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    Catalysts for enantioselective Biginelli reaction based on the composite silica-zirconia xerogels prepared using different zirconium sources [Electronic resource] / I. V. Krivtsov, Yu. A. Titova, M. V. Ilkaeva, V. V. Avdin, O. V. Fedorova, S. A. Khainakov, J. R. Garcia, G. L. Rusinov, V. N. Charushin // Journal of Sol-Gel Science and Technology . - 2014. - Vol.69, №2. - С. 448-452. - Bibliogr. : p. 452 (17 ref.)

ББК 54
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
SOL-GEL METHOD -- ZIRCONIUM OXYCHLORIDE -- SILICA-ZIRCONIA XEROGELS
Аннотация: 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.

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    Synthesis and physicochemical and catalytic properties of composites in the Sio2–Zro2 system / A. N. Murashkevich, O. A. Alisienok, E. S. Novik [et al.] // Inorganic materials. - 2020. - Vol. 56, № 4. - P430-436
Рубрики: ХИМИЧЕСКИЕ НАУКИ
Кл.слова (ненормированные):
ACID-BASE PROPERTIES -- CATALYSIS -- COMPOSITE -- SILICA -- SPECIFIC SURFACE AREA -- ZIRCONIA
Аннотация: Using coprecipitation, a sol–sol method, and molecular layering, we have synthesized SiO2–ZrO2 composites with SiO2 : ZrO2 ratios from 1 : 1 to 9 : 1 and a large specific surface area, which increases with growth silicon-containing component concentration. Using adsorption of Hammett indicators, we have assessed the concentration of acid–base centers in the pK range 1.3–9.6, which has been shown to vary from 68 to 160 μmol/g. Elemental analysis and IR spectroscopy data have demonstrated the presence of not only water but also nitrate ions and carbon dioxide on the surface of the samples. It has been shown that the use of nanoparticulate SiO2–ZrO2 oxides as heterogeneous catalysts—promoters for (2S,4R)-4-hydroxyprolyl-(S)-1-phenylethylamine trifluoroacetate, a chiral inducer in the asymmetric Biginelli reaction, makes it possible to raise ee (enantiomeric excess) from 39 to 68% and the reaction yield from 29 to 55%.

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