Ionic liquid, anions properties

Effect of Anion on Ionic Liquid Physicochemical Properties... 

Pringle J M, Golding J, Baranyai K, et al. The effect of anion fluorina-tion in ionic liquids—physical properties of a range of bis(methanesul-fonyl)amide salts. New J. Chem. 2003. 27, 1504-1510. 

However, there are still some problans to be solved, since most information of ionic liquids are not well known up to now and most of works are only performed in laboratory. The relationships between the properties and the structure of ionic liquids are not well understood. Variafions in cafions and anions can produce a large number (10 ) of ionic liquids, and properties of ionic liquids depend on the structure of ions. 

The most studied ionic liquids (ILs) in the literature are chloroaluminate-based ionic liquids. Chemical properties such as Lewis acidity depend on the nature of the anion, namely AI2CI7. Considering the acidity parameter as the key point to design a liquid-phase fluorination catalyst, a new range of acidic ILs has been set up [9]. These ILs have been synthesized starting from halogenated metallic acids MX, (with M = Ti, Nb, Ta, Sn, Sb and X = Cl and/or F), such as Ta(V)Cl Fj, Nb(V)Cl Fj, Ti(IV)Cl Fj, Sn(IV)Cl Fj, Sb(V)Cl Fj,. Among these compounds, anions derived from SbCl F, (x -i-y = 5,0[Pg.536]

Kurig, H., M. Vestli, K. Tonurist, A. Janes, and E. Lust. 2012. Influence of room temperature ionic liquid anion chemical composition and electrical charge delocalization on the supercapacitor properties. Journal of the Electrochemical Society 159 A944-A951. 

Ionic liquid anion nature also has an influence on the properties of Eu-containing luminescent materials [42]. The l-methyl-3-tetradecyl imidazolium ionic liquid with N(CN)2, CF3SO3, and N(CF3S02)2 anions doped with 1 % of [EuCl2Phen2(H20)2] C1DH20 complex was prepared, and the influence of the IL anion nature on luminescent spectra and lifetimes of europium complex was investigated. Therefore the presented Eu-containing ILs can be considered as potential perspective components for new optical materials and devices. 

Puntus LN, Pekareva IS, Ly ssenko KA et al (2010) Influence of ionic liquid anion nature on the properties of Eu-containing luminescent materials. Opt Mater 32 707-710... 

Torriero AAJ, Shiddiky MJA, Bullock JP, Boas JF, MacFarlane DR, Bond AM (2010) Electrooxidation of [(tf-CsHslFelCOljJj as a probe of the nucleophilic properties of ionic liquid anions. Inorg Chem 49(5) 2502-2511... 

The following discussion concerns the thermal liquidus ranges available in different ionic liquids, as functions of cation and anion structure and composition. In particular, those structural features of cation and anion that promote these properties (while providing other desirable, and sometimes conflicting characteristics of the liquid, such as low viscosity, chemical stability, etc.) and variations in liquidus ranges and stabilities are the focus of this chapter. 

The presence of several anions in these ionic liquids has the effect of significantly decreasing the melting point. Considering that the formation of eutectic mixtures of molten salts is widely used to obtain lower melting points, it is surprising that little effort has been put into identifying the effects of mixtures of cations or anions on the physical properties of other ionic liquids [17]. 

A wide variety of physical properties are important in the evaluation of ionic liquids (ILs) for potential use in industrial processes. These include pure component properties such as density, isothermal compressibility, volume expansivity, viscosity, heat capacity, and thermal conductivity. However, a wide variety of mixture properties are also important, the most vital of these being the phase behavior of ionic liquids with other compounds. Knowledge of the phase behavior of ionic liquids with gases, liquids, and solids is necessary to assess the feasibility of their use for reactions, separations, and materials processing. Even from the limited data currently available, it is clear that the cation, the substituents on the cation, and the anion can be chosen to enhance or suppress the solubility of ionic liquids in other compounds and the solubility of other compounds in the ionic liquids. For instance, an increase in allcyl chain length decreases the mutual solubility with water, but some anions ([BFJ , for example) can increase mutual solubility with water (compared to [PFg] , for instance) [1-3]. While many mixture properties and many types of phase behavior are important, we focus here on the solubility of gases in room temperature IFs. 

Ionic liquids have been described as designer solvents [11]. Properties such as solubility, density, refractive index, and viscosity can be adjusted to suit requirements simply by making changes to the structure of either the anion, or the cation, or both [12, 13]. This degree of control can be of substantial benefit when carrying out solvent extractions or product separations, as the relative solubilities of the ionic and extraction phases can be adjusted to assist with the separation [14]. Also, separation of the products can be achieved by other means such as, distillation (usually under vacuum), steam distillation, and supercritical fluid extraction (CO2). 

Depending on the coordinative properties of the anion and on the degree of the cation s reactivity, the ionic liquid can be regarded as an innocent solvent, as a ligand (or ligand precursor), as a co-catalyst, or as the catalyst itself... 

Obviously, there are many good reasons to study ionic liquids as alternative solvents in transition metal-catalyzed reactions. Besides the engineering advantage of their nonvolatile natures, the investigation of new biphasic reactions with an ionic catalyst phase is of special interest. The possibility of adjusting solubility properties by different cation/anion combinations permits systematic optimization of the biphasic reaction (with regard, for example, to product selectivity). Attractive options to improve selectivity in multiphase reactions derive from the preferential solubility of only one reactant in the catalyst solvent or from the in situ extraction of reaction intermediates from the catalyst layer. Moreover, the application of an ionic liquid catalyst layer permits a biphasic reaction mode in many cases where this would not be possible with water or polar organic solvents (due to incompatibility with the catalyst or problems with substrate solubility, for example). 

Notwithstanding their very low vapor pressure, their good thermal stability (for thermal decomposition temperatures of several ionic liquids, see [11, 12]) and their wide operating range, the key property of ionic liquids is the potential to tune their physical and chemical properties by variation of the nature of the anions and cations. An illustration of their versatility is given by their exceptional solubility characteristics, which make them good candidates for multiphasic reactions (see Section 5.3.4). Their miscibility with water, for example, depends not only on the hydrophobicity of the cation, but also on the nature of the anion and on the temperature. 

The ease of formation of the carbene depends on the nucleophilicity of the anion associated with the imidazolium. For example, when Pd(OAc)2 is heated in the presence of [BMIM][Br], the formation of a mixture of Pd imidazolylidene complexes occurs. Palladium complexes have been shown to be active and stable catalysts for Heck and other C-C coupling reactions [34]. The highest activity and stability of palladium is observed in the ionic liquid [BMIM][Brj. Carbene complexes can be formed not only by deprotonation of the imidazolium cation but also by direct oxidative addition to metal(O) (Scheme 5.3-3). These heterocyclic carbene ligands can be functionalized with polar groups in order to increase their affinity for ionic liquids. While their donor properties can be compared to those of donor phosphines, they have the advantage over phosphines of being stable toward oxidation. 

The purity of ionic liquids is a key parameter, especially when they are used as solvents for transition metal complexes (see Section 5.2). The presence of impurities arising from their mode of preparation can change their physical and chemical properties. Even trace amounts of impurities (e.g., Lewis bases, water, chloride anion) can poison the active catalyst, due to its generally low concentration in the solvent. The control of ionic liquid quality is thus of utmost importance. 

The types of ionic liquids shown in Figure 5.4 have been most extensively studied, especially ones based on chloroaluminate. Whilst these chloroaluminate materials also display useful Lewis acid properties they are highly air and moisture sensitive, which renders them relatively commercially unattractive. Newer ionic liquids containing C104 and NOa anions, for example, which are less air and moisture sensitive, are now being more widely studied, but these are less catalytically active. Other than lack of vapour pressure and catalytic properties there are several other features common to most ionic liquids that make them attractive reaction solvents. These include ... 

The anion in an ionic liquid can be varied, too. Many ionic liquids contain relatively simple inorganic anions, such as nitrate (NO3 ), tetrafluoroborate (BF4 ), or hexafluorophosphate (PFg ). Anions that are more exotic also are possible, such as the two shown below. Varying the anion provides another way of tuning the properties of an ionic liquid to match a desired application. 

Significant progress has been made in the application of ionic liquids (ILs) as alternative solvents to C02 capture because of their unique properties such as very low vapour pressure, a broad range of liquid temperatures, excellent thermal and chemical stabilities and selective dissolution of certain organic and inorganic materials. ILs are liquid organic salts at ambient conditions with a cationic part and an anionic part. 

Many ionic liquids are based on N,N-dialkylimidazolium cations (BMI) which form salts that exist as liquids at, or below, room temperature. Their properties are also influenced by the nature of the anion e. g. BF T PFg. The C-2(H) in imidazole is fairly labile but the C-4(H) and the C-5(H) are less so. Under microwave-enhanced conditions it is therefore possible to introduce three deuterium atoms (Scheme 13.4). As hydrogen isotope exchange is a reversible reaction this means that the three deuterium atoms can be readily exchanged under microwave irradiation. For storage purpose it might be best to back-exchange the C-2(D) so that the 4,5-[2H2] isotopomer can be safely stored as the solid without any dangers of deuterium loss. The recently... 

There are many good reasons for applying ionic liquids as alternative solvents in transition metal catalysed reactions. Besides their very low vapour pressure and then-good thermal stability [33], an important advantage is the possibility of tuning then-solubility [34] and acidity/coordination properties [35] by varying the nature of the anions and cations systematically. 

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