Ionic liquids in electrochemical devices and processes: managing interfacial electrochemistry

Investigation on solvation and protonation of meso-tetrakis(p-sulfonatophenyl)porphyrin in imidazolium-based ionic liquids by spectroscopic methods

The solvation and protonation of the meso-tetrakis(p-sulfonatophenyl)porphyrin (TPPS) were investigated by spectroscopic methods in pure or mixed imidazolium-based ionic liquids: 1-butyl-3-methyl-imidazolium terafluoroborate ([MBIM]BF(4)), 1-butylimidazolium terafluoroborate ([HBIM]BF(4)), 1-butyl-imidazolium dodecylalkylbenzenesulfonate ([HBIM]DS), 1-butyl-imidazolium p-toluenesulfonate ([HBIM]TS) and 1-butyl-imidazolium methylsulfonate ([HBIM]MS). Compared with absorption properties of TPPS in aqueous solution, Soret band of TPPS monomer was obviously red-shifted in the ionic liquids, while special absorption of TPPS J-aggregates was located at higher energy level, 483 nm and 702 nm, in protonic ionic liquids (PILs) [HBIM]BF(4). Next, the protonation of TPPS in aprotonic ionic liquids (AILs, i.e., [MBIM]BF(4)) is dependent not only on the concentration of protonic ionic liquids as proton sources, but also on the characteristic of anion and viscosity of PILs. The proton transfer constants between TPPS and four protonic ionic liquids are (2.32 +/- 0.23) x 10(2) for [HBIM]BF(4), (1.52 +/- 0.08) x 10(2) for [HBIM]MS, (1.12 +/- 0.21) x 10(2) for [HBIM]DS and (0.84 +/- 0.45) x 10(2) for [HBIM]TS, respectively.

On the chemical stabilities of ionic liquids

Ionic liquids are novel solvents of interest as greener alternatives to conventional organic solvents aimed at facilitating sustainable chemistry. As a consequence of their unusual physical properties, reusability, and eco-friendly nature, ionic liquids have attracted the attention of organic chemists. Numerous reports have revealed that many catalysts and reagents were supported in the ionic liquid phase, resulting in enhanced reactivity and selectivity in various important reaction transformations. However, synthetic chemists cannot ignore the stability data and intermolecular interactions, or even reactions that are directly applicable to organic reactions in ionic liquids. It is becoming evident from the increasing number of reports on use of ionic liquids as solvents, catalysts, and reagents in organic synthesis that they are not totally inert under many reaction conditions. While in some cases, their unexpected reactivity has proven fortuitous and in others, it is imperative that when selecting an ionic liquid for a particular synthetic application, attention must be paid to its compatibility with the reaction conditions. Even though, more than 200 room temperature ionic liquids are known, only a few reports have commented their effects on reaction mechanisms or rate/stability. Therefore, rather than attempting to give a comprehensive overview of ionic liquid chemistry, this review focuses on the non-innocent nature of ionic liquids, with a decided emphasis to clearly illuminate the ability of ionic liquids to affect the mechanistic aspects of some organic reactions thereby affecting and promoting the yield and selectivity.

Lithium-Ion-Conducting Electrolytes: From an Ionic Liquid to the Polymer Membrane

This work concerns the design, the synthesis, and the characterization of the N-butyl-N-ethylpiperidinium N,N-bis(trifluoromethane)sulfonimide (PP(24)TFSI) ionic liquid (IL). To impart Li-ion transport, a suitable amount of lithium N,N-bis-(trifluoromethane)sulfonimide (LiTFSI) is added to the IL. The Li-IL mixture displays ionic conductivity values on the order of 10(-4) S cm(-1) and an electrochemical stability window in the range of 1.8-4.5 V vs Li(+)/Li. The voltammetric analysis demonstrates that the cathodic decomposition gives rise to a passivating layer on the surface of the working electrode, which kinetically extends the stability of the Li/IL interface as confirmed by electrochemical impedance spectroscopy measurements. The LiTFSI-PP(24)TFSI mixture is incorporated in a poly(vinylidene fluoride-co-hexafluoropropylene) matrix to form various electrolyte membranes with different LiTFSI-PP(24)TFSI contents. The ionic conductivity of all the membranes resembles that of the LiTFSI-IL mixture, suggesting an ionic transport mechanism similar to that of the liquid component. NMR measurements demonstrate a reduction in the mobility of all ions following the addition of LiTFSI to the PP(24)TFSI IL and when incorporating the mixture into the membrane. Finally, an unexpected but potentially significant enhancement in Li transference number is observed in passing from the liquid to the membrane electrolyte system.

New insights into the fundamental chemical nature of ionic liquid film formation on magnesium alloy surfaces

Ionic liquids (ILs) based on trihexyltetradecylphosphonium coupled with either diphenylphosphate or bis(trifluoromethanesulfonyl)amide have been shown to react with magnesium alloy surfaces, leading to the formation a surface film that can improve the corrosion resistance of the alloy. The morphology and microstructure of the magnesium surface seems critical in determining the nature of the interphase, with grain boundary phases and intermetallics within the grain, rich in zirconium and zinc, showing almost no interaction with the IL and thereby resulting in a heterogeneous surface film. This has been explained, on the basis of solid-state NMR evidence, as being due to the extremely low reactivity of the native oxide films on the intermetallics (ZrO2 and ZnO) with the IL as compared with the magnesium-rich matrix where a magnesium hydroxide and/or carbonate inorganic surface is likely. Solid-state NMR characterization of the ZE41 alloy surface treated with the IL based on (Tf)2N(-) indicates that this anion reacts to form a metal fluoride rich surface in addition to an organic component. The diphenylphosphate anion also seems to undergo an additional chemical process on the metal surface, indicating that film formation on the metal is not a simple chemical interaction between the components of the IL and the substrate but may involve electrochemical processes.

Structural Characterization of Novel Ionic Salts Incorporating Trihalide Anions

The crystal structures of several low-melting salts containing trihalide ions, namely 1-ethyl-3-methylimidazolium tribromide ([C2mim][Br3]), 1-ethyl-1-methylpyrrolidinium tribromide ([C2mpyr][Br3]), and 1-propyl-1-methylpyrrolidinium triiodide ([C3mpyr][I3]), are reported for the first time. Thermal analysis reveals that the tribromide salts are lower-melting than their monohalide analogues. Analysis of the crystal structures allows examination of the influence of the anions on the physical properties of the salts.

Room-temperature and low-ordered, amphotropic-lyotropic ionic liquid crystal phases induced by alcohols in phosphonium halides

Tri- n-decylmethylphosphonium chloride and bromide ( 1P10X) salts are not liquid crystalline. However, mesophases are induced by adding very small amounts of an alcohol or water. The temperature ranges of the induced smectic A 2 (SmA 2) liquid-crystalline phases can be very broad and the onset temperatures can be below room temperature depending upon the concentration of the alcohol or water and the structure of the alcohol. At least one molar equivalent of hydroxyl groups is necessary to convert the 1P10X completely into a liquid crystal. Strong association between the hydroxyl groups of an alcohol or water and the head groups of the 1P10X is indicated by spectroscopic, diffraction, and thermochemical data. Unlike many other smectic phases, those of the 1P10X/alcohol complexes are easily aligned in strong magnetic fields and the order parameters of selectively deuterated alcohols as measured by (2)H NMR spectroscopy, approximately 10 (-2), are much lower than the values found when the host is a commonly employed thermotropic liquid crystal. The dependence of the specific values of the order parameters on temperature, the nature of the halide anion, and the structure and concentration of the alcohol are reported. In sum, a detailed picture is presented to explain how and why an alcohol or water induces liquid crystallinity in the 1P10X salts. The data also provide a blueprint for designing media with even lower order parameters that can be hosts to determine the conformations and shapes of guest molecules.