Physical and chemical properties, of ionic liquids

Many ionic liquids have been widely investigated with regard to applications other than as liquid solvents such as electrolytes, phase-transfer reagents, surfactants, and fungicides and biocides. The physical and chemical properties of ionic liquids can be varied over a wide range by the selection of suitable cations and anions. Some of the properties that depend on the cation and anion selection includes melting point, viscosity, density, acidity and coordination ability, solvation strength and solubility characteristics. ... 

The spectrum of physical and chemical properties of ionic liquids is much larger than that of classical organic or inorganic solvents. As well as wide liquid ranges, they offer ranges of physical properties such as density and viscosity and also have high heat conductivities. In addition, the miscibilities of ionic liquids with organic... 

The advantages and disadvantages of these solvents are shown in Table 1.1. A number of interesting and useful properties of ionic liquids can be exploited, and a summary of the most important physical and chemical properties of ionic liquids, along with their applications in synthetic chemistry, is shown in Table 1.2. Ionic liquids are sometimes described in the literature using other terms, including... 

An effective assessment of the use of ionic liquids as solvents in commercial liquid-liquid extraction and extractive distillation processes requires consideration of numerous factors associated with the thermo-physical and chemical properties of ionic liquids as well as the economical and environmental impact of the use of ionic liquids in the chemical and petrochemical industry. 

The chloroaluminate(III) ionic liquids - [EMIM][C1-A1C13], for example (where EMIM is l-ethyl-3-methylimidazolium) - are liquid over a wide range of AICI3 concentrations [24]. The quantity of AICI3 present in the ionic liquid determines the physical and chemical properties of the liquid. When the mole fraction, X(A1C13), is below 0.5, the liquids are referred to as basic. When X(A1C13) is above 0.5, the liquids are referred to as acidic, and at an X(A1C13) of exactly 0.5 they are referred to as neutral. 

There is a broad spectrum of physical and chemical properties among ionic liquids, allowing their tailoring for a wide range of applications (23). 

The quantity of AICJ3 present in the ionic liquid determines the physical and chemical properties of the liquid. When the mole fraction, X(AlCl3), is below 0.5 the liquids... 

The physical and chemical properties of the ionic liquids that make them interesting as potential solvents and in other applications are listed below. 

Highly Lewis-acidic chloroaluminate ionic liquids (ILs) are well known to be both versatile solvents and effective catalysts for Friedel-Crafts reactions [1,2]. Tailoring the physical and chemical properties of the ILs to the needs of a specific reaction allows for a high diversity of applications [3,4]. We could show that immobilising these ILs on inorganic supports yields very active catalysts for alkylation reactions. The immobilisation of ionic liquids leads to novel Lewis-acidic catalysts (NLACs). The methods presented include the method of incipient wetness (method 1, further on called NLAC I), which has been introduced in detail by Hoelderich et al. f5], but focus of this presentation lies on the methods 2 (NLAC II) and 3 (NLAC III). 

Suarez P A Z, Einloft S, Dulhus J E L, et al. Synthesis and physical-chemical properties of ionic liquids based on l-n-butyl-3-methylimi-dazolium cation. J. Chem. Phys. Phys. Chem. Biol. 1998. 95, 1626-1639. 

Water is unusual in all its physical and chemical properties (Table 2.23). Its boiling point (abnormally high), its density changes (maximum density at 4 °C, not at freezing point), its heat capacity (highest of any liquid except ammonia), and the high dielectric constant as well as the measurable ionic dissociation equilibrium, for example, are not what one would expect by comparison of water with other similar substances (hydrides). All the physical and chemical properties of water make our climate system unique and have shaped the course of chemical evolution. Water is the medium in which the first cell arose, and the solvent in which most biochemical... 

Ionic liquids (ILs) are low-melting-point salts, thus forming liquids that consist only of cations and anions. They are often applied to any compounds that have a melting point less than 100°C. The first useful IL, ethylammonium nitrate, described by Walden, seems to have generated little interest it was not until the 1980s that the physical and chemical properties of this salt were investigated [1]. This was followed by the discovery that several tetraalkylammonium salts form air- and moisture-stable ILs of... 

Membranes are semi-permeable barriers that are used to isolate and separate constituents from a fluid stream. The separatirai process can be accomplished through a number of physical and chemical properties of the membrane as well as the material being separated. Separation can occur through processes such as size, ionic char, solulnlity, and combinations of several processes. Membranes can remove materials ranging from large visible particles to molecular and ionic chemical species. Membrane materials are diverse and can consist of synthetic polymers, natural fabrics, porous metals, porous ceramics, or liquids. The surface of the membrane can be chemically or biologically altered to perform separations on specific chemical... 

IC-MS has also been applied for the characterization of ionic liquids (IL) and for the investigation of their long-term stability under process-like conditions. The term ionic liquid commonly refers to a class of molten salts that are by definition liquid below 100 °C. They usually consist of bulky organic cations such as alkylated imidazole, pyrrole, or pyridine derivatives, or quatemized alkyl amines and alkyl phosphines. Common counterions are halides, alkyl sulfates, fluorinated hydrocarbons, carboxylic acids, or amino acids [268]. The physical and chemical properties of ILs are customizable by different cation-anion combinations and by the length of the alkyl chain of the cation. Depending on the... 

The history of ionic liquids is well documented, and it is widely recognised that the work of Walden produced the first recorded materials that were deliberately ionic and molten at ambient temperature [1]. The classification of ionic liquids as salts that are liquid below 100°C is arbitrary and non-satisfactory because it does not answer the philosophical question When is an ionic liquid not an ionic liquid This seemingly poindess pedantry is inportant, as almost all uses of ionic fluids involve the dissolution of molecular conponents. The issue is therefore how much solute can be added before the molecular character dominates the ionic character. It has been shown by numerous authors that the inclusion of a small amount of certain inpurities can have a profound effect upon the physical and chemical properties of an ionic liquid 12-4]. 

In the following, the physical and chemical properties of such solvents that make them suitable for dissolving electrolytes and permit their ionic dissociation are presented and discussed. Properties of liquids not included in this limited list can be found in such compilations as [1-3]. Some of the solvents that are listed have low permittivities and are not particularly suited for the dissolution of electrolytes and their ionic dissociation, but have been employed for special purposes, such as in mixtures with water (e.g., 1,4-dioxane) or because of special donor properties (such as tetrahydrothiophene). Another solvent listed, ammonia, is not liquid at ambient conditions, but becomes so at low temperatures and moderately high pressures, and its ion solvation properties have been extensively studied. 

From the above discussion, the question arises as to how the relative arrangement of the ions, and the relative contributions of the diverse long and short range interactions between anions and cations, in particular hydrogen bond network formation, affect the physical and chemical properties of the bulk ionic liquid. In certain cases, specific and preferential interactions have indeed been made responsible for improvements in chemical applications (see below). 

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