Catalysts for enantioselective Biginelli reaction based on the composite silica-zirconia xerogels prepared using different zirconium sources

The composite silica-zirconia xerogels have been prepared via sol–gel method using zirconium oxychloride, oxynitrate, acetate and sodium silicate as the precursors. The prepared materials have been characterized using FTIR, TG/DTA, EDX and surface area analyses. It has been established that surface area of silica-zirconia xerogels significantly depends on the zirconium source, but phase transitions and structural features of the xerogels seem to be unaffected by the choice of the zirconia precursor. Prepared xerogels increase the activity of chiral inductor in the asymmetric Biginelli reaction. The anion of the zirconium salt adsorbed on the surface of the synthesized material and the presence of Si–O–Zr heterolinkages determines the reaction yield. The highest chemo- and enantioselectivity towards formation of ee isomer have been provided by the catalyst prepared from zirconium oxychloride.     

Effect of the Preparation Conditions on the Phase Composition and Texture of Mesoporous Zirconium Dioxide

Changes in the phase composition and textures of zirconium dioxide depending on the composition of the reaction medium and the conditions of the subsequent hydrothemal and thermal treatment have been elucidated. The conditions for preparing uniformly mesoporous zirconium dioxide with pore sizes of 50-64 have been determined. It has been established that treatment of zirconium dioxide hydrogel in alkaline solutions facilitates the formation of nano-sized particles, stable to agglutination.     

Interaction of Ytterbium Trifluoride with Zirconium in a NaF-ZrF4 Molten Mixture

The interaction of ytterbium trifluoride with zirconium in a molten mixture of sodium and zirconium fluorides have been studied by differential thermal analysis, X-ray diffraction, and electronic and IR spectroscopy. In the temperature range 440–640°C, zirconium reduces YbF₃ to ytterbium. The reaction products also contain low-valence zirconium and ytterbium compounds.     

Sorption studies of strontium on hydrous zirconium dioxide

Summary Hydrous zirconium dioxide was prepared to study the sorption behavior and the removal of strontium from radioactive waste solutions. The hydrous zirconium dioxide were identified and characterized. The parameters affecting the strontium adsorption were investigated. Sorption data have been interpreted in terms of Langmuir equations. Thermodynamic parameters for the sorption system have been determined at 303, 313, 323 and 333 K temperatures. The values ofDH°=102.30 kJ/mol andDG°=-26.03 kJ/mol at 313 K prove that the sorption of strontium on hydrous zirconium oxide is an endothermic and a spontaneous process.     

Mandelic acid and halogen-substituted mandelic acids as reagents for the determination of zirconium

o-, m-, and p-Fluoro- and -trifluoromethylmandelic acids have been prepared and an assessment made of their value as précipitants for zirconium. Though the p-derivatives are satisfactory there are no obvious advantages in their use. Direct weighings of zirconium mandelate and p-bromomandelate, about which there have been conflicting reports in the literature, have been investigated also. P-Bromomandelic acid has been used successfully for the determination of amounts of zirconium oxide between 3 and 50 mg per 100 ml but ignition of the precipitate to zirconium oxide is necessary. Of the acids examined, mandelic itself gives the only precipitate which is almost constant and stoichiometric in composition. The composition of this compound, however, varies slightly with the amount of zirconium present in the solution under test, and though an overall empirical factor can be applied its use is recommended only if a high order of accuracy is not required. If a series of determinations in a narrow range is to be carried out by direct weighing of zirconium mandelate, more accurate results might be obtained by determination of the appropriate factor for that range.     

Study of Sorption Properties of Amorphous Zirconium Phosphate

Amorphous zirconium phosphate ion-exchanger has been prepared in our laboratory according to the procedure given by Gal and Gal. The Chemical composition has been determined. Some chemical properties; stabilities and sorption of mono- to hexavalent cations have been studied in detail. It was found that washing the zirconium phosphate ion exchanger with alcohol before drying would increase the exchange capacity of amorphous zirconium phosphate.     

137Cs sorption on granular inorganic ion-exchangers based on titanium and zirconium hydroxophosphates

We have studied the sorption properties of some granular inorganic ion-exchangers synthesized by gel technology, such as titanium and zirconium hydroxophosphates (THP, ZHP), titanium and zirconium molybdophosphates and titanium and zirconium phosphate-ferrocyanides. A high selectivity of THP and ZHP modified with ferrocyanide and molybdate ions to¹³⁷Cs has been found. The possibility of applying inorganic sorbents for the purification of cesium-137 contaminated foodstuff is illustrated on the examples of fish treatment.     

Trace determination of zirconium using charged particle activation

Reaction yields on thick zirconium targets with proton, deuteron,³He and⁴He activation have been measured and compared. The most favorable reaction combining high sensitivity and selectivity was found to be Zr(p, xn)⁹⁰Nb. The absolute cross-section for this excitation function has been measured for proton energies up to 20 MeV. Analytical applications are illustrated with nondestructive zirconium analyses in glass. Yields from the thick target experiments indicate that the detection limit for this zirconium analysis method is ～1 ppb.     

Determination of zirconium and hafnium with xylenol orange and methylthymol blue

Both Xylenol Orange and Methylthymol Blue are highly selective and sensitive reagents for zirconium and hafnium forming intensely red complexes in an acidic medium. The factors affecting the color formation have been studied. The properties of the complexes have been determined and compared. In general, zirconium forms a more stable complex with the two dyes than hafnium, and Xylenol Orange forms a stronger complex with either zirconium or hafnium than Methylthymol Blue. Hydrogen peroxide can completely mask the zirconium complexes of either dye but only slightly affects the hafnium complex of Xylenol Orange. Zirconium and hafnium can both be determined without separation using peroxide as a masking agent and sulfate as a demasking agent. A bleaching reaction was observed when small amounts of hafnium were added to the red zirconium complex of Methylthymol Blue in 2.4 N perchloric acid or a small amount of zirconium was added to the red hafnium complex of Methylthymol Blue solution at pH 2 to 3.     

金属有机化合物的分析(Ⅴ)——双(烷基环戊二烯基)二卤化钛、锆、铪的纸色谱与核磁共振谱关系的研究

文献报导,仅Subbotina,A.I.等用纸色谱法研究了Cp₂TiCl₂与CpTiCl₅二化合物的分离。我们试图用薄层色谱法分离双(烷基环戊二烯基)二卤化钛、锆、铪化合物,未获成功。改用纸色谱法,取得良好的效果,并对各类化合物所得R_f值与它们的核磁共振谱的δ值之间的变化关系作了研究。     

Sorption-spectroscopy determination of zirconium on a PANV-KU-2 fibrous ion exchanger using Arsenazo III

The sorption and complexation of zirconium with Arsenazo III have been studied on a polyacry-lonitrile fibrous material filled with strongly acidic KU-2 cation exchanger in strongly acidic media. The optimal conditions have been chosen for the sorption-spectrophotometric and test determination of zirconium by diffuse reflection spectroscopy or visual testing. The limit of zirconium detection is 0.02 ??g/mL. The procedure was tested in the analysis of model solutions of ammonium molybdate and vanadate and copper chloride using the standard addition method.     

New Ti?PTMO and Zr?PTMO ceramer hybrid materials prepared by the sol gel method: Synthesis and characterization

New transparent flexible hybrid network “ceramer” materials have been synthesized by incorporating triethoxysilane capped polytetramethylene oxide with highly reactive titanium isopropoxide or zirconium n-propoxide without adding chelating agents. Both of these types of ceramer materials display high transparency while the zirconium systems show considerable transparency in the UV region. The titanium systems exhibit higher refractive index than the corresponding zirconium materials of equal alkoxide content.     

The foam separation of zirconium(IV) from aqueous solutions

Summary The foam separation of zirconium(IV) from chloride solutions has been investigated over the 1.8–12 pH range using sodium lauryl sulphate or cetyl(trimethyl)ammonium bromide as collectors. The effects of gas flow rate, bubbling time, collector and zirconium(IV) concentrations, ageing of the metal ion, and ionic strength have been studied and the results are discussed in relation to the hydrolytic behaviour of zirconium(IV). Under optimum conditions,ca. 99.5% removal can be achieved.     

Simultaneous determination of hafnium and zirconium in low grade uranium ores using INAA

A non-destructive neutron activation analysis technique has been developed for the determination of hafnium and zirconium in low grade uranium ores. In order to calculate the fission contribution of²³⁵U, thermal neutron absorption cross-section /_a/ for⁹⁴Zr has been determined. The study shows that 1 g of uranium produces the same activity as from 10.03 g of zirconium. Based on this fact, the degree of interferences have been calculated for each sample and the necessary corrections have been applied. The values have been compared with the reported IAEA and NBS values.     

New process to control hydrolysis step during sol-gel preparation of sulfated zirconia catalysts

Sulfated zirconia catalysts were prepared by sol-gel process using a new method allowing the control of the hydrolysis step of zirconium alkoxides. Prepared samples were characterized by N₂ adsorption (desorption) at 77 K, XRD, chemical analysis of total sulfur and XPS. Catalytic properties have been evaluated in n-butane and n-hexane isomerization reactions. Obtained results show that time necessary for gelation is significant and depends considerably on the nature of the zirconium precursor. Concerning the properties of the solids obtained by this method, it has been noted that the use of the zirconium propoxide led to a better retention of the sulfate species, which improves activity during isomerization reactions. It has been found also that an initial S/Zr molar ratio equal to 0.5 allowed to obtain an optimal sulfur content and a high specific surface area.     

Olefin isomerisation versus hydrozirconation: a case of a stable beta-hydrogen-containing Zr-alkyl derivative

Details of the olefin isomerisation mechanism followed by monohydride constrained-geometry zirconium complexes have been clarified using the allyldimethylsilylcyclopentadienyl zirconium hydride model compound. DFT calculations on the model systems agree with the experimental results.     

Sur la thermogravimétrie des précipités analytiques : Dosage du zirconium

With the help of the chevenard thermobalance, the authors have traced and examined the thermolysis curves of the precipitates proposed for the determination of zirconium. The methods in which picric acid, potassium iodate, ammonium arsenate and oxine are used, have been rejected; those in which ammonia, aniline, diethylaniline and in particular mandelic acid are used, are recommended for the automatic determination of zirconium. Zirconium hydroxide can be prepared in a pure state by means of aniline, while various other reagents smoothly afford zirconyl hydroxide. The problem of reduction of zirconium by pyrolysis of its arsenic(V) derivatives has been posed but not solved.     

Oxygen solubility in liquid nickel containing zirconium

The solubility of oxygen in liquid nickel containing zirconium at 1873 K has been experimentally studied for the first time. It has been shown that zirconium is a rather strong deoxidizing agent in liquid nickel. The equilibrium constant of the reaction of zirconium and oxygen dissolved in liquid nickel (logK_(1)(Ni) =–6.788), the interaction parameters characterizing these solutions (e_Zr(Ni)^O =–2.01; e_O(Ni)^Zr =–0.35; e_Zr(Ni)^Zr = 0.24), and the activity coefficient of zirconium in nickel at infinite dilution (γ_Zr(Ni)^o = 1.03 × 10^–8) have been determined. The zirconium content at the minimum of the oxygen solubility curve and the corresponding oxygen concentration have been determined.     

The determination of zirconium and aluminium in alloys slags and fumes by 14-mev neutron activation analysis

Aluminium and zirconium have beendetermined in alloys, slags and fumes by 14-MeV neutron activation analysis. Nuclear reactions with zirconium have been investigated, and the radioisotopes produced by 14-MeV neutron activation have been determined. The results for alloys and slags agree well with those obtained by chemical methods; precisions of 1.8% were obtained in ideal cases. The neutron activation method is capable of analysing 10–12 samples, in duplicate, per man-day.     

Direct determination of zirconium and chromium by first-derivative spectrophotometry

The solution properties of zirconium complex with the Schiff's base 2-(2-pyridylmethyl-eneamino)phenol have been studied by zero-order absorption spectrophotometry. The influence of pH, stability of the complexes with time and stability constants were investigated. The use of first-derivative spectrometry eliminates the interference of chromium and enables the simultaneous determination of zirconium and chromium without previous separation. The relative overall standard errors, of five independent simultaneous determinations of zirconium and chromium at the 1.0 μg/ml concentration level, were 2 and 4%, respectively. The proposed method has been successfully applied to the analysis of some real samples of zirconium/chromium bronzes.