A tungsten-tin mixed hydroxide as an efficient heterogeneous catalyst for dehydration of aldoximes to nitriles

Article abstract of DOI:10.1002/anie.200605004

(Chemical Equation Presented) Mix and match: A tungsten-tin mixed hydroxide (W-Sn hydroxide), prepared by the simple coprecipitation method, acts as a reusable heterogeneous catalyst for the dehydration of various aldoximes to the corresponding nitriles (see scheme, top). Furthermore, the W-Sn hydroxide catalyst could be applied to the direct one-pot synthesis of nitriles from hydroxylamine and the corresponding aldehydes (see scheme, bottom).

Full text of DOI:10.1002/anie.200605004

Communications
DOI: 10.1002/anie.200605004
Heterogeneous Catalysis
A Tungsten–Tin Mixed Hydroxide as an Efficient Heterogeneous
Catalyst for Dehydration of Aldoximes to Nitriles**
Kazuya Yamaguchi, Hiroshi Fujiwara, Yoshiyuki Ogasawara, Miyuki Kotani, and
Noritaka Mizuno*
Nitriles are versatile synthetic intermediates for pharmaceut-
unprecedented (see Table 1 and the Supporting Informa-
tion).
[
1]
[11–15]
icals, agricultural chemicals, and dyes. A nucleophilic
substitution of alkyl halides with a stoichiometric amount of
inorganic cyanide is a general method for the synthesis of
alkyl nitriles, which is frequently accompanied by the
elimination of hydrogen halides, especially with bulky alkyl
Herein, we report that a tungsten–tin mixed hydroxide
(W–Sn hydroxide, Sn/W molar ratio of 1.9), prepared by the
simple coprecipitation method (see the Experimental Sec-
tion), can act as a reusable heterogeneous catalyst for the
dehydration of various aldoximes to the corresponding
nitriles [Eq. (1)]. Furthermore, the W–Sn hydroxide catalyst
[
1]
halides. Aromatic nitriles (benzonitriles) can be synthesized
[
1]
by the Sandmeyer reaction and ammoxidation. Although
a,b-unsaturated nitriles can be synthesized by the Wittig
reaction of the corresponding aldehydes with cyanoalkyl
phosphate, the method often produces a mixture of E- and Z-
WꢀSn hydroxide
RꢀCH¼NOHƒƒƒƒƒƒ ƒƒ !RꢀCN þ H O
ð1Þ
2
[
1c]
isomeric nitriles. Therefore, many of these conventional
methods for nitrile synthesis require hazardous reagents, for
example, inorganic cyanide, and can be nonselective.
can be applied to the direct one-pot synthesis of nitriles from
hydroxylamine and the corresponding aldehydes [Eq. (2)].
0
WꢀSn hydroxide
0
R ꢀCHO þ NH
2
OHƒƒƒƒƒƒ ƒƒ !R ꢀCN þ 2 H
2
O
ð2Þ
The dehydration of aldoximes, which are easily prepared
from the corresponding aldehydes, is a candidate for clean
nitrile synthesis, and various procedures have been
[a]
Table 1: Dehydration of benzaldoxime by various catalysts.
[
2–15]
reported.
However, selective dehydration to the corre-
sponding nitriles is very difficult, and many reported proce-
dures require the use of reactive reagents in stoichiometric
[
2]
amounts, such as the Burgess reagent, N-chlorosuccinimide/
Entry
Catalyst
Conv. [%]
Select. [%]
[
3]
[4]
PPh3, and thionyl chloride. Such reagents present a severe
drawback for scaled-up and industrial applications. Therefore,
efficient catalytic procedures for the dehydration of aldox-
imes are still in great demand. Oxorhenium(VII) complexes,
Ga(OTf)3, InCl3, TiCl (OTf), and Cu(OAc)2 have been
reported to catalyze the dehydration homogeneously, for
example. Although heterogeneous dehydration systems are
environmentally and technologically the most desirable
procedures, widely usable truly heterogeneous catalysts are
1
2
3
4
5
6
7
8
9
W–Sn hydroxide
79
4
96
95
18
4
n.d.
8
trace
trace
11
37
15
12
41
29
8
96
97
[b]
Na WO ·2H O
2
4
2
[c]
[d]
SnCl ·5H O
20
4
2
[
5]
[
e]
[d]
Na WO ·2H O+SnCl ·5H O
15
2
4
2
4
2
[
6]
[7]
[8]
[9]
H
2
WO
51
>99
–
80
–
3
4
WO3
Sn(OH)4
[f]
WO +Sn(OH)
3
4
H-mordenite
H–Y
10
11
12
13
14
15
16
17
18
–
2
ꢀ
[g]
SO4 /ZrO
54
90
60
27
94
60
59
–
2
[
g]
WO /ZrO
3
2
[
g]
WO /SnO
3
2
[
h]
[
*] Dr. K. Yamaguchi, H. Fujiwara, Y. Ogasawara, Prof. Dr. N. Mizuno
Department of Applied Chemistry, School of Engineering
The University of Tokyo
montmorillonite
[
i]
KF/Al O
2
3
[j]
[{RuCl (p-cymene)} ]/C
2
2
7
-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)
MgO
none
Fax: (+81)3-5841-7220
n.d.
E-mail: tmizuno@mail.ecc.u-tokyo.ac.jp
[a] Reaction conditions: benzaldoxime (1 mmol), catalyst (0.1 g), o-
Dr. K. Yamaguchi, M. Kotani, Prof. Dr. N. Mizuno
Core Research for Evolutional Science and Technology (CREST)
Japan Science and Technology Agency (JST)
xylene (3 mL), 1538C, 0.5 h. Conversion and selectivity were determined
by GC analysis with biphenyl as an internal standard. Main by-products
were benzamide and benzaldehyde. n.d.=nitrile not detected.
4
-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)
[b] Na WO ·2H O
(0.17 mmol).
[c] SnCl ·5H O
(0.33 mmol).
2
4
2
4
2
[
**] We are grateful to Mr. S. Tamai (The Univ. of Tokyo) for his help in
experiments. This work was supported by the Core Research for
Evolutional Science and Technology (CREST) program of the Japan
Science and Technology Agency (JST) and a Grant-in-Aid for
Scientific Research from the Ministry of Education, Culture, Science,
Sports and Technology of Japan.
[d] Unidentified by-products (ca. 50% selectivity) were formed.
[e] Na WO ·2H O (0.17 mmol)+SnCl ·5H O (0.33 mmol). [f] WO3
2
4
2
4
2
(0.045 g)+Sn(OH) (0.049 g). [g] Prepared according to reference [20].
4
[h] Montmorillonite KSF. Purchased from Alfa Aesar. [i] Purchased from
Aldrich (40 wt% KF on Al O ; 0.69 mmol; 69 mol%). [j] Prepared
according to reference [11]; 0.1 g (Ru: 2.2 mol%). A similar result was
2
3
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
obtained when the reaction was performed with [{RuCl (p-cymene)} ]/C
in the presence of M.S. (4 Š, 200 mass% with respect to substrate).
2
2
3
922
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Angew. Chem. Int. Ed. 2007, 46, 3922 –3925

Angewandte
Chemie
First, the dehydration of benzaldoxime as a model
substrate was carried out with various catalysts, including
previously reported solid catalysts (Table 1). The W–Sn
hydroxide showed the highest catalytic activity for the
dehydration of benzaldoxime among various catalysts tested
(Table 1, entries 15 and 17). These results show that the
present dehydration is not a simple acid- or base-catalyzed
reaction. It is likely that the dehydration proceeds efficiently
in the presence of catalysts with a suitable acidity. Detailed
studies are in progress.
[
16]
(
Table 1, entry 1). To verify whether the observed catalysis
The scope of the present W–Sn hydroxide-catalyzed
system with regard to various kinds of structurally diverse
aldoximes was examined. The W–Sn hydroxide showed high
catalytic activities for the dehydration of activated, non-
activated, and heteroatom-containing aldoximes, as summar-
ized in Table 2. In the dehydration of benzaldoximes, the
substrates were smoothly converted to the corresponding
benzonitriles in excellent yields (Table 2, entries 1–9). Not
only aromatic aldoximes but also aliphatic ones could be
dehydrated to the corresponding aliphatic nitriles (Table 2,
entries 11–13). The present system was also effective for acid-
sensitive piperonaldoxime (Table 2, entry 10). The dehydra-
tion of 2-thiophenealdoxime and 2-furaldoxime gave the
corresponding nitriles in 80 and 73% selectivity, respectively,
because of the formation of amides as by-products (Table 2,
is truly heterogeneous or not, the W–Sn hydroxide was
separated from the reaction mixture by filtration at the
reaction temperature, and the reaction was again carried out
with the filtrate under the same conditions. The dehydration
was completely stopped by the removal of the W–Sn
hydroxide. Furthermore, it was confirmed by inductively
coupled plasma–atomic emission spectrometry (ICP–AES)
analysis that tungsten and tin species were hardly detected in
the filtrate (W< 0.0032%, Sn < 0.0025%). These results show
that the nature of the observed catalysis is truly heteroge-
[
17]
neous. The dehydration hardly proceeded in the absence of
catalysts (Table 1, entry 18) or in the presence of
Na WO ·2H O (Table 1, entry 2). In the presence of
2
4
2
SnCl ·5H O, the selectivity for benzonitrile was very low,
4
2
and many unidentified by-products
were formed (Table 1, entry 3).
[
a]
WO3, H WO , Sn(OH)4, and
a
Table 2: Dehydration of various aldoximes by W–Sn hydroxide.
2
4
physical mixture of WO3 and
Entry
Substrate
Product
t [h]
Conv. [%]
Select. [%]
Sn(OH) were not effective for the
4
1
2
3
4
1
1
1
1
94(82)
90
87
91
94
94
95
dehydration (Table 1, entries 5–8).
According to our experiments, pre-
viously reported solid catalysts such
[b]
[b]
[
b]
87
[
12]
[15]
as montmorillonite, KF/Al O ,
2
11]
3
[
5
1
>99(91)
>99(82)
95(85)
98
96
94
91
and [{RuCl (p-cymene)} ]/C were
2
2
not effective for dehydration under
the present conditions (Table 1,
entries 14–16). In the case of mont-
morillonite, benzaldehyde was
obtained as a main product (73%
selectivity).
6
7
8
1
1
1.5
96(87)
The acid strength of the W–Sn
hydroxide (as prepared) was esti-
mated by the Hammett indicator
9
0
3
1
94(72)
97(86)
86
94
[
18]
method.
The W–Sn hydroxide
reacted with benzeneazodiphenyl-
1
amine (pK = + 1.5) and did not
a
react
with
dicinnamalacetone 11
12
n-C H CH=NOH
n-C H CN
1
1
1
98(89)
>99(90)
96(95)
97
98
95
7
15
7
15
(
pK = ꢀ3.0), showing that the H
n-C
9
H
19CH=NOH
n-C
9
H19CN
a
0
1
3
n-C H CH=NOH
n-C H CN
11 23
value of the W–Sn hydroxide lies
between + 1.5 and ꢀ3.0. This result
suggests that the W–Sn hydroxide is
11 23
1
4
1.5
4.5
>99(65)
80
73
[c]
much less acidic than the zeo- 15
88
[
18,19]
lites.
However, the reaction
hardly proceeded in the presence 16
3
97(94)
96
of zeolites (Table 1, entries 9 and
2
ꢀ
17
5.5
1.5
89(73)
91
98
1
0). SO4 /ZrO , WO /ZrO , and
2 3 2
WO /SnO , which have been 18
>99(95)
3
2
[
20]
reported to be solid superacids,
[a] Reaction conditions: aldoxime (1 mmol), W–Sn hydroxide (0.1 g), o-xylene (3 mL), 1498C.
were much less active for this reac-
tion than the W–Sn hydroxide
Conversion and selectivity were determined by GC analysis with diphenyl or naphthalene as an internal
standard. Main by-products were amides and aldehydes. Values in parentheses are yields of isolated
product after complete consumption of aldoximes. [b] Reuse experiments; reuse 1 (entry 2), reuse 2
(
Table 1, entries 11–13). In addi-
tion, strong solid bases such as KF/
Al O3 and MgO were less active run with a fresh catalyst. [c] Not isolated.
(entry 3), and reuse 3 (entry 4). The initial rates for the reuse runs were almost the same as for the first
2
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www.angewandte.org
3923

Communications
entries 14 and 15). The dehydration of olefinic aldoximes such
sulfonyl chloride with dry Al O , and KF/Al O have been
utilized for the transformation.
2
3
2
3
[
21,22]
as trans-cinnamaldoxime, trans-2-octenaldoxime, and cis-8-
undecenaldoxime efficiently proceeded to afford the corre-
sponding nitriles without isomerization of the double bond
In conclusion, we have reported herein the noteworthy
features of the easily prepared W–Sn hydroxide for the
heterogeneously catalyzed dehydration of aldoximes and the
one-pot syntheses of nitriles. This catalyst could be applied to
various functional transformations.
(
Table 2, entries 16–18). The W–Sn hydroxide was reused in
the dehydration of benzaldoxime, and the high catalytic
activity and selectivity were maintained even after the third
reuse (Table 2, entries 2–4). The present system was appli-
cable to larger-scale production (50 mmol, heating at reflux,
bath temperature 1708C), and the corresponding nitrile could
be isolated in 97% yield after 6 h [Eq. (3)].
Experimental Section
The W–Sn hydroxide was prepared as follows: Na WO ·2H O (2.47 g,
2
4
2
7
.5 mmol) was dissolved in deionized water (15 mL) and SnCl ·5H O
4 2
(
5.26 g, 15 mmol) was immediately added in one portion. After
stirring the solution for 1 h at room temperature, deionized water
60 mL) was added to the solution in one portion, and the initially
(
colorless solution gradually turned into a white slurry. After stirring
the slurry for 24 h at room temperature, the resulting white
precipitate of W–Sn hydroxide was filtered off, washed with a large
amount of deionized water, and dried in vacuo to afford the W–Sn
2
ꢀ1
hydroxide as a white powder (4.4 g). BET surface area: 149 m g
.
3
ꢀ1
Pore volume: 0.074 cm g . The IR spectrum showed a very broad
ꢀ1
n(OH) band in the range of 3000–3700 cm . The X-ray photoelectron
spectrum of the W–Sn hydroxide showed that the W 4f7/2, W 4f5/2
Sn 3d5/2, and Sn 3d3/2 binding energies of the W–Sn hydroxide were
6.2 eV (full width at the half maximum (FWHM) 1.3 eV), 38.4 eV
,
3
Interestingly, the W–Sn hydroxide could be employed in
the one-pot syntheses of nitriles through the dehydrative
condensation of aldehydes and hydroxylamine with subse-
(FWHM 1.3 eV), 487.7 eV (FWHM 1.5 eV), and 496.1 eV
(FWHM 1.5 eV), respectively, indicating that the respective oxida-
tion states of W and Sn species in the W–Sn hydroxide are + 6 and
[
23]
[
21]
+ 4. The contents of W, Sn, Cl, and Na were 26.2, 31.8, 5.0, and less
quent dehydration (Table 3). The dehydrative condensa-
tion of benzaldehyde and hydroxylamine hardly proceeded in
the absence of catalyst at 808C. The rate in the presence of the
than 0.01%, respectively, and the formulation of the W–Sn hydroxide
was expressed by Sn1.9WClO6.3·9H O. The Raman spectrum of the W–
2
ꢀ1
Sn hydroxide showed an intense band at 959 cm corresponding to
ꢀ
1
W–Sn hydroxide was 4.0 mm min and more than two orders
=
n(W O). No bands arising from WO were observed in the Raman
3
of magnitude larger than that in the absence of catalyst
spectrum. The X-ray diffraction patterns of the W–Sn hydroxide
(Figure S1 in the Supporting Information) showed broad signals at
d = 3.3422, 2.6384, and 1.7619 Š. The signal positions almost agreed
ꢀ
1
(
0.035 mm min ), showing that the W–Sn hydroxide effi-
ciently catalyzes not only the dehydration of aldoximes but
also aldoxime formation. In this one-pot synthesis, the
catalysis was also heterogeneous in nature, and the catalyst
could be reused without a significant loss of catalytic activity.
Although this tandem one-pot synthesis of nitriles is a very
useful transformation and a topic of current interest in
organic synthesis, stoichiometric reagents such as triethyl-
amine sulfur dioxide, sulphuryl chloride fluoride, methane-
with those of SnO (rutile). Signals associated with SnO and WO3
2
phases were not detected. All these results suggest that a SnO -like
2
phase was predominantly formed in the W–Sn hydroxide and that
tungsten species were highly dispersed on SnO and/or incorporated
2
into the SnO matrix.
2
A typical procedure for the dehydration was as follows: W–Sn
hydroxide (0.1 g), benzaldoxime (1 mmol), and o-xylene (3 mL) were
successively placed into a glass vial. The reaction mixture was stirred
(800 rpm with a magnetic stir bar) at
1498C under 1 atm of Ar. The conver-
sion and product selectivity were peri-
odically determined by GC analysis.
After the reaction was finished, the
spent catalyst was separated by filtra-
tion, washed with acetone, and dried
in vacuo prior to being recycled. The
products were isolated by column chro-
matography (eluent: initially n-pentane,
after o-xylene was eluted n-pentane/
diethyl ether (1:1)). All products were
known and available as authentic sam-
ples. The products were confirmed by
[
a]
Table 3: One-pot synthesis of nitriles by W–Sn hydroxide.
Entry
Substrate
Product
t [h]
Conv. [%]
99(89)
Select. [%]
92
1
7
2
3
4
6.5
9.5
13
>99(94)
99(87)
99
92
87
the comparison of their GC retention
99(72)
1
times, mass spectra, and
H
and
1
3
C NMR spectra with those of the
authentic samples.
5
6
n-C H CHO
n-C H CN
n-C H CN
11 23
4
5
99(86)
98(89)
97
93
9
19
9
19
n-C H CHO
1
1
23
[
a] Reaction conditions: Aldehyde (1 mmol), NH OH·HCl (2 mmol), W–Sn hydroxide (0.1 g), o-xylene Received: December 11, 2006
2
(
3 mL), 1338C. Conversion and selectivity were determined by GC analysis with diphenyl as an internal Revised: March 2, 2007
standard. Values in parentheses are yields of isolated product after complete consumption of aldehydes. Published online: April 11, 2007
3
924 www.angewandte.org
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Angewandte
Chemie
Keywords: dehydration · heterogeneous catalysis · nitriles · tin ·
tungsten
[17] R. A. Sheldon, M. Wallau, I. W. C. E. Arends, U. Schuchardt,
.
Acc. Chem. Res. 1998, 31, 485.
[
[
18] A. Corma, Chem. Rev. 1995, 95, 559, and references therein.
19] It was confirmed by an IR spectrum of pyridine adsorbed on the
W–Sn hydroxide (Figure S2 in the Supporting Information) that
the quantities of Lewis and Brønsted acid sites were 0.34 and
[
1] a) A. J. Fatiadi in Preparation and Synthetic Applications of
Cyano Compounds (Eds.: S. Patai, Z. Rappaport) Wiley, New
York, 1983; b) J. S. Miller, J. L. Manson, Acc. Chem. Res. 2001,
ꢀ1
0.17 mmolg , respectively, and lower than those of zeolites such
as H-mordenite and H–Y (Figure S3 in the Supporting Informa-
[
18]
34, 563; c) P. Magnus, D. A. Scott, M. R. Fielding, Tetrahedron
tion). The IR spectrum was also recorded after the pretreat-
ment of the W–Sn hydroxide (evacuated at 1508C for 3 h, see the
Experimental Section). The acidity of the W–Sn hydroxide
Lett. 2001, 42, 4127.
[
[
[
[
[
[
2] B. Jose, M. S. Sulatha, P. M. Pillai, S. Prathapan, Synth. Commun.
2
000, 30, 1509.
3] N. Iranpoor, H. Firouzabadi, G. Aghapour, Synth. Commun.
002, 32, 2535.
4] S. S. Chaudhari, K. G. Akamanchi, Synth. Commun. 1999, 29,
741.
5] K. Ishihara, Y. Furuya, H. Yamamoto, Angew. Chem. 2002, 114,
109; Angew. Chem. Int. Ed. 2002, 41, 2983.
6] P. Yan, P. Batamack, G. K. S. Prakash, G. A. Olah, Catal. Lett.
005, 101, 141.
became much stronger by the pretreatment; the H value of the
0
pretreated sample lay between ꢀ5.6 and ꢀ8.2. However, the
2
reaction rate of benzaldoxime dehydration with the pretreated
ꢀ1
catalyst (R = 1.8 mm min under the conditions in Table 1) was
ꢀ1
1
lower than that with the as-prepared catalyst (8.7 mm min ).
This result is consistent with the fact that catalysts with strong
acidity, such as zeolites and solid superacids, are not effective for
the present dehydration.
3
2
[20] a) K. Arata, Appl. Catal. A 1996, 146, 3; b) M. Hino, K. Arata,
Bull. Chem. Soc. Jpn. 1994, 67, 1472; c) M. Hino, S. Takasaki, S.
Furuta, H. Matsuhashi, K. Arata, Catal. Commun. 2006, 7, 162;
d) M. Hino, K. Arata, J. Chem. Soc. Chem. Commun. 1988, 1259.
[21] a) H. Sharghi, M. H. Sarvari, Tetrahedron 2002, 58, 10323;
b) G. A. Olah, Y. D. Vankar, Synthesis 1978, 702; c) G. A. Olah,
S. C. Narang, L. A. Garcia, Synthesis 1980, 659; d) B. Movassagh,
S. Shokri, Tetrahedron Lett. 2005, 46, 6923.
7] D. C. Barman, A. J. Thakur, D. Prajapati, J. S. Sandhu, Chem.
Lett. 2000, 1196.
[
[
8] N. Iranpoor, B. Zeynizadeh, Synth. Commun. 1999, 29, 2747.
9] O. Attanasi, P. Palma, F. Serra-Zanetti, Synthesis 1983, 741.
[
[
[
[
10] S. H. Yang, S. Chang, Org. Lett. 2001, 3, 4209.
11] E. Choi, C. Lee, Y. Na, S. Chang, Org. Lett. 2002, 4, 2369.
12] H. M. Meshram, Synthesis 1992, 943.
13] B. Thomas, S. Prathapan, S. Sugunan, Microporous Mesoporous
Mater. 2005, 79, 21.
[22] We confirmed that the H–Y zeolites were stoichiometric
reagents rather than catalysts, because amounts of products
(0.09–0.54 mmol) were comparable to those of acid sites (0.18–
[
14] H. M. S. Kumar, P. K. Mohanty, M. S. Kumar, J. S. Yadav, Synth.
Commun. 1997, 27, 1327.
3
+
0.30 mmol, calculated from the amount of Al sites) in zeolites
(See Table S3 in the Supporting Information) while Das and co-
workers have reported that H–Y zeolite was active for the direct
synthesis of nitriles from hydroxylamine and aldehydes; see:
K. V. N. S. Srinivas, E. B. Reddy, B. Das, Synlett 2002, 625.
[23] a) G. P. Williams in CRC Handbook of Chemistry and Physics,
82nd ed. (Ed.: D. R. Lida), CRC Press, Washington DC, 2001,
sec. 10, p. 200 – 205; b) D. Briggs, M. P. Seah, Practical Surface
Analysis by Auger and X-ray Photoelectron Spectroscopy, Wiley,
Chichester, 1983.
[
[
15] B. Movassagh, S. Shokri, Synth. Commun. 2005, 35, 887.
16] Three kinds of W–Sn hydroxide catalysts with different Sn/W
molar ratios (0.9, 1.9, and 5.2) were prepared and used for the
dehydration of benzaldoxime. The W–Sn hydroxide with the Sn/
W molar ratio of 1.9 showed the highest catalytic activity, and
the order of reactivity was as follows: Sn/W= 1.9(79) > 5.2(9)
>
0.9(7), where the values in the parentheses are the percent
conversion of benzaldoxime under the conditions given in
Table 1.
Angew. Chem. Int. Ed. 2007, 46, 3922 –3925
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3925