Chitosan-based Schiff base-metal complexes (Mn, Cu, Co) as heterogeneous, new catalysts for the β-isophorone oxidation

A new chitosan-based Schiff base was prepared and complexed with manganese, cobalt and copper. These Schiff base metal complexes were used as heterogeneous catalysts for the air oxidation of β -isophorone to ketoisophorone. The obtained complexes were characterized by means of FT-IR, 1 HNMR spectroscopy, elemental analysis, powder X-ray diffraction, field emission gun scanning electron microscopy, electron spin resonance spectroscopy, ICP-AES and solubility tests. Thermal properties were also investigated using thermal gravimetric analysis. Data obtained by thermal analysis revealed that these complexes showed good thermal stability. The conversion and selectivity of β -isophorone to ketoisophorone for each prepared catalyst was studied using a batch reactor and gas chromatography for product identification and quantification. The results were compared against the homogeneous bis -salicylaldehyde ethylenedi-imine-Mn catalyst. The use of methanol, acetone, methyl isobutyl ketone and n -hexane as solvent and its effect on conversion and selectivity was also investigated. Acetone was found to be a promising solvent for the β -isophorone oxidation. The role of triethyl amine and acetyl acetone in the oxidation reaction has also been investigated. Graphical Abstract Heterogeneously catalyzed β-isophorone oxidation reaction by Chitosan-Schiff base-metal complexes was studied.