RESUMO
The low-viscous tricyanomethanide ([TCM](-))-based ionic liquids (ILs) are gaining increasing interest as attractive fluids for a variety of industrial applications. The thermophysical properties (density, viscosity, surface tension, electrical conductivity and self-diffusion coefficient) of the 1-alkyl-3-methylimidazolium tricyanomethanide [Cnmim][TCM] (n = 2, 4 and 6-8) IL series were experimentally measured over the temperature range from 288 to 363 K. Moreover, a classical force field optimized for the imidazolium-based [TCM](-) ILs was used to calculate their thermodynamic, structural and transport properties (density, surface tension, self-diffusion coefficients, viscosity) in the temperature range from 300 to 366 K. The predictions were directly compared against the experimental measurements. The effects of anion and alkyl chain length on the structure and thermophysical properties have been evaluated. In cyano-based ILs, the density decreases with increasing molar mass, in contrast to the behavior of the fluorinated anions, being in agreement with the literature. The contribution per -CH2- group to the increase of the viscosity presents the following sequence: [PF6](-) > [BF4](-) > [Tf2N](-) > [DCA](-) > [TCB](-) > [TCM](-). [TCM](-)-based ILs show lower viscosity than dicyanamide ([DCA](-))- and tetracyanoborate ([TCB](-))-based ILs, while the latter two exhibit a crossover which depends both on temperature and the alkyl chain length of the cation. The surface tension of the investigated ILs decreases with increasing alkyl chain length. [C2mim][TCM] shows an outlier behavior compared to other members of the homologous series. The surface enthalpies and surface entropies for all the studied systems have been calculated based on the experimentally determined surface tensions. The relationship between molar conductivity and viscosity was analyzed using the Walden rule. The experimentally determined self-diffusion coefficients of the cations are in good agreement with the molecular simulation predictions, in which a decrease of the self-diffusion of the cations with increasing alkyl chain length is observed with a simultaneous increase in viscosity and for the longer alkyl lengths the anion becomes more mobile than the cation.
RESUMO
A validated ion chromatographic method was developed and applied for the determination of the maximum solubility of pyridinium ionic liquids in several aromatic solvents. Elution was performed on a Metrosep C3-150 prototype column at 40°C with acetonitrile-water at a flow rate of 1.0 mL min(-1). Mixtures of pyridinium ionic liquids and aromatic solvents were diluted with acetonitrile and acetone on a 1:1:2 weight base before the analysis. The chromatographic time only took 20 min. The standard curves for both pyridinium ionic liquids ([4-mebupy]BF4 and [3-mebupy]N(CN)2) were linear (r(2) = 0.9980-0.9998) in all aromatic solvents (toluene, benzene, ethylbenzene and o-xylene) in the concentration range of 5.37-241 mg kg(-1). The intraday relative standard deviations (n = 3) for peak areas were 0.60-2.9%. Accuracy in the measurement of samples ranged from 98.5 to 105%. The limit of detection for both pyridinium ionic liquids in all solvents varied between 0.73 and 2.6 mg kg(-1). This assay has been successfully applied in the determination of the maximum solubilities of both pyridinium ionic liquids in several aromatic solvents. This method demonstrated that with increasing aromatic character and/or temperature the solubilities of both investigated pyridinium ILs in the aromatic solvents increase. This is primary caused by the nature of the anion.
RESUMO
Analysis of primary amines in aqueous samples remains a challenging analytical issue. The preferred approach by gas chromatography is hampered by interactions of free silanol groups with the highly reactive amine groups, resulting in inconsistent measurements. Here, we report a method for direct analysis of aliphatic amines and diamines in aqueous samples by gas chromatography (GC) with silanol deactivation using ionic liquids (ILs). ILs including trihexyl(tetradecyl)phosphonium bis 2,4,4-(trimethylpentyl)phosphinate (Cyphos IL-104), 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide [pmim][Tf(2)N] and Nâ³-ethyl-N,N,N',N'-tetramethylguanidinium tris(pentafluoroethyl)trifluorophosphate [etmg][FAP] were tested as deactivating media for the GC liner. Solutions of these ILs in methanol were injected in the system prior to the analysis of primary amines. Butane-1,4-diamine (putrescine, BDA) was used as a reference amine. The best results were obtained using the imidazolium IL [pmim][Tf(2)N]. With this deactivator, excellent reproducibility of the analysis was achieved, and the detection limit of BDA was as low as 1mM. The applicability of the method was proven for the analysis of two different primary amines (C4-C5) and pentane-1,5-diamine.
