Synthesis of a 3D-network polymer supported Bronsted acid ionic liquid based on calix[4]resorcinarene via two post-functionalization steps: a highly efficient and recyclable acid catalyst for the preparation of symmetrical bisamides

Abstract

In this work, for the first time, a 3D-network polymer-supported Bronsted acid ionic liquid was synthesized via two post-functionalization steps. Initially, the active homogeneous catalyst was chemically immobilized onto a polymeric support based on calix[4]resorcinarene by silylation of the hydroxyl groups to form a cationic polymer that contains imidazolium moieties. The formation of this cationic polymer was confirmed by elemental analysis, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and derivative thermogravimetric (DTG) analysis. Subsequently, HSO₄ anion was incorporated into the polymer along the imidazolium pendant groups via a well-known ion exchange reaction. Elemental analysis data revealed that the cationic polymer was conveniently loaded with the desired Bronsted acid anion; therefore, it provides a novel heterogeneous acid catalyst for achieving synthetic goals. The immobilized acidic ionic liquid effectively catalyzed the one-pot synthesis of symmetrical bisamides by the multicomponent condensation of two moles of amides with aldehydes. Interestingly, the catalyst exhibited a high turnover number (TON) and turnover frequency (TOF), which were even comparable with that of H₂SO₄. The unique features of this catalyst, such as superior thermal stability, recyclability, excellent catalytic activity in terms of yield and reaction time, high turnover number and turnover frequency, are potentially important for the applications of this catalyst in the industry.