Oxovanadium (IV) Schiff base complex immobilized on CPS microspheres as heterogeneous catalyst for aerobic selective oxidation of ethyl benzene to acetophenone

Abstract

In this work, chloromethylated crosslinked polystyrene microspheres (CMCPS microspheres) were used as starting carrier, and a new immobilized bidentate Schiff base oxovanadium (IV) complex catalyst was prepared. The chloromethyl groups of CMCPS microspheres were first transformed into aminomethyl groups via Delepine reaction with hexamethylene tetramine (HMTA) as reagent, obtaining aminomethylated (AM) microspheres AMCPS. And then the Schiff base reaction between the primary amino group of AMCPS microspheres and salicylaldehyde (SA) was allowed to be conducted, resulting in Schiff base-type resin microspheres, SAAM-CPS, on which bidentate Schiff base ligand SAAM were chemically anchored. Subsequently, the coordination reaction between the ligand SAAM of SAAM-CPS microspheres and vanadyl sulfate (VOSO4) was carried out, obtaining a new immobilized bidentate Schiff base-type oxovanadium (IV) complex, CPS-[VO(SAAM)2] microspheres, namely a new heterogeneous oxovanadium (IV) complex catalyst was prepared. On the basis of fully characterizing the microspheres CPS-[VO(SAAM)2], they were used in the catalytic oxidation of ethyl benzene with molecular oxygen. The experimental results show that in the oxidation reaction of ethylbenzene with molecular oxygen as oxidant, the heterogeneous oxovanadium (IV) complex catalyst, CPS-[VO(SAAM)2], has high catalytic activity and excellent catalytic selectivity. Under the mild conditions such as at ordinary pressure of dioxygen and at a relatively low temperature of 110°C, ethyl benzene can be transformed to acetophenone as a single product with a yield of 43%. It was found that the reaction temperature and the used amount of the solid catalyst effect on the oxidation reaction greatly. The catalyst CPS-[VO(SAAM)2] has excellent recycle and reuse property.