Piperidine and piperazine immobilized on iron oxide nanoparticles as magnetically recyclable heterogeneous catalysts for one-pot synthesis of β-phosphonomalonates

Article abstract of DOI:10.1007/s10562-014-1297-2

Piperidine and piperazine immobilized on silica-coated γ-Fe ₂O₃ magnetic nanoparticles were synthesized as new supported bases via the reaction of chloro-functionalized γ-Fe ₂O₃?SiO₂ with piperidine and piperazine, respectively. The resulting bases were employed as magnetically recyclable heterogeneous catalysts for the efficient one-pot three-component synthesis of β-phosphonomalonates. The catalysts were easily separated from the reaction mixture by using a magnet and recycled for five times without significant loss of the catalytic activity. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-014-1297-2

Catal Lett
DOI 10.1007/s10562-014-1297-2
Piperidine and Piperazine Immobilized on Iron Oxide
Nanoparticles as Magnetically Recyclable Heterogeneous
Catalysts for One-Pot Synthesis of b-Phosphonomalonates
•
Sara Sobhani Maryam Sadat Ghasemzadeh
•
Moones Honarmand
Received: 11 March 2014 / Accepted: 14 June 2014
Ó Springer Science+Business Media New York 2014
Abstract Piperidine and piperazine immobilized on sil-
ica-coated c-Fe2O3 magnetic nanoparticles were synthesized
as new supported bases via the reaction of chloro-func-
tionalized c-Fe2O3@SiO2 with piperidine and piperazine,
respectively. The resulting bases were employed as mag-
netically recyclable heterogeneous catalysts for the efficient
one-pot three-component synthesis of b-phosphonomalo-
nates. The catalysts were easily separated from the reaction
mixture by using a magnet and recycled for five times
without significant loss of the catalytic activity.
applications have made the development of a number of
methods for the synthesis of phosphonates. A versatile and
powerful tool for the synthesis of phosphonates is direct P–
C bond formation such as Arbuzov reaction [5, 6]. Another
significant existing route for P–C bond formation involves
the addition of a phosphorous nucleophile to an electron-
deficient alkene (phospha-Michael addition) [7–18]. These
protocols proceeded through two-pot procedure in which
P–C and C–C bonds formation occurred in separate steps.
Ethylenediamine diacetate [19], diethylamine [20], 1,5,7-
triazabicyclo[4.4.0]dec-5-ene [21], iron doped carbon
nanotube [22] and clay supported heteropoly acid [23] are
the catalysts which have been reported for the one-pot
synthesis of b-phosphonomalonates. We have also recently
used ionic liquids [5-hydroxypentylammonium acetate (5-
HPAA) and 2-hydroxyethylammonium acetate-SiO2 (2-
HEAA-SiO2)], iodine, micellar solution of sodium stearate,
n-propylsulfonated c-Fe2O3 (NPS-c-Fe2O3) and c-Fe2
O3@SiO2-La(OTf)2 for this purpose [24–29]. Although,
the reported methods are valuable, they suffer from one or
more of the following drawbacks: tedious work-up proce-
dures, requiring ultrasound irradiation or heat, and using
expensive, unrecyclable and toxic catalysts or solvents. So,
it is still preferable to follow an eco-friendly procedure that
applies an efficient and reusable catalyst for the one-pot
synthesis of b-phosphonomalonates.
Keywords Magnetic nanoparticles Á Piperidine Á
Piperazine Á Heterogeneous catalyst Á
b-Phosphonomalonates
1 Introduction
Among the organophosphorous compounds, phosphonate
derivatives are important key intermediates in biochemical
processes due to their wide biological applications as
enzyme inhibitors, metabolic probes, peptide mimetics,
antibiotics, and pharmacological agents [1–4]. These vast
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-014-1297-2) contains supplementary
material, which is available to authorized users.
Piperidine and piperazine are known as organic bases,
which are used as conventional active catalysts for the
synthesis of organic compounds [30–33]. Despite the high
catalytic activity of piperidine and piperazine, their sepa-
ration from homogeneous reaction mixtures requires neu-
tralization by acidic conditions, which lead to worthless
ammonium salts. Harmful effect of acidic work-up can be
removed by immobilization of piperidine and piperazine
onto solid supports to obtain heterogeneous catalysts. Both
S. Sobhani (&) Á M. S. Ghasemzadeh
Department of Chemistry, College of Sciences, University of
Birjand, Birjand, Iran
e-mail: sobhanisara@yahoo.com; ssobhani@birjand.ac.ir
M. Honarmand
Department of Chemical Engineering, Faculty of Mining,
Chemical and Material Engineering, Birjand University of
Technology, Birjand, Iran
123

S. Sobhani et al.
organic polymers like resins [34, 35] and inorganic
matrices such as silica [36–39] have been employed as
solid supports for this purpose. However, although the
supported catalysts can be recovered by filtration or cen-
trifugation methods, these techniques are energy and time
consuming and may cause loss of the catalyst during the
separation process. The use of magnetic nanoparticles
(MNPs) as supporting materials offers a solution to this
problem [40, 41]. MNPs are easily separated by an external
magnet. Magnetic separation of MNPs is simple, eco-
nomical and promising for industrial applications. This
type of separation is also typically more effective than
filtration or centrifugation as it prevents loss of the catalyst.
In this view, we have recently focused our efforts on the
development of new heterogeneous catalysts based on
magnetic nanoparticles [28, 29, 42–45]. Following these
studies, herein, we report the synthesis of piperidine and
piperazine immobilized on silica-coated c-Fe2O3 MNPs
(piperidine-MNPs and piperazine-MNPs) as new hetero-
geneous bases (Scheme 1).
Scheme 2 Synthesis of b-phosphonomalonates in the presence of
piperidine-MNPs or piperazine-MNPs
silica-gel polygram SILG/UV254 plates. Transmission
electron microscopy analysis was performed using TEM
microscope (Philips CM 10-H-100 kV). FT-IR spectra
were recorded on a Shimadzu Fourier transform infrared
spectrophotometer (FT-IR-8300). Thermo gravimetric
analysis (TGA) was performed using a Shimadzu thermo
gravimetric analyzer (TG-50). Elemental analysis was
carried out on a Costech 4010 CHNS elemental analyzer.
Mass spectra were recorded on a Shimadzu GCMS-
QP5050A. The morphology of the products was deter-
mined by using Hitachi Japan, model s4160 scanning
electron microscopy (SEM) at accelerating voltage of
15 kV. Power X-ray diffraction (XRD) was performed on a
Bruker D8-advance X-ray diffractometer with Cu Ka
(k = 0.154 nm) radiation.
To investigate the catalytic activity of piperidine-MNPs
and piperazine-MNPs in organic reactions, we have used
them as magnetically recyclable heterogeneous basic cat-
alysts for the synthesis of b-phosphonomalonates via one-
pot three-component reaction of aldehydes, malononitrile
and trialkyl phosphites. The catalysts could be readily
separated from the reaction mixture by using an external
magnet. This kind of separation removes the need of fil-
tration and facilitates recycling of the catalysts (Scheme 2).
2.2 Synthesis of c-Fe2O3@SiO2
The c-Fe2O3 nanoparticles were synthesized by a reported
chemical co-precipitation technique [46–48]. FeCl2Á4H2O
(3.98 g) and FeCl3Á6H2O (6.50 g) were dissolved in
deionized water (60 mL) under Ar atmosphere at room
temperature. A NH4OH solution (0.6 M, 400 mL) was then
added drop wise (drop rate = 1 mL min-1) to the stirring
mixture at room temperature to reach the pH of the reaction
solution to 11. The resulting black dispersion was contin-
uously stirred for 1 h at room temperature and then heated
to reflux for 1 h to yield a brown dispersion. The magnetic
nanoparticles were then purified by a repeated centrifuga-
tion (3,000–6,000 rpm, 20 min), decantation and redi-
spersion cycle three times. The as-synthesized sample was
heated in air at 2 °C min-1 up to 200 °C and then kept in
2 Experimental
2.1 General
Chemicals were purchased from Merck Chemical Com-
pany. NMR spectra were recorded on a Bruker Avance
DPX-250 and 400 using deutrated CDCl3 as solvent and
TMS as internal standard. The purity of the products and
the progress of the reactions were accomplished by TLC on
O
O
O
Piperidine
γ-Fe2O3
Si
N
N
SiO2
piperidine-MNPs
O
O
O
(MeO)3Si
Cl
γ-Fe2O3
Si
Cl
γ-Fe2O3
SiO2
SiO2
O
O
O
Piperazine
γ-Fe2O3
Si
NH
SiO2
piperazine-MNPs
Scheme 1 Synthesis of piperidine-MNPs and piperazine-MNPs
123

Piperidine and Piperazine on Iron Oxide Nanoparticles
the furnace for 3 h to give a reddish-brown powder. Con-
centrated solution of ammonia (3.5 mL) was then added to
the dispersed c-Fe2O3 nanoparticles (3.5 g) in deionized
water (40 mL)/ethanol (160 mL) and the resulting mixture
was stirred at 40 °C for 30 min. Subsequently, tetraethyl
orthosilicate (TEOS, 2.0 mL) was charged to the reaction
vessel and the mixture was continuously stirred at 40 °C
for 24 h. The silica-coated nanoparticles (c-Fe2O3@SiO2)
were collected by a permanent magnet followed by wash-
ing three times with EtOH and diethyl ether and dried at
100 °C in vacuum for 24 h.
2.3 Synthesis of Chloro-Functionalized c-Fe2O3@SiO2
A mixture of c-Fe2O3@SiO2 (2.0 g) in dry toluene
(40 mL) was sonicated for 45 min. 3-Chloropropyl tri-
methoxysilane (0.5 mL) was added to the dispersed c-
Fe2O3@SiO2 in toluene and slowly heated to 105 °C. The
reaction mixture was stirred at this temperature for 20 h.
The resulting chloro-functionalized c-Fe2O3@SiO2 was
separated by an external magnet and washed three times
with diethyl ether and CH2Cl2, and dried under vacuum.
The loading amount of Cl atom was 0.4 mmol per gram
catalyst based on elemental analysis and TGA.
Fig. 1 XRD pattern of c-Fe2O3 MNPs
3 Results and Discussion
3.1 Synthesis and Characterization of Piperidine-
MNPs and Piperazine-MNPs
At first, c-Fe2O3 nanoparticles were synthesized by a
reported chemical co-precipitation technique of ferric and
ferrous ions in alkali solution followed by thermal treat-
ment [46–48]. Figure 1 shows the XRD pattern of c-Fe2O3
MNPs. The observed diffraction patterns have a good
agreement with the cubic structure of maghemite (JCPDS
2.4 Synthesis of Piperidine-MNPs and Piperazine-
MNPs
Piperidine or piperazine (0.1 g) was added to chloro-
functionalized c-Fe2O3@SiO2 (1.7 g) in dry toluene
(15 mL), and the mixture was stirred for 6 h. The resulting
solid material was separated by an external magnet, washed
with diethyl ether and CH2Cl2, and dried at room temper-
ature in vacuum to afford piperidine-MNPs or piperazine-
MNPs.
˚
file No 04-0755), a unit cell dimension of 8.35 A and the
space group of P4132 (213). The average crystallite size
was calculated to be 13.1 nm using the Scherrer equation in
which K = 0.9 and k = 0.154 nm.
c-Fe2O3 MNPs suspension was sonicated in an alkaline
solution of tetraethyl orthosilicate (TEOS) to obtain MNPs
coated by silica. The shell of silica not only improves the
dispersibility but also provides suitable sites (Si–OH
groups) for further surface functionalization. The resulting
silica-coated c-Fe2O3 MNPs (c-Fe2O3@SiO2) were then
allowed to react with (3-chloropropyl)trimethoxysilane in
toluene under reflux conditions to give chloro-functional-
ized silica-coated c-Fe2O3. Piperidine-MNPs and pipera-
zine-MNPs were obtained by the reaction of chloro-
functionalized silica-coated c-Fe2O3 with excess amount of
piperidine and piperazine, respectively. The synthesized
piperidine-MNPs and piperazine-MNPs were characterized
by SEM, TEM, FT-IR, TGA and elemental analysis.
SEM images of piperidine-MNPs and piperazine-MNPs
were showed uniformity and spherical morphology of
MNPs (Fig. 2). The particle size distribution of piperidine-
MNPs and piperazine-MNPs were evaluated using TEM
(Fig. 3). The mean diameter of nanoparticles was 14 nm.
2.5 Synthesis of b-Phosphonomalonates
in the Presence of Piperidine-MNPs or Piperazine-
MNPs
Piperidine-MNPs (3 mol %, 0.083 g) or piperazine-MNPs
(3 mol %, 0.120 g) was added to a stirred mixture of
aldehyde (1 mmol), malononitrile (1 mmol) and trialkyl
phosphite (1 mmol). The reaction mixture was stirred at
room temperature for the appropriate time (Table 2). EtOH
(10 mL) was added to the reaction mixture. The catalyst
was separated by an external magnet, washed with EtOH,
dried and reused for a consecutive run under the same
reaction conditions. Solvent of the remaining solution was
evaporated under reduced pressure to give the crude pro-
ducts. The pure products were obtained by chromatography
on silica gel eluted with n-hexane:EtOAc (1:2).
123

S. Sobhani et al.
Fig. 2 SEM of a piperidine-MNPs and b piperazine-MNPs
Fig. 3 a TEM of piperidine-
MNPs, b TEM of piperazine-
MNPs, c particle size
distribution histogram of
piperidine-MNPs and d particle
size distribution histogram of
piperazine-MNPs
FT-IR spectra of c-Fe2O3, c-Fe2O3@SiO2, piperidine-
MNPs and piperazine-MNPs (Fig. 4) were showed broad
bands at around 550–650 cm-1, which were attributed to
Fe–O vibrations [49]. In the spectra of c-Fe2O3@SiO2,
piperidine-MNPs and piperazine-MNPs, the Si–O-Si
stretching modes of silica shell can be observed as a strong
broad peak at about 1,099–1,220 cm-1 [50]. In the spectra
of piperidine-MNPs and piperazine-MNPs, a typical band
at about 2,960 cm-1 was attributed to C–H stretching
vibrations of alkyl chains. An absorption band at
3,461 cm-1 was observed in the spectrum of piperazine-
MNPs which was related to the stretching vibration of N–H
bonds. These results indicated that piperidine and pipera-
zine were successfully grafted onto the c-Fe2O3@SiO2
MNPs.
The thermal stability of piperidine-MNPs and pipera-
zine-MNPs were investigated by thermogravimetric ana-
lysis (TGA) (Fig. 5). TG curve of piperidine-MNPs
123

Piperidine and Piperazine on Iron Oxide Nanoparticles
Table 1 One-pot reaction of benzaldehyde, malononitrile and
triethyl posphite under different conditionsa
a
Entry Catalyst (mol %)
Solvent
Time
3 h
Yieldb (%)
72
b
1
Piperidine-MNPs (1)
Piperidine-MNPs (3)
Piperidine-MNPs (5)
Piperazine-MNPs (1)
Piperazine-MNPs (3)
Piperazine-MNPs (5)
Piperidine-MNPs (3)
Piperidine-MNPs (3)
Piperidine-MNPs (3)
Piperidine-MNPs (3)
Piperidine-MNPs (3)
Piperazine-MNPs (3)
Piperazine-MNPs (3)
Piperazine-MNPs (3)
Piperazine-MNPs (3)
Piperazine-MNPs (3)
–
–
2
–
15 min 91
15 min 91
c
3
–
4
–
3 h
69
d
5
–
10 min 90
10 min 91
6
–
7
H2O
EtOH
24 h
24 h
62
69
42
70
74
55
64
51
67
78
62
60
61
8
9
n-Hexane 24 h
10
11
12
13
14
15
16
17
18
19
20
21
a
CH3CN
Toluene
H2O
24 h
24 h
24 h
24 h
4000
3400
2800
2200
1600
1000
400
Wave number (cm-1)
EtOH
n-Hexane 24 h
Fig. 4 FT-IR spectra of a c-Fe2O3, b c-Fe2O3@SiO2, c piperidine-
MNPs and d piperazine-MNPs
CH3CN
24 h
24 h
24 h
24 h
24 h
Toluene
–
–
–
–
–
c-Fe2O3 (0.083 g)
c-Fe2O3@SiO2 (0.083 g)
Piperidine (3)
10 min 92
10 min 91
Piperazine (3)
Reaction conditions: benzaldehyde (1 mmol), malononitrile
(1 mmol), triethyl phosphite (1 mmol), room temperature
b
Isolated yield
amount of piperidine supported on c-Fe2O3@SiO2 was
evaluated to be 0.36 mmol g-1. These results were in
agreement with those obtained by elemental analysis
(C = 3.46 % and N = 0.51 %). As shown in the TG curve
of piperazine-MNPs (Fig. 5b), the weight loss around
105 °C was attributed to the loss of adsorbed water mol-
ecules. Complete loss of organic moiety was seen in the
temperature range from 108 to 511 °C. Using TG curve,
the amount of piperazine supported on c-Fe2O3 was cal-
culated to be 0.25 mmol g-1. The loading amount of
piperazine on c-Fe2O3 was also quantified via elemental
analysis and it was 0.25 mmol g-1 based on carbon and
nitrogen content (C = 2.13 % and N = 0.71 %).
3.2 Synthesis of b-Phosphonomalonates Catalyzed
by Piperidine-MNPs and Piperazine-MNPs
Fig. 5 TGA of a piperidine-MNPs and b piperazine-MNPs
As part of our attempts orientated to the development of
new methods for the synthesis of phosphonate derivatives
[51–54], we have recently introduced acidic or neutral
conditions for the one-pot synthesis of b-phosphonomalo-
nates [24–29]. Herein, we have studied the application of
piperidine-MNPs and piperazine-MNPs as magnetically
showed the weight loss around 180 °C, which was related
to the adsorbed water molecules on the support. The
organic parts were decomposed completely in the temper-
ature range of 195–496 °C. According to the TGA, the
123

S. Sobhani et al.
Table 2 Synthesis of
Entry Aldehyde
Product
Catalyst
piperidine-MNPs piperazine-MNPs
b-phosphonomalonates in the
presence of piperidine-MNPs or
piperazine-MNPsa
Time
(min)
Yield
Time
(min)
Yield
(%)b
85
(%)b
91
CHO
CHO
CHO
O
(EtO)2P
1
15
15
15
15
20
15
CN
Cl
CN
Cl
1a
O
(MeO)2P
2
CN
83
75
89
75
Cl
CN
Cl
Cl
1b
Cl
O
(EtO)2P
3
CN
CN
1c
O
Cl
(EtO)2P
CHO
4
5
CN
20
15
75
91
20
10
80
90
CN
Cl
1d
CHO
O
(EtO)2P
CN
CN
1e
O
CHO
CHO
CHO
CHO
(EtO)2P
6
7
8
CN
CN
5
82
83
74
83
79
5
81
82
85
81
82
MeO
Me
MeO
1f
O
(EtO)2P
CN
CN
15
5
5
Me
1g
O
(EtO)2P
CN
5
Br
Br
CN
Br
Br
1h
O
(EtO)2P
9
CN
30
60
15
50
CN
1i
O
(EtO)2P
10
CHO
CHO
O
N
CN
O
CN
O
1j
(EtO)2P
11
12
13
5
94
76
72
5
96
75
74
CN
CN
N
1k
CHO
O
(EtO)2P
15
25
15
25
CN
a
Reaction conditions: aldehyde
CN
(1 mmol), malononitrile
(1 mmol), trialkyl phosphite
(1 mmol), catalyst (3 mol %),
room temperature
1l
CHO
O
(EtO)2P
CN
CN
b
1m
Isolated yield
123

Piperidine and Piperazine on Iron Oxide Nanoparticles
recyclable heterogeneous basic catalysts for the one-pot
three-component synthesis of b-phosphonomalonates.
At first, the reaction of benzaldehyde, malononitrile and
triethyl phosphite was chosen as a model reaction to opti-
mize the reaction conditions such as molar ratio of the
catalyst and solvent (Table 1, entries 1–16). It was found
that the best yield of the product was obtained at room
temperature under solvent-free conditions in the presence
of 3 mol % of piperidine-MNPs or piperazine-MNPs
(Table 1, entries 2 and 5). In order to show the role of the
catalyst, similar reactions in the absence of the catalyst and
in the presence of c-Fe2O3 and c-Fe2O3@SiO2 were also
examined. Under these conditions, the reactions led to the
formation of the desired product in 60–62 % yields after a
long reaction time (Table 1, entries 17–19). The role of
piperidine and piperazine as non-supported bases were also
studied in the reaction of benzaldehyde, malononitrile and
triethyl phosphite (Table 1, entries 20 and 21). The results
showed that the catalytic activity of piperidine and piper-
azine did not change after their supporting on the surface of
MNPs.
Table 3 Comparison of the catalytic activity of piperidine-MNPs
and piperazine-MNPs with various catalysts for the synthesis of
b-phosphonomalonate 1ea
Entry
Catalyst
Time
Yield (%)b
1
ZnO
24 h
61
56
54
50
63
59
51
54
35
38
41
50
52
56
44
30
31
43
91
90
2
CuO
24 h
3
Sb2O3
24 h
4
SnO2
24 h
5
HgO
24 h
6
PbO
24 h
7
MoO3
24 h
8
ZrO2
24 h
9
MgO
24 h
10
11
12
13
14
15
16
17
18
19
20
a
CaO
24 h
AP-SiO2
24 h
c-Fe2O3-pyridine based catalyst
HClO4–SiO2
H3PMo12O40
5-HPAA
24 h
24 h
24 h
20 min
15 min
24 h
2-HEAA-SiO2
I2
To establish the generality of this method, the synthesis
of various b-phosphonomalonates was studied using
malononitile, different aldehydes and trialkyl phosphites
under optimized reaction conditions (Table 2).
Sodium stearate
Piperidine-MNPs
Piperazine-MNPs
24 h
15 min
10 min
As the results of Table 2 indicate, b-phosphonomalo-
nates 1a and 1b were generated in high yields from the
reaction of 4-chlorobenzaldehyde and malononitrile with
triethyl and trimethyl phosphite, respectively (Table 2,
entries 1 and 2). The reaction of various substituted
benzaldehyde with malononitrile and triethyl phosphite
were proceeded well and produced the corresponding
products 1c-i in good to high yields (Table 2, entries 3–9).
Interestingly, piperidine-MNPs and piperazine-MNPs effi-
ciently promoted the synthesis of b-phosphonomalonates
using acid-sensitive aldehydes such as furfural and pyri-
dine-3-carbaldehyde without polymerization or decompo-
sition (Table 2, entries 10 and 11). These catalysts were
also applied successfully for the synthesis of b-phospho-
nomalonates from the reaction of triethyl phosphite and
malononitrile with aliphatic aldehydes (Table 2, entries 12
and 13).
Reaction conditions: benzaldehyde (1 mmol), malononitrile
(1 mmol), triethyl phosphite (1 mmol), catalyst (3 mol %), solvent-
free, room temperature
b
Isolated yield
To show the special catalytic behaviour of piperidine-
MNPs and piperazine-MNPs in the synthesis of b-phos-
phonomalonates, the reaction of benzaldehyde, malono-
nitrile and triethyl phosphite was performed in the presence
of a catalytic amount of metal oxides (ZnO, CuO, Sb2O3,
SnO2, HgO, PbO, MoO3, ZrO2, MgO and CaO), basic
catalysts {aminopropylated silica (AP-SiO2) [54] and c-
Fe2O3-pyridine based catalyst [43] }, BrØnsted acids
(HClO4-SiO2 and H3PMo12O40), ionic liquids (5-HPAA
and 2-HEAA-SiO2), iodine and sodium stearate (Table 3).
As is evident from Table 3, piperidine-MNPs and
Fig. 6 Catalyst separation from the reaction mixture using an
external magnet
piperazine-MNPs were the most effective catalysts for this
purpose leading to the formation of b-phosphonomalonate
1e in high yield in a short reaction time.
123

S. Sobhani et al.
Fig. 7 Reusability of piperidine-MNPs and piperazine-MNPs for the
synthesis of b-phosphonomalonate 1e
Fig. 9 FT-IR spectra of a piperidine-MNPs and b piperazine-MNPs
after five times reuse
The recovery and reuse of a catalyst is highly preferable
for a catalytic process. In this regard the recyclability of
piperidine-MNPs and piperazine-MNPs was investigated in
a model reaction of benzaldehyde, malononitrile and tri-
ethyl phosphite under optimized reaction conditions. After
the reaction was completed, EtOH was added to the reac-
tion mixture and the whole amount of the catalyst simply
separated from the product by an external magnet (Fig. 6).
The recovered catalyst was washed with EtOH, dried at
room temperature and reused for five consecutive trials
without loss of their catalytic activity (Fig. 7).
piperazine were grafted onto MNPs. These results indi-
cated that the catalysts were stable and could tolerate the
present reaction conditions.
4 Conclusions
In conclusion, novel supported piperidine and piperazine
onto silica coated c-Fe2O3 magnetic nanoparticles were
synthesized and characterized by different techniques.
These solid bases were applied as magnetically recyclable
heterogeneous catalysts for the one-pot three-component
reaction of aldehydes, malononitrile and trialkyl phos-
phites. b-Phosphonomalonates were obtained using this
protocol, in good to high yields at room temperature under
solvent-free conditions. More importantly, the catalysts
were easily separated by an external magnet and reused
five times without significant loss of their catalytic activity.
It is worth to note that the reusability test was stopped
after five runs. Comparison of TEM images (Fig. 8) and
FT-IR spectra (Fig. 9) of reused catalysts with those of the
fresh catalysts (Fig. 3a, 3b, 4c and 4d) showed that the
morphology and structure of piperidine-MNPs and piper-
azine-MNPs was remained intact after five recoveries.
Furthermore, the loading amount of the catalysts after five
times reuse was determined by elemental analysis, and
found that 0.34 and 0.24 mmol g-1 of piperidine and
Fig. 8 TEM image of a piperidine-MNPs and b piperazine-MNPs after five times reuse
123

Piperidine and Piperazine on Iron Oxide Nanoparticles
Acknowledgments We are thankful to University of Birjand
Research Council for their support on this work.
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