【作者】 陈丽娟；

【导师】 李光兴； 梅付名；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2008， 博士

【摘要】 Co-salen配合物具有结合氧能力强,结构稳定、合成简便的特点,广泛用于氧化反应和不对称手性合成的催化剂。有关Co-salen催化氧化羰化反应的报道较少,且使用的Co-salen以均相为主。我们以含不同取代基Co-salen为催化剂,成功用于苯胺氧化羰化反应,并且采用不同方法对其多相化,在保持Co-salen催化体系活性的同时,解决了催化剂和产物的分离问题,提高了催化剂稳定性和重复实用性。为了测试多相催化剂的活性,我们采取的目标反应是苯胺氧化羰化合成苯氨基甲酸甲酯（MPC）的反应。氨基甲酸酯的主要用途是作为聚氨酯（PU）单体异氰酸酯的合成中间体以及农药、药物合成方面,是一类具有重要商业价值和工业应用前景的化工原料,它的传统工艺合成一直是有毒,原子经济性较差的“光气法”,以CO为原料的羰化法为氨基甲酸酯的绿色合成提供了新的方法。CO作为低毒,低成本,来源广泛的化学试剂,除了作为还原剂,近年来,在一碳化工及有机合成中,它作为反应试剂合成多种羰基化合物应用越来越得到重视。在有CO介入的各类羰化反应中,离不开催化剂的参与,开发高活性,可重复使用和环境友好的催化体系一直是研究的热点。对于羰化法合成氨基甲酸酯取代光气法的绿色工艺,目前报导的催化剂主要有Ⅷ族过渡金属配合物及盐,无机非金属S、Se、Te等化合物,但对于后者,由于催化剂本身的毒性和难以分离,制约了其进一步的应用。本文首先研究了无醇条件下,苯胺氧化羰化合成N,N’-二苯脲的反应,提出了新型的Co（Ⅱ）salen/吡啶助剂均相催化体系。考察了不同Co（Ⅱ）salen/吡啶助剂催化体系的催化性能,研究了salen上取代基、不同吡啶衍生物助剂、主催化剂和助剂配比、催化剂装量以及温度、压力、原料气组成等反应条件对催化活性的影响,并在此基础上讨论了基于氨甲酰配合物中间体的反应机理。尽管Co（Ⅱ）salen均相催化体系具有很好活性,且和广泛使用的贵金属相比,更具有一定经济优势。但在使用中,存在和产物分离困难,溶剂用量大,不能重复使用等问题,而高效均相催化剂多相化是解决这些问题的有效途径。我们首先采用“瓶中装船”的方法,将上述合成的六种Co（Ⅱ）salen配合物成功封装于Y型分子筛的孔道内。采用FT-IR,UV-Vis,BET比表面分析,X射线粉末衍射（XRD）,X射线光电子能谱（XPS）,热重分析（TA）等方法对负载催化剂进行结构表征,并用原子吸收光谱法确定负载催化剂Co含量和反应前后Co的流失量。以苯胺氧化羰化合成苯氨基甲酸甲酯反应对负载催化剂进行活性测试,并和相应均相催化剂做比较。和均相催化剂相比,负载催化剂活性有所增加。对回收催化剂和新鲜催化剂进行XPS分析,Co的价态未发生改变。原子吸收结果表示,Co含量无明显变化,活性也无改变,说明催化剂在反应条件下是稳定和可重复使用的。利用不同活性基团对salen配体进行官能团修饰,使之和硅烷偶联剂反应,再和有机硅源进行水解共缩聚,使活性组分负载在SiO₂网络骨架上,是负载配合物催化剂广泛使用的策略。而采用此法负载Co（Ⅱ）salen催化剂用于苯胺氧化羰化合成氨基甲酸酯还未见文献报道。我们选用两种不同的salen配体,经氯甲基修饰后和氨丙基三乙氧基硅烷反应,再和TEOS按一定比例水解缩聚,制备了两种有机无机杂化催化剂。这两个负载催化剂同样在苯胺氧化羰化制氨基甲酸酯反应中显示出好的催化活性。在实验条件下,对于Co（Ⅱ）salen-NH-SiO₂,苯胺转化率为62.6%,MPC选择性为87.2%,对于Co（Ⅱ）salophen-NH-SiO₂,苯胺转化率为63.8%,MPC选择性为88.6%。催化剂循环五次,活性保持不变,AAS显示不存在Co流失。在进一步的研究中,考虑到含低含量TiO₂的SiO₂复合氧化物具有选择性氧化活性,我们以低含量的Ti对载体进行改性,采用溶胶-凝胶法制备负载Co（Ⅱ）salen催化剂。我们以5-氯甲基水杨醛为起始原料,合成5-醛基水杨醛,再和二胺缩合生成不同salen配体。再通过醛基和硅烷偶联剂上氨基反应,和TEOS水解或TEOS+TBOT共缩聚形成酰亚胺键合的有机无机杂化材料。采用FT-IR,UV-Vis,XRD,XPS,TEM,TG等对杂化材料进行结构表征,FT-IR谱显示Ti-O-Si键的存在,表明掺入的TiO₂和SiO₂间存在化学键作用,从而在SiO₂表面引入一定数量酸中心。以未担载配合物的Ti-Si复合氧化物为催化剂的活性测试结果显示,载体显示一定的催化活性,而负载在Ti-Si复合氧化物载体上的Co（Ⅱ）salen配合物相比于负载在SiO₂载体上的配合物活性显著增强。以苯胺氧化羰化合成苯氨基甲酸甲酯为目标反应,实验条件下,苯胺转化率为60.7%,MPC产率为53.5%,选择性达88.1%。催化剂在循环使用中保持稳定,原子吸收显示回收催化剂和新鲜催化剂的Co含量几乎相同,且在反应后除去催化剂的釜液中检测不到Co离子的存在。对基于负载Co（Ⅱ）salen和KI催化体系的苯胺氧化羰化机理进行了初步探索。对载体的影响进行了研究,分别选取高分子载体、介孔MCM-41分子筛载体、和无定型SiO₂载体共价键合负载相同Co（Ⅱ）salen配合物,并进行活性比较。结果显示介孔MCM-41上配合物活性最低,高分子载体负载配合物在第二次使用时,活性显著下降,原子吸收显示Co流失比较严重,而采用溶胶凝胶法负载在无定型SiO₂载体上配合物活性稳定,能重复使用。说明配合物的活性和载体结构的规整程度有一定关联,具有一定结晶性和规整孔结构的介孔分子筛并不适于做苯胺氧化羰化Co（Ⅱ）salen催化剂的合适载体。更多还原

【Abstract】 Co-salen complexes are widely used as catalysts in the fields of oxidation and asymmetric synthesis,which have the advantadges of powerful oxygen complexation and simple synthesis.There are few reports about their use in oxidative carbonylation of aniline, and even if most are used as homogeneous catalysts in the reaction.We successfully synthesized a series of Co-salen complexes with different substituents and applied them as homogeneous catalysts in oxidative carbonylation of aniline.In the further studies,we prepared supported Co-salen catalysts by different methods in order to solve the problems of separation catalyst from products,to maintain their activity and increase their stability and reusability.The activities of heterogeneous Co-salen catalysts are tested by oxidative carbonylation of aniline to methyl N-phenyl carbamate（MPC）.Carbamates are mainly used in the fields of polymers as intermediate of isocyantes,pesticides and synthesis of drugs.Their traditional manufacture is "phosgene process" in which toxic and pollutive phosgene used as raw material,and recently,carbonylation using CO offers a new green process for the manufacturation of MPC.CO is a reagent of low toxicity,low cost and accessibility,despite acting as reductant in reactions.In recent years,application of CO as a carbonylating reagent to synthesize many kinds of carbonyl compounds in the field of organic synthesis has been attracted more and more attention.All kinds of CO-induced carbonylation need catalyst,and a great amount of research work has been focused on the development of catalytic system of high catalytic activity,recovery and environmentally benignity.In the green process for carbamates via carbonylation,the widely reported catalysts include groupⅧmetal salts,complexes and some S,Se,Te compounds,for the latter,the inherit toxicity of catalysts,inseparable from product,limit its further application in industry.Firstly in this paper,we studied the oxidative carbonylation of aniline to N, N’-diphenyl urea without presence of alcohols,and proposed novel non- corrosive and effective Co（Ⅱ）salen in combined with pyridine base ligands catalytic system.Using salicylaldehyde derivatives with different substituents and various diamine as starting materials,we synthesized six salen ligands and corresponding Co（Ⅱ）salen complexes,the catalytic activity of various Co（Ⅱ）salen/pyridine catalytic system was investigated,the effect of substituent of salen,promoter,mole ratio of Co（Ⅱ）salen to promoter,catalyst loading,temperature,pressure and partial pressure ratio of feed gas CO to O₂ on the catalytic activity of catalyst were also studied.The best results emerged from Co（Ⅱ）salophen（OH）₂/4-methyl pyridine composite catalytic system,the conversion of aniline is 85.3%and the separate yield of diphenyl urea is 79.2.On the basis of the experimental results,a plausible mechanism was proposed based on the formation of carbamyl compound.Although homogeneous Co（Ⅱ）salen catalysts have comparable activity to noble base catalysts and cheaper than them,the disadvantages companied with the homogeneous catalysts such as separation,requirement of large amount of organic solvent and recovery are also serious.The efficient route to solve the problems is the heterogenization of homogeneous catalyst.Firstly we use a "ship in bottle" method to heterogenize six Co（Ⅱ）salen complexes.They are well characterized by FT-IR,UV-Vis,BET,XRD,XPS and thermal analysis（TA）,the content and leaching of Co are determined by AAS.The immobilized catalysts and their homogeneous analogues are evaluated by oxidative carbonylation of aniline to methyl N-phenyl carbamate（MPC）.The immobilized catalysts have superior activity to their homogeneous analogues.For example,when the reaction was performed over homogeneous Co（Ⅱ）- salophen -（OH）₂,the conversion of aniline is 51.6%and the yield of MPC is 38.8%,when it was encapsulated in Y zeolite,the conversion of aniline is promoted to 63.2%and the yield of MPC is raised to 45.4%.The XPS and AAS results demonstrated that the encapsulated catalysts have perfect stability and reusability,after 5 cycles,their activities keeps unchanged.Using muti-step procedure heterogenizing homogeneous complex catalysts on silica matrix is a widely applied strategy and well reported in a great amount of papers.This strategy involves the standard four steps,that is,functionalization of ligand with reactive group,reaction with silane coupling agent,complexation with metal ion and hydration and co-condensation with organic silica source.To the best of our knowledge,the application of immobilized Co（Ⅱ）salen catalyst on silica via covalent bond in the oxidative carbonylation of aniline to MPC has not been reported.We choose two salen ligands with different diamine bridge,functionalizing them with chloromethyl group,then reacting with 3-aminopropyl triethoxysilane to form silylating salen ligand.The silylated ligand coordinated with Co²⁺ ion,followed by hydration and co-condensation with TEOS in some ratio to prepare two hybrid catalysts.The two hybrid materials are characterized by FT-IR, UV-Vis,TA and XPS,and the possible structural formula is determined.The two supported catalysts also show good activity in the oxidative carbonylation of aniline to MPC.Under the experimental conditions,the conversion of aniline and selectivity of MPC are 62.6% and 87.2%for Co（Ⅱ）salen-NH-SiO₂,63.8%and 88.6%for Co（Ⅱ）salophen-NH-SiO₂.The supported catalysts are recycled for five times without the loss of activity,and no Co⁺⁺ leaching is detected by AAS.In the further research work,considering the mixed TiO₂-SiO₂ oxide with low content of Ti has selective oxidation activity for some reactions,we conclude that the introduction of low content TiO₂ in silica matrix is favored by partial oxidation of reactive substrates. We prepared supported Co（Ⅱ）salen on SiO₂ or TiO₂-SiO₂ modified with low content of Ti, their activity were tested and compared by oxidative carbonylation of aniline to MPC.The hybrid materials,Co（salen）-C=N-TS（x）,the letter x in bracket represents the Ti/Si ratio in preparation,were characterized by FT-IR,UV-Vis,XRD,XPS,TEM and TG,the IR spectra demonstrated the existence of Ti-O-Si hetero- linkages.Using pure TiO₂-SiO₂ as catalyst to catalyze oxidative carbonylation of aniline,we found that the acidic TiO₂-SiO₂ support showed some activity with 31.2%of the conversion of aniline and 10.9%of the yield of MPC.The activity of Co（Ⅱ）salen supported on TiO₂-SiO₂ is higher than that supported on SiO₂.Co（Ⅱ）salophen-C=N-TS（0.1） showed the best activity with 60.7%of the conversion of aniline,53.5%of the yield of MPC and 88.1%of the selectivity of MPC.The AAS results also confirm that the Co content of recovered catalyst is same as the fresh catalyst, and no Co⁺⁺ leaching in the reacted mixture is detected.The investigation into the mechanism of oxidative carbonylation catalyzed by Co（Ⅱ）salen/KI catalytic system is also conducted,and a plausible mechanism based on carbamyt intermediate is proposed.To study the effect of supports,organic crosslinked polystyrene,hexagonal mesoporous molecular sieve MCM-41,and amorphous SiO₂ were chosen to anchor the same Co（Ⅱ）salen complex via covalent bond.The catalytic activities of these heterogeneous catalysts were compared by oxidative carbonylation of aniline.According to the catalytic results,the Co（Ⅱ）salen supported on MCM-41 shows the lowest activity,and the activity of the Co（Ⅱ）salen complex supported on polystyrene shows a sharp decrease when the catalyst is reused for the second time,the AAS results demonstrates the serious leaching of Co⁺⁺ into solution.Comparing the two support,the Co（Ⅱ）salen complex supported on amorphous SiO₂ via sol-gel process shows good activity,and the activity can be perfectly maitained when they are reused for several times.These facts indicate that activity of the complex has some relationship to the regularity of the support,and the mesoporous molecular sieve with uniform pores distribution and partial crystallinity is not a suitable support for Co（Ⅱ）salen in oxidative carbonylation of aniline.更多还原