N-Propyl benzoguanamine sulfonic acid supported on magnetic Fe3O4 nanoparticles: A novel and efficient magnetically heterogeneous catalyst for the synthesis of 1,8-dioxo-decahydroacridine derivatives

Article abstract of DOI:10.1039/c7nj03508j

In this study, N-propyl-benzoguanamine-SO₃H-stabilized magnetic nanoparticles were prepared as a new heterogeneous acid catalyst in accordance with the principles of green chemistry. The new catalyst is used for the synthesis of derivatives of

Full text of DOI:10.1039/c7nj03508j

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N-Propyl benzoguanamine sulfonic acid
supported on magnetic Fe3O4 nanoparticles:
a novel and efficient magnetically
Cite this:DOI: 10.1039/c7nj03508j
heterogeneous catalyst for the synthesis of
1,8-dioxo-decahydroacridine derivatives†
Masoumeh Gholami Dehbalaei,a Naser Foroughifar, *a Hoda Pasdara and
Alireza Khajeh-Amirib
In this study, N-propyl-benzoguanamine-SO3H-stabilized magnetic nanoparticles were prepared as a
new heterogeneous acid catalyst in accordance with the principles of green chemistry. The new catalyst
is used for the synthesis of derivatives of 1,8-dioxo-decahydroacridine in one-stage via four-partial
condensation reactions between aromatic aldehydes, dimedone and ammonium acetate or aniline with
high yield and short reaction times. The structure of the nanoparticles obtained via Fourier transform
infrared spectroscopy (IR), field emission scanning electron microscopy (FE-SEM), transmission electron
microscope (TEM), energy-dispersive X-ray analysis (EDXA), X-ray diffraction (XRD), thermogravimetry
analysis (TGA), vibrating sample magnetometry (VSM), atomic absorption spectroscopy (AAS) and
inductively coupled plasma-mass spectrometry (ICP-MS) is assessed. The results show that the size of
the synthesized magnetic nanoparticles is about 25 nm. The heterogeneous catalyst can be easily
recovered by an external magnet and can be reused several times without a significant loss of cata-
lytic activity.
Received 14th September 2017,
Accepted 21st November 2017
DOI: 10.1039/c7nj03508j
rsc.li/njc
reactions because they are cheap, available, low toxicity, recyclable
and easy to separate from the reaction solution using a magnet.7,8
Introduction
Nanoscale materials have always been considered by researchers Important heterocyclic compounds with biological properties are
because of their physical and chemical multifunctional pro- easily synthesized with available materials by multi-component
perties.1 Magnetic nanoparticles (Fe3O4) are widely used in basic reactions (MCRs).9–12 Derivatives of 1,8-dioxo-decahydroacridine
science and catalysts.2–5
are interesting heterocyclic compounds that have many applica-
Non-coated Fe3O4 MNPs have high chemical activity, and are tions in the field of organic and medicinal chemistry because of
quickly oxidized in air (especially), usually resulting in loss of their remarkable biological properties. These compounds are used
magnetism and magnetite dispersibility. Therefore, providing a as anti-malaria,13 antimicrobial,14 antifungal,15 anti-cancer,16 and
suitable surface coating and developing some effective protec- anti-tumor agents,17 and as calcium b-blockers,18,19 as well as in the
tion strategies (to form core/shell structured materials) to keep production of laser colors.20,21 The widely used method for the
the stability of Fe3O4 MNPs is very important. Actually, in many synthesis of 1,8-dioxo-decahydroacridine consists of four partial
cases, the protecting shells not only stabilize the Fe3O4 MNPs, reactions between aromatic aldehydes, dimedone, and nitrogen
but can also be used for further function.6
sources such as ammonium acetate,22 hydroxy amines,23 urea,24
In recent years, magnetic nanoparticles of iron oxide (Fe3O4) aniline,25 ammonium bicarbonate26 and ammonium hydroxide.27
have been widely used as a heterogeneous catalyst in organic The reactions are conducted with various catalysts such as
DBH, DCH,28 amberlyst-15,29 ammonium chloride or L-proline,
a Department of Chemistry, Tehran North Branch, Islamic Azad University,
P.O. Box 1913674711, Tehran, Iran. E-mail: n_foroughifar@yahoo.com;
Fax: +98-2122222512; Tel: +98-2122222512
b Young Researchers and Elites Club, Yadegar-e Imam Khomeini (RAH) Shahre Rey
Branch, Islamic Azad University, P.O. Box 1913674711, Tehran, Iran
† Electronic supplementary information (ESI) available: 1H and 13C NMR and
IR spectra for the selected products. See DOI: 10.1039/c7nj03508j
Zn(OAc)2Á2H2O,30 nano CeO2,31 SO42À/ZrO2,32 nano-Fe3O4@SiO2-
SO3H,33 Brønsted acidic imidazolium salts containing perfluoro-
alkyl tails,34 b-cyclodextrin,25 ionic liquids,35,36 benzyltriethyl
ammonium chloride (TEBAC)37 and CAN.38
Ionic liquids possess many promising advantages, but their
widespread practical application is still hampered by various
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drawbacks which lead to economical and environmental pro- Results and discussion
blems because ionic liquids are synthesized at high tempera-
ture and time, and a large amount of organic solvents is used to
purify them.39
Characterization of the novel MNPs-N-propyl-benzoguanamine-
SO3H catalyst
MNPs-N-propyl-benzoguanamine-SO3H nanoparticles were pre-
pared via the procedure illustrated in Scheme 2. Fourier trans-
form infrared (FT-IR) spectroscopy, field emission scanning
electron microscopy (FE-SEM), transmission electron microscope
(TEM), energy-dispersive X-ray spectroscopy (EDAX), X-ray diffrac-
tion (XRD), thermogravimetric analysis (TGA) and vibrating
sample magnetometry (VSM), atomic absorption spectroscopy
(AAS) and inductively coupled plasma-mass spectrometry (ICP-MS)
were used to identify and characterize the prepared catalyst.
The FT-IR spectra of Fe3O4, Fe3O4/SiO2, Fe3O4/SiO2-propyl-Cl,
Fe3O4/SiO2-propyl-benzoguanamine and Fe3O4/SiO2-N-propyl-
benzoguanamine-SO3H are shown in Fig. 1.
The FT-IR spectrum of magnetic Fe3O4 MNPs shows the char-
acteristic Fe–O absorption around 579 cmÀ1 (Fig. 1a). Fe3O4/SiO2
shows characteristic FT-IR bands at around 1084 cmÀ1 (asymmetric
stretching), 954 cmÀ1 (symmetric stretching), 802 cmÀ1 (in plane
bending) and 454 cmÀ1 (rocking mode) for the Si–O–Si group and
confirm the formation of the SiO2 shell (Fig. 1b). A weak peak at
1625 cmÀ1 (twisting vibration mode of H–O–H adsorbed in the silica
shell) and broad peak at 3402 cmÀ1 (stretching vibration mode of
Si–OH) are apparent in the spectrum. The presence of the attached
alkyl groups is confirmed by the weak bands at 2920 and 3082 cmÀ1
related to C–H symmetric and asymmetric stretching modes
(Fig. 1c–e). Also, sharp peaks are present in the range of 3174–
3410 cmÀ1 (stretching N–H) and peaks appear at 1495–1660 cmÀ1
(CQN in heterocyclic rings) and 1394 cmÀ1 (CQC in heterocyclic
rings) indicating the bond formation of benzoguanamine (Fig. 1d). A
broad peak at 3692 cmÀ1 (stretching O–H band of sulfonic acid) is
apparent in the spectrum (Fig. 1e). According to the results, the
functional groups on the surface of the MNPs grafted properly.
In the previous applications, the size distribution of the
catalyst is not homogeneous.40 The synthesis of some nano-
particles requires calcination at a high temperature, or a huge
amount of catalyst is required for the reaction.41,42
The previous methods have disadvantages including low
yield, long reaction times,25 and the use of toxic solvents, and
expensive and dangerous catalysts.23,24
Therefore, the use of a suitable, environmentally friendly
and recyclable catalyst in this reaction is important. The pre-
sent study has investigated the synthesis of derivatives of
1,8-dioxo-decahydroacridine using four-component reactions
of aromatic aldehydes, dimedone and ammonium acetate or
aniline in the presence of 6 mg of magnetic nanoparticles with
acid factor (MNPs-N-propyl-benzoguanamine-SO3H) as a mag-
netically heterogeneous, new, efficient, retrievable, non-toxic
and environmentally compatible catalyst. Although the use of
benoguanamine and triethylamine alone is dangerous, when
they are deposited on the iron surface, their toxicity and
hazardousness disappear. Use of a green medium, low waste
products, highly efficient synthesis leading to high yield of
products, and the eco-friendly, economic and novel nature of the
nanocatalyst with short reaction time are the main advantages
of the method presented. Derivatives of 1,8-dioxo-decahydro-
acridine are produced with high efficiency and minimal reaction
time (Scheme 1). It is noteworthy that this is the first report
on the synthesis of magnetic nanoparticles (MNPs-N-propyl-
benzoguanamine-SO3H) that can be reused up to five times
without significant loss of catalytic activity.
Scheme 1 Synthesis of 1,8-dioxo-decahydroacridine derivatives using
novel MNPs-N-propyl-benzoguanamine-SO3H as a catalyst.
Scheme 2 Preparation of MNPs-N-propyl-benzoguanamine-SO3H nano-
particles.
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Fig. 3 TEM images of the MNPs-N-propyl-benzoguanamine-SO3H catalyst
at different magnifications.
Fig. 1 Comparison of FT-IR spectra for (a) Fe3O4, (b) Fe3O4/SiO2, (c) Fe3O4/
SiO2-propyl-Cl, (d) Fe3O4/SiO2-propyl-benzoguanamine and (e) Fe3O4/SiO2-
N-propyl-benzoguanamine-SO3H.
FE-SEM images of the MNPs-N-propyl-benzoguanamine-SO3H
nanoparticles are shown in order to determine the size and
morphology (Fig. 2). The diameter of the particles is 25 nm and
they are spherical in shape.
Fig. 3 shows the TEM image of the MNPs-N-propyl-benzo-
guanamine-SO3H nanocatalyst. This study showed a particle
size of approximately 25 nm for the synthesized catalyst.
Energy-dispersive X-ray spectrometry (EDAX) of the MNPs-
N-propyl-benzoguanamine-SO3H nanoparticles, as depicted in
Fig. 4, exhibits the components of the sample. EDAX analysis
clearly shows the presence of C, N, Fe, O, Si, and S in the
MNP catalyst. Thus, the clear presence of S signal in the EDAX
Fig. 4 EDAX spectrum of the MNPs-N-propyl-benzoguanamine-SO3H
nanoparticles.
spectrum indicates that the MNPs-N-propyl-benzoguanamine
nanoparticles have been functionalized successfully by SO3H
groups.
The crystal structure of the MNPs-N-propyl-benzoguanamine-
SO3H nanoparticles was investigated using the XRD technique
(Fig. 5). The XRD pattern of the synthesized nanoparticles shows
diffraction peaks at 18.2, 30.2, 35.7, 43.2, 53.7, 57.2 and 62.7
angles that can be dedicated to some surfaces of Fe3O4 such as
(111), (220), (311), (400), (422), (511) and (440). The peaks of the
magnetic nanoparticles in the XRD pattern are based on the
standard Fe3O4 (JCPDS file no. 98-007-7842) sample and show
that the Fe3O4 nanoparticles are of cubic spinel structure. The
mean crystal size of the MNPs-N-propyl-benzoguanamine-SO3H
nanoparticles is estimated using Debye–Scherrer’s (D = Kl/bcos y)
formula.43 The crystal size of the MNPs is nearly 25 nm, and is in
the range determined by FE-SEM analysis.
Thermal gravimetric analysis of TGA is used to evaluate
the stability of MNPs-N-propyl-benzoguanamine-SO3H (Fig. 6).
The TGA curve shows the mass loss of MNPs-NPBG-SA nano-
particles at T o 250 1C (10 wt%), attributed to the removal of
adsorbed solvents and surface hydroxyl groups. The next stage,
including the high amount of weight loss in the range of
Fig. 2 FE-SEM image of the MNPs-N-propyl-benzoguanamine-SO3H
nanoparticles.
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Fig. 7 Measured magnetic hysteresis loops of the MNPs-N-propyl-benzo-
guanamine-SO3H. Left inset: The catalyst was dispersed in the liquid and
captured by an external magnet.
magnetometer (VSM) at room temperature. The saturation mag-
netization for the MNPs-N-propyl-benzoguanamine-SO3H nano-
particles is about 6.15 emu gÀ1, showing that factorized magnetic
nanoparticles have lower magnetic properties, which is due to
the coated crust (Fig. 7). Basically, the saturation magnetization
for non-coated magnetic nanoparticles has been reported to be
73.7 emu gÀ1, and the average diameters of the unmodified iron
oxide nanoparticles are 7.6 nm, which has been measured from
the TEM images.45 However, the MNPs-N-propyl-benzoguanamine-
SO3H nanoparticles can be removed from the solution using an
external magnet. Thus, strong magnetization of the nanoparticles
is verified due to them being easily affected by external magnetic
gravity (Fig. 7, left inset).
Fig. 5 XRD diffraction pattern of MNPs-N-propyl-benzoguanamine-SO3H
nanoparticles.
Finally, in order to quantify the amount of iron in the nano-
catalyst, it was subjected to ICP-MS determination. The corres-
ponding iron loading was found to be 1.79 Â 10À4 mmol gÀ1. In
addition, to support the above observation, the sample was also
analyzed through AAS and it was found that the iron content
matched well with the ICP-MS result. After full characterization
of the MNPs-N-propyl-benzoguanamine-SO3H nanoparticles,
new derivatives of 1,8-dioxo-decahydroacridine have been
used as a heterogeneous catalyst for the synthesis (Scheme 1).
One of the important capabilities of this nanocatalyst is its
novelty and ease of separation from the reaction solution using
an external magnet without a need for filtering or centrifugation,
and it can be reused several times without significant perfor-
mance loss.
Fig. 6 TGA analysis for the MNPs-N-propyl-benzoguanamine-SO3H
nanoparticles.
Synthesis of 1,8-dioxo-decahydroacridine catalyzed by
MNPs-N-propyl-benzoguanamine-SO3H
250–600 1C, is attributed to the decomposition and evaporation
of organic groups (propyl, benzoguanamine and SO3H) grafted In order to optimize the method, the reaction of dimedone
to the surface of Fe3O4@SiO2 MNPs.44 Therefore, the TG analysis (2 mmol), aromatic benzaldehyde (1 mmol) and ammonium
detected that 75% of the product consists of organic layers and acetate or aniline (1.2 mmol) was examined. This model reac-
15% is Fe3O4@SiO2. Thus, the MNPs-N-propyl-benzoguanamine- tion with various solvents, temperatures and catalyst amounts
SO3H catalyst is stable at around or below 250 1C, confirming was studied to find the best conditions. As shown in Table 1,
that it could be safely used in organic reactions.
the nature of the solvent was observed to have a profound effect
The magnetic features of the MNPs-N-propyl-benzoguanamine- on both the activity of the catalyst and the yield of product. The
SO3H nanoparticles were evaluated using a vibration sample best performance was achieved using 3EtOH : 1H2O as the solvent.
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Table 1 Optimization of reaction conditions for the preparation of 1,8-dioxodecahydroacridine derivatives
Entry
Catalyst (mg)
Solvent
Temp. (1C)
Time (min)
Yielda (%) 4a
Yielda (%) 5a
1
2
3
4
5
6
7
8
—
—
EtOH
EtOH
EtOH
EtOH
CH3CN
CH2Cl2
H2O
EtOH
1EtOH : 1H2O
3EtOH : 1H2O
3EtOH : 1H2O
EtOH : H2O
3EtOH : 1H2O
3EtOH : 1H2O
3EtOH : 1H2O
3EtOH : 1H2O
3EtOH : 1H2O
r.t.
5 h
5 h
5 h
60
60
60
60
60
60
60
60
60
40
20
20
20
20
12
12
24
42
36
31
45
47
50
52
51
67
78
92
92
90
90
15
15
27
38
32
25
42
50
52
53
53
54
81
94
93
91
91
Reflux(80)
Reflux(80)
Reflux(80)
r.t.
r.t.
Reflux
Nano-Fe3O4 (10)
MNPs-N-propyl benzoguanamine (6)
MNPs-N-propyl benzoguanamine-SO3H (3)
MNPs-N-propyl benzoguanamine-SO3H (3)
MNPs-N-propyl benzoguanamine-SO3H (3)
MNPs-N-propyl benzoguanamine-SO3H (3)
MNPs-N-propyl benzoguanamine-SO3H (3)
MNPs-N-propyl benzoguanamine-SO3H (3)
MNPs-N-propyl benzoguanamine-SO3H (3)
MNPs-N-propyl benzoguanamine-SO3H (6)
MNPs-N-propyl benzoguanamine-SO3H (6)
MNPs-N-propyl benzoguanamine-SO3H (6)
MNPs-N-propyl benzoguanamine-SO3H (6)
MNPs-N-propyl benzoguanamine-SO3H (9)
MNPs-N-propyl benzoguanamine-SO3H (11)
40
9
Reflux(100)
Reflux(100)
Reflux(120)
60
10
11
12
13
14
15
16
17
60
Reflux(100)
Reflux(120)
Reflux(100)
Reflux(100)
a
Isolated yield.
In order to assess the effect of temperature on the reaction, we respect to green nature, polarity and clean workup procedure
carried out the reactions at various temperatures as shown in for this synthesis under reflux (100 1C) conditions (Table 1,
Table 1. Catalytic activity increases with increasing temperature. entry 14).
At 60 1C, some of the intact materials remain in the reaction
The conditions optimized for the production of the 1,8-dioxo-
vessel and do not participate in the reaction. With increasing decahydroacridine derivatives were evaluated using the MNPs-N-
temperature, the solubility of the materials and catalytic activity propyl-benzoguanamine-SO3H as a catalyst. The reaction of aromatic
increases. Use of a higher temperature had no significant effect aldehydes carrying either electron-donating or electron-withdrawing
on the reaction rate or the isolated yield of product (Table 1, substituents with dimedone and ammonium acetate was per-
entry 15). The best result was obtained under reflux 100 1C formed (Table 2).
(Table 1, entry 14). In the reactions of chemistry, time and yield
are important, so without catalyst, the time is long and the
yield is low. Thus, the reaction does not proceed completely.
Participation of the catalyst in the reaction was confirmed by
conducting a blank experiment without the catalyst. This blank
Table 2 Multicomponent one-pot synthesis of 1,8-dioxo-decahydro-
acridine derivatives using MNPs-N-propyl-benzoguanamine-SO3H as a
catalysta
Melting point (1C)
Entry aldehyde (R) Product (min) Yieldb (%) Found
Reported
experiment gave a 12–15% yield after 5 h (Table 1, entry 1). The
effect of the catalyst amount of the reaction was also investigated.
Use of a higher amount of catalyst had no significant effect on
the reaction rate or the isolated yield of product (Table 1, entries
16 and 17), while a decrease in the amount of catalyst decreased
the product yield. The best result was obtained using 6 mg of
catalyst. Overall, the ideal reaction conditions for the formation
of 1,8-dioxo-decahydroacridine derivatives were 3EtOH : 1H2O
as the solvent and 6 mg of the catalyst under reflux at
100 1C (Table 1, entry 14). With respect to yield of products
and reaction time, the best result is achieved using 6 mg of
MNPs-N-propyl-benzoguanamine-SO3H as a catalyst in 2 mL
Aromatic
Time
1
2
3
4
5
6
7
8
9
H
4-Me
4a
4b
4c
4d
4e
4f
4g
4h
4i
20
18
25
20
20
17
15
20
25
25
92
85
80
87
84
89
93
91
86
92
288–290 290–29136
279–281 278–28036
4-CH(Me)2
3-NO2
4-N(Me)2
3-OH
2-NO2
4-Cl
235–237c
—
306–308 307–30836
280–282 280–28246
308–310c
—
297–299 297–29947
298–301 298–30048
299–302 299–30247
288–290 287–29049
2-Me
3,4-(OMe)2
10
4j
a
Aromatic aldehyde (1 mmol), dimedone (2 mmol), ammonium acetate
(1.2 mmol) and 6 mg MNPs-N-propyl-benzoguanamine-SO3H, under
b
c
aqueous ethanol [V(ethanol) : V(H2O) = 3 : 1] as the solvent with reflux (100 1C) conditions. Isolated yield. New compound.
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Table 3 Multicomponent one-pot synthesis of 1,8-dioxo-decahydro-
acridine derivatives using MNPs-N-propyl-benzoguanamine-SO3H as a
catalysta
Melting point (1C)
Aromatic
Time
Entry aldehyde (R) Product (min) Yieldb (%) Found
Reported
1
2
3
4
5
6
7
8
H
4-Me
5a
5b
5c
5d
5e
5f
5g
5h
5i
20
20
25
15
18
20
17
15
25
25
15
20
94
88
91
85
91
84
95
86
90
87
91
93
253–255 253–25550
260–262 260–26251
4-CH(Me)2
3-NO2
4-N(Me)2
3-OH
2-NO2
4-Cl
2-Me
3,4-(OMe)2
2-Cl
160–162c
—
296–298 296–29752
166–168 165–16753
230–232c
187–189c
—
—
244–246 244–24652
9
172–174c
285–287 285–28854
215–217c
203–205 203–20553
—
10
11
12
5j
5k
5l
—
2-OH
a
Aromatic aldehyde (1 mmol), dimedone (2 mmol), aniline (1.2 mmol)
and 6 mg MNPs-N-propyl-benzoguanamine-SO3H, under reflux (100 1C)
b
c
conditions. Isolated yield. New compound.
Also, the reaction of aromatic aldehydes carrying either
electron-donating or electron-withdrawing substituents with
dimedone and aniline was performed (Table 3). From these
results, we could see that all the reactions proceeded smoothly
to afford the corresponding products in good yields.
A possible mechanism for the synthesis of 1,8-dioxo-
decahydroacridine is shown in Scheme 3. First, the MNPs-N-
propyl-benzoguanamine-SO3H catalyst changes the aldehyde
into a convenient electrophile via protonation of the carbonyl
group and then one molecule of dimedone condenses with the
aromatic aldehyde to produce intermediate 5. Then the active
methylene group of the second molecule of dimedone reacts
with 5 to give intermediate 6. Nucleophilic attack of the amine
group of amonium acetate or aniline on the carbonyl group
creates intermediate 7. In the next step, cyclization will occur by
the nucleophilic attack of the amine group to the carbonyl
group to obtain intermediate 8. Finally, by the removal of one
water molecule, the 1,8-dioxo-decahydroacridin derivatives 4
will be generated.
Scheme 3 Proposed mechanism for the synthesis of 1,8-dioxo-deca-
hydroacridine using MNPs-N-propyl-benzoguanamine-SO3H as a catalyst.
Catalyst recovery and reusability
The recovery and reusability of catalysts are valuable advan-
tages in modern catalysis research and commercial uses as well
as in green chemistry. In this respect, the recovery and reus-
ability of MNPs-N-propyl-benzoguanamine-SO3H (6 mg) were
Acidity of the MNPs-N-propyl-benzoguanamine-SO3H
To determine the acid amount on the surface of the MNPs-N- investigated in the reaction of dimedone (2 mmol), aromatic
propyl-benzoguanamine-SO3H, a back titration method was benzaldehyde (1 mmol), and ammonium acetate or aniline
used. The MNPs-N-propyl-benzoguanamine-SO3H nanocatalyst (1.2 mmol) in 2 mL aqueous ethanol [V(ethanol) : V(H2O) = 3 : 1]
(0.01 g) was added to an aqueous KCl solution (1 M, 10 mL) and as a safe solvent under reflux (100 1C) conditions. At the end of the
the resulting mixture was sonicated for 30 minutes; after process, MNPs-N-propyl-benzoguanamine-SO3H was readily sepa-
that, the pH of the solution decreased to 2, indicating an ion rated from the reaction mixture using an external magnet, washed
exchange between nanocatalyst protons and potassium ions. several times with ethanol and dried at 60 1C for 1 h. Then, the
The magnetic catalyst was then separated using an external recovered catalyst was reused for a subsequent fresh batch of
magnet, and the clear solution was retained for analysis. Two the reaction. The catalytic activity was studied for five succes-
drops of phenolphthalein solution were then added to the sive cycles, showing similar activity in each run. The recycled
remaining solution and the resulting mixture was titrated to nanocatalyst could be reused five times without an appreciable
neutrality using a standardized 0.1 M KOH solution to deter- reduction in catalytic activity or any additional treatment
mine the acid amount on the magnetic catalyst. The acid (Fig. 8). The recovered catalyst after five runs had no distinct
amount of the heterogeneous acidic catalyst was found to be change in structure, as shown by a comparison of the FT-IR
0.53 mmol gÀ1
.
spectra to that of a fresh catalyst (Fig. 9). The FE-SEM image of
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MNPs-N-propyl-benzoguanamine-SO3H as a catalyst in 2 mL
aqueous ethanol [V(ethanol) : V(H2O) = 3 : 1] as the solvent. This
one-pot green chemistry protocol is effective under mild reaction
conditions, and exhibits short reaction time, high yields and easy
recovery of the catalyst. Moreover, MNPs-N-propyl-benzoguanamine-
SO3H is environmentally secure and can be easily recovered by an
external magnet. This catalyst could be reused five times without
significant loss of catalytic activity.
Experimental
Fig. 8 Recyclability of the MNPs-N-propyl-benzoguanamine-SO3H in
the synthesis of 1,8-dioxo-decahydroacridine derivatives.
Materials and instrumentation
All chemicals were purchased from Merck or Fluka and were
used without further purification. The melting points were
uncorrected and measured using capillary tubes on an electro-
thermal digital apparatus. The IR spectra were recorded on a
1
Shimadzo (FT)-IR 300 spectrophotometer in KBr. The H-NMR
500 MHz and 13C-NMR spectra were obtained on Brucker
125 MHz spectrometers in CDCl3 or DMSO-d6 as the solvent with
TMS as an internal standard. The progress of the reaction was
monitored by TLC (thin-layer chromatography) using n-hexane/
EtOAc as an eluent. Nanoparticles were characterized using a
X-Pert Pro MPD X-ray diffraction (XRD) diffractometer (Cu-Ka,
k = 0.154056 nm) over the range 2y = 10–80 using 0.041 as the step
length. The scanning electron microscope measurement was
carried out on a Hitachi S-4700 field emission-scanning electron
microscope (FE-SEM). The TEM analysis of the catalyst was
recorded using a Zeiss-EM10C transmission electron microscope.
The thermogravimetric analysis (TGA) curves were recorded using
a Diamond TGA/DTA SII Perkin Elmer Company. The magnetiza-
tion was measured at room temperature using a vibrating sample
magnetometer (Model 7300 VSM system, Lake Shore Cryotronic,
Inc., Westerville, OH, USA). Inductively coupled mass spectro-
scopy (ICP-MS) was also done in order to confirm the iron loading
(Model Elan 6000 DRC). The iron content in the catalyst super-
natant was estimated by atomic absorption spectroscopy (AAS) on
a Model novAA-400p atomic absorption spectrometer.
Fig. 9 FT-IR spectra of a fresh catalyst and that reused five times.
Fig. 10 FE-SEM image of the MNPs-N-propyl-benzoguanamine-SO3H
nanoparticles after five cycles of recovery.
General procedure for the preparation of MNPs-N-propyl-
benzoguanamine-SO3H
Fe3O4 MNPs were prepared by chemical co-precipitation of Fe3+
and Fe2+ ions as described in the literature.55 The Fe3O4 coated
with SiO2 was prepared through a modified sol–gel method.56
The chloropropyl-modified silica-coated MNPs were prepared
according to a reported procedure.57 To a magnetically stirred
mixture of the prepared Fe3O4/SiO2-chloropropyl (1 g) was
the MNPs-N-propyl-benzoguanamine-SO3H nanoparticles after
five cycles of recovery is shown (Fig. 10).
Conclusions
In this work, we have reported a novel magnetic nanoparticle added benzoguanamine (10 mmol, 1.87 g) and triethylamine
catalyst that was successfully prepared and characterized by IR, (10 mmol, 1.39 mL) in dried toluene (50 mL) and the mixture
FE-SEM, TEM, EDXA, XRD, TGA, VSM AAS and ICP-MS of size was sonicated for 2 h under N2 atmosphere, and then stirred for
around 25 nm. MNPs-N-propyl-benzoguanamine-SO3H as a 48 h under reflux conditions. The obtained solid was magneti-
catalyst is suitable for the synthesis 1,8-dioxo-decahydro- cally collected from the solution and washed with water/ethanol
acridine derivatives. Thus, 1,8-dioxo-decahydroacridine deriva- (20 : 10 mL) three times and dried under vacuum for 5 h. To a
tives were obtained with high yields by reacting aromatic mixture of benzoguanamine-modified silica-coated Fe3O4 MNPs
aldehydes (1 mmol), dimedone (2 mmol) and ammonium acetate (1 g) in dried CHCl3 (3 mL), chlorosulfonic acid (ClSO3H, 1 mL)
or aniline (1.2 mmol) under reaction reflux by using 6 mg of was added dropwise at 0 1C over 2 h and then the mixture was
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filtered and washed with ethanol (5 mL) and dried at room 1723 (CQO), 2900–2955 (CH3 str.), 3381 (NH); H-NMR (CDCl3,
temperature to afford the title compound.
500 MHz) d ppm: 1.02 (6H, s, 2CH3), 1.15 (6H, s, 2CH3), 2.20–2.51
(8H, m, 4CH2), 6.04 (1H, s, CH), 7.24–7.55 (4H, m, Ar-H), 11.6
(1H, s, NH); 13C-NMR (CDCl3, 125 MHz) d ppm: 28.1, 28.5, 30.0,
31.9, 46.2, 46.8, 114.6, 124.3, 127.2, 129.6, 131.3, 132.1, 149.7,
General procedure for the synthesis of 1,8-dioxo-
decahydroacridin derivatives
To a mixture of dimedone (2 mmol), aromatic benzaldehyde 189.4, 190.4.
(1 mmol) and ammonium acetate or aniline (1.2 mmol) was
9-(4-Chlorophenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-
added MNPs-N-propyl-benzoguanamine-SO3H (6 mg) in 2 mL acridine-1,8(2H,5H)-dione (Table 2, entry 8). White solid; m.p.:
aqueous ethanol [V(ethanol) : V(H2O) = 3 : 1] as the solvent and the 298–301 1C; yield 91%; IR (KBr, cmÀ1) nmax; 673–885 (Cl), 1590
reaction mixture was stirred magnetically under reflux (100 1C) (CQO), 2881–3005 (CH3 str.), 3049 (NH); 1H-NMR (CDCl3,
conditions. The progress of the reaction was followed by thin-layer 500 MHz) d ppm: 1.09 (6H, s, 2CH3), 1.21 (6H, s, 2CH3), 2.29–
chromatography (TLC). After the completion of the reaction, 2.47 (8H, m, 4CH2), 5.47 (1H, s, CH), 7.00–7.02 (2H, d, Ar-H, J =
0.5 mL of water was added to the mixture and the mixture was 8.0 Hz), 7.21–7.23 (2H, d, Ar-H, J = 8.0 Hz), 11.87 (1H, s, NH);
stirred for a moment. Then, the reaction mixture was cooled to 13C-NMR (CDCl3, 125 MHz) d ppm: 27.2, 27.4, 29.2, 29.5, 31.3,
room temperature and the catalyst was easily separated using an 31.4, 32.1, 32.4, 40.8, 46.4, 47.0, 50.6, 115.2, 115.3, 128.1, 128.3,
external magnet. The solvent was evaporated to afford the crude 129.7, 131.5, 131.9, 136.7, 142.6, 162.4, 189.3, 190.5, 196.2.
solid. Finally, the resulting solid was filtered, then washed with
3,3,6,6-Tetramethyl-9,10-diphenyl-3,4,6,7,9,10-hexahydroacridine-
30% aqueous ethanol without further purification and dried in an 1,8(2H,5H)-dione (Table 3, entry 1). White solid; m.p.: 253–255 1C;
oven at 60 1C. The pure 1,8-dioxo-decahydroacridin derivatives yield 95%; IR (KBr, cmÀ1) nmax; 1595 (CQO), 2873–2962 (CH3 str.);
were obtained in excellent yields.
1H-NMR (CDCl3, 500 MHz) d ppm: 1.10 (6H, s, 2CH3), 1.24 (6H, s,
2CH3), 2.30–2.48 (8H, m, 4CH2), 5.55 (1H, s, CH), 7.09–7.28 (10H, m,
2Ar-H); 13C-NMR (CDCl3, 125 MHz) d ppm: 27.3, 29.5, 31.3, 32.7,
Selected spectral data
3,3,6,6-Tetramethyl-9-phenyl-3,4,6,7,9,10-hexahydroacridine- 46.4, 47.0, 115.5, 125.7, 126.7, 128.1, 138.0, 189.3, 190.4.
1,8(2H,5H)-dione (Table 2, entry 1). White solid; m.p.: 288–
290 1C; yield 93%; IR (KBr, cmÀ1) nmax; 1591 (CQO), 2879–2961
(CH3 str.), 3068 (NH); 1H-NMR (CDCl3, 500 MHz) d ppm:
1.11 (6H, s, 2CH3), 1.24 (6H, s, 2CH3), 2.30–2.49 (8H, m,
4CH2), 7.10–7.29 (5H, m, Ar-H), 11.91 (1H, s, NH); 13C-NMR
(CDCl3, 125 MHz) d ppm: 27.4, 29.6, 31.4, 32.7, 46.4, 47.0, 115.6,
125.8, 126.7, 128.2, 138.0, 189.4, 190.5.
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
3,3,6,6-Tetramethyl-9-(p-tolyl)-3,4,6,7,9,10-hexahydroacridine-
1,8(2H,5H)-dione (Table 2, entry 2). White solid; m.p.: 279–
281 1C; yield 85%; IR (KBr, cmÀ1) nmax; 1596 (CQO), 2878–2961
We gratefully acknowledge the financial support from the Research
Council of Islamic Azad University-Tehran North Branch.
1
(CH3 str.), 3021 (NH); H-NMR (CDCl3, 500 MHz) d ppm: 1.11
(6H, s, 2CH3), 1.24 (6H, s, 2CH3), 2.31 (3H, s, CH3), 2.32–2.49
(8H, m, 4CH2), 5.52 (1H, s, CH), 6.99–7.09 (4H, dd, Ar-H, J = 7.7
Hz), 11.93 (1H, s, NH); 13C-NMR (CDCl3, 125 MHz) d ppm: 20.7,
20.9, 27.2, 27.3, 29.1, 29.4, 31.2, 31.3, 32.0, 32.3, 40.7, 46.3, 46.9,
50.6, 115.5, 115.6, 126.5, 128.1, 128.6, 128.8, 134.8, 135.1, 135.5,
141.1, 161.9, 189.2, 190.2, 196.2.
9-(3-Hydroxyphenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-
acridine-1,8(2H,5H)-dione (Table 2, entry 6). Yellow solid; m.p.:
308–310 1C; yield 89%; IR (KBr, cmÀ1) nmax; 1617 (CQO), 2878–
2928 (CH3 str.), 3282 (NH), 3447 (OH); 1H-NMR (DMSO-d6,
500 MHz) d ppm: 0.87 (6H, s, 2CH3), 0.99 (6H, s, 2CH3), 1.97–
2.00 (2H, d, CH2, J = 16.1 Hz), 2.14–2.17 (2H, d, CH2, J = 16.1 Hz),
2.28–2.31 (2H, d, CH2, J = 17.0 Hz), 2.41–2.44 (2H, d, CH2, J =
17.0 Hz), 4.73 (1H, s, CH), 6.39–6.42 (1H, d, Ar-H, J = 11.0 Hz),
6.55–6.57 (1H, d, Ar-H, J = 7.65 Hz), 6.61 (1H, s, Ar-H), 6.89–6.92
(1H, t, Ar-H, J = 7.5 Hz), 9.03 (1H, s, NH), 9.23 (1H, s, OH);
13C-NMR (DMSO-d6, 125 MHz) d ppm: 26.5, 26.6, 27.9, 28.8, 31.9,
32.2, 32.6, 40.0, 46.6, 50.1, 50.3, 111.5, 112.5, 114.5, 114.7, 118.4,
128.7, 148.5, 149.3, 156.7, 157.1, 162.9, 194.5, 196.1.
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