Clean Oxidation Research Articles

ChemInform Abstract: Iron‐Catalyzed Direct C—H Thiolation of Trimethoxybenzene with Disulfides.

Abstract An iron-catalyzed thiolation access to sulfides from disulfides via arene C-H bond cleavage of trimethoxybenzene is described. The procedure tolerates methoxyl, fluoro, chloro, bromo, nitro, and heterocyclic groups, using air as the clean and terminal oxidant.

An N-bridged high-valent diiron–oxo species on a porphyrin platform that can oxidize methane

High-valent oxo-metal complexes are involved in key biochemical processes of selective oxidation and removal of xenobiotics. The catalytic properties of cytochrome P-450 and soluble methane monooxygenase enzymes are associated with oxo species on mononuclear iron haem and diiron non-haem platforms, respectively. Bio-inspired chemical systems that can reproduce the fascinating ability of these enzymes to oxidize the strongest C-H bonds are the focus of intense scrutiny. In this context, the development of highly oxidizing diiron macrocyclic catalysts requires a structural determination of the elusive active species and elucidation of the reaction mechanism. Here we report the preparation of an Fe(IV)(µ-nitrido)Fe(IV) = O tetraphenylporphyrin cation radical species at -90°C, characterized by ultraviolet-visible, electron paramagnetic resonance and Mössbauer spectroscopies and by electrospray ionization mass spectrometry. This species exhibits a very high activity for oxygen-atom transfer towards alkanes, including methane. These findings provide a foundation on which to develop efficient and clean oxidation processes, in particular transformations of the strongest C-H bonds.

Iron-Catalyzed Direct C-H Thiolation of Trimethoxybenzene with Disulfides

An iron-catalyzed thiolation access to sulfides from disulfides via arene C-H bond cleavage of trimethoxybenzene is described. The procedure tolerates methoxyl, fluoro, chloro, bromo, nitro, and heterocyclic groups, using air as the clean and terminal oxidant.

Assessment of natural attenuation of acid mine drainage pollutants in El Bierzo and Odiel basins: A case study

In the past, mining activities have generated major acid drainage sources, which usually carry dissolved metals that flow into the main rivers of the affected basins. The study looks at natural attenuation processes in local, sub-basin and basin areas, in the El Bierzo and Odiel basins of Spain, where coal and metal mining activities were formerly conducted. In this study, sampling and in situ monitoring of pH, Eh, dissolved oxygen, conductivity, temperature, flow, turbidity, acidity, alkalinity, Fe 2+ , Fe 3+ and total Fe were carried out during the hydrological cycle. Chemical analysis was also performed on water samples, following the water quality data of the ICA Network of the Spanish Environment Ministry for a period of 10 years. The results show that the main natural attenuation processes were: dilution by mixing with clean water, oxidation and hydrolysis of dissolved metals, reduction of anaerobic sulphates, and precipitation of secondary minerals.

Nanomagnet‐Supported Partially Brominated Manganese–Porphyrin as a Promising Catalyst for the Selective Heterogeneous Oxidation of Hydrocarbons and Sulfides in Water

AbstractA novel, magnetically recoverable porphyrin catalyst has been prepared by the coordinative anchoring of the [Mn(Br2TPP)OAc] complex on silica‐coated magnetic nanoparticles (Fe3O4@SiO2, SMNP) through an amine functionality. The heterogeneous catalyst was characterized by powder X‐ray diffraction, transmision electron microscopy, scanning electron microscopy, and FTIR spectroscopy. The catalyst loading on the magnetic support was determined by thermogravimetric (TG) analysis and inductively coupled plasma atomic emission spectroscopy. The catalyst nanoparticles were estimated to have a diameter of less than 10 nm. The TG curve demonstrated that the nanocatalyst was thermally stable up to almost 350 °C, exhibiting high thermostability. The epoxidation of olefins and the oxidation of saturated hydrocarbons to the corresponding ketones as well as sulfides to sulfones in an aqueous solution of tetra‐n‐butylammonium peroxomonosulfate (n‐Bu4NHSO5, TBAOX) were efficiently enhanced with excellent selectivity under the influence of the magnetically separable catalyst. Sulfoxides could also be selectively produced in a mixture of water and ethanol, which makes the title methodology a good alternative for both sulfoxide and sulfone production. The separation and recycling of the catalyst and the byproduct of the oxidant were simple, effective, and economic in this clean oxidation method. FTIR and leaching experiments after seven successive cycles showed that the catalyst was very strongly anchored to the SMNP support.

Ni/Fe-supported over hydrotalcites precursors as catalysts for clean and selective oxidation of Basic Yellow 11: Reaction intermediates determination

In this work, Basic Yellow 11 (BY 11) was employed as model compound to study catalytic wet air oxidation as a pre-treatment step to the conventional biological oxidation. Ni and Fe catalysts supported over hydrotalcite (HT) were prepared by incipient wetness and excess impregnation to obtain catalysts with different metal loadings (from 1 to 10wt.%). HTs were synthesized by co-precipitation and characterized with XRD, X-ray fluorescence (XRF), BET, thermogravimetric analysis and SEM. Results showed that dye conversion increased with Ni and Fe content up to 7wt.% and that the most effective catalyst were prepared by incipient wetness impregnation. The influence of metal loading in the catalyst, and the preparation method as well as the reaction conditions was investigated. A mechanism and reaction pathways for BY 11 during catalytic liquid phase oxidation have also been proposed.

An ionic compound containing Ru(III)-complex cation and phosphotungstate anion as the efficient and recyclable catalyst for clean aerobic oxidation of alcohols

A novel ionic compound (3, [RuCl4(L)2]3PW12O40) containing the Ru(III)-complex cation and α-Keggin-type phosphotungstate anion was synthesized and proven to be the efficient catalyst for aerobic oxidations of alcohols free of base and nitroxyl radical. Specially, 3 could be reused at least five runs without obvious activity loss. The stability of 3 was dramatically improved due to the incorporation of [PW12O40]3 − as the counter-anions, leading to its available recyclability.

The Copper‐Catalyzed C‐3‐Formylation of Indole CH Bonds using Tertiary Amines and Molecular Oxygen

AbstractA copper‐catalyzed formylation reaction has been developed by employing oxygen (O2) as the clean oxidant. The CH bonds of indoles were C‐3‐formylated by tetramethylethylenediamine (TMEDA) and water (H2O; in situ formed and external added water) as the carbonyl source in moderate to good yields with good functional group tolerance. Thus, it represents a facile procedure leading to 3‐formylindoles.

Two-Electron Redox Chemistry at the Dinuclear Core of a TePt Platform: Chlorine Photoreductive Elimination and Isolation of a TeVPtI Complex

As part of our interest in novel redox-active main group/transition metal platforms for energy applications, we have synthesized the chloride salt of [Te(III)Pt(I)Cl(o-dppp)(2)](+) ([1](+), o-dppp = o-(Ph(2)P)C(6)H(4)) by reaction of the new bis(phosphino) telluroether (o-(Ph(2)P)C(6)H(4))(2)Te with (Et(2)S)(2)PtCl(2). Complex [1](+) is chemically robust and undergoes a clean two-electron oxidation reaction in the presence of PhICl(2) to afford ClTe(III)Pt(III)Cl(3)(o-dppp)(2) (2), a complex combining a hypervalent four-coordinate tellurium atom and an octahedral platinum center. While the Te-Pt bond length is only slightly affected by the oxidation state of the TePt platform, DFT and NBO calculations show that this central linkage undergoes an umpolung from Te→Pt in [1](+) to Te←Pt in 2. This umpolung signals an increase in the electron releasing ability of the tellurium center upon switching from an eight-electron configuration in [1](+) to a hypervalent configuration in 2. Remarkably, the two-electron redox chemistry displayed by this new dinuclear platform is reversible as shown by the photoreductive elimination of a Cl(2) equivalent when 2 is irradiated at 350 nm in the presence of a radical trap such as 2,3-dimethyl-1,3-butadiene. This photoreductive elimination, which affords [1][Cl] with a maximum quantum yield of 4.4%, shows that main group/late transition metal complexes can mimic the behavior of their transition metal-only analogues and, in particular, undergo halogen photoelimination from the oxidized state. A last notable outcome of this study is the isolation and characterization of F(MeO)(2)Te(V)Pt(I)Cl(o-dppp)(2) (4), the first metalated hexavalent tellurium compound, which is formed by reaction of 2 with KF in the presence of MeOH.

Oxidation of o-chloro and o-hydroxy benzyl alcohols catalyzed by copper (II) tetraphenylporphyrin nanoparticles synthesized by mixed solvent method

. In order to avoid using toxic and dangerous oxidants, oxidative catalytic conversion of organic molecules has been developed in the recent years by using environmentally clean oxidants such as molecular oxygen or hydrogen peroxide. For example, benzyl alcohols have been oxidized by molecular oxygen, because this oxidant only produces water as a by product

Clean Oxidation of Cyclohexanone to Adipic Acid Catalyzed by Ammonium Phosphomolybdate with Dawson Structure under Microwave Irradiation

Ammonium Phosphomolybdate with Dawson structure was prepared by hydrothermal synthesis and characted by means of FT-IR, UV-Vis,XRD and SEM. The synthesis of adipic acid with cyclohexanone and 30 percent hydrogen peroxide under microwave irradiation was carried out as a probe reaction to study the catalytic activity. Effects of catalyst amount,30wt.% H2O2 amount,microwave power, reaction time were investigated and optimized with orthogonal experiments and simple fact experiments. The results show that under the optimal condition, i.e. the mole ratio of C6H10O: H2O2:H2C2O4•2H2O:(NH4)6P2Mo18O62•nH2O =100:500:2.0:0.087, the reaction temperature was 100°C, microwave power was 400W, irradiation time was 3.5 h，the isolated yield of adipic acid could reach 72.5%．The catalyst could be reused for 5 times and the isolated of adipic acid was still above 43.2%.

Expanding the Steric Coverage Offered by Bis(amidosilyl) Chelates: Isolation of Low-Coordinate N-Heterocyclic Germylene Complexes

The synthesis and coordination chemistry of a series of dianionic bis(amido)silyl and bis(amido)disilyl, [NSiN] and [NSiSiN], chelates with N-bound aryl or sterically modified triarylsilyl (SiAr(3)) groups is reported. In order to provide a consistent comparison of the steric coverage afforded by each ligand construct, various two-coordinate N-heterocyclic germylene complexes featuring each ligand set were prepared and oxidative S-atom transfer chemistry was explored. In the cases where clean oxidation transpired, sulfido-bridged centrosymmetric germanium(IV) dimers of the general form [LGe(μ-S)](2) (L = bis(amidosilyl) ligands) were obtained in lieu of the target monomeric germanethiones with discrete Ge═S double bonds. These results indicate that the reported chelates possess sufficient conformational flexibility to allow for the dimerization of LGe═S units to occur. Notably, the new triarylsilyl groups (4-RC(6)H(4))(3)Si- (R = (t)Bu and (i)Pr) still offer considerably expanded degrees of steric coverage relative to the parent congener, -SiPh(3,) and thus the use of substituted triarylsilyl groups within ligand design strategies should be a generally useful concept in advancing low-coordination main group and transition-metal chemistry.

Chemical-Mechanical Planarization Aided Dimple Etching for Self Alignment

Through silicon via (TSV) technology is becoming a mainstream method of building 3-dimensional integrated circuits (3D IC). In particular, TSV Cu CMP is a critical process to remove excess Cu and makes a planar surface which requires a removal rate higher than 5 microm/min and a dishing lower than 0.3 microm. This paper focuses on the development of a new self-alignment method using dimples on the TSV Cu back surface. We tried to find an application potential of a bump-dimple structure for self alignment using a pretest tool of a solder ball array structure. Chemical-mechanical planarization (CMP) aided dimple etching is carefully studied as a key solution for deep and uniform dimple formation. The experiment shows that CMP is an excellent process to generate a clean oxide surface and a clear dishing on the Cu TSV, resulting in a seed for etching. Finally, etching realizes a uniform dimple depth of 7 microm to 9 microm in spite of changes of via diameter from 10 microm to 50 microm after only 15 sec etching.

An efficient and mild carboxylation of multiwall carbon nanotubes using H2O2 in the presence of heteropolyacid

Abstract A clean, fast, and facile oxidation of multiwalled carbon nanotubes (MWCNTs) by H2O2/heteropolyacid (H3PW12O40) gave highly carboxylated MWCNTs under mild conditions, at a conveniently accessible temperature. After an easy workup, the product was characterized by SEM, XRD, and FT-IR.

Epoxidation of Soybean Oil with Tert-Butyl Hydroperoxide over Manganese (III) Tetraphenylporphyrin Chloride Catalyst

A new catalytic route was reported for the epoxidation of soybean oil (SBO) with tert-butyl hydroperoxide (TBHP, 65 wt. %) as the clean oxidant over manganese (III) tetraphenylporphyrin chloride (Mn (TPP) Cl) catalyst without carboxylic acid. Effect of tetraphenylporphyrin chloride with various metals (Mn, Fe, Co, Ni and Zn) on SBO epoxidation has been investigated. As biomimetic catalysts, the optimum reaction temperature of the system existed for catalytic activity, which was about 40 °C. The optimum reaction time was 6 h and the suitable promoter was pyrrole considering various factors. The suitable oxidant was TBHP of 65 wt. %. A mechanism for SBO epoxidation was discussed, and a role for high-valent metal peroxide intermediate with double bond directly as part of this mechanism was proposed, which was verified by in situ UV-Vis spectroscopy. The optimized reaction conditions were acquired.

Manganese(II) naphthenate as effective catalyst for the clean oxidation of 2-methylnaphthalene by hydrogen peroxide

Oxidation of 2-methylnaphthalene (2-MN) with aqueous hydrogen peroxide was conducted in acetic acid. The epoxidation pathway was investigated by increasing the CH3CO3H content and adding manganese(II) naphthenate (MnPc) as catalyst. 2-Methyl-1,4-naphthoquinone was obtained in 75.6% conversion and with 80.0% selectivity under the latter conditions. A probable mechanism in which MnPc catalyzes the oxidation of 2-MN by hydrogen peroxide in acetic acid is proposed.

Ruthenium/NHC-catalyzed tandem benzylic oxidation/oxidative esterification of benzylic alcohols with phenols

Abstract An efficient methodology to access benzoate derivatives via tandem benzylic oxidation/oxidative esterification of benzylic alcohols with phenols catalyzed by ruthenium/NHC was developed. This operationally simple one-pot process uses O 2 as the clean oxidant, producing esters in good to excellent yields.

Catalytic desulfitative homocoupling of sodium arylsulfinates in water using PdCl2 as the recyclable catalyst and O2 as the terminal oxidant

A green and convenient approach to symmetrical biaryls has been developed. The catalytic desulfitative homocoupling of various inexpensive and readily available sodium arylsulfinates in environment-friendly solvent, water, and under clean oxidant, molecular O2, afforded symmetrical biaryls in good yields. What's more, water can hold the noble catalyst PdCl2 for recycling several times easily, and facilitate separating insoluble organic product.

Controlled multistep oxidation of alcohols and aldehydes to carboxylic acids using air, sunlight and a robust metalloporphyrin sensitizer with a pH-switchable photoreactivity

A homogeneous photocatalytic reaction cascade for the stepwise biomimetic oxidation of alcohols to form either aldehydes or alternatively carboxylic acids is presented. The system is based on robust and abundant materials and efficiently utilizes dioxygen as a clean and sustainable oxidant. Photoassisted substrate transformation occurs upon exposure to visible light (<620 nm) or sunlight. The pH-dependent photoredox mechanism of the sensitizer can be reversibly switched between two different selectivity patterns to control the desired product formation.

Aqueous heterogeneous oxygenation of hydrocarbons and sulfides catalyzed by recoverable magnetite nanoparticles coated with copper(ii) phthalocyanine

In this work, a novel magnetically recoverable phthalocyanine catalyst was prepared by immobilization of the Cu(II) phthalocyanine-tetrasulfonic acid tetrasodium complex (CuPcS) on the silica coated magnetic nanoparticles (Fe3O4@SiO2, SMNP) via the amine functionality (ASMNP). The epoxidation of olefins and the oxidation of saturated hydrocarbons to the related ketones and also sulfides to the sulfones by an aqueous solution of tetra-n-butylammonium peroxomonosulfate (n-Bu4NHSO5, TBAOX) were efficiently enhanced with excellent selectivity under the influence of the catalytic activity of the magnetically separable catalyst. Sulfoxides could also be selectively produced in the mixture of water–ethanol, which makes the title methodology a good alternative for both sulfoxide and sulfone production. The separation and recycling of the catalyst and the reduced form of the oxidant were simple, effective and economical in this clean oxidation method. The FT-IR and leaching experiments after seven successive cycles showed that the catalyst was most strongly anchored to the magnetite nanoparticles.