超高效聚合物凝胶色谱法快速研究酸催化木质素解聚产物

该文以温和酸催化条件下的木质素磺酸盐解聚产物为研究对象，建立系统分离和分析测试木质素磺酸盐解聚后获得的低分子酚类产物的方法。选用4根油溶性的ACQUITY APC XT小孔径刚性填料色谱柱串联，在高分辨紫外检测器条件下，采用超高效凝胶渗透色谱（APC）对解聚产物实现了高效分离，获得了高灵敏度的木质素基酚类产物的相对分子质量及其分布色谱信息。探讨了反应温度、时间和催化剂浓度等对酸催化木质素磺酸盐解聚行为的影响，结果表明，对于木酚比（木质素：苯酚）为25%（质量分数）的木质素磺酸盐解聚体系，在催化剂和木质素物质的量比为2.334、130℃酸催化反应60 min时，获得了解聚效率高达80%以上的木质素基酚类产物，解聚获得的产物相对峰高分子质量（M_p）组成均分布在720、490和260 Da 3个低聚物区间，均具有很窄的分子质量分布指数（接近1）。由此可以初步推断，木质素磺酸盐在该研究采用的温和酸催化条件下，催化反应机理不受反应时间、温度以及催化剂浓度的影响，具有特定的解聚途径。     

功能化离子液体在聚酯PET降解与合成中的应用

离子液体作为一类新兴的绿色环保型溶剂和催化剂,具有性质可调、溶解性好、催化活性高、热力学稳定性好和易于回收等优点而备受人们关注。聚酯具有多种优良性能,产能巨大,适用范围广,但造成的白色污染和资源浪费问题带来了严重的负面社会效应。通过化学回收方法,聚酯可降解为单体或低聚物从而被循环利用。本文概述了国内外废聚酯常用化学降解方法,包括水解法、甲醇降解法、乙醇降解法、乙二醇降解法等,并对主要化学降解方法的优缺点进行了比较。重点介绍了近年来功能化离子液体催化剂在聚对苯二甲酸乙二醇酯(PET)降解过程中的应用以及Lewis酸性离子液体催化乙二醇醇解PET机理,同时也描述了离子液体在聚酯合成环节中的应用。最后,总结了近年来国内外PET产能及消费量,探讨了离子液体催化剂在催化聚酯降解与合成中面临的诸多挑战。     

MnZSM-5催化剂上NH3-SCR反应机理的研究

通过密度泛函理论（DFT）对Mn/ZSM-5催化剂上NH3-SCR反应机理进行了理论研究。一种为气态NO直接参与反应的E-R机理,NO分子与[NH2]反应生成中间体[NH2NO],该反应路径的能垒为43.35 kcal/mol;另一种为吸附态NO参与反应的L-H机理,[NO]与[NH3]反应生成[NH2NO],该反应路径的能垒为44.73 kcal/mol。因两种机理的反应能垒相差不大,因此在一定温度下遵循两种机理的反应皆能进行。     

新型Ni催化剂催化乙烯聚合的中性机理

用密度泛函理论中的B3LYP LANL2MB方法 ,研究了Ni 水杨亚胺催化剂催化乙烯聚合的中性反应机理并和阳离子活性中心的催化反应机理进行了比较 .计算结果表明 ,整个中性催化机理类似于阳离子催化机理 ,但是也有不同 .两种机理都是从带空位的活性催化剂开始 ,乙烯以垂直于催化剂平面的方式占据空位 ,为了有利于甲基的迁移 ,乙烯向甲基的方向旋转 90° ,形成四元环过渡态 .插入反应发生后 ,Ni和 β C之间形成一种氢桥键 ,协助新空位的形成 ,实现链的增长 .乙烯与中性活性中心的相互作用远远强于乙烯与阳离子活性中心的相互作用 .中性催化机理较阳离子催化机理容易引发 .阳离子催化的过渡态所需的活化能比中性催化所需的活化能低 ,表明阳离子反应机理比中性反应机理容易进行 ,甲基在中性催化过渡态中的迁移明显不同于在酸性液化过渡态中的迁移 .β agostic相互作用在中性催化反应机理中 ,在主导烷基给合物中Ni所带的电荷方面 ,起着关键性的作用 .     

4,4'-二（羟甲基）联苯的合成

以4,4'-二（氯甲基）联苯为原料,经水解生成苄醇类化合物4,4'-二（羟甲基）联苯。采用¹HNMR, IR, HPLC对产物进行了表征。研究讨论了反应条件、催化剂等因素对产物含量和收率的影响,并且优化了4,4'-二（羟甲基）联苯的合成工艺,提出了可能的催化反应机理。结果表明：聚乙二醇作为催化剂,可与溶液中的阳离子发生络合,增强了亲核试剂的反应活性,提高了反应速率。在优化工艺下反应12 h,粗产品HPLC含量可达97.2%,收率93.9%。     

原位DRIFTS研究分子筛Br?nsted酸和Lewis酸催化戊烯转化的作用机理

本研究基于原位水热合成和气相浸渍的方法分别合成了含有Br?nsted/Lewis酸的Beta分子筛和只含有Lewis酸的AlCl₃@Si-Beta样品,并通过原位漫反射红外技术对比研究了Br?nsted酸和Lewis酸催化直链和侧链戊烯同分异构体转化作用机理的差异。结果表明,同时含有Br?nsted/Lewis酸的Beta分子筛中,Br?nsted酸起主要的活化作用,催化戊烯进行异构和叠合反应时均遵循经典的碳正离子机理;而AlCl₃@Si-Beta中的Lewis酸不含氢质子或羟基,催化α-戊烯进行双键迁移和2-戊烯的顺反异构反应时遵循AB-AD机理,以类烯丙基物种作为中间体,无法催化戊烯进行骨架异构和叠合反应。     

钛改性对γ-Fe2O3选择催化还原脱硝性能强化机制的分子模拟研究

采用密度泛函理论（DFT）研究了典型过渡金属Ti掺杂改性对γ-Fe₂O₃选择催化还原（NH₃-SCR）脱硝性能强化影响的作用机制。构建了单Ti和双Ti在γ-Fe₂O₃（001）表面的不同Fe位置的掺杂模型，计算了表面掺杂形成能，探讨了O₂、NO和NH₃分子在Ti掺杂前后的γ-Fe₂O₃（001）表面的吸附特性，并进行了反应机理分析。结果表明，单Ti倾向于掺杂在八面体Fe_oct位，双Ti倾向于两个Fe_oct位。Ti的掺杂增强了催化剂表面对O₂的吸附能力，吸附性能随Ti掺杂量增加而增强。单Ti和双Ti的掺杂都抑制了NO以N端在催化剂表面的吸附。Ti能够强化NH₃的吸附，增强了Lewis酸位，有利于SCR反应。Ti的掺杂增大了NO₂生成的反应能垒，降低了γ-Fe₂O₃低温区的SCR反应。Ti的掺杂抑制了NH和N的形成，避免了NH₃的过度氧化，提高NH₃的利用率，有利于SCR反应，并且抑制了通过E-R机理产生的N₂O，具有良好的N₂选择性。Ti的掺杂能够改善γ-Fe₂O₃在NH₃-SCR中还原NO的性能。     

甲烷选择催化还原NO研究进展

 近十年来,甲烷选择催化还原NOx已引起各国环境研究工作者的关注．综述了近年来甲烷选择催化还原NOx方面的研究进展,着重分析了用于该反应的催化剂的研究状况,探讨了目前比较公认的甲烷选择催化还原NOx的反应机理（NO2机理）,详细介绍了目前催化剂用于提高甲烷DeNOx反应活性的方法;并展望了甲烷选择催化还原NOx今后的研究方向．     

β-二酮亚胺钛化合物催化乙烯和环戊二烯共聚合反应机理的密度泛函理论研究

运用密度泛函理论（DFT）对β-二酮亚胺钛化合物[PhNC（CH3）CHC（CF3）O]2TiCl2催化乙烯（E）和环戊二烯（CPD）共聚合反应的反应机理进行了理论研究.计算结果表明：乙烯和CPD的共聚反应中,CPD插入反应可以通过1,2插入和2,1插入两种路径进行,1,2插入能垒略低于2,1插入,因此我们预测两种路径...     

稀土催化聚酯和共聚酯的合成

研究Ｌｎ＾３＋化合物对聚对苯二甲酸乙二酯及其共聚酯合成反应的催化效果。发现Ｌｎ＾３＋档促进酯化反应的进行,并可在缩聚阶段作为Ｓｂ２Ｏ３的助催化剂使用,通过粘度降测试表明,添加Ｌｎ＾３＋不影响聚酯、共聚酯的热稳定性。对Ｌｎ＾３＋催化酯化和缩聚反应机制进行探讨。     

Theoretical study on the Diels-Alder reaction between 2-methylacrolein and cyclopentadiene catalyzed by a cationic oxazaborolidine Lewis acid

The reaction mechanism of the Diels-Alder reaction between 2-methylacrolein and cyclopentadiene catalyzed by a cationic oxazaborolidine Lewis acid has been characterized using density functional theory calculations. The solvent effect on the studied reaction is taken into account by optimizing all stationary points in CH(2)Cl(2) using the polarizable-continuum model. Our calculations show that the presence of this cationic oxazaborolidine catalyst changes the molecular mechanism of the studied reaction from concerted to stepwise, and lowers the activation barrier by more than 10.0 kcal/mol. A comparison of the results obtained for four different reaction channels reveals that the studied reaction is energetically favorable to occur along the exo/s-cis channel, which reasonably explains the stereoselectivity of the title reaction observed in related experiments. The electronic effect of this cationic oxazaborolidine complex in catalyzing the title reaction is found to be very similar to that of the commonly used Lewis acid BF(3).     

Mechanism of Ketone Allylation with Allylboronates as Catalyzed by Zinc Compounds: A DFT Study

The mechanism of the allylation reaction between 4‐chloroacetophenone and pinacol allylboronates catalyzed by ZnEt₂ with alcohols was investigated using density functional theory (DFT) at the M05‐2X/6‐311++G(d,p) level. The calculations reveal that the reaction prefers to proceed through a double γ‐addition stepwise reaction mechanism rather than a Lewis acid‐catalyzed concerted one. The intermediate with a four‐coordinated boron center, which is formed through proton transfer from EtOH to the ethyl group of ZnEt₂ mediated by the boron center, is the active species and an entrance for the catalytic cycle. The latter is composed of three elementary steps: 1) boron to zinc transmetalation leading to the formation of allylzincate species, 2) electrophilic addition of ketone to allylzincate species, and 3) generation of the final product with recovery of the catalyst. The boron to zinc transmetalation step has the largest energy barrier of 61.0 kJ mol^?1 and is predicted to be the rate‐determining step. The calculations indicate that the additive EtOH plays important roles both in lowering the activation free energy for the formation of the four‐coordinated boron active intermediate and in transforming the low catalytic activity ZnEt₂ into high activity zinc alkoxide species. The alcohols with a less sterically encumbering R group might be the effective additives. The substituted groups on the allylboronates might primarily affect the boron to zinc transmetalation, and the allylboronates with substituents on the C_γ atom is poor in reactivity. The comparison of the catalytic effect between the zinc compounds investigated suggest that Zn(OEt)₂, Zn(OH)₂, and ZnF₂ exhibit higher catalytic efficiency for the boron to zinc transmetalation due to the activation of the B? C_α bond through orbital interactions between the p orbitals of the EtO, OH, F groups and the empty p orbital of the boron center.     

Unusual concerted Lewis acid-Lewis base mechanism for hydrogen activation by a phosphine-borane compound

Density functional theory calculations have been carried out to investigate the possible reaction mechanisms for the reversible dihydrogen activation catalyzed by a phosphine-borane compound, (C6H2Me3)2P(C6F4)B(C6F5)2 (Welch, G. C.; Juan, R. R. S; Masuda, J. D.; Stephan, D. W. Science. 2006, 314, 1124-1126). The present calculations show that an unusual concerted Lewis acid-Lewis base mechanism is more favorable than the proton transfer or hydride transfer mechanisms suggested previously. In the concerted Lewis acid-Lewis base mechanism, the H-H heterolytic cleavage is achieved through the simultaneous electron transfer from the lone-pair orbital of the Lewis base P center to the sigma* orbital of H2 and from the sigma orbital of H2 to the empty orbital of the Lewis acid B center. The solvent is found to dramatically change the potential energy surface. The proposed mechanism can account well for the bimolecular H-D exchange process observed in deuteration experiments and the experimental fact that the H2 activation is reversible at mild conditions.     

Acid-catalyzed degradation mechanism of poly(phthalaldehyde): Unzipping reaction of chemical amplification resist

The acid-catalyzed degradation mechanism of chemical amplification resists based on end-capped poly(phthalaldehyde) has been elucidated by semi-empirical molecular orbital calculations. It is concluded that: (i) two different starting points exist in the degradation of end-capped poly(phthalaldehyde), the central part of the polymer as well as the polymer end; (ii) in both cases, after the first protonation, cationic hydroxyl compounds generated decompose to the identical cation intermediate, which can unzip itself to phthalaldehyde monomers successively (unzipping reaction); (iii) the hemiacetal type intermediates hardly degrade to the same intermediate without acid catalyst; (iv) the overall activation energy for the degradation reaction is less than 14 kcal/mol in all the cases. Thus, the poly(phthalaldehyde) resist can easily self-develop below 100°C, as reported in the literature. © 1997 John Wiley & Sons, Inc.     

Direct conversion of carbonyl compounds into organic halides: indium(III) hydroxide-catalyzed deoxygenative halogenation using chlorodimethylsilane

The reaction of carbonyls and chlorodimethylsilane was effectively catalyzed by indium(III) hydroxide and afforded the corresponding deoxygenative chlorination products, in which the carbonyl carbon accepted two nucleophiles (H and Cl) with releasing oxygen. Only In(OH)3 catalyzed the reaction, and typical Lewis acids such as TiCl4, AlCl3, and BF3.OEt2 showed no catalytic activity. The reaction mechanism of this deoxygenative chlorination includes initial hydrosilylation followed by chlorination. Other nucleophiles such as allyl or iodine were available for this methodology. The moderate Lewis acidity of indium catalyst enabled chemoselective reaction, and therefore ester, nitro, cyano, or halogen groups were not affected during the reaction course.     

A Facile One-Pot Synthesis of Vinpocetine

A one-pot synthesis of vinpocetine from vincamine was established. Lewis acids caused transesterification and/or dehydration of vincamine in EtOH. FeCl₃ catalyzed both transesterification and dehydration while Ti(OEt)₄ selectively catalyzed transesterification.     

Degradation of lithium polyphosphate in presence of ethanol

Summary Hydrolytic degradation of lithium polyphosphate catalyzed by ethanol was studied. Two samples with endgroup molecular weights of 4300 and 5500 were used. They were dissolved in 0.1 M NaBf and 30% (v/v) ethanol was used as the catalyst. The hydrolytic degradation of the samples catalyzed by 0.1 M hydrochloric acid was also studied. Kinetic results show that the energies of activation obtained for ethanol-catalyzed reactions were comparable to those obtained for acid-catalyzed reactions. The results are similar to those obtained earlier for water-soluble long-chain sodium polyphosphates and the mechanism of nucleophilic attack is also expected to be the same.     

聚酯催化缩聚与热降解过程的半经验量子化学研究

以苯甲酸β-羟乙酯(BAHET)为模型反应物,采用半经验量子化学方法(PM3),分析了生成聚酯的催化缩聚与热降解机理。计算结果表明,端羟基氧与酯羰基氧是反应物与金属催化剂作用的活性位。金属催化剂与两者作用后,可以使酯羰基碳的正电性与端羟基氧的负电性增加。由于静电作用力增加,促使缩聚反应得以进行。研究结果表明,在钛系催化体系中,端羟基氧和酯醚键氧能与钛原子作用形成热力学稳定的五元环结构,它的存在将影响钛系催化体系中聚酯的热降解行为。     

Mechanism of the Aerobic Homocoupling of Phenylboronic Acid on Au20−: A DFT Study

The mechanism of the gold nanocluster‐catalyzed aerobic homocoupling of arylboronic acids has been elucidated by means of DFT calculations with Au₂₀^? as a model cluster for the Au:[poly(N‐vinylpyrrolidin‐2‐one)] catalyst. We found that oxygen affects the adsorption of phenylboronic acid and, by lowering the energy barrier, a water molecule enhances dissociation of the C?B bond, which is probably the rate‐determining step. The key role of oxygen is in activating the surface of the gold cluster by generating Lewis acidic sites for adsorption and activation of the phenylboronic acid, leading to the formation of biphenyl through a superoxo‐like species. Moreover, the oxygen adsorbed on the Au nanocluster can act as an oxidant for phenylboronic acid, giving phenol as a byproduct. As shown by NBO analysis, the basic aqueous reaction medium facilitates the reductive elimination process by weakening the Au?C bond, thereby enhancing the formation of biphenyl. The coupling of phenyl and reductive elimination of biphenyl occur at the top or facet site with low‐energy‐barrier through spillover of phenyl group on Au NC. The present findings are useful for the interpretation or design of other coupling reactions with Au NC.     

Cooperative catalysis: Condensation-aromatization for synthesis of 2-(4-nitrophenyl)-1H-benzimidazole by silica immobilized Brønsted-Lewis acidic ionic liquid (Si-BLAIL)

Herein, pleasing the advantageous of both Brønsted and Lewis acidic site of Si-BLAIL the condensation-aromatization reaction has been carried out. The striking distinctiveness of work is optimum reaction condition, easy work-up, high yield, catalyst recyclability, non-inertness of reaction flask, simple catalyst loading method. The decreases in the amount of catalyst and reaction time shows good to high (71%–93%) yield suggests about the involvement of some interesting mechanism such as cooperative catalysis. The mechanism has been hypothesizes as, the Si-BLAIL increase the efficiency of condensation reaction possibly by providing the proton in 2-position of cationic imidazolium ring of BLAIL through the hydrogen bond interaction with carbonyl group and nucleophilic activation during aromatization by hydrogen bond acceptor ability of Lewis adduct anion of BLAIL. The catalyst Si-BLAIL shows massive affirm for industrial applications. The Si-BLAIL has identified as the best acid catalyst for 2-(4-nitrophenyl) benzimidazole synthesis with additional benefits of cooperative catalysis.