Nitrate Ionic Liquid Research Articles

Micelle formation of alkylimidazolium ionic liquids in water and in ethylammonium nitrate ionic liquid: A calorimetric study

Using isothermal titration calorimetry heats of dilution of the aqueous ionic liquid solutions [C 4MIM][C 8SO 4], [C 12MIM]Cl, [C 16MIM][BF 4], and [C 16MIM]Cl have been measured in the concentration range of (1–80, 1–35, 0.2–2.2, and 0.1–2.6) mmol dm −3 respectively at different temperatures between 283 K and 338 K. Formation of micelles has been observed. The CMC, the equilibrium constant of micellization as well as the enthalpy of micellization has been determined from the experimental data using a mass-action model with 3–5 parameters adjusted to the experimental data points of the heat of dilution over the whole concentration range. Three modified versions of the model have been tested providing similar results with exception of [C 16MIM][BF 4] solutions where one of the versions failed. The consistency of the model has been tested by comparing the model parameters of our own experimental results of Na[C 12SO 4] solutions with those obtained from experimental data of other authors in the literature. Our evaluation process shows that the CMC decreases in the order of [C 4MIM][C 8SO 4], [C 12MIM]Cl, [C 16MIM]Cl and [C 16MIM][BF 4]. The enthalpy of micellization changes its sign with temperature in all cases studied in aqueous solutions. It is positive at lower temperatures and becomes negative at higher temperatures. Also solutions of [C 16MIM][BF 4] and [C 16MIM]Cl in ethylammonium nitrate (EAN) have been studied in the same way. In contrast to the aqueous solutions the enthalpy of micellization is always negative without significant dependence on temperature.

Enzymatic ring‐opening polymerization of ε‐caprolactone by Yarrowia lipolytica lipase in ionic liquids

AbstractYarrowia lipolytica (YLL), Candida rugosa (CRL), and porcine pancreatic lipase (PPL) were employed successfully as catalysts in the enzymatic ring‐opening polymerization (ROP) of ε‐caprolactone in the presence of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1‐butylpyridinium tetrafluoroborate ([BuPy][BF4]), 1‐butylpyridinium trifluoroacetate ([BuPy][CF3COO]), 1‐ethyl‐3‐methylimidazolium nitrate ([EMIM][NO3]) ionic liquids. Poly(ε‐caprolactone)s (PCLs) with molecular weights (Mn) in the range of 300–9000 Da were obtained. 1H‐ and 13C‐NMR analyses on PCLs formed by YLL, CRL, and PPL showed asymmetric telechelic α‐hydroxy‐ω‐carboxylic acid end groups. Differences between CP‐MAS and MAS spectra are observed and discussed in terms of morphology. MALDI‐TOF spectra show the formation of at least seven species. Differential scanning calorimetry (DSC) and Wide Angle X‐Ray Scattering (WAXS) results demonstrate the high degree of crystallinity present in all the polyesters. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5792–5805, 2009

ChemInform Abstract: Solvent‐Free Chemoselective Synthesis of Some Novel Substituted 2‐Arylbenzimidazoles Using Amino Acid‐Based Prolinium Nitrate Ionic Liquid as Catalyst.

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Characterizing the properties of the cation and ion pair for the cyclic tetramethylguanidinium nitrate ionic liquid

We have carried out a detailed theoretical study for the geometrical structures and electronic properties of the cation and the ion pair of the cycle tetramethylguanidinium nitrate ionic liquid. It is found that in the cation, the triazolium ring presents almost a plane and the NMe 2 group is not coplanar with the ring. The central C2 atom carries high positive charge, which is expected to act as the most active site for the electrostatic attacking of an anion. For the ion pair, three most stable configurations have been located, where the anion lies on either side of the triazolium ring or between C5 and C6 in the cation via multiple hydrogen bonds. However, the calculated results show that the electrostatic interaction between cation and anion plays a crucial role for stabilizing the ion pair. Moreover, the charge-localized character of the cation effectively increases the electrostatic interaction between the cation and anion, which is mainly responsible for the high thermal stabilities of the ionic liquids. There is a close correlation between the charge on C2 and the relative stability of the ion pair: the more positive charge on C2, the more stable the ion pair. Natural bond orbital and frontier molecular orbital analyses reveal that the charge transfer from the anion to cation occurs mainly through the LP O → σ C – H ∗ , LP O → π C 2 – N 3 ∗ or LP O → π C 2 – N 1 ∗ interactions.

Frictional Dynamics of Alkylsilane Monolayers on SiO2: Effect of 1-n-Butyl-3-methylimidazolium Nitrate as a Lubricant

The effect of 1-n-butyl-3-methylimidazolium nitrate ionic liquid (IL) on the shear dynamics and tribological properties of contacting ordered alkylsilane self-assembled monolayers (SAM) on SiO(2) surfaces was studied using molecular dynamics simulation. Use of the IL as a lubricant was found to reduce the friction between the contacting monolayers in the studied range of applied loads. At low applied loads, complex behavior in the dependency of the frictional force on the normal load in both lubricated and dry monolayers is observed and is shown to be due to the rearrangement of the SAM chains under shear. In contrast, this dependency was found to be linear at high normal loads. The simulations also indicate that the ordering of the SAM chains may be disrupted by penetrating lubricant molecules, suggesting that the IL could incorporate into a damaged area of the SAM coating and restore tribological properties. To our knowledge, this is the first simulation study of the effect of an IL lubricant on the frictional dynamics of SAMs.

Transferable Coarse-Grained Models for Ionic Liquids

The effective force coarse-graining (EF-CG) method was applied to the imidazolium-based nitrate ionic liquids with various alkyl side-chain lengths. The nonbonded EF-CG forces for the ionic liquid with a short side chain were extended to generate the nonbonded forces for the ionic liquids with longer side chains. The EF-CG force fields for the ionic liquids exhibit very good transferability between different systems at various temperatures and are suitable for investigating the mesoscopic structural properties of this class of ionic liquids. The good additivity and ease of manipulation of the EF-CG force fields can allow for an inverse design methodology of ionic liquids at the coarse-grained level. With the EF-CG force field, the molecular dynamics (MD) simulation at a very large scale has been performed to check the significance of finite size effects on the structural properties. From these MD simulation results, it can be concluded that the finite size effect on the phenomenon of ionic liquid spatial heterogeneity (Wang, Y.; Voth, G. A. J. Am. Chem. Soc. 2005, 127, 12192) is small and that this phenomenon is indeed a nanostructural behavior which leads to the experimentally observed mesoscopic heterogeneous structure of ionic liquids.

Solvent‐free chemoselective synthesis of some novel substituted 2‐arylbenzimidazoles using amino acid‐based prolinium nitrate ionic liquid as catalyst

Abstract magnified imageA simple and eco‐friendly protocol for the synthesis of substituted 2‐arylbenzimidazoles is described. In this process, 2‐arylbenzimidazoles were prepared in the presence of a newly introduced ionic liquid prolinium nitrate [Pro]NO3 as catalyst, under solvent‐free condition. This process was performed under mild condition without using any oxidant with good to excellent yields and remarkable chemoselectivity in the absence of any byproduct. The ionic liquid can be recovered easily and reused. J. Heterocyclic Chem., 46, 74 (2009).

Molecular Dynamics Simulation of the Energetic Room-Temperature Ionic Liquid, 1-Hydroxyethyl-4-amino-1,2,4-triazolium Nitrate (HEATN)

Molecular dynamics (MD) simulations have been performed to investigate the structure and dynamics of an energetic ionic liquid, 1-hydroxyethyl-4-amino-1,2,4-triazolium nitrate (HEATN). The generalized amber force field (GAFF) was used, and an electronically polarizable model was further developed in the spirit of our previous work (Yan, T.; Burnham, C. J.; Del Popolo, M. G.; Voth, G. A. J. Phys. Chem. B 2004, 108, 11877). In the process of simulated annealing from a liquid state at 475 K down to a glassy state at 175 K, the MD simulations identify a glass-transition temperature region at around 250-275 K, in agreement with experiment. The self-intermediate scattering functions show vanishing boson peaks in the supercooled region, indicating that HEATN may be a fragile glass former. The coupling/decoupling of translational and reorientational ion motion is also discussed, and various other physical properties of the liquid state are intensively studied at 400 K. A complex hydrogen bond network was revealed with the calculation of partial radial distribution functions. When compared to the similarly sized 1-ethyl-4-methyl-1,4-imidazolium nitrate ionic liquid, EMIM+/NO3-, a hydrogen bond network directly resulting in the poorer packing efficiency of ions is observed, which is responsible for the lower melting/glass-transition point. The structural properties of the liquid/vacuum interface shows that there is vanishing layering at the interface, in accordance with the poor ion packing. The effects of electronic polarization on the self-diffusion, viscosity, and surface tension of HEATN are found to be significant, in agreement with an earlier study on EMIM+/NO3- (Yan, T.; Burnham, C. J.; Del Popolo, M. G.; Voth, G. A. J. Phys. Chem. B 2004, 108, 11877).

Liquid Structure and the Ion-Ion Interactions of Ethylammonium Nitrate Ionic Liquid Studied by Large Angle X-Ray Scattering and Molecular Dynamics Simulations

Room temperature ionic liquids (RTILs) are useful as new solvents or materials owing to their favorable properties such as negligible vapor pressure, non-flammability, and wide electrochemical window. For further development of new RTILs, it is indispensable to understand macroscopic properties as solvent and/or liquids of RTILs at a molecular or atomistic level. Here, liquid structure and the ion-ion interactions of room temperature ionic liquid ethylammonium nitrate (EAN) were studied by means of large angle X-ray scattering (LAXS) experiment and molecular dynamics simulations. X-ray interference function for EAN shows a small peak of 0.62 A–1 indicating nano-scale segregation in the ionic liquid. X-ray radial distribution function as the form of D(r) – 4πr2ρ0 evidently shows a peak of 3.4 and broad ones of 4.7, 8 and 12 A, suggesting that EAN has long range ordering in the liquid state. The intra-molecular X-ray interference function was estimated on the basis of molecular geometries found in crystals to yield the inter-molecular X-ray pair correlation functionG_mathrm{inter}mathrm{LAXS}(r). In G_mathrm{inter}mathrm{LAXS}(r), peaks of 3.0, 3.4, and 4.7 A were found as the atom-atom correlation. The peak of 3.0 A can be assigned to the atom-atom correlation of N (C2H5NH3+)mO (NO3–) in the NHmO hydrogen bonding. In addition, the peak of 3.4 A is also ascribable to C (C2H5NH3+)mO (NO3–) correlations in the CHmO interactions. Molecular dynamics simulations based on newly developed force fields to describe a series of primary ammonium cation were performed to ascribe the peaks found in G_mathrm{inter}mathrm{LAXS}(r). The X-ray interference function imathrm{MD}(s) and the pair correlation function Gmathrm{MD}(r) derived from simulations were reasonably in agreement with the experimental ones. According to the partial atom-atom correlation functions derived from the simulations, the experimentally observed peaks of 3.0 and 3.4 A can be ascribable to the NHmO and the CHmO correlations in the closest ethylammonium and nitrate interaction, respectively. The CHmO interactions may play an important role in macroscopic properties of this kind of ionic liquids.

Nitrate-containing ionic liquids as active membrane components of nitrate-selection electrodes

Two dialkylimidazolium nitrate ionic liquids (ILs) have been tested for use as an active component of plasticized PVC membranes in nitrate ion selective electrodes (ISEs). The potentiometric reversibility and the main electrochemical characteristics of the ISEs in KNO3 solutions have been studied. The test membranes contain 5% of the active component and demonstrate a near-Nernstian response to NO 3 − . The use of a more hydrophobic IL based on dioctadecylimidazolium increases the sensitivity and decreases the detection limit: the slope of the electrode function is 57 mV/pC, and C min = 3.7 · 10−6 mol/L. The pH range of the membrane performance has been studied, and the potentiometric selectivity to NO 3 − in the presence of several foreign anions has been determined. The new electrode exceeds the commercially available analogue (an ELIT 021 nitrate-selective electrode) in the detection limit and response time. The utility of the new electrode for the direct potentiometric determination of nitrate ILs in aqueous solutions has been demonstrated.

Acid–Base Property of Ethylammonium Nitrate Ionic Liquid Directly Obtained Using Ion-selective Field Effect Transistor Electrode

Abstract Ethylammonium nitrate (EAN) is a protic room-temperature ionic liquid and classified into an amphoteric solvent. The equilibrium constant KS = [EtNH2][HNO3] has directly been obtained for the first time by using an ion-selective field effect transistor (ISFET) electrode. The obtained KS value is of 10−10.0 mol2 dm−6, indicating that the neutral EAN involves HNO3 and EtNH2 molecules as much as 1.0 × 10−5 mol dm−3, or the pH (= −log[HNO3]) is 5 at 298 K.

Molecular Dynamics Simulation of Nanostructural Organization in Ionic Liquid/Water Mixtures

Molecular dynamics simulations have been carried out to investigate nanostructural organization in mixtures of 1-octyl-3-methylimidazolium nitrate ionic liquid and water at multiple water concentrations. Evolution of the polar network, water network, and micelle structures is visualized and analyzed via partial radial distribution functions. The calculated static partial structure factors show that within the range of water contents examined, polar networks, water networks, and micelles possess an approximately invariant characteristic length at around 20 A. Furthermore, the above calculations point out that, as the amount of water increases, the polar network is continuously broken up (screened) by the intruding water, while the structural organization of the water network and the micelle exhibits a turnover. At the turnover point, the most ordered micelle (cation-cation) structure and water (water-anion-water) network are formed. Thereafter, the structural organization abates drastically, and only loose micelle structure exists due to the dominant water-water interactions. The simulated turnover of structural organization agrees with the sharpest peak in the experimentally obtained structure factor in aqueous solutions of similar ionic liquids; the simulated water structure reveals that water can form liquidlike associated aggregates due to the planar symmetry and strong basicity of NO(3)-, in agreement with experiment. The turnover of structural organization of micelles results from the persistent competition between the hydrophobic interactions of the nonpolar groups and the breakup of the charged polar network with increasing water content, whereas the turnover of the water network results from the competition between the water-water and water-anion interactions.

Phase equilibria of didecyldimethylammonium nitrate ionic liquid with water and organic solvents

The phase diagrams for binary mixtures of an ammonium ionic liquid, didecyldimethylammonium nitrate, [DDA][NO 3], with: alcohols (propan-1-ol, butan-1-ol, octan-1-ol, and decan-1-ol): hydrocarbons (toluene, propylbenzene, hexane, and hexadecane) and with water were determined in our laboratory. The phase equilibria were measured by a dynamic method from T = 220 K to either the melting point of the ionic liquid, or to the boiling point of the solvent. A simple liquidus curve in a eutectic system was observed for [DDA][NO 3] with: alcohols (propan-1-ol, butan-1-ol, and octan-1-ol); aromatic hydrocarbons (toluene and propylbenzene) and with water. (Solid + liquid) equilibria with immiscibility in the liquid phase were detected with the aliphatic hydrocarbons heptane and hexadecane and with decan-1-ol. (Liquid + liquid) equilibria for the system [DDA][NO 3] with hexadecane was observed for the whole mole fraction range of the ionic liquid. The observation of the upper critical solution temperature in binary mixtures of ([DDA][NO 3] + decan-1-ol, heptane, or hexadecane) was limited by the boiling temperature of the solvent. Characterisation and purity of the compounds were determined by elemental analysis, water content (Fisher method) and differential scanning microcalorimetry (d.s.c.) analysis. The d.s.c. method of analysis was used to determine melting temperatures and enthalpies of fusion. The thermal stability of the ionic liquid was resolved by the thermogravimetric technique–differential thermal analysis (TG–DTA) technique over a wide temperature range from (200 to 780) K. The thermal decomposition temperature of 50% of the sample was greater than 500 K. The (solid + liquid) phase equilibria, curves were correlated by means of different G Ex models utilizing parameters derived from the (solid + liquid) equilibrium. The root-mean-square deviations of the solubility temperatures for all calculated data are dependent upon the particular system and the particular equation used. Comparison of the solubilities of different ammonium salts in alcohols, in hexane, in benzene, and in water are discussed.