Formation of oligomeric alkenylperoxides during the oxidation of unsaturated fatty acids: an electrospray ionization tandem mass spectrometry study

This study reports the identification of oligomeric alkenylperoxides by electrospray ionization mass spectrometry (ESI‐MS) and tandem mass spectrometry (ESI‐MS²), during the oxidation of oleic, linoleic and linolenic acids with Fenton's (Fe²⁺/H₂O₂) and Fe²⁺/O₂ systems. The reactions were followed by ferrous oxidation‐xylenol orange method together with GC‐MS and GC‐FID, allowing to observe that both oxidation systems are different in terms of hydroperoxide evolution, probably due to the presence of different intermediate reactive species: perferryl ion and OH^· radical responsible for the decomposition of lipid hydroperoxides and formation of new compounds. The analysis of ESI‐MS in the negative mode, obtained after oxidation of each fatty acid, confirmed the presence of the monomeric oxidation products together with other compounds at high mass region above m/z 550. These new ions were attributed to oligomeric structures, identified by the fragmentation pathways observed in the tandem mass spectra. Copyright © 2012 John Wiley & Sons, Ltd.     

The ozonization of model lignin compounds in aqueous solutions catalyzed by Mn(II) ions

The influence of Mn(II) ions on the rate of the reaction between ozone and model lignin compounds, guaiacol and veratrole, was studied. The catalyst did not influence the rate of the destruction of the aromatic ring and intermediate ozonolysis products, compounds with conjugated double bonds, in acid media but substantially increased the rate of oxidation of saturated carboxylic acids, ketoacids, and aldehydes. Ozone consumption then increased from 2 to 5 moles per mole of the transformed substrate. A mechanism of the catalytic action of Mn(II) in reactions between ozone and the compounds studied was suggested.     

Trapping of a Highly Reactive Oxoiron(IV) Complex in the Catalytic Epoxidation of Olefins by Hydrogen Peroxide

The generation of a nonheme oxoiron(IV) intermediate, [(cyclam)Fe^IV(O)(CH₃CN)]²⁺ ( 2 ; cyclam=1,4,8,11‐tetraazacyclotetradecane), is reported in the reactions of [(cyclam)Fe^II]²⁺ with aqueous hydrogen peroxide (H₂O₂) or a soluble iodosylbenzene (sPhIO) as a rare example of an oxoiron(IV) species that shows a preference for epoxidation over allylic oxidation in the oxidation of cyclohexene. Complex 2 is kinetically and catalytically competent to perform the epoxidation of olefins with high stereo‐ and regioselectivity. More importantly, 2 is likely to be the reactive intermediate involved in the catalytic epoxidation of olefins by [(cyclam)Fe^II]²⁺ and H₂O₂. In spite of the predominance of the oxoiron(IV) cores in biology, the present study is a rare example of high‐yield isolation and spectroscopic characterization of a catalytically relevant oxoiron(IV) intermediate in chemical oxidation reactions.     

Hydrolysis of Egyptian medicated cotton by HCL–FeCl3 reagent

The initial rate of hydrolysis of Egyptian medicated cotton with HCl or HCL-FeCl₃ as reagent, as well as the total carbonyl content of the hydrolysis products, were determined. The results obtained showed that although cellulose fibers are hydrolyzed more rapidly in an acid-FeCl₃ medium than in acid alone, the fibers resisted oxidation in a Fe³⁺ solution. Therefore the observed rate increase in Fe³⁺ solution cannot be explained on the basis of increased oxidation of hydroxyl groups. Consequently it has been suggested that the increase in the rate of hydrolysis is due to complexing between Fe³⁺ and the carbonium/oxonium ion or the leaving group. A comparison between the fine structure of the hydrolysis products of cotton cellulose by the use of HCl and HCl-FeCl₃ reagent is also given.     

Photoactivation of the oxidation process of <Emphasis Type="Italic">para</Emphasis>-chlorophenol in aqueous solutions

Kinetics of the oxidative destruction of para-chlorophenol in a combined iron-persulfate system under the action of simulated sunlight was studied. It was shown that, under additional photoirradiation, a deep conversion of chlorophenol and main intermediate products of its destruction is provided, with iron compounds serving not only as catalysts, but also as photochemical oxidation sensitizers. The degree of mineralization of para-chlorophenol and products of its oxidation under a photoactivated treatment for two hours reached a value of 60%, whereas that in the “dark” reaction did not exceed 1%. In the combined oxidizing system S₂O ₈ ^2– /Fe²⁺/UV-Vis, a considerable synergic effect was observed due to the formation of reactive oxygen intermediate both via decomposition persulfate and through reduction of Fe³⁺ from inactive Fe³⁺ intermediates.     

Electron-exchange processes on simple columns of kel-f supporting tetrachlorohydroquinone

The preparation of simple electron-exchange columns is reported. An organic porous material (Kel-F powder) is used to support a water-insoluble redox reagent. Of the organic compounds tested, tetrachlorohydroquinone was best. Very stable columns were obtained with a sufficiently high redox capacity (1.59 $\text{meq}\text{g}$ dry material) and a satisfactory reaction rate.The following oxidation reactions were carried out: Fe²⁺→Fe³⁺, Cu⁺→Cu²⁺, Sn²⁺→Sn⁴⁺, I^-→I,ascorbic acid → dehydroascorbic acid, as well as the following reduction reactions: Fe³⁺→Fe²⁺, I→I^-, Ce⁴⁺→Ce³⁺, V⁵⁺→V⁴⁺, Cr⁶⁺→Cr³⁺. The effect of hydrogen ion concentration on the redox reactions was also studied.The Kel-F-tetrachlorohydroquinone columns can be used for indirect titration of redox systems and for selective oxidations or reductions, e.g. Fe³⁺ in presence of Fe²⁺ and vice versa, Cr⁶⁺ in presence of Fe³⁺, Ce⁴⁺ in presence of Ce³⁺, ascorbic acid in the presence of glucose, and Sn²⁺ in presence of Sn⁴⁺ or Fe²⁺.     

Features of the Formation of the [(O)VIV(C2O4)(Phen)(H2O)] Complex in the Malic Acid Oxidation Process

Complex [(O)V^IV(C₂O₄)(Phen)(H₂O)] was obtained on the basis of V₂O₅ and malic acid in the presence of concentrated HNO₃ and phenanthroline. Its structure was determined by the X-ray structural analysis; its magnetic susceptibility was measured. The role of the \(\rm{VO}^+_2\) and VO²⁺ cations in the oxidation and complex-formation processes was considered. A method for the conversion of malic acid to oxalate anions through the formation of oxaloacetic acid and the intermediate products of its decarboxylation reactions was proposed. It was shown by the DFT M06/6-31G(d,p) method that the transition state energy decreases in the way of the HOC(O)C(0)CH₂-COOH bond breakage during decarboxylation compared with the free acid in the intermediate of its anion with VO²⁺.

     

可控粒径纳米Fe_3O_4的制备及其磁性研究

本文用空气氧化法,在可见光作用下,添加配合剂(EDTA、柠檬酸、酒石酸、谷氨酸)在室温进行了不同粒径纳米Fe3O4的制备及其磁性能研究。结果表明:在可见光作用下,随EDTA、柠檬酸、酒石酸、谷氨酸等配合剂的添加,得到纳米Fe3O4的粒径有所减小、分散性有所提高;配合剂及可见光共存时,体系反应速率得到提高,高的反应速率使纳米Fe3O4晶粒减小;控制适当的光照度和添加剂的量,室温可得到11.8~29.6nm的Fe3O4颗粒。不同粒径纳米Fe3O4分别呈现出超顺磁性、铁磁性特征。     

Characterization of the FeV=O Complex in the Pathway of Water Oxidation

Hypervalent Fe^V=O species are implicated in a multitude of oxidative reactions of organic substrates, as well as in catalytic water oxidation, a reaction crucial for artificial photosynthesis. Spectroscopically characterized Fe^V species are exceedingly rare and, so far, were produced by the oxidation of Fe complexes with peroxy acids or H₂O₂: reactions that entail breaking of the O?O bond to form a Fe^V=O fragment. The key Fe^V=O species proposed to initiate the O?O bond formation in water oxidation reactions remained undetected, presumably due to their high reactivity. Here, we achieved freeze quench trapping of six coordinated [Fe^V=O,(OH)(Pytacn)]²⁺ (Pytacn=1‐(2′‐pyridylmethyl)‐4,7‐dimethyl‐1,4,7‐triazacyclononane) ( 2 ) generated during catalytic water oxidation. X‐ray absorption spectroscopy (XAS) confirmed the Fe^V oxidation state and the presence of a Fe^V=O bond at ≈1.60 Å. Combined EPR and DFT methods indicate that 2 contains a S=3/2 Fe^V center. 2 is the first spectroscopically characterized high spin oxo‐Fe^V complex and constitutes a paradigmatic example of the Fe^V=O(OH) species proposed to be responsible for catalytic water oxidation reactions.     

Investigating the oxidation state of Fe from LiFePO4-based lithium ion battery cathodes via capillary electrophoresis

A capillary electrophoresis (CE) method with ultraviolet/visible (UV–Vis) spectroscopy for iron speciation in lithium ion battery (LIB) electrolytes was developed. The complexation of Fe²⁺ with 1,10-phenantroline (o-phen) and of Fe³⁺ with ethylenediamine tetraacetic acid (EDTA) revealed effective stabilization of both iron species during sample preparation and CE measurements. For the investigation of small electrolyte volumes from LIB cells, a sample buffer with optimal sample pH was developed to inhibit precipitation of Fe³⁺ during complexation of Fe²⁺ with o-phen. However, the presence of the conducting salt lithium hexafluorophosphate (LiPF₆) in the electrolyte led to the precipitation of the complex [Fe(o-phen)₃](PF₆)₂. Addition of acetonitrile (ACN) to the sample successfully re-dissolved this Fe²⁺-complex to retain the quantification of both species. Further optimization of the method successfully prevented the oxidation of dissolved Fe²⁺ with ambient oxygen during sample preparation, by previously stabilizing the sample with HCl or by working under counterflow of argon. Following dissolution experiments with the positive electrode material LiFePO₄ (LFP) in LIB electrolytes under dry room conditions at 20°C and 60°C mainly revealed iron dissolution at elevated temperatures due to the formation of acidic electrolyte decomposition products. Despite the primary oxidation state of iron in LFP of +2, both iron species were detected in the electrolytes that derive from oxidation of dissolved Fe²⁺ by remaining molecular oxygen in the sample vials during the dissolution experiments.     

Rate coefficient for the reaction of CCl3 radicals with ozone

The rate coefficient for the reaction of CCl₃ radicals with ozone has been measured at 303 ± 2 K. The CCl₃ radicals were generated by the pulsed laser photolysis of carbon tetrachloride at 193 nm. The time profile of CCl₃ concentration was monitored with a photoionization mass spectrometer. Addition of the O₃–O₂ mixture to this system caused a decay of the CCl₃ concentration because of the reactions of CCl₃ + O₃ → products (5) and CCl₃ + O₂ → products (4). The decay of signals from the CCl₃ radical was measured in the presence and absence of ozone. In the absence of ozone, the O₃–O₂ mixture was passed through a heated quartz tube to convert the ozone to molecular oxygen. Since the rate coefficient for the reaction of CCl₃ + O₂ could be determined separately, the absolute rate coefficient for reaction ( 5 ) was obtained from the competition among these reactions. The rate coefficient determined for reaction ( 5 ) was (8.6 ± 0.5) × 10^?13 cm³ molecule^?1 s^?1 and was also found to be independent of the total pressure (253–880 Pa of N₂). This result shows that the reaction of CCl₃ with O₃ cannot compete with its reaction with O₂ in the ozone layer. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 310–316, 2003     

Hydroxylamine Reactions with Peroxide Products of Alkenes Ozonolysis

Reactions were studied of peroxide ozonolysis products obtained from linear and cyclic alkenes with hydroxylamine prepared in situ from NH₂OH·HCl by hydrogen chloride neutralization with sodium acetate. A one-pot reactions sequence was performed: alkene oxidation with ozone → reduction to a carbonyl compound with hydroxylamine → condensation of the carbonyl compound with hydroxylamine providing a possibility of direct transformation of alkenes in keto- and aldoximes excluding the stage of preparation and isolation of the carbonyl compound.     

Interaction between ozone and the chloride ion in sulfuric acid solutions up to 6-M concentration

The effect of sulfuric acid concentration on Cl₂ evolution in the reaction between O₃ and Cl^? has been investigated. The catalytic effects of metal ions in this reaction have been studied as a function of solution acidity. The chlorine evolution rate increases markedly with increasing acid concentration. At acid concentrations below 4 mol/l, the most effective catalyst is Co²⁺. The catalytic activities of Fe³⁺ and Cu²⁺ peak at $C_{H_2 SO_4 } $ = 4.8 mol/l. In passing to highly acidic solutions ( $C_{H_2 SO_4 } $ > 5 mol/l), the catalytic activity of the metal ions decreases, but the chlorine evolution rate remains high owing to the high acidity. Kinetics of VO²⁺ oxidation with ozone in acid media have been studied, and the ozone solubility in aqueous sulfuric acid has been measured.     

Ozonocatalytic decomposition of glyoxal and glyoxylic and formic acids in the presence of iron(III) ions

Rate constants of reactions of ozone with glyoxal, glyoxylic and formic acid in aqueous solutions at pH 1.5 were determined. It was shown that iron(III) in the form of ions accelerates oxidation of glyoxal and glyoxylic acid, but does not influence reaction between ozone and formic acid. It was established that the catalyst acts effectively if its concentration is comparable to the concentration of the oxidized substrate, the optimal stoichiometric ratio (Fe³⁺/substrate) being close to 1/3. The catalytic reaction mechanism was studied using a competitive chelate ligand, oxalic acid. We concluded that the catalytic activity of iron(III) in the investigated reaction was due to its ability to form chelate complexes in which the substrate was more easily oxidized by molecular ozone.     

Ferrous ion oxidations by √H, √OH and H2O2 in aerated FBX dosimetry system

In the ferrous ion, benzoic acid and xylenol orange (FBX) dosimetric system, benzoic acid (BA) increases the G(Fe³⁺) value. Xylenol orange (XO) controls the BA sensitized chain reaction as well as forms a complex with Fe³⁺. In the aerated FBX system each √H, √OH and H₂O₂ oxidizes 8.5, 6.6 and 7.6 Fe²⁺ ions, respectively; and these values respectively increase to 11.3, 7.6 and 8.6 in oxygenated solution. About 8% √OH reacts with XO and the remaining with BA. The above fractional values are due to this competition. This √OH reaction with XO oxidizes 1.8% and 2.1% ferrous ions only in aerated and oxygenated solutions, respectively. There is a competition between √H reactions with O₂ and with BA, but both lead to the production of H₂O₂. The oxidation of Fe²⁺ by √OH reactions at different concentrations of H₂O₂ is linear with absorbed dose while the √H reactions make the oxidation of Fe²⁺ non-linear with dose. This is due to competition reaction of H-adduct of BA between O₂ and Fe³⁺.     

Rate constants for the reactions of methylvinyl ketone,methacrolein, methacrylic acid,and acrylic acid with ozone

Rate constants for the reaction of ozone with methylvinyl ketone (H₂C(DOUBLEBOND)CHC(O)CH₃), methacrolein (H₂C(DOUBLEBOND)C(CH₃)CHO), methacrylic acid (H₂C(DOUBLEBOND)C(CH₃)C(O)OH), and acrylic acid (H₂C(DOUBLEBOND)CHC(O)OH) were measured at room temperature (296±2 K) in the presence of a sufficient amount of cyclohexane to scavenge OH-radicals. Results from pseudo-first-order experiments in the presence of excess ozone were found not to be consistent with relative rate measurements. It appeared that the formation of the so-called Criegee-intermediates leads to an enhanced decrease in the concentration of the two organic acids investigated. It is shown that the presence of formic acid, which is known to react efficiently with Criegee-intermediates, diminishes the observed removal rate of the organic acids. The rate constant for the reaction of ozone with the unsaturated carbonyl compounds methylvinyl ketone and methacrolein was found not to be influenced by the addition of formic acid. Rate constants for the reaction of ozone determined in the presence of excess formic acid are (in cm³ molecule⁻¹ s⁻¹): methylvinyl ketone (5.4±0.6)×10⁻¹⁸; methacrolein (1.3±0.14)×10⁻¹⁸; methacrylic acid (4.1±0.4)×10⁻¹⁸; and acrylic acid (0.65±0.13)×10⁻¹⁸. Results are found to be consistent with the Criegee mechanism of the gas-phase ozonolysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 769–776, 1998     

Hydroxylation of Aromatics with the Help of a Non‐Haem FeOOH: A Mechanistic Study under Single‐Turnover and Catalytic Conditions

Ferric–hydroperoxo complexes have been identified as intermediates in the catalytic cycle of biological oxidants, but their role as key oxidants is still a matter of debate. Among the numerous synthetic low‐spin Fe^III(OOH) complexes characterized to date, [(L₅²)Fe(OOH)]²⁺ is the only one that has been isolated in the solid state at low temperature, which has provided a unique opportunity for inspecting its oxidizing properties under single‐turnover conditions. In this report we show that [(L₅²)Fe(OOH)]²⁺ decays in the presence of aromatic substrates, such as anisole and benzene in acetonitrile, with first‐order kinetics. In addition, the phenol products are formed from the aromatic substrates with similar first‐order rate constants. Combining the kinetic data obtained at different temperatures and under different single‐turnover experimental conditions with experiments performed under catalytic conditions by using the substrate [1,3,5‐D₃]benzene, which showed normal kinetic isotope effects (KIE>1) and a notable hydride shift (NIH shift), has allowed us to clarify the role played by Fe^III(OOH) in aromatic oxidation. Several lines of experimental evidence in support of the previously postulated mechanism for the formation of two caged Fe^IV(O) and OH ^. species from the Fe^III(OOH) complex have been obtained for the first time. After homolytic O? O cleavage, a caged pair of oxidants [Fe^IVO+HO ^. ] is generated that act in unison to hydroxylate the aromatic ring: HO ^. attacks the ring to give a hydroxycyclohexadienyl radical, which is further oxidized by Fe^IVO to give a cationic intermediate that gives rise to a NIH shift upon ketonization before the final re‐aromatization step. Spin‐trapping experiments in the presence of 5,5‐dimethyl‐1‐pyrroline N‐oxide and GC‐MS analyses of the intermediate products further support the proposed mechanism.     

Fe (II)-activated persulfate oxidation effectively degrades iodoform in water: Influential factors and kinetics analysis

Iodoform (CHI₃) is one of the disinfection by-products (DBPs) that is formed in the pre-oxidation and disinfection processes of drinking water treatment. In this study, Fe(II)-activated persulfate oxidation (Fe²⁺/PS) was employed to degrade iodoform, the effects of initial reactants concentration, reaction parameters, kinetics model were investigated, and the underlying mechanisms of CHI₃ degradation in Fe²⁺/PS oxidation process was unveiled. The results showed that the mole ratio Fe²⁺/PS of 1:5, initial PS concentration of 15 μmmol/L, and pH of 3.0 were identified as the optimum operating parameters. In addition, a relatively higher temperature could enhance CHI₃ removal and deiodination. The kinetic model has two different reaction steps: a fast one during the first ten minutes of reaction; then followed by a much slower one. Suppression of the reaction by TBA and MeOH showed that the combined effects of SO₄⁻· and ·OH contributed to the degradation of CHI₃, but ·OH played a dominant role. The degradation pathways and the products of total liberated iodine species demonstrate that the applicability of the Fe²⁺/PS oxidation process for CHI₃ degradation. These results indicated that the Fe²⁺/PS oxidation process is an effective advanced oxidation process for CHI₃ removal in water treatment.     

1H and 13C NMR spectroscopic study of oxidation of D,L‐cystine and 3,3′‐dithiobis(propionic acid) with hydrogen peroxide in aqueous solution

The oxidation of symmetrical disulfides [D ,L ‐cystine ( 1 ) and 3,3′‐dithiobis(propionic acid) ( 2 )] with hydrogen peroxide in D₂O–NaOH solution (pH 10–11) was studied by NMR spectroscopy. Assignments of the proton and carbon NMR signals of starting materials ( 1 and 2 ) and products of oxidation are based on conventional 1D NMR methods (DEPT, selective spin decoupling). Formation of C—S bond cleavage products or, in case of 2 , partially oxidized intermediates was not detected. The accelerating effect of Cu²⁺ cations, but not Fe³⁺ cations, on the oxidation rate of 1 in basic medium was demonstrated. Copyright © 2002 John Wiley & Sons, Ltd.     

A new fluorescence method for determination of ozone in ambient air

A new simple method for determination of ozone in ambient air is presented. The reaction employed is based on the known ozonolysis of indigo dye. The indigotrisulfonate molecule contains one carbon–carbon double bond (C═C), which reacts with ozone and generates isatinsulfonates and sulfoanthranilate. The quantitatively formed sulfoanthranilate presents fluorescence (λ_ex 245 nm, λ_em 400 nm). Ozone was collected using two cellulose filters coated with 40 μL of 1.0 × 10^{− 3} mol L^{− 1} of indigotrisulfonate. The analytical response was linear in the range 0–150 ppbv ozone, and a detection limit of 7 ppbv was achieved using a sampling time of 15 min and an optimum sampling air flow rate of 0.4 L min^{− 1}. There was no interference from sulfur dioxide, formaldehyde or nitrogen dioxide. The ozonolysis mechanism and the reaction products are discussed.