Post-Synthesis of Manganese Schiff Base Complex with Zr-Based Metal-Organic Framework Immobilized on Fe3O4 as a Recyclable Catalyst for Partial Oxidation of Cyclooctene

A magnetic type of Zr-based UiO-66 metal-organic framework (Fe3O4@UiO-66-NH2) was synthesized by co-precipitation and solvothermal method and then modified by a Schiff base reaction with salicylaldehyde. The Schiff base ligand was coordinated by manganese salt to develop a recyclable catalyst for the mild oxidation of cyclooctene. The catalyst characterization was performed by the techniques of adsorption analysis (BET), X-Ray Diffraction (XRD), Fourier Transform IR spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Vibrating-Sample Magnetometer (VSM). Oxidation experiments were carried out in different reaction conditions such as reaction temperature and time, the amount of oxidant, and solvents. The catalyst exhibited good selectivity for the production of 2-cyclooctene-1-one. It was found that the conversion and selectivity decreased in the presence of methanol as a protic solvent in order to the strong interaction between oxygenated intermediates and solvent molecules. In addition, increasing the molar ratio of oxidant to feed led to a decrease in ketone selectivity and an increase in epoxy products. The allylic path was suggested as the dominant mechanism of cyclooctene oxidation via the formation of cyclooctene 3-(tert-butyl) peroxide after oxidation of allylic C-H group and decomposition to form 2-cycloocten-1-one.