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

The allylic oxidation of alpha-pinene to its oxygenated products has been investigated using bis-salicylaldehyde-o-phenylene-diimine (Saloph) and substituted (Cl, Br and NO2) Salophs of ruthenium and cobalt in zeolite-Y. The oxidation of alpha-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 alpha-pinene oxidized per mole of Ru per hour) at 100degreesC and 30 atm air. The selectivity for epoxy and D-verbenone was found to be higher in alpha-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 TBHR 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 alpha-pinene proceeds through a free radical mechanism involving peroxoruthenium species as an active intermediate. (C) 2002 Elsevier Science B.V. All rights reserved.