【作者】 毛建拥；

【导师】 李浩然；

【作者基本信息】 浙江大学 ， 化学， 2009， 博士

【摘要】 由于氧化反应不仅是有机化合物官能团化的重要一环,同时也是污染十分严重的反应,给环境带来了极大的危害,所以氧化反应的绿色化一直是化学化工领域研究的热点。分子氧是最廉价,清洁的氧化剂,且理论氧化产物除目标产物就是水,在温和条件下实现分子氧氧化是将碳氢化合物转化为含氧有机物最理想的方法。然而,由于分子氧的惰性,一般情况下分子氧不能直接对底物进行氧化,而必须借助于合适的催化剂进行活化。因此,在分子氧氧化反应中,高效、高选择性,能够活化分子氧的催化剂的开发是研究的关键。本论文的研究以维生素E中间体β-异佛尔酮的氧化为模板,以空气为氧化剂,从环境和经济的角度设计和开发了适合这一反应的各种均相和非均相催化剂；同时通过反应过程的监控以及反应中间体的分析,对反应机理进行了猜测和证明。论文首先以天然氨基酸为原料,合成了一系列Salen型和三齿型氨基酸席夫碱-金属络合物,并首次应用于p-异佛尔酮催化氧化反应中。从反应效果来看,新合成的氨基酸类席夫碱比传统席夫碱类催化剂具有更好的催化活性及选择性。同时相比于Salen型席夫碱催化剂,三齿型氨基酸席夫碱催化剂结构更简单,便宜易得,且性质稳定,是适合工业应用的仿生催化剂。另一方面,通过不同氨基酸席夫碱催化性质的比较也发现,氨基酸侧链结构的变化对催化剂性质具有明显的影响。如增加侧链链长有利于提高反应选择性,而侧链上增加-COOH或者-OH等基团有利于催化剂活性的提高。这种构效关系的研究为设计和合成具有特定性质的席夫碱类催化剂提供了参考。其次,论文针对均相催化剂难以回收和重复利用的缺点,从非均相催化氧化的角度出发,设计与合成了活性多孔Si02支载金属盐催化剂和嵌段共聚物高分子支载金属盐催化剂。这两种不同方法得到的支载型催化剂都可以通过简单过滤对催化剂进行回收和重复利用。同时,进一步的研究也发现：活性多孔Si02通过吡啶改性以后,可以将FeCl3金属活性中心牢固的支载在多孔Si02孔道内,从而使得FeCl3发生“活性位分离”。这有效地抑制了FeCl3过渡活化引起的反应物二聚等现象。因而,相比于FeCl3,支载后的催化剂具有更高的选择性。另一方面,由于嵌段共聚物高分子具有双重性质,其一端可以和活性金属中心发生配位,从而达到支载的效果；而另一端仍旧保持良好的溶解性。从反应效果来看,由于这类支载型催化剂颗粒小,且在反应体系中具有良好的扩散性,同时金属离子和嵌段共聚物具有合适的配位结构,因此其表现出和均相催化剂类似的高活性和选择性。不仅如此,由于嵌段共聚物本身在温度升高的情况下容易自聚,利用这一性质可以通过调节温度来改变胶束聚集颗粒的大小,从而达到良好的催化剂一反应体系分离的效果。另一方面,针对金属催化氧化环境污染严重的缺点,论文利用PINO和TEMPO等氮氧自由基催化剂,对p-异佛尔酮进行非金属催化氧化的研究。由于在反应中完全避免了金属的参与,因而是环保的氧化路线。进一步的研究也发现,在没有任何金属或者非金属共催化剂存在的情况下,仅用催化剂量的氮氧自由基催化剂即可有效地催化氧化β-异佛尔酮,产物选择性超过90%。为了解释这一结果,论文通过对反应过程的分析,结合ESR捕获自由基以及理论计算等手段,提出了p-异佛尔酮非金属催化氧化的自由基反应机理。这个机理的提出,不仅解释了反应中只用少量氮氧自由基即可催化氧化的原因,同时也为推测和验证相关体系的氧化反应机理提供了新的思路。当然,论文中新设计合成的催化剂并不局限于p-异佛尔酮的氧化。为了证实这些催化剂的适用性,它们也被应用于其它不饱和碳氢化合物的氧化,主要包括α-蒎烯,环己烯及其衍生物等。从反应效果来看,新合成的均相及非均相催化剂都具有良好的催化活性和选择性。总的说来,论文的研究背景是传统氧化反应的绿色化改造,以β-异佛尔酮氧化反应绿色化为模板,合成和开发了几类具有不同性质与功能的均相及非均相催化剂。通过对不同催化剂的合成与表征,催化氧化过程的分析,以及对反应机理的猜测和证明,建立了一套研究催化氧化反应的方法,为进一步研究相关氧化反应提供了理论基础。更多还原

【Abstract】 Green oxidation of organic compounds has attracted much attention in the field of chemistry and chemical engineering. Molecular oxygen is the cheapest and cleanest oxidant, and when it is used in oxidation, its by-product is only H2O. Thus the best way for the conversion of hydrocarbons to oxygen-containing products is through molecular oxygen oxidation under mild conditions. However, since molecular oxygen is inert, it could not react with substrates directly. In fact, molecular oxygen must be activated firstly by appropriate catalysts. Therfore, the development of high active and selective catalysts is the key point for molecular oxygen oxidation. In the present work, the oxidation of (3-isophorone with molecular oxygen as the oxidant was studied. Several kinds of homogeneous and heterogeneous catalysts have been developed for the environmental and economical point of view. Meanwhile, the reaction mechanism was investigated by optimizing the reaction conditions, and the characterization of the intermediates.We firstly focused on the synthesis of a series of amino acid Schiff base catalysts (including salen-type Schiff bases and tridentate Schiff bases). All of them were applied in the oxidation of P-isophorone, and the reaction conditions have been optimized. The results indicated that all the obtained amino acid Schiff bases provided higher activity and selectivity than general Schiff bases used before. The tridentate Schiff bases were more simple, more stable, cheaper, and more facilitate to be synthesized, compared with the salen-type ones. On the other hand, detailed studies showed that the M-Ami-sal Schiff bases with different functional groups displayed an important role in the oxidation ofβ-isophorone. It was found that the tridentate Schiff bases containing hydroxyl group and/or carboxyl group on side chains was favorable for improving its activity, while increasing the alkyl length improved its selectivity. This result was valuable in designing of different Schiff base catalysts with special functions.Since the above homogeneous catalysts were difficult to be recycled and reused, we then developed the heterogeneous catalysts, including poros silica suppoted FeCl3 and di-block copolymers supported CuCl2. Both of them could be recycled through simple filtration from the reaction mixture. Further studies confirmed that pyridine modified silica could immobilize FeCl3 firmly. The active site (FeCl3) was isolated, and the silica support played the cooperation effect with the active site. Thus the supported catalysts provided higher selectivity than that using the support and the active site separately. On the other hand, the di-block copolymers were used as the ligand to coordinate with copper ions. Though PDMAEMA block decreased its dispersion ability due to the combination with copper ions, the PEG block in the periphery remained well dispersion ability. Thus the finely dispersed CuⅡ-PDMAEMA-b-PEG clusters and their nano-scaled particle size notably provided high activity for the oxidation ofβ-isophorone. Besides, the coordination of copper ions with PDMAEMA blocks resulted in a stable CuⅡ-N2O2 structure. Thus it presented as high selective homogeneous catalysts used before. Moreover, an important feature of the CuⅡ-PDMAEMA-b-PEG catalyst was that its particle size could be changed under different temperatures. Hence, it could be easily leached from the mixture and recovered through simple treatments, allowing for their reuse.All the above catalysts contained metal ions as the active site. Because the use of metal ions would produce much pollution to the environment, we developed the metal-free catalysis with nitroxyl radicals (such as PINO, TEMPO, etc.) as catalysts in the oxidation of P-isophorone for the first time. It was the most environmental benign method since no metal ions was participated in the oxidation reaction. Further studies found that only catalytic amounts of the nitroxyl radical catalysts were needed in the oxidation. They provided high efficiency (KIP yiled> 90%) in the absence of any metal-containing or non-metal containing co-catalysts. The oxidation mechanism was hypothesized and discussed with ESR, GC-MS and theoretical calculation methods. This oxidation mechanism well expained that why only catalytic amounts of the nitroxyl radicals without any metal-containing or non-metal containing co-catalysts, could efficiently catalyze the oxidation ofβ-isophorone.All the synthesized catalysts were not only used in the oxidation ofβ-isophorone. To check their applibility, all of them were used in the oxidation of some other cyclic olefins, includingα-pinene, cyclohexene, and their derivatives. The results confirmed that the novel synthesized catalysts provided higher activity and selectivity than general catalysts used before.The background of the present study was the green process of the traditional oxidations. Several kinds of homogeneous and heterogeneous catalysts were developed for the aerobic oxidation ofβ-isophorone. We have offered a new method for the synthesis, characterization and oxidation. These results provided more choises for the researches in other oxidations.更多还原