Solvent-free oxidation of cyclohexane over covalently anchored transition-metal salicylaldimine complexes to α-zirconium phosphate using tert-butylhydroperoxide

• New heterogeneous catalysts, α-ZrP.M(salicylaldimine) prepared by covalent bonding.
• Liquid phase oxidation of cyclohexane was studied using α-ZrP.M(salicylaldimine)/TBHP system.
• α-ZrP.Co(salicylaldimine) gave maximum 14.18% conversion with 92.33% selectivity (KA-oil).
• α-ZrP.Co(salicylaldimine) exhibit the excellent reusability.

Heterogeneous catalysts were prepared by covalent bonding of transition-metal salicylaldimine complex to α-zirconium phosphate, abbreviated as {α-ZrP.M(salicylaldimine) where M = Co, Mn and Cu}. The resulting compounds were characterized by BET surface area, TGA analysis, X-ray diffraction, Scanning electron micrograph, energy dispersive X-ray analysis, Fourier transform infrared and Atomic absorption spectroscopy. The catalytic activity of α-ZrP.M(salicylaldimine) was studied for the liquid phase oxidation of cyclohexane using tert-butylhydroperoxide as an oxidant under solvent free condition. In the oxidation reaction, cyclohexane was oxidized to cyclohexanol, cyclohexanone and some unidentified products. It was found that the reactivity of α-ZrP.M(salicylaldimine) catalyst for the oxidation reaction decreased in the order α-ZrP.Co(salicylaldimine) > α-ZrP.Mn(salicylaldimine) > α-ZrP.Cu(salicylaldimine). A maximum conversion of cyclohexane (14.18%) and selectivity of cyclohexanol (4.99%), cyclohexanone (87.34%) and some other products (7.67%) was observed for catalyst, α-ZrP.Co(salicylaldimine) after 6 h at 353 K. The catalyst, α-ZrP.Co(salicylaldimine) was reused for four cycles without significant loss of catalytic activity.

A heterogeneous catalytic system, α-ZrP.Co(salicylaldimine)/TBHP gave maximum 14.18% conversion and 92.33% selectivity for KA-oil in oxidation of cyclohexane. The catalyst can be reused for four cycles.Figure optionsDownload high-quality image (89 K)Download as PowerPoint slide