排序方式: 共有58条查询结果,搜索用时 109 毫秒
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应用从头算分子轨道法分别在RHF/6-31G**和UHF/6-31G**水平上对3腔┤┓肿拥幕?S0)和三重激发态(T1)单键旋转异构反应机理进行了研究,优化出反应物和产物在S0态和T1态的4种平衡态和过渡态的几何构型,通过振动分析得到的虚频和计算的内禀反应坐标对过渡态进行了确认,并得到了零点能,根据基态和激发态反应途径分析了光反应机理。计算结果表明,基态和激发态的3腔┤┓肿拥ゼ旃狗从ξ焕萁系停嘏湃菀追⑸永砺凵涎橹ち斯夥从κ笛橹屑钢忠旃固宓拇嬖凇? 相似文献
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Mixed ammonium-transition metal salts with formula of (NH4)xMyHzPMo12O40 (M = Ni2+, Co2+ or Fe 3+) denoted as MPMo12 have been investigated for the oxidation of propane, with molecular oxygen, at temperature range between 380℃ and 420℃ after in-situ pre-treatment performed at two heating rate of 5 or 9℃/min. They were characterized by BET method, XRD, UV-Vis and IR techniques. The catalysts were found to be active in the propane oxidation and selective to propene or acrolein, in particular for samples pre-t... 相似文献
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微波固相法制备ZnCl2/NaY催化剂ZnCl2/NaY在月桂烯Diels-Alder反应中的催化性能 总被引:13,自引:0,他引:13
比较了微波固相法、普通加热法和简单混合法制备的ZnCl2/NaY及溶液离子交换法制备的ZnNaY在月桂烯与丙烯醛Diels-Alder反应中的催化性能,发现微波固相法制备的催化剂表现出最高的环加成选择性和区域选择性.通过对微波固相法制备的催化剂中ZnCl2负载量的考察,揭示了微波诱导ZnCl2在NaY分子筛表面形成了不同催化活性中心的特点,分散在分子筛表面的ZnCl2具有更高的催化活性和区域选择性.微波辐射可成功地将ZnCl2固载于NaY分子筛中,当ZnCl2负载量为6.3%时,ZnCl2与NaY分子筛主要发生固态离子交换反应;当ZnCl2负载量达25%时,催化活性提高了3倍,区域选择性提高了1倍以上.而且,以微波固相法制备的ZnCl2/NaY催化剂,其环加成选择性和区域选择性随反应温度的升高而下降. 相似文献
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用共沉淀法制备了不同比例的MoCrTeO、MoCoTeO和MoCrTeCoO复合氧化物催化剂,考察其对丙烷选择氧化制丙烯醛反应的催化性能,并对反应温度、空速、原料气比例等条件进行优化,得到丙烯醛最高产率为22.96%.实验结果表明,Te元素的添加对提高丙烯醛的选择性和产率起了十分重要的作用,但过高的Te含量却不利于丙烷的转化率.X射线衍射表征结果表明,催化剂中正交系TeMo5O16相可能是丙烷选择氧化制丙烯醛反应的重要的活性相. 相似文献
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A radical polymerization reaction of acrolein is reported in this article. The free radical initiator which can effectively promote the free radical polymerization of acrolein is screened out. The optimal conditions of the reaction are investigated and the yield could be up to 93.67%, in which the ratio of initiator to monomer is 1:50, monomer concentration is 7.5 mol L?1, reaction temperature is 50 °C, and the reaction time is 6 h. The structure characterizations of the obtained polymers are performed using hydrogen nuclear magnetic resonance spectroscopy, fouriertransform infrared spectroscopy, and matrix‐assisted laser desorption ionization time of fligh mass spectroscopy. The results show that the structure of the polymer contains fragments generated by decomposition of the initiator, aldehyde groups, and vinyl groups. The reaction mechanism of acrolein polymerization in the presence of free radical initiator is proposed. Thus, a novel method for the preparation of polyacrolein via radical polymerization is provided in this article. 相似文献
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Carini M Aldini G Beretta G Arlandini E Facino RM 《Journal of mass spectrometry : JMS》2003,38(9):996-1006
Acrolein (ACR), the carbonyl toxin produced by lipid peroxidation, is significantly increased in Alzheimer's disease brain. Since ACR is one of the most reactive and neurotoxic aldehydes, and human brain contains both carnosine (beta-alanine-L-histidine) and homocarnosine (gamma-aminobutyryl-L-histidine), the aim of this work was first to evaluate the quenching ability of the two peptides towards ACR and then to characterize their reaction products by electrospray ionization tandem mass spectrometry (ESI-MS/MS; infusion experiments; positive-ion mode). The reaction progress of ACR with carnosine or homocarnosine was studied in phosphate buffer, by monitoring ACR consumption (by reverse-phase LC) and formation of the reaction products by ESI-MS/MS at different incubation times. N-Acetylcarnosine was used as reference compound to identify the sites of reaction. Both the dipeptides were able to quench ACR by almost 60% at 1 h and by more than 85% after 3 h incubation. Different reaction products between ACR and carnosine/homocarnosine were detected after 3 and 24 h, to indicate a complex reaction pathway involving sequential addition of 1, 2 and 3 moles of ACR/mole of the dipeptide to both the beta-alanine and histidine residues. The ESI mass spectra of ACR/carnosine reaction mixtures indicate formation of several molecular species, among which the predominant are: (a) the 14-membered macrocyclic derivatives, deriving from the formation of the iminic bond between the terminal amino group followed by intramolecular Michael addition of the C(3) of the ACR moiety to histidine; (b) the N(beta)-(3-formyl-3,4-dehydropiperidino) derivatives arising from the Michael addition of two acrolein molecules to the amino group of beta-alanine, followed by an aldol condensation and dehydration.The reaction of homocarnosine with ACR follows the same pathway, giving rise to the formation of homologous adducts. The results of this study shed light on the mechanism, until now never demonstrated, through which carnosine and homocarnosine detoxify the highly reactive aldehyde acrolein in a buffer system, and represent the starting point for further studies aimed at elucidating the biological role of these dipeptides in brain. 相似文献
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采用柠檬酸法制备了SnO2纳米材料,并采用差热-热重、 X射线衍射、透射电子显微镜和氮吸附等技术对其进行了表征,考察了其在丙烯醛还原制烯丙醇反应中的催化性能. 结果显示,制备的SnO2纳米材料粒径(尺寸为8~10 nm)均一, 并具有多孔性质(孔径4~6 nm); 在丙烯醛还原制烯丙醇反应中具有良好的催化性能,催化剂的初始活性很高,丙烯醛的初始转化率可达93.6%, 烯丙醇的最高选择性为60%, 烯丙醇的最高收率为47%. 表面结焦是造成催化剂失活的主要原因. 相似文献
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MoPO/SiO2催化剂上丙烷选择氧化制丙烯醛 总被引:6,自引:0,他引:6
研究了MoPO/SiO2催化剂对丙烷选择氧化制丙烯醛的催化性能.MoO/SiO2催化剂主要表现出对丙烷氧化脱氢的催化性能,在该催化剂中添加磷后,丙烷转化率和选择氧化产物丙烯醛的选择性明显提高.催化剂的X射线衍射、拉曼光谱、程序升温还原、吡啶吸附红外光谱和程序升温脱附等表征结果表明,MoO/SiO2催化剂主要含有MoO3晶相,添加磷后,形成了表面多钼酸物种,磷以PO4四面体结构存在于表面,可能形成部分Mo—O—P键,从而抑制了MoO3在MoPO/SiO2上的形成,起到分隔活性中心的作用.在MoO/SiO2催化剂中添加磷后,催化剂的B酸和L酸酸性均增强,有利于丙烷在MoPO/SiO2催化剂表面活性的提高.由此可见,催化剂表面结构和酸性的变化可能是导致MoPO/SiO2催化性能提高的原因. 相似文献
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Nature employs dihydroxyacetone phosphate (DHAP) as the donor component in various enzyme-catalyzed aldol reactions. Probably the most significant example in this regard is photosynthesis, in which D-glucose, the most widespread natural product, is formed in just a few steps from DHAP. In recent years a number of synthetic equivalents of DHAP have been reported that deserve particular attention, as their applicability in organic synthesis is not limited to (stereoselective) aldol reactions. The power of these reagents has also been demonstrated convincingly in numerous other asymmetric electrophilic alpha-substitution reactions in target-oriented syntheses. Furthermore, the related 1,3-dioxins are useful equivalents of 2-substituted acrolein derivatives. 相似文献