Ionic liquid, emim

We had no good way to predict if they would be liquid, but we were lucky that many were. The class of cations that were the most attractive candidates was that of the dialkylimidazolium salts, and our particular favorite was l-ethyl-3-methylimid-azolium [EMIM]. [EMIMJCl mixed with AICI3 made ionic liquids with melting temperatures below room temperature over a wide range of compositions [8]. We determined chemical and physical properties once again, and demonstrated some new battery concepts based on this well behaved new electrolyte. We and others also tried some organic reactions, such as Eriedel-Crafts chemistry, and found the ionic liquids to be excellent both as solvents and as catalysts [9]. It appeared to act like acetonitrile, except that is was totally ionic and nonvolatile. 

All the halide exchange reactions mentioned above proceed more or less quantitatively, causing greater or lesser quantities of halide impurities in the final product. The choice of the best procedure to obtain complete exchange depends mainly on the nature of the ionic liquid that is being produced. Unfortunately, there is no general method to obtain a halide-free ionic liquid that can be used for all types of ionic liquid. This is explained in a little more detail for two defined examples the synthesis of [BMIM][(CF3S02)2N] and the synthesis of [EMIM][BF4]. 

Ionic liquids [EMIM][PF3(CT5)3] Merck Patent GmbH, Germany 2001 22... 

Chloroaluminate(III) ionic liquid systems are perhaps the best established and have been most extensively studied in the development of low-melting organic ionic liquids with particular emphasis on electrochemical and electrodeposition applications, transition metal coordination chemistry, and in applications as liquid Lewis acid catalysts in organic synthesis. Variable and tunable acidity, from basic through neutral to acidic, allows for some very subtle changes in transition metal coordination chemistry. The melting points of [EMIM]C1/A1C13 mixtures can be as low as -90 °C, and the upper liquid limit almost 300 °C [4, 6]. 

The viscosities of non-haloaluminate ionic liquids are also affected by the identity of the organic cation. For ionic liquids with the same anion, the trend is that larger allcyl substituents on the imidazolium cation give rise to more viscous fluids. For instance, the non-haloaluminate ionic liquids composed of substituted imidazolium cations and the bis-trifyl imide anion exhibit increasing viscosity from [EMIM], [EEIM], [EMM(5)IM], [BEIM], [BMIM], [PMMIM], to [EMMIM] (Table 3.2-1). Were the size of the cations the sole criteria, the [BEIM] and [BMIM] cations from this series would appear to be transposed and the [EMMIM] would be expected much earlier in the series. Given the limited data set, potential problems with impurities, and experimental differences between laboratories, we are unable to propose an explanation for the observed disparities. 

The reported densities of ionic liquids vary between 1.12 g cm for [(n-QHi7)(C4H9)3N][(CF3S02)2N] and 2.4 g cm for a 34-66 mol% [(CH3)3S]Br/AlBr3 ionic liquid [21, 23]. The densities of ionic liquid appear to be the physical property least sensitive to variations in temperature. For example, a 5 degree change in temperature from 298 to 303 K results in only a 0.3 % decrease in the density for a 50.0 50.0 mol % [EMIM]C1/A1C13 [17]. In addition, the impact of impurities appears to be far less dramatic than in the case of viscosity. Recent work indicates that the densities of ionic liquids vary linearly with wt. % of impurities. For example, 20 wt. % water (75 mol %) in [BMIM][BF4] results in only a 4 % decrease in density [33]. 

The physical properties of ionic liquids can often be considerably improved through the judicious addition of co-solvents [55-58]. Flowever, surprisingly, this approach has been relatively underutilized. Flussey and co-workers investigated the effect of co-solvents on the physical properties of [EMIM]C1/A1C13 ionic liquids [55, 56]. They found significant increases in ionic conductivity upon the addition of a variety of co-solvents. Figure 3.6-5 displays representative data from this work. The magnitude of the conductivity increase depends both on the type and amount of the co-solvent [55, 56]. 

The first examples of Horner-Wadsworth-Emmons reactions have been reported by Kitazume and Tanaka [60]. Here the ionic liquid [EDBU][OTf] was used in the synthesis of a-fluoro-a,P-unsaturated esters (Scheme 5.1-32). It was found that when K2CO3 was used as a base, the E isomer was the major product and that when DBU was used as a base, the Z isomer was the major product. The reaction was also performed in [EMIM][BF4] and [EMIM][PFgj, but gave lower yields than with [EDBU][OTf] [60]. 

Other methods of nitration that Laali investigated were with isoamyl nitrate in combination with a Bronsted or Lewis acid in several ionic liquids, with [EMIM][OTf] giving the best yields (69 %, 1.0 1.0 o p ratio). In the ionic liquid [HNEt( Pr)2] [CE3CO2] (m.p. = 92-93 °C), toluene was nitrated with a mixture of [NH4][N03] and trifluoroacetic acid (TEAH) (Scheme 5.1-37). This gave ammonium trifluoroacetate [NH4][TEA] as a by-product, which could be removed from the reaction vessel by distillation (sublimation). 

Wilkes and co-workers have investigated the chlorination of benzene in both acidic and basic chloroaluminate(III) ionic liquids [66]. In the acidic ionic liquid [EMIM]C1/A1C13 (X(A1C13) > 0.5), the chlorination reaction initially gave chlorobenzene, which in turn reacted with a second molecule of chlorine to give dichlorobenzenes. In the basic ionic liquid, the reaction was more complex. In addition to the... 

A number of commercially important fragrance molecules have been synthesized by Friedel-Crafts acylation reactions in these ionic liquids. Traseolide (5-acetyl-l,l,2,6-tetramethyl-3-isopropylindane) (Scheme 5.1-63) has been made in high yield in the ionic liquid [EMIM]C1/A1C13 (X(A1C13) = 0.67) [95]. 

The Friedel-Crafts acylation reaction has also been performed in iron(III) chloride ionic liquids, by Seddon and co-workers [96]. An example is the acetylation of benzene (Scheme 5.1-66). Ionic liquids of the type [EMIM]Cl/FeCl3 (0.50 < X(FeCl3) < 0.62) are good acylation catalysts, with the added benefit that the ketone product of the reaction can be separated from the ionic liquid by solvent extraction, provided that X(FeCl3) is in the range 0.51-0.55. 

Another means of in situ metal-carbene complex formation in an ionic liquid is the direct oxidative addition of the imidazolium cation to a metal center in a low oxidation state (see Scheme 5.2-2, route b)). Cavell and co-workers have observed oxidative addition on heating 1,3-dimethylimidazolium tetrafluoroborate with Pt(PPli3)4 in refluxing THF [32]. The Pt-carbene complex formed can decompose by reductive elimination. Winterton et al. have also described the formation of a Pt-car-bene complex by oxidative addition of the [EMIM] cation to PtCl2 in a basic [EMIM]C1/A1C13 system (free CP ions present) under ethylene pressure [33]. The formation of a Pt-carbene complex by oxidative addition of the imidazolium cation is displayed in Scheme 5.2-4. 

The oxidation of alkenes and allylic alcohols with the urea-EL202 adduct (UELP) as oxidant and methyltrioxorhenium (MTO) dissolved in [EMIM][BF4] as catalyst was described by Abu-Omar et al. [61]. Both MTO and UHP dissolved completely in the ionic liquid. Conversions were found to depend on the reactivity of the olefin and the solubility of the olefinic substrate in the reactive layer. In general, the reaction rates of the epoxidation reaction were found to be comparable to those obtained in classical solvents. 

As new compounds, very limited research has been done to evaluate the biological effects of ionic liquids. The topical effect of [EMIM]C1/A1C13 melts and [EMIMjCl on the integument of laboratory rat has been investigated. The study reports that [EMIMjCl is not in itself responsible for tissue damage. However, the chloroaluminate salt can induce tissue irritation, inflammation, and necrosis, due to the presence of aluminium chloride. However, treatments for aluminium chloride and hydrochloric acid are well documented. This study needs to be expanded to the other ionic liquids, and their toxicity need to be investigated [46]. 

At first, the reaction was investigated in batch mode, by use of different ionic liquids with wealdy coordinating anions as the catalyst medium and compressed CO2 as simultaneous extraction solvent. These experiments revealed that the activation of Wilke s catalyst by the ionic liquid medium was clearly highly dependent on the nature of the ionic liquid s anion. Comparison of the results in different ionic liquids with [EMIM] as the common cation showed that the catalyst s activity drops in the order [BARF] > [Al OC(CF3)2Ph 4] > [(CF3S02)2N] > [BFJ . This trend is consistent with the estimated nucleophilicity/coordination strength of the anions. 

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