Imidazolium ionic hquids

Metal hahdes in imidazolium ionic hquids offer unique enviromnents able to facihtate dehydration reactions. Under such conditions certain metal halides are able to catalyze formal hydride transfer reactions that otherwise do not occur in the ionic liquid media. We have now discovered two systems in which this transformation has been observed. The initial system involves the conversion of glucose to fractose followed by dehydration the second system involves the dehydration of glycedraldehyde dimer followed by isomerization to lactide. CrCls" anion is the only catalyst that has been effective for both systems. VCI3" is effective for the glyceraldehyde dimer system but not for glucose. 

Another common reaction is the chlorination of alkenes to give 1,2-dihaloalka-nes. Patell et al. reported that the addition of chlorine to ethene in acidic chloroalu-minate(III) ionic liquids gave 1,2-dichloroethane [68]. Under these conditions, the imidazole ring of imidazolium ionic liquid is chlorinated. Initially, the chlorination occurs at the 4- and 5-positions of the imidazole ring, and is followed by much slower chlorination at the 2-position. This does not affect the outcome of the alkene chlorination reaction and it was found that the chlorinated imidazolium ionic Hquids are excellent catalysts for the reaction (Scheme 5.1-39). 

Jodry J J, Mikami K. New chiral imidazolium ionic hquids 3D-net-work of hydrogen bonding. Tetrahedron Lett. 2004. 45, 4429-4431. 

Mu Z, Zhou F, Zhang S, et al. Preparation and characterization of new phosphonyl-substimted imidazolium ionic hquids. Helv. Chim. Acta. 2004. 87, 2549-2555. 

F. Rodrigues, G.M. Do Nascimento, and P.S. Santos, Dissolution and doping of polyaniline emeraldine base in imidazolium ionic hquids investigated by spectroscopic techniques, Macromol. Rapid Commun., 28, 666 69 (2007). 

The palladium-catalyzed Heck reactions of 3- and 2-bromothiophene 111 with the electron-rich olefins butyl vinyl ether 112 and allyl alcohol 114 proceed effectively in the ionic hquid l-butyl-3-methylimidazolium tetrafluoroborate (Scheme 47) [340], The special feature of this reaction is that only branched olefin products are formed using the imidazolium ionic hquid, whereas the utilization of normal solvents gives rise to a mixture of regioisomers. 

H. L. Ngo, K. LeCompte, L. Hargens, A. B. McEwan, Thermal properties of imidazolium ionic hquids. Thermochim. Acta 2000, 357-358, 97. 

Dobbelin M, Pozo-Gonzalo C, Marcilla R, Blanco R, Segura JL, Pomposo JA, Mecerreyes D (2009) Electrochemical synthesis of PEDOT derivatives bearing imidazolium-ionic hquid moieties. J Polym Sci Pol Chem 47(12) 3010-3021. doi 10.1002/Pola.23384... 

Leclercq, L. Schmitzer, A. (2009a). Supramolecular effects involving the incorporation of guest substrates in imidazolium ionic hquid networks Recent advances and future... 

C. G. Hanke, N. A. Atamas and R. M. Lynden-Bell. Solvahon of small molecnles in imidazolium ionic hquids A simulation study. Green Chem. 4, 2002, 107. 

The rhodium catalyzed carbonylation of ethylene and methanol can be conducted in the absence of added alkyl halide if the reactions are conducted in iodide based ionic liquids or molten salts. In the case of ethylene carbonylation, the imidazolium iodides appeared to perform best and operating in the absence of ethyl iodide gave improved selectivities relative to processes using ethyl iodide and ionic hquids. In the case of... 

The pyridinium- and the imidazolium-based chloroaluminate ionic liquids share the disadvantage of being reactive with water. In 1990, Mike Zaworotko (Figure 1.4) took a sabbatical leave at the Air Force Academy, where he introduced a new dimension to the growing field of ionic Hquid solvents and electrolytes. 

In the binary haloaluminate ionic liquids, an increase in the mole percent of the imidazolium salt decreases the density of the Hquid (see Table 3.2-2). The bromo-aluminate ionic Hquids are substantially denser than their chloroaluminate counterparts, being between 0.57 g cm and 0.83 g cm denser than the analogous chloroaluminate ionic liquids (see Table 3.2-2). Variation of the substituents on the imidazolium cation in the chloroaluminate ionic liquids has been shown to affect the density on the basis of the cation size [17]. 

The room temperature conductivity data for a wide variety of ionic liquids are listed in Tables 3.6-3, 3.6-4, and 3.6-5. These tables are organized by the general type of ionic Hquid. Table 3.6-3 contains data for imidazolium-based non-haloaluminate alkylimidazolium ionic Hquids, Table 3.6-4 data for the haloaluminate ionic Hquids, and Table 3.6-5 data for other types of ionic Hquids. There are multiple listings for several of the ionic liquids in Tables 3.6-3-3.6-5. These represent measurements by different researchers and have been included to help emphasize the significant vari-... 

Diels lder reactions Neutral ionic liquids have been found to be excellent solvents for the Ehels-Alder reaction. The first example of a Diels-Alder reaction in an ionic Hquid was the reaction of methyl acrylate with cyclopentadiene in [EtNH3][N03] [40], in which significant rate enhancement was observed. Howarth et al. investigated the role of chiral imidazolium chloride and trifluoroacetate salts (dissolved in dichloromethane) in the Diels-Alder reactions between cyclopentadiene and either crotonaldehyde or methacroHne [41]. It should be noted that this paper describes one of the first examples of a chiral cationic ionic Hquid being used in synthesis (Scheme 5.1-17). The enantioselectivity was found to be < 5 % in this reaction for both the endo (10 %) and the exo (90 %) isomers. 

Ionic liquid crystals are liquid crystals containing ionic moieties. Ionic hquid crystals having ammonium and pyridinium salts were reported to show stable thermotropic liquid crystalline behavior [35 0]. Seddon, Bruce, and coworkers showed that some imidazolium and pyridinium salts exhibit low melting points and liquid crystalline behavior [41]. Ionic liquid crystals with lower temperature mesophase ranges are called hquid crystalline ionic liquids. A large variety of thermotropic liquid crystaUine ionic liquids exhibiting anisotropic fluid states were prepared. In particular, the ionic liquid crystals based on imidazolium salts 1 [42-46], 2... 

Yagupolskii Y L, Sokolenko T M, Petko K I, et al. Novel ionic hquids -imidazolium salts with a difluoromethylene fragment directly bonded to the nitrogen atom. J. Eluorine Chem. 2005. 126, 669-672. 

Kohnen G, Tosoni M, Tussetschlaeger S et al (2009) Counterion effects on the mesomorphic properties of chiral imidazolium and pyiidinium ionic hquids. Eur J Org Chem 32 5601-5609... 

Liu Z, Chen ZC, Zheng QG (2003) Mild oxidation of alcohols with o-iodoxybenzoic acid (IBX) in ionic hquid l-buthyl-3-methyl-imidazolium chloride and water. Org Lett 5 3321-3323... 

Crescenzo AD, Demurtas D, Fontana A et al (2009) Disaggregation of single-walled ctubon nanotubes (SWNTs) promoted by the ionic hquid-based surfactant l-hexadecyl-3-vinyl-imidazolium bromide in aqueous solution. Soft Matter 5 62-66... 

Yu P, Zhou H, Mao LQ et al (2009) A facile approach to construction of a stable water-miscible ionic hquid/electrolyte interface with interactions between imidazolium moiety and carbon nanotubes. Electrochem Commun 11 1393-1396... 

Thermal Stability According to a literature search, it is known that ionic liquids are thermally stable (300°C to 400°C). The imidazohum salts are reported to be thermally stable up to 300°C. Above 300°C, there is a cleavage of the C-N bond of the imidazolium nitrogen and the carbon of the alkyl chain (57, 66-68). It was found that different anions also affect the thermal properties of the ionic hquids (66-68). Ionic liquids with less nucleophilic or coordinating anions show a higher thermal stability (66-69). 

With respect to the ionic hquid s cation the situation is quite different, since catalytic reactions with anionic transition metal complexes are not yet very common in ionic liquids. However, the 1,3-dialkyhmidazolium cation can act as a hgand precursor for the dissolved transition metal. Its transformation under the reaction conditions into a ligand has been observed in three different ways (i) formation of metal carbene complexes by oxidative addition of the imidazolium cation (ii) formation of metal-carbene complexes by deprotonation followed by coordination of the imidazolylidene on the metal center (iii) dealkylation of the imidazolium cation and formation of a metal imidazole complex. These different ways are displayed in a general form in Scheme 5.3-2. 

In addition to the inter cial structure of the imidazolium cation, the organization of water at the sur ce was also determined using water-equilibrated ionic liquids. Here, nearly identical ice-like and water-like features were observed for both the water-silica sur ce and the water-containing ionic hquid-silica surface. Moreover, the water molecules assoc ted with the ionic liquids at the silica inter- ce were hydrogen-bonded in small, sttucturally defined configurations with the bis(perfluoroalkylsulfonyl)imide anions, consistent with previous infrared spectroscopic studies of similar materials [47]. 

Imidazolium cations can be deprotonated by bases to form neutral carbenes. These carbenes are surprisingly stable and can be distilled. The ionic hquid can be recycled by further reaction of the carbene with an acid. 

Different P Fg or NTfj imidazolium-based ionic liquids have been used as solvents and electrolytes for several typical electrochemistry reactions. Although the structure of molecular solvents and ILs are expected to be quite different, the main result is that the use of ionic hquids does not modify the nature of the mechanisms investigated using conventional organic media. An effect of the structure of ILs can nevertheless be observed in the case of bimolecular reactions (e.g., oxidative electrodimerization), as kinetic rate constants are lower in ionic liquids than in conventional polar solvents. This phenomenon cannot be simply attributed to the high viscosity of ILs but may be explained by a specific solvation of the reactants due to a high degree of ion association in ILs [59]. 

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