Versatile Oxidation Research Articles

Bromination of marine particulate organic matter through oxidative mechanisms

Although bromine (Br) is considered conservative in seawater, it exhibits a well established correlation with organic carbon in marine sediments. This carbon–bromine association was recently attributed to covalent bonding, with organobromine in sinking particulates providing a putative link between sedimentary organobromine and organic matter cycling in surface waters. We hypothesized that phytoplankton detritus, a major precursor of sedimentary organic matter, would be susceptible to bromination through oxidative attack. Through a series of model experiments, we demonstrate incorporation of Br into algal particulate detritus through peroxidative and photochemical mechanisms. Peroxidative bromination was enhanced by addition of exogenous bromoperoxidase, but the enzyme was not required for the reaction. Fenton-like reaction conditions also promoted bromination, especially under solar irradiation, implicating radical mechanisms in the euphotic zone as another abiotic source of brominated particulates. These reactions produced aliphatic and aromatic forms of organobromine, suggesting that lipid- and protein-rich components of algal membranes provide suitable substrates for bromination. Biogenic organobromines in certain genera of phytoplankton also appeared in both aliphatic and aromatic forms. Experimental evidence and samples from oceanic midwater sediment traps imply that the aromatic fraction is more stable than the aliphatic. These experiments establish Br as a versatile oxidant in the transformation of planktonic organic matter through both enzymatic and abiotic mechanisms. Organobromine may serve as a marker of oxidative breakdown of marine organic detritus, with the metastable component providing a short-lived indicator of early-stage oxidation. By altering the stability of aliphatic and aromatic moieties, bromination may affect the availability of organic matter to organisms, with consequences for the preservation and degradation of marine organic carbon.

Superoxide formation on isolated cationic gold clusters.

Gold nanoparticles are known to be highly versatile oxidation catalysts utilizing molecular oxygen as a feedstock, but the mechanism and species responsible for activating oxygen remain unclear. The reaction between unsupported cationic gold clusters and molecular oxygen has been investigated. The resulting complexes were characterized in the gas phase using IR spectroscopy. A strong red-shift in the observed ν(O-O) stretching frequency indicates the formation of superoxo (O2(-)) moieties. These moieties are seen to form spontaneously in systems, which upon electron transfer attain a closed shell within the spherical jellium model (Au10(+) and Au22(+)), whereas an oxygen induced self-promotion in the activation is observed for other systems (Au4(+), Au12(+), Au21(+)).

Mn(ii) acetate: an efficient and versatile oxidation catalyst for alcohols

A homogeneous catalytic system consisting of Mn(ii) acetate,tert-butylhydroperoxide, acetonitrile and trifluoroacetic acid oxidises various alcohols efficiently and selectively.

Model Studies with Gold: A Versatile Oxidation and Hydrogenation Catalyst

Historically, scientists have considered gold an inert catalyst constituent. However, in recent decades, chemists have discovered that nanoscale gold shows exceptional activity for many chemical reactions. They have investigated model gold surfaces in order to obtain fundamental understanding of catalytic properties. In this Account, we present our current understanding of oxidation and hydrogenation reactions on the Au(111) single crystal as a planar representative of gold catalysts, revealing the interesting surface chemistry of gold. We begin by comparing two inverse reactions, alcohol oxidation and aldehyde hydrogenation, on a Au(111) surface. Beyond the expected different chemistry, we observe intriguing similarities since the same surface is employed. First, both molecular oxygen and hydrogen have high barriers to dissociation on Au(111), and frequently chemists study reactions here by using atomic O and H to populate the surfaces. Recombinative desorption features of oxygen and hydrogen are apparent at ∼500 and ∼110 K, lower than other transition metals. These results indicate that oxygen and hydrogen have low desorption activation energies and weakly chemisorb on the surface, likely leading to selective reactions. On the oxygen-precovered Au(111) surface, alcohols are selectively oxidized to aldehydes. Similarly, weakly bound hydrogen atoms on Au(111) also show chemoselective reactivity for hydrogenation of propionaldehyde and acetone. The second similarity is that the gold surface activates self-coupling of alcohol or aldehyde with oxygen or hydrogen, resulting in the formation of esters and ethers, respectively, in alcohol oxidation and aldehyde hydrogenation. During these two reactions, both alkoxy groups and alcohol-like species show up as intermediates, which likely play a key role in the formation of coupling products. In addition, the cross coupling reaction between alcohol and aldehyde occurs on both O- and H-modified surfaces, yielding the production of esters and ethers, respectively. Thus, we can tune the molecular structure of both esters and ethers by selecting the corresponding aldehyde and alcohol for the coupling reaction. These studies indicate that gold is a versatile active catalyst for various reactions, including oxidation and hydrogenation transformations. Despite the very different chemistry for these two reactions, we can establish an intrinsic relationship due to the distinct catalytic properties of gold. It can show activity for selective reactions on both O- and H-covered Au(111) and further induce the coupling reaction between surface reactants and adsorbed O/H to produce esters and ethers. This comparison demonstrates the unique surface chemistry of gold and enhances understanding of its catalytic properties.

Alteration of discoidin domain receptor-2 expression: possible role in peroxynitrite-induced apoptosis in human cerebral vascular smooth muscle cells

Peroxynitrite(ONOO−), a product of nitric oxide and superoxide anion interaction, is a powerful and versatile oxidant. In this work, the human cerebral vascular smooth muscle cells (HCVSMCs) were cultured in vitro and subjected to different concentrations of ONOO−. Cell viability and morphological changes were measured by methylthiazoletetrazolium (MTT) assay and Ho33342/PI double staining respectively. The apoptotic rate was assessed by flow cytometry. The alterations in the expression of DDR2 at both mRNA and protein levels were examined by real-time PCR and Western-blot simultaneously. Direct exposure of HCVSMCs to ONOO− was able to inhibit the cell proliferation, which was further revealed via the apoptotic pathway. ONOO− exerted a dual-effect on DDR2 expression at both mRNA and protein levels that depended on the concentrations of ONOO−. Our results demonstrate for the first time that DDR2 gene may play an important role in ONOO−-induced apoptosis in HCVSMCs.

Development of Versatile Oxidation Systems Based on the Design of Oxoammonium Salts

Organic nitroxyl radical catalysts have recently attracted great attention because they realize efficient alcohol oxidation under mild and environmentally benign conditions. A representative of this class is 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). We have also developed 2-azaadamantane N-oxyls (AZADOs) as highly efficient oxidation catalysts. These nitroxyl radicals are generally oxidized by a cooxidant to generate oxoammonium salts, which are active species for alcohol oxidation. In the oxidation systems presented in this paper, we focus on the differences between these two species in terms of oxidation state and counter anion. Herein, the effects of a counter anion of an oxoammonium species on its reaction selectivity are shown. On the basis of the control of the counter anion, we have developed catalytic oxidative rearrangement of tertiary allylic alcohols to β-substituted α,β-unsaturated carbonyl compounds. Moreover, we have developed novel useful oxidation systems utilizing a catalytic oxoammonium salt; namely, a one-pot oxidation of primary alcohols to carboxylic acids and an aerobic alcohol oxidation.

Copper‐Catalyzed Aerobic Oxidative CH Functionalizations: Trends and Mechanistic Insights

The selective oxidation of C-H bonds and the use of O(2) as a stoichiometric oxidant represent two prominent challenges in organic chemistry. Copper(II) is a versatile oxidant, capable of promoting a wide range of oxidative coupling reactions initiated by single-electron transfer (SET) from electron-rich organic molecules. Many of these reactions can be rendered catalytic in Cu by employing molecular oxygen as a stoichiometric oxidant to regenerate the active copper(II) catalyst. Meanwhile, numerous other recently reported Cu-catalyzed C-H oxidation reactions feature substrates that are electron-deficient or appear unlikely to undergo single-electron transfer to copper(II). In some of these cases, evidence has been obtained for the involvement of organocopper(III) intermediates in the reaction mechanism. Organometallic C-H oxidation reactions of this type represent important new opportunities for the field of Cu-catalyzed aerobic oxidations.

Preparation of pure hydrogen peroxide and anhydrous peroxide solutions from crystalline serine perhydrate

Hydrogen peroxide is one of the most versatile oxidation reagents, still it has not fully been exploited by synthetic chemists since anhydrous (let alone pure) hydrogen peroxide requires hazardous preparation protocols. We have recently reported on the crystallization of serine and other amino acid perhydrates, thus paving the way for a new method for laboratory-scale production of anhydrous hydrogen peroxide solutions. Serine is insoluble in most organic solvents (e.g., methanol, ethyl acetate, and methyl acetate) that readily dissolve hydrogen peroxide. Moreover, since the adduct of hydrogen peroxide and serine is unstable in these organic solvents, crystalline serine perhydrate readily decomposes to give anhydrous solutions of hydrogen peroxide and crystalline precipitate of the amino acid. This procedure can then yield an anhydrous hydrogen peroxide solution in a single step. Moreover, filtration of the amino acid, and room temperature evaporation of the volatile solvent (e.g., methyl acetate), yields over 99% hydrogen peroxide.

MnII—A fascinating oxidation catalyst: Mechanistic insight into the catalyzed oxidative degradation of organic dyes by H2O2

The use of simple MnII ions as efficient catalyst precursors for the oxidation of different highly stable organic dyes using H2O2 as an environmentally benign oxidant under mild reaction conditions, is presented. The role of a series of aromatic dyes in the in situ formation and stabilisation of the active catalyst was studied in detail using stopped-flow techniques and UV–Vis detection. DFT calculations were employed to predict the nature of the role of the substrate in the stabilisation of highly reactive MnII intermediates. Furthermore, low-temperature EPR measurements were performed in order to characterize the in situ formed catalytically active MnIVO intermediate responsible for the fast and versatile oxidation of organic dyes in aqueous solution.

Practical and versatile oxidation of alcohol using novel Na 2WO 4–H 2O 2 system under neutral conditions

This paper presents a novel Na 2WO 4–H 2O 2 oxidation system. The oxidation of alcohol to ketone or aldehyde was carried out by using N, N-dimethylacetamide, hydrogen peroxide, and a catalytic amount of disodium tungstate dihydrate under neutral conditions. This method is very simple, practical for large-scale manufacturing, and applicable to a variety of substrates including an acid-sensitive substrate. Disodium tetraperoxotungstate dihydrate (Na 2[W(O 2) 4]·2H 2O) was isolated from a mixture of N, N-dimethylacetamide, hydrogen peroxide, and disodium tungstate dihydrate, and a proposal reaction mechanism is discussed in this paper.

Efficient Method for Oxidation of Ketones to Esters with 4-Aminoperoxybenzoic Acid Supported On Silica Gel

4-Aminoperoxybenzoic acid supported on silica gel was found to be a versatile and efficient oxidant for the oxidation of ketones to esters.

Molecular Cross Talk in Traumatic Brain Injury: Figure 1.

Peroxynitrite (PN), a product of the near-diffusion-limited reaction between nitric oxide (NO) and mitochondrially derived superoxide (O2−), is a potent and versatile oxidant produced after brain trauma. PN can cause lipid peroxidation, DNA fragmentation, and protein nitration ([Hall et al., 2004

Regioselective Oxyfunctionalization of Unactivated Carbons in Steroids by a Model of Cytochrome P-450: Osmiumporphyrin Complex/tert-Butyl Hydroperoxide System

tert-Butyl hydroperoxide catalyzed by (5,10,15,20-tetramesitylporphyrinate) osmium(II) carbonyl [Os(TMP)CO] complex was found to be a highly efficient versatile oxidant for C-H carbons in steroid substrates. When reacted with representative steroids with an estrane, pregnane, 5beta-cholane, or 5alpha-cholestane structure, regioselective oxyfunctionalization and/or oxidative degradation occurred to give a variety of novel and uncommon derivatives in one step.

Waste‐Free Electrochemical Oxidation of Alcohols in Water

AbstractWe describe a new sol‐gel molecular electrode made of a thin layer of organosilica doped with the nitroxyl radical TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl) electrodeposited on the surface of an ITO‐coated glass and its employment as a selective and versatile oxidation catalyst in the electrochemical conversion of different alcohols to carbonyl compounds. Environmentally friendly water or a water/acetonitrile mixture buffered with bicarbonate is used as solvent. The electrode is highly stable and it can be reused for a prolonged period of time allowing easy separation from the products.

Oxidation of Aldehydes and Ketones into Carboxylic Acids and Esters Using 4‐Amino‐2‐Chloroperbenzoic Acid Supported on Silica Gel

4‐Amino‐2‐chloroperbenzoic acid supported on silica gel was found to be a versatile and efficient oxidant for the oxidation of aldehydes and ketones to the corresponding carboxylic acids and esters.

Electronic Effects in Olefin Oxidation by Imidoosmium(VIII) Compounds

AbstractImido osmium(VIII) complexes are versatile oxidants for C−C double bond functionalisation. Despite their structural similarity with OsO4 their reactivity cannot always be compared with this seminal reagent. Detailed investigations including kinetic competition experiments are presented that uncover the electronic and steric preferences of osmium imido complexes. The different behaviour of OsO4 and its imido derivatives towards tertiary amines and diamines is clarified. Hammett correlation studies reveal that the reactivity spectrum of the respective oxidants ranges from a strongly electrophilic behaviour in the case of OsO4 to a rather nucleophilic character as encountered for OsO(NtBu)3. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Isolation, characterization, and reaction of activated iodosylbenzene monomer hydroxy(phenyl)iodonium ion with hypervalent bonding: supramolecular complex PhI+OH.18-crown-6 with secondary I...O interactions.

The isolation, characterization, and reaction of the active species hydroxy(phenyl)iodonium ion with hypervalent bonding are reported. Reaction of iodosylbenzene with HBF(4)-Me(2)O in the presence of equimolar 18-crown-6 in dichloromethane afforded the hydroxy-lambda(3)-iodane complex PhI(OH)BF(4).18-crown-6 as stable yellow prisms. X-ray structure analysis indicated that both the close contacts between the iodine(III) and the three adjacent oxygen atoms of 18-crown-6, and the hydrogen bonding OH.O(crown ether) will be responsible for the increased stability of the complex as compared to the uncomplexed PhI(OH)BF(4). The crown ether complex is highly reactive and serves as a versatile oxidant even in water: thus, the complex undergoes oxidative transformations of a variety of functional groups such as olefins, alkynes, enones, silyl enol ethers, sulfides, and phenols under mild conditions.

Polymer supported anionic peroxomolybdenum complexes as new, mild, efficient and versatile oxidants in organic synthesis

Two polymer supported anionic peroxomolybdenum compounds, namely [Amb] 2[Mo 2O 3(O 2) 4] and [Amb][MoO(O 2) 2(O 2C-Ph-NH 2)], are prepared and characterized by conventional methods. Their uses as stoichiometric oxidizing agents for a variety of organic compounds are described. With these reagents alcohols are converted to the corresponding carbonyl compounds. Decarboxylation of α-hydroxy acids proceeds quantatively. Also thiols are converted to disulfides, hydroquinones to quinones, benzylamines to carbonyl compounds, tertiary amines to the N-oxides, phosphines to phosphine oxides, and sulfides to sulfones. Deprotection of oximes and oxidative deprotection of silyl ethers proceed easily.

Clay-supported tetrabutylammonium periodate as a versatile oxidant for alcohols and sulfides

Clay-supported tetrabutylammonium periodate is found to oxidise efficiently benzylic alcohols to the corresponding aldehydes without overoxidation to acids. It also oxidises aryl sulfides selectively to the corresponding sulfoxides.

(μ-Oxo or hydroxo)bis(μ-carboxylato)diruthenium(III) complexes with tris(1-pyrazolyl)borate face-capping ligand, affording versatile oxidation states via a protonation/deprotonation couple

(µ-Oxo or µ-hydroxo)bis(µ-acetate)diruthenium(III) complexes with tris(1-pyrazolyl)borate, [Ru2III(µ-O)(µ-CH3COO)2(HBpz3)2] (1) and [Ru2III(µ-OH)(µ-CH3COO)2(HBpz3)2](PF6) (2), have been prepared and characterized by X-ray crystallography, and showed a wide range of redox processes, Ru2II↔RuIIRuIII↔Ru2III↔RuIIIRuIV↔Ru2IV, coupled with protonation/deprotonation at the bridged monoatom.