COMMUNICATION
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Supported monomeric vanadium catalyst for dehydration of amides
to form nitrilesw
a
a
a
Shoichiro Sueoka, Takato Mitsudome, Tomoo Mizugaki,
a
ab
Koichiro Jitsukawa and Kiyotomi Kaneda*
Received 7th July 2010, Accepted 3rd September 2010
DOI: 10.1039/c0cc02412k
Monomeric vanadium oxide species is created on the surface of
hydrotalcite (V/HT), which acts as a reusable solid catalyst for
the highly efficient dehydration of amides into the corresponding
nitriles.
system over the previously reported catalysts are the elimina-
tion of the need for additives and precious or toxic metals and
avoidance of any tedious separation of the catalyst from the
reaction mixture. Moreover, the V/HT catalyst can be reused
with retention of activity.
Nitriles are of great importance as synthetic intermediates for
the preparation of pharmaceuticals, agricultural chemicals and
dyes. Among the variety of known synthetic routes to nitriles,
dehydration of primary amides is one of the most straight-
V/HT was synthesized as follows. HT (1.0 g) was added to
3
100 mL of an aqueous VCl solution (4 mM) and then the
mixture was stirred at room temperature for 3 h. The obtained
slurry was filtered, washed with deionized water and dried
overnight at room temperature in vacuo to yield V/HT
(V: 1.9 wt%) as a pale gray powder. The XRD peak positions
of V/HT were similar to those of the parent HT, indicating
that the vanadium species is located on the surface of HT.
V/HT was also characterized by X-ray absorption fine struc-
ture (XAFS) and UV-vis diffuse reflectance spectroscopy. The
V K-edge X-ray absorption near-edge structure (XANES)
1
forward methods. Although many reports on the useful
dehydration of amides have been published, most of these
methods need excess amounts of stoichiometric reagents, such
2a
2b
2
2c
,
as P
2
O
5
,
SOCl
and POCl
3
which results in the produc-
tion of vast amounts of environmentally damaging wastes.
From the standpoint of Green Sustainable Chemistry, the
development of an efficient process for the catalytic dehydra-
tion of primary amides to nitriles has been desired because,
theoretically, water is the only byproduct. Several catalytic
dehydration systems have appeared to date; however, excess
amounts of additives are still often required to promote the
spectrum of V/HT showed that the edge energy value of
7
3 4
V/HT was consistent with that of Na VO (Fig. S1, ESIw).
V
The absorption edge was assigned to V species. The Fourier
3
transform (FT) of the k -weighted V K-edge EXAFS showed a
3
reaction. Only two examples of the successful catalytic
peak attributed to V–O bonds and no peaks for V–V bonds on
dehydration of amides under additive-free conditions have
4
been reported. In these cases, monomeric metal oxo com-
the surface of HT. The main peak of the inverse FT was well
˚
fitted to a single V–O shell (1.68 A) with a coordination
pounds of dibutyltin oxide and perrhenic acid were found to
be effective catalysts.
number of 4.1 (Fig. S2 and Table S1, ESIw). These results
revealed that the vanadium species on the HT surface is
Hydrotalcites (HTs, Mg
6
Al
2
(OH)16CO
3
) are layered anionic
located as a monomeric vanadium species with tetrahedral
8
clays consisting of positively charged two-dimensional brucite
layers and anionic species, such as hydroxide and carbonate,
located in the interlayer. HTs have attracted considerable
interest as catalysts because of their multifunctionality, including
their cation and anion exchange ability, surface tunable
coordination similar to that in Na
3
VO
4
.
The proposed
structure of the vanadium species was also confirmed by
UV-vis diffuse reflectance spectra of V/HT; the charge-transfer
band at 300 nm was assigned to a monomeric VO
9
species (Fig. S3, ESIw).
4
tetrahedral
5
basicity and metal adsorption capacity. The metal adsorption
Various HT-supported metals were synthesized, and their
ability to catalyze the dehydration of o-toluamide (1) was
examined; the results are summarized in Table 1. Among the
HT-supported metals tested, V/HT showed excellent catalytic
activity to afford o-tolunitrile (2) as the sole product with 91%
yield (entry 1). Other HTs such as Sn/HT, Re/HT, Mn/HT,
Mo/HT, W/HT and the parent HT, however, provided low
yields of 2 (entries 3–8). Next, the dehydration of 1 using
supported vanadium compounds was carried out. Interestingly,
ability of HT can provide strong protocols to create mono-
meric metal oxide species on the HT surface which show high
6
catalytic activities for various organic reactions. Herein, we
report that a monomeric vanadium oxide species is created on
the surface of HT (V/HT), which can act as a solid catalyst for
the highly efficient dehydration of versatile amides into the
corresponding nitriles. The advantages of the V/HT catalyst
a
Department of Materials Engineering Science,
Graduate School of Engineering Science, Osaka University,
-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
E-mail: kaneda@cheng.es.osaka-u.ac.jp; Fax: +81 6-6850-6260;
Tel: +81 6-6850-6260
Research Center for Solar Energy Chemistry, Osaka University,
good yields of 2 were obtained using V/MgO and V/SiO
in which the vanadium species are in monomeric states
entries 9 and 10). On the other hand, the polymeric vanadium
species in V/Al and V/TiO (Fig. S3, ESIw) were not
effective (entries 11 and 12). Non-supported vanadium com-
pounds, such as Na VO and V , also did not work as
2
,
1
(
2
O
3
2
b
1
-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
3
4
2 5
O
w Electronic supplementary information (ESI) available: Experimental
details, XAFS and UV-vis spectra of V/HT. See DOI: 10.1039/
c0cc02412k
catalysts (entries 14 and 15). These phenomena show that
V/HT had the best catalytic efficiency and a monomeric
This journal is c The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 8243–8245 8243