SO3H-functionalized ionic liquids: Green, efficient and reusable catalysts for the facile dehydration of aldoximes into nitriles

Article abstract of DOI:10.1002/cjoc.201190199

Easily synthesized aldoximes have been converted to the corresponding nitriles under very mild conditions by a simple reaction using two halogen-free SO₃H-functionalized ionic liquids, 3-methyl-1-(4-sulfonic acid)butylimidazolium hydrogen sulfate [MIM(CH₂)₄SO ₃H][HSO₄] and 1-(4-sulfonic acid)butylpyridinium hydrogen sulfate [PY(CH₂)₄SO₃H][HSO₄], as catalyst and reaction medium without any additional organic solvent. The method was equally effective for aromatic aldoximes bearing electron-donating and electron-withdrawing substituents. Taking into account environmental and economical consideration, the protocol presented here has the merits of environmentally friendly, simple operation, easy work-up and very good yields. The catalysts could be recycled and reused for several times without noticeably decreasing in their catalytic activities.

Full text of DOI:10.1002/cjoc.201190199

FULL PAPER
SO H-Functionalized Ionic Liquids: Green, Efficient and Re-
3
usable Catalysts for the Facile Dehydration of
Aldoximes into Nitriles
Davoodnia, Abolghasem*
Khojastehnezhad, Amir
Bakavoli, Mehdi
Tavakoli-Hoseini, Niloofar
Department of Chemistry, Faculty of Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Easily synthesized aldoximes have been converted to the corresponding nitriles under very mild conditions by a
3
simple reaction using two halogen-free SO H-functionalized ionic liquids, 3-methyl-1-(4-sulfonic acid)butylimi-
dazolium hydrogen sulfate [MIM(CH ) SO H][HSO ] and 1-(4-sulfonic acid)butylpyridinium hydrogen sulfate
2
4
3
4
[
PY(CH ) SO H][HSO ], as catalyst and reaction medium without any additional organic solvent. The method was
2 4 3 4
equally effective for aromatic aldoximes bearing electron-donating and electron-withdrawing substituents. Taking
into account environmental and economical consideration, the protocol presented here has the merits of environ-
mentally friendly, simple operation, easy work-up and very good yields. The catalysts could be recycled and reused
for several times without noticeably decreasing in their catalytic activities.
Keywords ionic liquid, aldoxime, nitrile, dehydration
1
8-20
Introduction
dehydes to nitriles using various catalysts.
Although these methods may be effective at dehy-
drating aldoxidmes, most of them encounter some limi-
tations such as long reaction times, unsatisfactory yields,
harsh reaction conditions, expensive or not readily
available reagents, hazardous organic solvents and te-
dious work-up procedure. Thus, alternative procedures
with more general applicability, considerably faster re-
action with high yields and environmentally friendly
conditions are still in demand.
The cyano moiety is a highly important one not only
due to its synthetic value as precursor to other function-
1
-3
alities but also due to its presence in a variety of
natural products, pharmaceuticals and bioactive mole-
4
,5
cules. Thus, methods for preparing organic nitriles are
highly desirable. The classical method for the synthesis
of alkyl cyanides involves nucleophilic substitution of
2
an alkyl halide with metal cyanides, whereas aromatic
nitriles are produced by the Sandmeyer reaction and
In recent years, ionic liquids (ILs) have attracted in-
creasing interest and been successfully used in variety
of catalytic reactions as environmentally benign sol-
vents and catalysts due to their relatively low vapor
pressure, reusability and high thermal and chemical sta-
bility, etc. Much attention has currently been focused on
the organic reactions with ILs as catalysts or solvents
and many organic reactions were performed in ILs with
6
,7
ammoxidation. However, these methods are associ-
ated with the use of NaCN/KCN/metal cyanides, which
are in general highly poisonous, and heavy metal cya-
nides such as zinc cyanide which leaves residue of
heavy metal salts. This is not desirable in the context of
a clean environment.
The most efficient route reported for preparing ni-
triles and one that has received much recent attention
involves the dehydration of aldoximes that is one of the
cleanest routes avoiding inorganic cyanides. A number
of dehydration agents have been employed for this
2
1,22
high performances.
The introduction of Brønsted-
acidic functional groups into cations or anions of the ILs,
especially the SO H-functional groups, obviously en-
3
2
3-25
hanced their acidities and water solubilities.
There-
transformation
including
Preyssler’s
anion,
fore, Brønsted-acidic ILs have been synthesized to re-
place traditional mineral liquid acids, such as hydro-
1
4－
8
9
10
[NaP
W
5 30
O
110
]
3
, thionyl chloride, ZnO/CH COCl,
1
1
12
26
triphenylphosphine/I
rosuccinimide/pyridine in CH
2
,
DMF at 135 ℃ and N-chlo-
chloric acid and sulfuric acid in chemical reactions.
1
3
3
CN. In addition, metals
Such acidic ILs play dual roles as solvent and catalyst in
2
7,28
and metal complexes have been used including iron
organic reactions.
1
4
15
29
porphyrins, titanium tetrachloride, copper(II) ace-
Recently, Ranu and co-workers have reported a
new approach for dehydration of aldoximes using
1
6
17
tate and certain ruthenium-based catalysts. There are
also methods published for the direct conversion of al-
1-pentyl-3-methylimidazolium
tetrafluoroborate
*
E-mail: adavoodnia@mshdiau.ac.ir; Tel.: 0098-0511-8435000; Fax: 0098-0511-8424020
Received September 17, 2010; revised December 23, 2010; accepted January 19, 2011.
978
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Chin. J. Chem. 2011, 29, 978— 982

3
SO H-Functionalized Ionic Liquids for the Facile Dehydration of Aldoximes into Nitriles
1
[
pmim]BF
4
, an IL, as catalyst and reaction medium.
4-Chlorobenzonitrile (2f) (Ar＝4-ClC
6 4
H ): H NMR
Although this method produces satisfactory yields of the
nitriles, it requires a long reaction time (3—5 h) and a
stoichiometric amount of IL, at the same time, this ionic
liquid contains halogen atom, which may cause—under
(CDCl
3
, 400 MHz) δ: 7.48 (d, J＝8.8 Hz, 2H), 7.62 (d,
－
1
J＝8.8 Hz, 2H); IR (KBr) ν: 2227 (CN) cm .
Results and discussion
3
0
certain conditions—serious concerns.
For our investigations, two SO
-methyl-1-(4-sulfonic acid)butylimidazolium hydrogen
sulfate [MIM(CH ) SO H][HSO ] (IL1) and
-(4-sulfonic acid)butylpyridinium hydrogen sulfate
PY(CH SO H][HSO ] (IL ) (Figure 1) were prepared
according to the literature procedure.
3
H-functionalized ILs,
Prompted by these findings and in continuation of
our previous works on the applications of reusable acid
3
31-34
2
4
3
4
catalysts in the synthesis of organic compounds,
1
[
herein we wish to report a green and efficient method-
ology for the dehydration of aldoximes to nitriles using
two halogen-free Brønsted-acidic ILs (Scheme 1).
2
)
4
3
4
2
3
5,36
Scheme 1
Experimental
1 2
Figure 1 Structures of Brønsted-acidic IL and IL .
All chemicals were commercially available and used
without further purification. The Brønsted-acidic ionic
In order to optimize the reaction conditions, the de-
hydration of 4-nitrobenzaldoxime (1c) in the presence
of IL was selected as a model reaction. When the reac-
1
3
5,36
liquids were synthesized according to the literature.
Melting points were recorded on an electrothermal type
100 melting point apparatus. The IR spectra were ob-
tion mixture was heated at 120 ℃ under neat condi-
tions, the product 2c was obtained in high yield after a
few minutes. The efficiency of the reaction is mainly
affected by the amount of the IL (Table 1). The optimal
amount of the catalyst was 20 mol% (Entry 6), the
higher amount of the catalyst did not increase the yield
noticeably. Also, the yields increased as the reaction
temperature was raised and at 120 ℃ the product 2c
was obtained in high yield (Entry 6).
9
tained on a 4300 Shimadzu spectrophotometer as KBr
1
disks. The H NMR (400 & 500 MHz) spectra were re-
corded on Bruker 400 & 500 spectrometer.
Typical procedure for the conversion of aldoximes to
nitriles using Brønsted-acidic ILs
A mixture of 4-nitrobenzaldoxime (2 mmol) and
Brønsted-acidic IL, [MIM(CH ) SO H][HSO ] or [PY-
2
4
3
4
(
2 4 3 4
CH ) SO H][HSO ], (0.4 mmol, 20 mol%) was heated
Table 1 Results of the dehydration of 4-nitrobenzaldoxime (1c)
using [MIM(CH ) SO H][HSO ] (IL ) under different condi-
tions
on the oil bath at 120 ℃. The progress of the reaction
was monitored by TLC. After completion of the reac-
tion, the reaction mixture was cooled to room tempera-
ture and then water was added. The precipitated solid
was filtered off and washed with water to give pure
2
4
3
4
1
a
4-nitrobenzonitrile 2c.
Recycling of the catalyst
The catalyst is soluble in water and could therefore
be recycled as the filtrate. The catalyst was recovered by
evaporation of the water, washed with diethyl ether,
dried at 50 ℃ under vacuum for 1 h and reused in an-
other reaction without appreciable reduction in the
catalytic activity.
b
Entry
n(IL)/n(substrate)
0.1/2
T/℃ Time/min
Yield /%
1
2
3
4
5
6
7
8
100
120
100
120
100
120
140
140
120
120
60
53
62
54
68
81
92
93
93
0.1/2
0.2/2
1
Selected FT-IR and H NMR data
0.2/2
60
1
3
-Nitrobenzonitrile (2b) (Ar ＝ 3-NO C H ):
H
2
6
4
0.4/2
10
NMR (CDCl
3
, 400 MHz) δ: 7.77 (t, J＝8.0 Hz, 1H),
0.4/2
10
8
.03 (dt, J＝7.6, 1.2 Hz, 1H), 8.50 (ddd, J＝8.4, 2.4, 1.2
0.4/2
15
Hz, 1H), 8.56 (t, J＝1.6 Hz, 1H); IR (KBr) ν: 2237
－
1
(
CN), 1535 & 1356 (NO
2
) cm .
0.6/2
15
1
a
b
4
-Nitrobenzonitrile (2c) (Ar ＝ 4-NO
2
C
6
H
4
):
H
All reactions were done under neat conditions; isolated yields.
NMR (DMSO-d
6
, 500 MHz) δ: 7.66 (d, J＝8.6 Hz, 2H),
7
.88 (d, J＝8.6 Hz, 2H); IR (KBr) ν: 2233 (CN), 1525
The effects of solvents such as CHCl , CH Cl ,
3
2
2
－
1
&
1348 (NO
2
) cm .
CH CN, EtOH, MeOH and H O were also studied, but
3
2
Chin. J. Chem. 2011, 29, 978— 982
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
979

Davoodnia et al.
FULL PAPER
in comparison with neat conditions the reaction times
were longer and the yields were considerably lower.
The scope and generality of this method were illus-
electron-donating groups. They were of high purity as
determined by TLC and H NMR spectroscopy. We
think that the IL works here as a catalyst as well as a
benign reaction medium. Also, the reactions in the
1
trated with several aldoximes in the presence of IL
1
and
IL , and the results are summarized in Table 2. The pro-
2
1
presence of IL were faster and the yields were more
cedure turned out to be general for a range of structur-
ally diverse aromatic aldoximes. Aromatic aldoximes
with electron-withdrawing or electron-donating groups
were cleanly, easily, and efficiently dehydrated and af-
forded excellent isolated yields of nitriles within a short
reaction time. The results also show that the aromatic
aldehydes with electron-withdrawing groups react faster
and the yields are more than the aromatic aldehyde with
than IL
2
.
Reusability of the catalyst was also investigated. For
this purpose, the same model reaction was again studied
in the optimized conditions. After the completion of the
reaction, the reaction mixture was cooled to room tem-
perature and then water was added. The precipitated
solid was filtered off and the catalyst was recovered
from the filtrate by evaporation of the water and reused
a
Table 2 Dehydration of aldoximes using [MIM(CH
2
)
4
SO
3
H][HSO
4
] (IL
1
) and [PY(CH
2
)
4
SO
3
H][HSO
4
2
] (IL )
b
c
Entry
1
Aldoxime
Product
Time/min (IL
1
/IL
2
)
Yield /% (IL
1
/IL
2
)
18/25
85/80
2
3
4
5
6
12/15
10/15
12/15
15/20
10/15
88/84
92/88
88/85
90/85
90/87
7
8
9
20/22
18/20
20/20
86/84
85/80
90/86
1
0
18/20
85/84
a
b
1
2
mmol of aldoxime, 0.4 mmol (20 mol%) of IL
1
or IL
2
at 120 ℃. All products were characterized by H NMR and IR spectral data
c
and comparision of their physical data with literature reports. Isolated yields.
9
80
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Chin. J. Chem. 2011, 29, 978— 982

3
SO H-Functionalized Ionic Liquids for the Facile Dehydration of Aldoximes into Nitriles
for the similar reaction. As shown in Figure 2, the cata-
lyst could be reused at least five times with only slight
reduction in catalytic activity.
Cyano Compounds, Eds.: Patai, S.; Rappaport, Z., Wiley,
New York, 1983.
3
Srinivas, K. V. N. S.; Reddy, E. B.; Biswanath, D. Synlett
2
002, 625.
4
5
Miller, J. S.; Manson, J. L. Acc. Chem. Rev. 2001, 34, 563.
Romero, M.; Renard, P.; Caignard, D. H.; Atassi, G.; Solans,
X.; Constans, P.; Bailly, C.; Pujol, M. D. J. Med. Chem.
2
007, 50, 294 and references cited therein.
Ellis, G. P.; Romney-Alexander, T. M. Chem. Rev. 1987, 87,
79.
6
7
8
9
7
Raja, R.; Adams, R. D.; Blom, D. A.; Pearl, W. C.; Gianotti,
E. Jr.; Thomas, J. M. Langmuir 2009, 25, 7200.
Heravi, M. M.; Sadjadi, S.; Hekmatshoar, R.; Oskooie, H.
A.; Bamoharram, F. F. Chin. J. Chem. 2009, 27, 607.
Telvekar, V. N.; Akamanchi, K. G. Synth. Commun. 2004,
3
4, 2331.
1
0
1
Sarvari, M. H. Synthesis 2005, 787.
Figure 2 Reusability of IL , [MIM(CH ) SO H][HSO ], for
model reaction.
1
2 4
3
4
1
Narsaiah, A. V.; Sreenu, D.; Nagaiah, K. Synth. Commun.
2
006, 36, 137.
1
2
Supsana, P.; Liaskopoulos, T.; Tsoungas, P. G.; Varvounis,
Although we did not investigate the reaction mecha-
2
9
37
G. Synlett 2007, 2671.
nism, based on Ranu’s and Hajipour’s suggestions, a
plausible mechanism for the present reaction may pro-
ceed as depicted in Scheme 2. Dehydration process is
promoted by the protonation of the hydroxyl group us-
ing a Brønsted acid, converting this moiety to a better
13 Gucma, M.; Golebiewski, W. M. Synthesis 2008, 1997.
14 Hart-Davis, J.; Battioni, P.; Boucher, J. L.; Mansuy, D. J.
Am. Chem. Soc. 1998, 120, 12524.
15 Lehnert, W.; Kunzer, W. Tetrahedron Lett. 1971, 12, 559.
16 Attanasi, O.; Palma, P.; Serra-Zanetti, F. Synthesis 1983,
741.
leaving group. Therefore, it is proposed that the IL
1
and
IL facilitate the formation of the intermediates that
2
convert to the corresponding nitriles 2a—2j by abstrac-
1
7
Choi, E.; Lee, C.; Na, Y.; Chang, S. Org. Lett. 2002, 4,
2369.
＋
2－
4
tion of H by SO
.
18
Khezri, S. H.; Azimi, N.; Mohammed-Vali, M.; Eftek-
hari-Sis, B.; Hashemi, M. M.; Baniasadi, M. H.; Teimouric,
F. Arkivoc 2007, 15, 162.
Scheme 2
1
9
0
Glass, R. S.; Hoy, R. C. Tetrahedron Lett. 1976, 1781.
Nishiyama, K.; Oba, M.; Watanabe, A. Tetrahedron 1987,
2
4
3, 693.
2
1
2
Ranu, B. C.; Banerjee, S. Org. Lett. 2005, 7, 3049.
2
Yadav, L. D. S.; Awasthi, C. Tetrahedron Lett. 2009, 50,
3
801.
23
Cole, A. C.; Jensen, J. L.; Ntai, I.; Tran, K. L. T.; Weaver,
K. J.; Forbes, D. C.; James, J.; Davis, H. J. Am. Chem. Soc.
Conclusion
2
002, 124, 5962.
In conclusion, we have developed a very simple and
efficient method for the dehydration of aldoximes to
nitriles using two halogen-free Brønsted-acidic ILs as
green and efficient catalysts under solvent-free condi-
tions. The catalysts can be reused after a simple
work-up, without appreciable reduction in their catalytic
activities. Other advantages of this protocol are high
yields, short reaction times, easy work-up and absence
of any volatile and hazardous organic solvents.
24 Qiao, K.; Yokoyama, C. Catal. Commun. 2006, 7, 450.
2
5
Wasserscheid, P.; Sesing, M.; Korth, W. Green Chem. 2002,
, 134.
4
26
27
28
Wilkes, J. S. J. Mol. Catal. A: Chem. 2004, 214, 11.
Wang, H.; Jiang, D.; Dai, L. Catal. Commun. 2008, 9, 2475.
Cheng, G.; Duan, X.; Qi, X.; Lu, C. Catal. Commun. 2008,
1
0, 201.
Saha, D.; Saha, A.; Ranu, B. C. Tetrahedron Lett. 2009, 50,
088.
Wasserscheid, P.; Hal, R. V.; Bösmann, A. Green Chem.
002, 4, 400.
29
30
31
32
6
References
2
Davoodnia, A.; Bakavoli, M.; Barakouhi, G.; Tavakoli-
Hoseini, N. Chin. Chem. Lett. 2007, 18, 1483.
1
Tennant, G. In Comprehensive Organic Chemistry, Vol. 1,
Eds.: Barton, D.; Ollis, D. W.; Sutherland, I. O., Pergamon,
Oxford, 1979, p. 528.
Davoodnia, A.; Heravi, M. M.; Rezaei-Daghigh, L.; Tava-
koli-Hoseini, N. Monatsh. Chem. 2009, 140, 1499.
2
Fatiadi, A. J. In Preparation and Synthetic Applications of
Chin. J. Chem. 2011, 29, 978— 982
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
981

Davoodnia et al.
FULL PAPER
33
34
35
Davoodnia, A.; Bakavoli, M.; Moloudi, R.; Khashi, M.; Ta-
vakoli-Hoseini, N. Chin. Chem. Lett. 2010, 21, 1.
Commun. 2008, 9, 337.
36 Gui, J.; Cong, X.; Liu, D.; Zhang, X.; Hu, Z.; Sun, Z. Catal.
Commun. 2004, 5, 473.
Davoodnia, A.; Heravi, M. M.; Safavi-Rad, Z.; Tava-
koli-Hoseini, N. Synth. Commun. 2010, 40, 2588.
37 Hajipour, A. R.; Khazdooz, L.; Ruoho, A. E. Catal. Com-
mun. 2008, 9, 89.
Wang, W.; Shao, L.; Cheng, W.; Yang, J.; He, M. Catal.
(E1009176 Li, L.)
9
82
www.cjc.wiley-vch.de
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2011, 29, 978— 982