Room-temperature ionic liquids imidazolium-type

The first MW-assisted intramolecular Stetter reaction was reported for the synthesis of chromanone derivatives using the imidazolium type of room temperature ionic liquids (RTILs) with thiazolium salts and Et3N as catalysts <2006ASC1826>. 

Van Leeuwen and coworkers [117] prepared a Xantphos-type ligand for application in RTILs (room-temperature ionic liquids) bearing remote imidazolium groups (Scheme 2.34). In the first step, the xanthene-based backbone was functionalized by Friedel-Crafts acylation using 5-bromovaleraldehyde. After reduction of the keto groups, two POP units were introduced. Final incorporation of methyl-imidazolium groups yielded the final ligand. In the first runs of the rhodium-catalyzed hydroformylation of 1-octene in [BMlM][PFg], a diminished activity was noted, obviously due to incomplete conversion of the precatalyst into... 

Zhou et al. have used the 3-ethyl-5-(2-hydroxyethyl)-4-methylthiazolium bromide for the microwave-assisted intramolecular Stetter reaction using imidazolium-type room temperature ionic liquids (RTILs) as solvents. The intramolecular Stetter reaction of ( )-methyl 4-(2-formylphenoxy) but-2-enoate was selected as a model to optimize the reaction conditions, using butylmethylimidazolium tetrafluoroborate [bmim]+[BF4]- as the solvent. It is known that salts of various heterocycles, including imidazolium salts, can also be used as catalysts. Therefore, the ionic liquids used as solvent is also able to function as a catalyst, even if it is less active than the usual thiazolium salts, and the yields of the desired product in that case are very poor. Subsequently, it was observed that when the quantity of thiazolium salt increased from 5 to 15 mol%, the yield improved accordingly to 96%. Under microwave irradiation, a variety of aromatic substrates undergo the intramolecular Stetter... 

Imidazolium-type room temperature ionic liquids (RTTLs) have been used for the Stetter reaction, affording the desired 1,4-dicarbonyl compounds (e.g. 167) in good yields together with the benzoin (e.g. 168). Thiazolium salts and EtsN are efficient catalysts for this reaction performed in ionic liquid. The possibility to recycle and reuse the solvent has been demonstrated, although it was not possible to recycle the thiazolium catalyst (Anjaiah et al. 2004). 

The electrochemical studies on EDOT and PEDOT have been extended by Re5molds and colleagues to the electropolymerization in the presence of so-called ionic liquids. They built supercapacitors of PEDOT and PProEXDT as electrode couples and investigated their switching and storage properties. This supercapacitor type was applied for a patent. The room-temperature ionic liquid material between the PEDOT and PProDOT electrodes consisted of l-ethyl-3-methyl- 1-H-imidazolium bis(trifluoromethylsulfonyl)imide (EMI-BTI) (see Figure 14.8) and was not used in pure form, but in propylene carbonate (PC) solution. 

The synthesis of cycUc carbonates from epoxides and CO2 (Scheme 1) is one of the major ways to transform CO2 to valuable chemicals. The first successful synthesis of cyclic carbonate using room temperature ILs of imidazolium and pyridinium salts was reported by Peng and Deng in 2001 [9]. It has been shown that cycloaddition of CO2 to propylene oxide (PO) producing propylene carbonate (PC) is effectively catalyzed by [BMIm]BF4. PO was quantitatively converted to PC with 2.5 MPa of CO2 at 110°C for 6 h in the presence of 2.5 mol% [BMIm]BF4. After the reaction, PC was distilled from the reaction mixture and the catalyst was recycled up to four times with only a minor loss in activity. The ionic liquid catalyst is recyclable for the cycloaddition of CO2 to PO. They also showed that the type of either cation or anion affect the activity of the ILs. The activity decreased in the orders of [BMIm]+ > [BPy]+ and of BF4 > Cl > PFe". 

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 liquid. Table 3.6-3 contains data for imidazolium-based non-haloaluminate alkylimidazolium ionic liquids. Table 3.6-4 data for the haloaluminate ionic liquids, and Table 3.6-5 data for other types of ionic liquids. 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-... 

The densities of ionic liquids are also affected by the choice of the cation and anion. For imidazolium ionic liquids the density decreases slightly as the alkyl chain of the cation increases in length. In addition, the absoption of water by ionic liquids by increasing nitric acid concentration can also cause a decrease in the density (Giridhar et al. 2004). Regarding imidazolium-based ionic liquids, by increasing the alkyl chain it was found that the surface tension decreased due to the orientation of hydrocarbon tails on the surface (Kilaru et al. 2007). The vapour pressure of an ionic liquid is usually unmeasurable at room temperature. Studies on the thermal stability of ionic liquids showed that the type of the associated anion has the primary effect on the thermal stability of the ionic liquids (Holbrey and Seddon... 

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