Zeolite encapsulated ruthenium and cobalt schiff base complexes catalyzed allylic oxidation of α-pinene

Abstract

The allylic oxidation of α-pinene to its oxygenated products has been investigated using bis-salicylaldehyde-o-phenylenediimine (Saloph) and substituted (Cl, Br and NO₂) Salophs of ruthenium and cobalt in zeolite-Y. The oxidation of α-pinene resulted in various products like camphene, 2,7,7-trimethyl SS pinene (3-oxatricyclo-4,1,1,02,4-octane), 2,3-epoxy (epoxy), campholene aldehyde and D-verbenone. Ru(III)Saloph-Y showed higher catalytic activity than Co(II)Saloph-Y with a turn over frequency >18 000 (mole of α-pinene oxidized per mole of Ru per hour) at 100 °C and 30 atm air. The selectivity for epoxy and d-verbenone was found to be higher in α-pinene oxidation with both Ru and Co catalyst systems. The catalytic performance of the encapsulated complexes was better than the neat complexes. Air was a more convenient oxidant than H₂O₂ and TBHP. No leaching of the metal complex in encapsulated systems were observed in the oxidation reaction. X-ray diffraction (XRD), thermogravimetric and X-ray photoelectron spectroscopy (XPS) studies supported the fact that the metal complexes were entrapped inside zeolite cages and not on its surface. Electronic spectra of the reaction mixture indicated that the oxidation of α-pinene proceeds through a free radical mechanism involving peroxoruthenium species as an active intermediate.