Fast Assembly of Metal Organic Framework UiO-66 in Acid-Base Tunable Deep Eutectic Solvent for the Acetalization of Benzaldehyde and Methanol

Abstract

Zirconium-based metal-organic frameworks (MOFs) have attracted extensive attention owing to their robust stability and facile functionalization. However, they are generally prepared in common volatile solvents within a long reaction time. Here, we introduced environmentally friendly, cheap, and acid-based tunable deep eutectic solvents (DESs) formed from 2-methyl imidazole (MIm) and p-toluenesulfonic acid (PTSA) which significantly accelerated the assembly of zirconium-based MOF (UiO-66) without any aggressive additives. PTSA in acidic DES and ZrOCl2 preliminarily formed Zr(IV) oxo organic acid framework, whereas basic DES completely dissolved the ligand of UiO-66. The strong hydrogen bond effect of PTSA and MIm efficiently accelerated the linker exchange between zirconium oxo organic coordination in acidic DES and benzenedicarboxylate linker in weak basic DES within a reaction time of 2 h at 50 °C. Thus, UiO-66 was quickly assembled with small particle sizes and used as an excellent catalyst for the acetalization of benzaldehyde and methanol. Therefore, the developed synthesis approach provides a new green strategy to quickly prepare and design various structures of metal-based compounds under mild reaction conditions.