Abstract:

The X-substituted cobalt tetraporphyrins (CoTXPP) (X=H, Cl, NO2) were easily bound to the side chains of the grafting particles poly(4-vinyl-pyridine-co-styrene)/SiO2 (P(4VP-co-St)/SiO2) via an axial coordination reaction to prepare supported catalysts CoTXPP-P(4VP-co-St)/SiO2. Structures of the CoTXPP-P(4VP-co-St)/SiO2 catalysts were characterized with FTIR. The axial coordination reaction between the copolymer P(4VP-co-St) and CoTXPP was studied using electronic absorption spectroscopy. Catalytic performances of the supported catalysts for the oxidation of phenylethane in the absence of any reductant or solvent were investigated and compared in detail. Experimental results show that CoTXPP-P(4VP-co-St)/SiO2 can effectively activate dioxygen and obviously catalyze the oxidation of phenylethane to phenylethanone. The catalytic activities of CoTXPP-P(4VP-co-St)/SiO2 increased as the degree of electron deficiency of the peripheral substituent on the porphyrin ring increased. The catalytic activity of CoTNPP-P(4VP-co-St)/SiO2 was found to be the best. At 120 ℃and under the ordinary pressure of oxygen, the catalyst CoTNPP-P(4VP-co-St)/SiO2 gave excellent results with a 25.53%(x) yield of phenylethanone and very little α-phenylethanol. Additionally, we found that: (1) CoTNPP-P(4VP-co-St)/SiO2 as a biomimetic catalyst had an optimumusage amount, and excess addition would decrease the catalyst's efficiency; (2) the immobilization density of CoTXPP on the surface of P(4VP-co-St)/SiO2 still had a maximum value; (3) the catalyst's activity was stable during six catalytic cycles. All these results indicate that the grafted particles P(4VP-co-St)/SiO2 protect the metalloporphyrins from oxidation and also promote the activation of O2 by the metalloporphyrins.

Key words: Catalytic oxidation, Poly(4-vinyl-pyridine-co-styrene), Grafting particles, Axial coordination, Supported-metalloporphyrin, Phenylethane