Preparation Of Immobilized NHPI Catalyst On Polymeric Microspheres And Investigating Its Catalytic Property In Oxidation Reaction

The oxidation of hydrocarbons and alcohols is an important chemical transformation process in organic synthesis. With the development of industry, environmental problem becomes more serious and most traditional oxidants were eliminated due to a lot of shortcomings. The green oxidation technology using molecular oxygen as an oxidant has obtained great development. In order to increase the reaction efficiency of substrate with molecular oxygen, a series of catalyst has been developed. Among the catalysts, N-hydroxyphthalimide (NHPI) has attracted much attention as an efficient organic catalyst. The immobilization of NHPI is one of the most important subjects in the study of catalytic oxidation. In our present investigation, a new preparation method of crosslinked polymeric microspheres(GMA/MMA) of glycidyl methacrylate (GMA) and methyl methacrylate (MMA) as the carrier to manufacturer immobilized NHPI catalyst has been designed. Subsequently, NHPI was synthesized and immobilized on GMA/MMA microspheres, and the functionalized microspheres GMA/MMA-NHPI were obtained through several polymer reaction steps. A co-catalyst system constituted with the solid catalyst and trace transition metal salt catalysts was used to the oxidation reaction of benzyl alcohol and ethylbenzene with molecular oxygen as oxidant. The catalytic properties of solid catalyst was investigated. This research has important scientific significance in the field of green catalytic oxidation technology.Crosslinked polymeric microspheres GMA/MMA were first prepared by suspension polymerization. Then glyoxylic acid was immobilized on the GMA/MMA microspheres by the ring opening reaction and modified microspheres GMA/MMA-AL were obtained. The effects of main factors on the catalytic oxidation reaction were examined. Experimentalresults show that both catalyst and temperature have effect on the ring opening reaction between glyoxylic acid and epoxy groups on the GMA/MMA microspheres. The addition of alkaline catalyst can effectively promote the reaction and the rise of temperature can improve the bonding amount of glyoxalic acid. The bonding amount of glyoxalic acid can reach1.1mmol/g under the best conditions. Then the microspheres GMA/MMA-PA were obtained through the Schiff base reaction between GMA/MMA-AL and4-Aminophthalic acid. The dehydration reaction of phthalic acid groups was followed and the intermediate product GMA/MMA-PPA was obtained. A novel GMA/MMA-NHPI heterogeneous catalyst was finally obtained through the reaction between GMA/MMA-PPA microspheres and hydroxylamine hydrochloride.On this basis, a co-catalyst system was constituted with GMA/MMA-NHPI and different transition metal’salts and was used in the oxidation reaction of benzyl alcohol by molecular oxygen.The catalytic acitivity of the co-catalyst system was examined and the effects of the main factors and the catalytic mechanism were researched. Experimental results show that the co-catalyst system consisting of GMA/MMA-NHPI and Co(OAc)2can efficiently catalyze the oxidation reaction of benzyl alcohol by molecular oxygen. Under mild conditions, benzyl alcohol was transformed to benzoic acid with96%selectivity and11.55%yield. The catalytic reaction were carried according to the chain reaction mechanism. Co(OAc)2performs best among the several transition metal salts.The trace addition of Co(OAc)2can obviously improve the reaction rate. Surprised to find that an excess addition of Co(OAc)2has a negative effect on the catalytic activity. The increase in the amount of co-catalyst and the rise of temperature both can enhance the yield of benzoic acid.The right amount of co-catalyst is10mol%and the right temperature is65℃. The GMA/MMA-NHPI heterogeneous catalyst has excellent recyclability.In the next step,the carrier was changed to CPGMA microspheres in order to improve the immobilized amount of NHPI. CPGMA microspheres were preparation using glycidyl methacrylate (GMA) and ethylene dimethacrylate(EGDMA). The CPGMA-NHPI heterogeneous catalyst was prepared through the same process as GMA/MMA-NHPI. Then a co-catalyst system was constituted with CPGMA-NHPI and different transition metal salts and was used in the oxidation reaction of ethylbenzene by molecular oxygen. The catalytic property of this co-catalyst system and the catalytic mechanism were investigated, and the effects of the main factors on this oxidation reaction were examined. The results show that the co-catalyst system CPGMA-NHPI+Co(OAc)2can efficiently catalyze the oxidation reaction of ethylbenzene by molecular oxygen. The temperature and solvent has a great influence on the conversion of ethylbenzene and selectivity of acetophenone. The conversion of ethylbenzene can reach26.1%and the selectivity of acetophenone is75.8%under the best conditions.