Oxidation by molecular oxygen using zeolite encapsulated Co(II)saloph complexes

Co(II) Schiff base complexes encapsulated in zeolite-Y having the general f ormula Co(II)L-Y (where L, = salicylaldehyde-o-phenylenediimine (saloph), c hloro-salicylaldehyde-o-phenylenediimine (Cl-saloph), bromo-salicylaldehyde -o-phenylenediimine, (Br-saloph) and nitro-salicylaldehyde-o-phenylenediimi ne (nitro-saloph) and Y = zeolite Na-Y) have been synthesized and character ized for their physicochemical and spectroscopic properties. The neat and e ncapsulated catalysts were tested for their catalytic activities in the oxi dation of beta -isophorone (BIP) to keto-isophorone (KIP) using air as an o xidant at ambient conditions of pressure and temperature. It was found that the catalytic activities of encapsulated catalysts were higher than their homogeneous analogues in the oxidation reaction. Among the catalysts, howev er, Co(II)Cl-saloph neat and its encapsulated forms were comparatively more active than other catalysts tested in the oxidation reaction. The catalyti c activities of neat and their encapsulated forms followed the same trend a nd the order of reactivities were: Co(II)Cl-saloph > Co(II)Br-saloph > Co(I I)nitro-saloph > Co(II)saloph. Kinetics of Co(II)Cl-saloph-Y catalyzed aeri al oxidation of BIP was investigated and the rates of oxidation have been o btained for variations made in catalyst, substrate and oxidant concentratio ns. Mechanism of oxidation involving Co(III)-O-O-. superoxo intermediate sp ecies in the oxidation of BIP has been established by UV-VIS using Co(II)sa loph neat complex. Effect of temperature on the rates of oxidation of BIP w as also studied and from Arrhenius plot, thermodynamic activation parameter s estimated have been reported. (C) 2001 Elsevier Science B.V. All rights r eserved.