- Anion Analysis of Ionic Liquids and Ionic Liquid Purity Assessment by Ion Chromatography
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The simultaneous determination of halide impurities (fluoride, chloride, bromide, and iodide) and ionic liquid (IL) anions (tetrafluoroborate, hexafluorophosphate, and triflimide) using ion chromatography was developed with a basic, non-gradient ion chromatography system. The non-gradient method uses the eluent Na2CO3/NaHCO3in water/acetonitrile (70:30 v:v) on the AS 22 column to enable a rapid and simultaneous analysis of different IL and halide anions within an acceptable run-time (22 min) and with good resolution R of larger than 2.4, a capacity k′ between 0.4 and 5.1, selectivities α between 1.3 and 2.1, and peak asymmetries Asof less than 1.5. Halide impurities below 1 ppm (1 mg·L–1of prepared sample solution) could be quantified. A range of ionic liquids with tetrafluoroborate [BF4]–, hexafluorophosphate [PF6]–, and bis(trifluoromethylsulfonyl)imide (triflimide) [NTf2]–anions combined with cations based on imidazole, pyridine, and tetrahydrothiophene could be analyzed for their anion purity. The IL-cations do not influence the chromatographic results. With the analysis of 18 ILs differing in their cation-anion combination we could prove the general applicability of the described method for the anion purity analysis of ionic liquids with respect to halide ions. The IL-anion purity of most ILs was above 98 wt %. The highest IL-anion purity was 99.8 wt %, implying anion impurities of only 0.2 wt %. The used halide anion from the synthesis route was the major anion impurity, yet with chloride also bromide and fluoride (potentially from hydrolysis of [BF4]–) were often detected. When iodide was used, at least chloride but sometimes also bromide and fluoride was present. However, even if the IL-anion content is above 99 wt %, it does not necessarily indicate an ionic liquid devoid of other impurities. From the IC analysis, one can also deduce a possible cation impurity if one takes into account the expected (calculated) IL-anion content. A matching experimental and theoretical IL-anion content excludes, a higher experimental content indicates the presence of residual KBF4, NH4PF6, or LiNTf2salt from the halide to IL-anion exchange.
- Rutz, Christina,Schmolke, Laura,Gvilava, Vasily,Janiak, Christoph
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supporting information
p. 130 - 135
(2017/02/05)
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- Densities and viscosities of imidazolium and pyridinium chloroaluminate ionic liquids
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The chloroaluminate ionic liquids are used in various types of reactions. However, due to their particular vulnerability on water, their physical properties have not been previously investigated very extensively. The densities and viscosities of series imidazolium and pyridinium chloroaluminate ionic liquids having alkyl (butyl, hexyl, octyl) or aralkyl (benzyl, ethylphenyl) chain at the cation, various effective molar fraction of AlCl3 (χAlCl3 = 0.5, 0.65, 0.7), as well as they mixture and mixture with common organic solvents (hexane, toluene) were measured at the temperature range 293.15-343.15 K (20-70 °C). Densities, and particularly viscosities decrease with the increase of temperature. The density decreases with the increase of the length of the alkyl chain. The type of cation also influences the density, however, the order is different than for non-haloaluminate ionic liquids and depends on the alkyl chain length. Viscosity increases with increasing alkyl chain length, but it is not a linear trend. The ionic liquid with meta position of the alkyl chain is considerably more dense and more viscous than para isomer. The presence of aromatic phenyl ring at the side chain of the cation increases both density and viscosity. Higher effective molar fraction of AlCl3 increases density and decreases viscosity, however, for the imidazolium ionic liquid the change of viscosity diminishes at higher temperatures. Organic solvents decrease both density and viscosity of the ionic liquids, but aliphatic hexane imposes much smaller effect than aromatic toluene. The mixture of two ionic liquids has density and viscosity between those for constituents. This extends the application of the aralkyl ionic liquids over temperatures, in which they are in solid state.
- Och?dzan-Siod?ak, Wioletta,Dziubek, Katarzyna,Siod?ak, Dawid
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- Does alkyl chain length really matter? Structure-property relationships in thermochemistry of ionic liquids
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DSC was used for determination of reaction enthalpies of synthesis of ionic liquids [Cnmim][Cl]. A combination of DSC with quantum chemical calculations presents an indirect way to study thermodynamics of ionic liquids. The indirect procedure for vaporization enthalpy was validated with the direct experimental measurements by using thermogravimetry. First-principles calculations of the enthalpy of formation in the gaseous phase have been performed for the ionic species using the CBS-QB3 and G3 (MP2) theory. Experimental DSC data for homologous series of alkyl substituted imidazolium, pyridinium, and pyrrolidinium based ionic liquids with anions [Cl] and [Br] were collected from the literature. We have shown that enthalpies of formation, enthalpies of vaporization, and lattice potential energies are linearly dependant on the alkyl chain length. The thermochemical properties of ILs generally obey the group additivity rules and the values of the additivity parameters for enthalpies of formation and vaporization seem to be very close to those for molecular compounds.
- Verevkin, Sergey P.,Zaitsau, Dzmitry H.,Emel'Yanenko, Vladimir N.,Ralys, Ricardas V.,Yermalayeu, Andrei V.,Schick, Christoph
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- Parallel microwave-assisted synthesis of ionic liquids and screening for denitrogenation of straight-run diesel feed by liquid-liquid extraction
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Fifty-six ionic liquids were efficiently synthesized in parallel format under one-pot, solvent-free microwaveassisted synthesis. These compounds were evaluated as extracting agents of nitrogen-containing compounds from a real Diesel feed before being submitted to the hydrodesulfurization process to obtain ultralow sulfur Diesel. Our results showed that halogenated ionic liquids are an excellent alternative due to these ionic liquids are relatively inexpensive, presenting a high selectivity for the extraction of nitrogen-containing compounds and can be regenerated and recycled.
- Ceron, Miguel A.,Guzman-Lucero, Diego J.,Palomeque, Jorge F.,Martinez-Palou, Rafael
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experimental part
p. 427 - 432
(2012/07/01)
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- Preparation of second generation ionic liquids by efficient solvent-free alkylation of N-heterocycles with chloroalkanes
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Non-conventional techniques, such as microwave (MW) and power ultrasound (US) as well as combined MW/US irradiation, have been used to promote one-pot synthesis of second-generation ionic liquids (ILs), cutting down reaction times and improving yields. However, the use of chloroalkanes in the alkylation of N-heterocycles requires more drastic conditions if results are to match those obtained with more reactive alkyl halides. The present paper describes a series of MW- or MW/US-promoted IL preparations starting from chloroalkanes and classic heterocycles (1-methylimidazole, pyridine and 1-methylpyrrolidine). When reactions were carried out under conventional heating in an oil bath they required longer reaction times and gave poorer yields. 1H-NMR analysis and ion-exchange chromatography showed that the present solventless procedure afforded ILs of satisfactory purity. The observed high yields (usually 70-98% isolated), and short reaction times showed that a straightforward access to ILs can be also achieved with the use of alkyl chlorides, resulting in a considerable reduction of costs.
- Cravotto, Giancarlo,Gaudino, Emanuela Calcio,Boffa, Luisa,Leveque, Jean-Marc,Estager, Julien,Bonrath, Werner
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p. 149 - 156
(2008/09/17)
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- Thermodynamic Properties of N-octyl-, N-decyl- and N-dodecylpyridinium Chlorides in Water
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Densities, heat capacities and enthalpies of dilution at 25 deg C and osmotic coefficients at 37 deg C were measured for N-octyl-, N-decyl- and N-dodecylpyridinium chlorides in water over a wide concentration region.Conductivity measurements were performed in order to evaluate the cmc and the degree of counterion dissociation.Partial molar volumes, heat capacities, relative enthalpies and nonideal free energies and entropies at 25 deg C were derived from the experimental data as functions of the surfactant concentration.The changes with concentration of these properties are quite regular with the exception of the heat capacities which display anomalies at about 0.9, 0.25 and 0.12 mol-kg-1 for the octyl, decyl and dodecyl compounds, respectively.At these concentrations there were also changes in the slopes of the specific conductivity and of the product of the osmotic coefficients and the molality vs. concentration.These pecularities can be ascribed to micelle structural transitions.The thermodynamic functions of micellization were graphically evaluated on the basis of the pseudo-phase transition model.These data have been compared to those for alkyltrimethylammonium bromides and alkylnicotinamide chlorides.It is shown that the introduction of the hydrophilic CONH2 group lowers the hydrophilic character of the pyridinium ring. KEY WORDS: N-octylpyridinium chloride; N-decylpyridinium chloride; N-dodecylpyridinium chloride; densities; heat capacities; enthalpies of dilution; osmotic coefficients; activity coefficients; partial molar volumes; partial molar heat capacities; partial molar relative enthalpies; nonideal free energies; nonideal entropies; thermodynamics of micellization
- Causi, S.,Lisi, R. De,Milioto, S.
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p. 1031 - 1058
(2007/10/02)
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