|关键词||甘油 间接法 1 基团保护 3 -二羟基丙酮|
Glycerol is large surplus with the development of biodiesel industry, which formed as a by-product during the production of biodiesel. Research efforts to find new applications of glycerol as a low-cost feedstock for functional derivatives have led to the development of a number of selective processes for converting glycerol into commercially valued products. Oxidation of the secondary hydroxyl-group yields the important fine chemical 1,3-dihydroxyacetone (DHA), which has become an international research hotspot. However, Good selectivity to 1,3-dihydroxyacetone at high glycerol conversion is difficult to achieve because of the tri-hydroxyl structure of glycerol and rapid over oxidation of 1,3-dihydroxyacetone. 1,3-dihydroxyacetone is currently produced by microbial fermentation of glycerol over Gluconobacter oxydans. The productivity, however, is relatively low due to the strict fermentation conditions and long fermentation time, also, it is hard to separate the target product. Efforts to obtain 1,3-dihydroxyacetone include the use of catalysts, such as Au/C or Au-Pd/C catalyst, which are expensive and a large number of by-products are often formed which decrease the selectivity. Furthermore, the catalyst is lost after reused. In the work of here, an indirect conversion route was designed, which include acetalization, oxidation and hydrolysis. 1、Condensation of glycerol with benzaldehyde. Traditionally, bronsted acid catalysts such as HCl and H2SO4 are commonly used in the industry. However, the generation of large volumes of toxic waste which poses environmental risk. The corrosion of equipment and by-production are some of the drawbacks of these catalysts. Therefore, the development of solid acid catalysts for liquid phase reactions is desired, but solid acid catalysts showed significant deactivation during the reaction by coking. Copper p-toluenesulfonate was prepared for replacing the bronsted acid, which has a strong corrosive and many side effects. It can be employed as the catalyst for the condensation of glycerol with benzaldehyde and reached a good result. Also, the catalyst can be reused. By optimizing the process with response surface methodology, the procedure was as follows. The molar ratio of benzaldehyde to glycerol was 1:1.3, the volume for petroleum ether was 1.3 times of benzaldehyde and the dosage of catalyst was 0.9mol% of benzaldehyde. The yield of benzaldehyde glycerol acetal showed the maximum conversion of 96.0%. The acetal was an isomer mixture of two kinds of substance. Direct separation of an isomer mixture is difficult. It was noticed that the bronstedacid-driving mechanism transformation between isomers by taking toluene as solvent. After transfer five ring to six ring, the high value of cis six-member ring was separated out extensively by crystallization under low temperature (about -20°C). 2、Oxidation of the 2-Phenyl-1,3-dioxan-5-ol. The second step of this process is the oxidation of hydroxyl groups, the acetalized glycerol 2-Phenyl-1,3-dioxan-5-ol can be oxidized thoroughly to the corresponding acetalized dihydroxyacetone (2-phenyl-1,3-dioxan-5-one) under mild condition without over-oxidation. Considering acetal is very sensitive to acid, it must be careful to choose oxidant. The common oxidants include manganese compounds, chromium compounds, peroxide and halogen-oxidant were studied., experimental result shows that the acetalized glycerol can be oxidized by 2,2,6,6-Tetramethyl-1-piperidinyloxy(TEMPO) efficiently with NaClO as the auxiliary oxidant. The reaction condition is mild and PH can be adjusted. When the molar ratio was n(TEMPO): n(NaClO): n(NaBr) = 0.02: 0.1: 1.5, The yield of oxidation achived.at 98.16% through 30 minutes oxidize. 3、hydrolysis of 2-phenyl-1,3-dioxan-5-one to obtain 1,3-dihydroxyacetone. The hydrolysis process is simple, because the product 1,3-dihydroxyacetone dissolved in water phase immediately, which can promote the hydrolysis. On the contrary, separating 1,3-dihydroxyacetone is relatively difficult. When using HCl as catalyst , the HCl will stay in the water phase. Benzaldehyde, which in water phase can use n-hexane to extraction, water can be removed by distillation. But when the temperature is high, the concentrated HCl bring carbonization, the low temperature is bad for removing water. Studies showed that the water-insoluble acid (Amberlyst-15), Amberlyst-15 is better than HCl due to its none-by-production and highly selective properties. Just filtering, it can be reusable. When the usage is 0.5g, the yield of hydrolysis is 67.5%, after 1.5h reaction. We designed an efficient route capable of producing 1,3-dihydroxyacetone from glycerol in high yield. It is better than microbial fermentation process. It can process in mild condition, the operation is simple and the cost is low. More important, glycerol derived from plant and animal oils and fats, the process has a strong industrial and social value.
|向华明. 甘油间接合成1,3-二羟基丙酮的研究[D]. 北京. 中国科学院大学,2015.|
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