Water In Room Temperature Ionic Liquids Research Articles

Detrimental effect of glass sample tubes on investigations of BF4−-based room temperature ionic liquid–water mixtures

Tetrafluoroborate (BF4−)-based ILs are susceptible to hydrolysis due to their hygroscopicity, which complicates their applications. The progress of tetrafluoroborate hydrolysis in a 2mol% N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate–water mixture was investigated by 19F and 11B NMR in both glass and plastic sample tubes. In the plastic (polypropylene) tube, hydrolysis reached equilibrium after one day, and the intrinsic hydrolysis was estimated to be 4% relative to the initial amount of BF4−. In contrast, in the glass tube, hydrolysis continued even 15days after the initial sample preparation due to reaction between glass and HF produced by the hydrolysis of BF4−. Additionally, we found that the dissolution of glass by HF proceeds slowly enough at 4°C that it can be ignored for approximately 1day. Therefore, experiments using BF4−-based ionic liquids can be carried out in glass tube at low temperatures of around 4°C, provided that they are performed quickly following sample preparation, or in plastic tube.

Direct Evidence of Confined Water in Room-Temperature Ionic Liquids by Complementary Use of Small-Angle X-ray and Neutron Scattering.

The direct evidence of confined water ("water pocket") inside hydrophilic room-temperature ionic liquids (RTILs) was obtained by complementary use of small-angle X-ray scattering and small-angle neutron scattering (SAXS and SANS). A large contrast in X-ray and neutron scattering cross-section of deuterons was used to distinguish the water pocket from the RTIL. In addition to nanoheterogeneity of pure RTILs, the water pocket formed in the water-rich region. Both water concentration and temperature dependence of the peaks in SANS profiles confirmed the existence of the hidden water pocket. The size of the water pocket was estimated to be ∼3 nm, and D2O aggregations were well-simulated on the basis of the observed SANS data.

Protonated/deprotonated properties of a room temperature ionic liquid–water system: N, N-Diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate

The pH oscillations related to the protonation/deprotonation process in a room temperature ionic liquid (RTIL)–water system were observed at fixed temperatures. The RTIL was hydrophilic N, N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate ([DEME][BF4]). The rhythmic oscillations of pH were observed only at a water concentration of approximately 90mol%, where the equilibrated pH value was approximately 3. In contrast, in the water-poor region from 6 to 10mol% H2O, the pH was almost constant at approximately 8 within the investigated timeframe. The acid–base properties of the [DEME][BF4]–water mixture are related to particular aggregations in the liquid phase.

UV–vis spectroscopic study of room temperature ionic liquid–water mixtures: N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate

N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate, [DEME][BF4], and H2O mixtures were investigated in optical properties by UV–visible spectroscopy. The concentration region of H2O in the mixtures was 0–100mol%. At room temperature, the mixtures of H2O exhibit absorption peaks at around 280nm and 750nm, which depend on H2O concentrations. At 90–95mol% H2O, the optical transmittance decreased over the whole region of UV–visible light. In X-ray diffraction, correlation over the medium-range such as network-forming materials develops at 90–95mol%. Also, in quenched glass, low glass transition temperature appeared at these H2O concentrations. The specific glass is induced by different molecular aggregation in liquid. Therefore, an optical anomaly is connected with the specific water network over the medium-range order.

Computational studies of room temperature ionic liquid–water mixtures

Room temperature ionic liquids (IL) have been used in numerous applications in chemistry. Addition of water alters many of their properties making it possible to custom design solvents for specific applications. Along with experiments, computational studies using various approaches have provided key insights into the structure and dynamics of IL systems, as well as aggregate formation and phase behavior of the IL/water mixtures. These systems provide computational challenges since ILs and IL/water mixtures are viscous liquids with intrinsically slow processes and structural organization over surprisingly large length scales, which push the limits of applicability of the available techniques. Recent developments in the studies of IL/water mixtures using computational methodologies are reviewed and the future prospects for the field are briefly discussed.

Water Solubility in Ionic Liquids and Application to Absorption Cycles

The absorption cooling cycle has been in use for more than 100 years. Although the vapor compression cycle is now used for most air-conditioning and refrigeration applications, the well-known refrigerant−absorbent systems (water−LiBr and ammonia−water) are still being used for space cooling and industrial refrigeration. Recently, absorption cooling cycles using water + room-temperature ionic liquids (RTILs) have been proposed as a replacement for the water + LiBr system. There have been a few reports in the literature since about the year 2000 on the solubility of water in RTILs, and some of the hydrophilic RTILs show extremely high mutual solubility with water, indicating formation of chemical complexes. Almost all solubility data have been correlated with the use of activity (or solution) models. In the present report, we apply an equation of state (EOS) model in order to understand the solubility characteristics, as well as the chemical complex formation, consistently with the same thermodynamic model....

The Partitioning Behavior of Tyramine and 2‐Methoxyphenethylamine in a Room Temperature Ionic Liquid–Water System Compared to Traditional Organic–Water System

Ionic liquids have been proposed as replacements for volatile organic solvents (VOSs) by a range of authors, due to their very low vapor pressure, ability to dissolve a range of organic, inorganic, and organometallic compounds, immiscibility with water, and ability to form biphasic systems depending on the choice of cation/anion combination making up the ionic liquid. In this study the room temperature ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate [bmim][PF6] was synthesized and a range of physical properties including the interfacial tension, viscosity, and density determined. The distribution of tyramine and 2‐methoxyphenethylamine (MPEA) as a function of pH was determined for the [bmim][PF6] system. This was compared to distribution data obtained for these solutes in conventional organic solvent/water systems: xylene/tributylphosphate (TBP)/water and xylene/Benzyl alcohol (BA)/water.