Alkane oxygenation with H2O2 catalysed by FeCl3 and 2,2′-bipyridine

The H₂O₂-FeCl₃-bipy system in acetonitrile efficiently oxidises alkanes predominantly to alkyl hydroperoxides. Turnover numbers attain 400 after 1 h at 60 °C. It has been assumed that bipy facilitates proton abstraction from a H₂O₂ molecule coordinated to the iron ion (these reactions are stages in the catalytic cycle generating hydroxyl radicals from the hydrogen peroxide). Hydroxyl radicals then attack alkane molecules finally yielding the alkyl hydroperoxide.     

Oxidations by the system ‘hydrogen peroxide-[Mn2L2O3][PF6]2 (L=1,4,7-trimethyl-1,4,7-triazacyclononane)-carboxylic acid’. Part 10: Co-catalytic effect of different carboxylic acids in the oxidation of cyclohexane, cyclohexanol, and acetone

Hydrogen peroxide oxidation of cyclohexane in acetonitrile solution catalyzed by the dinuclear manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ (L=1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN) at 25 °C in the presence of a carboxylic acid affords cyclohexyl hydroperoxide as well as cyclohexanone and cyclohexanol. A kinetic study of the reactions with participation of three acids (acetic acid, oxalic acid, and pyrazine-2,3-dicarboxylic acid, 2,3-PDCA) led to the following general scheme. In the first stage, the catalyst precursor forms an adduct. The equilibrium constants K₁ calculated for acetic acid, oxalic acid, and 2,3-PDCA were 127±8, (7±2)×10⁴, and 1250±50 M⁻¹, respectively. The same kinetic scheme was applied for the cyclohexanol oxidation catalyzed by the complex in the presence of oxalic acid. The oxidation of cyclohexane in water solution using oxalic acid as a co-catalyst gave cyclohexanol and cyclohexanone, which were rapidly transformed into a mixture of over-oxidation products. In the oxidation of cyclohexanol to cyclohexanone, varying the concentrations of the reactants and the reaction time we were able to find optimal conditions and to obtain the cyclohexanone in 94% yield based on the starting cyclohexanol. Oxidation of acetone to acetic acid by the system containing oxalic acid was also studied.     

A unique rate-accelerating effect of certain amino acids in the H2O2 oxidation of alkanes catalyzed by a dinuclear manganese complex containing 1,4,7-trimethyl-1,4,7-triazacyclononane

Certain amino acids used in small amounts (10 catalyst equiv) strongly accelerate the H₂O₂ oxidation of cyclohexane catalyzed by a dinuclear manganese(IV) complex with 1,4,7-trimethyl-1,4,7-triazacyclononane. The efficiency of the co-catalyst dramatically depends on the nature and structure of the acid. Pyrazine-2,3-dicarboxylic acid (2,3-PDCA) has been found to be the most efficient co-catalyst whereas picolinic acid is almost inactive in this oxidation. The highest rate has been attained when 2,3-PDCA was used in combination with trifluoroacetic acid.     

Oxidations by the system “hydrogen peroxide-[Mn2L2O3][PF6]2 (L = 1,4,7-trimethyl-1,4,7-triazacyclononane)-oxalic acid”. Part 6. Oxidation of methane and other alkanes and olefins in water

Oxidation of alkanes with hydrogen peroxide in water solution at 10-50 °C is efficiently catalyzed by the cationic dinuclear manganese (IV) derivative [Mn₂L₂O₃]²⁺ (1, with L = 1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN) in the form of the hexafluorophosphate salt ([1][PF₆]₂) if oxalic acid is present as a co-catalyst. Methane gives methanol and formaldehyde (turnover numbers, TONs, were 7 and 2, respectively, after reduction of the reaction mixture with ascorbic acid) whereas cyclohexane was oxidized with TONs up to 160 affording cyclohexyl hydroperoxide, cyclohexanone and cyclohexanol (the ketone was the main product, although at room temperature almost pure alkyl hydroperoxide was formed). In contrast to the oxidation in acetonitrile, the reaction with linear n-alkanes in water exhibits an unusual distribution of oxygenates. For example, in the oxidation of n-heptane the normalized reactivity of the methylene group in position 4 of the chain is 3-7 times higher than that of the CH₂ group in position 2. Dec-1-ene is epoxidized by hydrogen peroxide in water (a biphasic system) catalyzed by [1][PF₆]₂ and oxalic acid in the presence of a small amount of acetonitrile with TONs up to 1000 (no epoxidation has been detected in the absence of MeCN).     

A novel oxidative side-chain transformation of α-amino acids and peptides by methyltrioxorhenium/H2O2 system

N-Boc derivatives of Met, Cys, and Trp, the properties of which resemble those of the respective amino acid residues present in proteins, are efficiently oxidized by methyltrioxorhenium and H₂O₂. A high regioselectivity for the oxidation of these residues when embedded into peptides was also found.     

Efficient and convenient oxidation of organic halides to carbonyl compounds by H2O2 in ethanol

Various primary and secondary organic bromides were oxidized by hydrogen peroxide in refluxing ethanol to give the corresponding aldehydes/and ketones in high yield up to 94%; organic chlorides were oxidized to the corresponding aldehydes/and ketones by the same oxidant in ethanol in the presence of 10 mol % of KBr as the catalyst.     

Oxidations catalyzed by osmium compounds. Part 1: Efficient alkane oxidation with peroxides catalyzed by an olefin carbonyl osmium(0) complex

A carbonyl osmium(0) complex with π-coordinated olefin, (2,3-η-1,4-diphenylbut-2-en-1,4-dione)undecacarbonyl triangulotriosmium (1), efficiently catalyzes oxygenation of alkanes (cyclohexane, cyclooctane, n-heptane, isooctane, etc.) with hydrogen peroxide, as well as with tert-butyl hydroperoxide and meta-chloroperoxybenzoic acid in acetonitrile solution. Alkanes are oxidized to corresponding alcohols, ketones (aldehydes) and alkyl hydroperoxides. Thus, heating cyclooctane with the 1-H₂O₂ combination at 70 °C gave products with turnover number as high as 2400 after 6 h. The maximum obtained yield of all products was equal to 20% based on cyclohexane and 30% based on H₂O₂. The oxidation of linear and branched alkanes exhibits very low regio- and bond-selectivity parameters and this testifies that the reaction proceeds via attack of hydroxyl radicals on C-H bonds of the alkane. The oxygenation products were not formed when the reaction was carried out under argon atmosphere and it can be thus concluded that the oxygenation occurs via the reaction between alkyl radicals and atmospheric oxygen. In summary, the Os(0) complex is much more powerful generator of hydroxyl radicals than any soluble derivative of iron (which is an analogue of osmium in the Periodic System).     

Chemoselective sulfoxidation by H2O2 or HNO3 using a phosphate impregnated titania catalyst

A variety of organosulfur compounds have been selectively oxidized to the corresponding sulfoxides by either H₂O₂ or HNO₃ using a newly developed solid acid catalyst composed of 84.5% of TiO₂ and 15.5% of [Ti₄H₁₁(PO₄)₉]·nH₂O (n = 1-4). The chemoselective oxidation of sulfides in the presence of vulnerable groups such as -CN, -CC-, -CHO, or -OH, as well as sulfoxidation of substrates like benzothiazole, glycosyl sulfide, and dibenzothiophenes is some of the important attribute of the protocol. Nitric acid, under the present experimental conditions, brings about relatively better selectivity than hydrogen peroxide.     

Regioselective alkane oxygenation with H2O2 catalyzed by titanosilicalite TS-1

Titanosilicalite TS-1 catalyses oxidation of light (methane, ethane, propane and n-butane) and normal higher (hexane, heptane, octane and nonane) alkanes to give the corresponding isomeric alcohols and ketones. The oxidation of higher alkanes proceeds in many cases with a unique regioselectivity. Thus, in the reaction with n-heptane the CH₂ groups in position 3 exhibited a reactivity 2.5 times higher than those of the other methylene groups. This selectivity can be enhanced if hexan-3-ol is added to the reaction mixture, the 3-CH₂/2-CH₂ ratio becoming 10. It is assumed that the unusual selectivity in the oxidation of n-heptane (and other higher alkanes) is due to steric hindrance in the catalyst cavity. As a result, the catalytically active species situated on the catalyst walls can only easily react with certain methylenes of the alkane, which is adsorbed in the cavity taking U-shape (hairpin) conformations.     

Synthesis, characterization and performance of vanadium hexacyanoferrate as electrocatalyst of H2O2

The present work reports for the first time on the synthesis, characterization and performance of vanadium hexacyanoferrate (VHCF) as electrocatalyst of hydrogen peroxide. VHCF was synthesized by mixing V₂O₅ · nH₂O xerogel with ascorbic acid and K₄[Fe(CN)₆] in double distilled water. X-ray powder diffraction, energy dispersive spectroscopy, scanning electron microscopy, and IR-spectroscopy data suggest the formation of nanocrystalline (mean crystal size 11 nm) compound with a tentative molecular formula K₂(VO)₃[Fe(CN)₆]₂. Composite films of VHCF with poly(vinyl alcohol) were developed over a glassy carbon electrode, and then covered with different (neutral, positively or negatively charged) membranes. The effect of each membrane on the working stability of the resultant sensors was evaluated. Cyclic voltammetry experiments showed that composite films exhibit a pair of reversible redox peaks, and a remarkable low potential electrocatalysis on both the reduction and oxidation of hydrogen peroxide. A linear calibration curve over the concentration range 0.01–3.0 mM H₂O₂ was constructed. Limit of detection (S/N = 3) of 4 μM H₂O₂ was calculated. The proposed transducer is quite selective to hydrogen peroxide. No response was observed in the presence of 10 mM ascorbic acid.     

Novel supramolecular network in tri- and mono-nuclear oxovanadium(V)-salicyl-hydroximate: Synthesis,structure and catalytic oxidation of hydrocarbons using H2O2 as terminal oxidant

Two oxovanadium(V) salicylhydroximate complexes, [VO(SHA)(H₂O)] · 1.58H₂O (1) and [V₃O₃(CSHA)₃(H₂O)₃] · 3CH₃COCH₃ (2) have been synthesized by reaction of VO₄³⁻ with N-salicyl hydroxamic acid (SHAH₃) and N-(5-chlorosalicyl) hydroxamic acid (CSHAH₃), respectively, in methanol medium. Compound 1 on reaction with pyridine 2,6-dicarboxylic acid (PyDCH₂) yields mononuclear complex [VO(SHAH₂)(PyDC)] (3). Treatment of compound 3 with hydrogen peroxide at low pH (2-3) and low temperature (0–5 °C) yields a stable oxoperoxovanadium(V) complex H[VO(O₂)(PyDC)(H₂O)] · 2.5H₂O (4). All four complexes (1–4) have been characterized by spectroscopic (IR, UV–Vis, ⁵¹V NMR) and single crystal X-ray analyses. Intermolecular hydrogen bonds link complex 1 into hexanuclear clusters consisting of six {VNO₅} octahedra surrounded by twelve {VNO₅} octahedra to form an annular ring. While the molecular packing in 2 generates a two-dimensional framework hydrogen bonds involving the solvent acetone molecules, the mononuclear complexes 3 and 4 exhibit three-dimensional supramolecular architecture. The compounds 1 and 2 behave as good catalysts for oxygenation of benzylic, aromatic, carbocyclic and aliphatic hydrocarbons to their corresponding hydroxylated and oxygenated products using H₂O₂ as terminal oxidant; the process affords very good yield and turnover number. The catalysis work shows that cyclohexane is a very easily oxidizable substrate giving the highest turnover number (TON) while n-hexane and n-heptane show limited yield, longer time involvement and lesser TON than other hydrocarbons.     

Selective and mild oxidation of sulfides to sulfoxides or sulfones using H2O2 and Cp′Mo(CO)3Cl as catalysts

Dialkyl, aryl-alkyl, benzylic, and benzothiophenic sulfides are selectively oxidized to sulfoxides or sulfones, with stoichiometric amounts of H₂O₂ (aq) or TBHP, in the presence of complexes Cp′Mo(CO)₃Cl, CpMoO₂Cl and the mesoporous material MCM-41-2 as catalysts. The use of the thianthrene 5-oxide (SSO) probe shows that CpMo(CO)₃Cl/H₂O₂ or TBHP are electrophilic oxidants (Xso ? 15). The same conclusion is drawn from competition experiments with a mixture of p-ClC₆H₄SCH₃ and C₆H₅SOCH₃.     

Oxidation of aromatic aldehydes and ketones by H2O2/CH3ReO3 in ionic liquids: a catalytic efficient reaction to achieve dihydric phenols

A convenient and efficient application of hydrogen peroxide/methyltrioxorhenium in ionic liquids [bmim]BF₄ and [bmim]PF₆ for the oxidation of hydroxylated and methoxylated benzaldehydes and acetophenones to the corresponding phenols is described. Good yields of products were obtained in short reaction times.     

NiCo2O4对H2O2在碱性溶液中电化学还原反应的催化行为

利用溶胶-凝胶法合成纳米NiCo2O4,并利用X射线衍射和透射电镜分析其结构和表面形貌. 结果表明NiCo2O4具有尖晶石结构, 平均粒径约为15 nm. 利用电势线性扫描和恒电势法测定了其对H2O2在碱性溶液中电化学还原反应的催化性能. 发现NiCo2O4对H2O2电化学还原具有高的催化活性和稳定性, 在H2O2浓度低于0.6 mol·L-1时, 其电化学还原反应主要通过直接还原途径进行. 以NiCo2O4为阴极催化剂的Al-H2O2半燃料电池在室温下的开路电压达1.6 V; 在1.0 mol·L-1 H2O2溶液中, 峰值功率密度达209 mW·cm-2, 此时电流密度为220 mA·cm-2.     

Selective and efficient oxidation of ethylene to ethylene glycol acetates with H2O2 catalyzed by Pd(OAc)2-di(2-pyridyl)ketone-di(2-pyridyl)methanesulfonate system

Novel systems for palladium-catalyzed selective oxidation of ethylene to a mixture of ethylene glycol mono- and di-acetates as the major reaction products (90-95% selectivity) with H₂O₂ in acetic acid solution at ambient pressure and 20 °C were developed. The catalytic reaction is very efficient with up to 90% combined yield of glycol acetates with H₂O₂ as a limiting reagent and 1 mol% catalyst loading. The catalytic systems developed are comprised of a mixture of Pd(OAc)₂, and 6-methyl substituted (2-pyridyl)methanesulfonate and/or di(6-pyridyl)ketone ligands. Compositions of the binary, Pd(OAc)₂-dpk, Pd(OAc)₂-Me-dpms, and ternary, Pd(OAc)₂-dpk-Me-dpms, systems have been studied by means of ¹H NMR spectroscopy and ESI mass spectrometry. Kinetics studies were performed as well and plausible reaction mechanism was suggested, which features facially chelating ligand-enabled facile oxidation of Pd^IIC₂H₄OAc intermediates with H₂O₂ to form Pd^IVC₂H₄OAc transients.     

Facile oxygenation of organic sulfides with H2O2 catalyzed by Mn-Me3TACN compounds

Two binuclear Mn-Me₃TACN (Me₃TACN is 1,4,7-N,N′,N″-trimethyl-1,4,7-triazacyclononane) compounds catalyze the oxygenation of organic sulfides utilizing H₂O₂ under ambient conditions. Both phenyl sulfide and ethyl phenyl sulfide were converted to the corresponding sulfones and chloroethyl phenyl sulfide proceeds to its elimination product of phenyl vinyl sulfone.     

Free radical bromination by the H2O2-HBr system on water

An aqueous solution of hydrogen peroxide and hydrogen bromide illuminated by a 40 W incandescent light bulb serves as a source of bromine radicals. Various substituted toluenes (H, Me, tBu, Br, COOEt, COPh, NO₂) were brominated at the benzyl position. This haloperoxidase-like system for benzylic bromination does not require the presence of metal ions or an organic solvent for efficient conversion of methyl-arenes to benzyl bromides.     

TS-1/H2O2碱溶液中低温氧化愈创木酚制备马来酸（英）

可再生生物质资源的开发与利用能够缓解化石燃料产生的温室气体对环境的负面影响.在生物质燃料制备过程中联产高附加值化学品能大幅提高生物质炼制的经济性.愈创木酚是常见的木质纤维素快速热解产物.本文研究了低温液相氧化愈创木酚制备马来酸,并重点考察了催化剂添加量、pH值、反应时间和反应温度等反应条件的影响.研究发现,在钛硅沸石-过氧化氢碱溶液氧化反应体系中（80℃,pH=13.3）,20₃0mol%的愈创木酚可以选择性转化为马来酸.同时初步探讨了愈创木酚氧化开环转化为马来酸的反应机理.     

Direct synthesis of hydrogen peroxide from H2/O2 using Pd/Al2O3 catalysts

Pd/Al₂O₃ catalysts were prepared by the impregnation method and were used for the direct formation of hydrogen peroxide from H₂ and O₂. The H₂O₂ concentration and selectivity were strongly dependent on the solubility of hydrogen in the reaction medium. The modification of the support by halogenate has a beneficial effect on the selectivity. The state of the active Pd on Pd/Al₂O₃ catalysts was studied using X-ray photoelectron spectroscopy, and Pd(0) was found to be active.     

Synthesis of novel organoselenium as catalyst for Baeyer-Villiger oxidation with 30% H2O2

A novel diselenide was synthesized in good yield via only four steps from phenol, and was employed as the catalyst for the Baeyer-Villiger oxidation with 30% H₂O₂ to obtain lactones in good yields.