Oxidation number: issues of its determination and range

The paper is aimed at the issues of oxidation state determination and limiting values. The possibility of existence of compounds containing an atom with the oxidation number beyond the current common values, i.e., below −IV and above +VIII are discussed. Three principal modes of preparation of compounds with the oxidation number exceeding VIII, electrochemical anodic oxidation, photoionization, and nuclear β-decay, are evaluated. Failure to prepare compounds containing an atom with the oxidation number below −IV is rationalized. The paper provides an opinion on uncertainties in oxidation state determination in three kinds of compounds: binary compounds, nitrosyl complexes, and compounds containing mutually bonded atoms of the same element. The questions are discussed from the viewpoint of correlation of “man-made” quantities and objective, experimentally obtainable data.     

Nanosecond redox equilibrium method for determining oxidation potentials in organic media

A general, nanosecond equilibrium method is described for determining thermodynamically meaningful oxidation potentials in organic media for compounds that form highly reactive cation radicals upon one-electron oxidation. The method provides oxidation potentials with unusually high precision and accuracy. Redox ladders have been constructed of appropriate reference compounds in dichloromethane and in acetonitrile that can be used to set up electron-transfer equilibria with compounds with unknown oxidation potentials. The method has been successfully applied to determining equilibrium oxidation potentials for a series of aryl-alkylcyclopropanes, whose oxidation potentials were imprecisely known previously. Structure-property trends for oxidation potentials of the cyclopropanes are discussed.     

Effect of phenolic compounds and quinones on radiation-induced oxidation processes of hexane and ethanol

The radiation-chemical yields were determined for the products of γ-radiation induced oxidation of hexane and ethanol in the presence of natural and synthetic phenolic compounds and quinones. It was found that the commercial antioxidants ionol and bisphenol 2246 more effectively inhibit the hexane oxidation process while α-tocopherol and quinones are superior to other test compounds in the suppression of ethanol oxidation. The results indicate that the antioxidant properties of phenolic compounds and quinones depend not only on their structure but also on the nature of the oxidation substrate. The cause of this phenomenon is discussed.     

电催化醇选择性氧化为醛酮的研究进展

醇选择性氧化为相应的羰基化合物是有机化学中最常用的生成羰基化合物的反应,电催化氧化具有反应条件温和、环境友好等优点,是一种非常有前途的醇催化氧化绿色生产工艺.我们综述了直接和间接电催化氧化反应的方法,并对各类体系的催化效果进行了简要介绍.     

Integrated electrochemical-chemical oxidation mediated by alkoxysulfonium ions

Generation of carbocations by the "cation pool" method followed by reaction with dimethyl sulfoxide (DMSO) gave the corresponding alkoxysulfonium ions. Alkoxysulfonium ions could also be generated by in situ DMSO trapping of electrochemically generated carbocations. The resulting alkoxysulfonium ions were transformed into carbonyl compounds by treatment with triethylamine. The present integrated electrochemical-chemical oxidation can be applied to the oxidation of diarylmethanes to diaryl ketones, toluenes to benzaldehydes, and aryl-substituted alkenes to 1,2-diketones. Moreover, the oxidation of unsaturated compounds bearing a nucleophilic group in an appropriate position gives cyclized carbonyl compounds.     

Schiff base complexes and their versatile applications as catalysts in oxidation of organic compounds: part I

Schiff bases and their complexes are good candidates as versatile compounds which are synthesized by the condensation of a primary amino compound with either aldehydes or ketones for a variety of industrial applications. They can act as catalysts in the catalytic oxidation of organic compounds. Recent researches in oxidation catalysis have focused on how to employ the metal‐catalyzed oxidation of organic substrates. This review summarizes the current developments of the last few decades for the oxidations of organic compounds that proceed through Schiff base complexes. The chemical syntheses of Schiff bases and their complexes are outlined.     

Structural diversity of peroxidase-catalyzed oxidation products of o-methoxyphenols

[reaction: see text] The biocatalytic oxidation of o-methoxyphenolic compounds led to a variety of oligophenols (dimers to pentamers) and some of their oxidation products. The reaction was carried out in an aqueous medium at room temperature with hydrogen peroxide as the terminal oxidant in a facile and green route to potentially bioactive compounds. Detailed structural information on the products of peroxidase-catalyzed oxidation of o-methoxyphenols is presented for the first time.     

咪唑并[1,2-a]吡啶化合物的无溶剂合成及其抗氧化性能

无溶剂条件下,2-氨基吡啶、芳香醛和异氰基乙酸乙酯发生Groebke-Blackburn-Bienaymé三组分反应,高效合成了6个咪唑并[1,2-a]吡啶化合物,产率89%~97%,其结构经¹H NMR, ¹³C NMR和HR-MS（ESI）确证。并通过抑制HO·和还原型谷胱甘肽自由基(GS·)引发的DNA氧化反应体系,对化合物的抗氧化活性进行了检测。结果表明：在抑制HO·引发的DNA氧化反应体系中,6个化合物相对空白硫代巴比妥酸活性物质吸光度百分数（TBARS百分数）可达32.2%~72.1%;在抑制GS·引发的DNA氧化反应体系中,6个化合物的TBARS百分数可达34.8%~81.3%。     

The Catalytic Activity of Transition Metal Compounds in the Liquid-Phase Oxidation of Hydrocarbons

The way in which dissolved transition metal compounds affect the liquid-phase oxidation of hydrocarbons is demonstrated for compounds of cobalt, copper, and manganese. Kinetic investigations on model systems and comparisons with the non-catalyzed reaction show that the catalysts participate in all the oxidation steps.     

Superconductivity in copper, silver, and gold compounds

High-temperature superconductivity exists in layered, square-planar cuprates, but is almost absent in most other Cu(II) compounds and in most Ag(II) and Au(II) compounds. Valence state II is quite unusual in silver and gold and often disproportionates to valence states I and III ("negative-U compounds"). The two-electron difference in oxidation state is suggestive of electron pairing, a prerequisite for superconductivity. In the present paper the connection between disproportionation and geometrical structure on one hand and superconductivity on the other is discussed by using the accepted theory for mixed valence complexes. It is concluded that absence of superconductivity in gold and silver compounds can be connected to the instability of oxidation state II and the large difference in equilibrium geometry between oxidation states I and III.     

Direct and selective benzylic oxidation of alkylarenes via C-H abstraction using alkali metal bromides

A direct benzylic oxidation of alkylarenes via C-H bond abstraction was developed using alkali metal bromides and oxidants under mild conditions. This reaction proceeded with excellent selectivity by thermal oxidation or photooxidation to provide a broad range of carbonyl compounds containing electron-deficient aryl carbonyl compounds in high yields.     

构建光催化氧化-还原体系的研究进展

光催化氧化-还原体系能够同时驱动光催化氧化反应和还原反应,产生协同效应,从而提高光催化反应的活性。在此,提出了构建光催化氧化-还原体系的原则,并介绍了光催化还原硝基芳烃耦合氧化有机物、光催化还原重金属离子协同氧化有机物、光解水制氢协同氧化有机物三个方面的实例。接着,阐述了光催化氧化-还原体系的反应机理,期望通过构建光催化氧化-还原体系,更有利于太阳能转化并缓解环境和能源问题。     

Anodic oxidation of p-disubstituted benzenes in the presence of fluoride ion

Electrochemical oxidation of aromatic compounds in the presence of fluoride ion gives products derived from initial oxidation of aromatic substrate and subsequent reaction with fluoride ion. The second of the one-electron transfer steps leads to benzenium ions, which give either fluoroaromatic compounds (elimination) or fluorocyclohexadienes (addition). The elimination of a t-butyl-group during anodic oxidation of p-di-t-butylbenzene yielded p-fluoro-t-butylbenzene. Further examples of the reaction involve p-fluorodiphenyl, p-fluoro-t-butylbenzene, and p-fluorophenol ethers.     

A study of the initial act of the oxidation of Lignin and compounds modeling it

The initial stage of the oxidation of lignin and of compounds modeling it has been studied by differential oscillographic voltammetry. The half-wave oxidation potentials of the compounds are given, and it is shown that the phenoxyl radicals formed are extremely unstable and take part immediately in subsequent chemical reactions.     

Paradigms and Paradoxes: Common and Maximum Accessible Oxidation States of the Elements

Common and accessible oxidation states of numerous nonmetals and transition metals in compounds with high oxidation state are discussed. These oxidation state concepts are generally, disappointingly and surprisingly elusive.     

Oxydation ausgewählter δ,ϵ- und ϵ,ξ-ungesättigter Alkohole mit Blei(IV)-acetat

The lead tetraacetate (LTA) oxidation of dihydro-γ-jonol ( 2 ) gives the new bicyclic ether 4 in high yield. On the other hand, LTA oxidation of the alcohols 8, 14, 20 , results in the formation of complex mixtures of oxidation products, from which the spiro compounds 10, 16, 22 , the bicyclic ethers 11, 12, 17, 18, 23 , and the carbonyl compounds 13, 19 have been isolated.     

High Performance Liquid Chromatography/Electrochemistry/High Resolution Electrospray Ionization‐Mass Spectrometry (HPLC/EC/HR ESI‐MS) Characterization of Selected Cytokinins Oxidation Products

Electrochemistry combined with mass spectrometry represents an emerging analytical technique used to study the oxidation pathway of various drugs and in vivo occurring compounds, continuously showing a capability to generate many known metabolites or new oxidation products. An on‐line HPLC/EC/HR ESI‐MS method had been used to investigate the oxidation of selected cytokinin compounds. This setup allowed rapid identification and general structure elucidation of the obtained products. An electrochemical oxidation of isopentenyladenine resulted in five products, including hydroxylated and dehydrogenated products, which correlates very well with its in vivo metabolism. Electrochemical conversion of trans‐zeatin revealed six products, with two dehydrogenation products corresponding to its in vivo occurring metabolites. cis‐Zeatin oxidation in the electrochemical cell gave rise to eight products, resembling similarity to trans‐zeatin oxidation. All three compounds underwent a complete turnover mainly through two oxidation reactions occurring in the electrochemical cell? dehydrogenation and a less typical aliphatic hydroxylation. The resulting products are in correlation with their known in vivo metabolism.     

Oxidation of Organometallic Compounds

Stable organometallic compounds, notably of the later transition metals (groups VI–VIII), usually are characterized by closed shell electron configurations (typically 18-electron valence shells) which are destabilized by electron addition or removal. One-electron oxidation of such compounds results in the formation of unstable radical ions, whose characteristic reactivity patterns include susceptibility to nucleophilic attack, disproportionation, and metal-carbon bond dissociation. Two-electron oxidation may result in dissociation or oxidation of the organic ligand. In this review studies on the chemical and electrochemical oxidations of metal carbonyls, metal-olefin complexes, and alkyl transition-metal compounds are described. The studies encompass the following themes: (1) The kinetics and thermodynamics of the initial redox steps; (2) The characterization and reactivity patterns of the resulting oxidation products; (3) The synthetic and catalytic applications of organometallic redox processes.     

Chemoselective Oxidation of Alkenes by Metal-Organic Framework-Supported Copper Catalyst

Oxidation of alkenes to carbonyls or diols compounds is important in synthesizing fine chemicals and pharmaceutical intermediates. We report the synthesis and characterization of an aluminum metal-organic framework node-supported copper(II) chloride (DUT-5-CuCl), which is an efficient heterogeneous catalyst for the oxidation of alkenes using H₂O₂ as an oxidizing agent. Styrene and various substituted styrenes were transformed into the corresponding carbonyl compounds in excellent selectivity and yields. DUT-5-CuCl is tolerant with various functional groups and could be recycled and reused at least 5 times in the oxidation of α-methylstyrene. Unlike the oxidation of styrene derivatives, DUT-5-Cu catalyzed oxidation of aliphatic and cyclic alkenes produced 1,2-diols compounds selectively. The mechanism of the DUT-5-Cu catalyzed oxidation of styrene to benzaldehyde was investigated in detail by various experiments such as the determination of reaction intermediates and characterization of the catalyst after catalysis, and computational studies. This work highlights the importance of MOF-supported earth-abundant metal catalysts for oxidation reactions to produce fine chemicals.     

Ceramic-forming compounds based on polycarbosilane and modified polyorganosilazanes

Ceramic-forming compounds based on polycarbosilane and polyorganosilazanes modified with atoms of refractory metals (Ti and Zr) were studied. The curing and pyrolysis of the compounds in an inert medium and the thermal oxidation resistance of ceramic pyrolysis residues were examined by synchronous thermal analysis and extraction. A ceramic matrix composite material was prepared from the compounds studied and a carbon reinforcing filler, and the physicochemical properties and thermal oxidation resistance of this material were evaluated.