Reagent For Oxidation Research Articles

Pd-catalyzed selective oxidation of allyl alcohols to access enones and enals

Selective oxidation is quite important in synthesis. Here we report a Pd-catalyzed method to selectively oxidize allylic alcohols to enones and enals at room temperature. 27 compounds, including enones, and enals, have been obtained with moderate to excellent yields. Meanwhile, this approach proceeds well on a preparative scale giving a good yield. This work allows the efficient and selective oxidization of various allylic alcohols to access various enones and enals, even in the presence of benzylic alcohols. This procedure avoids the use of stoichiometric or superstoichiometric quantities of oxidant reagents such as MnO2 and uses free oxygen in the air as our green oxidant in the whole process.

Catalytic Oxidations with ortho-Substituted Modified IBXs

Abstract o-Iodoxybenzoic acid (IBX) is an oxidation reagent that has surged into prominence in the last two decades. It is cost-effective, environmentally benign, and readily prepared from o-iodobenzoic acid. However, its insolubility in common organic solvents and explosive attributes upon impact and heating are debilitating disadvantages. The development of modified IBXs (mIBXs) that exhibit improved solubility and enhanced reactivity, and obviate explosive attributes by judicious manipulation of the structure of IBX has been an incessant endeavor. In this account, common organic solvent-soluble mIBXs developed in our research group are collated with a discussion of the rationale underlying the design principles. Steric build-up around the iodoxolone moiety that is responsible for strong intermolecular interactions within the crystal lattice of IBX constitutes the key consideration in the design and development of modified λ5-iodanes that are reactive and sparingly soluble in common organic solvents. In situ generation of mIBXs from precursor iodo-acids in the presence of Oxone® permits their employment as organocatalysts for facile oxidative transformations. Reactive mIBXs generated in situ from precursor modified iodo-acids (mIAs, II) in the presence of Oxone® may offer unrivaled prospects for cost-effective oxidations. Applications of mIBXs, generated in situ or otherwise, for efficient oxidations are consolidated.1 Introduction2 Design and Synthesis of Modified IBXs and their Precursors Iodo-Acids3 Catalytic Oxidations with Modified IBXs3.1 Oxidation of Alcohols3.2 Oxidation of 1,2-Diols3.3 Conversion of Diols into Lactones3.4 One-Pot Oxidative Cleavage of Olefins3.5 One-Pot Transformation of Olefins into α-Bromo- and α-Azidoketones4 Conclusions

Cornforth's and Corey-Suggs Cr(VI) compounds as efficient reagents for selective oxidation of certain polyols in aqueous KHSO4 medium –A kinetic and mechanistic approach

• Kinetics of oxidation of certain polyols have been studied by Cornforth's and Corey-Suggs Cr(VI) compounds viz., Pyridinium dichromate (PDC), and Pridinium chlorochromate (PCC). • Under mineral acid-free conditions in aqous KHSO 4 medium. • Reactions obeyed second order kinetics with a first order in [PCC] (or [PDC]) and [Alcohol], and rate of oxidaion accelerated by increaing [KHSO 4 ]. • On the basis of observed results plausible mechanism involvement of ((PyH)CrO 3 + ) spesies and polyol (ROH) in the rate determining step is proposed in he case of PDC oxidation. • In the case of PCC oxidaion, the slow step involved [(PyH)OCrO(OH)Cl) + ], and ROH to give corresponding carbonyl compounds as products. Cornforth's Pyridinium dichromate (PDC), and Corey-Suggs Pyridinium chlorochromate (PCC) were accomplished as efficient reagents for selective oxidation of certain polyols (ROH) in aqueous KHSO 4 medium at different temperatures. Kinetic study of these reactions depicted second order kinetics with a first order in [PCC] or[PDC] and [ROH] in aqueous bisulfate medium. A ten-fold increase in KHSO 4 concentration increased the observed rate constant (k′) by ten times showing first order dependence on [KHSO 4 ]. Added olefinic monomers did not affect the rate of oxidation, indicating the absence of free radical intermediates. On the basis of observed kinetic features, participation of ((PyH)CrO 3 + ) and polyol (ROH) in the rate determining step to give products in PDC path. In the case of PCC system, the slow step involved [(PyH)OCrO(OH)Cl) + ], and ROH to give products.

Gram scale, metal-free and selective aerobic oxidation of alcohol and alkyl benzenes using homogeneous recyclable TAIm[MnO4] oxidative ionic liquid under mild conditions: Microwave/ ultrasonic-assisted to carboxylic acid

A homogeneous catalyst-free system has been developed for the selective oxidation of alcohols and alkyl benzenes to the corresponding carbonyl compounds using a recyclable TAIm[MnO4] oxidative ionic liquid. The reactions were performed in the presence of previously reported TAIm[MnO4]/ TAIm[OH] ionic liquids and KMnO4 at ambient temperature under solvent-free conditions. Benzyl alcohols were selectively transferred to benzaldehydes, while under ultrasonic or microwave irradiation, they oxidized to benzoic acid selectively and directly. Scalability of the process also studied at high scale. Also, the ionic liquid could be readily recycled from the aqueous mixture and reused for several consecutive times without any pre-treatment and loss of catalytic activity. In this work, the highly active and toxic KMnO4 salt has been transformed into a mild recyclable oxidant reagent with high selectivity towards alcohol oxidation.

Catalytic aerobic oxidation of P(I)/P(III) into P(V) over PdNi10 as a low-cost alternative catalyst rivaling Pd

Chemical oxidation is essential in treating P(I)/P(III)-bearing wastewater, while conventional oxidation processes suffer from low selectivity and high cost induced by oxidant reagents. Herein, a low-cost catalyst PdNi10 was developed to rival the noble metal Pd, which had been known as the only catalyst enabling chemical-free oxidation of P(I)/P(III) into P(V) by ambient O2. The PdNi10 fabricated via optimized method even outperformed Pd in catalytic activity at identical dosage (0.10 g L−1), achieving efficient conversion of 1.00 mM of P(I) into P(V) (>94% in 30 min) with wide applicable pH range from 3.0 to 9.0. The aerobic oxidation of P(I) and P(III) over PdNi10 was confirmed via scavenging experiments to be both dominated by non-radical pathways with apparent activation energies of 44.5 and 21.3 kJ mol−1, respectively. Interestingly, the individual roles of Ni components of PdNi10 in the catalytic oxidation were found negligible. The H2O-methanol binary solvent experiment suggested that H2O mediated the catalytic reaction and the interfacial OH groups as a result of H2O dissociation served as the main reactive oxidant species for P(I)/P(III) oxidation. Furthermore, synergistic mechanism was proposed for the Ni and Pd sites with favorable roles in the essential reaction steps of dehydrogenation and hydroxylation, respectively. This study is believed to advance the treatment strategy of P(I)/P(III)-rich wastewater and to shed new light on the development of low-cost catalysts enabling chemical-free aerobic oxidation processes under facile condition.

Catalytic synthesis of phenols with nitrous oxide

The development of catalytic chemical processes that enable the revalorization of nitrous oxide (N2O) is an attractive strategy to alleviate the environmental threat posed by its emissions1–6. Traditionally, N2O has been considered an inert molecule, intractable for organic chemists as an oxidant or O-atom transfer reagent, owing to the harsh conditions required for its activation (>150 °C, 50‒200 bar)7–11. Here we report an insertion of N2O into a Ni‒C bond under mild conditions (room temperature, 1.5–2 bar N2O), thus delivering valuable phenols and releasing benign N2. This fundamentally distinct organometallic C‒O bond-forming step differs from the current strategies based on reductive elimination and enables an alternative catalytic approach for the conversion of aryl halides to phenols. The process was rendered catalytic by means of a bipyridine-based ligands for the Ni centre. The method is robust, mild and highly selective, able to accommodate base-sensitive functionalities as well as permitting phenol synthesis from densely functionalized aryl halides. Although this protocol does not provide a solution to the mitigation of N2O emissions, it represents a reactivity blueprint for the mild revalorization of abundant N2O as an O source.

Antioxidant Activity and Carotenoid Content Responses of Three Haematococcus sp. (Chlorophyta) Strains Exposed to Multiple Stressors.

There has been increasing demands worldwide for bioactive compounds of natural origins, especially for the nutraceutical and food-supplement sectors. In this context, microalgae are viewed as sustainable sources of molecules with an array of health benefits. For instance, astaxanthin is a xanthophyll pigment with powerful antioxidant capacity produced by microalgae such as the chlorophyte Haematococcus sp., which is regarded as the most suitable organism for the mass production of this pigment. In this study, three Haematococcus sp. strains were cultivated using a batch mode under favourable conditions to promote vegetative growth. Their environment was altered in a second phase using a higher and constant illumination regime combined with either exposure to blue LED light, an osmotic shock (with NaCl addition) or supplementation with a phytohormone (gibberellic acid, GA3), a plant extract (ginger), an herbicide (molinate) or an oxidant reagent (hydrogen peroxide). The effects of these stressors were evaluated in terms of antioxidant response and astaxanthin and β-carotene accumulation. Overall, strain CCAP 34/7 returned the highest Trolox Equivalent Antioxidant Capacity (TEAC) response (14.1-49.1 µmoL Trolox eq.g- 1of DW), while the highest antioxidant response with the Folin-Ciocalteu (FC) was obtained for strain RPFW01 (62.5-155 µmoL Trolox eq.g- 1 of DW). The highest β-β-carotene content was found in strain LAFW15 when supplemented with the ginger extract (4.8mg. g- 1). Strain RPFW01 exposed to blue light returned the highest astaxanthin yield (2.8mg. g- 1), 5-fold that of strain CCAP 34/7 on average. This study documents the importance of screening several strains when prospecting for species with potential to produce high-value metabolites. It highlights that strain-specific responses can ensue from exposure of cells to a variety of stressors, which is important for the adequate tailoring of a biorefinery pipeline.

Investigation into La(Fe/Mn)O3 Perovskites Formation over Time during Molten Salt Synthesis.

Molten salt synthesis (MSS) of complex oxides is generally investigated by characterization of the product phases with no insight into evolution of particle morphology. In this work, LaFeO3 and LaMnO3 MSS was investigated in KF-KCl and LiCl-KCl at 850 °C using a "feeding-and-sampling" procedure. By feeding the oxide reagents into a molten salt, the reaction starting point was clearly defined, while subsequent sampling of the melt provided means for tracking the phase composition along with the shape and size of product particles during MSS. Samples taken just after 1 min contained perovskite particles along with reagents and intermediates, which were consumed over time to yield a pure product within 10-30 min. The shape and size of perovskite particles sampled at different times during MSS were virtually unchanged, revealing a lack of notable growth. The observed fast MSS along with prevailing nucleation provided means to control perovskite particle size by varying the extent of reagent dissolution. Thus, increasing the salt/reagent ratio (from 10:1 to 25:1) strikingly reduced the duration required to obtain a pure product, along with decreasing the size of product particles (from 0.5-1.5 μm to 80-200 nm). Furthermore, performing MSS in KF-KCl, which exhibits greater oxide solubility compared to LiCl-KCl, resulted in a shorter duration and smaller perovskite particles (80-200 nm and 0.6-2.0 μm, respectively). This insight into perovskite formation and growth during MSS and its kinetics provides valuable guidelines for tuning MSS conditions to better control synthesis duration and particle size.

Electrochemical Hydroxylation of Electron‐Rich Arenes in Continuous Flow

AbstractElectrochemical hydroxylation of arenes by trifluoroacetic acid provides a straightforward access to aryl oxygen compounds under the mild and environmental benign reaction conditions. Harmful and pollutant stoichiometric amounts of oxidation reagents and the use of metal‐catalysts can be avoided. Herein, we present a novel method for the synthesis of hydroxylated products from electron‐rich arenes that was achieved by the implementation of a continuous‐flow setup. The continuous nature of the process allowed to fine‐tune the reactions conditions in order to prevent the decomposition of the sensitive products expanding the reaction scope beyond electron‐poor and neutral arenes that were previously reported in the batch processes. Thus, synthetically valuable hydroxylated arenes were obtained in good yields with the residence time just over a minute. In order to demonstrate the reliability and the efficiency of the electrochemical flow setup, a scale up experiment was also performed.

Evaluating the Effect of Chemical Digestion Treatments on Polystyrene Microplastics: Recommended Updates to Chemical Digestion Protocols

AbstractEstablishing the toxicity and exposure consequences of microplastics (MPs) on marine organisms relies on the nondestructive isolation of plastics from biological matrices. MPs are commonly extracted from these matrices by chemical digestion using alkali (e.g., potassium hydroxide (KOH) and sodium hydroxide (NaOH)), oxidative (e.g., hydrogen peroxide (H2O2)) and/or acidic (e.g., nitric acid (HNO3)) reagents. Although these digestion conditions can be highly effective for MP extraction, they can also react with the plastics. This can attribute an inaccurate representation of plastic contamination by altering MP visual characteristics (size, shape, color), thereby impeding identification and potentially returning erroneous numbers of ingested particles. In this study, the degradative impacts are assessed of the routinely applied digestion reagents (i) KOH, (ii) NaOH, (iii) H2O2, and (iv) HNO3 on polystyrene (PS) based MPs sized between 200 µm and 5 mm. Degradation of the PS MPs is evaluated using FT‐IR, gel permeation chromatography, NMR, photoluminescence spectroscopy, and microscopy. These studies reveal HNO3 to be the most destructive for PS MPs, while the alkali and oxidative reagents result in negligible changes in plastic properties. These results are recommended to be used as a guideline to update current protocols to ensure the nondestructive treatment of MPs.

P-Quinol Ethers and p-Quinone Monoacetals as Arylation and Oxidation Reagents: Tandem N-Arylation and α-Functionalization of Pyrrolidine via Redox-Neutral Three-Component Reaction

AbstractThe value of functional pyrrolidines in the fields of biology, pharmacology, catalysis, and natural product synthesis stimulates an intensive interest in developing new synthetic methods for this class of compounds, and direct functionalization of the simple pyrrolidine represents an attractive and effective approach. Herein, a metal-free protocol for direct N-arylation and α-functionalization of pyrrolidine via redox-neutral three-component reactions is reported, in which p-quinol ethers or p-quinone monoacetals serve as the arylation components and the formal oxidants for α-functionalization of pyrrolidine.

Ammonium tetraborate tetrahydrate as a new boron source for the fabrication of p-type emitters in silicon solar cell

Ammonium tetraborate tetrahydrate (ATT, (NH4)2B4O5(OH)4·2H2O) is proposed as a new, inexpensive, and direct boron source that can achieve uniform diffusion at low temperatures. It is prepared by spin coating method to improve the uniformity and decrease the diffusion temperature (T). The effects of ATT solution concentration (CATT) and T on the boron doped-layer are systematically investigated. An excellent uniformity is achieved, and the standard deviation coefficient (σ) of mean sheet resistance (Rsheet) is ∼ 1% at T ≥ 900 ℃ (CATT = 3%), which is better than the previously reported σ (>4.8%). A variety of doping profiles with mean Rsheet ranging from 14.5 to 1170 Ω/sq are obtained by controlling T and CATT for a diffusion time of 45 min. The mean Rsheet is 80–300 Ω/sq for T less than 850 ℃. Furthermore, the effect of surface hydrophilicity treatment on σ and Rsheet is examined by immersing the wafers in oxidation reagents before spin coating. Better uniformity of σ ∼ 0.5% is realized by improving the surface hydrophilicity through nitric acid oxidation for 1–10 min at 120 ℃. However, if the immersion time is longer than 20 min, the mean Rsheet increases due to the barrier effects of thicker oxidization layer.

Construction of new sensors with copper and cobalt com¬ple¬xes anchored on organofunctionalized silica and their use for electrocatalytic oxidation of reagents of biological interest

This work describes the development and application of chemically modified carbon paste electrode (CMCPE) with metal ion complexes of transition metals Co(II) and Cu(II) anchored on functionalized silica (SF). The prepared CMCPE was used for the determination of dopamine (DA) in the presence of pyridoxine (VB6) in commercially available pharmaceutical formulation, without any treatment of samples. The CMCPEs were built by incorporating graphite and functionalized silica and complexes of metal ions (Cu and Co) anchored by nitrogen groups on the silica surface. The electrochemical analysis was performed by cyclic voltammetry, while a drug analyzed in the present study was Revivan ampoules (DA determination).

Generation and Characterization of Stable Redox-Reporter Mammalian Cell Lines of Biotechnological Relevance.

Cellular functions such as DNA replication and protein translation are influenced by changes in the intracellular redox milieu. Exogenous (i.e., nutrients, deterioration of media components, xenobiotics) and endogenous factors (i.e., metabolism, growth) may alter the redox homeostasis of cells. Thus, monitoring redox changes in real time and in situ is deemed essential for optimizing the production of recombinant proteins. Recently, different redox-sensitive variants of green fluorescent proteins (e.g., rxYFP, roGFP2, and rxmRuby2) have been engineered and proved suitable to detect, in a non-invasive manner, perturbations in the pool of reduced and oxidized glutathione, the major low molecular mass thiol in mammals. In this study, we validate the use of cytosolic rxYFP on two cell lines widely used in biomanufacturing processes, namely, CHO-K1 cells expressing the human granulocyte macrophage colony-stimulating factor (hGM-CSF) and HEK-293. Flow cytometry was selected as the read-out technique for rxYFP signal given its high-throughput and statistical robustness. Growth kinetics and cellular metabolism (glucose consumption, lactate and ammonia production) of the redox reporter cells were comparable to those of the parental cell lines. The hGM-CSF production was not affected by the expression of the biosensor. The redox reporter cell lines showed a sensitive and reversible response to different redox stimuli (reducing and oxidant reagents). Under batch culture conditions, a significant and progressive oxidation of the biosensor occurred when CHO-K1-hGM-CSF cells entered the late-log phase. Medium replenishment restored, albeit partially, the intracellular redox homeostasis. Our study highlights the utility of genetically encoded redox biosensors to guide metabolic engineering or intervention strategies aimed at optimizing cell viability, growth, and productivity.

Palladium‐Catalyzed Coupling Reaction of o‐Alkenyl Chloroformylaniline with o‐Alkynylaniline: An Approach to Indolylmethyl Oxindole

AbstractA palladium‐catalyzed cascade Heck cyclization/3‐(2‐oxindolyl)methylation on intramolecular amination of o‐alkynylanilines for the synthesis of indolylmethyl oxindoles is developed. This protocol exhibits high efficiency, good functional group tolerance and scalability from easily accessible starting materials. In this transformation, chloroformylaniline was used as an oxidative reagent and o‐alkynylaniline was used as a 3‐indolyl precursor.

Cornforth's and Corey-Suggs Cr(VI) Compounds as Efficient Reagents for Selective Oxidation of Certain Polyols in Aqueous KHSO <sub>4</sub> Medium -A Kinetic and Mechanistic Approach

Cornforth's and Corey-Suggs Cr(VI) Compounds as Efficient Reagents for Selective Oxidation of Certain Polyols in Aqueous KHSO <sub>4</sub> Medium -A Kinetic and Mechanistic Approach

A host-guest interaction activated Bobbitt oxidant for highly efficient oxidation of alcohols.

Host-guest complexation using hydrogen-bonded macrocycles was found to enable activation of the Bobbitt oxidant reagent, which greatly facilitates the highly efficient oxidation of unactivated primary alcohols. This work provides a complementary approach to the activation of Bobbitt's salt with shape-persistent macrocycles in supramolecular catalysis.

Does dietary intake of acrylamide affect hydroxyproline levels? An animal study

Acrylamide is a chemical that occurs due to high temperatures during cooking. It consists of an amino acid found in foods and sugars. Studies have shown that cancer formation occurs within the scope of oxidant reagents and DNA damage due to exposure to acrylamide. Our study aims to examine the effects of dietary acrylamide intake on plasma hydroxyproline levels in rats. In this study, 4 groups were formed with 8 rats in each group (total number=32). Blood samples were collected on days 14 and 28. Acrylamide solution was applied to each rat in the treatment group by gastric gavage process at 5 mg/kg three times a week. Hydroxyproline levels in rats’ plasma samples were measured. The median (IQR) hydroxyproline levels were 7.40(2.45) µg/L in group 1 (14. days control group) and 7.98(3.34) µg/L in group 2 (14. days acrylamide applied) who received acrylamide. The mean hydroxyproline levels were 7.25(1.96) µg/L in group 3 (28. days control group) and 9.76(2.64) µg/L in group 4 (28. days acrylamide applied) who received acrylamide. No difference was observed between the groups. Dietary acrylamide intake did not have a significant effect on hydroxyproline levels at the application dose and duration in our study.

Oxidation Dynamics of Supported Catalytic Cu Clusters: Coupling to Fluxionality

Copper oxide nanoclusters have a wide range of catalytic applications, such as the selective oxidation of hydrocarbons. O2 binding to the catalyst, activation, and release upon reagent oxidation are key events in these catalytic chemistries. These events are expected to be accompanied by significant structural changes of the Cu clusters, because O atoms integrate into the cluster, rather than bind to its surface. Topping the complexity of the problem, partially oxidized Cu clusters are known to exhibit strong fluxionality and feature diverse and interconverting structures and oxygen contents in conditions of oxidative dehydrogenation (ODH). Hence, a significant dynamic coupling between the “hot” O2 molecule impacting the cluster at reaction temperatures and the cluster fluxionality can be expected. In this work, we focus on the dynamics of dioxygen integration into a partially oxidized Cu cluster supported on hydroxylated amorphous alumina–a system recently reported to be an exceptionally selective catalyst for cyclohexane ODH with very little CO produced, whose mechanistic underpinnings are of utmost interest. The statistics over a swarm of adsorption and scattering trajectories where O2 hits various sites on the cluster at reaction temperature shows that the O2 binding does not only follow the minimal energy paths. O2 also rarely integrates into the cluster in a single step and instead first binds to a single Cu atom via either an η1-O2 or an η2-O2 mode. Surprisingly, this step often has a higher barrier than the subsequent O2 integration and dissociation, which in turn take multiple steps and complete the oxidation process. Dynamic trajectories starting from the key transition state of integration of the adsorbed O2 can also lead to different intermediate structures during or right after the dissociation, due to the energy released from the transition state and the thermal intracluster effects. From these activated O2 chemisorbed structures, O2 dissociation occurs with moderate barriers (∼0.5 eV), producing multiple final oxidized Cu4O4 states. Hence, a diversity of reaction profiles for the attack of supported Cu cluster by O2 emerges due to the dynamic effects, with implications for mechanisms, kinetic models, and catalyst design principles.

Imidazolium-urea low transition temperature mixtures for the UHP-promoted oxidation of boron compounds

Different carboxy-functionalized imidazolium salts have been considered as components of low transition temperature mixtures (LTTMs) in combination with urea. Among them, a novel LTTM based on 1-(methoxycarbonyl)methyl-3-methylimidazolium chloride and urea has been prepared and characterized by differential scanning calorimetry throughout its entire composition range. This LTTM has been employed for the oxidation of boron reagents using urea-hydrogen peroxide adduct (UHP) as the oxidizer, thus avoiding the use of aqueous H2O2, which is dangerous to handle. This metal-free protocol affords the corresponding alcohols in good to quantitative yields in up to 5 mmol scale without the need of further purification. The broad composition range of the LTTM allows for the reaction to be carried out up to three consecutive times with a single imidazolium salt loading offering remarkable sustainability with an E-factor of 7.9, which can be reduced to 3.2 by the threefold reuse of the system.