Chloroaluminate anions

Despite the utility of chloroaluminate systems as combinations of solvent and catalysts in electrophilic reactions, subsequent research on the development of newer ionic liquid compositions focused largely on the creation of liquid salts that were water-stable [4], To this end, new ionic liquids that incorporated tetrafiuoroborate, hexafiuorophosphate, and bis (trifiuoromethyl) sulfonamide anions were introduced. While these new anions generally imparted a high degree of water-stability to the ionic liquid, the functional capacity inherent in the IL due to the chloroaluminate anion was lost. Nevertheless, it is these water-stable ionic liquids that have become the de rigueur choices as solvents for contemporary studies of reactions and processes in these media [5],... 

The synthetic routes used to prepare ionic liquids vary depending upon the ionic liquid being made. Ionic liquids with metal halide anions are, at least in principle, very simple to prepare. Scheme 4.1 illustrates the synthesis of imidazolium-based ionic liquids with a chloroaluminate anion, commencing with methylimidazole [6],... 

Ionic liquids containing chloroaluminate anions are strong Lewis acids. This characteristic, coupled with the fact that they are relatively easy to handle, makes them attractive alternatives to standard Lewis and Bronsted acids such as HF. The IL can function both as a catalyst and a solvent for acid-catalyzed processes. Some of the first reactions studied in ILs were Friedel-Crafts alkylations and arylations. The [emim][Al2Cl7] affords complete conversion of benzene and acetyl chloride to acetophenone in less than 5 minutes at room temperature. 

Chloroaluminate systems have been intensively studied over the past few decades mainly in electrochemical research fields. Many of the electrochemical properties of RTILs have been sorted out using the chloroaluminate systems [50]. Chloroaluminate anions form RTILs with various organics, including not only EMI and BP but also triazolium [51] and aliphatic onium cations [7,52-54]. Other unique RTILs similar to the chloroaluminate systems such as the chlorogallate (GaCLj ) [55], chloroborate (BCL ) [56], and bromoaluminate (AIBr4 ) systems [57] have been reported. 

The electrodeposition of metals and alloys has been investigated extensively in the chloroaluminate ionic liquids. Many kinds of metal salts, mostly chlorides, can be dissolved in ionic liquids with their Lewis acidity or basicity controlled by changing the composition of AICI3. In the case of acidic ionic liquids that contain AICI3 at more than 50 mol%, a dimeric chloroaluminate anion, AI2CI7, acts as a Lewis... 

We will discuss the results using this classification in the following way IL with chloroaluminate anions... 

The cationic nickel complex [ /3-allylNi(PR3)]+, already described by Wilke etal. [21], as an efficient catalyst precursor for alkene dimerization when dissolved in chlorinated organic solvents. It proved to be very active in acidic chloroaluminate ionic liquids. In spite of the strong potential Lewis acidity of the medium, a similar phosphine effect is observed. Biphasic regioselective dimerization of propylene into 2,3-dimethylbutenes can then be achieved in chloroaluminates. However, there is a competition for the phosphine between the soft nickel complex and the hard aluminum chloride coming from the dissociation of polynuclear chloroaluminate anions. Aromatic hydrocarbons, when added to the system, can act as competitive bases thus preventing the de-coordination of phosphine ligand from the nickel complex [22 b]. Performed in a continuous way, in IFP pilot plant facilities, dimerization of propene and/or butenes with this biphasic system (Difasol process) compares... 

Salts Containing Chloroaluminate Anions as Solvents and Acidic Catalysts... 

Different ways to immobilize ILs are described, particularly for chloroaluminate-based ILs (see Section 5.2.1.3). Two preparation procedures can be envisioned. The simplest one is just an impregnation of the chloroaluminate IL to fiU the pores of the dehydrated inorganic solid. The chloroaluminate anion is grafted on the surface by reaction with the surface hydroxyl group. This method may present some disadvantages, such as destruction of the structure of the support and the modification of the acidity of the Lewis acid. 

Association of alkyl chloroaluminate anions with N,N -dialkylimidazohum cations leads to salts that are liquid at low temperatures. 

These chloroaluminate anions proved to be weakly coordinating toward nickel complex catalyst involved in our system. Moreover, the nickel active species is efficiently stabilized in the ionic medium, which plays both solvent and co-catalyst roles. 

A large variety of Lewis acid-promoted condensation reactions have been performed in chloroaluminate ILs. However, these reactions generate water as a principle byproduct, which reacts with the chloroaluminate anion reducing its acidity and eventually destroying the salt. " ... 

The formation of different anions is dependent on the chloride/AICb ratio. The addition of aluminum trichloride to the chloride initially results in the formation of the AlCU ion and this is essentially the only anion present at an aluminum trichloride mole-fraction of exactly 0.5. At x(AICl3)>0.5, multi-nuclear chloroaluminate anions are formed which are in equilibrium with one another, the AlCU ion and at very high AICI3 mole fractions with dimeric aluminum trichloride (Eq 2.27 and 2.28). Chloroaluminates are well known, however other ionic liquids may also be prepared from a halide and Lewis acid (Table 2.12). 

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