Chemically Modified Silica-Gel With an Azo-Schiff Ligand and Its Metal Complexes With Cu(II), Co(II), Ni(II) and Mn(II): Applications as Catalysts on the Oxidation of Cyclohexane Under Microwave Power

Abstract

A novel 2-hydroxy-5-((2-hydroxyphenyl)diazenyl)benzal- dehyde (L¹: HPDB) ligand was synthesized and bound to silica gel, which was activated with 3-aminopropyltriethoxysilane. Cu(II), Co(II), Ni(II), and Mn(II) complexes of silica-supported ligand (L²: MDPMP) were synthesized. A buffer (pH = 12) was used for a coupling reaction of diazonium electrophile to salicylaldehyde. The ligand and its complexes were characterized by using NMR, FT-MIR/FAR, elemental analysis, ICP-OES, TGA, and scanning electron microscopy. Catalytic properties of the complexes were investigated for the selective oxidation of cyclohexane under microwave power. Silica-supported L²-Cu(II) complex showed well selective catalytic activity for the oxidation of cyclohexane to cyclohexanol and cyclohexanone with 8.40% and 3.77% yields with 48.43% conversion.

Keywords:

• azo ligand
• catalysis
• cyclohexane
• oxidation
• silica-supported
• Schiff base

Acknowledgments

The authors would like to thank to Prof. Dr. M. Hakkı Alma (Kahramanmaraş Sütçü İmam Üniversity, ÜSKİM: University, Industry, Public Collaboration Development, Application and Research Center) for some measurements. The authors also thank Assist. Prof. Dr. H. Ökkeş Demir for his laboratory supports. They are grateful to Sütçü İmam University and Kilis 7 Aralık University for all laboratory supports.