Effect of supramolecular polymeric aggregation in room temperature ionic liquids (RTILs) on catalytic activity in the synthesis of 4H-chromene derivatives and Knoevenagel condensation

Abstract

RTILs exhibit supramolecular self-assembled polymeric aggregation due to noncovalent interactions. The influence of the aggregation behaviour of RTILs on catalytic activity is evident but still poorly understood. The present work focuses on establishing a relationship between the role of supramolecular self-assembly of RTILs on catalysis in organic reactions. Herein, we report four unreported, air and water stable, halide free, C2-symmetrical, third generation, hydrophobic imidazolium-based room temperature ionic liquids (RTILs 1–4), their synthesis and function as catalysts for the synthesis of 4H-chromene derivatives (terahydrobenzo[b]pyran) and Knoevenagel condensation. The RTILs showed unprecedented solubility/miscibility behaviour. The RTILs showed that 1,3-dihexylimidazolium 2-aminobenzoate [hhim][OAB] (RTIL-3) performed better in terms of yield and reaction time. Supramolecular polymeric aggregation was explored by employing ESIMS, while the critical aggregation concentration (CAC) was calculated via recording electrical conductivity of RTILs in absolute ethanol. We have also used rheometry experiments to explore forces governing the occurrence of aggregates in the liquid phase of RTILs.