Sole Source Of Oxygen Research Articles

Selective Oxidative Cleavage of Benzyl C-N Bond under Metal-Free Electrochemical Conditions.

With the growing significance of green chemistry in organic synthesis, electrochemical oxidation has seen rapid development. Compounds undergo oxidation-reduction reactions through electron transfer at the electrode surface. This article proposes the use of electrochemical methods to achieve cleavage of the benzyl C-N bond. This method selectively oxidatively cleaves the C-N bond without the need for metal catalysts or external oxidants. Additionally, primary, secondary, and tertiary amines exhibit good adaptability under these conditions, utilizing water as the sole source of oxygen.

An Open-Air Palladium-Catalyzed Stereoselective O-Glycosylation of Glycals via in-situ Generation of gem-Disubstituted Methanols from p-Quinone Methides.

We devised a palladium-catalyzed α-stereoselective glycosylation that incorporates oxygen via in-situ generation of gem-disubstituted methanols from p-quinone methides to access 2,3-unsaturated gem-diarylmethyl O-glycosides under open-air atmosphere at room temperature. Advantages of this environmentally friendly strategy include the absence of additives and ligands, using water as the green source of oxygen, mildest, operationally simple, exhibiting a wide functional group tolerance, and compatibility with a variety of glycal progenitors in appreciable yields. A mechanistic study has been verified via H2 18 O labeling, which validates that water (moisture) is a sole source of oxygen.

Electrochemical aerobic Wacker-type oxygenation of triaryl substituted alkenes to 1,2,2-triarylethanones.

An effective synthetic approach for various 1,2,2-triarylethanones from triaryl substituted alkenes has been developed via an electrochemical Wacker-type oxygenation with O2 as the sole oxygen source. It presents the first instance of the Wacker-type oxidation expanding its substrate scope to trisubstituted alkenes. The approach is transition-metal-free, compatible with various functional groups, and can be carried out under mild conditions resulting in satisfactory yields. Mechanistic experiments suggest the CO bond formation occurs through reactions between cationic carbon species and the superoxide radical, which involves the 1,2-shift of the electron-rich substituent.

Fine tuning of electrosynthesis pathways by modulation of the electrolyte solvation structure.

Electrosynthesis is a method of choice for designing new synthetic routes owing to its ability to selectively conduct reactions at controlled potentials, high functional group tolerance, mild conditions and sustainability when powered by renewables. When designing an electrosynthetic route, the selection of the electrolyte, which is composed of a solvent, or a mixture of solvents, and a supporting salt, is a prerequisite. The electrolyte components, generally assumed to be passive, are chosen because of their adequate electrochemical stability windows and to ensure the solubilization of the substrates. However, very recent studies point towards an active role of the electrolyte in the outcome of electrosynthetic reactions, challenging its inert character. Particular structuring of the electrolyte at nano- and micro-scales can occur and impact the yield and selectivity of the reaction, which is often overlooked. In the present Perspective, we highlight how mastering the electrolyte structure, both in bulk and at electrochemical interfaces, introduces an additional level of control for the design of new electrosynthetic methods. For this purpose, we focus our attention on oxygen-atom transfer reactions using water as the sole oxygen source in hybrid organic solvent/water mixtures, these reactions being emblematic of this new paradigm.

Controlling the Hydrophilicity of the Electrochemical Interface to Modulate the Oxygen-Atom Transfer in Electrocatalytic Epoxidation Reactions.

The electrocatalytic epoxidation of alkenes at heterogeneous catalysts using water as the sole oxygen source is a promising safe route toward the sustainable synthesis of epoxides, which are essential building blocks in organic chemistry. However, the physicochemical parameters governing the oxygen-atom transfer to the alkene and the impact of the electrolyte structure on the epoxidation reaction are yet to be understood. Here, we study the electrocatalytic epoxidation of cyclooctene at the surface of gold in hybrid organic/aqueous mixtures using acetonitrile (ACN) solvent. Gold was selected, as in ACN/water electrolytes gold oxide is formed by reactivity with water at potentials less anodic than the oxygen evolution reaction (OER). This unique property allows us to demonstrate that a sacrificial mechanism is responsible for cyclooctene epoxidation at metallic gold surfaces, proceeding through cyclooctene activation, while epoxidation at gold oxide shares similar reaction intermediates with the OER and proceeds via the activation of water. More importantly, we show that the hydrophilicity of the electrode/electrolyte interface can be tuned by changing the nature of the supporting salt cation, hence affecting the reaction selectivity. At low overpotential, hydrophilic interfaces formed using strong Lewis acid cations are found to favor gold passivation. Instead, hydrophobic interfaces created by the use of large organic cations favor the oxidation of cyclooctene and the formation of epoxide. Our study directly demonstrates how tuning the hydrophilicity of electrochemical interfaces can improve both the yield and selectivity of anodic reactions at the surface of heterogeneous catalysts.

An efficient electrochemical oxidation of C(sp3)-H bond for the synthesis of arylketones

An efficient electrochemical oxidation of C-H (sp3) bond was developed with carbon rod as the anode and platinum counter electrode as well as the routine tetrabutylammonium tetrafluoroborate as electrolyte in an undivided cell. Using water as both co-solvent and sole oxygen source, more than 20 examples of arylketones were facilely synthesized in good to excellent yields (up to 92%) in the air under the constant current of 6 mA without external oxidants, base or mediators. The possible electrochemical reaction mechanism was also proposed. And the key intermediate 2u of pharmaceutical dyclonine was highly efficiently prepared through applying this electrochemical method. This electrochemical driven oxidation reaction has the advantages of simple operation and mild reaction conditions, as will provide a sustainable approach for alkane oxidation to aldehyde or ketone. We envision that our method will be useful for applications in the future industrial production of fine organic chemicals.

Sustainable electrochemical C(sp3) − H oxygenation using water as the oxygen source

Electrochemical C(sp3) − H oxygenation of phenols derivatives were accomplished using H2O as the sole oxygen source. Thus, selectively oxidative 4-cresols to 4-acylphenols derivatives proved viable with the aid of indirect electrolysis, through metal- and external oxidant free environmental-friendly and safe electrocatalytic conditions. Advances of this strategy were proved by its ability to transform various sulfonamides with excellent site and regioselectivity. Detailed mechanistic studies allowed to delineate the exact profile of the generation of the oxygenation events.

Direct Oxygen Transfer from H2 O to Cyclooctene over Electron-Rich RuO2 Nanocrystals for Epoxidation and Hydrogen Evolution.

Production of more than 20 million tons of epoxides per year from olefins suffers from low atom economy due to the use of oxidants and complex catalysts with unsatisfactory selectivity, leading to huge environmental and economic costs. We present a proof-of-concept application of electron-rich RuO2 nanocrystals to boost the highly selective epoxidation of cyclooctene via direct oxygen transfer from water as the sole oxygen source under mild conditions. The enhanced electron enrichment of RuO2 nanocrystals via the Schottky effect with nitrogen-doped carbons largely promotes the capture and activation of cyclooctene to give a high turnover frequency (260 h-1 ) of cyclooctene oxide, far surpassing the reported values (<20 h-1 ) of benchmarked catalysts at room temperature with oxidants. Our electron-rich RuO2 electrocatalysts enable efficient and durable hydrogen production (Faradaic efficiency >90 %) on the cathode without impacting on the selectivity to epoxide (>99 %) on the anode.

Direct Oxygen Transfer from H2O to Cyclooctene over Electron‐Rich RuO2 Nanocrystals for Epoxidation and Hydrogen Evolution

AbstractProduction of more than 20 million tons of epoxides per year from olefins suffers from low atom economy due to the use of oxidants and complex catalysts with unsatisfactory selectivity, leading to huge environmental and economic costs. We present a proof‐of‐concept application of electron‐rich RuO2 nanocrystals to boost the highly selective epoxidation of cyclooctene via direct oxygen transfer from water as the sole oxygen source under mild conditions. The enhanced electron enrichment of RuO2 nanocrystals via the Schottky effect with nitrogen‐doped carbons largely promotes the capture and activation of cyclooctene to give a high turnover frequency (260 h−1) of cyclooctene oxide, far surpassing the reported values (&lt;20 h−1) of benchmarked catalysts at room temperature with oxidants. Our electron‐rich RuO2 electrocatalysts enable efficient and durable hydrogen production (Faradaic efficiency &gt;90 %) on the cathode without impacting on the selectivity to epoxide (&gt;99 %) on the anode.

Investigation of the possibility of culturing aerobic yeast with oxygen nanobubble addition and evaluation of the results of batch and semi-batch cultures of Saccharomyces cerevisiae

Nanobubble dispersions have been intensively studied in recent years. Their expanding applications include a wide range of industrial and biochemical processes. Nanobubble-saturated water intensifies the growth of bacteria, animal cell lines, plants, and animals. However, their influence on yeast growth has not been investigated. Yeast is an important microorganism in the biotechnology and food industries. Intensified growth of yeasts would be beneficial for basic and industrial purposes. In this study, the possibility of culturing Saccharomyces cerevisiae with oxygen nanobubbles as the sole source of oxygen was investigated. Batch, sequential batch, and semi-batch cultures were grown with the addition of oxygen nanobubbles, along with classical aeration of the bioreactor. The results were compared to batch cultures without nanobubble addition. Biomass, substrate, and oxygen profiles were determined throughout the time of culture. The Monod and Tsao–Hanson models were used to describe yeast growth. The balance of the bioreactor culture was determined using MATLAB software. The comparison of balance and kinetic parameters demonstrated a higher maximum specific growth rate of yeast in nanobubble cultures than in cultures without nanobubble addition.

Acceptorless dehydrogenative oxidation of primary alcohols to carboxylic acids and reduction of nitroarenes via hydrogen borrowing catalyzed by a novel nanomagnetic silver catalyst

A novel silver nano magnetic catalyst was devised for dehydrogenative oxidation of aromatic and aliphatic alcohols to the corresponding acid with water as the sole oxygen source and hydrogen gas as the only by-product. The designed catalytic system advantages from easy recovery of magnetic materials i.e. magnetic decantation, being economically viable and environmentally friendly. Furthermore, the catalytic reaction is able to reduce aryl nitro compounds in the absence of any reducing agent.

Thermodynamics of Water–Cationic Species–Framework Guest–Host Interactions within Transition Metal Ion-Exchanged Mordenite Relevant to Selective Anaerobic Oxidation of Methane to Methanol

Low-temperature anaerobic methane conversion to methanol (MTM) using copper ion-exchanged mordenite (Cu-MOR) as the catalyst and water as the sole source of oxygen is promising for sustainable utilization of methane. Integrating in situ calorimetric, spectroscopic, and structural methodologies, we report a systematic study on energetics of water-cationic species-framework guest-host interactions as a function of water loading for several mordenites relevant to low-temperature MTM. Notably, the near-zero coverage hydration enthalpy on Cu-MOR is -133.1 ± 6.0 kJ/mol water, which is related to Cu-MOR regeneration using water as oxidant. The copper oxo sites are thermally stable up to 915 °C and remain chemically intact as an oxygen source after complete hydration and dehydration. This study underscores the importance of manipulating the oxidation state and coordination chemistry of transition metal guest species in zeolites by fine-tuning the partial pressure of water as a strategy for rational design, synthesis, and modification of catalysts.

Fluid sources and stable isotope signatures in authigenic carbonates from the Northern Apennines, Italy

Authigenic carbonates are frequently associated with methane cold-seep systems, which extensively occur in various geologic settings worldwide. Of interest is the relation between the fluids involved in their formation and the isotopic signals recorded in the carbonate cements. Along the Northern Apennines foothills (Italy), hydrocarbons and connate waters still seeping nowadays are believed to be the primary sources for the formation of fossil authigenic carbonate found in Plio-Pleistocene marine sediments. Four selected outcrops of dolomitic authigenic carbonates were analysed to compare signature of seeping fluids with fractionation of stable carbon and oxygen isotopes recorded in the carbonate.Along the foothills, deep methane-rich fluids spontaneously rise to the surface through mud volcanoes or are exploited in wells drilled nearby to the fossil Plio-Pleistocene authigenic carbonates. The plumbing system providing fluids to present-day cold seeps was structurally achieved in Late Miocene and Plio-Pleistocene. δ13C values of methane, which vary from −51.9 to −43.0‰ VPDB, indicate that gas composition from the deep hydrocarbon reservoirs is relatively uniform along the foothills. On the contrary, δ13C in fossil authigenic carbonates strongly varies among different areas and also within the same outcrop.The different carbon sources that fed the investigated carbonates were identified and include: thermogenic methane from the deep Miocene reservoirs, 13C-enriched CO2 derived from secondary methanogenesis and microbial methane from Pliocene successions buried in the Po Plain. The δ13C variability documented among samples from a single outcrop testifies that the authigenic carbonates might represent a record of varying biogeochemical processes in the hydrocarbon reservoirs. The sources of stable oxygen isotopes in authigenic carbonates are often ascribed to marine water. Oxygen isotopic fractionation in the dolomite cements indicates that marine pore water couldn't be the sole source of oxygen. δ18O values provide a preliminary evidence that connate waters had a role in the carbonates precipitation. The concomitant occurrence of active cold seepages and fossil record of former plumbing systems suggests that generation and migration of hydrocarbons are long-lasting and very effective processes along the Northern Apennines foothills.

ChemInform Abstract: Highly Active Palladium‐Based Catalyst System for the Aerobic Oxidative Direct Coupling of Benzene to Biphenyl.

A highly efficient Pd-containing catalytic system for the intermolecular direct C−H homocoupling of benzene to biphenyl has been developed. The catalytic system was composed of Pd(OAc)2 with trifluoromethanesulfonic acid (TfOH) as an additive and O2 as the sole oxygen source in the absence of any metal-containing cocatalyst. An excellent efficiency of PdII with the acidic additive was attained in the aerobic oxidation of benzene to biphenyl. A high yield (25.3 %) and selectivity (98 %) were achieved by using a small amount of Pd(OAc)2 (0.07 mol %) and TfOH, which gave a high turnover number (180) for Pd species. Theoretical calculation by DFT and UV/Vis absorption spectra illustrated that the formation of electropositive PdII species in the presence of TfOH contributed to the high efficiency of the catalytic system.

Aerobic biodegradation of trichloroethylene and phenol co-contaminants in groundwater by a bacterial community using hydrogen peroxide as the sole oxygen source

Trichloroethylene (TCE) and phenol were often found together as co-contaminants in the groundwater of industrial contaminated sites. An effective method to remove TCE was aerobic biodegradation by co-metabolism using phenol as growth substrates. However, the aerobic biodegradation process was easily limited by low concentration of dissolved oxygen (DO) in groundwater, and DO was improved by air blast technique with difficulty. This study enriched a bacterial community using hydrogen peroxide (H2O2) as the sole oxygen source to aerobically degrade TCE by co-metabolism with phenol in groundwater. The enriched cultures were acclimatized to 2–8 mM H2O2 which induced catalase, superoxide dismutase and peroxidase to decompose H2O2 to release O2 and reduce the toxicity. The bacterial community could degrade 120 mg/L TCE within 12 days by using 8 mM H2O2 as the optimum concentration, and the TCE degradation efficiency reached up to 80.6%. 16S rRNA gene cloning and sequencing showed that Bordetella, Stenotrophomonas sp., Sinorhizobium sp., Variovorax sp. and Sphingobium sp. were the dominant species in the enrichments, which were clustered in three phyla: Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria. Polymerase chain reaction detection proved that phenol hydroxylase (Lph) gene was involved in the co-metabolic degradation of phenol and TCE, which indicated that hydroxylase might catalyse the epoxidation of TCE to form the unstable molecule TCE-epoxide. The findings are significant for understanding the mechanism of biodegradation of TCE and phenol co-contamination and helpful for the potential applications of an aerobic bioremediation in situ the contaminated sites.

Newsmakers

This week's Newsmakers are geoscientist Iain Stewart, who spent 48 hours in an airtight plastic chamber with about 160 plants as his sole source of oxygen as part of a new BBC documentary on plants; Italian veterinary scientist Ilaria Capua, winner of the 2011 World Leadership in Animal Health Award; and Victoria Xia, 15, who took first place and earned $25,000 at the third annual Math Prize for Girls contest.

Utilization of H2O2as the Oxygen Source by Bacteria of the Genera Pseudomonas and Rhodococcus

The growth of bacteria of the genera Pseudomonas and Rhodococcus in the presence of hydrogen peroxide as the sole source of oxygen was studied. The toxic effect of H2O2 in the concentration range of 100-200 microg/ml was shown to extend the lag phase by 2 to 3 days. Apart from the peroxide toxicity, the bacterial growth was inhibited by the toxic effect of dissolved oxygen in concentrations over 100 microg O2/ml; in the presence of a liquid hydrocarbon phase, this effect was alleviated. Under decreased partial pressure of oxygen in the presence of hydrocarbons (12-15 vol %), the culture growth was initiated at high initial concentrations of H2O2 (300 microg/ml). When hydrogen peroxide concentrations exceeded 320 microg/ml, no growth occurred, no matter how much hydrocarbon was added.

Titanium(II), -(III), and -(IV) Complexes Supported by Benzamidinate Ligands

The synthesis and reactivity of a wide range of titanium benzamidinates is described. Addition of 0.5 equiv of Me2Mg to the dichloride L2TiCl2 (L = PhC(NSiMe3)2) in Et2O yields the chloro−alkyl derivative L2Ti(Me)Cl in good yield. The addition of 2 equiv of PhCH2MgCl to the dichloride affords thermally sensitive L2Ti(CH2Ph)2 in moderate yield. Likewise, addition of 1 equiv of Me2Mg results in the clean formation of the dimethyl L2TiMe2. The dimethyl reacts with tert-butylamine in refluxing benzene to form the five-coordinate imido L2TiNCMe3, for which crystallographic data is presented. The imido reacts with acetone in C6D6 to form the bridging oxo derivative L2Ti(μ-O)2TiL[η1-NC(Ph)N(SiMe3)2]. Overnight reduction of the dichloride with 1% Na/Hg amalgam in tetrahydrofuran (THF) forms the Ti(III) derivative L2TiCl(THF), which is crystallized from hexanes in moderate yield. Carrying out the analogous reduction in toluene yields the base-free Ti(III) chloride, L2TiCl, for which crystallographic data is presented. Allowing the reaction (in toluene) to proceed for an additional 48 h results in further reduction and the formation of the end-on bound dinitrogen complex (L2Ti)2(μ-N2), which is isolated as dark blue crystals from hexanes in moderate yield. Reduction of L2Ti(Me)Cl with 1% Na/Hg amalgam in THF forms the Ti(III) methyl derivative which is isolated as the five-coordinate THF-free product L2TiMe upon evacuation and crystallization from hexamethyldisiloxane (HMDSO). The related Ti(III) alkyl L2TiCH2SiMe3 is readily prepared by reaction of LiCH2SiMe3 with L2TiCl in toluene. Carrying out the 1% Na/Hg amalgam reduction of the dichloride in the presence of CO results in the formation of the Ti(III) bridging-oxo species (L2Ti)2(μ-O), which is isolated in low yield. CO as the sole oxygen source is confirmed by the use of C18O, which yielded only labeled product. Analogous reduction in the presence of N,N,N‘,N‘-tetramethylethylenediamine (TMEDA) results in the C−N bond cleavage of an amidinate ligand and the cyclometalation of TMEDA. Two products, L2TiNSiMe3 and LTi[η2-Me3SiNC(H)Ph][η3-CH2N(Me)CH2CH2NMe2], are isolated in good yields by fractional crystallization from hexanes. The dinitrogen complex, (L2Ti)2(μ-N2), reacts with pyridine (Py) and 2,6-dimethylphenyl isocyanide (XylylNC) to form base adducts [L2Ti(Py)]2(μ-N2) and [L2Ti(CNXylyl)]2(μ-N2) without loss of the dinitrogen ligand. Crystallographic data for the Py adduct is presented. Oxidation reactions of (L2Ti)2(μ-N2) with a variety of oxygen and sulfur sources is reported. Reaction with dry O2 in the presence of pyridine gives the seven-coordinate peroxo complex L2Ti(η2-O2)Py. The related reaction with excess S8 yields the dark-green persulfido derivative L2Ti(η2-S2), for which crystallographic data is presented. The persulfido reacts overnight with Hg in toluene solution to give the bimetallic sulfido complex L2Ti(μ-S)2TiL[η1-NC(Ph)N(SiMe3)2], which is formed following a silyl-group migration. The analogous oxygen-containing product is best prepared by the reaction of powdered (L2Ti)(μ-N2) with dry O2. In the presence of excess pyridine, L2Ti(η2-S2) reacts with Hg to yield the terminal sulfido L2Ti(S)Py. The crystallographically characterized terminal-oxo derivative L2Ti(O)OPy is prepared by reaction of (L2Ti)(μ-N2) with an excess of pyridine N-oxide in toluene−pyridine.

Oxygen Consumption, Diffusing Capacity and Blood Flow of the Synovial Membrane in Osteoarthritic Rabbit Knee Joints

In osteoarthritis the changes of the synovial membrane may seriously alter the oxygen transfer characteristics from the capillaries of the membrane to the synovial fluid and hence impede or deprive the joint cartilage of its sole source of oxygen. In the present study we have estimated the blood flow (Q), diffusing capacity (DO2) and oxygen consumption (VO2) of the synovial membrane in the chronic non effusive stage of experimental osteoarthritis. In 14 osteoarthritic knee joints we found a statistically significant increase in oxygen consumption, compared to previously reported results from normal joints, whereas the diffusing capacity and the blood flow were unchanged. The implication of this is that the partial pressure difference required to overcome the increased oxygen consumption was increased with a factor 4.3 and that the oxygenation of the joint cartilage was reduced with approx. 30 Torr.

Source of oxygen in cytochrome P-450 catalyzed carbinolamine formation

N-Methylcarbazole was incubated in H 2O 18 and under an 18O atmosphere. N-Hydroxymethylcarbazole, 1-OH- and 3-OH-N-methylcarbazole were isolated by HPLC and analyzed for 18O content In incubations containing 18O, all three metabolites showed >95% 18O incorporation. In incubations containing H 2O 18, the N-hydroxymethyl metabolite showed 16O incorporation equal to control incubations in 100% H 2O. These data demonstrate that the sole source of oxygen in cytochrome P-450 catalyzed, NADPH supported N-hydroxymethylcarbazole formation is atmospheric oxygen.