Anion-functionalized ionic liquids

Gurkan BE, de la Fuente JC, Mindrup EM et al (2010) Equimolar C02 absorption by anion-functionalized ionic liquids. J Am Chem Soc 132(7) 2116-2117... 

The reaction of RS02Na with ArX or vinyl bromide was carried out in a binary mixture of solvents consisting of DMSO and anion-functionalized ionic liquids (Scheme 3.47) [85]. 

The introduction of functional groups on cations and (or) anions of ionic liquids allows for marked changes of the physicochemical properties and imparts a particular reactivity pattern to the ionic liquid. TSILs usually display negligible vapor pressure, a physical property close to analogous non-functionalized ILs. Other physicochemical properties, such as solubility in molecular solvents or thermal stability, and chemical properties, such as complexation ability for example and reactivity, largely depend on the nature of the functional group as well [19]. 

Recent advances in ionic liquids research has provided routes for achieving functionalized ionic liquids (Fig. 4) in which a functional group is covalently tethered to the cation or anion of the ionic liquid, especially to the two N atoms of the... 

During the last 8 years [82, 83], various types of functionalized ionic liquids (Fig. 13) expressly categorized as being task-specific ionic liquids have been designed and synthesized for specific purposes such as catalysis, organic synthesis, separation of specific materials, as well as for the construction of nanostructure materials and ion conductive materials, etc. The salts are defined as functionalized ionic liquids when they are ionic liquids in which a functional group is covalently tethered to (1) the cation, (2) the anion, or (3) a zwitterionic form of the salt. It is typically the cation that bears the reactive moiety. In fact, instances in which the anion comprises the active constituent are few. 

Recently, ionic liquids with amino acids as anions were synthesized by neutralization between [C2mim][OH] and amino acids [88], Tetrabutylphosphonium amino acids [P(C4)4][AA] were synthesized by the reaction of tetrabutylphosphonium hydroxide [P(C4)4][OH] with amino acids, including glycine, L-alanine, l-/1-alanine, L-serine and L-lysine [89], The esters or amide derivatives of bromoacetic acid were either commercially available or formed in one step via the reaction of bromoacetyl bromide with the appropriate alcohol or amine [90-92], An advantage of this route is that a wide range of ester and amide side chains can be prepared easily. For ionic liquids with anions other than bromide, a metathesis reaction was employed to introduce the counter ion of choice. Additionally, functionalized ionic liquids with electrophilic alkene-type appendages were synthesized. 

In this context, a functionalized ionic liquid, 1-(2-hydroxyethyl)-3-methyl imidazolium tetrafluoroborate [hemim][BF4], is reported as an efficient and recyclable reaction medium for the palladium catalyzed Heck reaction. The olefination of iodoarenes and bromoarenes with olefins generates the corresponding products in good to excellent yields under phosphine-ffee reaction conditions. After separation of the product, fresh starting materials are charged into the recovered ionic liquid which entraps the palladium catalyst. The reactions still proceed quantitatively for six cycles, without significant loss of catalytic activity. " The effect of both the cation and the anion on the chemical yield is shown in Figure 28. 

Qearly, the potential for the development of new TSILs is limited only by the imagination of the chemists working in the area. In addition to TS ILs with either functionalized cations or functionalized anions, the first examples of dual-functionalized ionic liquids in which both cation and anion contain functionalities have also been reported [23]. So far, the combination of several functionalized cations and anions in an ion soup that would allow a tuning and further increase of task-specificity by playing with different concentrations of the individual functionalized ions has remained completely unexplored. 

A very efiicient alternative method for the synthesis of functionalized ionic liquids in a simple two-step process has been proposed by Wasserscheid et al. [29]. In this approach, the imidazole or the required nucleophile is protonated by the acid whose anion vnU be incorporated into the final ionic liquid. A Michael acceptor. 

Fukumoto K, Ohno H (2006) Design and synthesis of hydrophobic and chiral anions from amino acids as precursor for functional ionic liquids. Chem Commun 2006 3081-3083... 

New, functionalized ionic liquid material f Cation Y Anion ... 

Other commonly used anions for ionic liquids, such as tetrafluoroborate and hexafluorophosphate, also imdergo hydrolysis at sufficiently rapid rates that would cause difficulties for their use with either aqueous solvents or hydroxylic cations. While the hexafluorophosphate anion imdergoes hydrolysis most rapidly only under acidic conditions (Freire et al. 2010), the preparation of the ionic liquids using hexafluorophosphoric add can lead to significant formation of the (hydrolyzed) phosphate salt (Lall et al. 2000). Similarly, the alternative approach for the prepwation of the phosphate salts (liquid ionic phosphates, LIPs) involving the use of 98% phosphoric acid (Lall et al. 2002) similarly experiences difficulty when cations are used that bear hydroxylic sites. Presumably the "anion exchange" method (Lall et al. 2002) would not experience this difficulty, but this process is extremely ineffident for the preparation of any sizable quantity of material. Similarly, the tetrafluoroborate anion imdergoes hydrolysis sufficient rapidly (Freire, et al. 2010) and can be anticipated to read with free hydroxyhc functions such that it would not be a useful anion for ionic hquids based on carbohydrate and carbohydrate-related materials. 

Moreover, the introduction of rare earth complex anion can lead to a functional ionic liquid which can combine the properties of ionic liquid and metal irm... 

A new one phase method for the synthesis of uniform monodisperse crystalline Ag nanoparticles in aqueous systems was developed by using newly synthesized mono and dihydroxylated ionic liquids and cationic surfactants based on 1,3-disubstituted imidazolium cations and halogens anions. The hydroxyl functionalized ionic liquids and hydroxyl functionalized cationic surfactants simultaneously act both as the reducing and protective agent. By changing the carbon chain length, alcohol structure and anion of the hydoxy-functionalized 1,3-imidazolium based ionic liquids and the hydroxyl functionalized cationic surfactants the particle size, uniformity and dispersibility of nanoparticles in aqueous solvents could be controlled (Dorjnamjin et al, 2008). 

Zhao Q, Eichhorn J, Pitner WR, Anderson JL (2009) Using the solvation parameter model to characterize functionalized ionic liquids containing the tris(pentafluoroethyl)trifluorophos-phate (FAP) anion. Anal Bioanal Chem 395(l) 225-234... 

Davis introduced some complimentary strategies for the synthesis of functional ionic liquids, by the inclusion of functional group (FG) to the cationic skeleton, in his review (Davis, 2004). The called "task-specific ionic liquids" have been synthesized, for example, by N-alkylation of alkyl halides covalently linked to FG with appropriate Lewis bases (e.g., imidazole, amine, phosphine, and sulfide Scheme 2a), accompanied by the anion metathesis to realize ionic liquids. One of other strategies is to use Michael reaction of alkyl vinyl ketones linked to FG with tertiary cations, as in Scheme 2b (Wasserscheid et al., 2003). It is noteworthy that this facile one-pot reaction dispenses with the need for a further anion metathesis step and are free from haUde-containing by-product. 

Scheme 2. Schematic synthetic routes of functional ionic liquids by (a) N-alkylation reaction (Davis, 2004) and (b) Michael addition reaction (Wasserscheid et al, 2003) to form ionic liquids of functional cations, and (c) the addition of acidic group to form ionic liquids of functional anion. A blank sphere represents a Lewis base such as imidazole, amine, phosphine, and sulfide, while a sphere with a plus sign represents the corresponding cation.

---