Synthesis of α-amino nitriles through Strecker-type reaction using SO3H -functionalized ionic liquid as a homogeneous and water tolerant-acidic catalyst

Article abstract of DOI:10.1016/j.crci.2011.12.005

Task-specific ionic liquid (TSIL) bearing a sulfonic acid group in imidazolium cation (10 mol %), was found to be an effective catalyst for a Strecker-type reaction in water at room temperature. A wide variety of aldehydes/ketones, amines and TMSCN as cya

Full text of DOI:10.1016/j.crci.2011.12.005

C. R. Chimie 15 (2012) 471–473
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Preliminary communication/Communication
Synthesis of
a–amino nitriles through Strecker-type reaction using
SO H -functionalized ionic liquid as a homogeneous and water
3
tolerant-acidic catalyst
Jafar Akbari
Chemistry Department, Buinzahra branch, Islamic Azad University, Buinzahra, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Task-specific ionic liquid (TSIL) bearing a sulfonic acid group in imidazolium cation
Received 12 August 2011
Accepted after revision 8 December 2011
Available online 28 April 2012
(
10 mol %), was found to be an effective catalyst for a Strecker-type reaction in water at
room temperature. A wide variety of aldehydes/ketones, amines and TMSCN as cyanide
source can be easily transformed into the corresponding -amino nitriles. The water
a
tolerant catalyst could be recycled five times without loss of any activity.
Keywords:
ß 2012 Published by Elsevier Masson SAS on behalf of Acad e´ mie des sciences.
Functionalized ionic liquid
Strecker
Recycling
Homogeneous
1
. Introduction
safe, easily-handled, most soluble in organic solvents and
more effective cyanide ion source for the nucleophilic
Organic compounds with versatile functional groups
such as -amino nitriles are extremely useful synthetic
intermediates. The nitrile functionality can be hydrolyzed
easily to produce -amino acids, and nucleophilic addi-
tions to the nitrile group provide access to -amino
aldehydes, -amino ketones, -amino alcohols, 1,2-
diamines and many nitrogen containing heterocycles [1].
The Strecker reaction [2], which proceeded via the addition
of alkaline metal cyanides or hydrogen cyanide to imine
addition reaction) catalyzed by Lewis or protic acids in
conventional organic solvents has been described [3–14].
In some cases, the protocols involve the use of strong and
expensive or unrecoverable catalysts, harsh acidic condi-
tions, toxic organic solvent, tedious work-up procedure
leading to the generation of large amount of metal-
containing waste and longer reaction times. Furthermore,
many of these catalysts are deactivated or sometimes
decomposed by amines and water that exist during imine
formation. There are also a few reports using no catalyst
[15], but their reaction time lies in the range of hours.
Therefore, it is still desirable to develop an efficient,
recyclable catalyst and practical method for this reaction
under mild conditions.
In recent years, the use of ionic liquids (ILs) has received
more attention as eco-friendly, reusable and alternative
reaction media in organic synthesis because of their
unique properties, such as high thermal and chemical
stability, negligible vapor pressure, no flammability, high
loading capacity, immiscibility with a number of organic
solvents and excellent electrical conductivity [16–20].
Moreover, ionic liquids are simple and easy to recycle and
a
a
a
a
a
proved to be an effective one for the preparation of
a-
amino nitriles on a laboratory, as well as on an industrial
scale. The classical Strecker reaction is usually carried out
in aqueous solution, which has some limitations, and the
work-up procedure is too tedious leading to generation of
large amount of toxic waste. In order to partially avoid
these inconveniences, several modifications of the Strecker
reaction via a three-component condensation of aldehyde,
amine and trimethylsilyl cyanide (a promising alternative
to alkali cyanide and HCN due to its nature as a simplest,
Email address: j_akbari@modares.ac.ir.
1
631-0748/$ – see front matter ß 2012 Published by Elsevier Masson SAS on behalf of Acad e´ mie des sciences.
doi:10.1016/j.crci.2011.12.005

4
72
J. Akbari / C. R. Chimie 15 (2012) 471–473
Table 1
Strecker reaction of aldehydes/ketones with amines catalyzed by task-specific ionic liquid (TSIL).
1
2
3
4
Entry R
R
R
R
Time (h)
Yield (%)
a
a Phenyl
H
H
H
H
H
H
H
Me
H
H
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Ethyl
H
10 min
15 min
15 min
1
98, 98, 98,98, 97, 96
b 4-Cl-Phenyl
H
98
96
95
94
95
92
98
94
96
c 4-O
2
N-Phenyl
H
d 2-Furyl
e tert-Butyl
f Cinnamyl
g Cyclohexyl
h Phenyl
H
H
1
H
30 min
3
H
H
15 min
1.5
i Phenyl
Ethyl
Benzyl
j Phenyl
Benzyl
1.5
a
The range of the yields of subsequent runs using the same recovered catalyst.
R4
N
CN
yield of a-amino nitrile obtained. The Strecker-type
reaction of benzaldehyde aniline and TMSCN is examined
in the presence of catalytic amount of TSIL at room
O
TSIL (10 mol%)
+
TMSCN
R
4
+
R1
R1
R2
R3
N
H
H
2
O
R2
R3
temperature in water. 10 mol % of catalyst give
a-amino
nitrile with 98% yield in 10 min in H O, while decreasing
2
TSIL:
N
N
the catalyst to 5 mol % gives lower yield of 70% in 10 min,
with 20 mol % catalyst the yield is increased that affords
3
SO H
the corresponding
0 min. Accordingly, 10 mol % TSIL catalyst loading in H
as a solvent is considered optimal for the synthesis of the
synthesis of -amino nitriles.
A series of -amino nitriles were synthesized by using
a-amino nitrile in 98% yield within
CF
3
SO
3
1
2
O
Scheme 1.
a
a
their properties can be fine-tuned by changing the anion or
the alkyl group attached to cation. Most recently, much
more attention has been focused on the preparation of
functionalized ionic liquids (FILs), through incorporation of
different functional groups as a part of the cation and/or
anion, so-called task-specific ionic liquids (TSILs), and their
applications in chemical transformations. The incorpo-
ration of functional groups offers flexibility to the chemist
to devise the most idealized solvent and catalyst, catering
for the need of any particular process. Moreover, specific
functional groups, such as acid can be incorporated into the
ionic liquids for task-specific purposes. For example,
BrØnsted acidic ionic liquids, which can take dual role in
organic reactions as solvents and catalysts. Many acid-
catalyzed organic reactions have been carried out success-
fully catalyzed by this ionic liquids [21–26]. They have
shown great promise not only as alternative green
solvents, but also as reagents or catalysts in organic
transformations [27–30]. Herein we wish to report the first
study on application of inexpensive and easily accessible
functionalized ionic liquid as catalyst for Strecker reaction
of aldehydes and ketones in mild condition (Scheme 1).
different aldehydes, amines and TMSCN in the presence of
TSIL (10 mol %) in water. The catalytic system worked well
with acid sensitive aldehydes,
a, b-unsaturated aldehyde
to generate the corresponding products without observing
the formation of other side products. Encouraged by the
above results, we continued our task to explore the
reactivity of different ketones with aniline and TMSCN
under similar reaction conditions. As shown in Table 1,
ketones could efficiently undergo reaction with aniline and
TMSCN to give the products in excellent yields. However,
the Strecker-type reaction using ketones and aromatic
amines has been repeatedly cited in the literature as a
challenge [33]. This catalytic effect of TSIL could be
ascribable to the presence of the solfonic group present
on the TSIL. Indeed, it has been previously shown that the
water content certainly has an effect on the activity of the
TSIL [34].
The recycling performance of TSIL was investigated by
the Strecker reaction of benzaldehyde with aniline under
the identical conditions (Table 1, entry a). As the data listed
show that this ionic liquid could be reused for at least five
times without noticeable decrease of the catalytic activity.
The reaction still provided a reasonable yield and the same
selectivity as initially. It should be noted that it is very easy
to separate the catalyst from the reaction system after
reaction by simple extraction with water.
[
4 4
BMIm][CLO ] and [BMIm][BF ] have been previously used
as reaction medium for Strecker reaction [31,32]. The
present paper could represent an advance since the
functionalized ionic liquid is catalytically used in water.
2
. Results and discussion
3. Conclusion
Initially we studied the Strecker reaction with benzal-
dehyde and aniline as model substrate with TMSCN using
TSIL for optimization. The rate of reaction was moderate
In summary, we have developed a clean and environ-
mentally friendly protocol for the one-pot synthesis of a-
and 35% yield of
performed at room temperature using TSIL in water as
solvent. The rate of the reaction was fast in H O and 98%
a
-amino nitrile obtained. The reaction was
amino nitriles in good to excellent yields, from ketones/
aldehydes in combination with an amine using BrØnsted
acidic ionic liquid as homogeneous and recyclable catalyst
2

J. Akbari / C. R. Chimie 15 (2012) 471–473
473
1
and TMSCN as cyanide source. The simple experimental
procedure, fast reaction, easy product separation and reuse
of ionic liquids makes the use of the above ionic liquid as
greener and economically viable catalyst for the Strecker
reaction compared with the traditional protocols. More-
over, the TSIL is stable in water in spite of other
nonfunctionalized one.
3
131.4, 145.5. Compound d: H NMR (90 MHz, CDCl ): d = 4.1
1
3
(
br s, 1H, NH), 5.4 (s, 1H), 6.3–6.5 (m, 3H), 7.1–7.8 (m, 5H).
C
3
NMR (125 MHz, CDCl ): d = 47.3, 102.3, 113.8, 114.6, 116.1,
1
18.0, 130.0, 133.4, 139.0, 147.8.
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1
[
2
Appendix A
1
[
1
13
The spectral data ( H, C NMR) of known compounds
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1
Compound a: H NMR (500 MHz, CDCl
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13
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