Physicochemical properties of 1-butyl-3-methylimidazolium acetate

Characteristic IR and UV absorption bands, as well as oxidation half-wave potential on a platinum disc electrode in the cyclic mode were determined for the low-temperature hydrophilic ionic liquid 1-butyl-3-methylimidazolium acetate. Temperature dependences of the refractive index, density, and ansolute viscosity were determined in the temperature range 298–328 K. The activation energy of viscous flow was calculated.     

Thermochemical properties of 1-butyl-3-methylimidazolium nitrate

Heat capacity for 1-butyl-3-methylimidazolium nitrate [C₄mim][NO₃] in the temperature range (5–370) K has been measured by adiabatic calorimetry. Temperatures and enthalpies of its phase transitions have been determined. Thermodynamic functions have been calculated for the crystalline and the liquid states. Phase transition temperatures for set of nitrate salts have been compared. Enthalpy of combustion and enthalpy of formation for crystalline [C₄mim][NO₃] have been determined using a static-bomb isoperibol combustion calorimeter. A correlation scheme for the estimation of C_p of ionic liquids has been developed.     

Homogeneous tritylation of cellulose in 1-butyl-3-methylimidazolium chloride

1-Alkyl-3-methylimidazolium-based ionic liquids, having chloride as a counter ion, were studied for cellulose solubility; and the influence of different alkyl chain lengths was also investigated. The alkyl chain length was incrementally varied from ethyl to decyl to determine structure-dissolution properties; a distinct odd-even effect was observed for short chain lengths. In addition, the tritylation of cellulose was performed in 1-butyl-3-methylimidazolium chloride using pyridine as base. The influences of reaction time and the ratio of trityl chloride per cellulose monomer unit on the degree of substitution were investigated in detail by elemental analysis and 1H NMR spectroscopy. A DS of around 1 was obtained after 3 h reaction time using a six fold excess of trityl chloride.     

Ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate,an efficient solvent for extraction of acetone from aqueous solutions

(Liquid + liquid) equilibrium (LLE) of the chemical system of {water + acetone + 1-Hexyl-3-methylimidazolium hexafluorophosphate (HMIMPF₆) ionic liquid} was studied at different temperatures of (293.2, 298.2 and 303.2) K and under atmospheric pressure of 81.5 kPa. The results show that HMIMPF₆ provides the acetone distribution coefficient and separation factor values within (0.8813 to 1.2351) and (3.0 to 54.4), respectively; indicating the high capability of the ionic liquid for extraction of acetone from aqueous solutions. In most cases, acetone solubility in the ionic liquid is higher than in water, especially at higher solute concentrations. Meanwhile, higher separation factor is relevant to the lower temperature due to lower (water + ionic liquid) miscibility. The consistency of tie line data, at each temperature, was examined with Othmer–Tobias correlation. The values were nicely reproduced with the well-known NRTL and UNIQUAC models. Accordingly, the required thermodynamic properties of HMIMPF₆ were obtained by the Density Functional Theory (DFT) calculations, carried out at the M06/6-311++G⁷ level of theory. The root mean square deviations (RMSD) between experimental and model concentration values were 0.0192 and 0.0255, respectively; indicating close agreement of the both models.     

Aggregation behavior of a fluorinated surfactant in 1-butyl-3-methylimidazolium ionic liquids

The aggregation behavior of a fluorinated surfactant (FC-4) was studied by surface tension measurements in 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4]) and hexafluorophosphate ([bmim][PF 6]) at various temperatures. A series of surface properties, including adsorption efficiency (p C 20), effectiveness of surface tension reduction (Pi CAC), maximum surface excess concentration (Gamma max) and minimum surface area/molecule (A(min)) at the air-water interface were estimated. By comparing the fluorinated surfactant with traditional surfactants, we deduced that the surface activity of the fluorinated surfactant in ILs was superior to the activity of other surfactants. From the CAC values and their temperature dependence, we estimated the thermodynamic parameters of aggregate formation. The thermodynamic parameters indicate that the aggregate of FC-4 in [bmim][BF 4] is a traditional micelle, while the aggregate of FC-4 in [bmim][PF 6] is nanodroplets composed of FC-4 molecules segregated from the solution phase. These results were further confirmed by (1)H NMR measurements.     

Linear viscoelasticity of poly(acrylonitrile-co-itaconic acid)/1-butyl-3-methylimidazolium chloride extended from dilute to concentrated solutions

The solution rheology of poly(acrylonitrile-co-itaconic acid) (poly(AN-co-IA)) in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) spanning dilute, semidilute unentangled and entangled regimes were investigated. The exponents in the specific viscosity η_sp ～ overlap parameter c[η] power law were 1, 2 and 4.7 for dilute, semidilute unentangled and entangled regimes, respectively, which were found to be consistent with the scaling prediction for neutral linear polymers in θ-solvent. For dilute solutions (lower than 0.9 wt.%), the linear viscoelastic responses were observed to be in good agreement with the Zimm model (Flory exponent ν = 0.5). While for semidilute unentangled solutions (between 0.9 and 8 wt.%), results obtained had been found to be consistent with Rouse model. Considering Flory exponent ν = 0.5 and the concentration dependences of the specific viscosity and relaxation time, it had been evaluated that poly(AN-co-IA) in [BMIM]Cl behaves as a neutral polymer in θ-solvent. It had also been suggested that according to the unusual deviation of Cox-Merz rule, poly(AN-co-IA)/[BMIM]Cl solutions are typical neutral polymeric liquids for the concentrated solutions but have shown a more complicated behavior at high deformation rates.     

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.     

Supported phospholipid membrane interactions with 1-butyl-3-methylimidazolium chloride

Quartz crystal microbalance with dissipation measurements were conducted for a 98/2 mole ratio of 1,2-dielaidoylphosphocholine (DEPC) and 1,2-dimyristoylphosphoglycerol (DMPG) on silica, gold, and a self-assembled monolayer of 11-mercapto-1-undecanol (11MU) and 11-mercaptoundecanoic acid (11MUA) at 50 mol % each. This study demonstrates that vesicles composed of DEPC and DMPG at 98 and 2 mol %, respectively, formed a supported bilayer with unruptured vesicles present when adsorbed onto the self-assembled monolayer. Also, the partially formed supported bilayer apparently deadsorbed in the presence of 1-butyl-3-methylimidazolium chloride, suggesting that surface-bilayer interactions are weaker on a hydrophilic modified gold surface composed of 50/50 11MU/11MUA than the surface-bilayer interactions on silica.     

Friedel-Crafts sulfonylation in 1-butyl-3-methylimidazolium chloroaluminate ionic liquids.

1-Butyl-3-methylimidazolium chloroaluminate ionic liquids have been employed as an unconventional reaction media and as Lewis acid catalyst for Friedel-Crafts sulfonylation reaction of benzene and substituted benzenes with 4-methyl benzenesulfonyl chloride. The substrates exhibited enhanced reactivity, furnishing almost quantitative yields of diaryl sulfones, under ambient conditions. Studies concerning the effect of Lewis acidity of the ionic liquid on the initial extent of conversion of this reaction has been carried out. (27)Al NMR spectroscopy has been exploited as a tool to investigate the mechanistic details of the reaction. (27)Al NMR spectral studies show the predominance of [Al(2)Cl(7)](-) species in [bmim]Cl-AlCl(3), N = 0.67, acidic ionic liquid in the presence of 4-methyl benzenesulfonyl chloride, and after the reaction with the aromatic hydrocarbon, [AlCl(4)](-) species predominates. This change in speciation of aluminum can be attributed to the interaction of the Lewis acidic species [Al(2)Cl(7)](-) of the ionic liquid with the formed HCl during the sulfonylation reaction, which is evidenced by the control experiment. Preliminary investigations on Friedel-Crafts acylation further substantiate the argument.     

Lipase-catalysed polyester synthesis in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid

1-Butyl-3-methylimidazolium hexafluorophosphate ionic liquid was employed as a reaction medium for lipase-catalysed aliphatic polyester synthesis. Lipase PS-C exhibited excellent catalysis in polycondensation of diethyl octane-1,8-dicarboxylate and 1,4-butanediol at room temperature and at 60°C. A relatively high molecular weight polymer was obtained at 60°C.     

Luminescence properties and water coordination of Eu3+ in the binary solvent mixture water/1-butyl-3-methylimidazolium chloride

The effect of relative water content on the luminescence properties and speciation of Eu3+ ions in solutions of EuCl3 in the binary solvent mixture water/[BMI]Cl is presented, where [BMI]Cl is the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride. Using luminescence techniques, the binding properties of water to Eu3+ are determined for samples with mole ratios of water-to-IL ranging from 0 to 5. Very little water binds to Eu3+ at mole ratios of water-to-IL less than 1, above which binding increases rapidly with increasing water concentration. It is shown that only certain hydration numbers for Eu3+ complexes are stable in the water/IL solutions. The data presented suggest that the Eu3+ species present are [EuClx]3-x, [EuCly(H2O)3-4]3-y, [EuClz(H2O)6]3-z, and [Eu(H2O)8-9]3+ (where x > y > z). Comparison of the positions of the 5D0<--7F0 transitions of the Eu3+ complexes in IL solution with those of model crystal systems provides insight into the extent of Cl- complexation. This study suggests that [BMI]Cl is a promising medium for luminescent lanthanide (Ln) compounds due to the low-energy phonon environment of the [LnClx]3-x complex and to the fact that moderate water contamination does not result in direct binding of water to Ln3+, which would result in luminescence quenching.     

Photoinduced electron-transfer reactions in two room-temperature ionic liquids: 1-butyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium hexafluorophosphate

Photoinduced electron transfer in two room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF(6)) and 1-octyl-3-methylimidazolium hexafluorophosphate (OMIM-PF(6)), has been investigated using steady-state fluorescence quenching of 9,10-dicyanoanthracene with a series of single electron donors. From these fluorescence quenching rates, reorganization energy (lambda) values and k(diff) values can be derived from a Rehm-Weller analysis. In many cases, these fluorescence quenching reactions occur at rates larger than what would be expected based on the Smoluchowski equation. In addition, lambda values of 10.1 kcal/mol and 16.3 kcal/mol for BMIM-PF(6) and OMIM-PF(6), respectively, have been determined.     

The salting-out effect and phase separation in aqueous solutions of tri-sodium citrate and 1-butyl-3-methylimidazolium bromide

The aim of this work is to obtain further evidence about the salting-out effect produced by the addition of tri-sodium citrate to aqueous solutions of water miscible ionic liquid 1-butyl-3-methylimidazolium bromide ([C₄mim][Br]) by evaluating the effect of tri-sodium citrate on the thermodynamic properties of aqueous solutions of this ionic liquid. Experimental measurements of density and sound velocity at different temperatures ranging from (288.15 to 308.15) K, the refractive index at 308.15 K and the liquid–liquid phase diagram at different temperatures ranging from (288.15 to 338.15) K for aqueous solutions containing 1-butyl-3-methylimidazolium bromide ([C₄mim][Br]) and tri-sodium citrate (Na₃Cit) are taken. The apparent molar volume of transfer of [C₄mim][Br] from water to aqueous solutions of Na₃Cit have positive values and it increases by increasing salt molality. Although at high IL molality, the apparent molar isentropic compressibility shows similar behaviour with that of the apparent molar volume. However at low concentrations of IL, the apparent molar isentropic compressibility of transfer of [C₄mim][Br] from water to aqueous solutions of Na₃Cit have negative values. The effects of temperature and the addition of Na₃Cit and [C₄mim][Br] on the liquid–liquid phase diagram of the investigated system have been studied. It was found that an increase in temperature caused the expansion of the one-phase region. The presence of Na₃Cit triggers a salting-out effect, leading to significant upward shifts of the liquid–liquid de-mixing temperatures of the system. The effect of temperature on the phase-forming ability in the system investigated has been studied based on a salting-out coefficient obtained from fitting the binodal values to a Setschenow-type equation for each temperature. Based on cloud point values, the energetics of the clouding process have been estimated and it was found that both of entropy and enthalpy are the driving forces for biphasic formation.     

Dynamics of solvent and rotational relaxation of Coumarin 153 in a room temperature ionic liquid, 1-butyl-3-methylimidazolium octyl sulfate, forming micellar structure

The solvent and rotational relaxation of Coumarin 153 (C-153) was investigated by picosecond time-resolved fluorescence spectroscopy in a room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium octyl sulfate ([C4mim][C8SO4]). This is a typical RTIL, which form micellar structure above certain concentration of the RTIL (0.031 M). Dynamic light scattering (DLS) measurements show that the average hydrodynamic diameter ( Dh) of a [C4mim][C8SO4]-water micelle is 2.8 (+/-0.2) nm. Both the solvent and rotational relaxation of C-153 are retarded in this micelle compared to the solvation time of a similar type of dye in neat water. However, the solvent relaxation in this ionic liquid surfactant is different from that of a conventional ionic surfactant. The slow component of the solvation dynamics in C8H17SO4Na or TX-100 micelle is on the nanoseconds time scale, whereas in [C4mim][C8SO4] micelle the same component is on the subnanoseconds time scale. The different molecular motions with different time scale is the main reason behind this difference in the solvation time in micelles composed of RTIL with other conventional micelles.     

Anomalous conformational change in 1-butyl-3-methylimidazolium tetrafluoroborate-D2O mixtures

We have investigated the effect of deuterated water on the conformational equilibrium between the gauche and trans conformers of the [bmim] cation in mixtures of water and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]), an ionic liquid, at room temperature. A comparison of the results obtained from solutions made with H(2)O and with D(2)O highlights an anomalous conformational change in the D(2)O solution showing an extended N-shaped behavior. The gauche conformer of the [bmim] cation in D(2)O increased up to x = ~50 (D(2)O mol %); however, it decreased up to higher water concentrations of x = ~85 before again increasing drastically toward x = ~100. We provide spectroscopic evidence that the anomalous conformational dynamics of the [bmim] cation in D(2)O is directly related to the H/D exchange reaction of the C-H group at position 2 of the imidazolium ring.     

Anodic oxidation of silver in 1-butyl-3-methylimidazolium bromide ionic liquid

Electrochemical oxidation of silver in the 1-butyl-3-methylimidazolium bromide ([BMIm]Br) ionic liquid is studied by cyclic voltammetry, chronopotentiometry, chronoammetry, and gravimetry. Two electrode processes irreversibly proceed on the silver electrode in the potential range studied: the formation of compound [BMIm]⁺[AgBr₂]^?, which is soluble in [BMIm]Br, and difficultly soluble AgBr.     

TX-100/water/1-butyl-3-methylimidazolium hexafluorophosphate microemulsions

Both ionic liquids and water are typical green solvents. In this work, the phase behavior of the ternary system consisting of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), TX-100, and water was determined at 25.0 degrees C. The water-in-bmimPF6, bicontinuous, and bmimPF6-in-water microregions of the microemulsions were identified by cyclic voltammetry method using potassium ferrocyanide K4Fe(CN)6 as the electroactive probe. Dynamic light scattering (DLS) and the UV-vis method were used to characterize the microemulsions. It was demonstrated that the hydrodynamic diameter (Dh) of the bmimPF6-in-water microemulsions is nearly independent of the water content but increases with increasing bmimPF6 content due to the swelling of the micelles by the ionic liquid. The UV-vis further confirmed the existence of water domains in the water-in-bmimPF6 microemulsions, and the salt potassium ferricyanide K3Fe(CN)6 could be dissolved in the water domains.     

The kinetics of thermal decomposition of 1-butyl-3-methylimidazolium hexafluorophosphate

It is demonstrated that 1-butyl-3-methylimidazolium hexafluorophosphate decomposes in a vacuum in the temperature interval of T=(410 to 505) K according to zero-order kinetics with the activation energy EA=68.0+/-2.8 kJ.mol-1.