using 1- methylimidazole as the base instead of conventional toxic tertiary amines, and by using excess amount of alcohols as solvents instead of dichloromethane. Overall, the method reported is effective and ‘greener’.

Abstract: Quartz crystal microbalance with dissipation (QCM-D) monitoring and atomic force microscopy (AFM) were combined to evaluate the defects created by an ionic liquid anion and a cation in a supported phospholipid bilayer composed of zwitterionic lipids on a silica surface. The cation 1-octyl-3-methyl imidazolium (OMIM⁺) was shown to remove lipids from the bilayer, increase the roughness to approximately 2.8 nm (~0.2 for stable supported bilayer) and possibly redeposit lipids with entrapped water. The anion bis(trifluoromethylsulfonyl)imide (Tf₂N^-) was found to leave distinct defects within the bilayer that had large pore-like interiors which left the surrounding bilayer intact. However, the ionic liquid 1-butyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-Tf₂N) formed a film over the supported bilayer. This work demonstrates, for the first time, the direct effects common components of ionic liquids have on a supported phospholipids bilayer.

Abstract: We report a new one phase method for the synthesis of uniform monodisperse crystalline Ag nanoparticles in aqueous systems that has been developed by using newly synthesized mono and dihydroxylated ionic liquids and cationic surfactants based on 1,3-disubstituted imidazolium cations and halogens anions. The hydroxyl functionalized ionic liquids (HFILs) and hydroxyl functionalized cationic surfactants (HFCSs) also simultaneously acts both as the reductant and protective agent. By changing the carbon chain length, alcohol structure and anion of the 1,3-imidazolium based HFILs and HFCSs the particle size, uniform and dispersibility of nanoparticles in aqueous solvents could be controlled. Transmission electron microscopy (TEM), electron diffraction, UV-Vis and NMR, were used for characterization of HFILs, HFCSs and silver nanoparticles. TEM studies on the solution showed representative spherical silver nanoparticles with average sizes 2-8 nm, particularly 2.2 nm and 4.5 nm in size range and reasonable narrow particle size distributions (SD-standard distribution) 0.2 nm and 0.5 nm respectively. The all metal nanoparticles are single crystals with face centered cubic (fcc) structure. The silver nanoparticles surface of plasmon resonance band (λ_max) around 420 nm broadened and little moved to the long wavelength region that indicating the formation of silver nanoparticles dispersion with broad absorption around infrared (IR) region. Silver complexes of these HFILs as well as different silver nanoparticles dispersions have been tested in vitro against several gram positive and gram negative bacteria and fungus. The silver nanoparticles providing environmentally friendly and high antimicrobial activity agents.

Abstract: The ¹H-NMR shifts of the imidazolium protons of some novel dimeric ionic liquids were examined in various deuterated solvents. Interactions between the solvent and the imidazolium salt of butyl substituted ionic liquids were observed to give higher chemical shifts than methyl substitution.