Fe3O4@SiO2-MoO3H nanoparticles: A magnetically recyclable nanocatalyst system for the synthesis of 1,8-dioxo-decahydroacridine derivatives

Article abstract of DOI:10.1039/c6ra25571j

Molybdic acid-functionalized silica-coated nano-Fe₃O₄ particles (Fe₃O₄@SiO₂-MoO₃H) have been prepared as a novel heterogeneous acid catalyst using a facile process. The material was subsequ

Full text of DOI:10.1039/c6ra25571j

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Fe3O4@SiO2–MoO3H nanoparticles: a magnetically
recyclable nanocatalyst system for the synthesis of
1,8-dioxo-decahydroacridine derivatives†
a
Cite this: RSC Adv., 2017, 7, 997
Mahtab Kiani and Mohammad Mohammadipourb
*
Molybdic acid-functionalized silica-coated nano-Fe3O4 particles (Fe3O4@SiO2–MoO3H) have been
prepared as a novel heterogeneous acid catalyst using a facile process. The material was subsequently
identified as an efficient catalyst for the synthesis of 1,8-dioxo-decahydroacridine derivatives under
solvent free conditions. The catalyst could be readily recovered using a simple external magnet and
reused several times without any significant loss in activity. Short reaction time, excellent yields and
simple work-up are the advantages of this procedure.
Received 20th October 2016
Accepted 22nd November 2016
DOI: 10.1039/c6ra25571j
www.rsc.org/advances
MNPs with controlled magnetism require the simultaneous
control of surface morphology and the thickness of nonmag-
netic silica layer relative to the size of magnetic core.10
Introduction
Nanocatalysis is a rapidly growing eld which involves the use
of nanomaterials as catalysts for a variety of homogeneous and
heterogeneous catalysis applications.1–3
Magnetic nanoparticles (MNPs) have attracted growing
interest in biomedical applications such as targeted drug
delivery, magnetic resonance contrast, therapeutic agents,
labeling and sorting of cells and bioseparation.4,5
Acridine-1,8-dione derivatives as a class of interesting
heterocyclic compounds exhibit numerous publications in
organic, pharmaceutical and medicinal chemistry elds
because of their potential biological activities and presence in
a variety of signicant natural products and synthetic dye--
stuffs.11 Acridine derivatives have been used as anti-tumor,12
cytotoxic,13 anti-fungal properties,14 antimicrobial,15 anti-
cancer16 and anti-multidrug-resistant.17
There are several methods reported in the literature for the
synthesis of 1,8-dioxo-decahydroacridines via three component
coupling of aldehydes, dimedone and amines in the presence of
diverse catalysts including proline,18 benzyltriethyl ammonium
chloride (TEBAC),19 uorotailed acidic imidazolium salts,20 1-
methylimidazolium triuoroacetate [Hmim]TFA,21 ceric
ammonium nitrate (CAN),22 silica-bonded N-propyl sulfamic
acid (SBNPSA),23 amberlyst-15,24 carbon-based solid acid
(SBSA),25 and 4-dodecylbenzenesulfonic acid (DBSA).26 However,
many of these methods suffer from disadvantages such as low
yields, toxic organic solvents, long reaction times, expensive
catalysts, the requirement of special apparatus, laborious work-
up procedures, and harsh reaction conditions. Thus, the
development of simple, efficient, high-yielding and eco-friendly
methods using new catalysts for the synthesis of these
compounds would be highly desirable.
Fe3O4 is a very popular magnetic media type absorber due to
its unique magnetic features, low-cost and strong absorption
characteristics.6 However, pure Fe3O4 materials usually suffer
from ease of oxidation, fast heat transfer and poor ame-
retardant effect, which limit their applications. To solve these
problems, various inorganic and polymeric materials have been
reported as carriers of magnetic materials.7 Among them, the
silica coating is a very good surface modier, because of its
excellent stability, biocompatibility, nontoxicity and easily
furthered conjugation with various functional groups, thus
enabling the coupling and labeling of biotargets with selectivity
and specicity.8
Magnetic hollow silica materials with different morphology
and structure have been synthesized by the different methods.9
The protective silica layer can minimize the aggregation of
MNPs by reducing the magnetic dipolar attraction and provides
a chemically inert surface to MNPs in biological environments.
Furthermore, silica-coated MNPs can be easily activated to
anchor various functional groups owing to abundant Si–OH
groups on the silica surface. The fabrication of silica-coated
During the course of our recent research program on the
development of new condition for organic transformations,27–29
recently, molybdic acid-functionalized silica-coated nano-Fe3O4
particles have been prepared in our laboratory. It displayed
a high stability and an impressive catalytic activity in the
synthesis of 1,8-dioxo-decahydroacridine derivatives under
solvent free conditions. The performance and recyclability
behavior of this nano magnetic catalyst in the preparation of
aYoung Researchers and Elite Club, Karaj Branch, Islamic Azad University, Karaj, Iran.
E-mail: mahtabkiani47@yahoo.com
bDepartment of Chemistry, Semnan University, Semnan 35131-19111, Iran
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra25571j
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 997–1007 | 997

View Article Online
RSC Advances
Paper
1,8-dioxo-decahydroacridine is reported in this study to extend
possibilities of this new catalyst.
General procedure for the preparation of nano-Fe3O4@SiO2–
OMoO3H 3
To an oven-dried (125 ꢀC, vacuum) sample of nano-Fe3O4@SiO2
(2 g) in a round bottomed ask (50 ml) equipped with
a condenser and a drying tube, thionyl chloride (8 ml) was
added and the mixture in the presence of CaCl2 as a drying
Experimental
Methods and materials
The chemicals were purchased from Merck and Aldrich chem- agent was reuxed for 48 h. The resulting dark powder was
ltered and stored in a tightly capped bottle. To a mixture of
Fe3O4@SiO2–Cl (1 g) and sodium molybdate (0.84 g) n-hexane (5
ml) was added. The reaction mixture was stirred under reuxing
ical companies. The reactions were monitored by TLC (silica-gel
60 F 254, hexane : EtOAc). Fourier transform infrared (FT-IR)
spectroscopy spectra were recorded on a Shimadzu-470 spec-
trometer, using KBr pellets and the melting points were deter- conditions (70 ꢀC) for 4 h. Aer completion of the reaction, the
mined on a KRUSS model instrument. 1H NMR spectra were reaction mixture was ltered and washed with distilled water,
recorded on a Bruker Avance II 400 NMR spectrometer at 400 and dried and then stirred in the presence of 0.1 N HCl (20 ml)
MHz, in which DMSO-d6 was used as solvent and TMS as the for an hour. Finally, the mixture was ltered, washed with
internal standard. X-ray diffraction (XRD) pattern was obtained distilled water, and dried to afford nano-Fe3O4@SiO2–OMoO3H.
by Philips X Pert Pro X diffractometer operated with a Ni ltered
Cu Ka radiation source. Transmission electron microscopy
General procedure for the preparation of 1,8-dioxo-
(TEM) images of the electrocatalyst were recorded using a Phi-
decahydroacridine derivatives 8
lips CM-10 TEM microscope operated at 100 kV. Field emission
A mixture of 1,3-cyclohexanedione (2 mmol), aromatic aldehyde
(1 mmol), ammonium acetate (1 mmol) and nano-Fe3O4@SiO2–
OMoO3H (0.02 g) in a round bottom ask was heated with stir-
scanning electron microscopy (SEM) and X-ray energy disper-
sive spectroscopy (EDS) analyses were carried out on a PHILIPS
XL30, operated at a 20 kV accelerating voltage. Thermo gravi-
metric analyses (TGA) were conducted on a Rheometric Scien-
ꢀ
ring in the oil bath at 100 C for appropriate times. During the
procedure, the reaction was monitored by Thin Layer Chroma-
tography (TLC). The reaction mixture was cooled, eluted with hot
ethanol (5 ml), and centrifuged to collect the catalyst. The
solvent was evaporated with reduced pressure to collect the
formed precipitate. The crude product was recrystallized from
ethanol to yield pure 1,8-dioxo-decahydroacridines.
tic Inc. 1998 thermal analysis apparatus under
a N2
atmosphere at a heating rate of 10 ꢀC minꢁ1. The magnetic
measurement was carried out in a vibrating sample magne-
tometer (Model 7407 VSM system, Lake Shore Cryotronic, Inc.,
Westerville, OH, USA) at room temperature. The inductively
coupled plasma (ICP-OES) spectra were recorded using a Perki-
nElmer Optima 7300 DV series.
Spectral data
General procedure for the preparation of nano-Fe3O4 1
9-Phenyl-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (7a).
Mp: 278–279 C; IR (KBr, cmꢁ1) n: 3273, 3196, 3080, 1624, 1601,
ꢀ
FeCl3$6H2O (20 mmol) and FeCl2$4H2O (10 mmol) were dis-
solved in distilled water (100 ml) in a three-necked round-
bottom ask (250 ml). The resulting transparent solution was
heated at 90 ꢀC with rapid mechanical stirring under N2
atmosphere for 1 h. A solution of concentrated aqueous
ammonia (10 ml, 25 wt%) was then added to the solution in
a drop-wise manner over a 30 min period using a dropping
funnel. The reaction mixture was then cooled to room temper-
ature and the resulting magnetic particles collected with
a magnet and rinsed thoroughly with distilled water.
1483, 1218, 1140. 1H NMR (400 MHz, DMSO): d 1.90–2.09 (m, 4H),
2.26–2.28 (m, 2H), 2.30–2.38 (m, 2H), 2.51–2.64 (m, 4H), 4.79 (s,
1H), 7.05–7.09 (t, J ¼ 7.6, 2H), 7.11–7.12 (d, J ¼ 8.4 Hz, 1H), 7.23–
7.31 (dd, J ¼ 8, 24.2, 2H), 9.17 (s, 1H). Anal. calc. for C19H19NO2; C
77.79, H 6.53, N 4.77, O 10.91; found: C 77.73, H 6.59, N 4.71, O
10.92.
9-(4-Bromophenyl)-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-
dione (7c). Mp: 311–312 C; IR (KBr, cmꢁ1) n: 3340, 3244, 2958,
ꢀ
2927, 1647, 1627, 1549, 1450, 1367, 1227, 1171. 1H NMR (400
MHz, DMSO): d 1.92–2.08 (m, 4H), 2.28–2.32 (m, 2H), 2.34–2.40
(m, 2H), 2.53–2.65 (m, 4H), 4.76 (s, 1H), 7.13–7.27 (m, 2H), 7.33–
7.43 (dd, J ¼ 30.6, 8.4 Hz, 2H), 9.38 (s, 1H). 13C NMR (100 MHz,
General procedure for the preparation of nano-Fe3O4@SiO2 2
Nano-Fe3O4@SiO2 was synthesized according to a previously DMSO-d6): d 20.10, 20.27, 27.13, 31.39, 36.76, 36.90, 112.08,
published literature method. Magnetic nano particles (1.0 g) 117.66, 127.83, 129.43, 146.47, 151.59, 171.19, 194.58. Anal. calc.
were initially diluted via the sequential addition of water (20 for C19H18BrNO2; C 61.30, H 4.87, N 3.76, O 8.60; found: C 61.33,
ml), ethanol (60 ml) and concentrated aqueous ammonia H 4.81, N 3.71, O 8.69.
(1.5 ml, 28 wt%). The resulting dispersion was then homoge-
9-(p-Tolyl)-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione
nized by ultrasonic vibration in a water bath. A solution of TEOS (7d). Mp: 254–255 ꢀC; IR (KBr, cmꢁ1) n: 3286, 3203, 3068, 2943,
1
(0.45 ml) in ethanol (10 ml) was then added to the dispersion in 2887, 1639, 1608, 1458, 1364, 1232, 1176. H NMR (400 MHz,
a drop-wise manner under continuous mechanical stirring. DMSO): d 1.96–2.07 (m, 4H), 2.26 (s, 3H), 2.29–2.42 (m, 4H),
Following a 12 h period of stirring, the resulting product was 2.52–2.69 (m, 4H), 4.79 (s, 1H), 7.03–7.05 (d, J ¼ 8 Hz, 2H), 7.12–
collected by magnetic separation and washed three times with 7.21 (d, J ¼ 7.6 Hz, 2H), 9.18 (s, 1H). 13C NMR (100 MHz, DMSO-
ethanol.
d6): d 20.31, 21.06, 27.15, 31.22, 36.98, 55.14, 113.52, 117.03,
998 | RSC Adv., 2017, 7, 997–1007
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Scheme 1 Schematic of the procedure for the preparation of Fe3O4@SiO2–MoO3H.
128.25, 128.84, 129.33, 135.86, 146.36, 150.53, 169.57, 194.52.
Anal. calc. for C20H21NO2; C 78.15, H 6.89, N 4.56, O 10.41;
found: C 78.19, H 6.83, N 4.58, O 10.45.
3,3,6,6-Tetra methyl-9-phenyl-3,4,6,7,9,10-hexahydroacridine-
1,8-(2H,5H)-dione (8a). Mp: 191–193 C; IR (KBr, cmꢁ1) n: 3279,
ꢀ
1
3209, 3063, 2955, 2932, 1636, 1605, 1481, 1365, 1219, 1142. H
Fig. 1 The comparative FT-IR spectra of (a) Fe3O4 NPs (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2–OMoO3H.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 997–1007 | 999

View Article Online
RSC Advances
Paper
(100 MHz, DMSO-d6): d 26.45, 29.13, 32.14, 32.86, 50.24, 111.47,
125.46, 127.56, 127.63, 147.15, 149.32, 194.36. Anal. calc. for
C23H27NO2; C 79.05, H 7.79, N 4.01, O 9.16; found: C 79.08, H
7.73, N 4.06, O 9.11.
9-(4-Methoxyphenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahy-
droacridine-1,8(2H,5H)-dione (8b). Mp: 275–277 ꢀC; IR (KBr,
cmꢁ1) n: 3277, 3203, 3070, 2959, 2870, 1643, 1606, 1508, 1483,
1367, 1223, 1171. 1H NMR (500 MHz, DMSO): d 0.90 (s, 6H), 1.04
(s, 6H), 2.08 (d, J ¼ 9.7 Hz, 2H), 2.26 (d, J ¼ 9.9 Hz, 2H), 2.48–
2.52 (m, 2H), 2.57 (d, J ¼ 10.8 Hz, 2H), 3.68 (s, 3H), 4.7 (s, 1H),
6.77–6.78 (t, J ¼ 4.1, 2H), 7.06–7.08 (t. J ¼ 5.12 Hz, 2H), 9.21 (s,
1H). Anal. calc. for C24H29NO3; C 75.96, H 7.70, N 3.69, O 12.65;
found: C 75.90, H 7.72, N 3.62, O 12.69.
9-(4-Fluorophenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-
acridine-1,8(2H,5H)-dione (8e). Mp: 289–291 ꢀC; FT-IR (KBr,
cmꢁ1) n: 3280, 3197, 3070, 2954, 2869, 1635, 1608, 1570, 1437,
1364, 1256, 1145. 1H NMR (400 MHz, DMSO): d 0.99 (s, 6H), 1.11
(s, 6H), 2.15–2.26 (dd, J ¼ 28, 16 Hz, 4H), 2.46 (s, 4H), 4.73 (s, 1H),
6.88–6.92 (t, J ¼ 8.8 Hz, 2H), 7.24–7.27 (d, J ¼ 10.8 Hz, 2H), 9.33 (s,
1H). 13C NMR (100 MHz, DMSO-d6): d 27.29, 29.26, 31.22, 32.20,
50.73, 111.94, 126.07, 127.80, 127.87, 147.17, 149.30, 149.60,
194.46. Anal. calc. for C23H26FNO2; C 75.18, H 7.13, N 3.81, O
8.71; found: C 75.13, H 7.18, N 3.78, O 8.76.
Fig. 2 X-ray powder diffraction patterns of (a) Fe3O4 NPs, (b) Fe3-
O4@SiO2–OMoO3H.
9-(4-Chlorophenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-
acridine-1,8(2H,5H)-dione (8f). Mp: 295–297 ꢀC; FT-IR (KBr,
cmꢁ1) n: 3288, 3205, 3068, 2956, 2869, 1643, 1608, 1475, 1363,
1223, 1171. 1H NMR (500 MHz, DMSO): d 0.91 (s, 6H), 1.04 (s, 6H),
2.08–2.11 (d, J ¼ 16, 2H), 2.26–2.29 (d, J ¼ 16, 2H), 2.50–2.60 (dd, J
¼ 14.65, 4H), 4.51 (s, 1H), 7.18–7.20 (d, J ¼ 8.2 Hz, 2H), 7.28–7.29
NMR (400 MHz, DMSO): d 0.84 (s, 6H), 0.99 (s, 6H), 1.96 (d, J ¼
21.5 Hz, 2H), 2.15 (d, J ¼ 21.5 Hz, 2H), 2.30 (d, J ¼ 22.8, 2H), 2.40–
2.49 (m, 2H), 4.8 (s, 1H), 7.00–7.14 (m, 5H), 9.28 (s, 1H). 13C NMR
Fig. 3 TEM image of Fe3O4@SiO2–MoO3H (a), histogram of particle size distribution (b), SEM image of Fe3O4@SiO2–MoO3H (c) and EDAX
spectrum of Fe3O4@SiO2–MoO3H (d).
1000 | RSC Adv., 2017, 7, 997–1007
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
9.32 (s, 1H). Anal. calc. for C23H26N2O4; C 70.03, H 6.64, N 7.10,
O 16.22; found: C 70.08, H 6.69, N 7.07, O 16.26.
3,3,6,6-Tetramethyl-9-(3-nitrophenyl)-3,4,6,7,9,10-hexahydro-
acridine-1,8(2H,5H)-dione (8j). Mp: 290–292 ꢀC; FT-IR (KBr,
cmꢁ1) n: 3282, 3193, 3070, 2957, 2930, 2889, 2870, 1649, 1612,
1577, 1434, 1364, 1225, 1171. 1H NMR (500 MHz, DMSO): d 0.91
(s, 6H), 1.05 (s, 6H), 2.09–2.12 (d, J ¼ 4.4 Hz, 2H), 2.27–2.30 (d, J
¼ 6.4 Hz, 2H), 2.55–2.63 (dd, J ¼ 7.2 Hz, 4H), 4.64 (s, 1H), 7.55–
7.58 (t, J ¼ 3.1 Hz, 1H), 7.65–7.67 (d, J ¼ 3 Hz, 1H), 7.99–8.02 (d, J
¼ 5.1 Hz, 2H), 9.31 (s, 1H). Anal. calc. for C23H26N2O4; C 70.03, H
6.64, N 7.10, O 16.22; found: C 70.06, H 6.70, N 7.08, O 16.24.
3,3,6,6-Tetramethyl-9-(naphthalen-2-yl)-3,4,6,7,9,10-hexahy-
droacridine-1,8(2H,5H)-dione (8k). Mp: 264–266 ꢀC; IR (KBr,
cmꢁ1) n: 3274, 3176, 3059, 2954, 2922, 1649, 1608, 1491, 1364,
1
1221, 1171. H NMR (400 MHz, DMSO): d 0.99 (s, 6H), 1.12 (s,
6H), 2.13–2.18 (d, J ¼ 18 Hz, 2H), 2.21–2.23 (d, J ¼ 9.6 Hz, 2H),
2.52 (s, 4H), 4.92 (s, 1H), 7.34–7.38 (d, J ¼ 16, 1H), 7.46–7.47 (d, J
¼ 6.8 Hz, 2H), 7.73–7.79 (m, 4H), 9.12 (s, 1H). Anal. calc. for
Fig. 4 TGA curve of Fe3O4@SiO2–MoO3H.
C
27H29NO2; C 81.17, H 7.32, N 3.51, O 8.01; found: C 81.22, H
(d, J ¼ 8.2 Hz, 2H), 9.32 (s, 1H). Anal. calc. for C23H26ClNO2; C
71.96, H 6.83, N 3.65, O 8.33; found: C 71.90, H 6.89, N 3.59, O
8.32.
7.35, N 3.54, O 8.08.
9-(4-Bromophenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-
acridine-1,8(2H,5H)-dione (8h). Mp: 310–312 ꢀC; FT-IR (KBr,
cmꢁ1) n: 3274, 3176, 3058, 2954, 2921, 1649, 1608, 1491, 1364,
1221, 1171. 1H NMR (400 MHz, DMSO): d 1.03 (s, 6H), 1.23 (s, 6H),
2.24–2.30 (dd, J ¼ 14.8, 8.8 Hz, 4H), 2.44 (s, 4H), 4.84 (s, 1H), 7.16
(d, J ¼ 6.8 Hz, 2H), 7.43 (d, J ¼ 17.6 Hz, 2H), 9.30 (s, 1H). Anal.
calc. for C23H26BrNO2; C 64.49, H 6.12, N 3.27, O 7.47; found: C
64.52, H 6.17, N 3.31, O 7.49.
Results and discussion
The MNPs 1 were prepared via a chemical co-precipitation30 and
were subsequently coated with a layer of silica using the sol–gel
method31 to provide reaction sites for further functionalization
and thermal stability. The Fe3O4@SiO2 nanoparticles 2 were
then transformed to Fe3O4@SiO2–Cl with thionyl chloride and
Fe3O4@SiO2–Cl were then transformed to Fe3O4@SiO2–
OMoO3H 3 via a nucleophilic substitution with anhydrous
sodium molybdate in n-hexane to afford a dark gray powder
(Scheme 1). We used acid–base potentiometric titration to
measure the acid capacities of this catalyst. To this account,
100 mg of the catalyst was added to 10 ml of a 1 M NaCl solution
and stirred continuously for 24 h at room temperature. The
3,3,6,6-Tetramethyl-9-(4-nitrophenyl)-3,4,6,7,9,10-hexahydro-
acridine-1,8(2H,5H)-dione (8i). Mp: 287–289 ꢀC; FT-IR (KBr,
cmꢁ1) n: 3384, 2958, 2908, 1643, 1602, 1514, 1447, 1364, 1221,
1
1171. H NMR (500 MHz, DMSO): d 0.91 (s, 6H), 1.05 (s, 6H),
2.08–2.11 (d, J ¼ 6.5 Hz, 2H), 2.27–2.30 (d, J ¼ 6.5 Hz, 2H), 2.50–
2.63 (m, 4H), 4.63 (s, 1H), 7.45–7.48 (m, 2H), 8.10–8.12 (m, 2H),
Fig. 5 Magnetization curves for the prepared Fe3O4 MNPs (a) and Fe3O4@SiO2–MoO3H (b).
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 997–1007 | 1001

View Article Online
RSC Advances
Paper
cmꢁ1 (attributed to the overlapping of peaks corresponding to
Si–O–Si, Fe–O–Si, and symmetric MoO2 stretching) indicated
that the MNPs possessed MoO3H groups.
The crystalline structure of the different synthesized mate-
rials was investigated by XRD. For the Fe3O4 particles (Fig. 2a),
the diffraction peaks at 2q ¼ 30.1ꢀ, 35.4ꢀ, 43.1ꢀ, 53.6ꢀ, 57ꢀ, and
62.8ꢀ corresponded to the spinel structure of Fe3O4, which can
be assigned to the diffraction of the (220), (311), (400), (422),
(511), and (440) planes of the crystals, respectively.32 For the
Fe3O4@SiO2–OMoO3H (Fig. 2b), the XRD pattern indicated that
the crystalline structure of the Fe3O4 particles was retained aer
the deposition of SiO2 layers. The broad peak at around 2q ¼ 20ꢀ
to 27ꢀ indicated the presence of amorphous silica in Fe3O4@-
Fig. 6 Digital camera images of the aqueous solution with dispersed SiO2–OMoO3H. The intensity of this peak increased with the
magnetic Fe3O4@SiO2–MoO3H composite particles (a) and after
applied magnetic field (b).
introducing of molybdate on the silica-coated magnetic nano-
particles, which can be attributed to the amorphous molybdate
supported on the composite. The XRD results showed that the
Fe3O4@SiO2 particles have been successfully coated with
molybdate.
The TEM image revealed that the Fe3O4@SiO2–MoO3H
nanoparticles were uniform with an average size in the range of
catalyst was separated using an external magnet, and the NaCl
solution was decanted and saved. According to the obtained
results, loading of acid sites was about 3.80 mmol H+ per g of
catalyst. The resulting MNP acid catalyst was characterized by
10–30 nm (Fig. 3a).
XRD, FT-IR, ICP-OES, TEM, SEM and EDX. The percentage of
The SEM image shown in (Fig. 3c) demonstrates that Fe3-
molybdenum (Mo) in catalyst was also determined by ICP-OES
at 8000–10 000 K which showed 1.68 (% w/w) molybdenum.
O4@SiO2–MoO3H nanoparticles are nearly spherical with more
than 20 nm in size.
FT-IR spectra of catalyst are presented the band in the region
The successful incorporation of molybdate groups was also
of 560 cmꢁ1 is attributed to the stretching vibrations of the (Fe–
conrmed by EDAX analysis (Fig. 3d), which showed the pres-
O) bond and the band at about 1090 cmꢁ1 belongs to (Si–O)
ence of to Fe, Si, Mo and O elements.
stretching vibrations. FT-IR analysis was used to characterize
The thermogravimetric analysis (TGA) was used to study the
the presence of the –MoO3H groups on the surface of the MNPs
thermal stability of the acid catalyst (Fig. 4). The rst weight loss
(Fig. 1). As shown in Fig. 1c, the FT-IR spectra of Fe3O4@SiO2–
MoO3H was clearly different from those of Fe3O4 (Fig. 1a) and
Fe3O4@SiO2 (Fig. 1b). The broad peak in range of 1080–1200
ꢀ
which occurred below 150 C, displayed a mass loss that was
attributable to the loss of adsorbed solvent or trapped water
from the catalyst. A weight loss of approximately 5% weight
Scheme 2 Synthesis of 1,8-dioxo-decahydroacridine derivatives by Fe3O4@SiO2–MoO3H.
1002 | RSC Adv., 2017, 7, 997–1007
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Fig. 7 Optimization of the catalyst amount.
occurred between 300 and 500 ꢀC which can be attributed to the
loss of molybdate groups covalently bound to silica surface.
Thus, it can be concluded that the catalyst is stable up to 300 ꢀC.
Typical magnetization curve for Fe3O4 nanoparticles and
Fe3O4@SiO2–MoO3H are shown in Fig. 5. Room temperature
specic magnetization (M) versus applied magnetic eld (H)
curve measurements of the sample indicate a saturation
magnetization value (Ms) of 20.30 emu gꢁ1, lower than that of
bare MNPs (59.14 emu gꢁ1) due to the coated shell.
Fig. 6a shows the photograph of Fe3O4@SiO2–MoO3H
microspheres that dispersed in water. Aer a magnet was
placed aside, the black microspheres can be magnetized in
3 min, leaving a clear solution (Fig. 6b). That is to say, the
Table 1 Optimization of model reaction by using various solvents and
amount of Fe3O4@SiO2–MoO3H
Catalyst
(mol%)
Time
(min)
Isolated yield
(%)
Entry
Solvent
1
2
3
4
5
6
7
8
9
1
2
3
1
1
1
1
1
2
3
EtOH
EtOH
EtOH
MeOH
CHCl3
Toluene
DMF
Solvent-free
Solvent-free
Solvent-free
80
80
80
50
45
35
55
30
20
25
93
90
88
80
100
140
220
35
35
35
10
Table 2 Preparation of 1,8-dioxo-decahydroacridine derivatives using Fe3O4@SiO2–MoO3H
Entry
R1]R2
R3
Product
Time (min)
Isolated yield (%)
Melting point (ꢀC)
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
4-Cl
4-Br
4-CH3
4-OH
4-OCH3
3-NO2
H
4-OCH3
4-OH
4-CH3
4-F
4-Cl
7a
7b
7c
7d
7e
7f
7g
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
35
20
25
45
55
50
25
25
40
45
55
30
20
20
25
35
30
45
50
93
89
91
88
86
86
90
92
90
88
90
94
92
90
91
93
91
86
88
278–279
295–297
311–312
254–255
303–305
302–304
280–282
291–293
275–277
302–304
267–269
289–291
295–297
222–224
310–312
287–289
290–292
264–266
217–219
9
10
11
12
13
14
15
16
17
18
19
2-Cl
4-Br
4-NO2
3-NO2
2-Naphthaldehyde
4-(CH3)2–N
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 997–1007 | 1003

View Article Online
RSC Advances
Paper
Scheme 3 Reasonable mechanism for the formation of decahydroacridine-1,8-diones.
Fe3O4@SiO2–MoO3H nanoparticles were shown good magnetic dioxo-decahydroacridines 7,8 was obtained was synthesized by
responsibility even if the SiO2–MoO3H layer was increased to condensation between dimedone (4) (2 mmol), benzaldehyde
20 nm.
In continuation of our interest in the development of novel, solvent-free conditions as a model reaction (Scheme 2).
efficient, and green procedures for the synthesis of organic The reaction conditions were optimized on the basis of the
compounds using safe catalysts,33–35 we decided to prepare 1,8- catalyst, solvent and different temperature for the synthesis of
(5) (1 mmol) and ammonium acetate (6) (1 mmol) under
1004 | RSC Adv., 2017, 7, 997–1007
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Fig. 8 Reusability of Fe3O4@SiO2–MoO3H for synthesis of 7a.
1,8-dioxo-decahydroacridines. This reaction was rstly exam- molecule of dimedone reacts with 9 to give intermediate 10.
ined in the absence of catalyst which did not show any appre- Nucleophilic attack of amine group of ammonium acetate to
ciable progress even aer 360 min. Upon screening, the results carbonyl group creates intermediate 11. In the next step, cycli-
well showed that the reaction proceeds efficiently by adding 1 zation will occur by the nucleophilic attack of amine group to
mol% of Fe3O4@SiO2–MoO3H. Also, increasing the catalyst carbonyl group to obtain intermediate 12. Finally, by the
amount did not improve the results (Fig. 7).
removal of one water molecule, the acridine derivatives 7 or 8
Eventually to making sure that the solvent free condition is will be generated.
appropriate, it has been decided to investigate the effect of
The design and synthesis of recoverable catalysts is a highly
different classical solvents such as EtOH, MeOH, CHCl3, challenging interdisciplinary eld, which combines chemistry,
toluene, and DMF (Table 1, entries 1–7). We found that polar materials science, and engineering from economic and envi-
and protic solvents, such as EtOH or MeOH, afford better yields ronmental perspective. The main disadvantage for many of the
than aprotic ones. As it is shown in Table 1, using these solvents reported methods is that the catalysts are destroyed in the work-
gave signicantly lower yields and longer reaction times. up procedure and cannot be recovered or reused. In this
Increasing the reaction times did not improve the yields. So the process, as outlined in Fig. 8, the recycled catalyst can be used
best yield of product was provided in solvent free conditions in up to eight cycles, during which there are negligible losses in
(Table 1, entry 8).
the catalytic activity. The percentage of molybdenum (Mo) in
Aer optimization of the reaction conditions, in order to recovered catalyst was also determined by ICP-OES at 8000–
extend the scope of this reaction, a wide range of aromatic 10 000 K which showed 1.67 (% w/w) molybdenum. Additionally
aldehydes were used with 4 and 6 (Table 2). All the products the acid capacity of catalyst was 3.7 mmol H+ per g aer eighth
were characterized by comparison of their spectra and physical recovery which conrms excellent efficiency of the immobili-
data with those reported in the literature.36,37
zation of acidic group on the surface of the catalyst.
As indicated in Table 2, the new conditions are very suitable
for a vast variety of aromatic aldehydes with both electron-
donating and electron-withdrawing groups to give correspond-
ing 1,8-dioxo-decahydroacridine derivatives in good to excellent
yields. In all cases, the reactions proceeded within 20–55
minute. However, it is notable that substituted aromatic alde-
hydes with electron-withdrawing groups increase the rate of
reaction (Table 2, entries 2, 3, 7, 12–17) probably by activating
the carbonyl group as electrophile center. Contrarily in the case
of electron-donating groups, the reaction was more slowly
(Table 2, entries 4–6 and 9–11).
The reaction mechanism is shown in Scheme 3. At rst, the
acid catalyst changes the aldehyde into convenient electrophile
via protonation of the carbonyl group and then one molecule of
dimedone condenses with the aromatic aldehyde to produce
intermediate 9. Then the active methylene group of the second
Fig. 9 FE-SEM images of (a) fresh Fe3O4@SiO2–MoO3H, (b) after
reused eight times.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 997–1007 | 1005

View Article Online
RSC Advances
Paper
Fig. 10 EDAX spectrum of Fe3O4@SiO2–MoO3H after reused eight times.
Aer the eight recycles, the recovered catalyst had similar
morphology as the fresh one (Fig. 9) and no noticeable change
in structure was observed, by reference to the EDAX analysis as
compared to the fresh catalyst (Fig. 10).
7 J. Liu, R. Che, H. Chen, F. Zhang, F. Xia, Q. Wu and M. Wang,
Small, 2012, 8, 1214–1221.
8 Y. Piao, A. Burns, J. Kim, U. Wiesner and T. Hyeon, Adv.
Funct. Mater., 2008, 18, 3745–3758.
9 C. Wang, J. Yan, X. Cui and H. Wang, J. Colloid Interface Sci.,
2011, 354, 94–99.
10 H. D. Oh and S. W. Lee, Mater. Res. Bull., 2013, 48, 2191–
2193.
11 M. A. Ghasemzadeh, J. Safaei-Ghomi and H. Molaei, C. R.
Chim., 2012, 15, 969–974.
12 Y. Mikata, M. Yokoyama, K. Mogami, M. Kato, I. Okura,
M. Chikira and S. Yano, Inorg. Chim. Acta, 1998, 279, 51–57.
13 I. Antonini, P. Polucci, L. R. Kelland, E. Menta, N. Pescalli
and S. Martelli, J. Med. Chem., 1999, 42, 2535–2541.
14 M. J. Wainwright, J. Antimicrob. Chemother., 2001, 47, 1–13.
15 L. Ngadi, A. M. Galy, J. P. Galy, J. Barbe, A. Cremieux,
J. Chevalier and D. Sharples, Eur. J. Med. Chem., 1990, 25,
67–70.
Conclusions
In summary, we found Fe3O4@SiO2–OMoO3H as an effective
and environmentally safe acidic magnetic catalyst which
successfully catalyzed to produce 1,8-dioxo-decahydroacridines
from aromatic aldehydes, an amine and a dimedone under
solvent free conditions. By this development, the scope of
heterocyclic compounds was increased. High catalytic activity
under solvent free conditions, high yields, a clean process,
reusable several times without loss of activity or selectivity
simple catalyst preparation, easy separation aer the reaction
by a magnet and green conditions are advantages of these
protocols.
16 S. A. Gamega, J. A. Spicer, G. J. Atwell, G. J. Finlay,
B. C. Baguley and W. A. Deny, J. Med. Chem., 1999, 42,
2383–2393.
Acknowledgements
17 S. Gallo, S. Ati, A. Mohamoud, C. Santelli-Rouvier,
K. Wolfart, J. Molnar and J. Barbe, Eur. J. Med. Chem.,
2003, 38, 19–26.
The authors gratefully acknowledge partial support of this work
by Semnan University and Karaj Islamic Azad University, Iran.
18 K. Venkatesan, S. S. Pujari and K. V. Srinivasan, Synth.
Commun., 2009, 39, 228–241.
Notes and references
19 X. S. Wang, D. Q. Shi, D. Q. Zhang, Y. F. Wang and S. J. Tu,
Chin. J. Org. Chem., 2004, 24, 430–432.
20 W. Shen, L. M. Wang, H. Tian, J. Tang and J. J. Yu, J. Fluorine
Chem., 2009, 130, 522–527.
21 M. Dabiri, M. Baghbanzadeh and E. Arzroomchilar, Catal.
Commun., 2008, 9, 939–942.
1 B. Zhang, H. Asakura, J. Zhang, J. Zhang, S. De and N. Yan,
Angew. Chem., Int. Ed., 2016, 55, 8319–8323.
2 E. L. S. Ngee, Y. Gao, X. Chen, T. M. Lee, Z. Hu, D. Zhao and
N. Yan, Ind. Eng. Chem. Res., 2014, 53, 14225–14233.
3 Y. Wang, S. De and N. Yan, Chem. Commun., 2016, 52, 6210–
6224.
22 M. Kidwai and D. Bhatnagar, Tetrahedron Lett., 2010, 51,
2700–2703.
23 F. Rashedian, D. Saberib and K. Niknam, J. Chin. Chem. Soc.,
2010, 57, 998–1006.
4 H. L. Ding, Y. X. Zhang, S. Wang, J. M. Xu, S. C. Xu and
G. H. Li, Chem. Mater., 2012, 24, 4572–4580.
5 J. Zou, Y. G. Peng and Y. Y. Tang, RSC Adv., 2014, 4, 9693–
9700.
24 B. Das, P. Thirupathi, I. Mahender, V. S. Reddy and
Y. Koteswara, J. Mol. Catal. A: Chem., 2006, 247, 233.
6 R. Zhao, K. Jia, J. J. Wei, J. X. Pu and X. B. Liu, Mater. Lett.,
2010, 64, 457–459.
1006 | RSC Adv., 2017, 7, 997–1007
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
25 A. Davoodnia, A. Khojastehnezhad and N. Tavakoli-Hoseini,
R. Z. Domingues and A. L. Andrade, Hyperne Interact.,
2010, 195, 265–274.
Bull. Korean Chem. Soc., 2011, 32, 2243.
26 T. S. Jin, J. S. Zhang, T. T. Guo, A. Q. Wang and T. S. Li, 32 L. Cabrera, S. Gutierrez, M. P. Morales, N. Menendez and
Synthesis, 2004, 12, 2001–2005.
P. Herrasti, J. Magn. Magn. Mater., 2009, 321, 2115–2120.
33 B. Karami and M. Kiani, J. Chin. Chem. Soc., 2015, 62, 756–
765.
34 B. Karami and M. Kiani, J. Iran. Chem. Soc., 2016, 13, 111–
116.
35 B. Karami, M. Kiani and M. A. Hoseini, Chin. J. Catal., 2014,
35, 1206–1211.
36 G. M. Ziarani, A. Badiei, M. Hassanzadeh and S. Mousavi,
Arabian J. Chem., 2014, 7, 335–339.
27 B. Karami and M. Kiani, Catal. Commun., 2011, 14, 62–67.
28 B. Karami, M. Kiani, S. J. Hosseini and M. Bahrami, New J.
Chem., 2015, 39, 8576–8581.
29 B. Karami and M. Kiani, Res. Chem. Intermed., 2016, 42,
3373–3383.
30 A. Bee, R. Massart and S. J. Neveu, J. Magn. Magn. Mater.,
1995, 149, 6–9.
31 R. V. Ferreira, I. L. S. Pereira, L. C. D. Cavalcante,
L. F. Gamarra, S. M. Carneiro, E. J. Amaro, J. D. Fabris, 37 M. Nasr-Esfahani and T. Abdizadeh, C. R. Chim., 2015, 18,
547–553.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 997–1007 | 1007