Magnetic solid sulfonic acid decorated with hydrophobic regulators: A combinatorial and magnetically separable catalyst for the synthesis of α-aminonitriles

Article abstract of DOI:10.1021/co500022g

A three-component, Strecker reaction of a series of aldehydes or ketones, amines, and trimethylsilyl cyanide for the synthesis of α-aminonitriles in the presence of a catalytic amount of a magnetic solid sulfonic acid catalyst, Fe₃O₄@SiO₂@Me&Et-PhSO₃H under solvent-free conditions have been investigated. This catalyst, with a combination of hydrophobicity and acidity on the Fe₃O ₄@SiO₂ core-shell of the magnetic nanobeads, as well as its water-resistant property, enabled easy mass transfer and catalytic activity in the Strecker reaction. The catalyst was easily separated by an external magnet and the recovered catalyst was reused in 6 successive reaction cycles without any significant loss of activity.

Full text of DOI:10.1021/co500022g

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Article
Magnetic solid sulfonic acid decorated with hydrophobic
regulators: A combinatorial and magnetically
separable catalyst for the synthesis of #-aminonitriles
Akbar Mobaraki, Barahman Movassagh, and Babak Karimi
ACS Comb. Sci., Just Accepted Manuscript • Publication Date (Web): 16 Jun 2014
Downloaded from http://pubs.acs.org on June 23, 2014
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Magnetic solid sulfonic acid decorated with
hydrophobic regulators: A combinatorial and
magnetically separable catalyst for the synthesis of
αꢀaminonitriles
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Akbar Mobaraki,† Barahman Movassagh,*,†and Babak Karimi ‡
†Department of Chemistry, K. N. Toosi University of Technology, P. O. Box 16315ꢀ6118,
Tehran, Iran, Fax: +98ꢀ21ꢀ22853650; Tel: +98ꢀ21ꢀ23064323; Eꢀmail: movassagh@kntu.ac.ir
‡Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Gava
Zang, Zanjan 45137ꢀ66731, Iran, Fax: +98ꢀ241ꢀ4153232; Tel: +98ꢀ241ꢀ4153225; Eꢀmail:
karimi@iasbs.ac.
KEYWORDS Heterogeneous catalyst, Coreꢀshell magnetic solid acid, Hydrophobicity, Strecker
reaction
Dedicated to Prof. Kristin BowmanꢀJames
ABSTRACT
A threeꢀcomponent, Strecker reaction of a series of aldehydes or ketones, amines, and
trimethylsilyl cyanide for the synthesis of αꢀaminonitriles in the presence of a catalytic amount
of a magnetic solid sulfonic acid catalyst, Fe3O4@SiO2@Me&EtꢀPhSO3H under solventꢀfree
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conditions have been investigated. This catalyst, with a combination of hydrophobicity and
acidity on the Fe3O4@SiO2 coreꢀshell of the magnetic nanobeads, as well as its waterꢀresistant
property, enabled easy mass transfer and catalytic activity in the Strecker reaction. The catalyst
was easily separated by an external magnet and the recovered catalyst was reused in 6 successive
reaction cycles without any significant loss of activity.
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INTRODUCTION
Because of their potential applications for replacing liquid mineral acids in industry, solid acid
catalysts have received significant attention;1 they exhibit the advantages of easy separation of
the catalyst from the liquid reaction medium, minimal corrosion, good recyclability, green
chemical process, and enhanced product selectivity.2 Among the solid acids, magnetic
nanoparticles have currently been actively investigated.3
The threeꢀcomponent Strecker reaction (Sꢀ3CR) using an aldehyde or ketone, an amine and a
cyanide source to synthesize αꢀaminonitriles is a wellꢀestablished process and is a useful way to
form C–C bonds in organic synthesis.4 αꢀAminonitriles are regarded as possible precursors to
corrins, porphyrins, nucleicꢀ and nicotinic acids,5 and have an immense number of applications
in the synthesis of a wide variety of pharmacologically relevant molecules of interest.6 They are
also regarded as versatile intermediates for the preparation of sulfurꢀ and nitrogenꢀcontaining
heterocycles, such as thiadiazoles and imidazoles.7 Furthermore, αꢀaminonitriles are the key
precursors of diverse αꢀamino acids for synthesizing proteins,8 and are also chiral building
blocks in the pharmaceutical industry.4a For instance, the (R)ꢀphenylglycinol derivative (a) plays
a key role in the synthesis of 7ꢀmethoxybenzolactamꢀV8, an intermediate of a potent activator of
protein kinase C (Fig. 1).9 Also, compounds (b) and (c) serve as precursors to biologically active
manzacidins10 and cytotoxin and mitosis inhibitor (–)ꢀhemiasterlin,11 respectively (Fig. 1).
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CN
O
Ph
R2
O
N
N
R1
H
N
H
OH
N
Ph
HN
H
CN
OMe
N
NC
OH
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CH3
R1, R2 = H, CH2Ph
(c)
(a)
(b)
Figure 1. The chemical structure of three pharmaceutically important αꢀaminonitriles
synthesized by Strecker type reaction as the basic step.
The classical Strecker reaction is generally carried out with hydrogen cyanide or alkaline
cyanides in aqueous solution4b,12 which has some limitations. To manage these limitations,
several modifications of the Strecker reaction have been reported. These modifications use other
alternative cyanating sources, such as TMSCN,13 K4[Fe(CN)6],14 (EtO)2P(O)CN,15 Bu3SnCN,16
and Et2AlCN.17 Among these cyanating agents, TMSCN has proven to be an effective, relatively
safe, and easilyꢀhandled cyanide anion source. However, many of the TMSCNꢀbased methods
involve the use of expensive reagents, extended reaction times, harsh conditions, and a tedious
aqueous workꢀup generating large amounts of toxic waste. Additionally, many of these catalysts
are deactivated or decomposed by amines and/or the water produced during imine formation.
Although a variety of profound modifications have been made to the original conditions,18ꢀ20 the
development of simple, efficient and general multicomponent procedures, utilizing ketones
remains an unsolved challenge.21
In many acidꢀcatalyzed reactions by solid sulfonic acids, particularly the Sꢀ3CR involving
hydrophobic and hydrophilic substrates, the water produced as a byꢀproduct is coꢀadsorbed on
the surface of the catalyst poisoning the surface and producing a more hydrophilic environment,
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resulting in reduced catalytic activity.3d,22,23 On the other hand, the polarities of the reactants and
products, hydrophobicꢀhydrophilic balance on catalyst’s surface, and the acidity of the catalyst
have considerable effect on the progress of the reaction. Further research studies addressed the
design, synthesis and utilization of the catalytic applications of surface modified –SO3H solid
materials in order to optimize these properties, and the performance of catalysts overall.23e,24,25
Due to the inherent properties of silicaꢀcoated magnetic nanoparticles (Fe3O4@SiO2) such as
biocompatibility, easy renewability and recovery by magnetic separation, thermal stability
against degradation, large surface area and higher loading of active sites, these magnetic particles
have emerged as a useful group of heterogeneous catalysts. Many investigations have been
conducted on the synthesis and characterization of acidic magnetic nanoparticles.3 However, no
attention has been paid to combining hydrophobicity with acidity of materials for providing
bifunctional Fe3O4@SiO2 coreꢀshell magnetic nanoparticles bearing both sulfonic acid and
terminal organic groups as hydrophobicity regulators on the surface of nanocomposites. The
introduction of sulfonic acid and organic groups onto the surface of Fe3O4@SiO2 coreꢀshell is
interesting since the combination of both functionalities26 allows creation of a less polar organic
environment with a relatively strong acidity for acidꢀcatalyzed reactions. As part of our efforts to
explore novel heterogeneous catalysts for organic reactions,24 we have recently reported the
results obtained for the Biginelli reaction using hydrophobic organosulfonic acidꢀfunctionalized
silicaꢀcoated magnetic nanoparticle catalyst Fe3O4@SiO2@Me&EtꢀPhSO3H (Fig. 2).24a In order
to further establish other waterꢀgenerating reactions with our catalyst, we herein report the Sꢀ
3CR of various aldehydes and ketones with amines and TMSCN (Fig. 3).
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HO3S
OH
H3C
O
SO3H
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6
Si CH3
O
Si
Si
O
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Si
O
O
O
O
O
HO
SiO2
Si
O
OH
O
O
Fe3O4
NP
CH3
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Si
H3C
O
O
O
O
O
O
Si
O
O
O
O
H3C
O
O
O
Si
Si
O
CH3
H3C
O
SO3H
HO
SO3H
Figure 2. Hydrophobic magnetic solid sulfonic acid catalyst Fe3O4@SiO2@Me&EtꢀPhSO3H.
RESULTS AND DISCUSSION
To find the best reaction conditions, we first examined the effect of different temperatures and
amounts of the catalyst Fe3O4@SiO2@Me&EtꢀPhSO3H for the Strecker reaction of
acetophenone (2 mmol), aniline (2 mmol), and TMSCN (2.4 mmol) under solventꢀfree condition
as a model reaction. It was found that at higher temperature and mol%, the catalyst performed in
shorter reaction times (Table 1, entries 1ꢀ5). Also, we have shown that reducing the amount of
the catalyst decreased the product yield at 60 °C (Table 1, entries 5ꢀ7). We also examined the
effect of higher temperatures (80 °C) and lower amounts of the catalyst (Table 1, entries 8 and
9). These results showed the significant effect of the catalyst in the reaction and gave the
expected product in a good yield. It was concluded that solventꢀfree conditions at 60 °C in the
presence of 0.5 mol% of the catalyst was the optimized condition for the Sꢀ3CR (Table 1, entry
5).
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O
R1 R2
NHR3
+
R1
CN
R2
R3 NH2
TMSCN
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Water-repellent
H2O
Figure 3. Waterꢀgenerating Sꢀ3CR in the presence of the catalyst in solventꢀfree condition.
To survey the generality of the procedure, we studied the Sꢀ3CR of ketones with amines and
TMSCN under solventꢀfree conditions. Representative results are listed in Table 2. A wide range
of ketones, such as alicyclic, strained cyclic, aliphatic and aromatic, as well as enolizable ketones
smoothly reacted with primary amines to give the corresponding αꢀaminonitriles in good to high
yields.
The reaction was almost equally facile with acetophenone derivatives (Table 2, entries 1ꢀ4, 14,
15 and 21); as expected, the reaction of acetophenone substituted with electronꢀwithdrawing
group occurred in higher yield and shorter reaction time than its electronꢀdonating counterpart
(Table 2, entries 2 and 3).
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Table 1. Effects of temperature and the amount of catalyst for the Sꢀ3CR.a
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Entry
Amount of catalyst
(mol%)
Temperature (°C)
Time (h)
Yield (%)b
9
1
2
3
4
5
6
7
8
9
0.5
25
25
40
40
60
60
60
80
80
48
36
15
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9
82
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80
88
91
83
75
90
83
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1
0.5
1
0.5
0.35
0.25
0.35
0.25
9
9
9
9
a)
Reaction conditions: acetophenone (2 mmol), aniline (2 mmol), TMSCN (2.4 mmol),
Fe3O4@SiO2@Me&EtꢀPhSO3H at various temperatures under solventꢀfree condition.
refer to the isolated pure products.
b)
Yields
The obtained results reveal that the strained and rigid 2ꢀadamantanone gave the corresponding
products in short reaction times and higher yields than other ketones (Table 2, entries 9 and 18).
Heteroaryl ketones, such as 3ꢀacetylindole and 2ꢀacetylfuran, provided good to high yields of the
desired αꢀaminonitriles (Table 2, entries 6 and 7). Acetone, with a relatively low boiling point,
rapidly underwent the condensation within 2 h in high yield despite the fact that its reaction took
place at room temperature (Table 2, entries 13, 20, and 27). Sterically hindered ketones, such as
benzophenone, also reacted with anilines and TMSCN to give the corresponding products in
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moderate to good yields although the reactions proceeded rather slowly and needed 1.5 mol% of
the catalyst (Table 2, entries 8 and 23) or even higher temperature (80 °C, Table 2, entry 17). To
assess the effect of the lower reactivity of aliphatic ketones in the reaction and also to study the
possibility of the formation of TMS enol ethers, the reaction of 2ꢀheptanone, as an enolizable
ketone with 4ꢀbromoaniline was investigated; in fact, the high yield of this reaction showed the
superiority of the imine formation and Sꢀ3CR as opposed to the TMS enol ether formation
(Table 2, entry 28). Also, sterically hindered 2ꢀmethylaniline 2(4), gave a high yield of the
corresponding αꢀaminonitrile in an appropriate time (Table 2, entry 29). Aliphatic amines were
also screened; while the reaction of acetophenone with benzylamine provided the desired product
in a good yield, the reaction of propiophenone with morpholine resulted in a mixture of products,
with very poor yield of the corresponding αꢀaminonitrile (Table 2, entries 30 and 31).
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Inspired by these results, the optimized conditions were also applied to the Sꢀ3CR with
aldehydes at room temperature. Therefore, different aliphatic, aromatic and heteroaromatic
aldehydes reacted with a range of amines, such as piperidine, morpholine, and benzylamine as
well as aniline derivatives, all at room temperature in a solventꢀfree environment. Table 3 shows
the results of these reactions, using the hydrophobic solid acid catalyst Fe3O4@SiO2@Me&Etꢀ
PhSO3H at 0.5 mol%. The reactions are clean and highly selective affording exclusively αꢀ
aminonitriles in high yields (81ꢀ95%) in a reaction time ranging time from 10 to 150 min. The
treatment of various aldehydes and anilines with TMSCN in the presence of the catalyst afforded
the corresponding products (Table 3, entries 1ꢀ9 and 15) in excellent yields within short reaction
times (10ꢀ40 min). This method is equally effective with aldehydes bearing electronꢀ
withdrawing, electronꢀdonating, and stericallyꢀhindered substituents in the aromatic ring (4(2),
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4(3), 4(6), and 4(7)). Moreover, an acid sensitive aldehyde, cinnamaldehyde, reacted well
5
6
without any polymerization under these reaction conditions.
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Table 2. Sꢀ3CR of various ketones and amines catalyzed by catalyst Fe3O4@SiO2@Me&Etꢀ
PhSO3H.a
NR3R4
O
Cat. (0.5 mol%)
R3R4NH
TMSCN
+
+
R1
R2
R1
CN
Solvent-free, 60 °C
R2
1
2
3
R3 R4
Ph
H
2(1)
2(2)
2(3)
2(4)
2(5)
2(6)
4-MeOC6H4
4-BrC6H4
H
H
H
H
2-MeC6H4
PhCH2
R3, R4 = -(CH2)2-O-(CH2)2-
O
O
O
O
O
CH3
CH3
CH3
CH3
CH3
MeO
Cl
OMe
1(1)
1(2)
1(3)
1(4)
1(5)
O
O
CH3
O
O
O
O
O
O
CH3
N
H
1(6)
1(7)
1(10)
1(11)
1(8)
1(9)
O
O
H3C
CH3
1(12)
1(13)
1(14)
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Entry
1
Ketone
1(1)
Amine
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(2)
2(2)
2(2)
2(2)
2(2)
2(2)
2(2)
2(3)
2(3)
2(3)
2(3)
2(3)
2(3)
Product
Time (h)
Yield (%)b
9
9
91
85
3{1(1),2(1)}
3{1(2),2(1)}
3{1(3),2(1)}
3{1(4),2(1)}
3{1(5),2(1)}
3{1(6),2(1)}
3{1(7),2(1)}
3{1(8),2(1)}
3{1(9),2(1)}
3{1(10),2(1)}
3{1(11),2(1)}
3{1(12),2(1)}
3{1(13),2(1)}
3{1(3),2(2)}
3{1(4),2(2)}
3{1(5),2(2)}
3{1(8),2(2)}
3{1(9),2(2)}
3{1(11),2(2)}
3{1(13),2(2)}
3{1(1),2(3)}
3{1(5),2(3)}
3{1(8),2(3)}
3{1(10),2(3)}
3{1(11),2(3)}
3{1(12),2(3)}
2
1(2)
3
9
94
1(3)
10
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4
7
89
1(4)
5
20
87
1(5)
6
24
81
1(6)
7
24
76
1(7)
8
32
78c
1(8)
9
0.75
20
92
1(9)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
83
1(10)
1(11)
1(12)
1(13)
1(3)
20
81
23
90
2
92d
20
89
20
78
1(4)
20 (24)e
32 (48)f
1.5
20
40 (72)e
21 (50)f
91
1(5)
1(8)
1(9)
62 (79)g
79d (90)d,g
90
1(11)
1(13)
1(1)
2
8
20
88
1(5)
32
57 (80)c
1(8)
20
86
1(10)
1(11)
1(12)
20
84
23
91
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2
91d
86
1(13)
1(14)
1(1)
2(3)
2(3)
2(4)
2(5)
2(6)
3{1(13),2(3)}
3{1(14),2(3)}
3{1(1),2(4)}
3{1(1),2(5)}
3{1(5),2(6)}
24
9
88
10
24
70
1(1)
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< 5
1(5)
a) Reaction conditions: ketones (2 mmol), amine (2 mmol), TMSCN (2.4 mmol), catalyst (0.5 mol%), at
b)
c)
d)
60 °C under solventꢀfree condition.
Isolated yields.
1.5 mol% of the catalyst was used.
Reactions were performed at room temperature. e) 1.75 mol% of the catalyst was used. 1.5 mol% of
catalyst at 80 °C was used. g) 1 mol% of the catalyst was used.
f)
Also, an enolizable aldehyde, such as 3ꢀphenylpropionaldehyde produced the corresponding αꢀ
aminonitrile in high yield (5{4(12),2(1)}), Table 3, entry 9). However, primary and secondary
aliphatic amines reacted with aldehydes but with relatively slow reaction rate due to the unstable
nature of the formed aliphatic imines (Table 3, entries 10ꢀ14 and 16). If the reaction time was
prolonged to 120ꢀ150 min, high yields of the products could be obtained.
The catalytic activity and reusability of this hydrophobic magnetic solid acid catalyst was also
studied for the Sꢀ3CR coupling reaction of adamantanone (2 mmol) with aniline (2 mmol) and
TMSCN (2.4 mmol) for 45 min at 60 °C under solventꢀfree condition. Upon completion of the
reaction, the mixture was diluted with EtOAc and the catalyst was easily separated and recovered
by an external magnet and washed with EtOAc and EtOH and finally dried at 100 °C for 30 min
prior to the next run. The crude product was recrystallized from EtOAc/nꢀhexane for further
purification. During the recycling experiment with fresh reactants, under the same reaction
conditions, no considerable change in the activity of the catalyst was observed for at least 6
successive runs which clearly demonstrate the stability of the catalyst for these conditions in the
Sꢀ3CR (Fig. 4).
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Table 3. Sꢀ3CR of various aldehydes and amines catalyzed by catalyst Fe3O4@SiO2@Me&Etꢀ
5
6
PhSO3H.a
7
8
9
O
NR3R4
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Cat. (0.5 mol%)
R3R4NH
R5
H
TMSCN
+
+
R5
CN
Solvent-free, r.t.
H
2
4
5
R3 R4
H
H
H
Ph
2(1)
2(7)
2(5)
4-ClC6H4
PhCH2
R3, R4 = -(CH2)2-O-(CH2)2-
2(6)
2(8)
R3, R4 = -(CH2)5-
CHO
CHO
MeO
CHO
CHO
O2N
CHO
CH3
4(5)
F
4(3)
4(2)
4(4)
4(1)
4(6)
CHO
CH3
CHO
S
CHO
CHO
Cl
CHO
4(10)
4(7)
4(9)
4(8)
CHO
CHO
CHO
4(11)
4(13)
4(12)
Entry
Aldehyde
Amine
Product
Time (min)
Yield (%)b
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1
2
13
20
95
90
94
91
91
89
87
90
89
89
90
83
81
89
92
85
4(1)
4(2)
4(4)
4(5)
4(6)
4(7)
4(8)
4(10)
4(12)
4(1)
4(3)
4(8)
4(13)
4(1)
4(11)
4(9)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(1)
2(5)
2(5)
2(5)
2(5)
2(6)
2(7)
2(8)
5{4(1),2(1)}
5{4(2),2(1)}
5{4(4),2(1)}
5{4(5),2(1)}
5{4(6),2(1)}
5{4(7),2(1)}
5{4(8),2(1)}
5{4(10),2(1)}
5{4(12),2(1)}
5{4(1),2(5)}
5{4(3),2(5)}
5{4(8),2(5)}
5{4(13),2(5)}
5{4(1),2(6)}
5{4(11),2(7)}
5{4(9),2(8)}
3
10
4
15
10
11
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60
5
20
6
20
7
30
8
30
9
40
10
11
12
13
14
15
16
120
120
120
150
150
25
150
a)
Reaction conditions: aldehyde (2 mmol), amine (2 mmol), TMSCN (2.4 mmol), catalyst (0.5 mol%), at room
temperature under solventꢀfree condition. b) Isolated yields.
Finally, we compared the catalytic performance of our catalyst with other catalytic systems
reported in the literature for the Sꢀ3CR of benzaldehyde, aniline, and TMSCN (Table 4). Table 4
clearly demonstrates the advantages of the present work over the other reported protocols, in
terms of the product yield, reaction temperature and time.
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Table 4. Comparison of different catalytic systems with the present work
5
6
7
8
9
Entry
1
Catalyst
NafionꢀFe (100 mg)
Solvent
CH2Cl2
CH2Cl2
CH2Cl2
EtOH
CH2Cl2
CH3CN
–
T (ºC)
60
Time
4 h
Yield (%)a
9527a
8727b
8027b
9722b
9427c
9827d
10025b
9027e
9819c
9227f
9227g
8727g
95b
10
11
12
13
14
15
16
17
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20
21
22
23
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25
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27
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29
30
31
32
33
34
35
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37
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59
60
2
NafionꢀSACꢀ13 (200 mg)
NafionꢀH (200 mg)
60
6 h
3
60
6 h
4
MCMꢀ41ꢀSO3H (5 mg)
r.t.
r.t.
r.t.
50
70 min
14 h
5 min
5 min
3.5 h
1 h
5
Silicaꢀbased Sc (III) interphase (5 mol%)
Silicaꢀsupported H3PW12O40 (7 mol%)
SBAꢀ15ꢀPhꢀPrSO3H (1 mol%)
Montmorillonite KSF clay (1 g)
βꢀCyclodextrin (0.1 mmol)
NiCl2 (5 mol%)
6
7
8
CH2Cl2
H2O
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
9
10
11
12
13
CH3CN
–
12 h
5 h
[Bmim]BF4 (1 ml)
[Bmim]PF6 (1 ml)
6 h
–
Fe3O4@SiO2@Me&EtꢀPhSO3H (0.5 mol%)
13 min
–
a) Reference. b) Present work.
CONCLUSIONS
In summary, we have presented a magnetic solid sulfonic acid modified with hydrophobic
regulators, Fe3O4@SiO2@Me&EtꢀPhSO3H which was efficiently used as a combinatorial and
heterogeneous catalyst for the threeꢀcomponent Strecker reaction for the synthesis of αꢀ
aminonitriles under solventꢀfree condition. This catalyst, with its hydrophobic surface, resulting
from the methyl groups bounded on the surface, enabled the repulsion of water; otherwise, the
sulfonic acid sites would have been deactivated. The catalyst was readily separated by an
external magnet and the recovered catalyst was reused for at least 6 reaction cycles without any
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significant loss of activity. The clean reaction conditions and high selectivity affording
exclusively αꢀaminonitriles in high yields, no observation of undesired side products, and
utilizing a green and magnetically separable heterogeneous catalyst were the advantages of this
work. These results expand the capability of the catalyst and antedate further progress by
creative research to explore the surface hydrophobicity of magnetic catalysts and magnetic
materials in other fields.
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(a)
92
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88
100
90
80
70
60
50
40
30
20
10
0
80
1
2
3
4
5
6
7
Run
(b)
(i)
(ii)
Figure 4. (a) Recyclability of the catalyst Fe3O4@SiO2@Me&EtꢀPhSO3H for the Sꢀ3CR of
adamantanone with aniline in the presence of trimethylsilyl cyanide. (b) The catalyst in a typical
reaction mixture in the absence (i) and the presence (ii) of a magnetic field.
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EXPERIMENTAL
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All chemicals were purchased from Merck and Aldrich Chemical Companies. Melting points
were determined on a Büchi melting point Bꢀ540 apparatus. NMR spectra were recorded at 400,
300 and 250 (1H), and 100.6, 75.4 and 62.9 (13C) MHz respectively, on commercial Bruker
DMXꢀ400, Bruker DMXꢀ300 and Bruker DPXꢀ250 instruments using CDCl3 as solvent. IR
spectra were recorded on an ABB Bomem Model FTLA 2000 spectrophotometer using KBr
discs.
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Preparation of Fe3O4@SiO2@Me&EtꢀPhSO3H catalyst
The synthesis of the Fe3O4@SiO2@Me&EtꢀPhSO3H catalyst was conducted according to the
procedure previously reported.24a In
chlorosulfonylphenyl)ethyltrimethoxysilane
a
typical preparation procedure, 2ꢀ(4ꢀ
(CSPETS, 0.2 g, 0.62 mmol) and
trimethoxymethylsilane (TMMS, 0.2 g, 1.47 mmol) were added to dry toluene (35 mL)
containing silicaꢀcoated magnetic nanoparticles (Fe3O4@SiO2, 1.0 g). The resulting mixture was
stirred for 24 h and then washed with toluene (2 × 15 mL) and distilled water. Finally, the solid
was suspended in H2SO4 (1 M) solution for 2 h, washed several times with water and dried at
room temperature under vacuum overnight to give the desired catalyst. The catalyst was also
characterized by FTꢀIR, VSM, XRD, SEM, TEM, TGꢀDTA, and elemental analysis data, as well
as water adsorptionꢀdesorption, and N2ꢀsorption isotherms. The concentration of sulfonic acid
groups was quantitatively estimated by ionꢀexchange pH analysis and the acid amount was
determined to be 0.7 mmolgꢀ1.24a
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General procedure for the oneꢀpot preparation of αꢀaminonitriles
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6
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8
9
A mixture of aldehyde/ketone (2 mmol), amine (2 mmol), trimethylsilyl cyanide (2.4 mmol) and
catalyst (14.2 mg, 0.5 mol%) were stirred in a sealed tube at r.t./60 °C, respectively for an
appropriate time in solventꢀfree condition (Table 2). The progress and completion of the reaction
was monitored by thin layer Chromatography (TLC). After the completion of the reaction, the
mixture was diluted with ethyl acetate and the catalyst was separated by magnetic decantation.
The crude product was either recrystallized from EtOAc/nꢀhexane or subjected to preparative
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13
TLC (silica gel) for further purification. All compounds were characterized by IR, H, and C
NMR spectroscopy.
ASSOCIATED CONTENT
Supporting Information. Experimental details, melting points, 1HꢀNMR, 13CꢀNMR spectra and
Deptꢀ135 spectra of selected αꢀaminonitriles. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Eꢀmail: movassagh@kntu.ac.ir
Present Addresses
†Department of Chemistry, K. N. Toosi University of Technology, P. O. Box 16315ꢀ6118,
Tehran, Iran, Fax: +98ꢀ21ꢀ22853650; Tel: +98ꢀ21ꢀ23064323.
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ACKNOWLEDGMENT
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This work was supported by the Research Council of the K. N. Toosi University of Technology
and the Iranian National Science Foundation (INSF, Grant No. 92013520). The authors express
their gratitude to Dr. Sogand Noroozizadeh for editing the English content of this manuscript.
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For Table of Contents Use Only
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Magnetic solid sulfonic acid decorated with hydrophobic
regulators: A combinatorial and magnetically separable catalyst
for the synthesis of αꢀaminonitriles
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Akbar Mobaraki,† Barahman Movassagh,*,†and Babak Karimi ‡
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