Influence of the preparation history of α-Fe2O3 on its reactivity for hydrogen reduction

TG experiments on the hydrogen reduction of α-Fe₂O₃ were carried out to elucidate the influence of the preparation history of the oxide on its reactivity. α-Fe₂O₃ samples were prepared by the thermal decomposition of seven iron salts in a stream of oxygen, air or nitrogen at temperatures of 500–1200°C for 1 h. Thirteen metal ions such as Cu²⁺, Ni²⁺, etc. were used as doping agents. The reactivity of the oxide was indicated by the initial reduction temperature (T_i. α-Fe₂O₃ prepared at lower temperatures showed lower T_i values and the reduction proceeded stepwise (Fe₂O₃ → Fe₃O₄ → Fe). T_i values increased with the rise in the preparation temperature of the oxide. The oxides prepared at higher temperatures showed that two reduction steps (Fe₂O₃ → Fe₃O₄ → Fe) proceed simultaneously. the preparation in oxygen gave higher T_i than that in air or nitrogen. The doping by metal ions, except Ti⁴⁺, lowered the T_i of α-Fe₂O₃. The Cu²⁺ ion showed the lowest T_i, while Ti⁴⁺ showed the highest T_i and the inhibition effect.The reduction process was expressed by two equations; Avrami—Erofeev's equation for α-Fe₂O₃ → Fe₃O₄ and Mampel's equation for Fe₃O₄ → Fe.     

Cationic polymerization of vinyl compounds in the presence of tetra-n-butylammonium salts

The effects of salts were examined in cationic polymerization of vinyl compounds. Cationic polymerization of styrene was carried out at 0°C, with acetyl perchlorate, stannic chloride, stannic chloride–trichloroacetic acid and boron trifluoride etherate as catalysts. Tetra-n-butylammonium perchlorate, fluoroborate and iodide were used as salts. The presence of small amounts of the salts changed both the polymerization rate and the molecular weight of polymer considerably. The consideration of various effects led to the conclusion that the results are explicable principally on the basis of counterion exchange. To confirm this, the copolymerization of 2-chloroethyl vinyl ether with γ-methylstyrene was investigated at ?78°C. The copolymer composition curve when stannic chloride was used as catalyst was changed and coincided with that of polymer obtained with acetyl perchlorate catalysis when the perchlorate salt was added. This supports the concept of counterion exchange.     

Hairpin versus extended DNA binding of a substituted beta-alanine linked polyamide

A series of alpha-substituted beta-alanine (beta) linked polyamides (DbaPyPyPy-beta*-PyPyPy) were prepared and examined. This resulted in the observation that while most substituents disrupt DNA binding, (R)-alpha-methoxy-beta-alanine (beta((R)-OMe)) maintains strong binding affinity and preferentially adopts a hairpin versus extended binding mode, providing an alternative hairpin linker to gamma-aminobutyric acid (gamma). A generalized variant of a fluorescent intercalator displacement assay conducted on a series of hairpin deoxyoligonucleotides containing a systematically varied A/T-rich binding site size was developed to distinguish between the extended binding of the parent beta-alanine 1 (DbaPyPyPy-beta-PyPyPy) and the hairpin binding of 3 (DbaPyPyPy-beta((R)-OMe)-PyPyPy).     

Multi-component catalysts with spinel structure for the selective reduction of nitrogen oxide by ethylene in lean-exhaust gas streams

The Ga₂O₃-Al₂O₃-ZnO (GAZ) multi-component spinel powders with incorporated Cu²⁺, Co²⁺, Fe²⁺, Ni²⁺, Mn²⁺ and In²⁺ metal cations were synthesized by co-precipitation method from a mixed solution of nitrate salts. Spinel crystal structure of each composition was confirmed by XRD measurements. The multi-component oxide powders were tested in the reduction of nitrogen oxide (NO) under lean conditions. Among the catalysts tested, In₂O₃-containing GAZ with a pure spinel phase structure showed promising catalytic activity in the NO reduction in the presence of 10% H₂O vapor. In addition, the effect of H₂O vapor and SO₂ on the selective reduction of NO over In₂O₃-GAZ/cordierite and In₂O₃-GAZ/metal honeycombs catalysts has been investigated.     

Use of a nitrate-form anion exchange resin for the determination of traces of gold in copper and cadmium by neutron activation analysis

A method is described for the determination of traces of gold in copper and cadmium by neutron activation analysis, using anion exchange resin as a preconcentration agent: gold was separated from large amount of copper or cadmium with Cl-form Dowex 1X8 AG, 100–200 mesh, resin. To reduce the interfering activities, the resin was irradiated in NO ₃ ⁻ -form and washed with dilute hydrochloric acid after irradiation.¹⁹⁸Au in the resin was then counted with a Ge(Li) or NaI(Tl) detector. The chemical yields were more than 99%. The concentration factors of gold for copper and cadmium samples were 1.1×10⁸ and 2.7×10⁶, respectively. The analytical results of gold in 99.99% copper and 99.999% cadmium were 65 and 0.15 ppb, respectively. The blank was 0.05 ng Au per 200 mg of wet resin.     

Photochemische Reaktionen. 110. Mitteilung [1]. Zur Photochemie γ,δ-Methano-α-enone

Photochemistry of γ,δ-Methano-α-enones Direct excitation (λ = 254 or ≥ 347 nm) converts the γ,δ-methano-α-enone (E)- 10 into the isomeric ether 23 and the isomeric diene-ketone 24 . Furthermore, on ¹π,π*-excitation (λ = 254 nm) (E)- 10 undergoes an 1,3-homosigmatropic rearrangement yielding the enone (E)- 25 . In addition (E → Z)-isomerization of (E)- 10 and conversion of 10 to the isomeric furan 28 is observed. The isomerization (E)- 10 → 23 , 24 and (E)- 25 proceeds by photocleavage of the C(γ), C(δ)-bond, whereas the formation of 28 occurs by photocleavage the C(γ), C(δ)-bond together with that of the C(γ), C(δ′)-bond of 10 . On direct excitation the bicyclic diene-ether 23 yields the methano-enone 10 , the dieneketone 24 and the tricyclic ether 29 . Evidence is given, that the conversion 23 → 10 is a singulet process. On the other hand, the isomerization 23 → 24 and the intramolecular [2 + 2]-photocycloaddition 23 → 29 are shown to be triplet reactions. Irradiation (λ = 254 nm) of the homoconjugated ketone 24 yields the isomeric ketone 27 by an 1,3-acyl shift. The excitation of the (E)-enone 25 induces (E → Z)-isomerization and photoenolization to give the homoconjugated ketone 26 .     

Syntheses and Peculiar Behavior in Solutions of Optically Active Telluronium Salts

A diastereomeric (epimeric) mixture of ethylmethylphenyltelluronium (1S)-(+)-camphor-10-sulfonate (dia.-1) was optically resolved by fractional recrystallization into the diastereomerically pure isomers (R)(Te)-1 and (S)(Te)-1. The absolute configurations of the isomers were determined by the X-ray crystallographic analysis of (R)(Te)-1. Enantiomerically pure (R)-ethylmethylphenyltelluronium perchlorate, tetrafluoroborate, p-chlorobenzenesulfonate, bornane-10-sulfonate, tetraphenylborate, and picrylsulfonate (R)-2-7 were isolated, respectively, by anion-exchange reactions of diastereomerically pure (R)(Te)-1. The optically active telluronium salts were found to show peculiar optical properties on their specific rotations and circular dichroism spectra in solutions compared with those of the corresponding sulfonium and selenonium salts. On the basis of NMR studies, the behavior on the optical properties of the optically active telluronium salts was found to be caused by a strong solvation in polar solvents.     

One-pot sequential four-component coupling via Cp*RuCl-catalyzed cyclotrimerization and Suzuki-Miyaura coupling

The catalytic intermolecular cyclotrimerization of alkynylboronates, propargyl alcohols, and terminal alkynes was accomplished by means of the ruthenium catalysis and the temporary tethering approach with the C-B-O linkage to give rise to highly substituted arylboronates with excellent selectivity. The resultant arylboronates were further converted to highly substituted biaryls via the Suzuki-Miyaura coupling with various aryl iodides using Pd₂(dba)₃/PCy₃ as a catalyst precursor in aqueous toluene. As a consequence, the four-component coupling approach to highly substituted biaryls was successfully established by combining these two operations into a sequential one-pot process.     

Synthesis of enol and vinyl esters catalyzed by an iridium complex

Enol and vinyl esters were successfully synthesized by the use of an iridium complex as a catalyst. The reaction of carboxylic acids with terminal alkynes in the presence of catalytic amounts of [Ir(cod)Cl]₂ and Na₂CO₃ gave the corresponding 1-alkenyl esters. The addition of carboxylic acids to alkynes principally took place in the Markovnikov fashion. In addition, by the use of an Ir complex combined with NaOAc various vinyl esters were prepared through the transvinylation between carboxylic acids and vinyl acetate.     

Synthesis of vinylsilanes by palladium-catalyzed reaction of trimethylsilylallyl acetates with nucleophiles

Treatment of 1-trimethylsilylallyl and 3-trimethylsilylallyl acetates with nucleophiles (active methylene compounds and enamines) in the presence of a catalytic amount of Pd(PPh₃)₄ affords vinylsilane derivatives selectively.