环糊精手性微反应器中苯乙烯的不对称环氧化反应

研究了酮与环糊精手性协同催化作用下,用非手性酮与过氧硫酸氢钾(商品名Oxone)原位产生的二氧杂环丙烷实现了对包合在环糊精手性微反应器中苯乙烯的不对称环氧化反应,考察了α-环糊精、β-环糊精、γ-环糊精与不同的酮协同催化反应效果,并对协同催化反应机理进行了探讨.结果表明,β-环糊精和甲基异丁基酮(MIBK)及Oxone原位形成的二氧杂环丙烷具有较好的协同催化作用;MIBK用量、碳酸氢钠用量、反应时间和温度等因素对反应产物的收率和对映体选择性有一定的影响.在优化条件下,环氧苯乙烷的ee值可达46%.     

羟醛缩合反应中酸碱双功能催化剂的研究进展

概述了羟醛缩合反应中酸碱双功能催化剂的分类、酸碱协同催化作用的主要影响因素并推测了酸碱协同催化反应机理。羟醛缩合反应中酸碱双功能催化剂,按其所提供的酸位和碱位的性质可以分为三类:(1)表面本身兼具酸位和碱位的双功能无机材料,(2)材料本身兼具酸位和碱位的双功能有机材料,(3)通过分别引入酸位和碱位所形成的双功能介孔材料。本文分别对这三类催化剂在羟醛缩合反应中的应用进行了综述;此外,还分析和探讨了酸碱中心的强度匹配、相对位置及空间位阻等因素对酸碱协同催化的影响并推测了酸碱协同催化反应机理;最后,对酸碱双功能催化剂在羟醛缩合反应中的应用前景进行了展望。     

Mn(Ⅱ),Fe(Ⅲ)和活性炭对S(IV)液相氧化的催化作用

在金属离子参与下S(Ⅳ)的催化氧化反应是大气含水体系中S(Ⅳ)转化为S(Ⅵ)的重要反应.普遍认为大气中的主要金属元素 Mn,Fe,Cu和 Co对 S(Ⅳ)的氧化有催化作用.尽管 Mn(Ⅰ)和 Fe(Ⅱ)对于 S(Ⅳ)催化氧化的化学动力学已被广泛研究,但至今尚未取得一致的结果;有关Mn(Ⅰ)和 Fe(Ⅱ)催化氧化的协同作用亦是人们争论的问题。本工作在分别研究了Mn(Ⅰ)和 Fe(Ⅱ)对 S(Ⅳ)氧化的催化作用的基础上,进一步考察了 Mn(Ⅰ)和 Fe(Ⅱ)是否存在着协同催化作用.另外,还探讨了Fe(Ⅱ)和活性炭、Mn(Ⅰ)和活性炭对S(Ⅳ)的氧化是否存在着协同催化作用.     

Ru/磺化石墨烯催化木糖直接转化制备糠醇

以氧化石墨烯为载体,在其表面引入酸性位-SO_3H和金属位Ru,制备了Ru/磺化石墨烯金属-酸双中心催化剂(Ru/SRGO).采用X-射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、激光拉曼光谱(Raman)、X-射线光电子能谱(XPS)、透射电子显微镜(TEM)和酸-碱滴定等技术对催化剂的结构和性质进行了表征.相对氧化石墨烯,磺化改性后石墨烯的特征衍射峰向低角度偏移(XRD),在Raman光谱中其D峰发生红移,G峰发生蓝移,结合I_D/I_G的比值证实其表面产生更多有利于活性金属Ru负载及其稳定的缺陷位.酸性表征显示催化剂表面-SO_3H密度随磺化过程中添加磺化试剂含量的增加而增加.在催化木糖直接制备糠醇的反应过程中,催化剂的活性与其表面的酸量呈正相关,而产物糠醇的选择性则随酸量的增加呈现"火焰山形态"分布,在金属和酸双中心量的匹配及其协同催化下,在150℃,1 MPa H_2条件下,实现了木糖高效转化制备糠醇,其收率达70.4%.     

脂肪酶催化作用下酰胺化反应的立体规则性研究

提出了在LipasefromCandidaAntrarctica(CAL)脂肪酶的催化作用下,含有手性中心C原子的胺类化合物酰胺化的异构选择性规则.与氨基相连的碳原子的立体结构对酰胺化反应有很大的影响.型胺类化合物呈R-型优先选择,型胺类化合物呈S-型优先选择.     

酸催化及竞争吸附对CeY分子筛吸附脱硫性能的影响（英文）

采用液相离子交换(LPIE)法制备了CeY分子筛,并研究烯烃和芳烃对其吸附脱硫性能的影响.利用固定床穿透曲线技术研究吸附剂的脱硫性能,结果表明:烯烃和芳烃的存在均导致吸附剂吸附硫容量减少,然而,烯烃的影响明显强于芳烃.采用原位傅里叶变换红外(FTIR)光谱技术研究噻吩、环己烯和苯的吸附行为,结果发现:烯烃和芳烃降低吸附剂脱硫性能的实质分别为吸附剂表面酸性导致的酸催化反应和π-络合吸附的芳烃分子与硫化物分子的竞争吸附.另外,烯烃的影响取决于吸附剂的表面酸性,尤其是强B酸(Br?nsted酸)中心.这是由于B酸中心会导致烯烃和噻吩发生质子化反应,且质子化物种易于进一步发生低聚反应.生成的低聚物覆盖吸附活性中心导致吸附剂对其它噻吩分子的吸附能力降低.     

改性纳米ZSM-5催化剂上正辛烷转化反应的研究

以纳米晶粒HZSM-5(20~50 nm)沸石为活性组分, 用碱性介质水热处理、 负载混合稀土和ZnO(或GaO)组合改性方法对纳米HZSM 5分子筛进行改性, 并用TEM， XRF， IR及XRD等手段对催化剂进行表征. 以正辛烷的芳构化和异构化为模型反应, 研究了改性纳米ZSM 5催化剂总酸和酸强度分布、 L/B酸位比例对正辛烷异构化和芳构化反应性能的影响以及催化剂酸强度、 L/B酸位比例与催化剂稳定性和积炭的关系. 结果表明, 碱性介质水热处理和混合稀土改性后, 总酸量减少和酸强度降低导致纳米HZSM-5催化剂的芳构化活性减弱, 异构化活性增强, 稳定性明显提高. 在碱性介质水热处理和负载混合稀土改性的基础上, 再负载适量氧化锌(或氧化镓)改性的催化剂， 总酸量增加, 强酸中心数量减少, B酸略有减少, 而L酸明显增加, L/B酸位比值增加. L酸中心和B酸中心的协同作用和较合适的L/B(1.4~1.7)比值使改性的纳米ZSM-5催化剂保持了较强的和稳定的芳构化和异构化活性, 催化剂积炭失活速率降低. 芳烃和异构烷烃产率分别达到约50%和30%, 高辛烷值的烷基芳烃(C7~C9)和异构烷烃(C4~C6)的选择性分别达到84%和80%.     

无酸条件下磷氰酸钠与胺反应合成磷代脲机理的密度泛函理论研究（英文）

磷氰酸钠与胺可以在室温、无酸的温和条件下反应生成磷代脲.利用密度泛函理论计算方法,在B3LYP/6-31G(d,p)水平上对磷氰酸钠与胺反应合成磷代脲的反应机理进行了研究,结果表明溶剂的辅助/催化作用可以显著降低该反应的反应势垒,使得反应快速、高转化率发生.     

聚氯乙烯热降解过程中HCl脱除机理的理论研究

使用B3LYP/6-311++G(d,p)方法对聚氯乙烯(PVC)几种可能模型化合物在热降解过程中HCl的脱除机理进行了理论计算.计算结果表明:PVC在第一阶段热降解过程中脱氯形成HCl时主要进行的是协同反应;缺陷结构的支链(如—CH_2CH_2Cl,—CHClCH_3和—CH_3)能显著降低邻近碳位脱除HCl的反应能垒;热降解产物HCl对热降解反应有催化作用;更为显著的是脱除HCl之后形成的氯丙烯基■—CHCl—)能降低HCl形成的反应能垒,而氯丁烯基■—CHCl—)对HCl的脱除几乎没有影响.     

烯烃对噻吩在介孔分子筛Al-MCM-41活性位物种上吸附脱硫机制的影响

采用后嫁接法制备了不同铝负载量的Al-MCM-41分子筛。运用XRD、N₂吸附-脱附、NH₃-TPD、Py-FTIR等方法对分子筛进行物性表征,利用固定床评价其对噻吩的吸附性能。通过将分子筛吸附噻吩能力与分子筛的酸性质及织构性质进行关联,考察烯烃存在对Al-MCM-41活性位物种吸附脱硫机制的影响。结果表明,铝物种的引入即产生了B酸中心,也同时产生了两种类型的L酸中心L₁和L₂。引入低含量铝物种利于形成B酸中心和L₁型酸中心,引入高含量铝物种利于形成L₂型酸中心。其中,L₂型酸中心对噻吩的吸附效果最佳。烯烃和噻吩在B酸中心发生竞争吸附和催化转化反应,且催化转化反应占主导地位。L₂酸中心的存在促进了B酸中心上的催化转化反应,其所生成的大分子硫化物取代噻吩吸附在分子筛酸活性中心上提高了Al-MCM-41分子筛的饱和吸附硫容量。     

Super Brønsted acid catalysis

Br?nsted acid catalysis has emerged as a new class of catalysis in modern organic synthesis. However, in order to make the utility of the Br?nsted acid catalysis as broad as the well-developed Lewis acid catalysis, it is desirable to develop Br?nsted acids demonstrating both high reactivities and selectivities. In this feature article, we will present our achievement in the design and development of strong Br?nsted acids and their application to organic reactions. Furthermore, we will describe the Tf(2)NH-catalyzed Mukaiyama aldol reaction of super silyl enol ethers. We also will highlight the differences in reactivity and chemo- and stereo-selectivity between Br?nsted and Lewis acid catalysis.     

H-MCM-22沸石分子筛中Brnsted/Lewis酸协同效应的~1H 和~(27)Al双量子魔角旋转固体核磁共振研究

采用各种固体核磁共振 (NMR) 技术详细研究了 H-MCM-22 分子筛中 Brnsted/Lewis 酸的协同效应. 二维 1H 双量子魔角旋转 (DQ-MAS) NMR 结果表明, 在脱铝 H-MCM-22 分子筛中 Brnsted 酸位 (骨架桥式羟基) 和 Lewis 酸位 (非骨架铝羟基) 之间是空间邻近的, 暗示着可能存在 B/L 酸协同效应. 二维 27Al DQ-MAS NMR 结果揭示了各种铝物种之间的空间邻近性, 表明 B/L 酸协同效应优先发生在 H-MCM-22 分子筛超笼中的骨架 T6 位铝和非骨架铝物种之间. 2-13C-丙酮探针分子实验发现, 因 B/L 酸协同效应而导致脱铝 H-MCM-22 分子筛酸性明显增强, 氘代吡啶探针分子实验也证实在 H-MCM-22 分子筛的超笼中发生了 B/L 酸协同效应. 上述结果将有助于我们理解在脱铝 H-MCM-22 分子筛上发生的多相催化机理.     

用密度泛函理论研究NO在H-ZSM-5分子筛不同酸性位的吸附

利用密度泛函理论(DFT),基于7T簇模型,在B3LYP/6-31G(d,p)水平上研究了NO分子在H-ZSM-5分子筛孔道中α,β,γ酸性位的吸附.在计算过程中,首先对H-ZSM-5的α,β,γ酸性位进行优化计算,然后对NO分子η1-N和η1-O两种吸附模式的红外光谱和吸附能进行计算.计算结果表明,NO分子以η1-N模式吸附于H-ZSM-5分子筛酸性位上,不同酸性位对NO分子的吸附能力排序为:α酸性位>β酸性位>γ酸性位.此外,H-ZSM-5分子筛直型孔道更有利于NO分子的吸附和扩散,因而可更有效地促进NO分子催化分解反应的进行.     

Chiral Brønsted acid catalysis for enantioselective Hosomi-Sakurai reaction of imines with allyltrimethylsilane

The chiral Br?nsted acid (1b or 1c) has been shown to initiate the Hosomi-Sakurai reaction of imines with excellent enantioselectivities. The combined Br?nsted acid system has been developed to offer a new class of chiral Br?nsted acid catalysis. The present system proceeds through regeneration of the chiral Br?nsted acid by proton transfer from additional Br?nsted acid to silylated chiral Br?nsted acid, a newly elucidated mechanism for the role of the additional Br?nsted acid.     

Identification and measurements of strong Brønsted acid site in ultrastable Y (USY) zeolite

By using the IRMS-TPD method in which IR (infrared) and MS (mass spectroscopy) worked together, acid sites of USY (ultrastable Y) zeolite were studied. A new band of OH playing a role of Br?nsted acid was clearly detected on Na2H2-ethylenediaminetetraacetic acid (EDTA)-treated USY at 3595 cm(-1) during an elevation in temperature after the adsorption of ammonia. MS-measured TPD (temperature-programmed desorption) of NH3 and IR-measured TPD of the NH4+ cation coincided well to show that this zeolite consisted of the Br?nsted acid sites. The MS-TPD profile at higher temperatures corresponded to the IR-TPD of the 3595-cm(-1) band, and therefore, this OH was identified as a strong acid site. From comparison between IR-TPD of OH and MS-TPD, numbers of three kinds of Br?nsted OH (i.e., those in super and sodalite cages of a Y zeolite structure) and created strong Br?nsted acid site were quantified. On the other hand, strength of the Br?nsted acid site DeltaH was determined individually by a simulation method, where the corrected IR-TPD of OH was simulated based on the proposed equation. Thus, a new strong Br?nsted acid site was identified in the EDTA-treated USY, and the amount and strength was measured quantitatively.     

Brønsted/Lewis acid synergy in dealuminated HY zeolite: a combined solid-state NMR and theoretical calculation study

The Br?nsted/Lewis acid synergy in dealuminated HY zeolite has been studied using solid-state NMR and density function theory (DFT) calculation. The 1H double quantum magic-angle spinning (DQ-MAS) NMR results have revealed, for the first time, the detailed spatial proximities of Lewis and Br?nsted acid sites. The results from 13C NMR of adsorbed acetone as well as DFT calculation demonstrated that the Br?nsted/Lewis acid synergy considerably enhanced the Br?nsted acid strength of dealuminated HY zeolite. Two types of Br?nsted acid sites (with enhanced acidity) in close proximity to extra-framework aluminum (EFAL) species were identified in the dealuminated HY zeolite. The NMR and DFT calculation results further revealed the detailed structures of EFAL species and the mechanism of Br?nsted/Lewis acid synergy. Extra-framework Al(OH)3 and Al(OH)2+ species in the supercage cage and Al(OH)2+ species in the sodalite cage are the preferred Lewis acid sites. Moreover, it is the coordination of the EFAL species to the oxygen atom nearest the framework aluminum that leads to the enhanced acidity of dealuminated HY zeolite though there is no direct interaction (such as the hydrogen-bonding) between the EFAL species and the Br?nsted acid sites. All these findings are expected to be important in understanding the roles of Lewis acid and its synergy with the Br?nsted acid in numerous zeolite-mediated hydrocarbon reactions.     

Sn-Al-β分子筛酸性在葡萄糖转化反应中作用的固体NMR研究

制备了一系列具有不同酸性质的β分子筛催化剂, 通过固体核磁共振(NMR)探针分子技术对其酸性质进行了表征, 并考察了其催化葡萄糖转化为乙酰丙酸甲酯的性能. 吸附三甲基磷的³¹P NMR实验结果表明, 含有骨架Sn以及Al原子的Sn-Al-β催化剂同时具有Br?nsted与Lewis酸性. 通过2-¹³C-丙酮探针分子区分出 3种酸强度的Br?nsted酸位, 其中一种酸强度接近“超强酸”, 可能是由于空间邻近的Br?nsted酸位和Lewis酸位发生协同作用产生的. 葡萄糖转化为乙酰丙酸甲酯的催化反应结果表明, 相比于分别只含有Lewis酸位和Br?nsted酸位的Sn-β和Al-β样品以及两者的物理混合样品, Sn-Al-β分子筛催化剂具有高催化活性与产物选择性, 这主要是由于Br?nsted酸位和Lewis酸位的协同作用产生了强Br?nsted酸位, 这种强Br?nsted酸位进一步导致了更高的催化活性.     

Catalysis of the Michael addition reaction by late transition metal complexes of BINOL-derived salens

Salen metal complexes incorporating two chiral BINOL moieties have been synthesized and characterized by X-ray crystallography. The X-ray structures show that this new class of Ni-BINOL-salen catalysts contains an unoccupied apical site for potential coordination of an electrophile and naphthoxides that are independent from the Lewis acid center. These characteristics allow independent alteration of the Lewis acidic and Br?nsted basic sites. These unique complexes have been shown to catalyze the Michael reaction of dibenzyl malonate and cyclohexenone with good selectivity (up to 90% ee) and moderate yield (up to 79% yield). These catalysts are also effective in the Michael reaction between other enones and malonates. Kinetic data show that the reaction is first order in the Ni*Cs-BINOL-salen catalyst. Further experiments probed the reactivity of the individual Lewis acid and Br?nsted base components of the catalyst and established that both moieties are essential for asymmetric catalysis. All told, the data support a bifunctional activation pathway in which the apical Ni site of the Ni*Cs-BINOL-salen activates the enone and the naphthoxide base activates the malonate.     

Plane-wave density functional theoretic study of formation of clay-polymer nanocomposite materials by self-catalyzed in situ intercalative polymerization.

It has recently been shown that the intercalation and subsequent in situ polymerization of organic monomers within the interlayer of clay minerals yields nanocomposites with novel material properties. We present results of plane-wave density functional theory (DFT) based investigations into the initial stages of the polymerization of methanal and ethylenediamine within the interlayer of sodium montmorillonite. Nucleophilic attack of the amine on the aldehyde is only observed when the aldehyde is protonated or coordinated to a metal ion. No evidence is found for the dissociation of water in the hydration sphere of the sodium counterions. The Br?nsted acidity of the hydroxyl groups present in the silicate layers is significantly affected by their proximity to sites of isomorphic substitution. However, the most obvious Br?nsted acid sources are shown to be unlikely to catalyze the reaction. Instead catalysis is shown to occur at the clay mineral lattice-edge where hydroxyl groups and exposed aluminum ions act as strong Br?nsted and Lewis acid sites, respectively.     

SO42-/TiO2-SiO2 mixed oxide catalyst, 3. An eco-friendly catalyst for esterification of acetic acid

The effect of addition of titania to silica was examined by various characterization techniques such as FT-IR, BET surface area, surface acid strength/acid sites by the Hammett indicator method and Br?nsted/Lewis acid sites by pyridine adsorbed IR study. Ti-O-Si bond is formed in case of TiO₂-SiO₂ sample, as observed from FT-IR data. Acid strength, surface acid sites, and rate constant for esterification of acetic acid are increased with Ti-O-Si bonding and sulfate impregnation. Both Br?nsted and Lewis acid sites are responsible for catalysing the esterification reaction. This revised version was published online in August 2006 with corrections to the Cover Date.