Efficient oxidative dimerization of 1-naphthols to 2,2-binaphthyls with dioxygen mediated by semiconductors

A novel and efficient oxidative dimerization of 1-naphthols 1 with dioxygen in the presence of several semiconductors including SnO₂, ZrO₂, and activated charcoal as catalytic mediators took place selectively to give the corresponding 2,2^′-binaphthols 2 or 2,2^′-binaphthyl-1,1^′-quinones 3 in excellent yields without light irradiation. Among these semiconductors, the catalytic activity of SnO₂ could be fully restored by appropriate reactivation treatment after oxidation. The products 2 and 3 should be useful as synthetic intermediates for natural binaphthyls.     

Aerobic oxidative dimerization of 1-naphthols to 2,2′-binaphthoquinones mediated by SnCl4 and its application to natural product synthesis

We developed a simple method for the direct synthesis of 2,2′-binaphthoquinones, utilizing oxidative dimerization via electron donor-acceptor complex formation of 1-naphthols with SnCl₄ in the presence of dioxygen. This oxidation involves a catalytic cycle of SnCl₄, and the reaction mechanism is discussed. As an application of this method to natural products synthesis, we describe facile biomimetic syntheses of the binaphthoquinones 3,3′-bijuglone, 3,3′-biplumbagin and elliptinone.     

Oxidative coupling of 2-substituted 1,2-dihydro-1-naphthols using Jones reagent: a simple entry into 3,3′-disubstituted 1,1′-binaphthyl-4,4′-diols

2-Substituted 1,2-dihydro-1-naphthols underwent regioselective oxidative dimerization, when treated with Jones reagent, to furnish 3,3′-disubstituted 1,1′-binaphthyl-4,4′-diols. A series of symmetrical binaphthols were prepared and it was shown that the coupling reaction proceeds via the sequential oxidation of 2-substituted 1,2-dihydro-1-naphthols to 2-substituted 1-naphthols, which oxidatively dehydrodimerized.     

Lewis acid-assisted oxidative cross-coupling of 2-naphthol derivatives with copper catalysts

The oxidative coupling reactions between 2-naphthol and 3-hydroxy-2-naphthoic acid derivatives using a copper catalyst under an O₂ atmosphere in the presence of a catalytic amount of the Lewis acid, such as Yb(OTf)₃, were carried out. A highly cross-coupling selective or specific reaction effectively proceeded to give a C₁ symmetrical BINOL derivative.     

Conductivity properties of Na2SO4/CaCO3 catalysts and their effect on catalytic activities for oxidative coupling of methane

A series of Na₂SO₄ doped CaCO₃ catalysts were prepared. It was observed that the C₂ yields and selectivities of Na₂SO₄/CaCO₃ catalysts for OCM are intimately related to their conductivities. The effect of conductivity on the catalytic activity is discussed together with the conductivities and catalytic activities of the catalysts. The higher the conductivities, the higher the C₂ yields and selectivities are.     

Highly selective oxidative cross-coupling of 2-naphthol derivatives with chiral copper(I)-bisoxazoline catalysts

The asymmetric oxidative coupling reaction of 3-hydroxy-2-naphthoate and 2-naphthol derivatives with the CuCl-(S)-(−)-2,2′-isopropylidenebis(4-phenyl-2-oxazoline) catalyst under an O₂ atmosphere was carried out. The reaction proceeded in a highly cross-coupling selective manner (?99.7%) with a moderate enantioselectivity of up to 65%.     

Biomimetic synthesis of the dinaphthofuranquinone violet-quinone, utilizing oxidative dimerization with the ZrO2/O2 system

The first total and biomimetic synthesis of violet-quinone (1), which has a dinaphthofuranquinone (DNFQ) framework, is described. This synthesis features the oxidative dimerization of 1-naphthol 4 and the construction of the DNFQ framework by photochemical ring closure of 2,2′-binaphthoquinone 7 as a key intermediate. Compound 7 was prepared by the novel oxidative dimerization of 4 with a semiconductor (such as ZrO₂) in the presence of dioxygen, followed by oxidation of the resulting 2,2′-binaphthyl-1,1′-quinone 6 with HNO₃.     

Solvent effect in the kinetics of cobaloxime(II)-catalyzed oxidative dehydrogenation of 3,5-di-tert-butylcatechol by O2

In the presence of triphenylphosphinecobaloxime(II), 3,5-di-tert-butylcatechol undergoes catalytic oxidative dehydrogenation to the corresponding 1,2-benzoquinone (DTBQ) at room temperature and atmospheric dioxygen pressure. The semiquinone anion radical (DBS^•−) and its cobaloxime(III), complex Co^III(DBSQ)^•−) have been detected as intermediates by ESR spectroscopy. The kinetics were followed in benzene by measuring the dioxygen uptake as a function of time. The reaction is somewhat faster in MeOH, which is due to the greater stability of the hydrogen-bonded intermediate (X) formed from superoxocobaloxime (Co^IIIO₂) and the catechol. H-atom abstraction occurs in the rate-determining decomposition of X. The system investigated is a functional model of catecholase (oxidase) activity, based on free-radical intermediates, a possibility recently demonstrated for certain oxidoreductases.     

钒氧化物催化CO2氧化异丁烷脱氢的研究

采用溶胶-凝胶法制备了一系列钒氧化物催化剂,并用于CO₂氧化异丁烷脱氢反应. 采用X射线衍射、低温N₂吸附-脱附、O₂程序升温氧化、程序升温表面反应和原位傅里叶变换红外光谱等方法研究了催化剂的性质. 反应结果表明,尽管所有钒氧化物催化剂的丁烯选择性都大于85%,但随着催化剂组成和制备方法的改变,催化活性和稳定性差异显著. 其中,12 wt% V₂O₅/Ce_0.6Zr_0.4O₂（7 wt%）-Al₂O₃的催化活性最高,而6 wt% V₂O₅-Ce_0.6Zr_0.4O₂（7 wt%）-Al₂O₃的稳定性最佳. 关联分析催化反应结果与催化剂表征表明,钒氧化物的催化活性取决于VO_x物种的结晶度和分散度,而催化剂表面所积重质焦炭的特性是决定催化剂稳定性的关键. 非稳态反应和原位光谱结果确认,CO₂氧化异丁烷脱氢遵循Mars-van Krevelen氧化还原机理.     

Photoelectrochemical behavior of coupled SnO2|CdSe nanocrystalline semiconductor films

A photoelectrochemical cell with a coupled SnO₂|CdSe nanocrystalline semiconductor electrode has been prepared by sequential deposition of SnO₂ and CdSe films onto an optically transparent electrode (OTE), and its photoelectrochemical behavior has been studied. The results show that the coupling of CdSe with SnO₂ leads to an improvement in the performance of OTE|SnO₂|CdSe over OTE|CdSe cells in terms of increased incident photon-to-current conversion efficiency, increased stability and smaller reversal of current. The favorable positioning of the energy bands of SnO₂ and CdSe is responsible for the above observations. Various photoelectrochemical parameters of the OTE|SnO₂|CdSe cell obtained for an incident light power of 0.31 mW cm⁻² at 470nm, are as follows: I_sc ≈ 25–30 μA cm⁻², V_oc ≈ 0.5–0.6 V, ƒƒ = 0.47 and a power conversion efficiency of about 2.25%.     

高活性Au/SnO2催化剂的制备及其在1,4-丁二醇氧化制γ-丁内酯反应中的催化应用

采用沉积沉淀法制备了一系列商业SnO₂负载的纳米Au催化剂, 通过电感耦合等离子体发射光谱、X射线粉末衍射、透射电镜和X射线光电子能谱等方法研究了溶液酸碱性、沉淀剂种类、Au负载量和焙烧温度等对催化剂性质的影响.结果表明, Au的负载量以及催化剂的焙烧温度对Au颗粒状态有较大影响.其中, 于573 K焙烧的3%Au/SnO₂催化剂在1,4-丁二醇氧化制备γ-丁内酯反应中的催化活性最好, TOF值是Au/TiO₂催化剂的15倍.这主要是由于SnO₂载体独特的性质对所负载的Au颗粒的影响.     

Growth Mechanism and Characterization of Single-crystalline Ga-doped SnO2 Nanowires and Self-organized SnO2/Ga2O3 Heterogeneous Microcomb Structures

Single-crystalline Ga-doped SnO2 nanowires and SnO2:Ga2O3 heterogeneous microcombs were synthesized by a simple one-step thermal evaporation and condensation method. They were characterized by means of X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). FE-SEM images showed that the products consisted of nanowires and microcombs that represent a novel morphology. XRD, SAED and EDS indicated that they were single-crystalline tetragonal SnO2. The influence of experimental conditions on the morphologies of the products is discussed. The morphology of the product showed a ribbon-like stem and nanoribbon array aligned evenly along one or both side of the nanoribbon. It was found that many Ga2O3 nanoparticles deposited on the surface of the microcombs. The major core nanoribbon grew mainly along the 110 direction and the self-organized branching nanoribbons grew epitaxially along 1110 or 1110 orientation from the (110) plane of the stem. A growth process was proposed for interpreting the growth of these remarkable SnO2:Ga2O3 heterogeneous microcombs. Due to the heavy doping of Ga, the emission peak in photoluminescence spectra has red-shifted as well as broadened significantly.     

Photocatalytic activity of TiO2/SnO2/Pt prepared by the sol-gel method

This investigation compares the photodegradation performance of C.I. Reactive Red 2 (RR2) in single- and coupled-photocatalyst systems. The photocatalysts were produced via the sol-gel method. PEG and Pt addition increases the decolorization rate (1.6–2.12 h⁻¹), the amount of sulfate released and the DOC reduction percentage in coupled photocatalyst systems the cause of PEG improving the homogeneity of the final product and incorporating Pt into the lattice reduced the band gap of photocatalysts.     

Selective endoperoxide formation by heterogeneous TiO2 photocatalysis with dioxygen

We report the selective formation of endoperoxides by aerobic TiO₂ photocatalysis through the cyclic addition of dioxygen and a non-conjugated diene, the first heterogeneous catalytic system for endoperoxide synthesis. This green protocol does not require any additive and the photocatalyst is abundant and recyclable, providing a yield up to 64% and >20:1 diastereoselectivity. Mechanistic investigations were carried out by using product analysis, kinetic studies, O-18 labelling experiments, electron-spin resonance and a set of quenching experiments. Superoxide (but not singlet oxygen, triplet oxygen or peroxide) is directly involved in the reaction cascade to form the endoperoxide product. The new findings may be helpful for future for designing eco-friendly and energy sustainable strategies for selective oxygenation reactions using semiconductors, O₂ and sunlight.     

Palladium catalyzed transformations of monoterpenes: stereoselective deuteriation and oxidative dimerization of camphene

Camphene undergoes a highly regio and stereoselective palladium catalyzed deuteriation in deuteriated acetic acid solutions of Pd(OAc)₂. NMR reveals that an outward oriented vinylic hydrogen is selectively exchanged for ²H, resulting in 90% camphene-d₁ (ca. 100% stereoselectivity) and 10% camphene-d₂ at 75% conversion of camphene (6 h, 25 °C). Neither π-allyl nor π-olefin palladium complexes are formed in detectable concentrations during the reaction, whereas palladium hydride (singlet at −6.86 ppm) and palladium deuteride (singlet at −6.78 ppm) intermediates have been detected by ¹H and ²H NMR, respectively. At higher temperature, oxidative coupling of camphene readily occurs giving the (E,E)-diene, i.e., bis(3,3-dimethyl-2-norbornylidene)ethane, which formally originates by abstracting the outward oriented vinylic hydrogens and coupling the resulting fragments of two camphene molecules. The reaction is catalytic at palladium in the Pd(OAc)₂-LiNO₃(cat)-O₂ and Pd(OAc)₂-benzoquinone systems. Similar mechanisms for the deuteriation and oxidative coupling of camphene are proposed, which involve the formation of σ-vinyl palladium hydride intermediates. No deuteriation neither oxidative coupling of limonene, myrcene and β-pinene were observed under the same conditions.     

Sensitization of the photoadsorption of O2 and NO on SnO2

Photoadsorption activity of SnO₂ with respect to O₂ and NO after CO chemisorption has been revealed to be drastically increased. Photoadsorption is suggested to be sensitized by surface carbonates formed due to CO chemisorption.

---

. , .

     

Catalytic Oxidation of Dimethyl Ether to Hydrocarbons over SnO2/MgO and SnO2/CaO Catalysts

A novel reverse microemulsion method was used to prepare SnO2/MgO and SnO2/CaO catalysts. It was found that both the catalysts were active for the reaction of catalytic oxidation of dimethyl ether (DME) in the temperature range of 275 to 300℃. SnO2/CaO catalyst exhibits much higher activity than SnO2/MgO. On SnO2/CaO catalyst, DME conversion of 21.8% was obtained at 300℃, while selectivities to methyl formate (MF) and dimethoxyethane (DMET) of 19.1% and 59.0% respectively were obtained at 275℃.     

LiMn_2O_4/TiO_2催化剂上甲烷氧化偶联反应性能的研究

采用固相反应法制备了具有尖晶石结构的LiMn_2O_4/TiO_2系列催化剂,探讨了TiO_2、Li/TiO_2、Mn/TiO_2、LiMn_2O_4及LiMn_2O_4/TiO_2等不同组成催化剂的甲烷氧化偶联反应性能,采用XRD、XPS、CO_2-TPD和H_2-TPR等表征方法对该系列催化剂进行了分析。结果表明,具有尖晶石结构的LiMn_2O_4化合物具有较高的甲烷氧化偶联催化活性,在775℃、0.1MPa、7200mL/(h·g),CH_4∶O_2(体积比)为2.5的条件下,甲烷转化率可达25.8%,C2选择性可达43.2%。TiO_2的存在不仅进一步提高了甲烷转化率和C2选择性,还有效抑制了甲烷完全氧化形成CO_2的过程。负载8%LiMn_2O_4的LiMn_2O_4/TiO_2催化剂性能达到最优,此时甲烷转化率达到31.6%,C2选择性为52.4%,CO_2选择性降低到26.3%。考察了不同焙烧温度对催化剂活性的影响,850℃为LiMn_2O_4/TiO_2催化剂的最佳焙烧温度。     

无溶剂条件下三聚氰胺-Br_3催化一锅法合成1-氨基烷基-2-萘酚(英文)

A facile and efficient method has been developed for the synthesis of 1-amidoalkyl-2-naphthols via the one-pot multi-component condensation of 2-naphthol with aromatic aldehydes and acetamide or thioacetamide in the presence of melamine-Br3 under solvent-free conditions. There are several advantages to this reaction, including high yields, short reaction time, and high catalytic efficiency.     

Et2SiH2 assisted the selective dimerization of terminal alkynes catalyzed by Cp2UMe2

A practical approach has been developed for the catalytic synthesis of short oligomers, dimers and/or trimers of terminal alkynes. The method allows control of the extent and, in some cases, the regiospecificity in the catalyzed oligomerization of terminal alkynes promoted by bis(pentamethylcyclopentadienyl)uranium dimethyl complex (Cp^*₂U(CH₃)₂, Cp^*=C₅Me₅). The metallocene precursor is known to promote the simultaneous production of a large number of differently sized oligomers in the presence of terminal alkynes. However, the addition of a specific secondary silane ensures the selective synthesis of short oligomers.