Delignification of deciduous wood under the action of hydrogen peroxide and ozone

Kinetic curves of the dependence of ozone specific absorption (Q _{r, sp} ) upon the ozonation of aspen wood pretreated with solutions of hydrogen peroxide of various concentrations (from 5 × 10^?4 to 2 × 10^?1 mol/L) are obtained. The water content in the samples being 56 ± 3%. The initial rate of ozone absorption and total ozone consumption (Q _inlet) are determined. Wood samples are investigated by IR and UV diffuse reflection spectroscopy. Based on the kinetics and spectral data, it is concluded that pretreating wood with a H₂O₂ solution allows the degree of delignification (DD) to be increased at a constant Q _inlet value. The DD is maximal at $ C_{H_2 O_2 } = 5 \times 10^{ - 3} $ mol/L and is 88% in contrast to a sample ozonated without H₂O₂ (DD = 85%). The role of pretreatment with hydrogen peroxide and the subsequent action of the O₃/H₂O₂ system in the process of delignification of wood is analyzed.     

Transformation of wood during ozonization in the presence of hydrogen peroxide

Samples of ozonized aspen wood pretreated with hydrogen peroxide solutions of various concentrations are investigated by UV diffuse reflectance spectroscopy, IR spectroscopy, and X-ray structural analysis. The general course of wood transformation under the action of the O₃/H₂O₂ system is associated with the destruction of lignin and oxidation of carbohydrates, raising the fraction of the crystalline phase in a lignocarbohydrate material. The possibility of varying the depth of the chemical and structural transformation of the substrate upon changing the hydrogen peroxide concentration in the O₃/H₂O₂ system is demonstrated.     

The ozonization of sodium lignosulfonate in the presence of hydrogen peroxide

The kinetics of ozonization of sodium lignosulfate (LS) in the presence of H₂O₂ was studied. The effective rate constants for the oxidation of LS and the total ozone consumption were determined. The k _eff = 30 ± 8 M^?1 s^?1 value was found to be independent of the concentration of H₂O₂. The total ozone consumption decreased as the concentration of H₂O₂ increased from 1.0 × 10^?4 to 1.0 × 10^?3 M because of the participation of the radicals generated in the O₃ + H₂O₂ reaction in LS transformations. The kinetic and UV and IR spectroscopy data allowed the conclusion to be drawn that the destruction of the LS aromatic system in the LS + O₃ + H₂O₂ reaction was caused by the interaction of LS with O₃, whereas radicals generated in this system contributed to deeper destruction of LS in the interaction of aliphatic LS macromolecule fragments with low-molecular-weight polymer oxidation products. The depth of polymer oxidation could be changed by varying the content of hydrogen peroxide in the system for LS ozonization.     

Oxidation and Destruction of Polyvinyl Alcohol under the Combined Action of Ozone–Oxygen Mixture and Hydrogen Peroxide

The oxidative transformations of a polyvinyl alcohol in aqueous solutions are studied under the simultaneous action of the two oxidizing agents, an ozone–oxygen mixture and a hydrogen peroxide. Effective parameters a and b, which characterize the first and second channels of carboxyl group accumulation, respectively, grow linearly upon an increase in the initial concentration of H₂O₂. After the temperature dependence of a and b parameters (331–363 K) in a PVA + O₃ + O₂ + H₂O₂ + H₂O reaction system is studied, the parameters of the activation of COOH group accumulation are found (where PVA is a polyvinyl alcohol). New data on the effect process conditions (length of oxidation, temperature, and hydrogen peroxide concentration) have on the degree of destructive transformations of polyvinyl alcohol in the investigated reaction system are obtained.     

Epoxidation of cyclohexene with molecular oxygen by electrolysis combined with chemical catalysis

This paper describes an electrochemical coupling epoxidation of cyclohexene by molecular oxygen (O₂) under mild reaction conditions. Herein, the electroreduction of O₂ to hydrogen peroxide (H₂O₂) efficiently proceeds in a relatively environmentally friendly acetone/water medium containing electrolytes at 25–30 °C on a self-assembled H type of electrolysis cell with tree electrodes system, providing ca. 44.3 mM concentration of H₂O₂ under the optimal electrolysis conditions. The epoxidation of cyclohexene with in situ generated H₂O₂ simultaneously occurs upon catalysis by metal complexes, giving ca. 19.8 % of cyclohexene conversion with 78 % of epoxidative selectivity over the best catalyst 5-Cl-7-I-8-quinolinolato manganese(III) complex (Q₃Mn^III (e)). The present electrochemical coupling epoxidation result is nearly equivalent to the epoxidation of cyclohexene with adscititious H₂O₂ catalyzed by the Q₃Mn^III (e).     

The mechanism and pathway of the ozonation of 4-chlorophenol in aqueous solution

Chlorophenols (CPs) have been widely used in dif- ferent formulations as preservatives, herbicides, insec- ticides, bactericides and solvents. Parts of chlorophe- nols were released to the natural environment during the usage. As a result, many water sources were con- taminated with CPs[1,2]. Furthermore, they also can be formed during the disinfection of phenol containing water by chlorination. Several CPs are recognized as the priority pollutants by the United States EPA (En- vironmenta…     

A Novel Fluorescent Reagent for Analysis of Hydrogen Peroxide

IntroductionTheoxidationofmanyclinicalsubstancesinbodyfluidsproducesaquantityofhydrogenperoxide ,sothedetermina tionoftracehydrogenperoxideisofconsiderableimportanceinclinicalchemistry .1Further,themonitoringofhydrogenperoxideisalsonecessarytoenvironmentalsciencesinceitisakeyspeciesinthereactionsofthetroposphere,beingin volvedinimportantreactionssuchasthecatalyzedoruncat alyzedaqueousphaseoxidationofSO2 andtheultraviolet en hancedaqueousphaseoxidationoforganicspecies.2 Uptonow ,variousmethods…     

The oxidative destruction of lignin in the ozonation of wood

The oxidative destruction of lignin in the ozonation of aspen wood was studied. The kinetic curves of ozone consumption for samples with different contents of water were obtained. The consumption of ozone increased as the content of water grew. The second derivatives of the UV absorption spectra of lignin were obtained to show that the principal direction of lignin transformations under the action of ozone was the destruction of its aromatic constituents with the formation of carboxyl- and carbonyl-containing compounds. Measurements of the UV diffuse reflectance and EPR spectra of wood showed that the ozonation of wood caused the destruction of lignin quinoid structures. Part of lignin remained unchanged under the action of ozone. A key role in the destruction of wood lignin was played by ozone dissolved in water. Varying the content of water in wood samples allows various lignin transformation products to be obtained through ozonation.     

Kinetics and mechanism of oxidation of manganese(III) acidoporphyrin complexes with hydrogen peroxide

The reactions of manganese(III) acidotetraphenylporphyrin complexes with hydrogen peroxide in an aqueous-organic medium at 288–308 K are studied by spectrophotometry. The reaction is the oxidation of the manganese(III) complex. The spectral and kinetic data correspond to a multistep mechanism including the step of coordination of a hydrogen peroxide molecule by the central manganese atom. A possibility of formation of oxidized complexes without macrocycle destruction upon the reaction with H₂O₂ makes manganese(III) porphyrins quite promising for use as models of natural catalases.     

Epoxidation of cycloolefins with hydrogen peroxide in the presence of heteropoly acids combined with phase transfer catalyst

Oxidation of cycloolefins (cyclohexene, cyclooctene, and cyclododecene) with a 30% solution of hydrogen peroxide at 65 °C in the presence of heteropoly acids (HPA) H₃PW_12–x Mo _x O₄₀ (x = 0—12), which are precursors of active peroxo complexes, and phase transfer catalysts Q⁺Cl^–, where Q⁺ is the quaternary ammonium cation containing C₄—C₁₈ alkyl groups or [C₅H₅NC₁₆H₃₃]⁺, was studied. The catalytic activity decreases in the HPA series: H₃PW₁₂O₄₀ > H₃PW₉Mo₃O₄₀ > H₃PW₆Mo₆O₄₀ > H₃PW₃Mo₉O₄₀ > H₃PMo₁₂O₄₀. The state of the H₃PW₁₂O₄₀—I₂I₂ system was studied using UV, IR, and ³¹P NMR spectroscopies with variation of the [H₂O₂] : [HPA] ratio from 2 to 200 during cyclohexene epoxidation. Despite different catalytic precursors, the reaction proceeds through the same peroxo complex.     

New data on the mechanism of hydrogen peroxide decomposition in acetic acid in the presence of vanadyl and cobalt (II) acetylacetonates

The process of catalytic hydrogen peroxide decomposition in acetic acid in the presence of vanadyl and cobalt (II) acetylacetonates was studied using modern spectroscopic and kinetic techniques. The formation of intermediates during the catalytic decomposition of hydrogen peroxide in the presence of VO(acac)₂ was observed using UV—Vis and ESR spectroscopy. The decomposition of H₂O₂ occurs both catalytically and via the radical route.     

Ammonium and caesium carbonate peroxosolvates: supramolecular networks formed by hydrogen bonds

Diammonium carbonate hydrogen peroxide monosolvate, 2NH₄⁺·CO₃²⁻·H₂O₂, (I), and dicaesium carbonate hydrogen peroxide trisolvate, 2Cs⁺·CO₃²⁻·3H₂O₂, (II), were crystallized from 98% hydrogen peroxide. In (I), the carbonate anions and peroxide solvent molecules are arranged on twofold axes. The peroxide molecules act as donors in only two hydrogen bonds with carbonate groups, forming chains along the a and c axes. In the structure of (II), there are three independent Cs⁺ ions, two of them residing on twofold axes, as are two of the four peroxide molecules, one of which is disordered. Both structures comprise complicated three‐dimensional hydrogen‐bonded networks.     

(2S,3S)‐2,6‐Dimethylheptane‐1,3‐diol,the oxygenated side chain of 22(S)‐hydroxycholestrol,and its synthetic precursor (R)‐4‐benzyl‐3‐[(2R,3S)‐3‐hydroxy‐2,6‐dimethylheptanoyl]‐1,3‐oxazolidin‐2‐one

(2S,3S)‐2,6‐Dimethylheptane‐1,3‐diol, C₉H₂₀O₂, (I), was synthesized from the ketone (R)‐4‐benzyl‐3‐[(2R,3S)‐3‐hydroxy‐2,6‐dimethylheptanoyl]‐1,3‐oxazolidin‐2‐one, C₁₉H₂₇NO₄, (II), containing C atoms of known chirality. In both structures, strong hydrogen bonds between the hydroxy groups form tape motifs. The contribution from weaker C—H...O hydrogen bonds is much more evident in the structure of (II), which furthermore contains an example of a direct short Osp³...Csp² contact that represents a usually unrecognized type of intermolecular interaction.     

The Crystal Structures of Peroxonium Hexafluoroantimonate H3O2SbF6 and Bis(dihydrogenperoxo)hydrogen Hexafluoroantimonate H5O4SbF6

Protonated hydrogen peroxide is produced from the reaction of antimony pentafluoride with bis(trimethylsilyl)peroxide in the presence of hydrogen fluoride. Depending on the stoichiometry of the reaction mixture, the compounds H₃O₂SbF₆ and H₅O₄SbF₆ are formed, which are stable up to room temperature and have been characterized by X-ray crystallography. The structure of the H₃O₂⁺ ion is shown on the right.     

Specific Behavior of Hydrogen Peroxide in a System of AOT Reverse Micelles

It is revealed that, in contrast to organic hydroperoxides, hydrogen peroxide (H₂O₂) is rapidly decomposed in a system of reverse micelles of sodium bis(2-ehylhexyl)sulfosuccinate (AOT) in n-decane. The yield of free radicals upon the decomposition of H₂O₂ in a system of reverse micelles upon the interaction between AOT and cobalt acetyl acetonate (Co(acac)₂) is studied by the inhibitor method using an original spin trap. It is established that the interaction between H₂O₂ and AOT proceeds with no radical formation. Co(acac)₂ catalyses the radical decomposition of H₂O₂ in an aqueous solution. In micellar AOT solutions in n-decane, H₂O₂ and Co(acac)₂ in practice do not react, because H₂O₂ is localized in a micelle water pool, Co(acac)₂ and the spin trap, in the organic phase. In this case, the generation of radicals is not observed.     

Hydrogen Peroxide and Di(hydroperoxy)propane Adducts of Phosphine Oxides as Stoichiometric and Soluble Oxidizing Agents

Aqueous hydrogen peroxide is widely used as an oxidizing agent in industry and academia. Herein, the hydrogen peroxide adducts of phosphine oxides, [tBu₃PO ? H₂O₂]₂ and [Ph₃PO ? H₂O₂]₂ ? H₂O₂, are described. Additionally, the corresponding di(hydroperoxy)propane adducts R₃PO ? (HOO)₂CMe₂ (R=Cy, Ph) were synthesized and characterized. All adducts could be obtained as large single crystals suitable for structural characterization by X‐ray crystallography and solid‐state NMR spectroscopy. The di(hydroperoxy)propane adducts are soluble in organic solvents which enables oxidation reactions in one phase. As the adducts are solid and molecular, they can easily be applied stoichiometrically. No loss of oxidizing power occurs upon long‐term storage of the single crystals at room temperature or the powders at ?20 °C.     

(Tetracycline)europium(III) Complex as Luminescent Probe for Hydrogen Peroxide Detection

Luminescence spectra of aqueous solutions containing a fixed concentration of tetracycline (TC) and increasing concentrations of Eu³⁺ were recorded both in the absence and presence of hydrogen peroxide (H₂O₂). In H₂O₂‐free solutions in which the Eu/TC molar ratio was varied from 1 : 1 to 8 : 1, the ⁵D₀→⁷F₀ transition consisted of only one peak at 580 nm. In the presence of H₂O₂, an extra peak appeared in the spectrum at 578 nm when the Eu/TC molar ratios were above 2.5. A detailed analysis of this spectral region revealed that at lower Eu/TC molar ratios (up to 2 : 1), the ⁵D₀→⁷F₀ transition experienced a slight blue shift. This indicates that at low Eu/TC molar ratios, the presence of H₂O₂ leads to two different environments of the trivalent europium ions, which most likely form bridged peroxide complexes with hydrogen peroxide (μ‐H₂O₂ ligand). Luminescence spectra measured in the presence of molybdate ions, which catalytically decompose H₂O₂, led to the disappearance of the extra europium(III) site that was formed in the presence of H₂O₂. The intensity of the hypersensitive ⁵D₀→⁷F₂ transition did not linearly depend on the H₂O₂/TC molar ratio. For H₂O₂/TC ratios up to 10, a sharp linear increase of the peak intensity was observed, but with further increase of the H₂O₂ concentration, the intensity remained nearly constant. For H₂O₂/TC ratios above 100, the intensity of this transition even started to decrease, which limits the use of the (tetracycline)europium(III) system to quantify hydrogen peroxide in solution.     

Polyferroorganosiloxanes as catalysts of oxidation processes

Polyferroorganosiloxanes were studied as catalysts for homogeneous oxidation of alkanes by hydrogen peroxide tinder mild conditions. In the oxidation of cyclohexane the catalysts are characterized by high efficiency (conversion of hydrogen peroxide is 25%) and stability Kip to 80 cycles per gat NJ The min product of the oxidation W do presence a 2,4,6-tri-tert-btitylphenol is cyclohexanol (tip to 35% per H₂O₂).     

Hydrogen Peroxide Insular Dodecameric and Pentameric Clusters in Peroxosolvate Structures

Peroxosolvates of 2‐aminonicotinic acid ( I ) and lidocaine N ‐oxide ( II ) including the largest insular hydrogen peroxide clusters were isolated and their crystal structures were determined by single‐crystal X‐ray diffraction. An unprecedented dodecameric hydrogen peroxide insular cluster was found in I . An unusual cross‐like pentameric cluster was observed in the structure of II . The topology of the (H₂O₂)₁₂ assembly was never observed for small‐molecule clusters. In I and II new double and triple cross‐orientational disorders of H₂O₂ were found. Cluster II is the first example of a peroxosolvate crystal structure containing H₂O₂ molecules with a homoleptic hydrogen peroxide environment. In II , a hydrogen bond between an H₂O₂ molecule and a peptide group ‐CONH⋅⋅⋅O₂H₂ was observed for the first time.     

Ozone treatment for mercury determination in white wines

A method was developed for the generation of mercury vapour by means of cold-vapour flow-injection atomic absorption spectrometry (FI-CV-AAS) from white wine samples after ozonation as sample pre-treatment. Two different reactors designs for sample ozonation were developed and investigated. The limit of detection and the limit of quantification were, respectively, 0.5 and 1.7 μg l⁻¹, and the relative standard deviation (n=10) was 2% for a concentration of 50 μg l⁻¹ and 7% for a concentration of 5 μg l⁻¹. The pre-treatment with ozone has allowed to reduce drastically the amount of chemical reagents (e.g. carrier agent and reducing agent) used in the FI-CV-AAS system. The mercury content of wine samples was also determined by FI-CV-AAS after pre-concentration in the presence of HNO₃ and H₂O₂. In general, there was no significant difference among data obtained from both methodologies, but pre-treatment with ozone is much faster.