A two-step route to synthesis of small-pored and thick-walled SBA-16-type mesoporous silica under mildly acidic conditions

Highly ordered SBA-16-type mesoporous silica materials were synthesized by using poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymer (EO(132)-PO(50)-EO(132), Pluronic F108) as template through a two-step pathway under mildly acidic conditions (pH 2.15-4.50). The highly ordered cage-like mesoporosity of the prepared SBA-16-type mesoporous silica materials having Im3m cubic mesostructure was proved by the well-defined X-ray diffraction patterns combined with transmission electron microscopy. Scanning electron microscopy shows a variation from the spherical agglomerations to the randomly shaped ones with an increase of pH value. The nitrogen adsorption-desorption analysis reveals that the prepared SBA-16-type mesoporous silica materials have a uniform small-sized pore diameter (3.37-4.24 nm) and very thick pore wall (8.84-10.2 nm). These features may make the SBA-16-type mesoporous silica materials synthesized in this study favor the incorporation of catalytically active heteroatoms in silica frameworks, and the functionalization of organic groups for applications in catalysis, sensor and separation. The two-step synthetic method under the mildly acidic conditions can also be extended to the production in the industrial scale as an environmentally friendly way.     

A new route to phenylenedimalononitrile and the analogues using palladium-catalyzed carbon-carbon bond formation

Phenylenedimalononitrile and the analogues, which are key intermediates in the synthesis of TCNQ and the analogues, are prepared directly by the Pd-catalyzed reaction of-diiodoarenes with malononitrile anion.     

The shortest synthetic route to puromycin analogues using a modified Robins approach

We are reporting on the utility of commercial vinyl isocyanate for a practical synthetic route from adenosine to N(6)-bis-demethylpuromycin in seven steps and 65% overall yield. A clean one-pot conversion of 3'-bromo-2'-carbamoyl derivative 8 to 3'-amino-3'-deoxyadenosine derivative 10 is the main feature of this synthetic pathway. This synthesis is the shortest synthetic route toward 3'-(aminoacylamido)deoxyadenosines to date.     

Investigation of a route to ibotenic acid analogues via a reduced pyroglutamate template

Two alternative "ring switch" based syntheses have been shown to give access to the reduced protected homochiral analogues, 27, 28 and 36, of the CNS active compound ibotenic acid.     

Aqueous dip-coating route to dense and porous silica thin films using silica nanocolloids with an aid of polyvinylpyrrolidone

An aqueous dip-coating route without using volatile alcohols for preparing dense and porous silica thin films is presented. The films were prepared by dip-coating on Si(100) and silica glass substrates using aqueous suspension of 8–11 nm colloidal silica where no alcohols were added. The addition of polyvinylpyrrolidone (PVP) in the suspension greatly improved the wettability, allowing homogeneous films to be formed on the substrates while the substrates showed poor wettability without PVP. When the as-deposited films were fired at 500–1,000 °C, optically transparent porous films with smooth surface were obtained. The porous films had homogeneous distribution and packing of silica nanoparticles, refractive indices of 1.24–1.33, and pencil hardness lower than 6B. The porous films underwent significant densification by viscous sintering when fired at temperatures over 1,000 °C. The viscous sintering was accompanied by the progress of condensation reaction and by the structural relaxation of siloxane network, which was revealed in the infrared absorption spectra. The resulting dense films had optical transparency, smooth surface, pencil hardness over 9H and refractive indices close to that of silica glass.     

A short and efficient route to novel scyphostatin analogues

[structure: see text]. Several novel scyphostatin analogues have been prepared in up to 18% yield over five steps from commercially available 4-bromoguaiacol, utilizing an organometallic addition to afford the desired syn-hydroxy-epoxides.     

New synthetic route to granulatimide and its structural analogues

The Stille coupling reaction of stannylindole 12 with 4-iodoimidazole 13 (or 24) in the presence of PdCl(2)(PPh(3))(2) gave the corresponding indole-imidazole coupling product 14 (or 25), thereby affording a new synthetic approach to the alkaloid granulatimide (7), isolated from the Brazilian ascidian Didemnum granulatum, as well as its structural analogues, 10-methylgranulatimide (23), 17-methylgranulatimide (30), 10,17-dimethylgranulatimide (31).     

Stereoselective alkylation of tartrate derivatives. A concise route to (+)-O-methylpiscidic acid and natural analogues

The lithium enolate of (2S,3S,5S,6S)-dimethoxy-2,3-dimethyl-1,4-dioxane-5,6-dithiocarboxylate undergoes stereoselective mono- and/or dialkylations to afford two new stereogenic centers. The alkylation products obtained possessed a cis stereochemistry, which was confirmed by the synthesis of natural 4'-O-methylpiscidic acid dimethyl ester .     

Standard enthalpy of formation of disodium hydrogen phosphate hexahydrate and sodium diphosphate

Commercial disodium hydrogen phosphate dodecahydrate (Na₂HPO₄·12H₂O) was used as a precursor for synthesizing disodium hydrogen phosphate hexahydrate (Na₂HPO₄·6H₂O) and sodium diphosphate (Na₄P₂O₇). The purity of the synthesized products was checked up by IR spectroscopy and X-ray diffraction. The heat of dissolution of these compounds, in acid solutions of several concentrations (w/w) of H₃PO₄ was measured in a C-80 SETARAM calorimeter. Many dilution and mixing processes were also realized in the calorimeter in order to get the standard enthalpy of formation of these products. The values obtained for the enthalpies of formation are: (?3210.5) and (?3516.5) kJ · mol^?1 for sodium diphosphate (Na₄P₂O₇) and disodium hydrogen phosphate hexahydrate (Na₂HPO₄·6H₂O), respectively.     

An eco-friendly route to magnetic silica microspheres and nanospheres

A green and inexpensive alternative to existing methods for the preparation of magnetic iron oxide/silica nanocomposite particles has been investigated. The use of water-in oil emulsions based on vegetable oils instead of usual solvents led to microsized or nanosized magnetic silica spheres exhibiting similar characteristics to those of classical procedures. Furthermore this approach is very general since a large class of porous magnetic colloids differing in size or iron oxide fraction has been obtained. This work emphasizes the importance of the level of the shearing during the emulsification step with regard to the size and monodispersity of the prepared beads. All the materials prepared were fully characterized (SEM and TEM microscopies, SQUID magnetometry, N(2) sorption volumetry, etc.). In addition, samples functionalized by thiol groups have been synthesized and successfully tested for the removal of heavy metals in water-treatment.     

Synthesis of alpha-fluorinated phosphonates from alpha-fluorovinylphosphonates: a new route to analogues of lysophosphatidic acid

A versatile, efficient method for the preparation of alpha-monofluoromethylene (-CHF-) phosphonates from alpha-fluorovinylphosphonate provides access to a class of lysophosphatidic acid (LPA) receptor-subtype agonists. In addition, sn-2 O-methylation of alpha-monofluoromethylene phosphonates using trimethylsilyldiazomethane generated sn-1-acyl, 2-O-methyl alpha-monofluoromethylene derivatives. Finally, a novel method for the selective etherification of 1,2-diols was developed and a new class of sn-1 O-methyl, 2-acyl alpha-monofluoromethylene LPA analogues was prepared. [reaction: see text]     

Production of fumaric acid using rice bran and subsequent conversion to succinic acid through a two-step process

The fungal production of fumaric acid using rice bran and subsequent bacterial conversion of succinic acid using fungal culture broth were investigated. Since the rice bran contains abundant proteins, amino acids, vitamins, and minerals, it is suitable material that fungi use as a nitrogen source. The effective concentration of rice bran to produce fumaric acid was 5 g/L. A large amount of rice bran caused excessive fungal growth rather than enhance fumaric acid production. In addition, we could produce fumaric acid without the addition of zinc and iron. Fungal culture broth containing appro × 25 g/L of fumaric acid was directly employed for succinic acid conversion. The amount of glycerol and yeast extract required for succinic acid conversion was reduced to 70 and 30%, respectively, compared with the amounts cited in previous studies.     

Stereoselective expoxidation of allylic and homoallylic alcohols with 30% hydrogen peroxide catalyzed by tungstic acid in buffered media

The aqueous tungstic acid-catalyzed hydrogen peroxide epoxidation of allylic alcohols affords the same major diastereoisomer as the VO(acac)₂/tBuOOH system with quite comparable stereoselectivities. In contrast, epoxidation of homoallylic alcohols appears to be much less stereoselective.     

Equations for calculation of the pH of buffer solutions containing sodium or potassium dihydrogen phosphate, sodium hydrogen phosphate, and sodium chloride at 25°C

Published thermodynamic data measured in aqueous mixtures of sodium or potassium dihydrogen phosphate with hydrogen phosphate and chloride at 25°C were used to test recently developed methods for calculation of the pH of phosphate buffer solutions. Equations for ionic activity coefficients are used in these methods. It is shown that all data used in the tests up to an ionic strength of about 0.5 mol-kg^-1 can be accurately predicted by the two methods recommended. In one of these methods, equations of the Hückel type are used for ionic activity coefficients and in the other equations of the Pitzer type. Several sets of phosphate buffer solutions are recommended,e.g., for calibrations of glass electrode cells. In the recommended sets, the pH of the buffer solutions can be calculated either by the Hückel or Pitzer method, and the pH predictions of these methods agree in most cases within 0.005 at least up to ionic strengths of about 0.2 mol-kg^-1. The pH values of the two primary pH standards endorsed by IUPAC based on aqueous mixtures of KH₂PO₄ and Na₂HPO₄,i.e., pH values of 6.865 and 7.413, can also be accurately predicted by the equations recommended in this study.     

Preparation of sodium borosilicates using sodium silicate and boric acid

The gelling behaviour of an aqueous sodium silicate solution with boric acid was investigated for different initial compositions and solid sodium borosilicate samples were obtained by drying the gels at 100°C, 225°C and 450°C. The chemical composition, dissolution, pH, loose-packed bulk density, B.E.T. surface area, moisture, size distribution and XRD/IR patterns of the sodium borosilicate particles were determined. The minimum gelling times were observed at pH values between 9–10 and although no gels were obtained using HCl at pH = 11, the silicate solution was gelled with boric acid suggesting borate ions promote the formation of siloxane network and behave as a crosslinking agent.     

Water/silica nanoparticle interfacial kinetics of sulfate, hydrogen phosphate, and dithiocyanate radicals

The values of the rate constants for the reactions of the sulfate (2.5 x 10(9) M(-1) s(-1)) and hydrogen phosphate (2.2 x 10(8) M(-1) s(-1)) radicals with silica nanoparticles are obtained by flash photolysis experiments with silica suspensions containing S(2)O(8)(2-) or P(2)O(8)(4-), respectively. The interaction of these radicals with the silica nanoparticles leads to formation of transients, probably adsorbed sulfate and hydrogen phosphate radicals, with absorption maxima at around 320 and 350 nm, respectively. A different mechanism takes place for the interaction of the less oxidizing dithiocyanate radicals with the silica nanoparticles. These radicals selectively react with the dissociated silanol groups of the nanoparticles with a rate constant at 298.2K of 7 x 10(7) M(-1) s(-1) (per mol of SiO(-) groups), and there is no evidence for their adsorption at the surface. All the results are discussed in terms of the Smoluchowski equation and redox potential of the inorganic radicals.     

Rotational diffusion of tungstic acid colloids in microgravity studied by free-fall experiments. Effects of sodium chloride and ethyl alcohol

Rotational relaxation times (τ) of anisotropic tungstic acid colloids in aqueous suspension containing sodium chloride or ethyl alcohol are studied in microgravity achieved by free-fall experiments. Experimental errors at 0 G, in many cases, are small compared with those at 1 G, which is ascribed to the lack of the convection of suspension in microgravity. Much more reliable data of the diffusion coefficients are obtained in microgravity. The limiting slopes of the relaxation curves in the plots of the transmitted-light intensity against time at 1 G depend on the flow direction of the suspension in the flow cell, whereas those at 0 G are close to zero irrespective of the flow direction. Sodium chloride decreases τ, whereas ethanol addition increases this time. These effects are ascribed to the thinning of the electrical double layers and to the increase in the suspension viscosity. Received: 5 July 2000 Accepted: 21 September 2000     

Thermoanalytical investigation of mixtures containing oxalic acid,sodium hydrogen oxalate and sodium oxalate

The ternary system containing H₂C₂O₄ · 2H₂O, NaHC₂O₄ · and Na₂C₂O₄ was investigated. It was ascertained that the termal curves of the mixtures were not the algebraic sums of their component curves. All thermal decomposition stages were interpreted and the means of performing qualitative and quantitative analyses in the system were given.

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Zusammenfassung Das H₂C₂O₄ · 2 H₂O, NaHC₂O₄ · H₂O und Na₂C₂O₄ enthaltende ternäre System wurde untersucht. Es wurde festgestellt, daß die thermischen Kurven der Gemische nicht den algebraischen Summen ihrer Komponentenkurven entsprachen. Sämtliche Stufen der thermischen Zersetzung wurden zugeordnet und die Möglichkeiten der Durchführung qualitativer und quantitativer Analysen im System angegeben.

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Résumé On a étudié le système ternaire contenant H₂C₂O₄ · 2H₂O, NaHC₂O₄ · H₂O et Na₂C₂O₄. On a établi que les courbes thermiques des mélanges ne correspondaient pas à la somme algébrique de leurs courbes composantes. On a interprété toutes les étapes de la décomposition thermique et donné les moyens d'effectuer des analyses qualitatives et quantitatives du système.

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, ₂₂₄. 2₂, NaHC₂O₄. ₂ Na₂C₂O₄. , . .

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The authors thank Mr E. Chromiak for the preparation of sodium hydrogen oxalate monohydrate, and Mrs Z. Wietrzyska-Lalak for her help in X-ray analysis.