The catalytic activity of poly(N-vinylimidazole)/SiO2-supported metalloporphyrins in ethyl benzene oxidation

Abstract

In this paper, novel kind of supports for immobilizing metalloporphyrin catalysts, poly(N-vinylimidazole)/SiO2 (PVI/SiO2) were prepared in the manner of “grafting from”. Then, various metalloporphyrins (MPs), such as cobalt, iron and manganese tetraphenylporphyrins (CoTPP, FeTPP, MnTPP), cobalt tetra (para-nitrophenyl) porphyrin (CoTNPP), and cobalt tetra (para-chlorophenyl) porphyrin (CoTClPP), were immobilized on the supports PVI/SiO2 via the axial coordination reaction between MPs and the imidazole groups of the grafted PVI, resulting in the heterogenized catalysts MPs–PVI/SiO2. The supported catalysts were characterized by IR and UV–Vis spectra. The catalytic performances of MPs–PVI/SiO2 for the oxidation of ethyl benzene in the absence of any reductant and solvent were investigated and compared in detail. The experimental results revealed that MPs–PVI/SiO2 could effectively activate dioxygen, and obviously catalyze the oxidation of ethyl benzene to acetophenone. The catalytic activities of MPs–PVI/SiO2 increased with increase of the electron-deficient degree of the peripheral substituent attached to the benzene ring outside the porphyrin ring. The catalytic activities of MPs–PVI/SiO2 differed among the different metals and the different substitutional groups according to the following sequences: Co(II) > Fe(III) > Mn(III), and CoTNPP > CoTClPP > CoTPP. In comparison, the catalytic activity of CoTNPP–PVI/SiO2 was the best. Under the reaction conditions of 120 °C and the ordinary pressure of oxygen, the catalyst CoTNPP–PVI/SiO2 gave wonderful results with 33.4 mol% yield of acetophenone.