Synthesis of Imidazolium-functionalized Ionic Liquid Specialties

Eric Sylvester, Annegret Stark, Markus Hoffmann

Abstract


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Ionic liquids (ILs) are defined as salts that are stable in the liquid state at 100°C or less. ILs have long been considered as designer solvents in preparatory chemistry because they can be made task-specific for a target application. The synthesis of imidazolium-based ILs tailored with functional groups will be presented for the potential use in synthesis.

There are generally two routes to synthesize ILs commonly referred to as the “conventional” Menschutkin reaction [P. Bonhôte, A.-P. Dias, N. Papageorgiou, K. Kalyanasundaram, M. Grätzel, Inorg. Chem., 35, (1996), 1168-1178.] and the “unconventional” modified Radziszewski reaction[B. Radziszewski, Ber. Dtsch. Chem. Ges., 15, (1882), 1493-1496. J. Zimmermann, B. Ondruschka, A. Stark, Org. Proc. Res. Dev., 14, (2010), 1102-1109.]. The conventional synthesis is an alkylation reaction where an amine and an alkyl halide react to form the IL cation while the halide acts as the IL anion. The unconventional synthesis is a one-pot-synthesis where five molecules react to the desired IL: formaldehyde, glyoxal, an acid and two molar equivalents of an amine. The use of the unconventional synthesis to obtain functionalized ILs was the main focus of this project. However, instead of the ILs, three internal salt derivatives of the desired ILs were surprisingly obtained with high yields (> 89%) and in high purity.


Keywords


ionic Liquids, Ring Closing Reactions, Chirality

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