Presence Of Phosphotungstic Acid Research Articles

Interfacial Engineering of Block Copolymer Nanostructures: Morphology and Solvent Stability.

Interfacial engineering is a critical pathway for modulating the self-assembled nanostructures of block copolymers (BCPs) during solvent exchange. Herein, we demonstrated the generation of different stacked lamellae of polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) nanostructures during solvent exchange by using phosphotungstic acid (PTA) or PTA/NaCl aqueous solution as the nonsolvent. The participation of PTA in the confined microphase separation of PS-b-P2VP in droplets increases the volume fraction of P2VP and decreases the tension at the oil/water interface. Moreover, the addition of NaCl to the PTA solution can further increase the surface coverage of P2VP/PTA on droplets. All factors impact the morphology of assembled BCP nanostructures. In the presence of PTA, ellipsoidal particles composed of alternatively stacked lamellae of PS and P2VP were formed (named BP), whereas, in the coexistence of PTA and NaCl, they changed to stacked disks with PS-core-P2VP-shell (called BPN). The different structures of assembled particles induce their different stabilities in solvents and different dissociation conditions as well. The dissociation of BP particles was easy because PS chains were only entangled together which can be swollen in toluene or chloroform. However, the dissociation of BPN was hard, requiring an organic base in hot ethanol. The structural difference in BP and BPN particles further extended to their dissociated disks, which makes the cargo (like R6G) loaded on these disks to show a different stability in acetone. This study demonstrated that a subtle structural change can greatly affect their properties.

Thermal stabilization of polyoxymethylene by copolymerization and modified phenolic stabilizer: examining the effects of catalyst, retardant, and stabilizer

ABSTRACT Due to the low stability of oxymethylene units and their high heat sensitivity, polyoxymethylene (POM) shows weak thermal resistance. Therefore, by using a stabilizer the thermal stability of POM would be improved. In this study, the in-situ ring-opening copolymerization of 1,3,5-trioxane (TOX) as a monomer and 1,3-dioxolane (DOX) as a comonomer was investigated which was carried out in the presence of phosphotungstic acid (PTA) as the catalyst and the reactive antioxidant during the reactive blending. Then POM samples were characterized by Fourier-transform Infrared spectroscopy (FTIR), and Hydrogen Nuclear Magnetic Resonance spectroscopy (1H-NMR). Also, to scrutinize the crystallinity and the thermal degradation of POM Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA) were performed, respectively. The Crystalline structure of the samples was also studied by X-ray diffraction (XRD). According to the results, The synthesized polymer had a hexagonal structure and the best quantity of catalyst was 50 ppm. The presence of retardant improved the thermal resistance of POM while the addition of 1 wt.% of stabilizer as an optimum amount has no upward or ascending effect.

Cover: Journal of the Chinese Chemical Society 10/2018

In this paper, a high‐yielding, atom‐efficient, and green protocol for the synthesis of novel pyrazolo‐fused benzophenazines utilizing a multicomponent condensation reaction between 2‐hydroxynaphthalene‐1,4 ‐dione, o‐phenylenediamine, aromatic aldehydes, and 4‐ methylbenzenesulfonohydrazide in the presence of phosphotungstic acid (H3PW12O40) under microwave irradiation (MWI) in EtOH is reported. The novel series of 1H‐benzo[a]pyrazolo[3,4‐c]phenazine derivatives may be useful for biological screening tests. More details will be discussed by Dr. Razieh Mohebat and her co‐workers on page 1259‐1265 in this issue. image

Green synthesis of novel pyrazolo‐fused benzophenazines using H3PW12O40 as efficient and recyclable catalyst under microwave irradiation

A high‐yield, atom‐efficient, and green protocol for the synthesis of novel pyrazolo‐fused benzophenazines utilizing a multicomponent condensation reaction between 2‐hydroxynaphthalene‐1,4‐dione, o‐phenylenediamine, aromatic aldehydes, and 4‐methylbenzenesulfonohydrazide in the presence of phosphotungstic acid (H3PW12O40) under microwave irradiation (MWI) in EtOH is reported. We provide a novel series of 1H‐benzo[a]pyrazolo[3,4‐c]phenazine derivatives interesting for biological screening tests. This protocol offers several advantages satisfying many principles of green chemistry, including atom economy, energy saving, clean reactions, inexpensive reagents, reusability of H3PW12O40, the absence of any tedious work‐up or purification, and avoidance of hazardous or toxic reagents/catalysts/solvents.

Effect of Jeffamine®‐Modified Phosphotungstic Acid on Porphyrin Synthesis in Water

AbstractSynthesis of porphyrin derivatives in water can be challenging due to the inimical conditions associated with the initial condensation equilibrium. Here in, we report the synthesis of meso‐tetraphenyl porphyrin (H2TPP) in water in presence of phosphotungstic acid (PTA) and its liquid‐derivative with a polyether amine (Jeffamine®). The PTA‐Jeffamine® derivative was found to simultaneously catalyze both the condensation as well as oxidation stages of H2TPP formation. Few other derivatives of H2TPP were synthesized. All the products were characterized by UV‐vis, FTIR and NMR spectroscopy. Singlet oxygen efficiency of the catalytically synthesized H2TPP matched well with that of H2TPP obtained from conventional process. The PTA‐Jeffamine® derivative showed better yield compared to the reaction with pure PTA.

Toward an inherently safer alternative for operating N-oxidation of alkylpyridines: Effect of N-oxide on lutidine – water phase separation

The N-oxidation of alkylpyridines is an industrially important reaction since it produces alkylpyridine N-oxides that are pharmaceutical intermediates. The aqueous hydrogen peroxide used to oxidize the alkylpyridine has a tendency to decompose during the reaction thereby introducing serious hazards for the process. The decomposition is accelerated during the N-oxidation of higher order alkylpyridines (lutidines, collidines) due to mass transfer limitations caused by the separation of the liquid into organic and aqueous phase. Also, the presence of phosphotungstic acid (catalyst) in the aqueous phase further intensifies the peroxide decomposition reducing the safety and efficiency of the process. The current work investigates the influence of the product N-oxide on the mixing between alkylpyridine and water, which is primarily responsible for the liquid phase heterogeneity during the N-oxidation. Ternary mixtures of 2,6-lutidine, 2,6-lutidine N-oxide and water were analyzed at 110°C to determine phase separation compositions. It was found that extent of heterogeneity between 2,6-lutidine and water is reduced dramatically by the presence of 2,6-lutidine-N-oxide as indicated by the phase diagram. The results could be used to implement the inherent safety concept – “hybridization” to the N-oxidation system wherein the concentration of product N-oxide can be controlled to maintain a less hazardous environment.

Synthesis of tetrasubstituted 1H-indazolo[1,2-b]phthalazinedione derivatives bearing three-dimensional turbine-type structures via domino reaction of phthalhydrazide and vinylketones

A domino reaction of phthalhydrazide and vinylketone in the presence of phosphotungstic acid was established, and 3D turbine-type tetrasubstituted 1H-indazolo[1,2-b]phthalazinedione derivatives were conveniently obtained with up to 95% yield.

Bulk copolymerization of 1,3,5-trioxane and 1,3-dioxolane in presence of phosphotungstic acid catalyst and tetrahydrofuran as retarder: crystallinity and thermal properties

In this study, cationic ring opening in situ copolymerization of 1,3,5-trioxane (TOX) and 1,3-dioxolane (DOX) occurred during bulk polymerization in the presence of phosphotungstic acid as a catalyst. In another part of the study, copolymerization occurred in the presence of retarder tetrahydrofuran (THF), and its effect on the crystallization and thermal stability of the samples was also investigated. The findings from 1HNMR spectrometry indicated that the synthesized samples of random acetal copolymer are comprised of an independent oxyethylene unit in an oxymethylene main-chain sequence. The findings from DSC indicated that crystallinity decreases with increasing comonomer content. Furthermore, the sample with retarder revealed greater crystallinity than the samples without retarder. From TGA results, it was revealed that the sample with retarder caused a larger quantity of comonomer to enter the chain and increased the thermal stability compared to the samples without retarder.

Comparative Study on the Electrodeposition and Corrosion Resistance of Polypyrrole Doped by Phosphotungstate and Benzalkonium Chloride

Polypyrrole (PPy) coating and PPy composite coatings were successfully electrodeposited on mild steel in the electrolytes of oxalic acid in the absence and presence of dopants using cyclic voltammetry. Two types of doping ions were employed: phosphotungstate (PW12O403–) and benzalkonium chloride (BAC). Corrosion-resistant performances of the coatings in 0.1 M HCl showed that PPy composite coatings in the presence of phosphotungstic acid and BAC exhibit more effective protection for iron in comparison with PPy formed in 0.3 M oxalic acid, and corrosion resistance of PPy–BAC is better than PPy–PW12 even though PPy–PW12 shows nobler open-circuit potential for a longer period of time than PPy–BAC. Impedance measurements show that, after immersion of 12 h in 0.1 M HCl, the polarization resistances of PPy–PW12 and PPy–BAC coatings reach 1860 and 3110 Ω cm2, respectively, compared to 640 Ω cm2 of PPy deposited from 0.3 M oxalic acid.

System-forming functions of bound water in the mechanism of topochemical reactions of formation of ultrathin layers on water surface

The system-forming role of the surface layer of water in the process of formation of ultrathin layers from the epoxide oligomer and triethylenetetramine or phosphotungstic acid on the surface of the aqueous phase is shown. Previously, this process was studied experimentally. The surface layer of the aqueous phase plays the role of a matrix, on which an epoxide oligomer monolayer and triethylenetetramine or phosphotungstic acid molecules are immobilized by hydrogen-bonding with water molecules from above or from below this matrix, respectively. Thus, topochemical reactions between the epoxide oligomer and triethylenetetramine or between the epoxide oligomer molecules in the presence of phosphotungstic acid become possible, so that ultrathin network epoxide-triethilenetetramine or epoxide layers are formed on the surface of water.

Ultrasound-assisted oxidative desulfurization (UAOD) using phosphotungstic acid: effect of process parameters on sulfur removal

The oxidation of dibenzothiophene (DBT) and benzothiophene (BT) from a model diesel fuel, using hydrogen peroxide (H2O2) as an oxidant, was carried out in the presence of phosphotungstic acid and phase transfer agent (PTA) at 50–80°C. The desulfurization efficiency and selectivity for the various compounds were examined and compared on the basis of the amount of sulfur converted to polar sulfone. The effect of process parameters (temperature, amount of catalyst, amount of PTA, and H2O2 concentration) were investigated to determine the highest reaction rate on the conversion of BT and DBT. The results indicate that using [PW12O40]3- as a catalyst accelerates the reaction rate on the conversion of BT and DBT to their corresponding polar sulfones. High conversion (>99%) was achieved as the temperature was increased from 50 to 80°C. The activity of BT also increased markedly when the amount of oxidant increased. For DBT, as low as 0.02M of H2O2 was enough to lower the concentration from 500 to 10 ppm at 80°C. The Arrhenius equation was appropriately applied to describe the data by using the pseudo-first-order reaction kinetic equation. The apparent activation energies for BT and DBT were determined to be 60.52 and 45.01 kJ/mol, respectively.

Directed nanoparticle reduction on graphene

A simple, green mechanism for the UV assisted synthesis of graphene in the presence of phosphotungstic acid (PTA) is presented. The reduced graphene oxide (RGO) after UV exposure in the presence of PTA has been further identified as an efficient UV-absorber due to its complexation with PTA. This in turn could be used as an excellent template for the decoration of metal nanoparticles (NPs) on RGO. HRTEM analysis corroborates the localized reduction of metal NPs on the graphene matrix. The RGO-NP templated configurations further demonstrate an interesting microsecond delay of electron transfer from the recombination of electron–hole pairs; an enviable property for next generation optoelectronic devices.

ChemInform Abstract: An Efficient Synthesis of Symmetrical N,N′‐Alkylidene Bisamides Catalyzed by Phosphotungstic Acid.

Symmetrical N,N′-alkylidene bisamides have been synthesized in excellent yield by the condensation of aromatic ′aldehydes and amides in the presence of phosphotungstic acid as a catalyst under thermal and neat microwave irradiation conditions. It is the first successful report of phosphotungstic acid being used as Bronsted acid catalyst for the preparation of symmetrical N,N′-alkylidene bisamides. The remarkable advantages offered by this method are green catalyst, mild reaction conditions, simple procedures and excellent yield of product.

Chemical Induction of Misfolded Prion Protein Conformers in Cell Culture

Prion-infected cells accumulate a heterogeneous population of aberrantly folded PrP conformers, including the disease-causing isoform (PrP(Sc)). We found that specific chemicals can modulate the levels of various PrP conformers in cultured cells. Positively charged polyamidoamines (dendrimers) eliminated protease-resistant (r) PrP(Sc) from prion-infected cells and induced the formation of insoluble, protease-sensitive PrP aggregates (designated PrP(A)). Larger, positively charged polyamidoamines more efficaciously induced the formation of PrP(A) and cleared rPrP(Sc), whereas negatively charged polyamidoamines neither induced PrP(A) nor cleared rPrP(Sc). Although the biochemical properties of PrP(A) were shown to be similar to protease-sensitive (s) PrP(Sc), bioassays of PrP(A) indicated that it is not infectious. Our studies argue that PrP(A) represents an aggregated PrP species that is off-pathway relative to the formation of rPrP(Sc). It remains to be established whether the formation of PrP(A) inhibits the formation of rPrP(Sc) by sequestering PrP(C) in the form of benign, insoluble aggregates.

Properties of ZnSe films pulse electrodeposited in the presence of phosphotungstic acid

ZnSe films were pulse-electrodeposited on conducting glass substrates with and without the addition of phosphotungstic acid. X-ray diffraction studies indicated the formation of single phase cubic ZnSe. Addition of phosphotungstic acid resulted in films with nanocrystallites. The band gap of the films was found to increase due to addition of phosphotungstic acid. The films had a crystallite size of the order of 15nm and a surface roughness of 1.8nm. Laser Raman studies exhibited the LO phonon peaks of ZnSe. The films were found to possess a slight excess of Se as evident from the energy dispersive X-ray analysis measurements.

Chemical and electrochemical polymerisation of pyrrole on polyester textiles in presence of phosphotungstic acid

Polypyrrole (PPy) was chemically synthesised on polyester (PES) textiles to produce conducting textiles. Two different types of counter ion were employed: anthraquinone sulfonic acid (AQSA) and phosphotungstate (PW12O403-). Textiles covered with PPy were characterised by means of FTIR-ATR, SEM, EDX, cyclic voltammetry (CV), surface resistivity measurements and electrochemical impedance spectroscopy (EIS). Additionally, friction and washing assays were done to test the resistance of the layer of conducting polymer (PPy/PW12O403−). Electropolymerisation of PPy/PW12O403− in acetonitrile medium onto chemically synthesised PES–PPy/PW12O403− showed the improvement of the coating properties.

Determination of pyridoxine hydrochloride in pharmaceutical preparations by calixarene based potentiometric sensor

A simple, rapid and sensitive sensor for the assay of pyridoxine hydrochloride has been developed. The method is based upon the use of calix-8-arene as a neutral carrier in the presence of phosphotungstic acid as an ion extruder and di isooctyl phthalate as plasticizer. The sensor was found to have a short response time of 20 s to pyridoxine concentration. Perfectly Nernstian slope of 60.4 ± 3.1 mV/decade of activity between pH 3.0 and 7.2 for the monovalent pyridoxine hydrochloride over a wide concentration range of 1 × 10 −1 M to 6.2 × 10 −6 M was observed. The detection limit observed was 1.6 × 10 −6 M. The selectivity coefficients of the developed sensor indicated excellent selectivity for pyridoxine hydrochloride over a number of species, which normally accompany pyridoxine in various pharmaceutical formulations. The mediator o-nitrophenyl octyl ether significantly increased the lifetime of the sensor. The results obtained for pharmaceutical sample analysis using this sensor were satisfactory with excellent recovery percentage comparable and sometimes even better than the ones obtained by other routine methods for the assay.

Effects of solvent on microstructure and proton conductivity of organic–inorganic hybrid membranes

Effects of solvent on the microscopic structure and proton conductivity of organic–inorganic hybrids containing heteropolyacid are reported. The organic–inorganic hybrids were prepared by sol–gel synthesis of 1,8-bis(triethoxysilyl)octane (TES-Oct) in the presence of phosphotungstic acid (PWA). The proton conductivity of the membranes prepared under different solvents exhibited greater values in the order methanol<1-butanol<2-propanol<ethanol<1-propanol<2-butanol. The conductivity strongly correlated to the amount of incorporated PWA in the membranes, which was determined by titration of the solutions containing PWA leaked from the membrane. Small-angle X-ray scattering (SAXS), atomic force microscopy (AFM) and thermogravimetric analysis (TGA) were employed to reveal the relationship between the proton conductivity and microscopic structure of the TES-Oct/PWA membranes. It was found that there is an optimal condition for the formation of the condensed domain structure, indicating the important role of the structures in the membrane conductivity.

Studies on Microscopic Structure of Sol−Gel Derived Nanohybrids Containing Heteropolyacid

The microscopic structure of organic−inorganic hybrid membranes containing heteropolyacid has been investigated by atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and Fourier transform infrared spectroscopy (FT-IR). The hybrids were prepared by hydrolysis and condensation reactions, the so-called sol−gel reaction of 1,8-bis(triethoxysilyl)octane (TES-Oct) in the presence of phosphotungstic acid (PWA) with hydrated water. The characteristic lengths evaluated by using AFM and SAXS revealed the evolution of the domain structures upon increasing PWA concentration. Thermogravimetric analysis (TGA) indicated that increasing PWA concentration led to remarkable increase in the characteristic temperature for a weight loss. By combination of analysis using TGA and FT-IR, it was found that highly condensed domains were disintegrated, leading to the formation of loose networks with defect structures in the vicinity of the characteristic temperature. Correspondingly, the organic bridge was further broken. Variation of the characteristic temperature with the PWA concentration was strongly correlated to the evolution of the interdomain distance and the surface characteristic length scales, which were respectively observed by SAXS and AFM. Such a well-developed ionic domain structure offered fairly good performance of the proton conductivity in range 10-4 to 10-2 (S/cm) in spite of the rigid matrix of the sol−gel network.

DLS and AFM Studies on the Cluster Evolution of Organically Modified Silica Gels Catalyzed by a Super Strong Acid

Time evolution of cross-linking clusters prepared by the sol−gel method was investigated by dynamic light scattering (DLS) and atomic force microscopy (AFM). The samples were prepared by the sol−gel synthesis of 1,8-bis(triethoxysilyl)octane (Tes-Oct) in the presence of phosphotungstic acid (PWA) as a super strong acid. The reaction batches were quenched at various reaction times, followed by dilution with a large amount of the solvent. DLS and AFM techniques simultaneously revealed that there exists a maximum cluster size, Rh and rAFM, respectively, for a specific PWA concentration. The information on the clusters density, ρcluster = (rAFM/Rh)3, generated during the reaction process was obtained by systematically comparing the DLS data obtained in the swollen state to the AFM data measured in the shrunken state of the cross-linked clusters. It was found that not only the cluster size but also ρcluster exhibited a maximum for [PWA]/[Tes-Oct] = 0.10 near the gel point of the Tes-Oct clusters. Since PWA is ...