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Molecular Oxygen Oxidation of Glucose Catalyzed by Metalloporphyrins in Water

Author: FengGuiXiang
Tutor: LiuQiang
School: Hunan University
Course: Organic Chemistry
Keywords: Metalloporphyrin Molecular oxygen Glucose C-H Cleavage C-C Cleavage Selective oxidation Hydrogen peroxide
CLC: O643.32
Type: Master's thesis
Year: 2010
Downloads: 105
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Abstract

The selective catalytic oxidation of glucose, as model compound of carbonhydrate, is still a great challenge.In this thesis, the selective oxidation of glucose with moleculer oxygen catalyzed by metalloporphyrin was studied, many kinds of technic factors which influence selelctive C-C cleavage and C-H cleavage were investigated via the systematic studies of the reaction parameters. The mechanism of hydrogen peroxide production and glucose catalyzed oxidation by metalloporphyrin was also discussed.The main work in this thesis as follows:1.A new mild glucose oxidation system was established, the system used the metal porphyrins as catalyst, dioxygen as the oxidant, low concentration NaOH solution as solvent, in the medium-pressure and lower temperature. The system has the charateristics of simple reaction equipment, efficient catalyst, clean oxidant, green solvent, little equipment corrosion and low cost.2.We have established three quantitative analysis methods:HPLC(RID) method for test glucose、fructose、sucrose、maltose; HPLC(DAD) methods for quantitative analysis of oxidation products of glucose and products of glucose plus hydrogen peroxide through the optimization of chromatographic conditions. The three methods possess high accuracy and good reproducibility.3.Eight metallporphyrins were synthesized, and its catalytic properties were investigated in the process of catalytic oxidation glucose by dioxygen. From the selectivity:We find that when no catalyst was used, the product of C-H oxidation cleavage at glucose’s aldehyde group is main; when catalysts were used, the products of C-C oxidation cleavage turn to the main products, the selectivity of C-C cleavage oxidation products much larger than the selectivity of C-H cleavage product. The order of catalytic effects of metalloporphyrins were:FeTSPPCl>CuTSPP>CoTSPP> MnTSPP.4.We also investigated the applicability of substrate, the conversion of soluble carbohydrate is higher than non-soluble carbohydrate. Total selectivity of C-C cleavage product for monosaccharide and disaccharide are high, but the polysaccharide are low. It is confirmed that monosaccharides and disaccharides have good applicability, but the polysaccharide have poor applicability in this system.5.FeTSPPCl was selected as a catalyst for a systematic study on glucose oxidation by molecular oxygen. Reaction time, reaction temperature, catalyst type, alkali intensity of solution, the amount of catalyst, the amount of substrate, dioxygen pressure were studied. When the reaction time increased, the glucose conversion increased, the total selectivity of C-C cleavage oxidation increased too, if the time is too long, the selectivity of product reduced, this may be caused by the decarboxylation of products. Temperature greatly influenced this reaction, low temperature C-H oxidation cleavage product have high selectivity, increasing temperature promots the conversion and total selectivity of C-C oxidation cleavage. Too high temperature tend to cause decarboxylation seriously especially when higher than 160℃. Alkali intensity had a great impact on metalloporphyrin catalyzed glucose oxidation, as alkali intensity increased, the conversion gradually increased, selectivity of gluconic acid is increased. But too high alkali intensity is not conducive to the formation of C-C cleavage product. As the amount of FeTSPPCl increased, conversion increased, but selectivity of gluconic acid decreased, total selectivity of products of C-C cleavage increased, when amount of catalyst too high will lead to selectivity drop. As the amount of glucose increased, the conversion gradually decreased, the selectivity of C-H cleavage product increased at first then decreased and keep stable finally, total selectivity of C-C cleavage product keep in a stable level. As pressure increased, conversion increased, selectivity of gluconic acid first increased and then decreased, total selectivity of C-C cleavage product first increased then decreased, the selectivity higher in 2.00 MPa.6.By spectrophotometer and HPLC combined with comparative experiments we proved hydrogen peroxide exist in the reaction of glucose catalystic oxidation. We find glucose and NaOH are the key factors for hydrogen peroxide generate. We examed stability of FeTSPPCl、MnTSPP、CoTSPP in alkali and alkali adding glucose by UV and HPLC. Possible mechanism of Metalloporphyrin catalytic glucose oxidation by dioxygen had offered on the basis of the experimental and literature.

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