SO 3H -functionalized magnetic Fe 3O 4 nanoparticles as an efficient and reusable catalyst for one-pot synthesis of α -amino phosphonates

Article abstract of DOI:10.1007/s12039-018-1530-4

Abstract: Nanomagnetic Fe ₃O ₄@ SiO ₂-SO ₃H (SO ₃H-MNPs) was prepared via grafting sulfonic acid on the silica-coated Fe ₃O ₄ magnetite nanoparticles (MNPs). The catalytic activi

Full text of DOI:10.1007/s12039-018-1530-4

J. Chem. Sci. (2018) 130:128
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-018-1530-4
REGULAR ARTICLE
SO3H-functionalized magnetic Fe3O4 nanoparticles as an efficient
α
and reusable catalyst for one-pot synthesis of -amino
phosphonates
HOSEIN HAMADI∗ and MEYSAM NOROUZI
Chemistry Department, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran
E-mail: H.Hammadi@scu.ac.ir
MS received 22 January 2018; revised 24 June 2018; accepted 23 July 2018
Abstract. Nanomagnetic Fe3O4@SiO2-SO3H (SO3H-MNPs) was prepared via grafting sulfonic acid on the
silica-coated Fe3O4 magnetite nanoparticles (MNPs). The catalytic activity of the prepared SO3H-MNPs was
α
α
probed through the one-pot synthesis of N-hydroxy- -amino phosphonates and -amino phosphonates via
three-component couplings of phenylhydroxylamine or amines with aldehydes and trialkyl phosphites at room
temperature. The synthesized SO3H-MNPs were characterized by XRD, FT-IR, and SEM. The recoverability
of the catalyst was achieved by a simple magnetic decantation and reused at least five times without significant
degradation in catalytic activity.
α
Keywords. Magnetic nanoparticle; N-hydroxy- -amino phosphonate; catalysis; one-pot synthesis;
multicomponent reaction.
1. Introduction
SmI2,22 ZnCl2,23 SnCl4,24 TaCl5–SiO2,25 SiO2-ZnBr2,26
alumina supported reagents,27 MgClO4,28 LiClO4,29
Sn(OTf)2,30 CF3CO2H,31 Scandium tris(dodecyl sul-
phate) Sc(DS)3,32 BF3-Et2O,33 aq. HCOOH,34 (CO
OH)2,35 Cd(ClO4)2·xH2O,36 PEG-SO3H,37 KH2PO4,38
Magnetic nanoparticle,39 Aluminium pillared interlay-
ered clay (Al-PILC),40 Pentafluorophenylammonium
triflate (PFPAT),41 and Cellulose-SO3H.42
The amino phosphonates compounds and their
derivatives are known as biologically active com-
pounds with broad range applications in different
fields. These compounds are structural analogues of
natural amino acids and their biologically effects as
anti-cancer agents,1 enzyme inhibitors,2 antibiotics,3
anti-thrombotic agents,4 peptidases, proteases,5 HIV
protease,6 fungicides,7 herbicides, insecticides and
plant growth regulators,8 indicate the importance of
scientific research to develop their synthetic proce-
dures.9–11
On the other hand, N-hydroxy-amino phosphonic
acids which are fascinating biologically active com-
α
pounds, are phosphorus analogue of N-hydroxy- -
amino acid, which have an important role in many
metabolic and biological processes.43 N-hydroxy- -
α
Although a number of synthetic methods have been
developed for the synthesis of -amino phosphonates,
there are only a few methodologies for the synthesis of
amino phosphonates were also announced as suitable
synthons for pseudo peptides and illustrate herbicidal
and growth-regulating activity.44 They are also used for
α
α
N-hydroxy- -amino phosphonates. The basic method
α
the preparation of -amino phosphonates and phospho-
rylated nitrones.45
α
for the preparation of -amino phosphonates, involves
the condensation of a primary or secondary amine, a
carbonyl compound (aldehyde or ketone) and dialkyl or
trialkyl phosphite,12–17 which have been promoted by
Lewis or Brønsted acids such as Yb(OTf)3,18 ytterbium
perfluorooctanoate [Yb(PFO)3],19 Cu(OTf)2,20 InCl3,21
α
The efficient oriented synthesis of N-hydroxy- -
amino phosphonates has been reported using different
reagents and catalysts. However, these methods have
various drawbacks like their difficulties in the prepa-
ration of catalysts such as LPDE (lithium perchlorate-
diethylether)andreagentssuchasdimethyl(trimethylsi-
lyl) phosphate.45,46 Palladium hydrogenation of
*
For correspondence
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s12039-018-1530-4) contains
supplementary material, which is available to authorized users.
0123456789().: V,-vol

128 Page 2 of 11
J. Chem. Sci. (2018) 130:128
CHO
NHOH
P(OEt)3
HO
N
Fe3O4@SiO2-SO3H
CH2Cl2 / r.t
O
P
R
OEt
EtO
1
3
2
R
4
R'
CHO
NH2
Fe3O4@SiO2-SO3H
CH2Cl2/ r.t
HN
O
P(OR")3
R
R'
P
OR"
"RO
3
1
5
R
6
α
Scheme 1. Synthesis of -amino phosphonate derivatives catalyzed by Fe3O4@SiO2-SO3H.
α
N-hydroxy- -imino phosphonates using Brønsted acid imine. All the products are well known and compared
α
as activator also reported to produce the N-hydroxy- - with the reported literature.
aminophosphonates.43 Asanalternative, theuseofionic
liquid [bmim][BF4] as a catalyst has been reported to
catalyze the combination of hydroxylamine derivatives
2. Experimental
with carbonyl groups.47
Among various catalyst separations in organic 2.1 General
reaction, a simple magnetic isolation process eliminates
Iron (II) chloride tetrahydrate (99%), iron (III) chloride
the requirement of catalyst filtration and centrifugation.
Magnetic nanoparticles (MNPs) have gained consider-
able attention as a solid support for immobilization of
homogeneous catalysts.48,49 Nanoparticles can be well
dispersed in the reaction medium providing a large
surface for ready access of catalytic sites. After com-
pleting the reactions, the MNPs supported catalysts
can be isolated efficiently from the solution through
a simple magnetic separation.50,51 Furthermore; there
hexahydrate (98%), aromatic aldehydes and other chemi-
cals were purchased from Fluka and Merck companies and
used without further purification. Products were characterized
1
by comparison of their physical data, IR and H NMR and
13C NMR spectra with known samples. NMR spectra were
recorded on a Bruker Advance DPX 400 MHz instrument
spectrometer using TMS as an internal standard. The infrared
spectra were recorded on a Perkin Elmer spectrum two FT-IR
spectrometers. The purity determination of the products and
are no reports on the use of the nanomagnetic catalysts reactionmonitoringwasaccomplishedbyTLConTLC-Cards
Silica gel-G/UV 254 nm. X-ray diffraction (XRD) patterns
of samples were taken on a Philips X-ray diffractometer
as promoters for three-component coupling reaction of
aldehydes, hydroxylamines and trialkyl phosphites to
(Model PW 1840) in the range 2 range 50–70. SEM images
θ
α
produce N-hydroxy- -amino phosphonates.
were also recorded using Philips XL30 scanning electron
microscope.
As part of an ongoing development of efficient
protocols for the preparation of phosphonate com-
pounds and in continuation of our recently reported
work on MCR,39 herein, we report SO3H-functionalized
silica-coated magnetic nanoparticles [Fe3O4@SiO2-
SO3H] as an efficient and recoverable catalyst for
2.2 Preparation of the Fe3O4@SiO2
Fe3O4 MNPs and Silica-coated Fe3O4 nanoparticles
(Si-MNPs) were prepared according to the procedure reported
by Kiasat and Ghasemzadeh.52–54 Briefly, a solution of
FeCl3 · 6H2O (55.98 mmol, 15.13 g) and FeCl2 · 4H2O
(31.9 mmol, 6.34 g) in 640 mL of deionized water was stirred
at 80 ◦C and then 80 mL of concentrated ammonia (25%)
was added until the pH reached 11–12. The mixture was
stirred vigorously at 80 ◦C until precipitation. Afterwards, the
α
the synthesis of N-hydroxy- -amino phosphonates◦and
α
-amino phosphonates at room temperature (25 C),
through three-component reaction of aromatic alde-
hydes, trialkyl phosphite and phenylhydroxylamine or
amines (Scheme 1). The reaction occurred via in situ
formations of nitrone, a highly reactive intermediate, or

J. Chem. Sci. (2018) 130:128
Page 3 of 11 128
Figure 1. FT-IR spectra of Fe3O4@SiO2-SO3H.
Figure 2. X-ray diffraction for Fe3O4@SiO2-SO3H.
prepared magnetic NPs were separated magnetically, washed
with deionized water and then dried at 70 ◦C for 8 h.
In order to prepare the Silica-coating Fe3O4 nanoparticles,
2 g of the prepared Fe3O4 NPs were sonicated in a mixture of
ethanol (450 mL), deionized water (120 mL) and concentrated
ammonia aqueous solution (10 mL, 25 wt%), followed by the
addition of TEOS (2 mL). After stirring at room temperature
for 15 h, the Fe3O4@SiO2 was separated using an external
magnet and washed several times with deionized water and
dried under vacuum at 60 ◦C overnight.
2.3 Preparation of the Fe3 O4@SiO2-SO3H
Accordingtotheliterature56 theas-synthesizedFe3O4@SiO2
(2.5 g) was added to dry CH2Cl2 (75 mL) in a 500 mL
suction flask bearing constant pressure dropping funnel
Figure 3. SEM image of Fe3O4@SiO2-SO3H.

128 Page 4 of 11
J. Chem. Sci. (2018) 130:128
Table 1. Optimization of the reaction conditionsa.
Entry Catalyst (g) Solvent Temp. (◦C) Time (h) Yield (%)
1
2
3
4
5
6
7
8
9
10
No catalyst Neat
No catalyst Neat
25
100
25
25
25
25
25
25
40
25
4
4
3
4
4
3
3
2
2
2
Trace
Trace
66
45
20
62
78
88
89
0.05
0.05
0.05
0.05
0.07
0.1
CH2Cl2
CH3CN
EtOH
CHCl3
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
0.1
0.15
88
aBenzaldehyde (1.0 mmol), phenylhydroxylamine (1.2 mmol),
triethyl phosphite (1.2 mmol), Fe3O4@SiO2-SO3H.
Ph
O
HO
Ph
O
HO
Ph
O
N
HO
HO
N
N
P
P
P
OEt
OEt
EtO
EtO
Ph
OEt
O2N
EtO
4c (74%)
4b (75%)
4a (88%)
Ph
Ph
Ph
HO
HO
N
O
P
N
N
O
O
P
P
OEt
EtO
OEt
OEt
F
EtO
EtO
MeO
4d (70%)
4f (75%)
4e (78%)
α
Scheme 2. Synthesis of N-hydroxy- -amino phosphonates 4.
linked to the gas outlet. The mixture was homogenized by
ultrasonic for 10 min. Then chlorosulfonic acid (1.75 g,
ca. 1 mL, 15 mmol) in dry CH2Cl2 (20 mL) was added
dropwise over a period of 30 min at room temperature.
After completion of the addition, the mixture was shaken for
90 min, while the residual HCl was eliminated by suction.
Then, the Fe3O4@SiO2-SO3H was separated by an external
magnet from the mixture and washed several times with dried
CH2Cl2. Finally, Fe3O4@SiO2-SO3H was dried under vac-
uum at 60 ◦C. The identities of the catalyst were confirmed
according to the reference by XRD, SEM and FT-IR.
100
90
80
70
60
50
40
30
20
10
0
2.4 General procedure
1
2
3
4
5
0.1 g the catalyst (Fe3O4@SiO2-SO3H) was added to the
solution of Aldehyde (2 mmol), phenylhydroxylamine
(2 mmol, 22 mg), and diethyl phosphite (2 mmol, 28 mg) in
Figure 4. Recyclability of the catalyst.
2 mL CH2Cl2 and stirred at room temperature (25 ◦C) for the reaction mixture and the organic layer was simply decanted
appropriate time (Table 2). The progress of the reaction was by means of an external magnet. The isolated solution was
monitored by TLC. In the end, CH3Cl was added to dilute the purified on a silica-gel plate to obtain the pure product. The

J. Chem. Sci. (2018) 130:128
Page 5 of 11 128
O
Ph
R
R
N
OH
R
R
- CH3OH
Ph
OSO3H
P(OCH3)2
H
O
O
R
OSO3
N
OH
R
R
R
P(OCH3)2
Ph
O
NH
H2O
CH3
HO
Ph
H
N
Ph
HO
R
OH
R
P(OCH3)3
N
O
N
R
H2O
R
R
R
R
R
OSO3
H2O
OSO3
α
Scheme 3. The proposed mechanism for the synthesis of N-hydroxy- -amino phosphonates.
1
identities of the products were confirmed by FT-IR and H 6.51–6.53 (d, J = 7.6 Hz, 2H), 6.6–6.64 (t, J = 7.6 Hz, 1H),
NMR spectral data related to reference.47–49,51,55,56
7.01–7.05 (m, 2H), 7.18–7.21 (m, 1H), 7.24–7.27 (m, 2H),
7.39–7.40 (m, 1H) ppm. IR (KBr, υmax cm−1): 3298, 2988,
1607, 1494, 1241, 1047, 986, 799, 747.
2.5 Representative spectroscopic data
6n: Viscous colorless liquid; 1H NMR (400.13 MHz, CDCl3):
1.10–1.14 (t, J = 7.2 Hz, CH3), 1.23–1.26 (t, J = 7.2 Hz,
CH3 Hz), 3.73–3.77 (m, 1H), 3.96–3.99 (m, 1H), 4.06–4.14
(m, 2H), 5.48–4.56 (dd, 1H), 5.8 (brs, NH), 6.45–6.47 (d,
J = 8.4 Hz, 1H), 6.56–6.60 (t, J = 1.2 Hz, 1H), 7.25–7.36
(m, 4H), 7.52–7.54 (t, J = 1.2 Hz, 2H), 8.05–8.07 (t, 1H)
ppm.
4a: Viscous liquid; 1H NMR (400 MHz, CDCl3): δ 1 (t, J =
6.8 Hz, CH3), 1.26 (t, J = 6.8 Hz, CH3), 3.51–3.56 (m, 1H),
3.79–3.85 (m, 1H), 4.11–4.18 (m, 2H), 4.98 (brs, OH), 5.24–
5.31 (d, 1H, JP−H = 22 Hz), 6.51–6.59 (d, J = 8.1 Hz, 2H),
6.61–6.63 (t, J = 7.6 Hz, 1H), 7.01–7.06 (m, 3H), 7.17–7.21
(m, 1H), 7.48–7.50 (m, 2H) ppm. IR (KBr, υmax cm−1): 3375,
2970, 1602, 1499, 1227, 1022, 967, 748, 670.
1
6g: Yellow solid, M.p.: 123–125 ◦C; H NMR (400 MHz,
3. Results and Discussion
CDCl3): 1.18–1.22 (t, J = 7.1 Hz, CH3), 1.26–1.34 (t, J =
7.1 Hz, CH3), 3.88–3.90 (m, 1H), 4.03–4.09 (m, 1H), 4.13–
4.19 (m, 2H), 4.85–4.91 (d, JP−H = 24.8 Hz, 1H), 6.55-6.57
(d, J = 8 Hz, 2H), 6.74–6.78 (t, J = 6.8 Hz, 1H), 7.12–
The catalyst was synthesized according to the report52
and characterized by X-ray powder diffraction (XRD),
Scanning electron microscope (SEM) and Fourier trans-
7.15 (t, J = 7.6 Hz, 2H), 7.67–7.70 (m, 2H), 8.20–8.23 (d, form infrared (FT-IR). The Fe3O4 magnetic nanopar-
J = 8.8 Hz, 2H) ppm.
ticles as the catalyst core were prepared by a simple
method using the co-precipitation of FeCl2 and FeCl3
in ammonia solution. The synthesis of sulphuric acid
1
6i: Viscous liquid; H NMR (400.13 MHz, CDCl3): 1.05–
1.10 (t, J = 7.2 Hz, CH3), 1.32–1.36 (t, J = 7.2 Hz, CH3),
immobilized on Si-MNPs was achieved by using the
3.61–3.64 (m, 1H), 3.89–3.93 (m, 1H), 4.21–4.28 (m, 2H),
4.08–4.19 (m, 2H), 5.35–5.41 (d, JP−H = 24.4 Hz, 1H),
6.62–6.64 (d, J = 8.4 Hz, 2H), 6.70–6.73 (t, J = 7.2, 1H),
7.11–7.15 (t, J = 8.4 Hz, 3H), 7.27–7.30 (t, J = 7.6, 1H),
7.57–7.62 (t, J = 8.4, 2H) ppm.
reported method.52
The FT-IR spectrum of Fe3O4@SiO2-SO3H shows
the peaks at 1090, 806 and 462 cm−1 assigned to the
Si-O-Si. The presence of sulphonyl group is confirmed
by 1217 and 1124 cm−1 bands that were covered by a
stronger absorption of the Si-O bond at 1092 cm−1. In
addition, the characteristic peaks of Fe-O at 580 cm−1
1
6j: Yellow solid, M.p.: 62–65◦C; H NMR (400.13 MHz,
CDCl3): δ 1.02–1.05 (t, J = 7.2 Hz, CH3), 1.19–1.23 (t,
J = 7.2 Hz, CH3), 3.54–3.65 (m, 1H), 3.84–3.87 (m, 1H),
4.01–4.07 (m, 2H), 4.66–4.72 (d, JP−H = 24.4 Hz, 1H), and Si-OH at 956 cm−1 were also observed (Figure 1).

128 Page 6 of 11
J. Chem. Sci. (2018) 130:128
a
α
Table 2. Synthesis of -amino phosphonates (6) in the presence of Fe3O4@SiO2-SO3H via Scheme 1 .
Time
(min)
Yield
(%)b
Entry
a
Aldehyde
C6H5CHO
Amine
P(OR)3
P(OEt)3
C6H5NH2
45
92
OEt
OEt
O
O
P
P
N
H
b
C6H5CHO
C6H5NH2
P(OMe)3
50
96
OMe
OMe
N
H
c
d
e
f
C6H5CHO
4-CNC6H4NH2
4-CNC6H5NH2
C6H5NH2
P(OEt)3
P(OEt)3
P(OMe)3
P(OEt)3
P(OEt)3
60
40
55
55
60
92
90
92
85
88
OEt
OEt
CN
O
P
N
H
OEt
OEt
4-MeC6H4CHO
4-PhC6H4CHO
4-PhC6H4CHO
4-NO2C6H4CHO
CN
O
P
H3C
N
H
OMe
O
OMe
P
Ph
N
H
OEt
OEt
C6H5NH2
O
P
Ph
N
H
Br
g
3-BrC6H5NH2
OEt
OEt
O
P
O2N
N
H
h
i
4-HOC6H4CHO
2-ClC6H4CHO
C6H5NH2
C6H5NH2
P(OEt)3
P(OEt)3
60
70
82
88
OEt
O
P
OEt
P
HO
N
H
OEt
OEt
O
N
H
Cl

J. Chem. Sci. (2018) 130:128
Table 2. continued
Page 7 of 11 128
Time
(min)
Yield
(%)b
Entry
j
Aldehyde
Amine
P(OR)3
P(OEt)3
2-BrC6H4CHO
C6H5NH2
70
85
OEt
OEt
O
P
N
H
Br
OEt
k
l
4-NO2C6H4CHO 4-CNC6H5NH2
P(OEt)3
P(OEt)3
65
55
82
84
CN
O
OEt
P
O2N
N
H
4-NO2C6H4CHO
C6H5NH2
C6H5NH2
OEt
O
OEt
P
O2N
N
H
O
m
n
P(OEt)3
P(OEt)3
70
90
84
65
OEt
O
OEt
P
H
N
H
C6H5CHO
OEt
OEt
O
NH2
P
N
N
H
N
aAll reactions were carried out at room temperature, 1 mmol aldehyde, 1 mmol amine, 1 mmol trialkyl
phosphite and 0.15 g catalyst.
bIsolated yields.
The X-ray diffraction patterns of Fe3O4@SiO2-SO3H temperature and 100 ◦C in the absence of Fe3O4@
are shown in Figure 2. XRD diagram of the bare MNPs SiO2-SO3H was performed in order to establish the real
displayed patterns consistent with the patterns of spinel effectiveness of the catalyst (Table 1, entry 1, 2). It
ferrites described in the previous report.52 The average was found that no conversion to product was obtained
MNPs core diameter Fe3O4@SiO2-SO3H was calcu- even after 4 hours of heating (Monitoring by TLC). To
lated to be 8.2 and 9.6 nm, respectively from the XRD optimize the catalyst loading, a model reaction using
results by Scherrer’s equation. The average size of the phenylhydroxylamine, benzaldehyde, and triethyl phos-
crystallitescanbecalculatedusingtheScherrerequation phite was carried out under different amount of catalyst
(D = K /β cos ), wherein this equation D is the mean in different solvents (Table 1). It was observed that
λ
θ
crystalline size, K is a grain shape dependent constant 0.1 g loading of the catalyst in CH2Cl2 provides the max-
(0.9), is the incident beam wavelength (0.154), is imum yield in minimum time (Table 1, entry 8). Higher
λ
θ
the Bragg reflection angle and β is the full width at half percentage loading of the catalyst neither increased the
maximum (FWHM) of the main diffraction peak.57–59
The SEM image of Fe3O4@SiO2-SO3H is presented
yield nor lowered the reaction time.
By using the optimized reaction conditions, the
in Figure 3, shows a spherical shape with nano dimen- efficiency of this protocol was studied for the syn-
α
thesis of various N-hydroxy- -amino phosphonates,
sion ranging from 117 to 220 nm.
The loading capacity of the Fe3O4@SiO2-SO3H was and the results are summarized in Scheme 2. In most
determined by titration and found to be 2.58 mmol/g. cases, the reaction proceeded with high efficiency and
test reaction using phenylhydroxylamine, broad functional-group tolerance on aldehyde which
benzaldehyde, and triethyl phosphite at room displayed high reactivity under the optimized reaction
A

128 Page 8 of 11
J. Chem. Sci. (2018) 130:128
α
α
Table 3. Comparison of various catalysts in Synthesis of N-hydroxy- -amino phosphonates and -amino phos-
phonates.
Reaction
Catalyst
Solvent Temp. (◦C) Time Yield (%)
Ref.
47
α
Synthesis of N-hydroxy- -
aminophosphonates
[Bmim]BF4
–
r.t
2.5 h
92
[
]
47
[Bmim]PF6
LPDE
Fe3O4@SiO2-SO3H CH2Cl2
–
–
r.t
r.t
r.t
r.t
3.5 h
15 min
2 h
89
90
88
91
[
]
45,46
[
]
This work
27
Synthesis of
SbCl3/Al2O3
CH3CN
3 h
[
]
α
-aminophosphonates
37
39
36
21
PEG-SO3H
Nano Fe3O4
Cd(ClO4)2·xH2O
In/HCl
–
–
–
50
50
r.t
r.t
r.t
3.5h
98
94
92
88
92
[
[
[
[
]
]
]
]
48 min
40 min
1.5 h
H2O
Fe3O4@SiO2-SO3H CH2Cl2
45 min
This work
conditions and generated the desired products in high
We investigated various aromatic and heteroaromatic
yields. However, unfortunately, when some aliphatic aldehyde containing electron withdrawing or electron
aldehydes such as isobutyraldehyde and cyclohexane donating functional groups as well as an amine with
carboxaldehyde were used in this protocol under the trialkyl phosphonate P(OR)3 (R: Me, Et) at r.t. (25 ◦C)
above-optimized conditions, the desired products could (Table 2). The given results in Table 2 show that this
not be obtained.
one pot, three component condensations completed
Since the catalyst was separated by simple magnetic within 45–95 min, with good isolated yields. The 2-
decantation, it was washed with ether and reused in the aminopyridine gave less yield and required more time,
subsequent reaction. Yields of the product decreased probably due to the low reactivity of amino group. The
only slightly after four time’s reuse of catalyst. For reaction was compatible with various functional groups
example, the reaction of benzaldehyde, phenylhydrox- such as Cl, Br, CN, OMe, NO2, and OH not interfer-
ylamine and triethyl phosphite afforded the corre- ing with the competitive complex formation with the
α
sponding N-hydroxy- -amino phosphonates in 88%, catalyst.
86%, 85%, 85% and 84% yields over five cycles
(Figure 4).
The activity of Fe3O4@SiO2-SO3H by considering
theyieldforthemodelreactioniscomparedwithvarious
A possible mechanism for the synthesis of heterogeneous catalysts in Table 3. In addition to easily
α
N-hydroxy- -amino phosphonates catalyzed by magnetic decantation of Fe3O4@SiO2-SO3H, it showed
Fe3O4@SiO2-SO3H has been proposed (Scheme 3). The efficient catalytic activity in relatively short reaction
reaction proceeds via the nitrone intermediate, which time, with excellent yields.
was formed by the nucleophilic addition of phenyl-
hydroxylamine to an aldehyde. Fe3O4@SiO2-SO3H as
Brønsted acid plays a role in increasing the electrophilic
character of the starting aldehyde. Subsequent nucle-
4. Conclusion
ophilic addition of the triethyl phosphite provides the In summary, this paper describes the three-component
adduct intermediate that on subsequent reaction fol- reaction of aromatic aldehydes, trialkyl phosphite and
lowed by elimination of MeOH afforded the product.
According to the mechanism of these reactions, the
phenylhydroxylamine or amines to produce N-hydroxy-
α
α
-aminophosphonatesand -aminophosphonatesusing
planar nitrone and iminium intermediate are formed fol- SO3H-functionalized silica-coated magnetic nanopar-
lowed by nucleophilic attack of the trialkyl phosphite. ticles [Fe3O4@SiO2-SO3H] as a novel promoter. The
It can be concluded that racemic mixture of the product simple operation combined with easy recovery and re-
is obtained.
Bearing in mind the important properties of -amino economical and user-friendly process for the synthe-
use of this novel catalyst, make this a more convenient,
α
α
α
phosphonates, we decided to explore this magnetically sis of N-hydroxy- -amino phosphonates and -amino
α
effective catalyst for the preparation of -amino phos- phosphonates of biological and medicinal importance.
phonates using the optimized condition (Scheme 1). The Our results here did not detect leaching of acidic
results are summarized in Table 2.
site spices and the Fe3O4@SiO2-SO3H can be easily

J. Chem. Sci. (2018) 130:128
Page 9 of 11 128
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Acknowledgements
The authors thank Shahid Chamran University of Ahvaz for
financial support (Grant No. 31400.02.3.95).
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