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有机多相催化体系对醇选择性氧化反应的研究

Studies on Selective Oxidation of Alcohols Catalysed by Heterogeneous Organo-catalytic System

【作者】 雷娣

【导师】 张华;

【作者基本信息】 大连理工大学 , 应用化学, 2011, 硕士

【摘要】 由醇选择性氧化制备相应的醛或酮在实验室研究和工业生产中都有重要的意义。近年来,以H202、02尤其是空气作为氧化剂,以有机小分子2,2,6,6-四甲基哌啶-N-氧自由基(TEMPO)作为催化剂的绿色环保、经济高效的催化体系的开发成为研究的热点。本论文研究了以空气为氧化剂,以固载化的TEMPO作为主催化剂,以吸附的NOx(x=l,2)作为助催化剂的醇类选择性多相催化氧化体系。建立了高效、高选择性、环境友好、后处理简单、适用面广泛的醇类有氧氧化制备醛或者酮的方法。首先,将主催化剂4-氧-2,2,6,6-四甲基哌啶-N-氧自由基(4-oxo-TEMPO)固载到多孔硅珠(PSB:porous silica bead)的表面上得到多相催化剂PSB-TEMPO,再将助催化剂NOx气体吸附至多孔硅珠的孔道中得到PSB-TEMPO-NOX。以苯甲醇为底物,考察了PSB-TEMPO-NOx用量对苯甲醇的催化氧化效果的影响,当催化剂PSB-TEMPO-NOX用量为0.5 g时,1 mmol苯甲醇在4 h内完全转化为苯甲醛。随后,用溶胶-凝胶法制备了硅胶固载催化剂。在甲醇中,通过氰基硼氢化钠催化的还原氨化反应将4-oxo-TEMPO连接到三氨丙基三乙氧基硅烷上,再加入正硅酸乙酯(TEOS)和水,控制Si:H2O:MeOH为1:8:5,上述混合物发生水解和缩合反应,最后经过陈化,洗涤和研磨得到固载化催化剂S1-TEMPO。将助催化剂NOx气体吸附至S1-TEMPO的孔道中得到S1-TEMPO-NOx,以苯甲醇作为底物,当S1-TEMPO-NOx用量为0.3 g时,1 mmol苯甲醇在2.5 h内完全转化为苯甲醛。进一步,在使用溶胶-凝胶法制备硅胶固载催化剂时,若使用三乙酰氧基硼氢化钠替代氰基硼氢化钠催化还原氨化反应时,可以用乙醇作为溶剂,同样控制Si:H2O:MeOH为1:8:5,经过水解和缩合反应,得到固载化催化剂S2-TEMPO,将助催化剂NOx气体吸附至S2-TEMPO的孔道中得到S2-TEMPO-NOX,仍旧以苯甲醇作为底物,当催化剂S2-TEMPO-NOX用量为0.3 g时,1 mmol苯甲醇在2 h内完全转化为苯甲醛。采用上述两种多相催化体系,分别考察了不同醇类化合物的氧化反应。研究发现,这两种催化体系均能使芳香族伯、仲醇,脂肪族伯、仲醇,以及含杂原子O的醇类化合物在常温常压下空气中高效地、高选择性地转化为相应的醛或酮。上述3种多相催化剂在催化效率不变的情况下都可循环使用10次。结合多相催化剂的元素分析(C、H、N),FT-IR, N2吸附-脱附,NOx-TPD, TEM以及XRD测试结果,推测出了这两种多相催化体系的孔道内反应过程及机理。

【Abstract】 The selective oxidation of alcohols to the corresponding aldehydes or ketones plays a central role both in lab research and industrial production. Rencently, the development of environmental friendly and economy efficient catalytic oxidation systems is becoming the focus of the world. In these catalytic oxidation systems, hydrogen peroxide, molecular oxygen and especially air are used as clean oxidation reagents, and 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) is used as the catalyst.In our heterogeneous organo-catalytic system which is for the selective oxidation of alcohols, air was used as a oxidation reagent. TEMPO was used as a major catalyst, NOx was used as a cocatalyst. We developed an efficient, high selective, environmental friendly, easy handling and broad using method for the preparation of aldehydes and ketones from alcohols.Firstly,4-oxo-2,2,6,6-tetramethylpiperidinyl-1-oxy (4-oxo-TEMPO) which is major catalyst was immobilized on the surface of porous silica beads (PSB) to generate a heterogeneous catalyst PSB-TEMPO. NOx gas was adsorpted into the pore canal of PSB to generate PSB-TEMPO-NOx. Benzyl alcohol was used as the model substrate, we studied how the amount of PSB-TEMPO-NOx would affect the catalytic oxidation of benzyl alcohol, and it came out that 1 mmol benzyl alcohol was totally converted into benzaldehyde in 4 hours when the ammout of PSB-TEMPO-NOx was set to 0.5 g.Subsequently, S1-TEMPO was produced using sol-gel method. In methanol, 4-oxo-TEMPO was linked to aminopropyltriethoxysilane through a reductive amination reaction which is catalysed by sodium cyanoborohydride, and then tetraethoxy silicone (TEOS) and water was added to the methanol solution, Si:H2O:MeOH=1:8:5. Hydrolysis reaction and condensation reaction occurred in the mixture, after the aging process, washing and grinding. S1-TEMPO was finally obtained. NOx gas was adsorpted into the pore canal of S1-TEMPO to generate S1-TEMPO-NOx. Benzyl alcohol was used as the model substrate, we studied how the amount of S1-TEMPO-NOx would affect the catalytic oxidation of benzyl alcohol, and it came out that 1 mmol benzyl alcohol was totally converted into benzaldehyde in 2.5 hours when the ammout of S1-TEMPO-NOx was set to 0.3 g.Further more, Sodium triacetoxyborohydride was used to replace sodium cyanoborohydride in the reductive amination reaction, and correspondingly, methanol was replaced by ethanol, Si:H2O:MeOH=1:8:5. After the hydrolysis reaction and condensation reaction, S2-TEMPO was finally obtained. NOx gas was adsorpted into the pore canal of S2-TEMPO to generate S2-TEMPO-NOx. Benzyl alcohol was used as the model substrate, we studied how the amount of S2-TEMPO-NOx would affect the catalytic oxidation of benzyl alcohol, and it came out that 1 mmol benzyl alcohol was totally converted into benzaldehyde in 2 hours when the ammout of S2-TEMPO-NOx was set to 0.3 g.Finally, the oxidation of a broad range of alcohols were studied under the two above-mentioned heterogeneous catalytic systems. And it turned out that the two catalytic systems could efficiently and high selectively catalyse the convertion of a broad range of alcohols which contain aromatic primary and secondary alcohols, aliphatic primary and secondary alcohols and O-heteroatom alcohol to their corresponding aldehydes and ketones under mild conditions. The 3 heterogeneous catalysts could be used for over 10 times without the loss of activity. The pore canal reaction mechanism was proposed according to the data of the elemental analysis, FT-IR, N2 adsorption/desorption analysis, NOX-TPD, TEM and XRD analysis.

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