阳极氧化法制备TiO2多孔薄膜

本文综述了制备TiO₂薄膜的各种方法,详细介绍了阳极氧化法制备TiO₂多孔膜的进展,在非含氟电解液体系中,对纯钛进行阳极氧化处理可制得表面呈无规则生长的多孔膜结构;在含氟电解液体系中,则可自组织形成高度有序的TiO₂纳米管阵列,并指出阳极氧化法是可在常温低压下进行、操作工艺简单、薄膜性能稳定、再现性好的一种最具工业化应用潜力的制备方法。     

新型大环磺酰胺肽模拟物的设计及其关键前体的合成

动植物、微生物和病毒等都含有微量的环肽 ,其中大多具有明显的生理活性 ,因此 ,受到科学家们的高度重视 [1] .设计与合成具有生理活性的新型环肽是目前有机合成的前沿课题 [2～ 4 ] .烯烃复分解闭环反应 ( RCM)已成为构成碳环和杂环的重要手段 [5～ 7] .由于 Schrock和 Grubbs催化剂的高活性和官能基适用性 ,烯交换闭环反应已被应用于肽的合成 [8～ 10 ] .在研究通过烯交换闭环反应设计与合成新型肽化合物的基础上 [11] ,我们设计了通过烯交换闭环反应从含有两个末端烯双键化合物合成新型大环磺酰胺肽模拟物的新途径 ,如 Scheme 1 ,其中…     

Ring‐Closing Olefin Metathesis for the Synthesis of Benzene Derivatives

Benzene derivatives were synthesized in excellent yield from 1,4,7‐trien‐3‐ols by tandem ruthenium‐catalyzed ring‐closing olefin metathesis (RCM)/dehydration. The method was extended to the tandem RCM/oxidation process to obtain phenol and aniline derivatives. This method displays many advantages over aromatic‐substitution‐based classical routes.     

Anodic Oxidation of Hypophosphite on a Nickel–Phosphorus Electrode in the Presence of Some Organic Compounds

The effects some sulfur-, nitrogen-, or oxygen-containing organic compounds exert on the hypophosphite oxidation are compared. Catalytic and inhibiting effects of additives, which depend on their nature and occur in different concentration intervals, are discovered and examined. The inhibiting effect, exerted by all substances studied, is accompanied by a shift of steady-state potential in the positive direction and is determined by the adsorbability of substances, which is a function of the nature and number of heteroatoms and substituents. The best inhibiting properties are intrinsic to an additive with an –S–S– fragment and NH₂ groups. Catalytic influence, which is typical only for sulfur-containing compounds at low concentrations, is accompanied by a shift of steady-state potential in the negative direction and may be related to a surface modification and a change in the metal–hydrogen bond energy.     

Catalytic Activity of Nickel Alloys in Anodic Oxidation of the Hypophosphite Ion as a Function of Their Composition

The rate of anodic oxidation of the hypophosphite ion on alloys Ni-P, Ni-B, and Ni-Mo-P is studied as a function of their composition and structure. The organic compounds that are customarily used to stabilize electrolytes of electroless nickel plating are shown to come useful when controlling composition of the Ni-P coatings at the expense of their different influence on the rates of partial processes of deposition of the alloy components. The formation of catalytic activity of such coatings is affected mostly by a structural factor. With alloys Ni-P, Ni-B, and Ni-Mo-P, whose composition was varied by altering the concentration of the source of the alloying component, dependence of catalytic activity of the surface on the composition is defined mainly by an electronic factor.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 972–980.Original Russian Text Copyright © 2005 by Sotskaya, Dolgikh, Ryabinina.     

宽电压范围下阳极氧化制备TiO_2纳米管阵列及其热稳定性

采用电化学阳极氧化技术,以含有NH4F和H2O的甘油溶液为电解液,在宽氧化电压范围(20~100V)下于纯钛表面制备了结构高度有序的TiO2纳米管阵列。利用扫描电子显微镜(SEM)考察了阳极氧化工艺(氧化电压、NH4F浓度、环境温度、水分含量等因素)及退火处理对纳米管形貌的影响;采用X射线衍射分析(XRD)表征了不同氧化电压和退火前后TiO2纳米管阵列的物相;并从电流-时间曲线出发简要地分析了纳米管阵列的形成机理。结果表明,纳米管的内外径和管长随氧化电压的增大而增大;NH4F浓度和环境温度对纳米管形貌有一定的影响;水分含量的多寡决定了能否在高电压下自组装形成纳米管阵列;TiO2纳米管阵列具有良好的热稳定性,管状形貌可以保持到700℃;直接制备的TiO2纳米管阵列均为无定型结构,经450℃退火处理后,无定型的TiO2纳米管转变为锐钛矿相,而600℃退火处理后,部分锐钛矿相转变为金红石相。     

0.1%Pt-0.02%Pd/不锈钢整体催化剂上丙酮氧化性能及稳定性(英文)

制备了0.1%Pt-0.02%Pd/不锈钢整体催化剂。选取不锈钢为该催化剂的载体,可克服传统γ-Al2O3和堇青石蜂窝载体热稳定性差的缺点。采用阳极氧化技术在不锈钢上自生长了结构致密的多孔阳极氧化膜,并在其上负载Pt和Pd制备得到挥发性有机物(VOCs)净化催化剂。结果表明,经500、800和1000℃不同温度焙烧后,该催化剂完全氧化丙酮的温度分别为160、160和200℃。该催化剂表现出以下优点:(a)高温稳定性能好;(b)低温催化活性高;(c)贵金属负载量低。通过SEM和EDX等技术对该催化剂的结构及活性组分分散情况进行了表征。     

Olefin Cross‐Metathesis: Studies towards the Total Synthesis of (+)‐Bitungolide F

A stereoselective synthesis of (5S,6S)‐6‐[(2S,5S,7R,8E,10E)‐5‐(benzyloxy)‐7‐{[(tert‐butyl)dimethylsilyl]oxy}‐11‐phenylundeca‐8,10‐dien‐2‐yl]‐5‐ethyl‐5,6‐dihydro‐2H‐pyran‐2‐one (=(+)‐9‐O‐benzyl‐11‐O‐[(tert‐butyl)dimethylsilyl]bitungolide F) is reported. The strategy involves Gilman reaction, olefin cross‐metathesis, and Horner? Wadsworth? Emmons olefination as key steps.     

A Facile Method of Synthesis of a Calix[4]arene Amide and the Crystal Structure of a Self-assembled Calix[4]arene Amide via van Der Waals Interaction

A new facile method of synthesis of calix[4]arene amide via the aminolysis of the calix[4]arene esters was reported. One ethyl ester of the compound (2) was aminolysized byn-butylamine. The crystal structure of compound (1)shows that one ethyl ester of compound (1) enters into thecavity of another compound (1) forming a long chainhost-guest supramolecule. From the 2D NMR data, the compound(1) does not assemble in THF or CHCl₃ solution. The CH- interaction and crystallization energy might be theimportant driving forces for forming the self-assembledcalix[4]arene.     

Electrolytic Macrocyclizations: Scalable Synthesis of a Diazonamide‐Based Drug Development Candidate

An electrochemical method to synthesize the core macrolactam of diazonamides is described. Large ring‐forming dehydrogenation is initiated by anodic oxidation at a graphite surface. The reaction requires no tailoring of the substrate and occurs at ambient temperature in aqueous DMF in an undivided cell open to air. This unique chemistry has enabled a concise, scalable preparation of DZ‐2384; a refined analog of diazonamide A slated for clinical development as a cancer therapeutic.     

聚苯乙烯基N,O-二酰基磺酰羟胺树脂: 一种双酰基转移试剂在合成酰胺库中的应用

用聚苯乙烯基磺酰羟胺树脂1与酰氯2反应合成了聚苯乙烯基N,O-二酰基磺酰羟胺树脂3. 树脂3作为一种新的双酰基转移试剂可与胺4发生酰基转移反应, 合成了含有24个结构类似的酰胺化合物库. 改变酰氯的种类, 结果发现双对硝基苯甲酰树脂3a的活性较高. 双酰基树脂3胺解结果表明, 由脂肪族胺得到的酰胺收率较芳香族胺高. 当解脱试剂同时含有羟基和氨基时, 双酰基树脂3能选择性地在氨基端发生酰基转移, 而羟基端不受影响.     

Advances in the Partial Oxidation of Methane to Synthesis Gas

The conversion and utilization of natural gas is of significant meaning to the national economy,even to the everyday life of people. However, it has not become a popular industrial process as expected due to the technical obstacles. In the past decades, much investigation into the conversion of methane,predominant component of natural gas, has been carried out. Among the possible routes of methane conversion, the partial oxidation of methane to synthesis gas is considered as an effective and economically feasible one. In this article, a brief review of recent studies on the mechanism of the partial oxidation of methane to synthesis gas together with catalyst development is wherein presented.     

Advances in the Partial Oxidation of Methane to Synthesis Gas

The conversion and utilization of natural gas is of significant meaning to the national economy,even to the everyday life of people. However, it has not become a popular industrial process as expected due to the technical obstacles. In the past decades, much investigation into the conversion of methane,predominant component of natural gas, has been carried out. Among the possible routes of methane conversion, the partial oxidation of methane to synthesis gas is considered as an effective and economically feasible one. In this article, a brief review of recent studies on the mechanism of the partial oxidation of methane to synthesis gas together with catalyst development is wherein presented.     

Unique Reactivity of a Diphenyldisilane Unit Incorporated into the Bicyclic Ring System: Generation of a Disilanyllithium via Silicon-Phenyl Bond Cleavage with Lithium

A bicyclic diphenyldisilane bearing two tetramethylene tethers reacts with lithium to form predominantly the disilanyllithium as a result of Si-C_Ph bond fission, while the pentamethylene homolog undergoes ordinary Si-Si bond cleavage to afford the expected phenylsilyllithium. The compressed Si-Si bond incorporated in the bicyclic ring system may be kinetically stabilized (compression effect), resulting in the unusual Si-C bond fission. When the reaction is carried out in the presence of chlorotrimethylsilane, a Calas-type reaction takes place on the phenyl rings. This result suggests that electron transfer to the phenyl group is the primary process in these bicyclic disilanes, followed by Si-Si or Si-C bond cleavage to afford the corresponding silyllithium species.     

Catalyst‐Controlled Stereoselective Olefin Metathesis as a Principal Strategy in Multistep Synthesis Design: A Concise Route to (+)‐Neopeltolide

Molybdenum‐, tungsten‐, and ruthenium‐based complexes that control the stereochemical outcome of olefin metathesis reactions have been recently introduced. However, the complementary nature of these systems through their combined use in multistep complex molecule synthesis has not been illustrated. A concise diastereo‐ and enantioselective route that furnishes the anti‐proliferative natural product neopeltolide is now disclosed. Catalytic transformations are employed to address every stereochemical issue. Among the featured processes are an enantioselective ring‐opening/cross‐metathesis promoted by a Mo monoaryloxide pyrrolide (MAP) complex and a macrocyclic ring‐closing metathesis that affords a trisubstituted alkene and is catalyzed by a Mo bis(aryloxide) species. Furthermore, Z‐selective cross‐metathesis reactions, facilitated by Mo and Ru complexes, have been employed in the stereoselective synthesis of the acyclic dienyl moiety of the target molecule.     

Developing the Low-Temperature Oxidation Mechanism of Cyclopentane: An Experimental and Theoretical Study

At present, the reactivity of cyclic alkanes is estimated by comparison with acyclic hydrocarbons. Due to the difference in the structure of cycloalkanes and acycloalkanes, the thermodynamic data obtained by analogy are not applicable. In this study, a molecular beam sampling vacuum ultraviolet photoionization time-of-flight mass spectrometer (MB-VUV-PI-TOFMS) was applied to study the low-temperature oxidation of cyclopentane (CPT) at a total pressure range from 1–3 atm and low-temperature range between 500 and 800 K. Low-temperature reaction products including cyclic olefins, cyclic ethers, and highly oxygenated intermediates (e. g., ketohydroperoxide KHP, keto-dihydroperoxide KDHP, olefinic hydroperoxides OHP and ketone structure products) were observed. Further investigation of the oxidation of CPT – electronic structure calculations – were carried out at the UCCSD(T)-F12a/aug-cc-pVDZ//B3LYP/6-31+ G(d,p) level to explore the reactivity of O₂ molecules adding sequentially to cyclopentyl radicals. Experimental and theoretical observations showed that the dominant product channel in the reaction of CPT radicals with O₂ is HO₂ elimination yielding cyclopentene. The pathways of second and third O₂ addition – the dissociation of hydroperoxide – were further confirmed. The results of this study will develop the low-temperature oxidation mechanism of CPT, which can be used for future research on accurately simulating the combustion process of CPT.     

Highly Chemoselective Synthesis of Indolizidine Lactams by SmI2‐Induced Umpolung of the Amide Bond via Aminoketyl Radicals: Efficient Entry to Alkaloid Scaffolds

Samarium(II) iodide enables a wide range of highly chemoselective umpolung radical transformations proceeding by electron transfer to carbonyl groups; however, cyclizations of important nitrogen‐containing precursors have proven limited due to their prohibitive redox potential. Herein, we report the first reductive cyclizations of unactivated cyclic imides onto N‐tethered olefins using SmI₂/H₂O. This new umpolung protocol leads to the rapid synthesis of nitrogen‐containing heterocycles that are of particular significance as precursors to pharmaceutical pharmacophores and numerous classes of alkaloids. The reaction conditions tolerate a wide range of functional groups. Excellent chemoselectivity is observed in the cyclization over amide and ester functional groups. Such unconventional reactivity has important implications for the design and optimization of new bond‐forming reactions by umpolung radical processes. The reaction advances the SmI₂ cyclization platform to the challenging unactivated N‐tethered acyl‐type radical precursors to access nitrogen‐containing architectures.     

The Direct Electrochemical Oxidation of Ammonia in Propylene Carbonate: A Generic Approach to Amperometric Gas Sensors

The direct electrochemical oxidation of ammonia in propylene carbonate is reported for the first time. The voltammetric responses at glassy carbon, boron‐doped diamond, edge and basal plane pyrolytic graphite electrodes are explored and compared with the outcome indicating that the optimum electrode substrate for analytical purposes in this solvent is glassy carbon. Proof‐of‐concept is shown for the amperometric detection of ammonia using basal plane pyrolytic graphite electrodes abrasively modified with glassy carbon spheres. Given the significantly lower vapor pressure of propylene carbonate in comparison to water the implications for extending the life‐time of practical sensors are evident. Propylene carbonate shows a wide potential window with glassy carbon electrodes permitting this approach to be used for a potential diversity of gaseous analytes.