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981.
The catalytic action of acid solutions involves an equilibrium step in the formation of a reactive complex of reactant molecules with catalyst entities. The relative concentrations of these complexes are determined by using thermodynamic parameters (acidity functions and activities of catalyst components). Data on the structure of complexes with strong H-bonds can be obtained from the vibrational spectra of these species. These data are required for establishing the mechanisms of catalytic reactions and for predicting the catalytic properties of acid solutions containing these complexes. 相似文献
982.
Amorphous precursors for PbZrO3 and PbTiO3 ceramics were prepared from lead acetate and the transition metaln-propoxide inn-propanol orn-butoxide inn-butanol and hydrolysed with an excess of water.
According to GLC and TGA/EGA analyses, the type of alkoxide group influences distinctly the structure of heterometallic precursors,
i.e., oxo or acetate bridging, and the amounts of hydroxyl and organic groups bound to the metal network.
The local environments of metal atoms in the amorphous precursors were also studied by EXAFS. The analysis reveals that in
Pb−Zr precursors alkoxide groups modify the coordination spheres of the zirconium atoms. Conversely, local environments of
both lead and titanium atoms within the analysed range of 3.4 A depend weakly on the type of alkoxide used. 相似文献
983.
A carborane-containing stable simple enol — 1-2-isopropyl-o-carboran-I-yl)-1-phenyl2-mesityl-2-lrydroxyctlrylcne — has been synthesized. This enol does not isomerize to the starting ketone or keto-enol mixture even after prolonged heating in benzene in the presence of CF3COOH.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1561–1563, June, 1996. 相似文献
984.
1,2,2-Trimethyldisilane-1,1,2-triol (1) is formed as an unstable intermediate upon hydrolysis of oligo(trimethyldisilanylsesquiazane). In the absence of trapping
agents it undergoes rapid condensation to give ether-soluble poly(trimethyldisilanyloxane) which contains silanol groups.
Treatment of the hydrolysis products with chlorotrimethylsilane in the presence of triethylamine affords trimethylsiloxy derivatives,
(Me3SiO)2MeSiSiMe2(OSiMe3),5,6, and [Si2Me3O
x
(OSiMe3)
y
]
n
. The isolation of these products indicates that disilanetriol1 readily undergoes condensation to form hydroxylcontaining six-membered rings and polysiloxanes. The condensation of compound1 in the presence of Me3SiOH has been studied. The ratio between the isomeric cyclosiloxanes5 and6 has been determined both by1H NMR spectroscopy and by a chemical method (chlorinolysis).
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1788–1792, October, 1993. 相似文献
985.
A paradox was observed in a previous study of the electrophoresis of linear DNA fragments in agarose gels (D. L. Holmes and N. C. Stellwagen, Electrophoresis 1990, 11, 5-15). The pore size of the agarose matrix was more accurately determined if the root-mean-square radius of gyration was used to measure DNA macromolecular size. However, the Ogston equations were obeyed and other gel parameters such as the apparent fiber radius and fiber volume appeared to be better described if the geometric mean radius was used to measure DNA size. This paradox can be resolved if relative mobilities (with respect to the smallest DNA molecule in the data set) are used to construct the Ferguson plots, instead of absolute mobilities. Using relative mobilities and the root-mean-square radius of gyration, the Ogston equations are obeyed and the pore size of the matrix is consistent with values determined by other methods. 相似文献
986.
A simple and rapid method is proposed for the spectrofluorimetric determination of anionic surfactants. It is based on formation of an ion-pair at pH 2 with safranine-T and its subsequent extraction into chloroform. Fluorescence intensity is increased by a factor of about 5 with respect to that of the reagent. The calibration graph is linear in the concentration range 0.015–0.40 mg l?1 dodecyl sulfate; the relative standard deviation is 5.6% at 0.22 ml l?1 surfactant. The method is applied to determine anionic surfactants in city waste-waters, giving recoveries close to 100%. 相似文献
987.
We have studied the kinetics of the process of epoxidation of 1-octene by tert-butyl hydroperoxide in the presence of molybdenum boride MoB2. We have studied the effect of the concentrations of starting materials and reaction products on the process. We suggest a kinetic scheme and we calculate the kinetic parameters of the process. 相似文献
988.
989.
The effect of addition of Re, Zr, Sc, and Sn on an aluminoplatinum catalyst in the reaction of dehydrogenation of propane was investigated. It was shown that addition of 0.2–0.5% Zr, Sc, or Re virtually does not alter the catalytic properties of the aluminoplatinum catalyst (APC); addition of 0.2% Sn increases the activity, selectivity, and stability of Pt/Al2O3. The amount of coke deposited on the APC after the first 5 min of work decreases by three times in the presence of Sn. The coke is more enriched with hydrogen than the other systems formed on the surface of Pt-Sn/Al2O3.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 765–771, April, 1991. 相似文献
990.