Supramolecular polymeric aggregation behavior and its impact on catalytic properties of imidazolium based hydrophilic ionic liquids

摘要

Ionic Liquids (ILs) self-assemble to form supramolecular polymeric clusters/aggregates. The aggregation behavior of ILs influences its activity in the organic synthesis. However, the precise role of ILs in organic reactions is still unknown. It is, therefore, important to comprehend the supramolecular polymeric aggregation behavior of ILs. We are exploring the supramolecular polymeric aggregation behavior of ILs using Electrospray Ionization Mass Spectrometry (ESI-MS). We have synthesized four hydrophilic ILs (1-4) and investigated their aggregation behavior and its impact on catalytic activity in Carbon-Carbon bond formation (Knoevenagel and ClaisenSchmidt condensation). Here, we show that the aggregation behavior of ILs depends on the type and nature of cation and anion. ESI-MS (-ve) spectra reveals two different type of aggregation i.e. [C(n)A(n+1)](-) & [A(2) + H+](-). We have found that catalytic activity increases with increased [C(n)A(n+1)](-) supramolecular aggregation. Consequently, highest yield of products obtained in lb which show decreased anion-anion aggregation [A(2) + H+](-) abundance in ESI-MS. We anticipate our results to be a starting point for the establishment of desired ILs for organic synthesis. (C) 2019 Elsevier B.V. All rights reserved.