Design, synthesis, characterization and catalytic performance of a new cellulose-based magnetic nanocomposite in the one-pot three-component synthesis of α-aminonitriles

Article abstract of DOI:10.1002/aoc.3443

A sulfonated magnetic cellulose-based nanocomposite was prepared and characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Then, it was used as a green nanoca

Full text of DOI:10.1002/aoc.3443

Full paper
Received: 22 December 2015
Accepted: 4 January 2016
Published online in Wiley Online Library: 18 February 2016
(wileyonlinelibrary.com) DOI 10.1002/aoc.3443
Design, synthesis, characterization and catalytic
performance of a new cellulose-based magnetic
nanocomposite in the one-pot three-
component synthesis of α-aminonitriles
Ali Maleki*, Elnaz Akhlaghi and Reza Paydar
A sulfonated magnetic cellulose-based nanocomposite was prepared and characterized using scanning electron microscopy,
energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Then, it was used as a green
nanocatalyst for the synthesis of α-aminonitriles by a one-pot three-component condensation reaction of aldehydes or ketones,
amines and trimethylsilylcyanide in ethanol at room temperature. The reaction procedure is simple, yields are very high, reaction
time is very short and the catalyst can be easily separated from the reaction mixture and reused in subsequent reactions without
significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web-site.
Keywords: cellulose nanocomposite; magnetic nanoparticles; α-aminonitriles; multicomponent reaction; green synthesis
K2PdCl4,[26] sulfated tungstate,[27] iron,[28] Zr(HSO4)4,[29] 2,4,6-trichloro-
Introduction
1,3,5-triazine (cyanuric acid)[30] and PVP–SO2 complex.[31]
In recent years, green chemistry has been one of the most impor-
tant aspects of chemists’ experimental and industrial efforts.[1]
Due to their considerable atom efficiency and significant diversity,
multicomponent reactions (MCRs) have occupied an important part
of the green chemistry world. MCRs are defined as one-pot reac-
tions in which more than two starting materials incorporate to form
a product. MCRs have also some other unique properties such as
atom economy, being convergent and high bond-forming index.[2]
The Strecker reaction is an important MCR that for the first time
was reported by Adolph Strecker in 1850, and it is the oldest
synthesis of α-amino acids.[3] Furthermore, this reaction is one of
the most convenient and economical methods for obtaining
α-amino acids on either a laboratory scale or technical scale.[4]
Since the first documenting of the Strecker reaction, it has
attracted more and more attention of organic chemists and
biochemists and even today, more than one-and-a-half centuries
after its discovery, it is one of the most popular reactions in
organic and pharmaceutical chemistry. Nowadays this reaction is
extensively used because it provides a robust, direct and econom-
ically viable access to various α-amino acids.[5] Over recent years,
many catalysts for the Strecker reaction and synthesis of α-amino
nitriles have been introduced and developed: sulfuric acid-
modified PEG-6000,[6] tin exchanged zeolite,[7] γ-Al2O3-supported
12-tungstosilicic acid,[8] sulfamic acid-functionalized magnetic
Fe3O4 nanoparticles,[9] SO3H-functionalized ionic liquid,[10] xanthan
sulfuric acid,[11] guanidine hydrochloride,[12] Zr-MCM-41
nanoreactors,[13] nano-powder TiO2 P25,[14] cellulose sulfuric acid,[15]
chitosan,[16] SBA-15-supported sulfonic acid,[17] N-heterocyclic
carbene amidate palladium(II) complex,[18] B-MCM-41,[19] mont-
morillonite KSF clay.[20] magnesium oxide,[21] indium(III) iodide,[22]
Al-MCM-41,[23] MCM-41-anchored sulfonic acid,[24] Fe(Cp)2PF6,[25]
Nevertheless, most of these methods suffer from long reaction
times, expensive reagents, harsh reaction conditions, tedious
workup procedures and usually low yields. Therefore, due to the
importance of the Strecker reaction in organic and pharmaceutical
chemistry, introducing a new, green, rapid, efficient and inexpen-
sive catalyst for this reaction is of prime importance. The synthesis
of nanoscale cellulose composites and their applications in various
chemical and pharmaceutical fields have attracted much attention,
because of their high strength and stiffness combined with low
weight, biodegradability and renewability.[32] Furthermore, the
magnetic property of materials is one of the most important
aspects in the study and application of catalysts. Accordingly, using
an eco-friendly magnetic nanocatalyst in the Strecker reaction
seems useful.
In continuation of our previous works on the preparation of new
catalysts and their application in MCRs,[15,33,34] herein we introduce
Fe3O4@cellulose-OSO3H (MCSA) as a green nanocatalyst for the
synthesis of α-aminonitriles 4a–y by a one-pot three-component
reaction of aldehydes or ketones 1, amines 2 and trimethyl-
silylcyanide (TMSCN) 3 in EtOH at room temperature (Scheme 1).
To the best of our knowledge, this is the first report of the prepara-
tion and application of the MCSA nanocomposite as a catalyst in
organic reactions.
*
Correspondence to: Ali Maleki, Catalysts and Organic Synthesis Research
Laboratory, Department of Chemistry, Iran University of Science and
Technology, Tehran 16846-13114, Iran. E-mail: maleki@iust.ac.ir
Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry,
Iran University of Science and Technology, Tehran, 16846-13114, Iran
Appl. Organometal. Chem. 2016, 30, 382–386
Copyright © 2016 John Wiley & Sons, Ltd.

Design, synthesis and performance of a new nanocomposite
Results and discussion
Catalyst characterization
Scheme 1. MCSA-catalysed Strecker reaction.
Fourier transform infrared (FT-IR) spectroscopy
FT-IR spectroscopy was used for the confirmation of the formation
of MCSA (Fig. 1). The FT-IR spectral data indicate the formation of
O S bonds between cellulose and SO3H and O H bonds between
cellulose and Fe3O4.
Scanning electron microscopy (SEM)
The particle size was studied using SEM as illustrated in Fig. 2, and
the identification of MCSA is based on the analysis of SEM images.
The obtained SEM images of the nanoparticles clearly show that
Fe3O4 nanoparticles are properly supported on cellulose–OSO3H.
Energy-dispersive X-ray spectroscopy (EDX)
To identify the elemental composition of MCSA, EDX was used.
According to Fig. 3(a), it can be seen clearly from the EDX pattern
that Fe3O4 nanoparticles are present in the cellulose matrix
resulting in the target nanocomposite, and chemical characteriza-
tion of a typical sample shows that it is composed of iron, sulfur,
carbon and oxygen elements.
Figure 1. FT-IR spectra of cellulose, cellulose–OSO3H and MCSA.
(a)
(b)
(c)
Figure 2. SEM images of MCSA.
Figure 3. (a) EDX pattern of MCSA. (b, c) XRD patterns of MCSA.
Appl. Organometal. Chem. 2016, 30, 382–386
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

A. Maleki, E. Akhlaghi and R. Paydar
X-ray diffraction (XRD)
Catalytic properties
XRD was also used to determine the crystal structure of the
superparamagnetic nanoparticles. The XRD pattern of MCSA is
shown in Fig. 3(b). The XRD pattern of MCSA indicates the cellulose
sheets along their stacking direction and diffraction peaks corre-
spond to appropriate crystal indexes, which is in agreement with
those measured by EDX. The diffraction signals, positions and
relative intensities of all peaks are confirmed with the standard
XRD pattern of Fe3O4.
For the optimization of the reaction conditions, the condensation of
4-chlorobenzaldehyde (1 mmol), aniline (1 mmol) and TMSCN
(1.2 mmol) in the presence of a catalytic amount of MCSA nano-
composite was performed with stirring at ambient temperature in
various solvents and solvent-free conditions. The results show that
the best efficiency and the highest yield of the reaction are when it
is carried out in EtOH and that is much better than other solvents
such as H2O, MeOH, CH3CN, CH2Cl2 and EtOAc or under solvent-free
conditions (Table 1, entry 3).
To investigate the optimized amount of catalyst in this case, the
reaction was carried out with various amounts of catalyst. It turns
out that 40 mg of catalyst is the best and optimized amount
(Table 1, entry 3).
Table 1. Optimization of reaction conditions in the reaction of
4-chlorobenzaldehyde, aniline and TMSCN at room temperature
Entry Solvent
Catalyst
Amount (mg) Time (min) Yield (%)
We also investigated the individual catalytic potential of
cellulose, cellulose–OSO3H, Fe3O4@cellulose and Fe3O4 in pilot ex-
periments (Table 1, entries 12–15). Cellulose catalyses the reaction
in the same time, but the yield of the reaction is low (Table 1, entry
12). Cellulose–OSO3H catalyses the reaction in the same time but
the yield of the reaction is lower than that with MCSA and higher
than that with cellulose (Table 1, entry 13). In addition, when
cellulose or cellulose–OSO3H is separated from the reaction mix-
ture, the catalyst recyclability decreases. Moreover, the colour of
cellulose and cellulose–OSO3H, in most cases, is similar to the
product and this engenders problems during catalyst separation
and makes the product indistinguishable from the catalyst. In the
case of MCSA, due to the magnetism, separation is very simple
and recoverability is significant (Table 1, entry 3).
1
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
H2O
—
—
30
40
50
60
80
40
40
40
40
40
40
40
40
40
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
0
2
MCSA
87
95
93
91
85
80
77
47
67
65
55
71
69
53
3
MCSA
MCSA
MCSA
MCSA
MCSA
4
5
6
7
8
CH3CN MCSA
CH2Cl2 MCSA
EtOAc MCSA
9
10
11
12
13
14
15
—
EtOH
EtOH
EtOH
EtOH
MCSA
Cellulose
Cellulose–OSO3H
Fe3O4@cellulose
Fe3O4
To investigate the efficiency and applicability of this catalyst in
the three-component synthesis of α-aminonitriles 4a–y, the reac-
tion was extended to other substituted aldehydes and amines at
Table 2. Synthesis of α-aminonitriles (4a–y) in the presence of a catalytic amount of MCSA in EtOH at room temperature
Entry
R1
R2
R3
Product
Time (min)
Yield (%)
1
4-Chlorophenyl
2-Chlorophenyl
Phenyl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
4a
4b
4c
10
15
15
25
30
25
15
15
30
25
90
50
60
50
45
90
45
90
20
30
25
30
30
120
90
95
91
87
93
95
90
95
90
93
92
88
90
82
85
90
80
90
88
90
93
83
90
92
80
85
2
3
4
4-Methoxyphenyl
4-Methylphenyl
4-Hydroxyphenyl
3-Nitrophenyl
4-Nitrophenyl
2-Nitrophenyl
2,4-Dichlorophenyl
2,6-Dichlorophenyl
3-Hydroxyphenyl
Furan
4d
4e
4f
5
6
7
4 g
4 h
4i
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
4j
4 k
4 l
4 m
4n
4o
4p
4q
4r
Thiophene
Styrene
4-Dimethylaminophenyl
Naphthalene
para-Benzoic acid
4-Chlorophenyl
4-Nitrophenyl
4-Methoxyphenyl
3-Nitrophenyl
Phenyl
4-Methylphenyl
4-Methylphenyl
4-Methylphenyl
4-Methylphenyl
4-Methylphenyl
Phenyl
4 s
4 t
4u
4v
4w
4×
4y
Phenyl
Methyl
Cyclohexane
Cyclohexane
Phenyl
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Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 382–386

Design, synthesis and performance of a new nanocomposite
room temperature in EtOH (Table 2). The best result is obtained for
the condensation of 4-chlorobenzaldehyde (1 mmol), aniline
(1 mmol) and TMSCN (1.2 mmol) to produce 4a after 10 min in
95% yield (Table 2, entry 1).
completion of the reaction, MCSA can be adsorbed onto the
magnetic stirring bar, recovered and reused several times in subse-
quent runs using the same recovered catalyst without significant
loss of catalytic activity (Fig. 4). In addition, the catalyst is very active,
green, stable to air and moisture, and inexpensive.
Proposed mechanism
Conclusions
A proposed mechanism for the synthesis of α-aminonitriles 4a–y in
the presence of MCSA as a promoter is shown in Scheme 2. It is
obvious that the initial event is the formation of iminium from an
activated aldehyde or ketone and an amine.[15] On the basis of
the chemistry of reaction of TMSCN with imines, the product is
produced by nucleophilic attack of CNÀ to iminium. In this reaction,
no undesired side product (such as cyanohydrin trimethylsilyl ether
that is an adduct between aldehyde or ketone and TMSCN) is
observed because of the rapid formation of the iminium intermedi-
ate in the reaction pot.
In summary, we have introduced a new biopolymer-based hetero-
geneous magnetic nanocatalyst applicable in the synthesis of
organic compounds. Then, efficient and selective synthesis of
α-aminonitriles was carried out starting from simple and readily
available precursors including benzaldehyde, aniline and TMSCN
in the presence of a catalytic amount of magnetically recoverable
MCSA. The novelty in the reaction conditions would be a superior
proton source in comparison with supported inorganic solid acids
and acidic resins. High yields, ‘greenness’ and recyclability of the
catalyst with no loss in its activity, simple separation of the catalyst,
simple experimental procedure and product isolation, and use of
nontoxic, noncorrosive and inexpensive magnetic solid acid
catalyst are important features of this new protocol for the prepara-
tion of α-aminonitriles.
Catalyst recycling
One of the most important aspects of our innovation in the
introduced catalyst is its magnetism. This property allows the
recoverability of the catalyst and facilitates its separation. After
Experimental
All solvents, chemicals and reagents were purchased from Merck,
Fluka or Aldrich. Melting points were measured with an Electrother-
mal 9100 apparatus and are uncorrected. FT-IR spectra were
recorded with a Shimadzu IR-470 spectrometer by the method of
1
KBr pellet. H NMR and 13C NMR spectra were recorded with a
Bruker DRX-500 Avance spectrometer at 500 and 125 MHz,
respectively. SEM images were obtained with a Seron AIS 2100.
EDX spectra were recorded with a Numerix DXP–X10P. XRD
measurements were carried out using a JEOL JDX–8030 (30 kV,
20 mA). The products were identified by comparison of their
spectroscopic and analytical data with those of authentic samples.
Synthesis of MCSA nanocomposite
Scheme 2. Proposed mechanism for the synthesis of α-aminonitriles 4a–y.
Initially, an aqueous solution of NaOH, urea and water was prepared
in a ratio of 7:12:81, respectively, and its temperature was
decreased to À12°C using ice and salt. Then 2.0 g of cellulose was
dissolved directly in the solution. Then, 3.0 g of FeCl2Á4H2O and
8.0 g of FeCl3Á6H2O were dissolved in 100 ml of deionized water
and then added dropwise to the solution, thus forming
Fe3O4@cellulose. Fe3O4@cellulose microcrystals (5.00 g) were
added to 20 ml of CHCl3 and stirred vigorously. Chlorosulfonic acid
(1.00 g) was added dropwise at 0°C during 2 h. When addition was
completed, the mixture was stirred for 2 h. Then, the solution was
filtered and washed with methanol (3 × 10 ml) and dried at room
temperature to afford a brown powder. In this way, MCSA, which
is a new nanocomposite, was synthesized.
Typical procedure for preparation of 2-(N-anilino)-2-(4-
chlorophenyl)acetonitrile (4a)
A mixture of 4-chlorobenzaldehyde (0.140 g, 1 mmol), aniline
(0.093 g, 1 mmol) and TMSCN (0.120 g, 1.2 mmol) in 3 ml of EtOH
was stirred for 10 min at ambient temperature in the presence of
MCSA nanocomposite (0.040 g). After completion of the reaction,
as indicated by TLC (ethyl acetate–n-hexane, 1:3), the catalyst was
Figure 4. Reusability of MCSA in the synthesis of 4a.
Appl. Organometal. Chem. 2016, 30, 382–386
Copyright © 2016 John Wiley & Sons, Ltd.
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Supporting Information
Additional supporting information may be found in the online
version of this article at the publisher’s web site.
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 382–386