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

Abstract

Co(II) Schiff base complexes encapsulated in zeolite-Y having the general formula Co(II)L-Y (where L=salicylaldehyde- o-phenylenediimine (saloph), chloro-salicylaldehyde- o-phenylenediimine (Cl-saloph), bromo-salicylaldehyde- o-phenylenediimine, (Br-saloph) and nitro-salicylaldehyde- o-phenylenediimine, (nitro-saloph) and Y=zeolite Na-Y) have been synthesized and characterized for their physicochemical and spectroscopic properties. The neat and encapsulated catalysts were tested for their catalytic activities in the oxidation of β-isophorone (BIP) to keto-isophorone (KIP) using air as an oxidant 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, however, Co(II)Cl-saloph neat and its encapsulated forms were comparatively more active than other catalysts tested in the oxidation reaction. The catalytic activities of neat and their encapsulated forms followed the same trend and the order of reactivities were: Co(II)Cl-saloph>Co(II)Br-saloph>Co(II)nitro-saloph>Co(II)saloph. Kinetics of Co(II)Cl-saloph-Y catalyzed aerial oxidation of BIP was investigated and the rates of oxidation have been obtained for variations made in catalyst, substrate and oxidant concentrations. Mechanism of oxidation involving Co(III)OO superoxo intermediate species in the oxidation of BIP has been established by UV–VIS using Co(II)saloph neat complex. Effect of temperature on the rates of oxidation of BIP was also studied and from Arrhenius plot, thermodynamic activation parameters estimated have been reported.