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DOI: 10.1002/cctc.201300126
Clean Synthesis of Amides over Bifunctional Catalysts of
Rhodium-Loaded Titanosilicates
[
a]
Le Xu, Ningning Li, Hong-gen Peng, and Peng Wu*
Rhodium-loaded titanosilicates were prepared and employed
as efficient bifunctional catalysts in the one-pot synthesis of
benzamide from benzaldehyde, hydrogen peroxide, and am-
monia, which took place through a tandem reaction including
ammoximation of benzaldehyde to benzaldehydeoxime and
a sequential dehydration–rehydration reaction to benzamide.
Various parameters that influenced the activity and product se-
lectivity were investigated, such as crystalline topologies of the
titanosilicate supports, types of transition metals, rhodium con-
for loading the Rh(OH) species. Rh(OH) /Ti-MWWgave 84.9%
x x
of benzaldehyde conversion and 86.9% of benzamide selectivi-
ty, and it was also catalytically active for the transformation of
a variety of aldehydes to the corresponding amides. The reus-
ability of the bifunctional catalyst was also investigated. The
in situ FTIR technique confirmed that the one-pot reaction in-
cluded Ti-catalyzed ammoximation of benzaldehyde to the
benzaldehyde oxime intermediate and sequential rhodium hy-
droxide related dehydration–rehydration reaction of oximes to
amides.
tent, reaction temperature, time, solvent, and NH /benzalde-
3
hyde molar ratio. Ti-MWW was proved to be a suitable support
Introduction
Amides, the key intermediates for manufacturing engineering
plastics in chemical industry, are also widely used in the areas
tanosilicate, and the gas-phase Beckmann rearrangement on
[12]
solid acid catalyst of Silicalite-1 (MFI structure).
[
1–3]
of medical, agriculture, and biology,
because they partici-
Nevertheless, acid-catalyzed Beckmann rearrangement reac-
tions are generally not useful for the transformation of aldox-
pate in a variety of useful reactions including dehydration, hy-
drolysis, Hofmann degradation, and substitution reactions.
Conventionally, amides are synthesized from the correspond-
[13,14]
imes to primary amides.
Transition-metal species, such as
Rh, Ru, Pd, and Ir, have been recently shown to serve as effi-
cient catalysts for the liquid-phase transformation of aldoximes
[
4–8]
ing carbonyl derivatives such as nitriles.
These manufacture
[15–22]
processes, however, have encountered serious problems, such
as using harmful acid and poisonous reactants, and coproduc-
ing a large quantity of byproducts. Such processes are thus
considered to be environmentally unfriendly in terms of green
and sustainable chemistry. Besides, the transformation of
oximes to amides through Beckmann rearrangement is another
to primary amides.
Mizuno et al. reported that the
Rh(OH) /Al O catalyst was capable of converting the aldoximes
x
2
3
to the corresponding primary amides in water as a solvent
[23]
without using hazardous reactants. The Rh(OH) /Al O cata-
x
2
3
lyst not only showed a high catalytic activity for the conversion
of various aldoximes, but also exhibited a high selectivity for
the desired amides and a high stability in catalytic reuse. More-
over, one-pot synthesis of amides has also been demonstrated
possible from aldehydes and hydroxylamine derivatives on the
[
9,10]
well-known pathway for amide synthesis.
A typical example
is the manufacture of e-caprolactam, the starting material for
[
11]
nylon-6 synthesis.
The lactam is prepared by the liquid-
[24]
phase Beckmann rearrangement reaction of cyclohexanone
oxime using a sulfuric acid catalyst, whereas the oxime is pro-
duced through noncatalytic oximation of cyclohexanone with
hydroxylamine derivatives. Recently, an innovative process for
lactam production has been developed by combining two zeo-
lite-catalyzed reactions, that is, the liquid-phase ammoximation
of cyclohexanone, ammonia, and hydrogen peroxide on TS-1 ti-
Rh(OH) /Al O catalyst directly. This discovery would open up
x 2 3
the possibility of developing environmentally benign chemical
processes for the production of primary amides through heter-
ogeneous catalysis routes. Greener and more atom-efficient
processes, however, are expectable if aldehydes, ammonia, and
hydrogen peroxide are employed in a one-pot synthesis as re-
actants instead of using expensive and explosive aldoximes
and sulfate or hydrochloride hydroxylamine. In this sense, it
would be a desirable alternative to combine in situ hydroxyl-
amine generation with sequential dehydration and rehydration
of aldoxime, both operated with heterogeneous catalytic sys-
tems.
[
a] L. Xu, N. Li, H.-g. Peng, Prof. P. Wu
Shanghai Key Laboratory of Green Chemistry
and Chemical Processes
Department of Chemistry, East China Normal University
3
663 North Zhongshan Road, Shanghai 200062 (P.R. China)
Titanosilicates containing tetrahedral Ti active sites in the
Fax:(+86)21-62232292
E-mail: pwu@chem.ecnu.edu.cn
[25]
[26]
zeolite framework, especially TS-1,
Ti-MWW,
have been used as catalysts in the liquid-phase
ammoximation of ketones or aldehydes with NH and H O ,
and
[27,28]
Ti-MOR,
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201300126.
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2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 2462 – 2470 2462