Ceria-supported ruthenium catalysts for the synthesis of indole via dehydrogenative N-heterocyclization

Simple heterogeneous Ru/CeO2 catalysts as well as Ru/ZrO2 catalysts were found to be quite effective for the selective direct synthesis of indole via intramolecular dehydrogenative N-heterocyclization of 2-(2-aminophenyl)ethanol, while catalysts supported on SiO2, Al2O3, TiO2, and MgO were less effe...

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Bibliographic Details
Published in:Catalysis science & technology 2011-01, Vol.1 (8), p.1340-1346
Main Authors: Shimura, Shun, Miura, Hiroki, Wada, Kenji, Hosokawa, Saburo, Yamazoe, Seiji, Inoue, Masashi
Format: Article
Language:English
Subjects:
Catalysis
Catalysts
Dehydrogenation
Emission analysis
Indoles
Inductively coupled plasma
Spectroscopy
Titanium dioxide
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Summary:Simple heterogeneous Ru/CeO2 catalysts as well as Ru/ZrO2 catalysts were found to be quite effective for the selective direct synthesis of indole via intramolecular dehydrogenative N-heterocyclization of 2-(2-aminophenyl)ethanol, while catalysts supported on SiO2, Al2O3, TiO2, and MgO were less effective. Ru/CeO2 catalysts that were calcined at a relatively low temperature, 200 [degree]C, showed excellent activity and gave indole in a yield over 99% by the reaction at 140 [degree]C for 24 h (Ru catalyst 2.5 mol%). Spectroscopic studies of the Ru/CeO2 catalysts indicated the formation of RuIV[double bond, length as m-dash]O species on the surface, which is considered to be transformed into the catalytically-active species at the initial stage of the reaction. Hot filtration tests and an ICP-AES analysis indicated that these Ru/CeO2 catalysts act heterogeneously and that the leaching of ruthenium species into the solution is negligible. These catalysts could be recycled without a significant loss of activity, which suggests that the present oxide-supported catalysts are promising alternatives to conventional homogeneous catalysts.
ISSN:2044-4753
2044-4761
DOI:10.1039/c1cy00235j