12-钼磷酸—聚乙烯醇的光电子转移反应

12-钼磷酸—聚乙烯醇体系具有不可逆光致变色的特性。根据X射线光电子能谱、电子自旋共振谱、紫外及可见光谱的测试结果,笔者认为:在PMo_(12)-PVA的光电子转移反应中,PMo_(12)既是氧化剂也是光敏剂。PMo_(12)分子中氧可分成O_p、O_b和O_t三种情况.其中O_t可成为光化学的活性位置,它和PVA羟基上的氧均较易被紫外光激活。激活的0_t边使周围的一个电荷向金属原子(Mo~(Ⅵ))转移,边与PVA羟基上被激活的氧作用,电子就由此羟基上的氧向O_t转移,致使体系中部分PMo_(12)与PVA发生二电子或四电子氧化还原反应,形成Mo(Ⅵ、Ⅴ)配合物而变色,同时,PVA分子的部分羟基及该羟基位的碳上脱氢形成羰基而具有酮结构。此外,从Mo(V)的ESR特征信号随时间变化而减弱,但其吸收光谱的吸光度未变,于是推断该光化学反应过程中尚有Mo(Ⅳ)生成,已由XPS谱证实。     

Fabrication of lead titanate single crystalline nanowires by hydrothermal method and their characterization

Single crystalline nanowires of lead titanate (PbTiO₃) were fabricated by hydrothermal method at 200°C using lead acetate and n-tetrabutyl titanate as starting materials, where sodium hydroxide was served as a mineralizer. Crystalline phases, microstructure and optical properties of PbTiO₃ nanowires were investigated. The PbTiO₃ nanowires were uniform and continuous along the long axis, and were composed of single crystalline PbTiO₃ with a tetragonal perovskite structure. The diameter of a single nanowire was around 12 nm and the length reached up to 3 μm. The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy (XPS). The ultraviolet/visible absorption spectroscopic investigation suggested that the absorption edge of optical transition of the first excitonic state occurred at around 320 nm. A blue-green light emission peaking at about 471 nm (2.63 eV) is observed at room temperature, and the intensity of this emission increased with increasing excitation wavelength. Oxygen vacancies are responsible for the light emission of PbTiO₃ nanowires.     

Sc(OTf)3-catalyzed alkylation of indoles with propargyl alcohols: an expeditious synthesis of 3-substituted indoles

Indoles undergo smooth alkylation with propargylic alcohols in the presence of 10 mol % of scandium triflate under mild conditions to produce 3-propargylated indoles in excellent yields with high selectivity.     

Nucleophilic substitution in 1-alkyl-4,5-dichloro-3-nitropyridazin-6-ones

Treatment of 1-alkyl-4,5-dichloro-3-nitropyridazin-6-one with C-nucleophiles and with ambident nucleophiles (2-azahetarylacetonitriles) leads to a selective substitution of a chorine atom by the quaternary carbon atom of the carbanion formed from a substituted acetonitrile. The pK_a of the CH-acid 2-(1-alkyl-5-chloro-3-nitro-6-oxo-1,6-dihydro-4-pyridazinyl)malononitrile was determined by potentiometric titration. Reaction of 2-(1-alkyl-5-chloro-3-nitro-6-oxo-1,6-dihydro-4-pyridazinyl)-2-hetarylacetonitriles with primary amines gives 6,7-dihydro-1H-pyrrolo[2,3-d]pyridazin-7-ones. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 556–564, April, 2006.     

One-step synthesis of N-alkyl-2-aryl-2-oxoacetamides and N,N-dialkyl-2-aryl-4H-1,3-benzodioxine-2,4-dicarboxamides

Alkyl isocyanides react with 2-hydroxybenzaldehyde or 2-hydroxy-5-nitrobenzaldehyde to afford N-alkyl-2-aryl-2-oxoacetamides and N²,N⁴-dialkyl-2-aryl-4H-1,3-benzodioxine-2,4-dicarboxamides in nearly 1:1 ratios. Treatment of 2,6-dimethylphenyl isocyanide with 2-hydroxy-5-nitrobenzaldehyde affords only the 2-oxoacetamide derivative.     

Synthesis and Crystal Structure of 3-（Trichloroacetyl） Indole

1 INTRODUCTION Indole and its derivatives have attracted much at-tention due to their chemical properties as well asbiological activities[1, . They have been widely used 2]as the materials for producing pigment, perfume,plant growth regulators, etc. Recently, it has alsobeen found that some indole derivatives present anti-tumor and antiviral activities[3～5]. During our sear-ches for bioactive compounds, a series of indole deri-vatives were synthesized, among …     

Carbon dendron nano-chains with π-extended conjugation based on end-capped N,N-dimethylamino in linear 1,4-phenylethynyl or in 1,5-naphthylethynyl subunits: fluorescence analysis

The synthesis of dendrons with the end-capped 5-(N,N-dimethylamino)naphthyl-1-ethynyl unit connected to conjugated naphthylethynyl or p-phenylethynyl chains, as the branches of the 1,3,5-substituted benzene core, have been undertaken by heterocoupling reaction between 1,3,5-triiodobenzene and the convenient end-capped 5-(N,N-dimethylamino)naphthylacetylene or 5-(N,N-dimethylamino)naphthylethynylphenylacetylene in the presence of the palladium-copper catalyst system, in excellent yields. The influence of the alternating naphthylethynyl-phenylethynyl chains on the fluorescence emission radiation, in the dendron structures, has been analyzed.     

The effects of cationic and zwitterionic micelles on the keto-enol interconversion of 2-phenylacetylfuran and 2-phenylacetylthiophene

The presence of micelles from cationic and zwitterionic surfactants increases the apparent acidity of either the keto and the enol forms of 2-phenylacetylfuran (2PAF) and 2-phenylacetylthiophene (2PAT). This effect can be attributed to the affinity of the surfactant micelles for the enolate of the two substrates. Although the equilibrium constants for keto-enol tautomerism of 2PAF and 2PAT, K_T=[enol]/[ketone]=pK_a^KH−pK_a^EH, do not change much, the presence of micelles provides an efficient method for producing appreciable quantities of the enolates under mild experimental conditions and in aqueous solutions. The obtained rate-profiles for the ketonisation reactions and the consistency of the kinetic rate constants over a wide range of ‘pH’ in several overlapping buffers indicate that the pH of the aqueous pseudophase (but not that at the micellar surface) can be controlled by buffers. Moreover, the increase of the acidity and the decrease of the ‘water’ rate of ketonisation of the enols of 2PAF and 2PAT upon addition of surfactants allow the uncovery of a metal ion catalysed pathway that cannot be observed in absence of surfactants.     

Stereoconvergent preparation of chiral vinylsilanes by cuprate substitution of α-acetoxyallylsilanes. Application to the synthesis of (S)-(+)-bishomomanicone

Enantiomerically enriched (E)- and (Z)-configured α-acetoxyallylsilanes have been prepared starting from a chiral acylsilane bearing an asymmetric unit at the silicon portion. Treatment of these compounds with organocuprates afforded the respective vinylogous substitution products in high yields and high stereoselectivities. The transformations proceed essentially by complete anti attack of the nucleophiles to the allylic acetates and predominantly via transition states leading to the (E)-configured vinylsilane products. By the proper choice of the double bond geometry in the starting material, the configuration of the newly formed stereogenic center can be controlled. The method represents a new and flexible entry into chiral vinylsilanes that can be used for subsequent transformations. As an example, the α,β-unsaturated γ-chiral, naturally occurring ketone (S)-(+)-bishomomanicone was synthesized with this method, which represents the first synthetic access to this compound.     

Aza Diels—Alder reactions of methyl trifluoropyruvate sulfonyl- and phosphorylimines with 1,3-dienes

2-Trifluoromethyl-substituted 1,2,3,6-tetrahydro-2-pyridyl carboxylates were synthesized in one step by the aza Diels—Alder reactions of methyl trifluoropyruvate sulfonyl- and phosphorylimines with 1,3-dienes.