Nano-Fe3O4@SiO2-SO3H: A magnetic, reusable solid-acid catalyst for solvent-free reduction of oximes to amines with the NaBH3CN/ZrCl4 system

Article abstract of DOI:10.1002/jccs.201800030

In this study, the immobilization of sulfonic acid on silica-layered magnetite was carried out by the reaction of ClSO₃H with silica-layered magnetite. The prepared magnetic nanoparticles of Fe₃O₄@SiO₂-SO₃H were then characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and transmission electron microscopy. The sulfonated nanocomposite exhibited excellent catalytic activity and reusability in the reduction of various aldoximes and ketoximes with NaBH₃CN in the presence of ZrCl₄. All reactions were carried out under solvent-free conditions (r.t. or 75–80°C) within 3–70 min to afford amines in high to excellent yields.

Full text of DOI:10.1002/jccs.201800030

Received: 20 January 2018
Revised: 11 November 2018
Accepted: 12 November 2018
DOI: 10.1002/jccs.201800030
A R T I C L E
Nano-Fe O @SiO -SO H: A magnetic, reusable solid-acid
3
4
2
3
catalyst for solvent-free reduction of oximes to amines with
the NaBH CN/ZrCl system
3
4
Leila Sadighnia | Behzad Zeynizadeh | Shiva Karami | Mohammad Abdollahi
Faculty of Chemistry, Urmia University,
In this study, the immobilization of sulfonic acid on silica-layered magnetite was
Urmia 5756151818, Iran
carried out by the reaction of ClSO H with silica-layered magnetite. The prepared
Correspondence
3
Leila Sadighnia, Faculty of Chemistry, Urmia
University, Urmia 5756151818, Iran.
Email: l_sadignia80@yahoo.com
magnetic nanoparticles of Fe O @SiO -SO H were then characterized using scan-
3
4
2
3
ning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction,
Fourier transform infrared spectroscopy, vibrating sample magnetometry, and
transmission electron microscopy. The sulfonated nanocomposite exhibited excel-
lent catalytic activity and reusability in the reduction of various aldoximes and
ketoximes with NaBH CN in the presence of ZrCl . All reactions were carried out
Funding information
Research Council of Urmia University
3
4
ꢀ
under solvent-free conditions (r.t. or 75–80 C) within 3–70 min to afford amines
in high to excellent yields.
KEYWORDS
amines, Fe O @SiO -SO H, NaBH CN, oximes, reduction, ZrCl
4
3
4
2
3
3
1
| INTRODUCTION
to amines is an attractive two-step procedure for the reduc-
[
12]
tive amination of carbonyl compounds.
A literature
Reduction of functional groups plays an important role in
the production of a large variety of intermediates in industry
and laboratory experiments. In this context, hydride transfer-
ring agents derived from the element boron were frequently
review shows that most of the reported protocols in this con-
text suffer from some drawbacks. Overcoming the limita-
tions always requires the development and introduction of
more efficient protocols using green and benign reaction
conditions.
[1–4]
used for the reduction of functional groups.
Sodium
borohydride as a mild reducing agent has been recognized as
the reagent of choice to reduce carbonyl compounds, acyl
NaBH CN, carrying an electron-withdrawing cyanide
3
group, is one of the few borohydrides that tolerates strong
acidic media. Because of the cyano group, the reducing
[
5]
chlorides, thiol esters, and imines in protic solvents. Cur-
rently, the application of NaBH is significantly increasing,
4
power of NaBH CN greatly varies with pH and the adequate
3
and hundreds of substituted hydroborate agents have been
[
13,14]
[
6]
reduction rates are obtained only under pH 3–4.
Under
introduced to control the reducing power of this reagent.
acidic conditions, NaBH CN reduces oximes to the corre-
3
Consequently, NaBH CN as a modified and remarkable
3
sponding hydroxylamines without over-reduction to primary
resistant hydroborate agent in strong acidic media was also
widely used in chemical processes for the reduction of vari-
[
14]
amines.
It is also notable that by using strong acidic
[7–11]
media, the restriction to use acid-sensitive functional groups
is arrived in synthetic organic chemistry. As a solution and
to the complete reduction of oximes to amines, the combina-
ous organic molecules.
On the other hand, reduction of oximes to amines is a
subject of more interest because oximes are stable deriva-
tives of carbonyl compounds and their subsequent reduction
tion of NaBH CN with the nano-Fe O /ZrCl system at
3 3 4 4
©
2018 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2018;1–8.
http://www.jccs.wiley-vch.de
1

2
SADIGHNIA ET AL.
solvent-free condition was recently reported by our research
group.
In line with the outlined strategies, and in continuation
of our research program to explore the reducing capability of
microscopy (SEM), energy dispersive X-ray spectroscopy
(EDX), X-ray diffraction (XRD), Fourier transform infrared
spectroscopy (FT-IR), vibrating sample magnetometry
(VSM), and transmission electron microscopy, and TEM
analyses.
[
15]
NaBH CN in the absence of strongly acidic media as well
3
under mild reaction conditions, here we introduce magnetic
nanoparticles of Fe O @SiO -SO H as a heterogeneous
The surface morphology and size distribution of the pre-
pared Fe O , Fe O @SiO and Fe O @SiO -SO H MNPs
3
4
2
3
3
4
3
4
2
3
4
2
3
solid-acid catalyst for the solvent-free reduction of various
aldoximes and ketoximes to the corresponding primary
amines with the NaBH CN/ZrCl system (Scheme 1).
were determined using SEM. The obtained SEM images
show that the prepared nanoparticles are granular with the
average size of 23 nm (Fe O ), 12 nm (Fe O @SiO ), and
3
4
3
4
3
4
2
1
0 nm (Fe O @SiO -SO H), proving the mesoporous struc-
3 4 2 3
ture of the prepared materials (Figure 1a,d). Comparison of
the morphology and size distribution of the particles shows
that on going from Fe O to Fe O @SiO -SO H MNPs, the
porosity of magnetic material is dramatically increased,
whereas, in contrast, the size of nanoparticles tends toward a
smaller range. This is attributed to carrying out more pro-
2
| RESULTS AND DISCUSSION
3
4
3
4
2
3
Because of the great importance of amines in the synthesis
of fine chemicals such as agrochemicals, pharmaceuticals,
polymers, dyes, pesticides, photographic, antioxidants, and
corrosion inhibitors,
to the preparation of amines.
the primary amines with hydroborates is one of the most
important and practical methods for the preparation of
amines. Moreover, the principles of green chemistry calls for
new reaction conditions and chemical processes with the
advantages in product selectivity, operational simplicity,
reusability of the applied catalyst, health, and environmental
[
16–20]
special attention has been devoted
cesses on the magnetite cores (layering of SiO followed by
[21,22]
2
Reduction of oximes to
the immobilization of sulfonic acid moiety). Because of this,
making additional shells decreases the magnetic property of
the Fe O nucleus to attract the others for agglomeration.
3
4
EDX is a useful technique to determine the elemental
profile of materials. The EDX spectrum of sulfonated
silica-layered magnetite shows the presence of Fe, O, Si, and
S elements, demonstrating the successful synthesis of
Fe O @SiO -SO H MNPs (Figure 2).
[
23]
safety.
In the area of catalyst recyclability and reusability,
3
4
2
3
great efforts have been made in the use of magnetic nanopar-
ticles (MNPs). The catalysts incorporated with magnetic spe-
cies can be easily separated from the reaction mixture using
an external magnetic field.
nates the need for traditional filtration or other inappropriate
Next, XRD patterns of Fe O , Fe O @SiO , and
3
4
3
4
2
Fe O @SiO -SO H MNPs were used for their structural
3
4
2
3
analysis. Figure 3a shows the diffraction peaks at 2θ values
[24]
Magnetic separation elimi-
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
of 30.2 , 35.5 , 43.3 , 53.7 , 57.2 , and 62.9 corresponding
[25–28]
procedures for recycling precious catalysts.
In addi-
tion, the modification of magnetic nanoparticles via surface
functionalization is an elegant way to bridge homogeneous
and heterogeneous catalysts and prevent the particles from
[
29,30]
aggregation.
In this context, the development of silica-
layered magnetite nanoparticles has attracted the attention of
chemists as an excellent catalyst support in many chemical
[
31,32]
processes.
In following up the mentioned strategies and in continua-
tion of our research program toward increasing the reducing
power of NaBH CN by solid-acid promoters rather than
3
using strenuous acidic solutions, we were prompted to study
the acidity influence of the core–shell magnetic nanoparti-
cles of Fe O @SiO -SO H in the cyanoborohydride reduc-
3
4
2
3
tion of oximes to amines under mild conditions. The starting
point was the synthesis of Fe O @SiO -SO H MNPs
3
4
2
3
[
33,34]
according to reported procedures.
The prepared nano-
catalyst was then characterized using scanning electron
R
R
NaBH CN/ZrCl /Nano Fe O @SiO -SO H
3
4
3
4
2
3
NOH
NH2
o
Solvent-free, r.t. or 75-80 C
R'
R'
CN under solvent-free
SCHEME 1 Reduction of oximes with NaBH
3
3 4 3 4 2
FIGURE 1 SEM images of (a) Fe O , (b) Fe O @SiO , and (c,d)
conditions
Fe @SiO -SO H MNPs
3
O
4
2
3

SADIGHNIA ET AL.
3
remained intact. In addition, a comparison of the XRD pat-
terns of Fe O , Fe O @SiO , and Fe O @SiO -SO H
8
7
6
5
4
3
2
1
00
00
00
00
00
00
00
00
0
3
4
3
4
2
3
4
2
3
MNPs shows that through the immobilization of sulfonic
acid moiety on the surface of Fe O @SiO MNPs, based on
FeKα
3
4
2
diminishing the sharpness of signals and the appearance of a
ꢀ
O Kα
broad absorption peak at 2θ = 24–26 , the crystallinity of
Fe O @SiO -SO H MNPs has decreased. It means that
3
4
2
3
S Kα
there is a small amorphous phase in the sulfonated nanocom-
SiKα
[
35]
posite.
The average crystallite size for Fe O @SiO -
3 4 2
FeLα
SO H MNPs was calculated as 11.84 nm by Scherrer's
3
ꢀ
equation using the peak at 2θ = 35.5 (Figure 3c).
Structural elucidation of MNPs was also carried out by
the analysis of the recorded FT-IRs. Figure 4a shows the
FeKβ
S Kβ
FT-IR spectrum of Fe O4 MNPs. In this spectrum, the
keV
10.00
3
−
1
0
absorption bands at around 1,623 and 3,408 cm
are
assigned to the O–H deformation and stretching vibrations
3 4 2 3
FIGURE 2 EDX spectrum of Fe O @SiO -SO H MNPs
of the adsorbed water, respectively. The band appearing at
1
5
72 cm− is also attributed to the vibration of Fe–O bond.
to the (220), (311), (400), (422), (511), and (440) crystal
planes of Fe O . The obtained magnetite has crystalline
The FT-IR spectrum of Fe O @SiO MNPs is shown in
3
4
2
3
4
Figure 4b. The spectrum shows absorption peaks at around
−
1
cubic spinel structure, which is in good agreement with that
of the standard Fe O (JCPDS 65-3107). Accordingly, the
7
98 and 1,086 cm , corresponding to the symmetric and
3
4
asymmetric stretching vibration of Si–O–Si. In Figure 4c,
the bands at around 1,197 and 1,130 cm− are, respectively,
attributed to the asymmetric and symmetric stretching vibra-
1
XRD patterns of Fe O @SiO and Fe O @SiO -SO H
3
4
2
3
4
2
3
MNPs also show that both patterns include all characteristic
peaks of the bare magnetite (Figures 3b,c). This shows that
during the layering and immobilization of SiO and SO H,
tion of SO . In this context, the absorption band correspond-
2
−
1
2
3
ing to the symmetric stretching of SO2 (1,130 cm ) is
overlapped with a wide and strong absorption peak due to
respectively, the cubic spinel structure of magnetite
−1
the Si–O bond (1,081 cm ). Moreover, the absorption
peaks at around 656 and 3,390 cm− are related to the S–
OH and O–H stretching vibration of sulfonic acid and water
molecules, respectively. Based on these results, the success-
ful immobilization of sulfonic acid moiety as well as layer-
1
ing of SiO on the magnetite nucleus is demonstrated.
2
More investigations on the magnetic property of Fe O ,
3
4
Fe O @SiO and Fe O @SiO -SO H MNPs were also car-
3
4
2
3
4
2
3
ried out by the VSM technique under an applied external
magnetic field of up to 20 kOe (Figure 5). The saturation
magnetization (M ) values of Fe O , Fe O @SiO , and
s
3
4
3
4
2
Fe O @SiO -SO H were 67, 29, and 19.68 emu/g, respec-
3
4
2
3
tively. It is clear that through the layering of silica, followed
(
a)
b)
(
(
c)
5
00
1000
1500
2000
2500
3000
3500
4000
-
1
Wavenumbers (cm )
FIGURE 3 XRD patterns of (a) Fe
c) Fe @SiO -SO H MNPs
3
O
4
, (b) Fe
3
O
4
2
@SiO , and
FIGURE 4 FT-IR spectra of (a) Fe
(c) Fe @SiO -SO H MNPs
3
O
4
, (b) Fe
3
O
4
2
@SiO , and
(
3
O
4
2
3
3
O
4
2
3

4
SADIGHNIA ET AL.
[
15]
8
6
4
2
0
0
0
0
0
Lewis acidity of ZrCl4
encouraged us to examine the pro-
(
a)
moter activity of ZrCl toward the reduction of benzalde-
hyde oxime with the NaBH CN/Fe O @SiO -SO H system.
As seen in Table 1, although ZrCl and nano-Fe O @SiO -
SO H did not individually affect the reduction of benzalde-
hyde oxime (Table 1, entries 2 and 4), the reducing ability of
NaBH CN in the presence of both Fe O @SiO -SO H and
ZrCl dramatically increased. More investigations showed
that the use of molar equivalent of oxime/NaBH CN/ZrCl4
(1:5:1) and Fe O @SiO -SO H MNPs (0.05 g) was the
4
3
3
4
2
3
(b)
4
3
4
2
(c)
3
-
9000 -7000 -5000 -3000 -1000
1000
3000
5000
7000
9000
-
-
-
-
20
40
60
80
3
3
4
2
3
4
3
3
4
2
3
Applied field (Oe)
requirement for the complete reduction of benzaldehyde
oxime to benzylamine within 10 min under solvent-free con-
dition (Table 1, entry 10).
FIGURE 5 Magnetization curves of (a) Fe
c) Fe @SiO -SO H MNPs
3
O
4
3 4 2
, (b) Fe O @SiO , and
(
3
O
4
2
3
The usefulness of NaBH CN/ZrCl /nano-Fe O @SiO -
3
4
3
4
2
SO H system was further studied with the solvent-free
3
by the immobilization of sulfonic acid moiety on the cores
of magnetite, the magnetization value is diminished. How-
ever, it is sufficient for any magnetic separation.
reduction of various aldoximes. Table 2 shows the general
trend and versatility of this synthetic protocol. As seen, all
aldoximes containing electron-releasing or electron-
withdrawing groups were reduced easily and efficiently with
In continuation, from the TEM images of sulfonated
silica-layered magnetite, the synthesis of Fe O @SiO -
3
4
2
5
:1 M equiv of NaBH CN/ZrCl in the presence of nano-
3 4
SO H MNPs in the core–shell form was also demonstrated
3
Fe O @SiO -SO H (0.05 g) under solvent-free conditions
3
4
2
3
(Figure 6).
ꢀ
(
75–80 C). The corresponding amines were obtained in high
The influence of acidity of Fe O @SiO -SO H MNPs
3
4
2
3
to excellent yields within 10–70 min.
on the reducing ability of NaBH CN was then investigated
3
The reactivity of ketoximes toward the NaBH CN/ZrCl /
3
4
through the reduction of oximes. To optimize the reaction
conditions, we carried out the reduction of benzaldehyde
nano-Fe O @SiO -SO H system was also examined by the
3
4
2
3
solvent-free reduction of acetophenone oxime under the opti-
mized conditions. Using 5:1 M equiv of NaBH CN/ZrCl and
oxime as a model compound with NaBH CN in the absence
3
and presence of nano-Fe O @SiO -SO H (Table 1, entries
3
4
3
4
2
3
nano-Fe O @SiO -SO H (0.05 g) reduced 1 molar equiva-
1
–12). The results show that the use of solvent-free media
3
4
2
3
ꢀ
(75–80 C) was the best choice, and significant progress of
lent of acetophenone oxime to α-methylbenzylamine within
15 min and 90% yield (Table 3, entry 1). The reducing ability
of the examined protocol was further studied by the success-
ful reduction of various ketoximes to the corresponding pri-
mary amines (Table 3). All reactions were carried out
perfectly within 3–45 min to afford amines in high yields.
Comparison of the results in Tables 2 and 3 shows that
ketoximes were reduced generally faster than aldoximes. In
addition, aryl aldoximes having a nitro group showed good
chemoselectivity in their reductions, and only the oxime
group was reduced during the progress of the reaction. In the
case of aryl ketoximes with the substituted nitro group, the
protocol was not selective, and both oxime and nitro groups
were reduced with the same reactivity (Table 2, entries 5, 6;
Table 3, entry 6).
the reaction was achieved using NaBH CN (5 mmol) and
nano-Fe O @SiO -SO H (0.05 g) per 1 mmol of the oxime
3
3
4
2
3
(Table 1, entry 4). Further experiments revealed that increas-
ing the amount of Fe O @SiO -SO H decreased the rate of
reaction. In continuation, our good experience with the
3
4
2
3
The possibility of recycling the nanocatalyst was also
examined in the reduction of benzaldehyde oxime with the
NaBH CN/ZrCl /Fe O @SiO -SO H MNPs system. After
3
4
3
4
2
3
completion of the reaction, the magnetic nanoparticles of
Fe O @SiO -SO H were separated from the reaction mix-
3
4
2
3
ture by an external magnet and then reused (after washing
with distilled water/acetone and dried under vacuum) for the
next runs. The recycled nanocatalyst could be reused at least
three times without any significant loss of its catalytic activ-
ity (Figure 7).
3 4 2 3
FIGURE 6 TEM images of Fe O @SiO -SO H MNPs

SADIGHNIA ET AL.
5
3 4 3 4 2 3
TABLE 1 Optimization experiments for the reduction of benzaldehyde oxime to benzylamine with the NaBH CN/ ZrCl /nano-Fe O @SiO -SO H system
a
b
Entry
Reaction components (molar ratio)
Catalyst (g)
—
Condition
Time (min)
Conv. (%)
1
2
3
4
5
6
7
8
9
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
Oxime/NaBH
3
3
3
3
3
3
3
3
3
3
3
3
CN (1:5)
Solvent-free/oil bath
Solvent-free/oil bath
Solvent-free/rt
120
120
60
0
CN/ZrCl
CN (1:5)
CN (1:5)
CN (1:5)
CN (1:5)
CN (1:5)
4
(1:5:1)
—
20
0
0.05
0.05
0.1
Solvent-free/oil bath
Solvent-free/oil bath
60
40
30
0
60
0.05
0.05
0.1
CH
3
CN/reflux
120
120
10
THF/reflux
0
CN/ZrCl
CN/ZrCl
CN/ZrCl
CN/ZrCl
CN/ZrCl
4
(1:5:2)
(1:5:1)
(1:5:1)
(1:5:0.5)
(1:5:1)
Solvent-free/oil bath
Solvent-free/oil bath
Solvent-free/oil bath
Solvent-free/oil bath
Solvent-free/oil bath
Mix.
90
100
60
80
4
4
4
4
0.1
30
1
1
1
0
1
2
0.05
0.05
0.04
10
60
60
a
ꢀ
Temperature of oil bath was 75–80 C.
b
Mix. means mixture of products.
2.1 | Conclusion
analyses. The core–shell nanocomposite showed excellent
catalytic activity in the successful reduction of various aldox-
In this work, we prepared magnetic nanoparticles of
sulfonated silica-layered magnetite and then characterized
them using SEM, EDX, XRD, FT-IR, VSM, and TEM
imes and ketoximes to the corresponding amines with the
NaBH CN/ZrCl4 system. All reactions were carried out
3
a
TABLE 2 Reduction of aldoximes with the NaBH
3
CN/ZrCl
4
/nano-Fe
3
O
4
@SiO
2
-SO
3
H system
b
c
ꢀ
Bp or Mp ( C)
[37–41]
Entry
Substrate
CH=NOH
Product (a)
Molar ratio
Time (min)
Yield (%)
1
1:5:1
10
93
185@760 mmHg
217@760 mmHg
221@760 mmHg
CH NH
2
2
2
3
1:5:2
1:5:1
70
45
90
87
Cl
Cl
CH=NOH
CH=NOH
Cl
Cl
CH NH
2 2
CH NH2
2
Cl
Cl
4
5
Cl
Cl
Cl
Cl
1:5:1
1:5:2
50
50
89
90
252@760 mmHg
295@760 mmHg
CH=NOH
CH NH2
2
CH=NOH
CH NH
2 2
O N
O N
2
2
6
7
1:5:1
1:5:1
50
20
90
83
298@760 mmHg
291@760 mmHg
O N
CH=NOH
CH=NOH
O N
CH NH2
2
2
2
CH NH2
2
8
9
1:5:1
1:5:1
1:5:1
20
30
15
92
90
88
195@760 mmHg
237@760 mmHg
193–195
Me
CH=NOH
Me
CH NH
2 2
MeO
MeO
CH=NOH
CH=NOH
MeO
MeO
CH NH
2
2
1
0
1
CH NH
2
2
HO
HO
1
NOH
H
1:5:1
20
86
219@760 mmHg
CH NH
2
2
a
b
c
ꢀ
All reactions were carried out in the presence of nano-Fe
Molar ratio as: Subs./NaBH CN/ZrCl
Yields refer to isolated pure products.
3
O
4
@SiO
2
-SO H (0.05 g) in an oil bath (75–80 C) under solvent-free conditions.
3
3
4
.

6
SADIGHNIA ET AL.
a
TABLE 3 Reduction of ketoximes with the NaBH
3
CN/ZrCl
4
/nano-Fe
3
O
4
@SiO
2
-SO
3
H system
b
c
ꢀ
Bp or Mp ( C)
[37–41]
Entry
Substrate
Product (b)
NH2
Molar ratio
Time (min)
Yield (%)
1
NOH
1:5:1
15
90
186@760 mmHg
2
Ph
Ph
Ph
1:5:1
40
87
300@760 mmHg
NOH
NH2
Ph
3
4
5
NOH
NOH
NOH
NH2
NH2
1:5:1
1:5:1
1:5:1
45
20
30
93
90
88
208@760 mmHg
240@760 mmHg
82@2.8 mmHg
Me
Me
MeO
Cl
MeO
Cl
NH2
6
7
NOH
NH2
1:5:1
20
86
55–58
O N
H N
2
2
NOH
NH2
1:5:1
1:5:1
20
5
96
92
328@760 mmHg
d
8
138–145
HON
NOH
H N
NH2
2
d
9
1:5:1
1:5:1
3
5
83
85
134@760 mmHg
279@760 mmHg
NOH
NH2
d
1
0
NOH
NH2
@SiO -SO
a
b
c
d
ꢀ
All reactions were carried out in the presence of nano-Fe
Molar ratio as: Subs./NaBH CN/ZrCl
3
O
4
2
3
H (0.05 g) in an oil bath (75–80 C) under solvent-free conditions.
3
4
.
Yields refer to isolated pure products.
The reaction was carried out at r.t.
within 3–70 min under solvent-free conditions (r.t. or
3 | EXPERIMENTAL
ꢀ
75–80 C), affording the product amines in high to excellent
yields. Clean reactions, short reaction times, reusability of the
nanocatalyst, easy work-up procedure, high yield of products,
solvent-free conditions, and using Fe O @SiO -SO H MNPs
All reagents and solvents were purchased from Merck with
high quality and used without further purification. Oximes
were prepared in high purity according to the reported proce-
3
4
2
3
[
36] 1
13
as a solid-acid catalyst for NaBH CN reduction of oximes
dures.
H and C NMR spectra were recorded with a
3
rather than using strong aqueous acidic media are the advan-
tages of this method, which make the current protocol a
synthetically useful addition to the present methodologies.
300-MHz Bruker spectrometer at room temperature with
CDCl as solvent. The FT-IR spectra were recorded on a
3
Thermo Nicolet Nexus 670 FT-IR spectrometer. The XRD
data were collected using a Philips X'pert Pro diffractometer
ꢀ
ꢀ
using Cu Kα radiation (2θ = 10 –80 , λ = 1.54056 Å). The
surface morphology of the particles was assigned by SEM
using an FESEM-TESCAN MIRA3 instrument. The chemi-
cal composition of Fe O @SiO -SO H MNPs was deter-
93
9
9
9
8
8
2.5
92
3
4
2
3
1.5
mined using EDX. The magnetic property of the materials
was determined using a vibrating sample magnetometer
under magnetic fields up to 20 kOe. TEM was carried out
on a Zeiss-EM10C instrument operated at 100 kV. An ultra-
sonic bath with temperature control (FALC, model LBS2)
was used for sonication. TLC was used for the purity deter-
mination of substrates, products, and reaction monitoring,
over silica gel 60 F254 aluminum sheet. All products are
known and so were characterized by comparison of their
spectra and physical data with those available in the
91
0.5
90
9.5
89
8.5
1
2
3
Run
FIGURE 7 Reusability of Fe
3
O
4
@SiO
2
-SO
3
H MNPs in the reduction of
benzaldehyde oxime
[
37–41]
literature.

SADIGHNIA ET AL.
7
3
.1 | Preparation of Fe O @SiO -SO H MNPs
3.3.3 | α-Methylbenzylamine (1b)
3
4
2
3
−1
FT-IR (KBr, υ cm ) 3,293, 3,259, 1,663, 1,435, 1,179,
Magnetic nanoparticles of Fe O were prepared via the
chemical co-precipitation of Fe and Fe ions in an alkali
medium.
silica layer (Fe O @SiO )
sulfonic acid through reported procedures.
pared nanoparticles of Fe O @SiO (1 g) were dispersed in
3
4
1
2
+
3+
1,040, 961, 743; H NMR (300 MHz, CDCl ) δ 1.41 (d,
3
[
42]
J = 6.6 Hz, 3H, CH ), 1.83 (s, 2H, NH ), 4.12 (q,
3
2
The particles were subsequently coated with a
1
3
[43]
J = 6.6 Hz, 1H, CH), 7.19–7.39 (m, 5H, Ph-H); C NMR
(75 MHz, CDCl ) δ 29.68, 51.33, 125.37, 125.71, 126.90,
28.51.
and then functionalized with
3
4
2
[33,34]
3
The pre-
1
3
4
2
dry CH Cl (10 mL) by ultrasonication for 30 min. Subse-
2
2
3
.3.4
|
Diphenylmethylamine (2b)
quently, ClSO H (1 mL) was added dropwise to a cooled
3
−1
FT-IR (KBr, υ cm ) 3,430, 3,354, 3,214, 3,005, 1,600,
1
δ 3.65 (bs, 2H, NH , exchangeable with D O), 4.77 (s, 1H,
CH), 7.27–7.48 (m, 10H, 2Ph-H); C NMR (75 MHz,
mixture of Fe O @SiO (ice bath) within 30 min at room
1
3
4
2
,496, 1,278, 1,174, 762, 692; H NMR (300 MHz, CDCl )
3
temperature. After the addition, the mixture was stirred for
hr to complete the extrusion of HCl. The resulting mag-
2
2
6
13
netic nanoparticles were separated using an external magnet
and washed with ethanol and water before drying in an oven
CDCl ) δ 59.74, 126.90, 126.95, 128.47, 145.55.
3
ꢀ
at 70 C to give Fe O @SiO -SO H MNPs as a brown pow-
3
4
2
3
3.3.5
|
α-Methyl-4-methylbenzylamine (3b)
+
der. The number of H sites (0.31 mmol/g) was determined
by acid–base titration.
−1
FT-IR (KBr, υ cm ) 3,349, 3,215, 3,038, 1,600, 1,499,
1
[44]
1
,278, 985, 753; H NMR (300 MHz, CDCl ) δ 1.39 (d,
3
J = 6.6 Hz, 3H, CH ), 2.06 (s, 2H, NH ), 2.34 (s, 3H, CH ),
3
2
3
1
3
4
.09 (q, J = 6.6 Hz, 1H, CH), 7.14–7.27 (m, 4H, Ph-H);
C
3.2 | Typical procedure for the solvent-free reduction
NMR (75 MHz, CDCl ) δ 25.47, 29.68, 51.01, 125.60,
3
of benzaldehyde oxime to benzylamine with the
NaBH CN/ ZrCl /Fe O @SiO -SO H MNP system
1
29.14, 136.42, 144.45.
3
4
3
4
2
3
3
.3.6 | 4-Chloro-α-methylbenzylamine (5b)
A mixture of benzaldehyde oxime (0.121 g, 1 mmol) and
nano-Fe O @SiO -SO H (0.05 g) was ground in a porcelain
−1
FT-IR (KBr, υ cm ) 3,430, 3,354, 3,214, 1,602, 1,468,
3
4
2
3
1
mortar. ZrCl (0.233 g, 1 mmol) was then added, and grind-
1,276, 752; H NMR (300 MHz, CDCl
J = 6.6 Hz, 3H, CH ), 1.75 (s, 2H, NH
J = 6.6 Hz, 1H, CH), 6.98–7.41 (m, 4H, Ph-H); C NMR
75 MHz, CDCl ) δ 29.68, 50.71, 127.14, 128.53, 132.35,
3
) δ 1.35 (d,
4
ing was continued for a while at r.t. The mortar was heated
3
2
), 4.10 (q,
1
3
ꢀ
in an oil bath to keep the temperature at 75–80 C.
(
1
NaBH CN (0.314 g, 5 mmol) was then added portion-wise,
3
3
46.04.
and the mixture was ground for 10 min in an oil bath
ꢀ
(
75–80 C). After completion of the reaction, H O (5 mL)
2
3
.3.7 | α-Methyl-3-nitrobenzylamine (6b)
was added and the mixture was stirred for 5 min. The mix-
ture was extracted with EtOAc (2 × 5 mL) (all nano-
Fe O @SiO -SO H remained around the stirring bar) and
−1
FT-IR (KBr, υ cm ) 3,347, 3,275, 2,923, 1,605, 1,535,
1
J = 5.8 Hz, 3H, CH ), 1.81 (bs, 2H, NH ), 4.25 (q,
1
,345, 840; H NMR (300 MHz, CDCl ) δ 1.42 (d,
3
3
4
2
3
3
2
then dried over anhydrous Na SO . Evaporation of the sol-
2
4
1
3
J = 5.8 Hz, 1H, CH), 7.10–8.24 (m, 4H, Ph-H); C NMR
CDCl , 75 MHz) δ 38.47, 53.41, 110.14, 114.58, 120.86,
vent afforded the pure liquid benzylamine in 93% yield
0.1 g, Table 2, entry 1).
(
1
3
(
21.87, 129.35, 132.19.
3.3 | Spectral data for selected products
ACKNOWLEDGMENT
3
.3.1 | Benzylamine (1a)
This work was supported by the Research Council of Urmia
University.
−
1
FT-IR (KBr, υ cm ) 3,368, 3,292, 3,061, 3,026, 2,920,
2
2
1
,858, 1,605, 1,452; H NMR (300 MHz, CDCl ) δ 1.51 (s,
3
13
H, NH ), 3.87 (s, 2H, CH ), 7.23–7.38 (m, 5H, Ph-H);
C
2
2
ORCID
NMR (75 MHz, CDCl ) δ 46.54, 126.76, 127.05, 128.53,
3
Leila Sadighnia
https://orcid.org/0000-0001-6433-2352
https://orcid.org/0000-0003-0485-5455
143.37.
Behzad Zeynizadeh
3
.3.2 | 2,4-Dichlorolbenzylamine (3a)
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−
1
FT-IR (KBr, υ cm ) 3,349, 3,215, 3,038, 2,963, 1,600,
1
CDCl ) δ 1.58 (s, 2H, NH ), 3.91 (s, 2H, CH ), 7.25–7.38
[
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