Ionic liquids room-temperature molten salts

Ionic liquids (room-temperature molten salts, ILs) are reviewed in Section 3.5.3 of this book. They have an essentially negligible vapor pressure and the ability to dissolve a wide range of organic and inorganic compounds, which makes them an attractive alternative reaction medium to volatile organic compounds. 

Ionic liquids (room-temperature molten salts) with chiral cations were efficiently used as reaction media to prepare homochiral MOFs [33], But the use of homochiral ligands as precursors in the synthesis is even more efficient For instance, Lin et al. [34] prepared MOFs with BINOL (l,l -bi-2,2 -naphthol) and BINAP (2,2 -his(diphenylphosphino)-1,1 -binaphthyl) as chiral linkers. Unfortunately, attempts to use such chiral catalysts in asymmetric catalysis showed some but not high enantiomeric excess in the studied reactions, perhaps the flexibility of the ligands in the MOF framework is not sufficient to induce the chirality effect in the reactions. The most illustrative example was presented hy Lin [35] the reaction of asymmetric hydrogenation of aromatic ketones demonstrated a 99.2% ee for Ru-BINAP/MOF systems. 

What constitutes an ionic liquid, as distinct from a molten salt It is generally accepted that ionic liquids have relatively low melting points, ideally below ambient temperature [1, 2]. The distinction is arbitrarily based on the salt exhibiting liquidity at or below a given temperature, often conveniently taken to be 100 °C. However, it is clear from observation that the principle distinction between the materials of interest today as ionic liquids (and more as specifically room-temperature ionic liquids) and conventional molten salts is that ionic liquids contain organic cations rather than inorganic ones. This allows a convenient differentiation without concern that some molten salts may have lower melting points than some ionic liquids . 

Commonly is used a short term ionic liquid instead of room temperature ionic liquid or room temperature molten salt , which makes no distinction between salts liquid at room temperature and those liquid below 100°C. 

Figure 1.2 Captain (Dr.) John S. Wilkes at the U.S. Air Force Academy in 1979. This official photo was taken about when he started his research on ionic liquids, then called room-temperature molten salts. ...

Excision reactions are sometimes accompanied by redox chemistry. For example, dissolution of the 2D solid Na4Zr6BeCli6 in acetonitrile in the presence of an alkylammonium chloride salt results in simultaneous reduction of the cluster cores (144). Here, the oxidation product remains unidentified, but is presumably the solvent itself. As a means of preventing such redox activity, Hughbanks (6) developed the use of some room temperature molten salts as excision media, specifically with application to centered zirconium-halide cluster phases. A number of these solids have been shown to dissolve in l-ethyl-2-methylimidazolium chloride-aluminum chloride ionic liquids, providing an efficient route to molecular clusters with a full compliments of terminal chloride ligands. Such molten salts are also well suited for electrochemical studies. 

Between 1980 and about 2000 most of the studies on the electrodeposition in ionic liquids were performed in the first generation of ionic liquids, formerly called room-temperature molten salts or ambient temperature molten salts . These liquids are comparatively easy to synthesize from AICI3 and organic halides such as Tethyl-3-methylimidazolium chloride. Aluminum can be quite easily be electrode-posited in these liquids as well as many relatively noble elements such as silver, copper, palladium and others. Furthermore, technically important alloys such as Al-Mg, Al-Cr and others can be made by electrochemical means. The major disadvantage of these liquids is their extreme sensitivity to moisture which requires handling under a controlled inert gas atmosphere. Furthermore, A1 is relatively noble so that silicon, tantalum, lithium and other reactive elements cannot be deposited without A1 codeposition. Section 4.1 gives an introduction to electrodeposition in these first generation ionic liquids. 

It was John Wilkes who realized that room-temperature molten salts would only experience a widespread interest and uptake if they were stable under environmental conditions. Wilkes group published details of the first such liquid in 1992 using the BF]j" and the PFj anions, the latter showing a miscibility gap with water. Thus these liquids could, in principle, be made water free. (Today we know that ionic liquids containing BFJ and PF are subject to decomposition in the presence of water.) Electrochemical studies showed that even these early ionic liquids had wide electrochemical windows of about 4 V with cathodic limits of-2 to -2.5 V. vs. NHE. This cathodic limit should, from the thermodynamic point of view, be wide enough to electrodeposit many reactive elements. 

Molten salts constitute a category of liquids which is called ionic liquids or molten electrolytes. These liquids have some characteristics which are different from that of liquids at room temperature. Molten salt studies are very important for understanding of the liquid state because molten salts consist of ions, and the... 

Ionic liquids, mainly molten salts. These include melts for high-temperature electrochemistry and room temperature molten salts. 

Ionic liquids are sometimes, especially in the older literature, also referred to as molten salts, non-aqueous ionic liquids or room temperature molten salts. While all of these names are entirely valid, their meaning has somewhat changed over the years. The term molten salt is now used less frequently in the field of ionic liquids and generally refers to salts with melting points greater than 100°C. The expression non-aqueous ionic liquid was originally coined to differentiate synthetic ionic liquids from water, since... 

An ionic liquid (IL) , or classically a room-temperature molten salt , is an interesting series of materials being investigated in a drive to find a novel electrolyte system for electrochemical devices. ELs contain anions and cations, and they show a liquid nature at room temperature without the use of any solvents. The combination of anionic and cationic species in ILs gives them a lot of variations in properties, such as viscosity, conductivity, and electrochemical stability. These properties, along with the nonvolatile and flame-resistant nature of ILs, makes this material especially desirable for lithium-ion batteries, whose thermal instability has not yet been resolved despite investigations for a long time. In this chapter we discuss the efforts made for battery application of ILs. 

Ambient temperature molten salt can be obtained by several methods. One effective way to obtain a room-temperature molten salt is by the introduction of polyether chains to ions. The term polyether/salt hybrid is used in this chapter as a common name for polyether oligomers having anionic or cationic charge(s) on the chain (Figure 22.1). Polyethers, such as poly-(ethylene oxide) (PEO), are known as representative ion conductive polymers [1]. Polyether/salt hybrids have been studied as a kind of room-temperature molten salt apart from the development of onium-type ionic liquids [2]. The preparation of ionic liquids consisting of metal ions has been one of the important goals in this research field. Polyether/salt hybrid derivatives give one such solution for this task. 

Then what are the ionic liquids In people s usual opinions, the salts that consist of organic cations and inorganic or organic anions, in the form of liquid at or around the ambient temperature, are called usually the room-temperature ionic liquid (RTIL), the ambient-temperature ionic liquid (ATIL), or the room-temperature molten salts (RTMS), the room-temperature fused salts (RTFS), and can be called the ionic liquid (IL) for abbreviation. The feature of ionic liquids being liquid at the room temperature is attributed to the asymmetric structures of the ionic liquids with big difference in volume of anions and cations leading to little electrostatic attraction. 

Room temperature ionic liquids (RTILs) are molten salts whose melting points are below room temperature. RTILs are formed when the constituent ions are sterically mismatched, thereby hindering crystal formation [17]. As polar solvents, RTILs have unique applications as tunable and environmentally benign solvents with very low volatility, high fire resistance, excellent chemical and thermal stability and wide liquid temperature range and electrochemical windows [17-19]. Solvent applications of RTILs include, for example, organic synthesis [17,20, 21], separations [22, 23], storage and transportation of hazardous chemicals [24], polymeric electrolytes [25, 26], dissolution of natural products [27] and synthesis of hollow metal oxide microspheres [28]. 

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