Oxidation with the “O2−H2O2—vanadium complex—pyrazine-2-carboxylic acid” reagent

The vanadium complex—pyrazine-2-carboxylic acid (PCA) system catalyzes oxidation of styrenes PhRC=CHR′ (R=H, Me; R′=H, Ph), or phenylacetylenes PhC=CR (R=H, Ph) with hydrogen peroxide in air to give aldehydes, ketones, and carboxylic acids. The reaction begins with H₂O₂ coordination to the vanadium ion followed by the formation of hydroxyl radicals. Catalytic action of PCA facilitates the reduction of the V^V complex to the V^IV complex and/or the stage of the formation of a peroxide derivative of vanadium.     

The kinetics and mechanism of oxidation of isopropanol with the hydrogen peroxide-vanadate ion-pyrazine-2-carboxylic acid system

The vanadate anion in the presence of pyrazine-2-carboxylic acid (PCA) was found to effectively catalyze the oxidation of isopropanol to acetone with hydrogen peroxide. The electronic spectra of solutions and the kinetics of oxidation were studied. The conclusion was drawn that the rate-determining stage of the reaction was the decomposition of the vanadium(V) diperoxo complex with PCA, and the particle that induced the oxidation of isopropanol was the hydroxyl radical. Supposedly, the HO^· radical detached a hydrogen atom from isopropanol, and the Me₂ C^· (OH) radical formed reacted with HOO^· to produce acetone and hydrogen peroxide. The electronic spectra of solutions in isopropanol and acetonitrile and the dependences of the initial rates of isopropanol oxidation without a solvent and cyclohexane oxidation in acetonitrile on the initial concentration of hydrogen peroxide were compared. The conclusion was drawn that hydroxyl radicals appeared in the oxidation of alkanes in acetonitrile in the decomposition of the vanadium diperoxo complex rather than the monoperoxo derivative, as was suggested by us earlier.     

Molybdenum(VI)–oxodiperoxo complex containing an oxazine ligand: synthesis,X-ray studies,and catalytic activity

A new mononuclear molybdenum(VI)–oxodiperoxo complex [MoO(O₂)₂(phox)] with a simple bidentate ligand, 2-(2′-hydroxyphenyl)-5,6-dihydro-1,3-oxazine (Hphox), has been synthesized and characterized by X-ray structure analysis, elemental analysis, infrared, and ¹H NMR spectroscopy. A triclinic space group P-1 was determined by X-ray crystallography from single-crystal data of this complex. The resulting complex functioned as a facile sulfide oxidation catalyst with urea hydrogen peroxide as terminal oxidant at room temperature. The catalyst showed efficient reactivity in oxidation of sulfides giving high yield and selectivity.     

Oxodiperoxo tungsten complex-catalyzed synthesis of adipic acid with hydrogen peroxide

An amphiphilic oxodiperoxo complex of tungsten using 8-quinolinol (QOH) as ligand has been synthesized and characterized by elemental analyses, gravimetry, chemistry titration, TG/DSC, IR and UV-vis spectroscopy. Oxidation of cyclohexene, cyclohexanol, cyclohexanone, cyclohexene oxide and 1,2-cyclohexane-diol to adipic acid in one-step was conducted by this complex catalyst using 30 wt.% hydrogen peroxide in the absence of organic solvent and phase-transfer catalyst. The effect of the reaction conditions on the oxidation of cyclohexene was studied by varying the amount of the catalyst, reaction temperature, reaction time and the amount of hydrogen peroxide. The results showed that oxodiperoxo tungsten complex with QOH as ligand could achieve 89.8% yield of adipic acid at 90°C by refluxing for 20 h.     

Catalytic oxidation of furan and hydrofuran compounds oxidation of furan by hydrogen peroxide in the presence of vanadium compounds under the conditions of phase-transfer catalysis

Oxidation of furan in system containing hydrogen peroxide, vanadium compound, chlorinated hydrocarbon, water, and phase-transfer catalyst was studied for the first time. In addition to the main product of this process-cis-β-formylacrylic acid-the formation of other products not previously found at oxidation of furan with hydrogen peroxide was detected. They included 2(5H)-furanone, 2,5-dihydroxy-2,5-dihydrofuran, and maleic dialdehyde. Small amounts of maleic and fumaric acids and also the product from polymerization of dihydroxydihydrofuran and dialdehyde were formed. The influence of the type of organic solvent, vanadium and phase-transfer catalysts, and the ratios of the reagents on the yield of the oxidation products were investigated. For Communication 5, see [1]. Kuban State Technological University, Krasnodar, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1322–1329, October, 1999.     

Selective oxidation of aromatic hydrocarbons by potassium and phosphorous-modified iron oxide–silica nanocomposite

Abstract  

Supported iron catalysts are active for hydrocarbon oxidation with H₂O₂, but the hydrogen peroxide dismutation is a shortcoming that may constrain their applications. Herein, we attempted to address this problem using potassium and phosphate-doped iron oxide–silica nanocomposite (KPFeSi) synthesized via sol–gel methods. The promoted silica–iron oxide nanocomposite has been characterized by elemental analyses, FTIR, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface-size determination. The synthesized KPFeSi was an active catalyst in the low-temperature liquid phase oxidation of various alkyl aromatics with hydrogen peroxide in conversions of 31–78%. Furthermore, the direct oxidation of benzene into phenol using hydrogen peroxide has been achieved in the absence of any acid with this KPFeSi compound.     

Oxo‐vanadium(IV) Schiff base complex supported on modified MCM‐41: a reusable and efficient catalyst for the oxidation of sulfides and oxidative S–S coupling of thiols

Oxo‐vanadium(IV) Schiff base complex supported on MCM‐41 as an organic–inorganic hybrid heterogeneous catalyst was synthesized with post‐grafting of MCM‐41 with 3‐aminoropropyltrimethoxysilane and subsequent reaction with 3,4‐dihydroxybenzaldehyde and then complexation with oxo‐vanadium acetylacetonate salt. The catalyst was analysed using a series of characterization techniques such as Fourier transform infrared spectroscopy, small‐angle X‐ray diffraction, nitrogen absorption isotherm, transmission electron microscopy and thermogravimetric analysis. The data collected provided evidence that the vanadium complex was anchored onto MCM‐41. High catalytic activity of this catalyst was observed in the oxidation of various sulfides and thiols (into sulfoxides and disulfides, respectively) with urea hydrogen peroxide as oxidant in high to excellent yields and selectivity under mild conditions. The heterogeneous catalyst could be recovered easily and reused several times without significant loss in catalytic activity and selectivity. Copyright © 2015 John Wiley & Sons, Ltd.     

Peroxidative bromination and oxygenation of organic compounds: Synthesis, X-ray crystal structure and catalytic implications of mononuclear and binuclear oxovanadium(V) complexes containing Schiffbase ligands

Treatment of of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H₂L¹) in methanol with aqueous NH₄VO₃ solution in perchloric acid medium affords the mononuclear oxovanadium(V) complex [VOL¹(MeOH)]·ClO₄ (1) as deep blue solid while the treatment of same solution of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H₂L¹) with aqueous solution of VOSO₄ leads to the formation of di-(μ-oxo) bridged vanadium(V) complex [VO₂L²]₂ (2) as green solid where HL² = (R,R)-N-salicylidene cyclohexane 1,2-diamine. The ligand HL² is generated in situ by the hydrolysis of one of the imine bonds of HL¹ ligand during the course of formation of complex [VO₂L²]₂ (2). Both the compounds have been characterized by single crystal X-ray diffraction as well as spectroscopic methods. Compounds 1 and 2 are to act as catalyst for the catalytic bromide oxidation and C-H bond oxidation in presence of hydrogen peroxide. The representative substrates 2,4-dimethoxy benzoic acid and para-hydroxy benzoic acids are brominated in presence of H₂O₂ and KBr in acid medium using the above compounds as catalyst. The complexes are also used as catalyst for C-H bond activation of the representative hydrocarbons toluene, ethylbenzene and cyclohexane where hydrogen peroxide acts as terminal oxidant. The yield percentage and turnover number are also quite good for the above catalytic reaction. The oxidized products of hydrocarbons have been characterized by GC Analysis while the brominated products have been characterized by ¹H NMR spectroscopic studies.     

Oxidation with the “O2−H2O2-vanadium complex-pyrazine-2-carboxylic acid” reagent

The oxidation of cyclohexene with hydrogen peroxide catalyzed by a vanadium complex and pyrazine-2-carboxylic acid (PCA) in air results in the formation of cyclohex-2-enyl hydroperoxide as the main product and cyclohex-2-enol, cyclohex-2-enone, cyclohex-3-enyl hydroperoxide, cyclohex-3-enol, cyclohexanol, cyclohexane, and 1,2-epoxycyclohexane in lesser amounts. The composition of the products of oxidation of decalin isomers with the system in question is similar to those obtained in the photochemical oxidation with hydrogen peroxide in air and in the oxidation with air in the presence of anthraquinone. A proposed mechanism for the oxidation includes the initiation by hydroxyl radicals generated from hydrogen peroxide under the action of the V-PCA system. For Part 8, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 253–258, February, 1998.     

Application of rhodamine B hydrazide as a new fluorogenic indicator in the highly sensitive determination of hydrogen peroxide and glucose based on the catalytic effect of iron(III)-tetrasulfonato-phthalocyanine

A sensitive, selective and rapid spectrofluorimetric method is proposed for the determination of hydrogen peroxide using rhodamine B hydrazide as a fluorogenic substrate catalyzed by iron(III)-tetrasulfonatophthalocyanine. It is based on the oxidation of rhodamine B hydrazide, a colorless, non-fluorescent spirolactam hydrazide, by hydrogen peroxide which generates the highly fluorescent product rhodamine B. Under optimum conditions, the responses for hydrogen peroxide were linear from 2.0 × 10⁻⁸ to 2.0 × 10⁻⁶ mol L⁻¹, with a detection limit of 3.7 × 10⁻⁹ mol L⁻¹ in a 3.5 min reaction period. It can easily be incorporated into the determination of biochemical substances that produce hydrogen peroxide under catalytic oxidation in the presence of their oxidase. The possibility has been tested for the determination of glucose in human sera as an example.     

Decomposition of hydrogen peroxide catalyzed by vanadium(v) compounds: the pathways for the formation of ozone

Reactions of H₂O₂ in trifluoroacetic acid catalyzed by vanadium(v) compounds were studied. The system under study exhibits unusual behavior: along with oxygen, large quantitaties (10–15 %) of ozone are found in the products of hydrogen peroxide decomposition; difficultly oxidizable compounds (alkanes, arenes, and perfluoroalkenes) are oxidized under mild conditions. The rates of the oxidation of individual substrates are commensurable. However, when two compounds are simultaneously present in the reaction mixture, cyclohexane stops the oxidation of all of the other substrates, arenes suppress the oxidation of perfluoroolefins, and perfluoro-1-octene stops the consumption of internal perfluoroolefins. The effect of the oxidizable substrates on the amount of ozone evolved was studied. Based on the kinetic data obtained, a mechanism that involves the consecutive formation of several active complexes of vanadium(v) responsible for the oxidation of substrates and for the formation of ozone is suggested. In terms of the scheme suggested, the inner-sphere oxidation of the peroxo ligand by the coordinated peroxotrifluoroacetic acid affords a complex incorporating O ₃ ^2– as a ligand. The latter acts as the precursor of the ozone. A mathematical model that adequately describes the experimental data is proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 605–619, April, 1995.     

Selective determination of total vanadium in water samples by cloud point extraction of its ternary complex

A highly sensitive micelle-mediated extraction methodology for the preconcentration of trace levels of vanadium as a prior step to its determination by flame atomic absorption spectrometry (FAAS) has been developed. Vanadium was complexed with 1-(2-pyridylazo)-2-naphthol (PAN) and hydrogen peroxide in acidic medium (0.2 mol L⁻¹ phosphoric acid) using Triton X-100 as surfactant and quantitatively extracted into a small volume of the surfactant-rich phase after centrifugation. The color reaction of vanadium ions with hydrogen peroxide and PAN in phosphoric acid medium is highly selective. The chemical variables affecting cloud point extraction (CPE) were evaluated and optimized. The R.S.D. for 5 replicate determinations at the 20 μg L⁻¹ V level was 3.6%. The calibration graph using the preconcentration system for vanadium was linear with a correlation coefficient of 0.99 at levels near the detection limits up to at least 0.6 μg L⁻¹. The method has good sensitivity and selectivity and was applied to the determination of trace amounts of vanadium in water samples with satisfactory result. The proposed method is a rare application of CPE-atomic spectrometry to vanadium assay, and is superior to most other similar methods, because its useful pH range is in the moderately acidic range achieved with phosphoric acid. At this pH, many potential interferents are not chelated with PAN, and iron(III) as the major interferent is bound in a stable phosphate complex.     

Zeolite-encapsulated vanadium picolinate peroxo complexes active for catalytic hydrocarbon oxidations

Zeolite-encapsulated vanadium (IV) picolinate complexes were prepared by treatment of dehydrated VO(2+)–NaY zeolite with molten picolinic acids. Treatment of the NaY-encapsulated VO(pic)₂ complex with urea hydrogen peroxide adduct in acetonitrile allowed to generate peroxovanadium species. The structure of vanadium peroxo species was studied by UV–vis, Raman and XAFS spectroscopies which suggested the formation of monoperoxo monopicolinate complex which could be active intermediate for various oxidation reactions with the catalysts. To elucidate effect of the encapsulation on catalytic performance, the catalytic properties of the encapsulated complexes were compared with that of corresponding homogeneous catalyst H[VO(O₂)(pic)₂]·H₂O. The novel `ship-in-a-bottle' catalysts retain solution-like activities in aliphatic and aromatic hydrocarbon oxidations as well as in alcohol oxidation. In addition, the encapsulated vanadium picolinate catalysts showed a number of distinct features such as preferable oxidation of smaller substrates in competitive oxidations, increased selectivity of the oxidation of terminal CH_3⁻ group in isomeric octanes and preferable (sometimes exclusive) formation of alkyl hydroperoxides in alkane oxidations. The distinct features were explained in terms of intrazeolitic location of the active complexes that imposed transport discrimination and substrate orientation. On the basis of the experimental data, a possible mechanism was discussed. Stability of the vanadium complexes during the liquid phase oxidations and leaching from the NaY zeolite matrix were also examined.     

Kinetics of vanadium (V) catalyzed oxidation of gallic acid by potassium bromate in acid medium

The kinetics of oxidation of gallic acid with potassium bromate in the presence of vanadium(V) catalyst in aqueous acid medium has been studied under varying conditions. The active species of catalyst and oxidant in the reaction were understood to be HBrO₃ and VO₂⁺. The autocatalysis exhibited by one of the products, i.e. Br⁻, was attributed to complex formation between bromide and vanadium(V). A composite scheme and rate law were possible, some reaction constants involved in the mechanism have been evaluated. © 1996 John Wiley & Sons, Inc.     

Hydrogen Peroxide Oxidation of Hydrocarbons Catalyzed by a Silica Supported Iron Precursor

 Silica supported iron(II) was found to be an efficient catalyst for oxidation of hydrocarbons with hydrogen peroxide.     

C3 vanadium(V) amine triphenolate complexes: vanadium haloperoxidase structural and functional models

The C 3 vanadium(V) amine triphenolate complex 1f has been characterized as a structural and functional model of vanadium haloperoxidases. The complex catalyzes efficiently sulfoxidations at room temperature using hydrogen peroxide as the terminal oxidant, yielding the corresponding sulfoxides in quantitative yields and high selectivities (catalyst loading down to 0.01%, TONs up to 9900, and TOFs up to 8000 h (-1)) as well as bromination of 1,3,5-trimethoxybenzene (catalyst loading down to 0.05%, TONs up to 1260, and TOFs up to 220 h (-1)).     

清洁催化氧化合成己二酸

以新颖的过氧钨酸盐——有机酸配位络合物为催化剂,在无溶剂和无相转移剂的条件下,用30％的过氧化氢氧化环己烯合成己二酸,其收率可达93－95％。本文讨论了配位体种类及催化剂用量对反应的影响。     

Synthesis of the scalemic form of alkaloid (−)-dipthocarpamine

The scalemic form of active alkaloid (−)-dipthocarpamine was synthesized by asymmetric oxidation ofN-isopropyl-N′-(methylthiohexyl)urea with hydrogen peroxide in the presence of vanadium(IV) complexes with chiral Shiff's bases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 564–565, March, 2000.     

Efficient catalytic cycloalkane oxidation employing a "helmet" phthalocyaninato iron(III) complex

We have examined the catalytic activity of an iron(III) complex bearing the 14,28-[1,3-diiminoisoindolinato]phthalocyaninato (diiPc) ligand in oxidation reactions with three substrates (cyclohexane, cyclooctane, and indan). This modified metallophthalocyaninato complex serves as an efficient and selective catalyst for the oxidation of cyclohexane and cyclooctane, and to a far lesser extent indan. In the oxidations of cyclohexane and cyclooctane, in which hydrogen peroxide is employed as the oxidant under inert atmosphere, we have observed turnover numbers of 100.9 and 122.2 for cyclohexanol and cyclooctanol, respectively. The catalyst shows strong selectivity for alcohol (vs. ketone) formation, with alcohol to ketone (A/K) ratios of 6.7 and 21.0 for the cyclohexane and cyclooctane oxidations, respectively. Overall yields (alcohol + ketone) were 73% for cyclohexane and 92% for cyclooctane, based upon the total hydrogen peroxide added. In the catalytic oxidation of indan under similar conditions, the TON for 1-indanol was 10.1, with a yield of 12% based upon hydrogen peroxide. No 1-indanone was observed in the product mixture.     

Reaction of hydrogen peroxide with tetraazamacrocyclic complex of iron(II) in the presence of nitrogeneous bases

The kinetics of hydrogen peroxide oxidation of Fe(II) to Fe(III) complexed with tetraazamacrocyclic ligand was studied, and a decrease in the reaction rate was observed in the presence of nitrogeneous bases, capable of forming hexacoordinated complexes with tetraazamacrocyclic compound of iron(II). The rate of reaction is proprotional to the concentration of the iron complex and hydrogen peroxide and inversely proportional to the concentration of the nitrogeneous base. A mechanism for the course of the reaction has been proposed, and the rate constants of the oxidation of the pentacoordinated iron(II) complexes have been calculated. It was shown that the addition of the fifth donor particle (in particular imidazole) activates the iron(II) atom with respect to the oxidation reaction. It was found that a tetraazamacrocyclic complex of iron(II) is capable of displaying a peroxidase type activity.Translated from Teoreticheskaya Eksperimental'naya Khimiya, Vol. 22, No. 3, pp. 309–316, May–June, 1986.