Sulfonic Acid Functionalized MIL-101(Cr) Metal-Organic Framework for Catalytic Production of Acetals

A simple and green process for acetalization of benzaldehyde derivatives in the presence of a new solid acid nanocatalyst is reported. For this purpose, MIL-101(Cr) was synthesized in the absence of HF and then sulfonic acid functionalized MOF was prepared under mild conditions without using hazardous chemicals. First, the MIL-101(Cr) was functionalized with cysteamine as a non-toxic material to afford MIL-101(Cr)-SH. Then, reaction of the MIL-101(Cr)-SH with hydrogen peroxide as a clean oxidant followed by acidification with diluted sulfuric acid produced MIL-101(Cr)-SO3H solid acid nanocatalyst. Characterization of the prepared nanocatalyst was carried out with various physicochemical methods. The results of elemental analysis and FT-IR spectroscopy confirmed the stepwise functionalization of MIL-101(Cr) with sulfonic acid groups. Nitrogen adsorption-desorption analysis indicated the reduction of surface area after functionalization of pristine MIL-101(Cr). X-ray diffraction (XRD) analysis showed that the MIL-101(Cr) kept its crystal structure during the modification steps. Finally, the activity of prepared catalyst was evaluated in the clean acetalization of benzaldehyde derivatives with ethylene glycol which exhibited excellent efficiencies and produced water as the only byproduct. The nanocatalyst was consecutively recovered and applied 5-times without notable loss of its activity.