Hydrogen Peroxide Oxidation Of Glucose Catalyzed By Metalloporphyrins

The selective catalytic oxidation of glucose, as model compounds of cellulose, which is the most abundant carbonhydrates on the earth is still a great challenge. In this paper, the selective oxidation of glucose with hydrogen peroxide catalyzed by metalloporphyrin was studied, and the influence factors on selelctive aldehyde group C-H bond cleavage and C-C bond cleavage was investigated via the systematic studies of the reaction parameters. The kinetics model and mechanism in the metalloporphyrin catalytic system were discussed.The details are summarized as follows:1. The qualitative and quantitative analysis of oxidation products of glucose were studied by GC-MS and HPLC methods. The main products in this reaction system are gluconic acid, glycolic acid and formic acid, Furthermore, there are a small amounts of lactic acid, acetic acid, etc. A HPLC-RID method for the quantitative analysis of glucose and a HPLC-DAD method for quantitative analysis of the oxidation products of glucose were established. By means of optimizing the chromatographic conditions, the two quantitative methods of HPLC were established with high accuracy and reproducibility.2. Seven metalloporphyrins were synthesised, and the catalytic performance on the oxidation of glucose with hydrogen peroxide were investigated. Taking glucose conversion into consideration, the catalytic effects of metalloporphyrins are as follows: iron porphyrin > cobalt porphyrin > manganese porphyrin.3. The FeTSPPCl was selected as catalyst for a systematic study on the hydrogen peroxide oxidation of glucose. The effects of reaction time, reaction temperature, amount of catalyst, molar ratio of hydrogen peroxide and glucose were studied. With the increase of reaction time, the conversion rate of glucose and the total selectivity of C-C bond cleavage products increase, but the over-long reaction time it will cause the decarboxylation of carboxylic acid, resulting in lower product selectivity. We found that the temperature has a great influence on the selelctive C-C bond cleavage and aldehyde group C-H bond cleavage. In the low temperature, the oxidation products selectivity of aldehyde group C-H bond cleavage is high, while high temperature is favor to conversion rate of glucose and the total selectivity of C-C bond cleavage products. If the temperature is higher than 100℃, it will cause the decarboxylation of carboxylic acid, and cause the decrease of the carboxylic acid selectivity. The more the molar ratio of oxidant-glucose increased, the greater glucose conversion and the selectivity of C-C bond cleavage products improved. Howerver, the glucose conversion did not have significant increase when the molar ratio was 2. With the increase in the amount of catalyst, the reaction rate accelerates, the C-C bond cleavage oxidation products and the total selectivity of C-C bond cleavage products increase. When the amount of metalloporphyrin was 100 ppm, the glucose conversion rate did not significantly increase.4. Combination of the reaction of the glucose oxidation and the comparison experiment, we studied the kinetics and mechanism of the hydrogen peroxide oxidation of glucose catalyzed by metalloporphyrin, and the half-empirical equation was:r=-k[DG]2.0[Por.]0.7.The kinetic datas indicated that the temperature has a great impact on the proportion of the oxidation products. The conversation of the glucose increased as the reaction temperature rised. The concentration of the catalyst also significantly affects the reaction. Through the hydroxyl radical capture experiments by using DMSO, we found that there was hydroxyl radical exists in the reaction of oxidation of glucose with hydrogen peroxide catalyzed by metalloporphyrin.