Organic–Inorganic Hybrid Catalysts Based on Ordered Porous Structures for Carbon–Carbon Bond Forming Reactions |
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Authors: | Yoshihiro Kubota Yoshihiro Sugi Takashi Tatsumi |
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Institution: | (1) Division of Materials Science and Chemical Engineering, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku Yokohama, 240-8501, Japan;(2) Department of Materials Science and Technology, Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan;(3) Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku Yokohama, 226-8503, Japan |
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Abstract: | Two types of organic–inorganic hybrid base catalysts are prepared. Organic-functionalized molecular sieves (OFMSs); in particular,
“amine-immobilized porous silicates” are designed based on common idea to immobilize catalytic active sites on silicate surface.
Silicate–organic composite materials (SOCMs), such as “ordered porous silicate–quaternary ammonium composite materials”, are
the precursors of ordered porous silicates obtained during the synthesis. Both the OFMS and the SOCM are used as the catalysts
for Knoevenagel condensation and Michael addition reactions. Among the OFMSs, there is clear tendency that the use of molecular
sieve with larger pore volume and/or surface area gives the product in higher yield. Aminopropylsilyl (AP)-tethered mesoporous
silicate such as AP-MCM-41 gives the Knoevenagel condensation product in high yield under mild conditions. No loss of activity
is observed after repeated use for three times. The SOCMs are also active for the same reaction. The OFMSs are effective when
the supports have large pore volume and/or surface area and the reaction is carried out in polar solvents ethanol and DMF.
However, the activity of the OFMSs is considerably low in a non-polar solvent such as benzene. In contrast, the SOCMs are
remarkably active in benzene. The organic cation–MCM-41 composite is more active than the composite of an organic cation and
a microporous silicate such as zeolite beta and ZSM-12. In the SOCM catalysts, (SiO)3SiO−(+NR4) moieties located at the accessible sites are considered to play some important roles. The active species are absent in the
liquid phase after the reaction. The recycle of the catalyst was possible without significant loss of activity when the substrates
are enough reactive. The mechanism of the reaction over SOCM catalyst is discussed. |
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Keywords: | Mesoporous silicate Heterogeneous base catalyst Composite material Knoevenagel reaction Michael reaction |
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