Dialkylimidazolium conductivity

In recent years ionic liquids have also been employed as media for reactions catalyzed both by isolated enzymes and by whole cells, and excellent reviews on this topic are already available [47]. Biocatalysis has been mainly conducted in those room-temperature ionic liquids that are composed of a 1,3-dialkylimidazolium or N-alkylpyridinium cation and a noncoordinating anion [47aj. 

Room temperature ionic liquids (RTILs), such as those based on A,A-dialkylimidazolium ions, are gaining importance (Bradley, 1999). The ionic liquids do not evaporate easily and thus there are no noxious fumes. They are also non-inflammable. Ionic liquids dissolve catalysts that are insoluble in conventional organic chemicals. IFP France has developed these solvents for dimerization, hydrogenation, isomerization, and hydroformylation reactions without conventional solvents. For butene dimerization a commercial process exists. RTILs form biphasic systems with the catalyst in the RTIL phase, which is immiscible with the reactants and products. This system is capable of being extended to a list of organometallic catalysts. Industrial Friedel-Crafts reactions, such as acylations, have been conducted and a fragrance molecule tra.seolide has been produced in 99% yield (Bradley, 1999). 

The physical properties of ionic liquids have been extensively studied and some trends are beginning to emerge. In particular, ionic liquids based on 1,3-dialkylimidazolium cations have been investigated in detail, partly due the their wide use as solvents to conduct synthesis and catalysis. The attraction of the imidazolium cation in synthetic applications is because the two substituent groups can be varied to modify the properties of the solvent. For example, Table 4.1... 

Friedel-Crafts and related reactions conducted in a dialkylimidazolium haloaluminate appear in increasing frequency. The splitting of ethers with simultaneous acylation to afford alkyl benzoates is a recent example. ... 

This observation was supported by subsequent evaluations from the same group [22] who conducted a comprehensive study on the biological effects of 1,3-dialkylimidazolium ionic liquids on luminescent bacteria (Vibriofisdwri) and two... 

Fannin, A.A., Floreani, D.A., King, L.A., Landers, J.S., Piersma, B.J., Stech, D.J., Vaughn, R. L., Wilkes, J.S., Williams, J.L. Properties of 1,3-dialkylimidazolium chloride aluminum-chloride ionic liquids. 2. phase-transitions, densities, electrical conductivities, and viscosities. J. Phys. Chem. 88, 2614-2621 (1984)... 

Ionic liquids are salts that form a stable fluid at or near room temperature and are expected to replace hazardous and volatile organic solvents because they have low vapor pressure, non flammability, high polarity and relative inertness. Most ionic liquids consist of bulky organic cations, for example Af,Af-dialkylimidazolium, A-alkylpyridinium, quaternary ammonium, quaternary phosphonium, and common weakly coordinating anions such as AlCU", Bp4 , PP6 , CFsSOs", TfO , (CP3S03)2N and some of them, such as Af,Af-dialkylimidazolium salts, show excellent conductivity [222]. Typical chemical structures of cations and anions are reported in Fig. 1.19. 

This study, and a H NMR study conducted in parallel on single ionic liquids with ethanol as cellulose model, clearly demonstrated that as halide anions exhibit strong and preferential interactions with the H2 of the 1,3-dialkylimidazolium cation rather than with the cellulose (or ethanol) hydroxyl group, the cellulose-dissolving anion... 

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