Phosphotungstic Heteropoly Acid Research Articles

Effect of interfacial activity of quaternary ammonium cation on kinetics of epoxidation of allyl chloride with hydrogen peroxide

A series of quaternary ammonium phosphotungstic heteropoly acid catalysts with different carbon chain lengths [(CnH2n+1)2(CH3)2N]3{PO4[W(O)(O2)2]4} (n = 8, 10, 12, 14, 16) were synthesized for the epoxidation of allyl chloride with H2O2. The hydrophilic and hydrophobic structure of the catalysts were regulated to optimize the interfacial activity by changing the carbon chain lengths of the quaternary ammonium cations. The reaction system using catalyst [(C10H21)2(CH3)2N]3{PO4[W(O)(O2)2]4} showed the lowest interfacial tension between oil and water, the smallest particle size of emulsion droplets and the largest interfacial area, which resulted in the highest catalytic performance. The reaction kinetics and interface properties studies, including the activation energy, interfacial tension, and microscopic imaging of droplets, were conducted to provide strong proof. The epoxidation reaction rates were significantly associated with the surface activity of different carbon chain length catalysts and their effects on the allyl chloride-H2O2 interfacial properties.

Highly stereocontrolled total synthesis of racemic codonopsinol B through isoxazolidine-4,5-diol vinylation.

A new highly diastereoselective synthesis of the polyhydroxylated pyrrolidine alkaloid (±)-codonopsinol B and its N-nor-methyl analogue, starting from achiral materials, is presented. The strategy relies on the trans-stereoselective epoxidation of 2,3-dihydroisoxazole with in situ-generated DMDO, the syn-selective α-chelation-controlled addition of vinyl-MgBr/CeCl3 to the isoxazolidine-4,5-diol intermediate, and the substrate-directed epoxidation of the terminal double bond of the corresponding γ-amino-α,β-diol with aqueous hydrogen peroxide catalyzed by phosphotungstic heteropoly acid. Each of the key reactions proceeded with an excellent diastereoselectivity (dr > 95:5). (±)-Codonopsinol B was prepared in 10 steps with overall 8.4% yield. The antiproliferative effect of (±)-codonopsinol B and its N-nor-methyl analogue was evaluated using several cell line models.

Effective Epoxidation of Fatty Acid Methyl Esters with Hydrogen Peroxide by the Catalytic System H3PW12O40/Quaternary Phosphonium Salts

Six quaternary phosphonium salts (QPSs) in combination with phosphotungstic heteropolyacid, H3PW12O40, were tested in the epoxidation of rapeseed oil fatty acid methyl esters with a hydrogen peroxide aqueous solution. The QPSs consisted of trihexyl(tetradecyl)phosphonium [P6], tributyl-tetradecylphosphonium [P4] or tetraoctylphosphonium [P8] cation and different anions—chloride (Cl−), bromide (Br−), tetrafluoroborate (BF4−), bis(trifluoromethylsulfonyl)amide (NTf2−), bis(2,4,4-trimethyl-pentyl)phosphinate (Phosf−). The influence of the kind of QPS and temperature on the epoxy number, iodine number, glycol content has been determined. The epoxidation was confirmed using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and elemental analysis CHO. Two QPSs with a trihexyltetradecyphosphonium cation—[P6][Fosf] and [P6][Cl]—were selected as the most effective in the studied epoxidation process. The proposed kinetic model takes into consideration the two reactions, namely, epoxidation and epoxy ring opening involving the formation of hydroxyl groups. The rate constants and activation energies for epoxidation fatty acid methyl esters were determined.

The electronic structure of phosphotungstic (H3PW12O40) heteropolyacids modified by Fe2+ cation

In this paper the influence of substituting the tungsten atom with an iron ion in the primary structure of the phosphotungstic heteropolyacid with the Keggin anion structure was investigated. Characterization of the electronic structure of the modified heteropolyacid was performed using: population analysis according to NBO scheme, total (TDOS) and partial (PDOS) density of states spectra, energy and chemical character of frontier orbitals (HOMO / LUMO) and the size of the HOMO-LUMO band gap. Additionally, the mechanism of interaction between the Fe2+ with H2O molecule, acting as a chemical reaction medium, was investigated. Most cases showed a significant effect of the introduced transition metal ion (Fe2+) on the above-mentioned properties in relation to the nonmodified heteropolyacid H3PW12O40.

Performance of NOx capture with Dawson polyoxometalate H6P2W18O62·28H2O

Aiming at developing an effective approach to removing NOx, the Dawson type phosphotungstic heteropolyacid (H6P2W18O62·28H2O, HP2W for short) was studied initially as adsorbent for capturing NOx. The HP2W was prepared and characterized with the aid of IR, XRD and TGA. Effects of temperature, gas velocity, crystal water and pretreatment of HP2W on NOx adsorption were examined. The optimum NOx adsorption temperature was 200 °C. With the increase of space velocity, the capacity of NOx adsorption declined, and the maximum adsorption efficiency of 78% was observed at the SV of 5000 h−1. Two types of crystal water were observed on HP2W by TGA measurement, among which the physically adsorbed water would hinder the NOx adsorption, while the chemically adsorbed water would improve it. HP2W was pretreated in the atmosphere of O2, H2 and He respectively before adsorbing NOx. IR and XRD spectra were taken to investigate the adsorption mechanism, and we found that most of the NOx was adsorbed in the forms of NO linkage in the secondary structure of the solid heterpolyacid and a small quantity of NOx was adsorbed as N2O3 and NO2+. Alternative methods for NOx desorption by raising temperature and by cooling with wet air were evaluated, with the latter found to be much more effective in that it enables the reuse of HP2W. Hence an effective and reusable adsorbent HP2W, deserving further study, was obtained.

Study on leaching behaviour of tungstates in acid solution containing phosphoric acid

For decades, methods for leaching scheelite based on the generation of soluble phosphotungstic heteropoly acids have been continuously studied. These methods can be performed under normal pressure and can achieve a high leaching ratio when treating scheelite, but their most obvious disadvantage is that the leaching speed is very slow when treating wolframite, which has limited their application in the leaching of wolframite-containing ores. Considering the difference between the crystal forms of these two minerals, the relationship between the crystal structure of MeWO4-type tungstate and the leaching rate in acid solution containing phosphoric acid was systematically studied. The results showed that the leaching rates of all tetragonal tungstates were significantly higher than those of monoclinic and triclinic tungstates. Even in H3PO4-H2SO4 solution, sulfate precipitates were produced when leaching tetragonal tungstates, but their leaching rates were still significantly higher than those of other crystalline tungstates. In addition, the tungsten leaching rate was roughly proportional to the volume occupied by the MeWO4 unit, and NiWO4, with the closest-packed atomic arrangement, had the lowest leaching rate. It was found that the evolution of the tungstate crystal structure parameters was gradual and regular with the gradual change in the CX (cилoвыe xapaктepиcтики, obtained by the ratio of a cation's n-th ionization potential to its orbital radius), although these divalent cations are in different regions of the periodic table. Furthermore, leaching in the acid solution containing phosphoric acid yielded a better relationship between the change in the tungsten leaching rate and the change in the cation's CX in the same group or period of the periodic table.

Ethylene Conversion over Catalysts Based on Solid Superacids and Heteropoly Acids

Catalytic properties of solid superacids (WO3/ZrO2 and SO4/ZrO2), and monolith and H-Beta zeolite-supported phosphotungstic heteropoly acid in gas-phase alkylation of benzene with ethylene to ethylbenzene and in the side reaction of ethylene oligomerization are studied. It was found that H-Beta zeolite had the highest activity and selectivity to ethylbenzene. The use of solid superacid (WO3/ZrO2) was shown to be more efficient in low-temperature oligomerization of ethylene.

Acidic Dressing Based on Agarose/Cs2.5H0.5PW12O40 Nanocomposite for Infection Control in Wound Care.

Regulation of wound pH from alkaline to acidic is a simple and powerful approach to reduce wound microbial colonization and infection. Here, we present a nanocomposite material possessing intrinsic acidic surface pH as an innovative antimicrobial wound dressing. This material comprises an agarose matrix nanocomposite containing nanoparticles (NPs) of the cesium salt of phosphotungstic heteropolyacid (Cs2.5H0.5PW12O40). Self-supporting films were prepared by a casting method incorporating 5-20 wt % Cs2.5H0.5PW12O40 NPs into the matrix. Films are flexible with tensile strengths between 28.55 and 32.15 MPa and exhibit broad biocidal activity against neutralophilic pathogens, including Gram-positive bacteria, Gram-negative bacteria, yeast, and filamentous fungi. The nano-antimicrobial Cs2.5H0.5PW12O40 functions as an efficient and self-controlled proton delivery agent that lowers the surface pH of the nanocomposites to the range 7.0 > pH ≥ 3.0. Nanocomposite films containing 20 wt % Cs2.5H0.5PW12O40 NPs presented a surface pH of 3.0 and highest antimicrobial activity. Using quantitative reverse transcription polymerase chain reaction, we demonstrated that the antimicrobial mechanism of the nanocomposites is acid-induced because of the transcriptional induction of glutamate-dependent acid resistance genes in Escherichia coli. Additionally, nanocomposite films do not damage skin according to an in vivo rabbit skin model with no derived edema or erythema. The wound care safety of this material is due to low release of heavy metal heteropolyanions ([PW12O40]3-), no nanoparticle leaching, and proton controlled release resulting in nonirritating acid levels for human skin models.

Combating pathogens with Cs2.5H0.5PW12O40 nanoparticles: a new proton-regulated antimicrobial agent.

The transfer of pathogens from contaminated surfaces to patients is one of the main causes of health care-associated infections (HCAIs). Cases of HCAIs due to multidrug-resistant organisms have been growing worldwide, whereas inorganic nano-antimicrobials are valuable today for the prevention and control of HCAIs. Here, we present a cesium salt of phosphotungstic heteropolyacid (Cs2.5H0.5PW12O40) as a promising nanomaterial for use in antimicrobial product technologies. This water-insoluble Keggin salt exhibits a broad biocide spectrum against Gram-positive and Gram-negative bacteria, yeasts, and filamentous fungi even under dark conditions. The Cs2.5H0.5PW12O40 nanoparticles (NPs) act as a proton-regulated antimicrobial whose activity is mediated on the release of hydronium ions (H3O+), yielding an in situ acidic pH several units below those tolerable by most of the fungal and bacterial nosocomial pathogens.

Ion transfer asymmetry in Nafion membranes with gradient distribution of acid salts of heteropoly acids

We describe the effect caused by the modification of Nafion membranes with nanoparticles of rubidium and cesium acid salts of phosphotungstic and silicotungstic heteropoly acids (HPAs) using layer-by-layer casting on the properties of the membranes depending on the dopant type and the percent modified layer thickness. The ionic conductivity and diffusion permeability of hybrid materials have been studied. The modification is shown to increase the ionic conductivity at low relative humidity. The highest conductivity is observed for the membranes where the modified layer amounts to 35–50% of the total membrane thickness. On the contrary, diffusion permeability is reduced upon modification. Asymmetric ion transfer is observed: the ion transfer rate from the modified layer is lower than from the unmodified layer. This asymmetry arises from the anion concentration gradient in the membrane, which is directed from the modified to unmodified side of the membrane. An asymmetric membrane oriented so that its modified side faces the anode can potentially increase the power of a fuel cell.

Acid Activation of Natural Zeolite with High Content of Iron Oxides in Creation of Selective Sorbents and Catalysts

The paper studies the influence of the nature of modifying acids (mineral, organic and heteropolyacids), and their combination on the composition and structure of the iron oxide rich clinoptilolit from Shankanay field in Kazakhstan for creation of selective catalysts in hydracarbon processing and sorbents for extracting ions of lanthanide and actinide elements. It is shown that sequential processing of natural zeolite in optimal conditions, by hydrochloric and sulfosalicylic acids lead to intensive decationization and dealumination, as well as maximum removal of iron ions from the zeolite framework without destroying it. It is found that the combination of activated clinoptilolite with hydrochloric acid and phosphotungstic heteropolyacid contributes to obtain catalyst system with high surface area and acidity.

Heteropolyacids like new anticorrosion pigment in organic paints

Abstract This paper is focused on the heteropoly acids as another new possibility of dopant for conducting polymers which can be used as anticorrosive pigments for steel protection. The newly prepared pigments, silicotungstic and phosphotungstic heteropoly acids, were characterized by determination of oil number and density. The value of critical pigment volume concentration was determinated by these values. The pigment volume concentration was 0.5; 1; 3 and 5 % in epoxyester-resin witch was used as a binder. Organic coatings were applicated on steel panels which were tested by mechanical and corrosion tests. The main exam was exposition of testing sample in sulphur dioxide atmosphere. Another important exam was measuring the specific electrical conductivity and determination of corrosion loss. After 1584 hours, the samples were evaluated. Values of anticorrosion efficiency are increased for silicotungstic heteropoly acid pigment. But with long-term exposition, phosphotungstic heteropoly acid pigment has better and higher anticorrosion efficiency than the other sample.

Synthesis of novel urushiol-like compounds from tung oil using silica-supported phosphotungstic heteropoly acid catalyst

Tung oil, a kind of natural plant oil, has recently received increasing attention due to its high value of research and application. In this study, we report a facile approach to synthesize novel urushiol-like compounds (CAT-ME) starting from tung oil using silica-supported phosphotungstic heteropoly acid (PW/SiO2) as an effective and recyclable catalyst. To be specific, firstly, eleostearic acid glyceride, the main component of tung oil, is reacted with methanol by trans-esterification to obtain methyl eleostearate. And then Friedel-Crafts alkylation reaction of methyl eleostearate with catechol is carried out in the presence of a solid acid catalyst PW/SiO2. And the CAT-ME productive rate is about 69.3%. Furthermore, the chemical structures of the target compound CAT-ME are characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet and visible spectrophotometer (UV–vis), proton nuclear magnetic resonance spectra (1H NMR), carbon nuclear magnetic resonance spectra (13C NMR) and mass spectra. The characterization results show the designed alkylation products similar to urushiol have been synthesized successfully. Noting that urushiol (the major component of raw lacquer) can be cured by UV irradiation under air atmosphere without any photoinitiator. Thus, this present study develops a promising approach to guide the further modifications of tung oil and other unsaturated natural oils, which can improve the functional properties and expand the application fields of unsaturated natural plant oils by introducing new UV curing system.

Electrocatalytic and transport properties of hybrid Nafion® membranes doped with silica and cesium acid salt of phosphotungstic acid in hydrogen fuel cells

This work is devoted to preparation of a hybrid material based on Nafion® 212 membrane doped with nanoparticles of silica and cesium acid salt of phosphotungstic heteropolyacid. The benefits of this material are concerned with its increased conductivity at low humidity. Conductivity and properties of the membranes were studied as a function of relative humidity under the FC operating regime at room temperature. As compared with the commercial Nafion® 212 membrane, the MEA based on this material shows a lower power density at 100% relative humidity of the supplied gases (hydrogen, air). As the relative humidity decreases, power density of the cell based on hybrid membrane increases and overruns the performance of the commercial Nafion® 212 membrane at 100% RH. Explanation of the observed phenomena is proposed.

Heteropoly acid encapsulated into zeolite imidazolate framework (ZIF-67) cage as an efficient heterogeneous catalyst for Friedel–Crafts acylation

A new strategy has been developed for the encapsulation of the phosphotungstic heteropoly acid (H3PW12O40 denoted as PTA) into zeolite imidazolate framework (ZIF-67) cage and the PTA@ZIF-67(ec) catalysts with different PTA content were prepared. The structure of the catalysts was characterized by XRD, BET, SEM, FT-IR, ICP-AES and TG. The catalytic activity and recovery properties of the catalysts for the Friedel-Crafts acylation of anisole with benzoyl chloride were evaluated. The results showed that 14.6–31.7wt% PTA were encapsulated in the ZIF-67 cage. The PTA@ZIF-67(ec) catalysts had good catalytic activity for Friedel-Crafts acylation. The conversion of anisole can reach ~100% and the selectivity of the production can reach ~94% over 26.5wt% PTA@ZIF-67(ec) catalyst under the reaction condition of 120°C and 6h. After reaction, the catalyst can be easily separated from the reaction mixture by the centrifugation. The recovered catalyst can be reused five times and the selectivity can be kept over 90%.

Kinetics of the epoxidation of soybean oil with H2O2 catalyzed by phosphotungstic heteropoly acid in the presence of polyethylene glycol

In this work, the kinetics of “in situ” epoxidation of soybean oil with H2O2 (30% w/w), catalyzed by phosphotungstic heteropoly acid [π‐C5H5N(CH2)15CH3]3[PW4O16] (PHA) phase transfer catalyst and polyethylene glycol (PEG) as interfacial agent in dichloroethane, were investigated at 40, 50, 60, and 70°C. Assuming that the epoxidation reaction occurred in the pseudo‐homogeneous catalytic system and the side reaction of epoxy ring cleavage was negligible, the results appeared that the epoxidation reaction of soybean oil in the presence of PEG was a second‐order with respect to double bond concentration and a first‐order to the H2O2 concentration. The corresponding apparent activation energy (42.12 kJ/mol) was lower than that of PHA alone (49.23 kJ/mol), indicating that PEG could decrease the activation energy and speed up the epoxidation reaction of soybean oil.Practical applications: An environmentally friendly catalyst is eagerly needed to produce peroxided soybean oil for low yield and to prevent polluting the environment through the epoxidation of soybean oil with peracid. Phosphotungstic heteropoly acid phase transfer catalyst and polyethylene glycol improve the conversion and selectivity of the epoxidation reaction of soybean oil, and enhance its production efficiency.The activation energy of the soybean oil epoxidation reaction with H2O2 catalyzed by phosphotungstic heteropoly acid (PHA) in the presence of polyethylene glycol (PEG) was lower than that of PEG alone, accounting for the results showing that the epoxy group band of the former (PHA + PEG) appeared quicker than the latter (PHA) in IR spectra.

Membranas de PVA e sílica para aplicação em célula a combustível de alimentação direta de álcool

Membranas de PVA/sílica foram sintetizadas através do processo sol-gel em condições ácidas. Tetraetilortossilicato (TEOS) foi utilizado como precursor em concentrações de 5 a 30% em dois grupos distintos. Um grupo foi utilizado como controle contendo apenas PVA/TEOS. A inserção dos grupamentos necessários para a condutividade ocorreu através da introdução de 12% em massa de heteropoliácido fosfotúngstico hidratado (HPW) em relação à massa de TEOS, formando o segundo grupo. As avaliações quanto ao grau de inchamento, permeabilidade ao etanol e condutividade protônica demonstraram que a membrana contendo 30% em massa de TEOS apresenta os melhores resultados entre as membranas produzidas. Os melhores resultados foram 0,28 mS/cm de condutividade protônica e fluxo de 1,5 kg/m².h de solução de etanol. Nessas condições, considera-se a reticulação das membranas de PVA/SiO2 com o precursor TEOS uma boa alternativa para a reticulação de membranas de PVA visto que as membranas mostraram-se mais seletivas ao fluxo de solução de etanol. Entretanto, para aplicação como eletrólito de célula a combustível, ainda é necessário investigar outras formas de aumentar a condutividade sem prejudicar a estabilidade dimensional.

Synthesis and study of hybrid materials based on Nafion membranes, hydrated silica, phosphotungstic acid, and its acid salts

The results of research of the properties of hybrid materials based on Nafion membranes, silica, phosphotungstic acid, and its acid salts (potassium, rubidium, and cesium) prepared by the in situ method has been described. Modification leads to an increase in the water content and a significant increase in the conductivity of the hybrid membranes, particularly at a low relative humidity. The materials containing slightly soluble acid salts of phosphotungstic heteropoly acid exhibit a lower conductivity than the material that contains the acid; however, the former are more stable. It has been found that the diffusion permeability of an HCl solution in Nafion + SiO2 + M x H3−x PW12O40 systems is lower than in Nafion + SiO2 and further decreases with increasing ionic radius of the cation. An explanation of the causes of these changes in the properties has been proposed.

Real‐time monitoring of ring‐opening polymerization of tetrahydrofuran via in situ Fourier Transform Infrared Spectroscopy

ABSTRACTThe polymerization of tetrahydrofuran (THF) was carried out in CH2Cl2 by using phosphotungstic heteropolyacid as initiator and epichlorohydrin as promoter. This cationic ring‐opening polymerization process was monitored by in situ mid‐infrared spectroscopy system (ReactIR) to further study the thermodynamics and kinetics of THF polymerization. It was observed that the sharp infrared peak of COC stretching vibrations will shift from about 1068 to 1109 cm−1 in THF ring‐opening step. The changes in absorbance intensity of the two characteristic peaks were used for determining instantaneous concentration of linear polymer and ring monomer. The experimental results demonstrated that the kinetics of THF polymerization proved to be typically first‐order. Thermodynamic parameters were determined from the temperature dependence of the monomer equilibrium concentration [M]e over the range from −5 to 25°C. The values of kapp were obtained via the plots of ln{([M]0−[M]e)/([M]t−[M]e)} vs reaction time, for polymerization under specific conditions. The apparent activation energy (Ea) and frequency (A) were determined from the Arrhenius plot of kapp vs. T−1. Besides, the in situ kinetic investigation revealed that more chain‐transfer occurred at higher temperatures, leading to a reduction in propagation species concentration and a deviation from first‐order propagation at the later stage of polymerization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40503.

Electrophysical properties of polyaniline doped with heteropoly acids

Composites of polyaniline with phosphotungstic and phosphomolybdic heteropoly acids of Keggin type were studied by impedance spectroscopy. Doping of polyaniline with these acids allows the proton conductivity of the polymer in the composites to be increased by six orders of magnitude.