Efficient homogeneous catalysis of heteropoly acid and its characterization through etherifications of alcohol

A Keggin-type heteropoly acid revealed high catalytic activity for the etherification such as diethylene glycol with ethanol and cyclization of diethylene glycol in the homogeneous liquid. The catalytic activities of the heteropoly acid were much higher than those of conventional acid catalysts such as sulfuric acid, p-toluene sulfonic acid and phosphorous acid at the same catalyst concentrations or the same proton concentrations. On the basis of comparative measurement of electrical conductivity, acidity, and softness of anion for the solutions of acid catalysts, the efficient acid catalysis by heteropoly acid was suggested to due to be the specific properties of the heteropoly anion, which can be characterized by very weak basicity and great softness, together with the large size of the polyhedral structure.     

杂多酸在活性炭表面含氧基团上的化学键合作用

杂多酸作为一种新型多功能催化剂，近年来匕成为催化领域的研究热点之一［’l杂多酸在均相对许多反应表现出优异催化性能，正逐步为工业催化过程所采用问．较早的研究表明，吸附在活性炭上的杂多酸可部分牢固地存留干其表面不被溶脱，并可保持一定的催化活性＊．关干活性炭表面上杂多酸吸附作用的本质，一直没有明确的结论．本文通过吸附在活性炭表面和溶于含氧有机溶剂中杂多酸的光谱特征，探讨活性炭表面上杂多酸吸附的化学键合作用．1实验部分（且）药品：杂多酸均为市售商品，未经任何处理，直接使用．硅钨酸分子式为儿出风。0。。‘24…     

杂多酸对二甘醇脱水环化反应的催化作用

研究了杂多酸对二甘醇脱水环化的催化作用。结果表明,磷钨酸,硅钨酸,硅钼酸具有较高的催化活性,而磷钼酸的催化活性较低。采用ＴＧ,ＩＲ,ＧＣ－ＭＳ,电导等测试技术,对正丁胺酸性,杂多阴离子碱度,还原特性的测定及对产物结构的分析。     

钨钼杂多酸及其盐与二甲基亚砜加合物的制备和性质研究

在乙腈和水的混合溶剂中制备了9种钨钼杂多酸和杂多酸盐的二甲基亚砜加合物。研究结果表明,加合物中杂阴离子的Keggin结构基本不变。配体DMSO以S=O键上的氧作为配位原子,它不直接与杂阴离子骨架结构发生配位作用,而是与杂多酸中的质子氢或杂多酸盐中的金属阳离子以氢键或配位键相配位,生成的质子(钅羊)离子和金属配离子再通过离子缔合键与杂阴离子相结合,形成杂多酸或杂多酸盐加合物。     

Selective Recognition of Calcium Ion through Liquid Membrane

The mole transport rate of alkaline earth metal ions through a bulk liquid membrane and a supported liquid membrane using a series of proton diionizable acyclic polyethers was measured. Among alkaline earth metal ions, the calcium ion was observed to be selectively transported in both single and competitive transport experiments. Potentiometric titration and solution calorimetric titration also gave calcium selectivity over other alkaline earth metal ions. Acyclic polyether bearing a diethylene glycol unit andn-tetradecyl lipophilic chain at the α position of carboxylic acid affords the best selectivity for the calcium ion in bulk and supported liquid membranes.     

Change in permselectivity between sulfate and chloride ions through anion exchange membrane with hydrophilicity of the membrane

The transport number of sulfate ions relative to chloride ions through an anion exchange membrane was measured by electrodialyzing a sodium sulfate and sodium chloride mixed solution containing diethylene glycol after immersing the membrane in diethylene glycol because the membrane had good affinity to ethylene glycol and diethylene glycol. The transport number of sulfate ions relative to chloride ions increased in the presence of diethylene glycol in the membrane. This is due to the increase in the uptake of sulfate ions in the membrane compared with chloride ions, not to the change in a ratio of mobilities of both anions.     

Catalysis of heteropoly acidic salts for synthesis of diethylene glycol ethyl ether with diethylene glycol and ethanol

Ag₃PW₁₂O₄₀ and Ag₄SiW₁₂O₄₀ showed high activity and stability in the synthesis of diethylene glycol ethyl ether with diethylene glycol and ethanol, on which the conversion is 80.2% and 78.4%, respectively, and the selectivity of diethylene glycol ether is 75.4% and 80.6%, respectively. After the third reaction cycle, Ag₃PW₁₂O₄₀ and Ag₄SiW₁₂O₄₀) still showed higher activity and selectivity, on which the conversion is 72. 6% and 77.5% respectively. But the activity of Ag₃PMo₁₂O₄₀ is lower, the conversion is only 21.0%. IR, XRD, TG and n‐butylamine titrimetry showed that the catalysis may be connected with two kinds of acidic centers owned by heteropoly acidic salt.     

Highly active and reusable catalyst for fries rearrangement of phenyl acetate

Silica-12-tungstophosphoric acid core-shell nanoparticles were prepared by sol-gel method followed by steaming. The catalytic activity of fresh and steamed catalysts was studied in Fries rearrangement of phenyl acetate. The reaction parameters, such as catalyst loading and reaction temperature, were optimized. The structural properties of the prepared catalysts were analyzed by X-ray diffraction and transmission electron microscopy techniques. The nature and strength of acid sites in the catalysts were analyzed by pyridine adsorption followed by infrared spectroscopy and differential scanning calorimetry measurements. The XRD and TEM analyses confirm the formation of silica-12-tungstophosphoric acid core-shell nanoparticles during steaming process. Acidity measurement indicates that both fresh and steamed catalyst samples carry weak acid sites and Brøsted acid sites. In addition, the steaming of heteropoly acid contained silica enhances the strength of Brøsted acid sites. The catalytic activity of fresh as well as steamed catalysts in liquid-phase Fries rearrangement showed that the steam treated sample exhibits higher conversion and selectivity to the desired product compared to the fresh catalyst sample. The higher activity of steam treated catalysts has been explained in terms of surface acidity of the catalysts. Reusability of the steamed catalyst shows that there is no appreciable change either in the conversion rate or product selectivity.     

New network copolymers of 1-vinyl-1,2,4-triazole as efficient sorbents of mercury

The possibility of preparing copolymers by radical copolymerization of 1-vinyl-1,2,4-triazole with divinyl sulfide and divinyl diethylene glycol ether in the bulk was examined. The sorption characteristics of the new cross-linked copolymers with respect to mercury(II) ions under static conditions in acid solutions were studied.     

Determination of Arsenic(V) as a Heteropoly Acid after Its Adsorption on a Fibrous Anion Exchanger

The conditions were found for determining arsenic(V) as a heteropoly acid after its adsorption on a fibrous anion exchanger. A blue form of a molybdoarsenic heteropoly acid formed on the adsorbent at any order of the adsorption of the reactants; however, the sensitivity of determination was higher if arsenic was adsorbed first. A detection limit of 4 ng/mL was attained using adsorption from a 100-mL portion of a test solution. The sensitivity and selectivity of the proposed method are significantly higher than those of known methods because of the preconcentration of arsenate ions on an anion exchanger as a heteropoly acid followed by the direct determination of the heteropoly acid in the solid phase.     

Dielectric losses and proton conductivity of polyantimonic acid membranes

Composite membranes consisting of polyvinyl alcohol and disperse particles of polyantimonic acid with different ratios of components were studied. Processes related to the relaxation and proton transport in a heterogeneous system were considered. The proton transport in the membranes was shown to occur both within the particle (along the chains of alternating wcapacitorater molecules and oxonium ions), forming macrodipoles, and in the intercrystallite space in the polymer matrix. The relaxation was described by the two-layer Maxwell–Wagner capacitor with an effective relaxation time. The relaxation activation energy obtained from the dielectric loss data coincided with the proton conductivity activation energy in the frequency-independent region, which points to the same nature of ion transport.     

Formation of diethylene glycol as a side reaction during production of polyethylene terephthalate

Polymers of poly(ethylene terephthalate) (PET) always contain a certain amount of incorporated diethylene glycol (DEG), substituting the incorporated glycol. DEG is formed in a side reaction during the ester interchange of dimethyl terephthalate (DMT) with ethylene glycol or during direct esterification of terephthalic acid with ethylene glycol, and to a smaller extent during the polycondensation of the low-molecular material. DEG is formed via an unusual type of reaction: ester + alcohol → ether + acid. Some evidence of this type of reaction is given by the formation of dioxane in low molecular PET and of methyl Cellosolve and methyl carbitol during the ester interchange of DMT with ethylene glycol and diethylene glycol, respectively. The strongest support for this type of reaction, however, was obtained from kinetic data. Polyesters of low molecular weight with OH group contents ranging from 3 to 0.5 mole/kg were heated at 270°C in sealed tubes for 1–7 hr. The kinetic equation for the proposed reaction is: d[DEG]/dt = k[OH] [ester]. With the aid of one rate constant the formation of DEG in all esters could be described.     

Transport Selectivity of a Diethylene Glycol Dimethacrylate- Based Thymine-imprinted Polymeric Membrane over a Cellulose Support for Nucleic Acid Bases

The binding mechanism between 9-vinyladenine and pyrimidine base thymine in methanol was studied with UV-visible spectrophotometric method. Based on this study, using thymine as a template molecule, 9-vinyladenine as a novel functional monomer and diethylene glycol dimethacrylate as a new cross-linker, a specific diethylene glycol dimethacrylate-based molecularly imprinted polymeric membrane was prepared over a cellulose support. Then, the resultantly polymeric membrane morphologies were visualized with scanning electron microscopy and its permselectivity was examined using thymine, uracil, cytosine, adenine and guanine as substrates. This result showed that the imprinting polymeric membrane prepared with diethylene glycol dimethacrylate exhibited higher transport capacity for the template molecule thymine and its optimal analog uracil than other nucleic acid bases. The membrane also took on higher permselectivity than the imprinted membrane made with ethylene glycol dimethacrylate as a cross-linker. When a mixture including five nucleic acid bases thymine, uracil, cytosine, adenine and guanine passed through the diethylene glycol dimethacrylate-based thymine-imprinted polymeric membrane, recognition of the membrane for the template molecule thymine and its optimal analog uracil was demonstrated. It was predicted that the molecularly imprinted membrane prepared with diethylene glycol dimethacrylate as cross-linker might be applicable to thymine assay of absolute hydrolysates of DNA or uracil assay of absolute hydrolysates of RNA in biological samples because of its high selectivity for the template molecule thymine and its optimal analog uracil.     

Secondary and tertiary oxonium ions in the polymerization of 1,3-dioxolane initiated with HOSO2 CF3: 1H-NMR studies

In the polymerization of 1,3-dioxolane (DXL) initiated with trifluoromethanesulfonic acid (TFAc) the proton originated from acid [underlined in the scheme (1)] may form either the hydroxy end-group or the secondary oxonium ion: (1) where is a part of linear or cyclic macromolecule (or monomer). In ¹H-NMR spectra, due to the fast exchange, only one averaged signal of proton is observed, its chemical shift reflecting the relative concentration of both species. The chemical shift of proton, measured at different monomer and initiator concentrations changes, indicating that the proportion of macromolecules bearing OH end-groups increases with increasing [monomer]_o/[initiator]_o ratio. This observation is fully consistent with a mechanism, according to which secondary oxonium ions are formed by inter-or intramolecular reaction between growing species and OH end-groups of linear macromolecules.     

Bifunctional even-electron ions: 1—Fragmentation behaviour of ω-methoxy-, ω-hydroxy- and ω-chloro-oxonium ions

Bifunctional oxonium ions—generated from tertiary aliphatic alcohols containing an additional hydroxy, methoxy or chloro group at the end of an alkyl side-chain—do not markedly exhibit fragmentations typical of ordinary oxonium ions, but show as the main reactions those caused by functional group interaction, through-space interaction being the dominant factor. The main primary fragmentation is loss of the additional functional group X as HX, followed by loss of the side-chain originally separating the two functional groups, leading to carbonyl cations. This typical reaction sequence is initiated by proton migration from the oxonium moiety to the additional functional group. The reaction behaviour of the bifunctional ions is discussed. The lowest homologues show specific deviations from the general fragmentation behaviour.     

一缩二乙二醇二甲基丙烯酸酯接枝真丝的结构

通过电子扫描电镜 (SEM)、红外光谱 (IR)、双折射、X 射线衍射及氨基酸分析等手段 ,研究了真丝用一缩二乙二醇二甲基丙烯酸酯 (P 2 )接枝后其结构与接枝率之间的关系 .氨基酸分析结果表明P 2接枝主要在真丝大分子中酪氨酸、丝氨酸、组氨酸和精氨酸的NH2 、OH和—NH—活性基团上 .通过X 射线衍射分析 ,P 2接枝并不直接影响结晶区 ,但引起分子取向的下降 ,接枝后真丝双折射下降说明接枝后因大分子取向度下降 ,接枝真丝的红外光谱显示出真丝具有 β折迭结构和P 2高聚物的结构特征峰 ,从而说明P 2接枝在纤维的无定型区内部进行 .当接枝率大于 35 %时 ,纤维的表面覆盖了一层高聚物 (P 2 ) ,并且纤维的横截面表现出明显的分纤现象 ,接枝真丝的红外光谱表明了纤维与P 2重叠吸收峰 ,说明了P 2在丝纤维内部接枝聚合 .     

Spectrophotometric Evidence for the Formation of a Mixed Bismuth-Phosphorus Heteropoly Acid

Abstract

Spectrophotometric evidence is presented to show that bismuth interacts with phosphate and molybdate in acid solution to form a mixed bismuth-phosphorus heteropoly acid. The complex is similar to 12-molybdophosphoric acid by virtue of its degree of dissociation in both concentrated and dilute acid solutions. The complex is more stable than 12-molybdophosphoric acid because it is formed when bismuth is added to a solution of 12-molybdophosphoric acid. The proposed bismuth-phosphorus compound is reduced much more readily to a heteropoly blue than is 12-molybdophosphoric acid, a fact that has contributed to a false belief that the bismuth may have been acting catalytically in the reduction of 12-molybdophosphoric acid.     

Reactions of α-chloronitrones with unsaturated ethers

The Ag⁺ induced reaction of α-chloronitrones with unsaturated ethers goes in two parallel competitive directions. On the one hand cycloadducts like 3 are formed and on the other hand oxonium ions like 4. Formation of analogous oxonium compounds occurs also when α-alkoxynitrones are treated with Et₃O⁺BF₄^? in 1,2-dichloroethane. Formation of oxonium compounds with the enol-ethers is practically irreversible and leads to enol-ether fragmentation. With the saturated ethers compounds like 25 were formed and were used as a potential source of N-alkyl-N-vinyl-nitrosonium ions.     

Interpolymer complexes of copolymers of vinyl ether of diethylene glycol with poly(acrylic acid)

 The complex formation reactions of poly(vinyl ether of diethylene glycol) as well as vinyl ether of diethylene glycol–vinyl butyl ether copolymers with poly(acrylic acid) have been studied in aqueous and alcohol solutions. The formation of interpolymer complexes which were stabilized by hydrogen bonds was shown. The effects of molecular weight of poly(acrylic acid) and the nature of the nonionic polymer on the composition and stability of interpolymer complexes were clarified. The critical pH values of complexation were determined for different systems with various molecular weights and hydrophobic–hydrophilic balances. The stability of the interpolymer complexes formed in aqueous and alcohol solutions with respect to dimethylformamide addition was evaluated. The role of hydrophobic interactions and the presence of active groups on stability of the interpolymer complexes is discussed. Received: 23 July 2001 Accepted: 27 September 2001     

Self assembled 12-tungstophosphoric acid-silica mesoporous nanocomposites as proton exchange membranes for direct alcohol fuel cells

A highly ordered inorganic electrolyte based on 12-tungstophosphoric acid (H(3)PW(12)O(40), abbreviated as HPW or PWA)-silica mesoporous nanocomposite was synthesized through a facile one-step self-assembly between the positively charged silica precursor and negatively charged PW(12)O(40)(3-) species. The self-assembled HPW-silica nanocomposites were characterized by small-angle XRD, TEM, nitrogen adsorption-desorption isotherms, ion exchange capacity, proton conductivity and solid-state (31)P NMR. The results show that highly ordered and uniform nanoarrays with long-range order are formed when the HPW content in the nanocomposites is equal to or lower than 25 wt%. The mesoporous structures/textures were clearly presented, with nanochannels of 3.2-3.5 nm in diameter. The (31)P NMR results indicates that there are (≡SiOH(2)(+))(H(2)PW(12)O(40)(-)) species in the HPW-silica nanocomposites. A HPW-silica (25/75 w/o) nanocomposite gave an activation energy of 13.0 kJ mol(-1) and proton conductivity of 0.076 S cm(-1) at 100 °C and 100 RH%, and an activation energy of 26.1 kJ mol(-1) and proton conductivity of 0.05 S cm(-1) at 200 °C with no external humidification. A fuel cell based on a 165 μm thick HPW-silica nanocomposite membrane achieved a maximum power output of 128.5 and 112.0 mW cm(-2) for methanol and ethanol fuels, respectively, at 200 °C. The high proton conductivity and good performance demonstrate the excellent water retention capability and great potential of the highly ordered HPW-silica mesoporous nanocomposites as high-temperature proton exchange membranes for direct alcohol fuel cells (DAFCs).