Catalytic oxidation of olefins with hydrogen peroxide catalyzed by [Fe(III)(salen)Cl] complex covalently linked to polyoxometalate

The catalytic activity of a hybrid compound [Fe(salen)-POM] (1) consisting of Fe(III)(salen)Cl [H₂salen = N,N′-bis(salicylidene)ethylenediamine] complex covalently linked to a Keggin type polyoxometalate, K₈SiW₁₁O₃₉, (POM) was studied in the oxidation of various olefins in acetonitrile, using hydrogen peroxide as oxygen source. While, [Fe(salen)-POM] catalyst showed moderate to good catalytic activity and product selectivity in the oxidation reactions, the complex Fe(III)(salen)Cl showed poor catalytic activity in these reactions. The effect of other parameters such solvent, oxidant, temperature and the metal type in Schiff base complex were also investigated.     

Oxidation of hydrocarbons with hydrogen peroxide catalyzed by maltolato vanadium complexes covalently bonded to silica gel

The bis(maltolato)oxo complexes of vanadium(V) and vanadium(IV) both in a soluble form and anchored to chemically modified silica gel, when used in combination with pyrazine-2-carboxylic acid (PCA), catalyze the oxidation of benzene to phenol and alkanes to the corresponding alkyl hydroperoxides with H₂O₂ at 40–50 °C. Heterogenizing the complexes leads to changes in regioselectivity and bond selectivity parameters of the alkane oxidation, and this opens new routes to the enhancement of the selectivity in oxidation processes.     

Kinetics of the oxidative color removal and degradation of bromophenol blue with hydrogen peroxide catalyzed by copper(II)-supported alumina and zirconia

Copper-supported alumina and zirconia catalysts were prepared and their catalytic activity towards the oxidative color removal and degradation of bromophenol blue with H₂O₂ was investigated. The rate of reaction with alumina is greater than that with zirconia, which ascribed to the increased amount of copper loaded on the catalyst as well as to the increased surface area. A brown intermediate (peroxo-compound), formed at the early stages of the reaction, inhibited the reaction rate. The rate of reaction increased with increase in pH of the medium as well as with added chloride ions. Both catalysts are very stable and can be used for several times without notable loss in their catalytic activities.     

改性V_2O_5催化过氧化氢氧化异丁香酚制香草醛

V₂O₅经甘油还原,再以邻苯二甲酸或其二钠盐溶液浸渍,制备了改性V₂O₅催化剂用于异丁香酚的过氧化氢氧化。运用FT-IR、紫外可见漫反射光谱（DR UV-Vis）、XRD等对催化剂进行了表征。结果表明,还原-浸渍法可以有效调变V₂O₅的价态与晶体结构从而提升其催化性能,其中以甘油在120 ℃还原V₂O₅所得前体浸渍邻苯二甲酸二钠所得催化剂 (PVO)-120性能较佳。考察了N,N-二甲基甲酰胺（DMF）等助剂、DMF用量和反应时间等对氧化反应的影响。最优反应条件为：以 (PVO)-120为催化剂,以DMF-CH₃COCH₃（20%,体积比）为介质,异丁香酚：H₂O₂=1∶2（摩尔比）,20 ℃反应4 h,异丁香酚转化率可达87.3%,香草醛收率达到78.0%。     

Highly efficient K7NiV13O38-catalyzed hydroxylation of aromatics with aqueous hydrogen peroxide (30%)

K₇NiV₁₃O₃₈·16H₂O was found to be an efficient homogeneous catalyst in a mixture solvent of CH₃CN and acetic acid for the hydroxylation of aromatics with 30% aqueous H₂O₂. The new catalytic system showed an unprecedented catalytic activity and selectivity for the hydroxylation of aromatics bearing an electron-withdrawing group. In the case of methyl benzoate, the yield of hydroxylated products reached 73%.     

New catalytic systems for selective oxidation of aromatic compounds by hydrogen peroxide

Some new water-soluble catalytic systems based on iron complexes of polyethylene oxide and block copolymers of ethylene oxide and propylene oxide functionalized by catechol or β-cyclodextrin have been developed. These complexes were examined as catalysts for biomimetic hydroxylation of benzene and phenol by hydrogen peroxide. It is shown that the introduction of β-cyclodextrin into the polyethylene oxide molecule is favourable for rate and selectivity of hydroxylation of aromatic compounds in a two-phase system.     

Degradation of polycyclic aromatic hydrocarbons by hydrogen peroxide catalyzed by heterogeneous polymeric metal chelates

Chelating sorbents with 8-hydroxyquinoline (IVa), 8-hydroxyquinoline-5-sulfonic acid (IVb), and tris(2-aminoethyl)amine (VI) ligands immobilized on macroporous methacrylate matrix were prepared and saturated with Co(II), Cu(II), and Fe(II). All these chelates catalyze cleavage of H₂O₂ yielding highly reactive hydroxyl radicals. All were able to degrade by this mechanism polycyclic aromatic hydrocarbons (anthracene, benzo[a]pyrene and benzo[k]fluoranthene). The most effective catalysts IVa-Fe, IVb-Fe, and VI-Cu (25 mg with 100 μmol H₂O₂) performed complete decomposition of 33 μg anthracene and benzo[a]pyrene during one 7-day catalytic cycle at 25 °C. The fastest decomposition proceeded during the 1st day of incubation; 75% of anthracene and 74% of benzo[a]pyrene were decomposed by IVb-Co within the first 24 h. More than 25% decomposition within the 1st day was also achieved with IVb-Fe, VI-Cu, IVa-Cu, and VI-Co for anthracene and more than 30% benzo[a]pyrene was decomposed by IVb-Fe, VI-Cu, IVa-Cu, and IVb-Cu during the same period. 1,4-Anthracenedione was the main product of anthracene oxidation by all catalysts. The catalysts were stable at pH 2–11 depending on their structure and able to perform sequential catalytic cycles without regeneration.     

Detoxication of water containing 1,1-dimethylhydrazine by catalytic oxidation with dioxygen and hydrogen peroxide over Cu- and Fe-containing catalysts

A number of Cu- and Fe-hydroxide containing catalysts, supported on oxide carriers, were prepared to provide the removal of 1,1-dimethylhydrazine from aqueous solutions via its oxidation by hydrogen peroxide and air oxygen. The Cu-containing samples as well as Fe/ZSM-5 are the most active catalysts in this reaction. The reaction products were analyzed by gas chromatography and UV–Vis spectroscopy. The effect of nature of the oxidizer and catalyst, pH and temperature on both the reaction rate and product composition was studied.     

Iron-substituted polyoxotungstates as catalysts in the oxidation of indane and tetralin with hydrogen peroxide

The homogeneous liquid phase oxidation of indane and tetralin with hydrogen peroxide catalysed by tetrabutylammonium salts of iron(III)-substituted polyoxotungstates of general formula [XW₁₁Fe(H₂O)O₃₉]ⁿ⁻, X = P, Si or B is described. The system presented here gives rise to benzylic monooxygenation and dioxygenation products. Indane oxidation reactions produce also dehydrogenation and hydroperoxidation products. As a result, 1H-indene and indane hydroperoxide are formed. Interestingly, tetralin gives rise to the cleavage of carbon–carbon bond, producing 4-(2-hydroxyphenyl)butanal. In the present conditions, this aldehyde is probably arising from tetralin hydroperoxide. Depending on the reaction conditions, moderate selectivities for the corresponding ketones are obtained, affording conversions as high as 59% and 34% for indane and tetralin, respectively. In order to understand the reactions pathway, the oxidation of 1-indanol, 1-indanone, 1H-indene, 1-tetralol and 1-tetralone is also carried out with an iron(III)-substituted polyoxotungstate as catalyst and H₂O₂ as oxidant. The results show that 1-indanol and 1-tetralol give an important contribution for the formation of the corresponding ketones. As far as we know, the use of iron-substituted polyoxotungstates in the oxidation of these arenes is presented for the first time.     

Oxidation of sulfur components in diesel fuel using Fe-TAML catalysts and hydrogen peroxide

Dibenzothiophene-derivatives are catalytically oxidized to their corresponding sulfone product in homogeneous and two-liquid phase systems by H₂O₂ with an iron containing tetraamidomacrocyclic ligand (TAML) catalyst, Fe-TAML^®. The reaction medium is slightly caustic, pH 8, and uses t-BuOH as a co-solvent for solubilizing the dibenzothiophene starting compounds and their oxidation products. Fe-TAML^® catalyst concentrations are in the low micromolar range. H₂O₂ consumption is nearly stoichiometric (two-equivalents) in homogeneous conditions and only slightly less efficient under two-liquid phase conditions. The catalytic process when applied to a sample of commercial diesel fuel occurs under mild conditions with respect to temperature (50 °C), pressure (1 atm), and time (3 h), to remove greater than 75% of the total sulfur content of the fuel after secondary treatment with silica. Both alkyl-benzothiophenes and alkyl-dibenzothiophenes compounds in the diesel fuel were oxidized by the Fe-TAML^®/H₂O₂ system which facilitated their adsorption onto the silica. The mild reaction conditions result in no detectable over-oxidation of alkyl-dibenzothiophenes.     

Efficient liquid phase oxidation of olefins and aromatic alcohol catalyzed by reusable polymer anchored Schiff base complexes

BACKGROUND: Heterogenization of homogeneous catalyst has become an interesting process for the catalytic oxidation of olefins and aromatic alcohol. This may provide a new kind of catalyst that is not only friendly to the environment but also exhibits higher thermal and chemical stabilities. RESULTS: Polymer anchored Schiff‐base complexes of iron(III), copper(II) and cobalt(II) have been synthesized and characterized. The catalytic potential of these complexes has been tested for the oxidation of cyclohexene. The effect of varying solvent, oxidant, substrate oxidant molar ratio, temperature and catalyst amount has been studied. Under optimized reaction conditions 91, 88 and 81% conversion of cyclohexene was obtained with Fe(III), Cu(II) and Co(II) catalysts, respectively. Moreover, the oxidation of other substrates, such as styrene, benzylalcohol, toluene and 1‐hexene were also efficiently carried out by these catalysts. CONCLUSION: The immobilized complexes showed excellent catalytic activity along with high selectivity for the oxidation of olefins and alcohols. The catalysts can be recycled more than five times without any noticeable loss of catalytic activity. Copyright © 2009 Society of Chemical Industry     

Wet oxidation of phenol by hydrogen peroxide using heterogeneous catalysis Fe-ZSM-5: a promising catalyst

This letter presents an original approach to the treatment of phenolic aqueous wastes using H₂O₂ with heterogeneous catalysts. The experimental results indicate that the system using Fe-ZSM-5 zeolite with MFI structure is promising since it allows total elimination of phenol and significant total organic carbon (TOC) removal under mild working conditions. Moreover, Fe-ZSM-5 remains active after after successive runs. Compared with processes using homogeneous catalysis, the possibility of induced pollution caused by the metal ions in the solution is avoided.     

Oxidation of dibenzothiophene by hydrogen peroxide in the presence of bis(acetylacetonato)oxovanadium(IV)

In the presence of bis(acetylacetonato)oxovanadium(IV), dibenzothiophene was oxidized by hydrogen peroxide to form sulfoxide and sulfone products. The percentage of dibenzothiophene remaining after the oxidation and the ratio of these oxidation products, as determined by ¹H NMR spectroscopy, was largely dependent on the solvent used. Reactions in acetonitrile consumed more than 99% of the dibenzothiophene in the reaction and yielded the sulfone as the major product. The efficacy of biphasic oxidations performed in heptane and acetonitrile were dependent on the ratio of acetonitrile to heptane with a higher proportion of acetonitrile resulting in greater consumption of dibenzothiophene. After multiple oxidations, all of the dibenzothiophene was removed from the heptane solution.     

Simple and efficient method for the oxidation of sulfides to sulfones using hydrogen peroxide and a Mo(VI) based catalyst

A simple and efficient method for the oxidation of sulfides to sulfones at room temperature using ammonium heptamolybdate and 30% H₂O₂ is developed. The reactions provide excellent yields within short time, also sensitive functional groups such as allyl, vinyl, propargyl, alcohol, ketone, ester, pyridine and nitrile are found to be tolerated.     

Treatment of odorous sulphur compounds by chemical scrubbing with hydrogen peroxide—Application to a laboratory plant

Hydrogen peroxide (H₂O₂) has proved its efficiency when it is used as an oxidant in chemical scrubbing towers. The important H₂O₂ decomposition in basic solutions has been investigated and slowed down by addition of a stabiliser: poly-α-hydroxyacrylic acid. The objective of this work is to implement this alternative in a laboratory scrubbing pilot. H₂S and CH₃SH removals were studied in order to characterise the performances of the process. The consumption of reactants (H₂O₂ and NaOH) was quantified in continuous working with recycling of the scrubbing solution or not. Using hydrogen peroxide in a scrubbing tower gave quite satisfactory results for hydrogen sulphide, and encouraging ones for methylmercaptan. Hydrogen peroxide decomposition observed was economically acceptable, even if compared with the chlorine process. However, sodium hydroxide consumption was found important because of the carbon dioxide competitive absorption.     

Decolorization of synthetic dyes by hydrogen peroxide with heterogeneous catalysis by mixed iron oxides

Heterogeneous catalysts based on magnetic mixed iron oxides (MO·Fe₂O₃; M: Fe, Co, Cu, Mn) were used for the decolorization of several synthetic dyes (Bromophenol Blue, Chicago Sky Blue, Cu Phthalocyanine, Eosin Yellowish, Evans Blue, Naphthol Blue Black, Phenol Red, Poly B-411, and Reactive Orange 16). All the catalysts decomposed H₂O₂ yielding highly reactive hydroxyl radicals, and were able to decolorize the synthetic dyes. The most effective catalyst FeO·Fe₂O₃ (25 mg mL⁻¹ with 100 mmol L⁻¹ H₂O₂) produced more than 90% decolorization of 50 mg L⁻¹ Bromophenol Blue, Chicago Sky Blue, Evans Blue and Naphthol Blue Black within 24 h. The fastest decomposition proceeded during the first hour of the reaction. In addition to dye decolorization, all the catalysts also caused a significant decrease of chemical oxygen demand (COD). Individual catalysts were active in the pH range 2–10 depending on their structure and were able to perform sequential catalytic cycles with low metal leaching.     

Phenol photodegradation with oxygen and hydrogen peroxide over TiO2 and Fe-doped TiO2

Photodegradation of phenol was investigated with two types of oxidant agents in water, oxygen and hydrogen peroxide, at two different reaction pH with a series of nanosized iron-doped anatase TiO₂ catalysts with different iron contents. The catalysts have been prepared by a sol–gel/microemulsion method. Firstly, iron-doped titania catalysts were studied with respect to their activity behavior when oxygen was used as oxidant agent in the photocatalytic degradation of aqueous phenol in comparison with un-doped reference catalysts. Secondly, two catalysts (TiO₂ and 0.7 wt.% Fe-doped TiO₂) were selected to extend the study for the employment of hydrogen peroxide as oxidant at different concentrations and two initial reaction pHs. An enhancement of the photocatalytic activity is observed only for relatively low doping level (ca. 0.7 wt.%) in catalyst calcined at 450 °C preferably using hydrogen peroxide as oxidant agent which is attributable to the partial introduction of Fe³⁺ cations into the anatase structure. Nevertheless, it has been demonstrated that catalyst surface properties can play an important role during phenol photodegradation process on the basis of the analysis of differences found in the photoactivity as a function of reaction pH.     

Mild and highly efficient transformation of thiols to symmetrical disulfides using urea–hydrogen peroxide catalyzed by a Mn(III)–salen complex

The oxidative coupling of aromatic thiols into the corresponding disulfides with urea–hydrogen peroxide using a Mn(III)–salen complex as catalyst under mild conditions is described. This system provides an efficient, convenient and practical method for the syntheses of symmetrical disulfides.     

Oxidation of herbicides by in situ synthesized hydrogen peroxide and fenton’s reagent in an electrochemical flow reactor: study of the degradation of 2,4-dichlorophenoxyacetic acid

This paper reports an investigation of H₂O₂ electrogeneration in a flow electrochemical reactor with RVC cathode, and the optimization of the O₂ reduction rate relative to cell potential. A study of the simultaneous oxidation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by the in situ electrogenerated H₂O₂ is also reported. Experiments were performed in 0.3 M K₂SO₄ at pH 10 and 2.5. Maximum hydrogen peroxide generation rate was reached at −1.6 V versus Pt for both acidic and alkaline solutions. Then, 100 mg L⁻¹ of 2,4-D was added to the solution. 2,4-D, its aromatic intermediates such as chlorophenols, chlororesorcinol and chlorinated quinone, as well as TOC were removed at different rates depending on pH, the use of UV radiation and addition of Fe(II). The acidic medium favored the hydroxylation reaction, and first order apparent rate constants for TOC removal ranged from 10⁻⁵ to 10⁻⁴ s⁻¹. In the presence of UV and iron, more than 90% of TOC was removed. This value indicates that some of the intermediates derived from 2,4-D decomposition remained in solution, mainly as more biodegradable light aliphatic compounds.