Confinement of Brønsted Acidic Ionic Liquids into Covalent Organic Frameworks as Catalyst for Dehydrative Formation of Isosorbide from Sorbitol

The confinement of Bronsted acidic 1-methyl-3-(3-sulfopropyl)-1H-imidazol-3-ium hydrosulfate ([PSMIm][HSO4]) into the channel walls of two dimensional (2D) COFs using a one-pot self-assembly strategy was addressed by incorporating imine-linked TPB-DMTP-COF (TPB, triphenylbenzene; DMTP, dimethoxyterephthaldehyde) as the host. A proper loading of [PSMIm][HSO4] is crutial for the BIL-COF hybrids to maintain proper geometry in the channel and sufficient acidity sites for sorbitol substrate and sorbitan intermediate to enter and react. The best yield of isosorbide (97%) from sorbitol to date was obtained in the presence of BIL-COF-30 as the catalyst under optimized conditions. Besides, BIL-COF-30 can be recycled for at least five runs without activity loss.