IBX/n-Bu4NBr/CH2Cl2-H2O: a new mild system for selective oxidation of secondary alcohols

A new alternative system for the chemoselective oxidation of secondary hydroxyl group to ketone with IBX/n-Bu₄NBr in CH₂Cl₂-H₂O has been developed. Under the reaction conditions, the secondary hydroxyl group was highly chemoselectively oxidized to the corresponding ketone, in moderate to good yields at rt, in the presence of primary hydroxyl group within the same molecule.     

A metal-free approach to access ketones,amides, and nitriles employing TBAI/TBHP oxidative system in water

Hydrocarbons, benzylamines, and heteroaromatic-bearing amines have been efficiently employed as substrates in allylic and benzylic oxidations via C(sp3)–H bond activation by TBAI/TBHP in water. This operationally simple method allows access to ketones, nitriles, and amides in moderate to high yields and a regio- and chemoselective late-stage functionalization.     

甲烷直接氧化制甲醇研究进展概述

目前,天然气转化为高附加值化工产品的应用越来越受到人们关注.甲烷作为天然气的主要成分,其转化和应用是天然气化工领域的重要研究方向.而甲烷直接氧化制甲醇长久以来一直是研究重点.甲烷直接氧化制甲醇与传统的甲烷二步法间接转化相比,有节能和工艺简化的突出特点.然而,甲醇直接氧化制甲醇过程所面临的主要问题有：(1)甲烷分子的活化能很高,需要苛刻的操作条件才能活化参与反应;(2)反应进行的程度难以控制,生成的甲醇会进一步被氧化生成较多副产物,大大降低甲醇收率.因此,高效活化甲烷分子和抑制甲醇深度氧化是促进该过程工业化的重要研究内容.本文主要论述了非均相、气相均相和液相体系中甲烷直接氧化制甲醇的研究进展.在甲烷非均相氧化过程中,采用过渡金属氧化物作为催化剂在高温条件下催化甲烷部分氧化反应,其中,钼系和铁系催化剂的研究最为广泛.研究表明, MoO3可作为催化剂的主要活性组分,尤以 MoO3/Ga2O3催化剂性能最好,得到甲醇收率最高.在铁系催化剂中, Fe-ZSM-5 催化反应的甲醇选择性和收率都相对较高;但是每次反应后催化剂都需要重新活化,这种间歇性操作会增加成本,不利于工业化应用.总之,甲烷的非均相氧化过程存在易形成金属聚集体、催化剂选择性低以及甲醇收率低(5%)等问题,需要深入系统地研究解决.然而,与非均相氧化过程相比,操作较为简单的甲烷气相均相氧化作为目前最有工业前景的过程受到越来越多关注.在此过程中,影响反应的主要因素有反应器、反应条件(反应压力、反应温度和反应时间等)以及添加的介质等.反应器的特殊设计需要考虑的方面有反应产物的分离与转移、反应热的移除以有效提高甲烷的转化率,比如膜反应器对物质的分离作用.反应压力对反应过程的影响较为复杂.基于动力学因素,提高反应压力可以较大幅度地增加甲醇收率,同时最佳反应温度降低,但是,当压力高于8.0 MPa时,设备成本消耗大幅增加.另外,研究表明,进料中加入 NOx作为添加介质可以提高甲烷转化率和甲醇选择性,同时降低初始反应温度.与前两个氧化体系相比,液相均匀氧化过程能够获得较高的甲烷转化率与甲醇选择性.但是液相体系中强腐蚀性介质的使用增加了设备成本,阻碍了该过程工业化的应用进程.因此,促进液相体系工业化的关键就是开发绿色高效的催化剂.     

Synthesis and analysis of aminochromes by HPLC-photodiode array. Adrenochrome evaluation in rat blood

The catecholamine oxidation process induces cardiotoxicity and neurotoxicity. Catecholamines can oxidize to aminochromes through autoxidation or by enzymatic or non-enzymatic catalysis. Although some toxic effects seem to be related to the formation of aminochromes there is still scarce information concerning the identification and evaluation of these compounds in in vivo models. In this study five catecholamines were oxidized to their respective aminochromes: adrenaline/adrenochrome; noradrenaline/noradrenochrome; dopa/dopachrome; dopamine/dopaminochrome; and isoproterenol/isoprenochrome. The evaluation of the catecholamines oxidation profile was performed by HPLC with photodiode array detection and using either enzymatic (tyrosinase) or non-enzymatic [Ag(2)O, CuSO(4), NaIO(4) and K(3)Fe(CN)(6)] catalytic systems. The NaIO(4) was found to be the most efficient oxidant of catecholamines. An isocratic reverse-phase HPLC method was developed to analyse each pair of catecholamine-aminochrome. The analytical system was then applied to the detection of adrenochrome in rat blood at 490 nm. Thus, adrenochrome was administered i.p. to rats and its concentration in whole blood was monitored after 5, 15 and 25 min. Blood treatment for adrenochrome evaluation consists of an acidification for protein precipitation followed by a rapid neutralization. The results showed a rapid decrease of adrenochrome concentration in blood after its administration. The adrenochrome present in blood was characterized by UV and tandem mass spectrometry.     

Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-palygorskite

Palygorskite-supported Sn complexes were prepared by a simple procedure. Cyclic ketones and acyclic ketones were oxidized by hydrogen peroxide in a reaction catalyzed by palygorskite-supported Sn complexes, affording corresponding lactones or esters with selectivity for the product of 90-100%. The catalysts can be recycled for several times without significant decline in catalytic activity.     

Ni催化剂上甲烷部分氧化制合成气反应性能与碳物种的关系

In the partial oxidation of methane (POM) to syngas, carbon deposition on the catalyst causing catalyst deactivation or reactor plugging was reported[1～3]. Our previous work showed that methane dissociation on metallic sites to H2 and NixC is an initial step of POM over Ni/Al2O3[4]. If NixC can not be consumed immediately after its formation, it has a tendency to dissolve into the nickel crystal to form carbon whiskers. The bulk carbon and carbon whiskers are more difficult to be oxidized than NixC. Therefore, prohibiting the transformation of NixC to bulk carbon and carbon whiskers can depress the formation of carbon deposition effectively.     

NHPI, CoSPc和TBAB催化的乙苯液-液非均相绿色氧化反应研究

以水为催化剂溶剂与原料乙苯组成液-液非均相体系,以NHPI结合CoSPc组成催化体系,在TBAB为相转移催化剂的作用下,对乙苯的氧化反应条件进行了研究.研究发现乙苯在该催化体系中的最佳氧化条件依次是:水油体积比为3∶1;n(TBAB)∶n(乙苯)=1∶40;n(NHPI)∶n(乙苯)=1∶10,n(NHPI)∶n(CoSPc)=24∶1,反应温度110℃,氧气压力0.75 MPa,搅拌速率350 rpm,反应时间0.5 h.在最佳反应条件下乙苯转化率为60.6%,苯乙酮的选择性为95.2%,1-苯乙醇的选择性为4.5%,产物总选择性达到了99.7%.在此基础上延长反应时间并不能提高乙苯的转化率,苯乙酮的选择性也会下降,研究发现NHPI的分解是乙苯转化率不随反应时间的延长而提高的原因,而苯乙酮的过度氧化为苯甲酸是产物选择性下降的原因.     

Pulse radiolysis study of one-electron oxidation of thionine in aqueous solutions

One-electron oxidation of thionine has been studied using specific oxidizing radicals such as Cl⁻Tl(II) and N₃ generated by pulse radiolysis of aqueous solutions. The semioxidized thionine exhibited threepK’s indicating four conjugate acid-base forms. N₃ radicals were found to be less efficient in oxidizing thionine as compared to Cl ₂ ⁻ , Tl²⁺ and Tl(OH)⁺. The rate constants for electron abstraction from thionine by Cl ₂ ⁻ , Tl²⁺, Tl(OH)⁺, Tl(OH)₂ and N₃ were evaluated. The spectra of different protonated forms of semioxidized thionine and the extinction coefficients at λ_max are presented. Reaction of OH radicals with thionine gave transient products whose spectra and acid-base properties were different from those of semioxidized thionine. The rate constant for formation of the product transient agrees well with competition kinetic value for reaction of OH with thionine reported earlier.     

Lysozyme oxidation by singlet molecular oxygen: Peptide characterization using [18O]‐labeling oxygen and nLC‐MS/MS

Singlet molecular oxygen (¹O₂) is generated in biological systems and reacts with different biomolecules. Proteins are a major target for ¹O₂, and His, Tyr, Met, Cys, and Trp are oxidized at physiological pH. In the present study, the modification of lysozyme protein by ¹O₂ was investigated using mass spectrometry approaches. The experimental findings showed methionine, histidine, and tryptophan oxidation. The experiments were achieved using [¹⁸O]‐labeled ¹O₂ released from thermolabile endoperoxides in association with nano‐scale liquid chromatography coupled to electrospray ionization mass spectrometry. The structural characterization by nLC‐MS/MS of the amino acids in the tryptic peptides of the proteins showed addition of [¹⁸O]‐labeling atoms in different amino acids.     

Transition metal-free and substrate-selective oxidation of alcohols using water as an only solvent in the presence of β-cyclodextrin

A facile, substrate-selective and transition metal-free oxidation of benzylic and allylic alcohols catalyzed by β-cyclodextrin with NaOCl oxidant using water as an only solvent was developed.     

Pd-Mn/Stainless Steel Wire Mesh Catalyst for Catalytic Oxidation of Toluene,Acetone and Ethyl Acetate

A new 0.1%Pd‐6%Mn/stainless steel wire mesh catalyst was prepared and used for volatile organic compounds (VOC) elimination. The supported palladium and manganese catalyst over the stainless steel wire mesh was prepared by using an impregnation method. When an anodic oxidation technology was employed, an anodic oxidation membrane appeared on the stainless steel wire mesh. On the 0.1%Pd‐6%Mn/stainless steel wire mesh catalyst calcined at 500°C, the total oxidation of toluene, acetone and ethyl acetate was respectively at 260, 220 and 320°C. The activity could be stable for over 700 h for toluene oxidation. The scanning electron microscopy (SEM) investigation of the Pd‐Mn/stainless steel wire mesh catalyst shows that the presence of anodic oxidation membrane on the support surface is important for better dispersion of active phases.     

Kinetics and mechanism of oxidation of thiocarbohydrazide in the free state and in its metal complex and thiocarbohydrazone by chloramine-T and dichloramine-T

Kinetics of oxidation of thiocarbohydrazide (TCH) in the free state and as its metal complex, and as a hydrazone by chloramine-T (CAT) in aqueous HClO₄ medium, and by dichloramine-T (DCT) in 1:1 (v/v) water-methanol medium in the presence of HClO₄ have been studied. Rates of oxidation of TCH in the free state and in metal complex by CAT were determined. The rate law for the oxidation of TCH at high [H⁺ ] and for complex oxidations were identical to that for CAT oxidations. The conversion of TCH into its hydrazone changed the order in [H⁺] from a positive to a negative value, probably signalling the change of reaction site. The rate law for oxidation under these conditions was determined. Addition of the reduced product of the oxidants had no effect on the rate of oxidations. Variation in ionic strength of the medium had little positive effect, while decrease in dielectric constant of the medium decreased the rate in both the oxidations. Oxidation processes generally follow a Michaelis-Menten type of mechanism. Constants of the rate limiting steps have been calculated at different temperatures and these constants have been used to calculate the activation parameters from the Arrhenius plots. The proposed mechanisms are supported by investigations with HOC1 under identical reaction conditions. Metal complexation of the substrate decreased the reactivity, while conversion of TCH into its hydrazone changed the rate dependence on [H⁺].     

Electrochemical Formation of Fe(IV)=O Derived from H2O2 on a Hematite Electrode as an Active Catalytic Site for Selective Hydrocarbon Oxidation Reactions

The high-valence iron species (Fe(IV)=O) in the cytochrome P450 enzyme superfamily is generated via the activation of O₂, and serves as the active center of selective hydrocarbon oxidation reactions. Furthermore, P450 can employ an alternate route to produce Fe(IV)=O, even from H₂O₂ without O₂ activation. Meanwhile, Fe(IV)=O has recently been revealed to be the reactive intermediate during H₂O oxidation to O₂ on hematite electrodes. Herein, we demonstrated the generation of Fe(IV)=O on hematite electrodes during the electrochemical oxidative decomposition of H₂O₂ using in situ UV-visible absorption spectra. The generation of Fe(IV)=O on hematite electrodes from H₂O₂ exhibited 100 mV lower overpotential than that from H₂O. This is because H₂O₂ serves not only as the oxygen source of Fe(IV)=O, but also as the additional oxidant. Finally, we confirmed that the Fe(IV)=O generated on hematite electrodes can serve as the catalytic site for styrene epoxidation reactions.     

Real and Virtual Degrees of Oxidation of d Elements in Coordination Compounds

The "degree of oxidation" or "state of oxidation" are extremely long-lived concepts in inorganic and coordination chemistry. In this paper such concepts as real and virtual degrees of oxidation are introduced, and possible ways of using them for the production of new materials are demonstrated. The concepts are undoubtedly related in the closest manner to coordination chemistry. The degrees of oxidation of elements of the transfermium group are examined, and this provides the possibility of predicting the degrees of oxidation of these elements. It was found that the d ⁵, d ⁷, d ⁹ elements do not form coordination compounds with an overall negative electric charge.     

多金属氧酸盐催化的水氧化研究进展

氢气以其清洁无污染、燃烧值高等优点成为未来最具潜力的可再生能源之一,而清洁生产氢气的最佳选择之一即为裂解水. 利用太阳能模拟光合作用实现水的全分解产生氢气和氧气是目前最为理想的能源转化方式,并且已经引起了众多研究者的关注. 水分解的半反应之一--水氧化反应由于其过程复杂,一直是制约水分解的瓶颈. 所以寻找高效、稳定的水氧化催化剂便成为了突破该瓶颈的关键. 多金属氧酸盐是一类以前过渡金属氧簇为基本单元形成的多金属氧簇化合物. 由于多金属氧酸盐在物理、化学性质方面具有无法比拟的特性,使得其在催化、药物、纳米科技和材料科学等方面已被广泛地应用. 多金属氧酸盐的全无机配体可很好地抵御水氧化反应的强氧化性环境,故将其作为水氧化催化剂越来越引起研究者们的注意,并且已有多种多金属氧酸盐被设计为水氧化催化剂. 本文详细介绍了各种不同过渡金属取代的多金属氧酸盐水氧化催化剂的研究进展.     

Sensitive Determination of Acetaminophen in the Presence of Dopamine and Pyridoxine Facilitated by their Extent of Interaction with Single‐walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWCNTs) were immobilized on glassy carbon (GC) electrode by drop casting The resulting modified electrode (represented as GC/SWCNTs) efficiently oxidizes acetaminophen (AC), dopamine (DA) and pyridoxine (PY) by decreasing the respective oxidation potentials and increasing peak currents in comparison to bare GC electrode. The extent of lowering of overpotentials is in the order of AC>PY>DA, in agreement with the order of decrease in the HOMO‐LUMO energy gap (ΔE) of these analytes, as determined from Density Functional Theory (DFT) calculations. DFT calculations further reveal that due to the interaction of the analytes on the SWCNT(10,10) there is a negative charge density transfer (higher probability of electron transfer, lower ΔE value) to the frontier molecular orbitals of the analytes, which eases their oxidation. Since AC, DA and PY oxidize distinctly at distinct potential values, the present SWCNTs modified electrodes could be used to simultaneously determine them. Cyclic voltammetry, differential pulse voltammetry and amperometry techniques are utilized to understand the electrochemical characteristics of the analytes (AC, DA and PY) and subsequent sensing of them at the GC/SWCNTs electrode. The electrode is then applied to the determination of AC as a case study. Sensitivity, detection limit and linear calibration range for the AC are found to be 7.9 μA μM^?1 cm^?2, 1.1 μM and 2.0–100.0 μM, respectively. The increased electroactive surface area of the GC/SWCNTs increases the oxidation peak currents and hence increases the sensitivity of the determination.     

Mechanistic interpretation of photochemical thallimetric oxidations catalysed by chloride and bromide ions

The thallimetric oxidation of carboxylic acids appears to proceed through free radical and intermediate activated complex mechanisms. The thermal and photochemical uncatalysed oxidation reactions appear to proceed through the formation of an intermediate metal-substrate complex that eventually decomposes to give the products. However, photochemical oxidation in the presence of chloride and bromide ions appears to proceed through a two-electron step via a halo bridge mechanism. In the presence of bromide at 2–3 times the concentration of thallium(III), the photochemical reduction mainly proceeds through a free radical mechanism involving a one-electron step via the formation of thallium(II) species. The nature and concentration of halide ions appear to be critical in deciding the path of the reaction.     

Pt的氧化状态对甲醇氧化活性的影响

采用NaBH4还原法制备了XC-72碳黑负载的Pt电催化剂,并在化学还原后用H2O2处理部分催化剂以改变Pt的氧化状态,以期改善Pt活性中心上水的离解而提高催化活性.X射线光电子能谱结果表明,经H2O2处理的催化剂含有较多的氧化态Pt.通过循环伏安法和记时电流法考察了经处理和未经处理的催化剂在酸性条件下的甲醇氧化的催化...     

Synthesis of Well-Defined High-Valent Palladium Complexes by Oxidation of Their Palladium(II) Precursors

The last decade has witnessed the rapid development of high-valent Pd-involved organic transformations. This has also led to a steadily growing number of publications concerning the preparation of isolable and characterizable palladium(III) and palladium(IV) complexes. A variety of one-electron and two-electron oxidants have been employed to give access to high-oxidation-state Pd compounds. Undoubtedly, the study of these stoichiometric reactions has great implications for relevant Pd-mediated catalysis. In this minireview, the focus is on the synthetic approaches to structurally determined Pd^III/IV complexes starting from their Pd^II precursors, and the advances in this research area from early 2010 to late 2019 will be highlighted. Chemical oxidations exploiting various oxidizing agents including 1) hypervalent iodine reagents; 2) halogens; 3) electrophilic fluorination reagents; 4) alkyl/aryl halides; 5) ferrocenium salts; 6) peroxides/O₂; 7) sulfonyl chlorides; and 8) others are covered. A “greener” electrooxidation manner has also been reviewed.     

Clean and selective Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-palygorskite

An environmentally benign and selective Baeyer-Villiger oxidation system is introduced. Palygorskite-supported Sn complexes were prepared by a simple procedure. Cyclic ketones and acyclic ketones were oxidized by hydrogen peroxide in a reaction catalyzed by palygorskite-supported Sn complexes, affording corresponding lactones or esters with selectivity for the product of 90-99%. The influence of the solvents, reaction temperature, the amount of catalyst used and the reaction time on the catalytic activity and product selectivity were investigated in detail. The catalyst is cheap, easy to be prepared in large scale and can be recycled.