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Cleaner solvents for sustainable chemistry

Synthesis and catalysis

Solvents for catalysis and organic synthesis

Ionic liquids are used as solvents in various reactions such as Frield-Craft alkylations, C-C couplings, the Diels-Alder cycloadditions, hydrogenation, oxidation reactions or Heck reactions.
They can optimize processes by obtaining better selectivity and by increasing performance.

Recyclability is one of the most attractive features of ionic liquids. In some reactions, the catalytic system (ionic liquid + catalyst) can be easily recycled maximizing the lifetime of the catalyst.
For example, a catalytic reaction where the interest of ionic liquids is most significant is the Heck reaction. Indeed, ionic liquids significantly improve the selectivity in this reaction. Thus, Xiao and colleagues found in the presence of ionic liquid 1-butyl-3-methylimidazolium tetrafluorobate a selectivity superior to 99% for the arylation compound in the coupling reaction between the 
1-bromonaphtaléne and the butyl vinyl ether. In toluene and acetonitrile, the selectivity is respectively 46% and 69% for the compound (2).

(2)L.Xu, W.Chen, J. Ross and J. Xiao, Org; Lett., 2001, 3, 295

Kinetics resolution of a racemic mixture of epoxyde2:

At the end of the reaction, the epichlorhydrine (S) is distilled with the THF under vacuum.  It is then obtained pure by distillation under vacuum at 20°C.  The diol as for it is isolated of the ionic liquid by extraction with water, then distillation. The catalyst always remains active in the liquid ionic phase and the system can be recycled.

2 C. R. Oh, D. J. Choo, W. H. Shim, D. H. Lee, E. J. Roh, S. Lee, C. E. Song Chem. Commun., 2003, 1100.


Extraction by Naproxen3 :

In this example, the reaction takes place in a biphasic environment    ionic liquid /isopropanol, the product of the reaction being extracted in the isopropanol phase. The catalysor can be recycled without any loss of selectivity.

3 A. L. Monteiro, F. K. Zinn, R. F. de Souza, J. Dupont Tetrahedron: Asymmetry, 1997, 8, 177

Extraction of caprolactame with water

The ionic liquid TISC was especially conceived to support the formation of the caprolactame in the following reaction4.  The caprolactame resulting from the Beckmann's rearrangement can be easily extracted with water in which the ionic liquid is not soluble.

4 J. Gui, Y. Deng, Z. Hu, Z. Sun Tet. Lett., 2004, 45, 2681.