Ionic task-specific

The second element of general importance in the synthesis of a task-specific ionic liquid is the source of the functional group that is to be incorporated. Key to success here is the identification of a substrate containing two functional groups with different reactivities, one of which allows the attachment of the substrate to the core, and the other of which either is the functional group of interest or is modifiable to the group of interest. Functionalized alkyl halides are commonly used in this capacity, although the triflate esters of functionalized alcohols work as well. 

Although the first ionic liquid expressly categorized as being task-specific featured the incorporation of the function within the cation core, subsequent research has focused on the incorporation of functionality into a branch appended to the cation [11]. In this fashion, a number of task-specific ionic liquids built up from 1-methyl- and 1-butylimidazole have been prepared, produced by means of the reaction between these imidazoles and haloalkanes also incorporating a desired functional group (Scheme 2.3-1). Bazureau has used this approach to prepare imida-... 

Scheme 2.3-1 General synthesis of task-specific ionic liquids from l-alkylimidazoles.

Scheme 2.3-4 Synthesis of a cheiating task-specific ionic iiquid and its utiiization for metai...

Figure 2.3-5 Imidazolium-based task-specific ionic iiquids with cation-appended fiuorous taiis.

Apart from being employed solely as solvents, ILs can also be used as reagent carriers (TSlLs, task-specific ionic liquids). An efficient system that uses ILs as solvents and anchoring/acylating reagents for the CAL B-catalyzed separation of racemic alcohols is shown in Scheme 5.17 [69]. 

Visser AE, Swatloski RP, Reichert WM, Mayton R, Sheff S, Wierzbicki A, Davis JH, Rogers RD (2001) Task-specific ionic liquids for the extraction of metal ions from aqueous solutions. Chem Commun 1 135-136... 

Visser, A.E., Swatloski, R.P., Reichert, W.M. et al. (2001) Task-Specific Ionic Liquids for the Extraction of Metal Ions from Aqueous Solutions. Chemical Communications, 1, 135-136. 

Using a similar protocol, Loupy and coworkers have reported the synthesis of chiral ionic liquids based on (ll ,2S)-(-)-ephedrinium salts under microwave irradiation conditions (Scheme 4.21a) [75]. Importantly, the authors were also able to demonstrate that the desired hexafluorophosphate salts could be prepared in a one-pot protocol by in situ anion-exchange metathesis (Scheme 4.21b). The synthesis and transformation of so-called task-specific ionic liquids is discussed in more detail in Section 7.4. 

The second group of recently developed ionic liquids is often referred to as task specific ionic liquids in the literature [15]. These ionic liquids are designed and optimised for the best performance in high-value-added applications. Functionalised [16], fluorinated [17], deuterated [18] and chiral ionic liquids [19] are expected to play a future role as special solvents for sophisticated synthetic applications, analytical tools (stationary or mobile phases for chromatography, matrixes for MS etc.), sensors and special electrolytes. 

Figure 7.3. Examples of task specific ionic liquids...

In recent times, the development of new ionic liquids has made great progress. Important developments include a range of new halogen-free ionic liquids (e.g., benzenesulfonates [13], toluenesulfonates, alkylsulfates [14], hydro-gensulfate [15, 16], dicyanamides [17], thiocyanates [18], etc.), as well as functionalized (task-specific) [19-23], fluorinated [24], deuterated [25] and chiral ionic liquids [26-30]. 

Ionic liquids have also been applied in transfer hydrogenation. Ohta et al. [110] examined the transfer hydrogenation of acetophenone derivatives with a formic acid-triethylamine azeotropic mixture in the ionic liquids [BMIM][PF6] and [BMIM][BF4]. These authors compared the TsDPEN-coordinated Ru(II) complexes (9, Fig. 41.11) with the ionic catalyst synthesized with the task-specific ionic liquid (10, Fig. 41.11) as ligand in the presence of [RuCl2(benzene)]2. The enantioselectivities of the catalyst immobilized by the task-specific ionic liquid 10 in [BMIM][PF6] were comparable with those of the TsDPEN-coordinated Ru(II) catalyst 9, and the loss of activities occurred one cycle later than with catalyst 9. 

Fig. 41.11 R u-complex and task-specific ionic liquid for the hydrogenation of acetophenone derivatives.

Furthermore, to clarify the difference between task specific ionic hquids (or also called functionahzed ionic hquids) and chiral ionic hquids, one very successful example of a task specific ionic hquid 63 is presented in Scheme 65. This catalyst with a loading of 15 mol% under neat conditions gave up to 100% yield and 99% ee in the Michael addition of cyclohexanones to nitroolefms [179]. This catalyst belongs to the field of the prohne catalyzed reactions. 

Legeay JC, Goujon JY, Eynde JJV, Toupet L, Bazureau JP (2006) Liquid-phase synthesis of polyhydroquinoline using task-specific ionic liquid technology. J Comb Chem 8 829-833... 

Dong F, Jun L, Xinli Z, Zhiwen Y, Zuliang L (2007) One-pot green procedure for Biginelli reaction catalyzed by novel task-specific room-temperature ionic liquids. J Mol Catal A Chem 274 208-211... 

Ionic liquids are also alternative reaction media considered as green, mostly because of their lack of vapor pressure and the possibility of reuse [68, 69]. Base-catalyzed Knoevenagel reactions have been described in these media [70-73]. The development of task specific ionic liquids in which the solvent and promoter are coupled is a real breakthrough in the field and some of them have been used in the Knoevenagel condensation [74—81]. 

Keywords Asymmetric synthesis, Chiral ionic liquids, Ion pairing, Local structure. Nuclear Overhauser effect. Task-specific ionic liquids... 

In addition, ILs bearing one or more functional groups on the cation or anion able to impart specific properties have also been synthesized and applied as designer media in catalysis and material sciences [13]. These salts, which are generally defined task-specific ionic liquids (TS-ILs), may show an increased... 

Supported analogs of ionic liquid catalysts Task specific ionic liquids (TSIL) Telomerization in ILs... 

The literature of room temperature ionic liquids (RTILs) was reviewed to select and report on those RTILs involved directly in chemical reactions either as a solvent for a catalyst, a conversion agent, or a task specific ionic liquid. Special emphasis was placed on manuscripts appearing in the literature in the last ten years. 

---