Effects of water and methanol on the molecular organization of 1-butyl-3-methylimidazolium tetrafluoroborate as functions of pressure and concentration

The structural organization in mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)])/water or methanol was studied by infrared spectroscopy. No drastic change in the concentration dependence of the alkyl C-H band frequency was observed at high concentration of the ionic liquid. This behavior indicates a clustering of the ionic liquid in alkyl regions. Nevertheless, the presence of methanol significantly perturbs the ionic liquid-ionic liquid associations in the imidazolium region. On the basis of the responses to change in pressure and concentration, two different types of O-H species, i.e., free O-H and bonded O-H, were observed in the O-H stretching region. For [bmim][BF(4)]/water mixtures, the compression leads to loss of the free O-H band intensity. It is likely that free O-H is switched to bonded O-H as high pressures are applied. For [bmim][BF(4)]/methanol mixtures, the free O-H is still stable under high pressures.     

离子液体[bmim][BF4]对联苯甲酰光化学反应影响的瞬态吸收光谱

利用纳秒级激光光解瞬态吸收光谱研究了联苯甲酰(BZ)在离子液体1-丁基-3-甲基咪唑四氟硼酸盐([bmim][BF₄])与乙腈(MeCN)混合体系中的光化学反应行为. 考察了探针分子BZ存在下[bmim][BF₄]/MeCN比例对体系中化学反应动力学的影响. 实验发现: 在N₂饱和条件下, BZ溶液经激光辐照后产生的激发三线态³BZ^*遵循一级反应动力学规律衰减. 离子液体(IL)相对比例增加对³BZ^*瞬态吸收峰的位置和强度没有产生明显影响. 但离子液体体积分数V_IL的变化对[bmim][BF₄]/MeCN混合溶剂中光诱导电子转移的影响却非常显著, 总体上电子转移产生的自由基的表观生成速率常数k_gr随[bmim][BF₄]的V_IL增大而减小. 在[bmim]BF₄]比例足够大的情况下, ³BZ^*与三乙胺或四甲基对苯二胺之间的电子转移被抑制.     

Ionic liquid induced changes in the properties of aqueous zwitterionic surfactant solution

Modifying properties of aqueous surfactant solutions by addition of external additives is an important area of research. Unusual properties of ionic liquids (ILs) make them ideal candidates for this purpose. Changes in important physicochemical properties of aqueous zwitterionic N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (SB-12) surfactant solution upon addition of hydrophilic IL 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF 4], are reported. Dynamic light scattering results indicate a dramatic reduction in the average micellar size in the presence of [bmim][BF 4]; micellar (or micelle-like) aggregation in the presence of as high as 30 wt % [bmim][BF 4] is confirmed. Responses from fluorescence probes are used to obtain critical micelle concentration (cmc), aggregation number ( N agg), and dipolarity and microfluidity of the micellar pseudophase of aqueous SB-12 in the presence of [bmim][BF 4]. In general, increasing the amount of [bmim][BF 4] to 30 wt % results in decrease in N agg and increase in cmc. Increase in the dipolarity and the microfluidity of the probe cybotactic region within the micellar pseudophase is observed on increasing [bmim][BF 4] concentration in the solution. It is attributed to increased water penetration into the micellar pseudophase as [bmim][BF 4] is added to aqueous SB-12. It is proposed that IL [bmim][BF 4] behaves similar to an electrolyte and/or a cosurfactant when present at low concentrations and as a polar cosolvent when present at high concentrations. Electrostatic attraction between cation of IL and anion of zwitterion, and anion of IL and cation of zwitterion at low concentrations of [bmim][BF 4] is evoked to explain the observed changes. Presence of IL as cosolvent appears to reduce the efficiency of micellization process by reducing the hydrophobic effect.     

Ideal gas solubilities and solubility selectivities in a binary mixture of room-temperature ionic liquids

This study focuses on the solubility behaviors of CO2, CH4, and N2 gases in binary mixtures of imidazolium-based room-temperature ionic liquids (RTILs) using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][Tf2N]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim][BF4]) at 40 degrees C and low pressures (approximately 1 atm). The mixtures tested were 0, 25, 50, 75, 90, 95, and 100 mol % [C2mim][BF4] in [C2mim][Tf2N]. Results show that regular solution theory (RST) can be used to describe the gas solubility and selectivity behaviors in RTIL mixtures using an average mixture solubility parameter or an average measured mixture molar volume. Interestingly, the solubility selectivity, defined as the ratio of gas mole fractions in the RTIL mixture, of CO2 with N2 or CH4 in pure [C2mim][BF4] can be enhanced by adding 5 mol % [C2mim][Tf2N].     

Effect of 1-butyl-3-methylimidazolium tetrafluoroborate on the formation rate of CO2 hydrate

The effect of the addition of 1-butyl-3-methylimidazolium tetrafluoroborate （[C4mim][BF4]） on the formation rates of CO2 hydrates was investigate. The isothermal and isobaric methods were used to measure the formation rates of CO2 hydrates. As compared to those of pure water, the data of phase equilibrium changed greatly. The effects of pressure, temperature, and the concentration of [C4mim][BF4] aqueous solution on the formation rates of CO2 hydrates were investigated. With a constant concentration of [C4mim][BF4], the rate of gas consumption was enhanced with the lowering of experimental temperature. However, a decrease in pressure exerted an opposite effect on the rate of gas consumption. Moreover, the addition of [C4mim][BF4] raised the equilibrium pressure of hydrate formation at the same temperature.     

Unique role of hydrophilic ionic liquid in modifying properties of aqueous Triton X-100

Modification of important physicochemical properties of aqueous surfactant solutions can be achieved by addition of environmentally benign room temperature ionic liquids (ILs). While low aqueous solubility of "hydrophobic" ILs limits the amount of IL that may be added to achieve desired changes in the physicochemical properties, hydrophilic ILs do not have such restrictions associated to them. Alterations in the key physicochemical properties of aqueous solutions of a common nonionic surfactant Triton X-100 (TX100) on addition of up to 30 wt % hydrophilic IL 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) are reported. The presence of micellar aggregates in as high as 30 wt % [bmim][BF4]-added aqueous TX100 solutions is established by dynamic light scattering and fluorescence probe behavior. Increasing the concentration of [bmim][BF4] results in decrease in average micellar size and aggregation number and increase in critical micelle concentration, indicating an overall unfavorable aggregation process. Increase in the dipolarity and the microfluidity of the probe cybotactic region within the palisade layer of the micellar phase upon [bmim][BF4] addition implies increased water penetration and the possibility of TX100-[bmim][BF4] interactions. While the changes in some of the physicochemical properties indicate the role of [bmim][BF4] to be similar to a cosurfactant, the IL acts like a cosolvent as far as changes in other properties are concerned. Effectiveness of IL [bmim][BF4] in modifying physicochemical properties of aqueous TX100 is demonstrated.     

Vibrational spectroscopy and dynamics of small anions in ionic liquid solutions

Fourier-transform infrared (FTIR) and time-resolved IR spectroscopies have been used to study vibrational band positions, vibrational energy relaxation (VER) rates, and reorientation times of anions in several ionic liquid (IL) solutions. The ILs primarily investigated are based on the 1-butyl-2,3-dimethylimidazolium ([BM(2)IM]) cation with thiocyanate (NCS-), dicyanamide (N(CN)2-), and tetrafluoroborate (BF4-) anions. Spectroscopic studies are carried out near 2000 cm-1 for the C[Triple Bond]N stretching bands of NCS- and N(CN)2- as the IL anion as well as for NCS-, N(CN)2-, and azide (N3-) anions dissolved in [BM2IM][BF4]. The VER studies of N(CN)2- are reported for the first time. VER of N3-, NCS-, and N(CN)2- is measured in normal solvents, such as N-methylformamide, to compare with the IL solutions. The spectral shifts and VER rates of the anions in IL solution are quite similar to those in polar aprotic, conventional organic solvents, i.e., dimethylsulfoxide, and significantly different than those in methanol, in which there is hydrogen bonding. Similar studies were also carried out for the anions in another IL, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), in which the C2 hydrogen is present. The results for the anions are similar to those in the [BM2IM] containing ILs, in which the C2 hydrogen is methyl substituted. This suggests that substituting this hydrogen has, at most, a minor effect on the degree of hydrogen bonding in the anion-IL solvation interaction based on the infrared spectra and dynamics.     

Study of Imidazolium Ionic Liquids:Temperature-dependent Fluorescence and Molecular Dynamics Simulation

The steady-state fluorescence spectra and molecular dynamics simulations were explored to investigate the temperature dependent organization in some imidazolium ionic liquids:1-butyl-3-methylimidazolium hexafluo-rophosphate([bmim][PF6]),1-ethyl-3-methylimidazolium ethylsulfate([emim][EtSO4]) and 1-butyl-3-methylimida-zolium tetrafluoroborate([bmim][BF4]).The pure room temperature ionic liquids(ILs) exhibit a large red shift at more than an excitation wavelength of around 340 nm,which demonstrates the hetero...     

Ionic liquid acceleration of solid-phase suzuki-miyaura cross-coupling reactions

[reaction: see text] Room-temperature ionic liquids promote various transition metal-catalyzed reactions in the solution phase. Here, for the first time, we show that these effects are translatable to solid-phase reactions. The Suzuki-Miyaura cross-coupling of 4-iodophenol immobilized on polystyrene-Wang resin with various arylboronic acids was significantly accelerated by the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)(-)]).     

Effect of the structure of imidazolium cations in [BF4](-)-type ionic liquids on direct electrochemistry and electrocatalysis of horseradish peroxidase in Nafion films

The direct electrochemistry and bioelectrocatalysis of horseradish peroxidase (HRP) in Nafion films at glassy carbon electrode (GCE) was investigated in three [BF(4)](-)-type room-temperature ionic liquids (ILs) to understand the structural effect of imidazolium cations. The three ILs are 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF(4)]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]) and 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF(4)]). A small amount of water in the three ILs is indispensable for maintaining the electrochemical activity of HRP in Nafion films, and the optimum water contents decrease with the increase of alkyl chain length on imidazole ring. Analysis shows that the optimum water contents are primarily determined by the hydrophilicity of ILs used. In contrast to aqueous medium, ILs media facilitate the direct electron transfer of HRP, and the electrochemical parameters obtained in different ILs are obviously related to the nature of ILs. The direct electron transfer between HRP and GCE is a surface-confined quasi-reversible single electron transfer process. The apparent heterogeneous electron transfer rate constant decreases gradually with the increase of alkyl chain length on imidazole ring, but the changing extent is relatively small. The electrocatalytic reduction current of H(2)O(2) at the present electrode decreases obviously with the increase of alkyl chain length, and the mass transfer of H(2)O(2) via diffusion in ILs should be responsible for the change. In addition, the modified electrode has good stability and reproducibility; the ability to tolerate high levels of F(-) has been greatly enhanced due to the use of Nafion film. When an appropriate mediator is included in the sensing layer, a sensitive nonaqueous biosensor could be fabricated.     

Evidence for spin diffusion in a H,H-NOESY study of imidazolium tetrafluoroborate ionic liquids

The ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-methyl-3-propylimidazolium tetrafluoroborate ([PMIM][BF4]) were studied by H,H-NOESY NMR using a cross-relaxation matrix analysis. Cross-peak intensities are seen to increase with increasing mixing time. Experimental and theoretical hydrogen-hydrogen distances are in agreement at short mixing times (50 ms). Mixing times longer than 50 ms result in an increasing contribution of spin diffusion that produces unrealistically short hydrogen-hydrogen distances. Gas-phase ab initio molecular structures are obtained using Hartree-Fock (HF) and density functional theory (B3LYP) methods at the 6311 + G(2d,p) basis set level. The hydrogen-hydrogen distances obtained from the theoretical structures are in reasonable agreement with those calculated from the cross-relaxation matrices.     

Density and Viscosity for Binary Mixtures of the Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate with 2-Propanol,N,N-Dimethylacetamide and N,N-Dimethylformamide at 293.15–323.15 K: Experimental and PC-SAFT Modeling

Journal of Solution Chemistry - For three binary mixtures composed of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) with 2-propanol, N,N?dimethylacetamide (DMA) and...     

Compressed CO2-enhanced solubilization of 1-butyl-3-methylimidazolium tetrafluoroborate in reverse micelles of Triton X-100

We carried out the first study about the effect of a compressed gas on the properties of reverse micellar solutions with ionic liquid (IL) polar cores. And the properties of compressed CO2/cyclohexane/1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4])/Triton X-100 (TX-100) system were investigated at 288.2, 293.2, 298.2, 308.2 K and different pressures by using phase behavior measurement, small-angle x-ray scattering, and UV-Vis techniques. The concentration of the surfactant in the solution was 0.3 mol/l (M). It was found that compressed CO2 could enhance solubilization of the IL in the reverse micelles considerably at suitable pressures, and formation of the reverse micelles could be controlled easily by pressure. Increase of CO2 pressure resulted in decrease of the micellar sizes at fixed [bmim][BF4]-to-surfactant molar ratios (w), and the size of the reverse micelles increased with the increase of w values. The polarity of the IL cores increased continuously with increasing w value.     

Morphology of poly(ethylene oxide) dissolved in a room temperature ionic liquid: a small angle neutron scattering study

Solutions of deuterated poly(ethylene oxide) (d-PEO) in 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF4]), a prototype room-temperature ionic liquid (RTIL), have been studied at room temperature over a range of polymer concentrations, using small angle neutron scattering (SANS), characterizing the conformation of PEO dissolved in RTILs. [bmim][BF4] behaves as a good solvent for d-PEO, which organizes in this solvent in non entangled random coils. These findings will help in optimizing the designing of microemulsions in these potentially environmentally friendly solvents.     

ILs-based microwave-assisted extraction coupled with aqueous two-phase for the extraction of useful compounds from Chinese medicine

Ionic liquids-based microwave-assisted extraction (ILs-MAE) of medicinal or useful compounds from plants was investigated as an alternative to conventional organic solvent extractions. The extraction and the preconcentration of aqueous two-phase (ATP) systems have been integrated. Various operating parameters were systematically considered by single-factor and L(9) (3(4)) orthogonal array experiments. 1-Butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]) has been selected to extract Apocynum venetum. The extract was then converted to the top phase by [bmim][BF(4)]/NaH(2)PO(4) system which was suitable for the preconcentration. Reversed phase high performance liquid chromatography (RP-HPLC) with ultraviolet detection was employed for the analysis of hyperin and isoquercitrin in Apocynum venetum. The optimal experiment approach could provide higher detection limit of hyperin and isoquercitrin which were 3.82 μg L(-1) and 3.00 μg L(-1) in Apocynum venetum. The recoveries of hyperin and isoquercitrin were 97.29% (RSD = 1.02%) and 99.40% (RSD = 1.13%), respectively, from aqueous samples of Apocynum venetum by the proposed method. Moreover, the extraction mechanism of ILs-MAE and the microstructures and chemical structures of the herb before and after extraction were also investigated. The method exhibited potential applicability with other complicated samples.     

Structure of aqueous solutions of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate by small-angle neutron scattering

The structure of aqueous solutions of a prototype ionic liquid, the short alkyl chain 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) has been investigated by small-angle neutron scattering. Concentration fluctuations and Kirkwood-Buff integrals have been calculated, and the results are in good agreement with corresponding data calculated herein from vapor pressure measurements. The large concentration fluctuations and Kirkwood-Buff integral values indicate that the system is in the vicinity of phase separation, which is known to occur some 20 K below room temperature, at a salt mole fraction of around 0.075.     

Molecular dynamics simulation of room-temperature ionic liquid mixture of [bmim][BF4] and acetonitrile by a refined force field

1-Butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) is one of the promising room-temperature ionic liquids. To test the refined force field for [bmim][BF4] proposed in our previously work (J. Phys. Chem. B, 2004, 108, 12978-12989), thermodynamic properties of mixtures of [bmim][BF4](1)+ acetonitrile (2) are presented by using molecular dynamics over the whole concentration range. The calculated densities are in good agreement with the experimental data with deviations less than 2%, indicating the force field is applicable to the mixtures. In addition, the diffusion constants, viscosities, heats of vaporization, cohesive energy densities and excess properties of the mixtures are reported. The microscopic structures are discussed in detail, corresponding to the thermodynamic properties.     

Effect of water and organic solvents on the ionic dissociation of ionic liquids

The effect of water and several organic solvents on the density, viscosity, and conductivity of ionic liquids (ILs) 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), and 1-n-butyl-3-methylimidazolium trifluoroacetate ([bmim][CF3CO2]) was studied at 298.15 K in wide composition ranges. The density, viscosity, and conductivity of the three neat ILs were also determined at various temperatures. Upon the basis of the molar conductivity of the mixtures and that of the neat ILs of the same viscosity, the degree of dissociation of ILs in the solutions was investigated. It can be deduced that the organic solvents enhance the ionic association of the ILs, the effect depending on the solvent dielectric constant, while water promotes dissociation significantly due to its high dielectric constant and its ability to form strong hydrogen bonds with the anions of the ILs.     

Dynamically coated silica monolith with ionic liquids for capillary electrochromatography

An ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) was introduced as dynamic coating of a silica monolithic column for capillary electrochromatography of phenols and nucleoside monophosphates. The run-to-run and column-to-column repeatability of migration time for six phenols were satisfactory on this column with relative standard deviation values less than 0.90 and 4.31%, respectively. Anodic electroosmotic flow (EOF) was observed, which increased with the increase of [BMIM][BF4] concentration within 120 mM and when [BMIM][BF4] concentration was above 120 mM, EOF leveled off due to the saturation of [BMIM][BF4] on the monolith. Efficient separation of phenols and nucleoside monophosphates on this dynamically coated monolithic column was obtained, compared with a dynamically coated fused-silica column and unmodified silica monolithic column. The retention behavior of uncharged phenols is mainly manipulated by hydrophobic interactions due to the presence of butyl groups, and that of nucleoside monophosphates is governed by the electrostatic attraction mechanism based on the interaction between positively charged [BMIM][BF4] moieties and negatively charged phosphate groups. In addition, silica matrix also contributes to the separation resolution.