Diazabicyclo[2.2.2]octane stabilized on Fe3O4 as catalysts for synthesis of coumarin under solvent-free conditions

Article abstract of DOI:10.1007/s13738-013-0270-0

Fe₃O₄-diazabicyclo[2.2.2]octane (Fe₃O ₄-DABCO) magnetic nanoparticles (MNPs) catalyst was readily prepared from inexpensive starting materials in aqueous media which catalyzed the synthesis of coumarin. FTIR spectroscopy, X-ray diffraction, transmission electron micrographs were employed to characterize the properties of the synthesized Fe₃O₄-DABCO MNPs. High catalytic activity and ease of recovery from the reaction mixture using external magnet, and several reuse times without significant losses in performance are additional eco-friendly attributes of this catalytic system.

Full text of DOI:10.1007/s13738-013-0270-0

J IRAN CHEM SOC
DOI 10.1007/s13738-013-0270-0
ORIGINAL PAPER
Diazabicyclo[2.2.2]octane stabilized on Fe O as catalysts
3
4
for synthesis of coumarin under solvent-free conditions
Mohammad Ali Nasseri Seyed Mohsen Sadeghzadeh
•
Received: 23 December 2012 / Accepted: 9 May 2013
Ó The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract Fe O -diazabicyclo[2.2.2]octane (Fe O -DAB-
3
functional shell structures have received especial attention
4
3 4
CO) magnetic nanoparticles (MNPs) catalyst was readily
prepared from inexpensive starting materials in aqueous
media which catalyzed the synthesis of coumarin. FTIR
spectroscopy, X-ray diffraction, transmission electron
micrographs were employed to characterize the properties
of the synthesized Fe O -DABCO MNPs. High catalytic
because of their potential applications in catalysis, drug
storage/release, selective separation, chromatography, and
chemical or biologic sensors [7–12]. The magnetic core has
good magnetic responsibility, and can be easily magnetized.
Therefore, the composites with magnetic core can be con-
veniently collected, separated or fixed by external magnet.
1,4-Diazabicyclo[2.2.2]octane (DABCO), a cage-like
compound, is a small diazabicyclic molecule with weak
alkalescency and medium-hindrance [13]. DABCO has been
applied as an inexpensive, eco-friendly, high reactive and
non-toxic base catalyst for various organic transformations,
including ring opening of aziridines with amines or thiols
[14], oxidativedeprotectionof(tetrahydropyranyl)ethersand
silyl ethers [15], conversion of tetrahydropyranyl ethers into
acetates [16], regioselective nucleophilic aromatic substitu-
tion reaction [17], synthesis of isoxazolines [18], synthesis of
N-arylphthalimides [19], synthesis of industrially important
polyurethane foams [20], and Baylis–Hillman reactions [21,
22]. Nevertheless, in many of these cases, DABCO has not
been recovered, and eliminated as a residue.
3
4
activity and ease of recovery from the reaction mixture
using external magnet, and several reuse times without
significant losses in performance are additional eco-
friendly attributes of this catalytic system.
Keywords Fe O -DABCO Á Coumarin Á Magnetic
3
4
nanoparticles (MNPs) Á Green chemistry Á One-pot
synthesis
Introduction
In recent years, core–shell multi-components have attracted
intense attention because of their potential applications in
catalysis [1]. Different from single-component that can only
supply people with one function, the core–shell multi-com-
ponents can integrate multiple functions into one system for
specific applications [2–6]. Moreover, the interactions
between different components can greatly improve the per-
formance of the multi-components system and even generate
new synergetic properties. Among the core–shell structured
composites, the composites with magnetic core and
Herein we report the fabrication of DABCO incorporated
into a surface magnetite nanoparticles which catalyzed the
synthesis coumarin under solvent-free conditions. The pre-
pared Fe O -DABCO MNPs are multi-functional. The Fe O
3
4
3 4
core makes them very easy to be separated and recycled from
solution with the help of an external magnet (Scheme 1).
Experimental
M. A. Nasseri (&) Á S. M. Sadeghzadeh
Department of Chemistry, College of Sciences, University
of Birjand, P.O. Box 97175-615, Birjand, Iran
e-mail: mohammadali.nasseri@yahoo.com;
manaseri@birjand.ac.ir
Materials and methods
Chemical materials were purchased from Fluka and Merck
in high purity. Melting points were determined in open
123

J IRAN CHEM SOC
Scheme 1 Synthesis of
coumarin from phenol and ethyl
acetoacetate in the presence of
OH
O
O
O
O
Fe O -DABCO
3
4
R
R
+
3
Fe O
4
-DABCO
Me
OEt
r.t.
1
2
3
Me
capillaries using an Electrothermal 9100 apparatus and are
uncorrected. Powder X-ray diffraction data were obtained
using Bruker D8 advance model with Cu ka radiation.
FTIR spectra were recorded on a VERTEX 70 spectrom-
eter (Bruker) in the transmission mode in spectroscopic
grade KBr pellets for all the powders. The particle size and
structure were observed by using a Philips CM10 trans-
mission electron microscope operating at 100 kV. The
thermo-gravimetric analysis (TGA) curves were recorded
under air atmosphere using TGA/DTA Shimadzu-50 with
platinum pan. The samples were heated in air from 25 to
water in sequence, and then dried under vacuum at 60 °C
for 2 h for further use.
General procedure for the preparation of Fe O -
3
4
DABCO
For the synthesis of Fe O -DABCO MNPs, 2 mmol of
3
4
Fe O MNPs was dispersed in a mixture of 80 mL of
3 4
ethanol, 20 mL of deionized water and 2.0 mL of 28 wt%
concentrated ammonia aqueous solution (NH ÁH O), fol-
3
2
lowed by the addition of 20 mmol of compound n-propyl-
4-aza-1-azoniabicyclo[2.2.2]octane. After vigorous stirring
for 24 h, the final suspension was repeatedly washed, fil-
tered for several times and dried at 60 °C in the air.
1
,000 °C with a heating rate of 10 °C/min. The weight
losses as a function of temperature were recorded. NMR
spectra were recorded in DMSO on a Bruker advance
DRX-400 MHz instrument spectrometer using TMS as
internal standard. The purity determination of the products
and reaction monitoring were accomplished by TLC on
silica gel polygram SILG/UV 254 plates. Mass spectra
were recorded on Shimadzu GCMS-QP5050 mass
spectrometer.
General procedure for the synthesis of coumarin
A mixture of phenol (1 mmol), ethyl acetoacetate
(1 mmol), and Fe O -DABCO MNPs (0.0007 g) was stir-
3 4
red at 90 °C for 35–45 min. EtOH was added to the reac-
tion mixture and the Fe O -DABCO MNPs were separated
3
4
General procedure for the preparation of Fe O
3
4
by external magnet. Then the solvent was removed from
solution under reduced pressure and the resulting product
was purified by recrystallization using ethanol.
nanoparticles
The synthesis procedure is illustrated as follows: (1)
0
.01 mol FeCl Á4H O and 0.03 mol FeCl Á6H O were
2
2
3
2
dissolved into 200 mL distilled water, followed by the
addition of PEG (1.0 g, MW 6,000), (2) sodium hydroxide
Results and discussion
(
NaOH) was added to the solution and the pH value was
Due to the reasonable needs to clean and green recovery of
the heterogenous catalyst, we synthesized Fe O -DABCO
controlled in the range 12 B pH B 13, and (3) different
amount of hydrazine hydrate (N H ÁH O, 80 % concen-
3
4
2
4
2
as a new catalyst nanomagnetic iron oxide simply (Fig. 1).
The synthesized Fe O -DABCO was then characterized by
tration) was added to the above suspension. The reaction
was continued for about 24 h at room temperature. During
this period, the pH value was adjusted by NaOH and kept
in the range of 12 B pH B 13. The black Fe O NPs were
3
4
different methods such as X-ray power diffraction (XRD),
transmission electron microscopy (TEM), and FTIR.
3
4
then rinsed several times with ionized water.
XRD
General procedure for the preparation of n-propyl-4-
aza-1-azoniabicyclo[2.2.2]octane
The structural properties of synthesized Fe
nanoparticle were analyzed by XRD. As shown in Fig. 2,
XRD patterns of the synthesized Fe -DABCO nano-
O -DABCO
3 4
2
mmol DABCO and 2 mL THF were mixed together in a
O
3 4
beaker, and then 2 mmol of NaH was dispersed into the
mixture by ultrasonication. 2.5 mmol 3-chloropropyl-
triethoxysilane was added drop-wise at room temperature
and stirred for another 16 h at 60 °C. The resultant prod-
ucts were collected and washed with ethanol and deionized
particle display several relatively strong reflection peaks in
o
the 2h region of 20–80 , which is quite similar to those of
Fe O nanoparticles reported by other group. The dis-
3 4
cernible six diffraction peaks in Fig. 2 can be indexed to
(220), (311), (400), (422), (511), and (440), which match
1
23

J IRAN CHEM SOC
Fig. 1 Schematic illustration of
the synthesis for Fe
DABCO MNPs
3
O
4
-
EtO
EtO
EtO
N
EtO
EtO
EtO
+N
Si
Cl
+
N
Si
Cl-
N
A
B
C
Fe O
3
4
O
+N
Fe O
3
O
Si
Cl-
4
O
N
D
TGA
The thermal behavior of Fe O -DABCO MNPs is shown in
3
4
Fig. 5. This was evaluated to be 1.5 % according to the TG
analysis. The analysis showed two decreasing peaks. First
peak appears at temperature around 130–150 °C due to
desorption of water molecules from the catalyst surface.
This is followed by a second peak at 425–450 °C, corre-
sponding to the loss of the organic spacer group (Fig. 5).
According to the TGA, the amount of DABCO function-
-
1
alized on Fe O is evaluated to be 2.2 mmol g
3
.
4
Catalytic activity of Fe O -DABCO MNPs
3 4
Fig. 2 XRD analysis of Fe
3 4
O -DABCO MNPs
for the one-pot synthesis of coumarin
well with the database of magnetite in JCPDS (JCPDS
Card: 19-629) file.
We thought to optimize the reaction conditions; the same
reaction was carried out in various solvents under similar
conditions. In this study, it was found that solvent-free is a
more efficient and superior solvent (Table 1, entry 14) over
other solvents (Table 1, entries 1–13) with respect to
reaction time and yield of the desired coumarin.
TEM
The size and structure of the Fe O -DABCO were also
3
4
evaluated using TEM (Fig. 3a, b). From TEM images
Fig. 3b), it can be seen that Fe O MNPs are uniformly
At this stage, the amount of catalyst necessary to pro-
mote the reaction efficiently was examined (Fig. 6). It was
observed that the variation for Fe O -DABCO MNP had an
(
3
4
coated with DABCO layer. The average size of Fe O
3
4
3 4
MNPs is about 15–25 nm (Fig. 3a). After being coated
with a DABCO, the typical core–shell structure of the
Fe O -DABCO can be observed, and the average size
effective influence. The best amount of Fe O -DABCO
3 4
MNP is 0.0007 g which afforded the desired product in
93 % yields (Fig. 6).
3
4
increases to about 40–50 nm (Fig. 3b).
Under the optimal conditions, the reaction progress in
the presence of 0.0007 g of Fe O -DABCO MNPs was
3
4
FTIR
monitored by GC (Fig. 7). Using this catalyst system,
excellent yields of coumarin can be achieved in 35 min at
90 °C. No apparent by-products were observed by GC in
all the experiments and the cyclic carbonate was obtained
cleanly in 93 % yield.
The successful conjugation of DABCO onto the surface of
the Fe O nanoparticles was confirmed by the FTIR spectra
3
4
-
Fig. 4). The peaks at 3,415 and 590 cm appear in all the
1
(
FTIR spectra, which are assigned to the –OH group and
the Fe–O group, respectively (Fig. 4a). In FTIR spectra of
It is important to note that the magnetic property of
Fe O -DABCO MNPs facilitates its efficient recovery from
3
4
?
the Fe O -DABCO MNPs, the C–N stretching at
the reaction mixture during work-up procedure. The
activity of the recycled catalyst was also examined under
the optimized conditions. After the completion of reaction,
the catalyst was separated by an external magnet, washed
3
4
-
1
-1
1
,615 cm , CH bending at 1,480 cm , Si–C stretching
2
-
1
-1
at 1,210 cm , and Si–O stretching at 1,110–1,090 cm
are observed as a broad band (Fig. 4b).
123

J IRAN CHEM SOC
Fig. 3 TEM images of a Fe
3 4
O ,
3 4
b Fe O -DABCO MNPs
Fig. 4 FTIR spectra of
a Fe , b Fe -DABCO
MNPs
O
3 4
3 4
O
In order to show the unique catalytic behavior of Fe O -
3
4
DABCO MNPs in these reactions, we have performed one-
pot reaction of phenol and ethyl acetoacetate in the presence
of a catalytic amount of H PW O , NbCl , PEG-SO H,
3
12 40
5
3
InCl , Pd(PPh ) , cerium(IV) ammonium nitrate, nano-SiO ,
3 4
3
2
nano-RuO , nano-TiO , nano-Fe O , nano c-Fe O , and
2
2
3
4
2 3
nano-FeNi (Table 2). As it is evident from Table 2, Fe O -
3 3 4
DABCO MNP is the most effective catalyst for this purpose,
leading to the formation of coumarin in a good yield.
After optimization of the reaction conditions, this
methodology was evaluated using variety of different
substituted phenol in the presence of nanocatalyst under
similar conditions. The reaction proceeded smoothly and
was completed for 35–50 min at 90 °C (Table 3).
3 4
Fig. 5 TGA diagram of Fe O -DABCO MNPs
A plausible mechanism for the reaction between phenol
and ethyl acetoacetate on Fe O -DABCO MNPs surface
3
4
with methanol and dried at the pump. The recovered cat-
alyst was reused for six consecutive cycles without any
significant loss in catalytic activity (Fig. 8).
during the synthesis of coumarin is depicted in Scheme 2.
The Fe O -DABCO MNP has lewis acid and lewis basic
3
4
sites.
1
23

J IRAN CHEM SOC
Table 1 Solvent screening for the reaction between phenol and ethyl
acetoacetate
a
9
9
9
9
9
9
8
5
4
3
2
1
0
9
Entry
Solvent
Yield (%)
1
2
3
4
5
6
7
8
9
2
H O
79
EtOH
CH CN
THF
CH Cl
64
3
53
34
2
2
28
Toluene
EtOAC
20
1
2
3
4
5
6
reuse
63
n-Hexane
Trace
Trace
48
Fig. 8 Reuse performance of the catalysts
CHCl
3
1
1
1
1
1
0
1
2
3
4
DMSO
Selected spectroscopic data
MeOH
55
-
1
Dioxane
Trace
49
Compound (3a): IR (KBr): t cm : 3162, 1684, 1379,
225, 1059, 973, 849, 750, 580, 532, 436. H NMR: d
0.50 (brs, 1H), 7.54–7.51 (d, J = 9 Hz, 1H), 6.77–6.74 (d,
1
DMF
1
Solvent-free condition
93
1
J = 8 Hz, 1H), 6.66 (s, 1H), 6.07 (brs, 1H), 2.31 (brs, 3H).
1
Reaction conditions: phenol (1 mmol), ethyl acetoacetate (1 mmol),
solvent (10 ml), Fe
3
3
O
4
-DABCO MNPs (0.001 g) at 100 °C for
C NMR: d 161.58, 160.69, 155.25, 153.81, 126.89,
13.25, 112.42, 110.67, 102.57, 18.46.
4
0 min
1
a
Isolated yields
Fig. 6 Effect of increasing
amount of Fe -DABCO
MNPs on the preparation of
coumarin (reaction of phenol
and ethyl acetoacetate in the
100
3 4
O
90
80
70
60
3 4
presence of Fe O -DABCO
MNPs at 100 °C)
50
40
30
20
10
0
0
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0.0007
0.0008
0.0009
Fe3O4-DABCO (g)
Fig. 7 Reaction progress
monitored by GC
100
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
90
100
110
T (°C)
123

J IRAN CHEM SOC
-
1
Table 2 Comparison of the catalytic efficiency of Fe
with various catalysts
3
O
4
-DABCO
Compound (3d): IR (KBr): t cm : 3198, 2925, 1684,
568, 1372, 1308, 1082, 953, 857, 805, 731, 598, 539. H
1
1
a
NMR: d 10.34 (s, 1H), 7.39–7.36 (d, J = 8.75 Hz, 1H),
Entry Catalyst
Fe -DABCO MNP
Time (min) Yield (%)
6
2
1
.83–6.80 (d, J = 8.5 Hz, 1H), 6.06 (s, 1H), 2.31 (s, 3H),
13
1
2
3
4
5
6
7
8
9
1
1
1
1
a
O
3 4
50
50
50
50
50
50
93
.11 (s, 3H). C NMR: d 160.85, 159.30, 154.09, 153.23,
23.47, 112.35, 112.06, 111.08, 110.30, 18.54, 11.20.
H
3
PW12
O
40
32
NbCl
PEG-SO
InCl
Pd (PPh
5
Trace
Trace
25
-1
Compound (3e): IR (KBr): t cm : 3263, 1608, 1446,
3
H
1
1
373, 1152, 1084, 976, 910, 832, 685, 536. H NMR: d 10.45
3
(
s, 1H), 6.56 (s, 1H), 6.53 (s, 1H), 5.99 (s, 1H), 2.50 (s, 3H),
3
1
3
)
4
38
2
1
.24 (s, 1H). C NMR: d 160.25, 156.86, 155.74, 155.21,
43.13, 111.97, 108.14, 106.93, 101.35, 24.32, 21.56.
Cerium (IV), ammonium nitrate 50
Trace
46
-
1
Nano-SiO
Nano-RuO
Nano-TiO
Nano-Fe
Nano c-Fe
Nano-FeNi
2
50
50
50
50
50
50
Compound (3f): IR (KBr): t cm : 3054, 1712, 1613,
386, 1322, 1264, 1190, 1142, 1019, 952, 877, 805, 753,
2
55
1
7
1
0
1
2
3
2
48
10, 571, 524, 437. H NMR: d 7.65–7.62 (d, J = 8.25 Hz,
3
O
4
59
1H), 7.20 (brs, 1H), 7.17 (s, 1H), 6.30 (s, 1H), 2.39 (br,
1
3
2
O
3
63
6H). C NMR: d 160.39, 153.68, 153.44, 143.22, 125.83,
125.50, 117.64, 116.90, 113.73, 21.46, 18.46.
3
65
-
1
Compound (3g): IR (KBr): t cm : 2953, 1724, 1619,
512, 1454, 1383, 1279, 1209, 1148, 1067, 1019, 975, 857,
Phenol (1 mmol), ethyl acetoacetate (1 mmol) at 90 °C for 35 min
1
7
1
98, 748, 707, 633, 528, 491, 454. H NMR: d 7.68–7.64
3 4
Table 3 Synthesis of coumarin derivatives catalyzed by Fe O -
(
d, J = 8.5 Hz, 1H), 6.96 (s, 1H), 6.93–6.92 (d,
J = 2.5 Hz, 1H), 6.19 (s, 1H), 3.84 (s, 3H), 2.38 (s, 3H).
DABCO MNPs
Product
R
Time (min)
Yield (%)
13
C NMR: d 162.83, 160.61, 155.24, 153.86, 126.91,
13.52, 112.57, 111.53, 101.16, 56.34, 18.57.
1
3
3
3
3
3
3
3
3
3
3
3
a
a
b
c
d
e
f
3-OH
35
35
35
45
40
40
35
45
40
45
35
93
97
95
96
93
90
95
83
86
85
89
-
1
Compound (3h): IR (KBr): t cm : 2924, 1729, 1650,
2,3-(OH)
3,5-(OH)
2
2
1
1
6
3
1
384, 1080, 849. H NMR: d 7.105 (s, 1H), 6.979 (s, 1H),
.135 (s, 1H), 2.317 (s, 3H), 2.148 (s, 3H), 1.300–1.217 (brs,
2-Me-3-OH
3-Me-5-OH
3-Me
1
3
H). C NMR: d 164.60, 160.18, 154.76, 142.11, 137.51,
29.85, 115.82, 115.02, 111.60, 24.73, 19.49, 14.77.
-
1
Compound (3i): IR (KBr): t cm : 3437, 3350, 3243,
616, 1540, 1445, 1395, 1260, 1212, 1154, 1057, 834, 709,
g
h
i
3-MeO
1
6
1
6
5
1
1
3,5-(Me)
3-NH
2
1
39, 529, 453. H NMR: d 7.393–7.359 (d, J = 8.5 Hz,
2
H), 6.562–6.527 (dd, J = 6 Hz, J = 2.25 Hz, 1H),
.388–6.379 (d, J = 2.25 Hz, 1H), 6.068 (brs, 2H),
g
k
1-Naphthol
4-OH
1
3
.877–5.873 (s, 1H), 2.276–2.272 (s, 3H). C NMR: d
61.16, 155.90, 154.18.153.51, 126.63, 111.60, 109.28,
07.91, 98.96, 18.44.
Reaction condition: phenol (1 mmol), ethyl acetoacetate (1 mmol),
Fe
-DABCO MNPs (0.0007 g) at 90 °C
Yield refers to isolated product
3 4
O
b
-1
Compound (3j): IR (KBr): t cm : 2919, 1712, 1464,
1
1
373, 1168, 1079, 941, 847, 809, 745, 563. H NMR: d
8
.36–8.32 (m, 1H), 8.04-8.00 (m, 1H), 7.86–7.65 (m, 4H),
-
1
13
Compound (3b): IR (KBr): t cm : 3445, 1866, 1678,
610, 1519, 1453, 1362, 1283, 1184, 1050, 1005, 956, 851,
6.48 (s, 1H), 2.51 (s, 3H). C NMR: d 160.09, 154.62,
134.81, 129.09, 128.41, 127.82, 124.36, 122.65, 122.06,
121.69, 115.54, 114.29, 19.10.
1
8
2
1
08, 758, 718, 643, 605, 508. H NMR: d 9.10–10.13 (brs,
H), 7.07–7.04 (d, J = 8.5 Hz, 1H), 6.80–6.77 (d,
1
Compound (3k): H NMR: d 9.71 (s, 1H), 7.22–7.19
1
3
13
J = 8.5 Hz, 1H), 6.10 (s, 1H), 2.32 (s, 3H). C NMR: d
(brs, 1H), 7.00 (br, 2H), 6.33 (s, 1H), 2.34 (s, 3H).
C
1
60.65, 154.31, 149.86, 143.78, 132.60, 115.89, 113.23,
NMR: d 160.49, 154.19, 153.21, 146.64, 120.61, 120.23,
117.75, 114.93, 109.98, 18.49.
1
12.57, 110.64, 18.65.
-
1
Compound (3c): IR (KBr): t cm : 3491, 3167, 1619,
465, 1363, 1295, 1158, 1070, 1017, 919, 830, 757, 665,
1
5
1
1
9
1
46. H NMR: d 10.50 (s, 1H), 10.28 (s, 1H), 6.23 (brs,
Conclusions
1
3
H), 6.14 (brs, 1H), 5.81 (s, 1H), 2.46 (s, 3H). C NMR: d
61.48, 160.55, 158.36, 156.92, 155.40, 109.28, 102.51,
9.48, 94.95, 23.86.
In conclusion, we have developed the current important
areas of heterogenization of DABCO, which is a rapidly
1
23

J IRAN CHEM SOC
Scheme 2 Plausible
mechanism for the synthesis of
+N
H
N
coumarin on Fe
surface
3 4
O -DABCO
O
HCl
O
O
1
-
O
+
Me
OEt
HCl
2
-EtOH
N
+N
Cl-
4
O
O
Me
N
O
+N
Cl-
5
O
O
HCl
-
HCl
O
O
O
O
Me
O
+N
N
Me OH
Me
3
6
developing research area. The main objectives are solvent-
free conditions, a rapid (immediately) and easy immobili-
zation technique, and low-cost precursors for the preparation
of highly active and stable MPs with high densities of
functional groups. Furthermore, applying the young area of
magnetite particles which are intrinsically not magnetic, but
can readily be magnetized by an external magnet, can have a
positive effect on high activity on one hand and separation
and recycling on the other hand.
7. J.L. Lyon, D.A. Fleming, M.B. Stone, P. Schiffer, M.E. Williams,
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