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Document Type |
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Article In Conference |
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Document Title |
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Solvent-free oxidation of alcohols by hydrogen peroxide over chromium Schiff base complexes immobilized on MCM-41: optimization of catalytic activity by modificating the local environment of active complexes Solvent-free oxidation of alcohols by hydrogen peroxide over chromium Schiff base complexes immobilized on MCM-41: optimization of catalytic activity by modificating the local environment of active complexes |
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Subject |
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كيمياء |
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Document Language |
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English |
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Abstract |
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Oxidation of alcohols to aldehydes and ketones is a ubiquitous transformation in
organic synthesis. Recent demand for eco-friendly chemical processes encouraged the
development of clean reactions. Hydrogen peroxide as an oxidant are atom efficient and
produce water as the only by-product [1]. On the other hand, solvent-free reactions are
of general interest due to their potential in combinational chemistry, simple processes,
easy work-up, low cost and reduction in noxious waste materials. however, only a
limited number of such useful oxidation procedures have been reported. Development
of efficient biomimetic heterogeneous oxidation catalysts containing metal complexes,
especially the heterogenised transition metal Schiff base complexes is eye-catching for
their more accessible synthesis conditions and versatile coordination structures [2].
In the present work, a conventional chromium Schiff base complex was
successfully immobilized MCM-41. In order to optimize the catalytic performance of
immobilized complexes, a series of typical methyl regulators were further used to
finely modify the local environment of active sites in immobilized complex. By
changing the kinds and amounts of methyl regulators and their relative position to
active sites, a series of methyl-containing immobilized chromium complexes were
prepared and used for the selective oxidation of alcohols with 30% H2O2.
Elemental analysis and 13C CP/MAS NMR, FTIR and UV spectra showed that
the homogeneous chromium complexes had been immobilized on MCM-41, and that
the methyl regulators were also successfully introduced. The powder XRD patterns
and N2 sorption isotherms displayed that all immobilized complexes still exhibited
typical ordered hybrid mesophases. Furthermore, with the introduction of methyl
regulators, the surface polarity of immobilized complexes decreased while their
hydrophobicity increased. This indicated that the local environment of active sites in
immobilized complexes changed significantly.
The immobilized complexes were effective catalysts and all exhibited much
higher catalytic performance than their corresponding homogeneous analogues.
Simultaneously, the catalytic performance of immobilized complexes was closely
related to the kinds, amounts and relative localities to active complexes of methyl
regulators. Under the optimal reaction conditions, aliphatic secondary alcohols, cyclic
alcohols and benzylic alcohols were all oxidized in good yields, and the major
products were their corresponding ketones or aldehydes, while primary alcohols were
mainly oxidized to carboxylic acid. |
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Conference Name |
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Tenth International Symposium on Heterogeneous Catalysis |
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Duration |
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From : 22/8/1429 AH - To : 26/8/1429 AH
From : 23/8/2008 AD - To : 27/8/2008 AD |
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Publishing Year |
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1429 AH
2008 AD |
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Article Type |
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Article |
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Added Date |
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Sunday, February 22, 2009 |
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Researchers
| Xiaoli Wang | Xiaoli Wang | Researcher | Doctorate | |
| Gongde Wu | Gongde Wu | Researcher | Doctorate | |
| Junping Li | Junping Li | Researcher | Doctorate | |
| Fukui Xiao | Fukui Xiao | Researcher | Doctorate | |
| Wei Wei | Wei Wei | Researcher | Doctorate | |
| Yuhan Sun | Yuhan Sun | Researcher | Doctorate | |
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