Use of Ionic Liquids in the Solid Phase

The concept of transferring liquid to solid catalysts was envisioned with acidic ILs. 

It is important to consider the support material and its properties, such as surface area, pore width, and thermal and chemical stability during the reaction. If properly chosen, the support may bring better dispersion and accessibility of the acidic active sites and an improvement in the separation of the reaction products. However, the main problem to be addressed for these supported catalysts is their instability, their regeneration, and the leaching of the active site under operational conditions. 

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. 

ILs can also be anchored to the support through the imidazoHum cation. The cation is first grafted on the support. The Lewis acid is added in a second step. As an example, IL has been anchored by reaction of a chloroaluminate ofa 1-triethoxy-silyl derivative of 3-methylimidazolium on the wall of silica MCM-41. Another approach is to anchor the cation on the support using a sol-gel method. The potential of these supported ILs has been investigated for aromatic hydrocarbon alkylation reactions (see below). 

Many examples of acid-mediated reactions are described using ILs. Some of them are described in recent reviews. The most important transformations that find applications in industrial chemistry, refinery, or petrochemistry are described below. 

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