Dialkylimidazolium tetrafluoroborate

In comparison, the l,3-dialkylimidazolium-2-carboxylate isolated by Tommasi et al. [27, 40] was revealed to be a more versatile catalyst that allowed the synthesis of benzoylacetic acid from benzophenone and C02 in good yield and under mild conditions (isolated yield 81%). The presence of tetrafluoroborate- or tetraphenyl-borate sodium salts in the reaction was essential, as this allowed the formation of the related 1,3-dialkylimidazolium tetrafluoroborate or tetraphenylborate and the concomitant quantitative trans-carboxylation to sodium benzoylacetate. Likewise, compounds such as acetone, cyclohexanone, and phenylacetonitrile could also be converted with this system to afford the corresponding carboxylate salts (methyl a-cyanophenylacetate) (Scheme 5.8). Following the same general procedure, acetone was carboxylated, being simultaneously the cosolvent and reagent. 

The use of 1,3-dialkylimidazolium tetrafluoroborates and other ionic solvents in catalytic reactions is discussed. 

Scheme 2 One-pot five-component synthesis of 1,3-dialkylimidazolium tetrafluoroborate ILs.

A relatively inexpensive route to halide-free tetrafluoroborate ionic liquids has been reported, shown in Scheme 2.3. In this one-pot reaction between glyoxal, methylamine, w-butylaminc, formaldehyde, and tetrafluoroboric acid a mixture of dialkylimidazolium tetrafluoroborate salts... 

Abstract The corrosion of metals (copper, zinc, and plain carbon steel) in dialkylimidazolium tetrafluoroborates depends on the presence of traces of impurities in the ionic liquids. Water, chlorides, and especially simultaneous presence of the both impurities enhances the pitting corrosion of metals. The products of corrosion contain the metal of interest as well as nitrogen, boron, chlorine, fluorine, carbon, and oxygen. 

Dialkylimidazolium tetrafluoroborates belong to the most well-known ionic liquids, and they have been studied with respect to their possible applications in organic synthesis [1,2], biocatalysis [3,4], extraction [5,6], as electrolytes in chemical power sources including electrochemical capacitors [7,8], as heat-transfer media [9,10], in chemical analysis [11,12] as lubricants [13,14], etc. 

Dialkylimidazolium ionic liquids with BF4 and IT), anions are quite stable and while being polar (see below) are also non-nucleophilic. They can be prepared in a variety of ways, most commonly by metathesis reactions21-23 and also by a methylation reaction.24 These reactions are illustrated in Schemes 2 and 3, respectively. The chloride produced in the metathesis reactions (Scheme 2) is very difficult to remove completely and it effects the physical properties of the liquid and can also effect certain reactions carried out in the liquid. Figure 6 shows how the viscosity of l-butyl-3-methylimidazolium tetrafluoroborate varies with chloride concentration.25... 

Ionic liquids have recently appeared as clean alternatives to classical organic solvents for a wide variety of biochemical processes due to their unique properties [22-26]. Ionic liquids are organic salts which are liquid close to room temperature. They normally consist of an organic cation (e.g. dialkylimidazolium, tetraalkylam-momium) and a polyatomic inorganic cation (e.g. hexafluorophosphate, tetrafluoroborate, bis(trifluoromethylsulphonyl)imide) (Fig. 8.2). 

Heck couplings of aryl halides with alkenes in room temperature ionic liquids have been reported [44]. Dialkylimidazolium and n-hexylpyridinium hexafluoro-phosphate and tetrafluoroborate ionic liquids were used as solvents, Pd(OAc)2 and PdCl2 as catalysts, and an amine as base. Addition of ligands such as triphe-nylphosphine, tri-o-tolylphosphine, and triphenylarsine usually had a negative affect on product yield. Addition of cosolvents such as DMF was not necessary. Palladium-catalyzed Heck reactions involving aryl bromides have been performed... 

Researchers have also prepared and studied nonaqueous RMs where water has been replaced by polar solvents that possess relatively high dielectric constants and that are immiscible with the continuous nonpolar solvent [6].These nonaqueous RMs have attracted interest from both fundamental and practical perspectives [48-69]. As reaction media, these RMs are particularly attractive for water-sensitive reactions [70]. In this sense, ionic liquids (ILs) emerge as a powerful and attractive alternative to conventional molecular organic solvents [71-76], and they have received much attention as a class of neoteric solvents [71-83]. The most commonly used ILs are based on A,A -dialkylimidazolium cations, especially l-butyl-3-methyUmidazohuin, [bmim], with different anions such as tetrafluoroborate [BFJ or bis(trifluoromethylsulfonyl) imide [Tf N]" (see structures in Fig. 14.3). Recent studies on RMs with an IL... 

Dialkylimidazolium-based tetrafluoroborate and hexafluorophosphate were the most studied ILs because of their facile preparation and purification process. It was well known that these anions would be degraded when contacted with moisture or exposed to microwaves, heat, and so on. Although the two anions all could produce F in the process of degradation, there was still a difference in the final products. 

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