Fe2+ supported on hydroxyapatite-core–shell-γ-Fe2O3 nanoparticles: Efficient and recyclable green catalyst for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthene derivatives

Article abstract of DOI:10.1007/s11164-015-2318-5

In this work, Fe²⁺ supported on hydroxyapatite-core–shell-γ-Fe₂O₃ nanoparticles (γ-Fe₂O₃–HAp-Fe²⁺ NPs) has been prepared and characterized by Fourier transform infrared spectroscopy, X-ray

Full text of DOI:10.1007/s11164-015-2318-5

Res Chem Intermed
DOI 10.1007/s11164-015-2318-5
Fe2+ supported on hydroxyapatite-core–shell-c-Fe2O3
nanoparticles: Efficient and recyclable green catalyst
for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthene
derivatives
Hakimeh Sadat Haeri1 Sobhan Rezayati1
•
•
Eshagh Rezaee Nezhad1 Hamed Darvishi1
•
Received: 28 July 2015 / Accepted: 8 October 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract In this work, Fe2? supported on hydroxyapatite-core–shell-c-Fe2O3
nanoparticles (c-Fe2O3–HAp-Fe2? NPs) has been prepared and characterized by
Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron
microscopy, scanning electron microscopy, and vibrating sample magnetometry
spectra. Then, c-Fe2O3–HAp-Fe2? NPs were used as an efficient, reusable and
heterogeneous nanocatalyst for one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xan-
thenes via the one-pot condensation reaction of arylaldehydes and 2-naphthol under
solvent-free conditions in good to excellent yields. This procedure has a lot of
advantages such as very easy reaction conditions, simplicity in operation, short
reaction time, high yield, and green aspects by avoiding toxic conventional catalysts
and solvents. Additionally, c-Fe2O3–HAp-Fe2? NPs were easily recycled from the
reaction mixture and were reused seven times without any loss in activity.
Keywords c-Fe2O3–HAp-Fe2? Á Magnetic nanoparticle Á
14H-dibenzo[a,j]xanthenes Á Lewis acid Á Nanocatalyst Á Reusable catalyst
Introduction
The synthesis of xanthene and benzoxanthene compounds has received great
attention from various pharmacological activities and organic chemists because of
their broad spectrum of biological and pharmaceutical properties, such as anti-viral
[1], antioxidant [2], anti-cancer [3], antibacterial and antifungal [4, 5], analgesic and
Electronic supplementary material The online version of this article (doi:10.1007/s11164-015-2318-5)
contains supplementary material, which is available to authorized users.
&
Sobhan Rezayati
sobhan.rezayati@yahoo.com
1
Department of Chemistry, Payame Noor University, P.O. Box 19395-4697, Tehran, Iran
123

H. S. Haeri et al.
anti-inflammatory [6, 7], cytotoxic [8], and anti-proliferative properties [9].
Moreover, xanthene and benzoxanthene derivatives can be used as sensitisers in
dye-sensitised solar cells (DSSCs) [10–12], in the food industry as additives [13], in
laser technologies [14], in photodynamic therapy [15], as fluorescent materials for
the visualisation of biomolecules [16], and also as hole-transporting materials in
organic light-emitting devices (OLEDs) [17]. Xanthenes and their derivatives are
rare in natural plants [18, 19]. Blumeaxanthene (A), blumeaxanthene (B), and
3-isopropyl-9a-methyl-1,2,4a,9a-tetrahydroxanthene (C) are examples of natural
xanthenes (Scheme 1). Compounds A and B have been used to treat gynecological
disorders, and compound C has been used in traditional Indian medicine as an
antidote for all snake venoms.
A number of methods have been developed and reported for the synthesis of
xanthenes and benzoxanthenes. These methods include the cyclocondensation
reaction between 2-tetralone and 2-hydroxyarylaldehydes under acidic conditions
[20], the palladium-catalysed cyclisation of polycyclic aryltriflate esters [21], the
reaction of alkylphenoxy magnesium halides with triethylorthoformate [22], and the
reaction of the condensation of cyclic 1,3-diketones with aryl aldehydes catalysed
by molybdate sulphonic acid [23]. Also, 14-aryl-14H-dibenzo[a,j]xanthene deriva-
tives can be prepared by condensation of 2-naphthol with aldehydes in the presence
of different catalysts, including Lewis acids and Brønsted acids. For example,
carbon-based solid acid [24], functionalized mesoporous materials [25], cellulose
sulfuric acid [26], P2O5/Al2O3 [27], amberlyst-15 [28], silica sulfuric acid [29],
HClO4–SiO2 [30], heteropoly acid [31], montmorillonite K-10 [32], Yb(OTf)3 [33],
phospho sulfonic acid (PSA) [34], boron sulfonic acid (BSA) [35], molecular iodine
[36], and boric acid [37] have been used as catalysts for the synthesis of xanthenes.
However, some of these methods suffer from drawbacks such as strongly acidic
wastes, high cost, reagent toxicity, unsatisfactory yields, tedious work-up proce-
dures, harsh conditions and nonrecyclable reagents. Recently, the application of
nanoparticles (NPs) has received great attention from organic chemists because of
their high surface area and unique magnetic properties. Moreover, they have a wide
range of usage in various fields, such as data storage [38], environmental
remediation [39], biology and medical applications [40], magnetic resonance
imaging (MRI) [41], and magnetic fluids [42]. c-Fe2O3–HAp-Fe2?NPs are
important both environmentally and economically, because they can be conve-
niently handled, making the experimental procedure simple, low cost and eco-
CH3
O
O
HO
O
OH
OH
O
O
OH
O
O
CH3
OCH3
H3C
Cl
C
A
B
Scheme 1 Examples of natural xanthenes
123

Fe2? supported on hydroxyapatite-core–shell-c-Fe2O3…
friendly. Also, the catalyst can be recovered from the reaction mixtures and reused.
Recently, we used a magnetic NP with a high surface area, narrow pore size
distribution and large pore volume as a recoverable heterogeneous catalyst in some
organic transformations [43–49]. Therefore, in the current work, it seems that the
major task of current research is developing more acceptable methods based on the
use of Fe2? supported on hydroxyapatite-core–shell-Fe2O3 (c-Fe2O3–HAp-Fe2?
)
NPs as an efficient and reusable Lewis acid catalyst for the one-pot synthesis of
14-aryl-14H-dibenzo[a,j] xanthenes in good to excellent yields and in short reaction
times under solvent-free conditions at 90 °C (Scheme 2). (Please see supporting
information for experimental procedures for the synthesis of c-Fe2O3–HAp-Fe2?
NPs, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning
electron microscopy (SEM), vibrating sample magnetometry (VSM ), and Fourier
transform infrared spectroscopy, (FTIR)].
Experimental
Materials and methods
All chemicals were purchased from Merck or Fluka chemical companies. All the
products are know compounds and were characterized by comparing the proton
nuclear magnetic resonance (1H-NMR) and carbon-13 (13C)-NMR spectroscopic
data and their melting point literature values. The uncorrected melting points of all
O
Ar
Ar
H
Solvent-free,
90 oC, 10-35 min
1
OH
O
3a-t
2
γ-Fe2O3
Fe2+
HAp
Scheme 2 The reaction of 2-naphthol with aldehydes catalyzed by c-Fe2O3–HAp-Fe2? NPs under
solvent-free conditions
123

H. S. Haeri et al.
compounds were measured in an open capillary in a paraffin bath. NMR chemical
shifts are reported in (d) ppm relative to tetramethylsilane (TMS, d = 0.00) with the
residual solvent as an internal reference [deuterated chloroform (CDCl3), d
1
7.26 ppm for H-NMR and d 77.0 for 13C-NMR]. Data are reported as follows:
chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet,
m = multiplet), coupling constants (Hz) and integration. Mass spectrometry (MS)
analyses were performed on a PerkinElmer Clarus 680 gas chromatograph (GC)
equipped with a Clarus SQ 8T mass spectrometer. Infrared (IR) spectra were
recorded on a Frontier FT-IR (Perkin Elmer) spectrometer using a potassium
bromide (KBr) disk. The phases present in the magnetic materials were analyzed
´
using a powder X-ray diffractometer, Philips (Holland), model X0 Pert with X Pert
˚
with CuKa1 radiation (k = 1.5401 A), and the X-ray generator was operated at
40 kV and 30 mA. Diffraction patterns were collected from 2 h = 20°–80°.
Preparation of c-Fe2O3–HAp-Fe21NPs
In this study, c-Fe2O3–HAp-Fe2? NPs were prepared in two steps. The iron oxide
magnetic particles (IOMPs) were synthesized by a chemical co-precipitation
technique of ferric and ferrous chlorides in aqueous solution. Solutions of
FeCl3Á6H2O (0.25 mol L-1) and FeCl2Á4H2O (0.125 mol L-1) were mixed and
precipitated with NH4OH solution (25 %) at pH 12, while stirring vigorously. The
black suspension, which formed immediately, was maintained at 70 °C for
approximately 1 h and washed several times with ultrapure water until the pH
decreased to 7. IOMP/HAp was prepared by the impregnation method according to
known procedures with some modifications [50]. Then hydroxyapatite-encapsulated
c-Fe2O3 (0.6 g) was introduced into 100 ml of distilled water containing 6.4 mmol
of FeCl2Á4H2O. The mixture was stirred (500 rpm) for 24 h, filtered, and washed
several times with ethanol. The recovered solid was dried at 70 °C overnight
(Scheme 3). The mean size and the surface morphology of the c-Fe2O3–HAp-Fe2?
NPs were characterized by TEM, SEM, VSM, XRD and FTIR techniques [43].
Procedure for preparation of 14-aryl-14H-dibenzo[a,j]xanthenes 3a–t
To a mixture of aldehyde (1 mmol) and 2-naphthol (2 mmol), c-Fe2O3–HAp-Fe2?
NPs (20 mg) were added and the mixture was inserted in an oil bath and heated at
300 o
C
FeCl2 4H2O
48 H, 25 o
Ca (NO3)2 4H2O
FeCl2 4H2O NH4OH (25%)
+
25 oC, O2
FeCl3 6H2O
3h
C
(NH4)2HPO
90oC, 2 h
γ-Fe2O3@HAP-Fe2+
γ-Fe2O3
γ-Fe2O3@HAP
Fe2+
γ-Fe2O3
HAP
Scheme 3 The synthesis of Fe2? supported on hydroxyapatite-core–shell c-Fe2O3 (c-Fe2O3–HAp-Fe2? NPs)
123

Fe2? supported on hydroxyapatite-core–shell-c-Fe2O3…
90 °C for the appropriate time (Table 3). Completion of the reaction was indicated
by thin-layer chromatography (TLC). After completion of the reaction, the reaction
mixture was cooled to room temperature. The reaction mixture was dissolved in
ethylacetate and the catalyst was separated by simple filtration. Excess solvent was
removed under reduced pressure and the crude product was recrystallized with
ethanol to afford the pure product in 81–95 % yield. All the products were known
1
compounds and characterized by comparing Melting points, H-NMR 13C-NMR,
and Mass spectra with those reported in the literature. The spectral data for some
selected compounds are given below.
14-(Phenyl)14H-dibenzo[a,j]xanthenes (3a)
1
Pale yellow solid; H-NMR (300 MHz, CDCl3): d 5.39 (1H, s, CH), 7.28–7.31 (d,
2H, J = 8.5 Hz, Ar–H), 6.68–6.74 (4H, m, Ar–H), 5.89–6.80 (11H, m, Ar–H);
13C-NMR (75 MHz, CDCl3): d 38.03, 117.31, 118.01, 122.68, 124.23, 126.37,
126.78, 128.25, 128.47, 128.79, 128.85, 131.04, 131.44, 144.98, 148.71; MS (EI),
m/z: 358 (M?), 282, 281, 252, 250, 179.
14-(2-Nitrophenyl)-14H-dibenzo[a,j]xanthenes (3b)
1
Yellow solid; H-NMR (300 MHz, CDCl3): d 5.91 (1H, s, CH), 6.08–6.43 (8H, m,
Ar–H), 6.48–6.51 (2H, m, Ar–H), 6.68–6.72 (4H, m, Ar–H), 7.41–7.44 (2H, d,
J = 8.53, Ar–H); 13C-NMR (75 MHz, CDCl3): d 32.5, 117.5, 118.0, 122.5, 124.6,
124.9, 127.3, 127.5, 128.7, 129.4, 130.9, 131.7, 132.2, 134.1, 140.8, 147.0, 149.3;
MS (EI), m/z: 403 (M?), 282, 281, 252, 250, 178, 141.
14-(4-Bromo)-14H-dibenzo[a,j]xanthenes (3e)
1
Pink solid; H-NMR (300 MHz, CDCl3): d 7.19–7.22 (m, 2H), 6.16–6.75 (m, 4H),
6.15–6.75 (m, 10H), 5.34 (s, 1H); 13C-NMR (75 MHz, CDCl3): d 37.18, 115.18,
115.47, 117.07, 118.03, 122.46, 124.33, 126.88, 128.89, 129.56, 129.67, 131.04,
131.26, 140.80, 148.68; MS (EI), m/z: 438, 436 (M?), 282, 281, 252, 250, 179.
14-(4-Methyl)-14H-dibenzo[a,j]xanthenes (3f)
White solid; 1H-NMR (300 MHz, CDCl3): d 7.32–7.29 (m, 2H), 6.74–6.67 (m, 4H),
6.51–6.15 (m, 8H), 5.87–5.85 (m, 2H), 5.36 (s, 1H), 1.04 (s, 3H); 13C-NMR
(75 MHz, CDCl3): d 20.91, 37.63, 117.44, 118.01, 122.71, 124.21, 126.76, 128.11,
128.79, 129.18, 131.07, 131.45, 135.90, 142.13, 148.67; MS (EI), m/z: 372 (M?),
282, 281, 252, 250, 186.
14-(4-methoxyphenyl)-14H-dibenzo[a,j]xanthenes (3g)
1
Pink solid; H-NMR (300 MHz, CDCl3): d 2.49 (3H, s, OMe), 5.36 (1H, s, CH),
5.59–5.61 (2H, d, J = 8.66 Hz, Ar–H), 6.32–6.45 (6H, m, Ar–H), 6.49–6.55 (2H,
m, Ar–H), 6.69–6.76 (4H, m, Ar–H), 7.31–7.33 (2H, d, J = 8.48, Ar–H); 13C-NMR
123

H. S. Haeri et al.
(75 MHz, CDCl3): d 37.17, 55.05, 113.89, 117.58, 118.06, 122.77, 124.28, 126.81,
128.80, 128.87, 129.23, 131.13, 131.47, 137.45, 148.69, 157.89; MS (EI), m/z: 388
(M?), 282, 281, 252, 250, 194, 187.
14-(4-Nitrophenyl)-14H-dibenzo[a,j]xanthenes (3i)
Pale yellow solid; 1H-NMR (300 MHz, CDCl3): d 5.44 (1H, s, CH), 6.33–6.57 (8H,
m, Ar–H), 6.71–6.76 (4H, m, Ar–H), 6.85–6.89 (2H, d, Ar–H), 7.15–7.18 (2H,
J = 8.3, Ar–H); 13C-NMR (75 MHz, CDCl3): d 37.88, 115.75, 118.06, 122.04,
123.86, 124.58, 127.19, 128.96, 129.06, 129.59, 131.07, 146.27, 148.75, 152.01;
MS (EI), m/z: 388 (M?), 282, 281, 252, 250, 178, 177.
14-(2-Chlorophenyl)-14H-dibenzo[a,j]xanthenes (3p)
1
White solid; H-NMR (300 MHz, CDCl3): d 5.69 (1H,s, CH), 5.81–5.82 (2H, d,
Ar–H), 6.27–6.40 (5H, m, Ar–H), 6.50 (2H, d, Ar–H), 6.55–6.67 (4H, m, Ar–H),
7.63–7.66 (2H, J = 8.5, d, Ar–H); 13C-NMR (75 MHz, CDCl3): d 34.63, 118.02,
118.11, 123.46, 124.44, 126.93, 127.87–127.94, 128.66, 129.08, 129.60, 130.13,
130.89, 131.76, 131.81, 143.57, 148.95; MS (EI), m/z: 394, 392 (M?), 282, 281,
252, 250, 178, 177.
Results and discussion
In this study, initially the Fe2? supported on hydroxyapatite-core–shell-c-Fe2O3 NPs
were prepared according to the reported procedures (Scheme 3). Then, they were
fully characterized by TEMSEM, XRD, VSM, and FTIR techniques.
Herein, we wish to report for the condensation of 2-naphthol and various
aromatic aldehydes in the presence of c-Fe2O3–HAp-Fe2? NPs as a green, reusable
and Lewis acid catalyst for the preparation of 14-aryl-14H-dibenzo[a,j]xanthenes
derivatives under solvent-free conditions (Scheme 2).
To optimize the reaction conditions for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthene derivatives, the reaction between 2-naphthol and benzalde-
hyde under solvent-free conditions was selected as a model reaction to provide
compound 3a (Table 4, entry 1). At first, we examined the catalytic activity of
various acids in a model reaction (Table 1). As it can be seen in Table 1, the high
yield and short reaction time of compound 3a was obtained when c-Fe2O3–HAp-
Fe2? was utilized as catalyst (Table 1, entry 6).
In the next step, the model reaction was tested using different amounts of c-
Fe2O3–HAp-Fe2? at the various temperatures. The results are summarized in
Table 2. It can be seen in Table 2 that this reaction was strongly influenced by the
amount of catalyst and temperature. The best results were obtained using 20 mg of
catalyst in 15 min at 90 °C. (Table 2, entry 4). Accordingly, 20 mg of catalyst was
selected for use in these reactions due to its low concentration, which resulted in
excellent yields and short reaction times. Moreover, the product yield was not
changed by increasing the amount of the catalyst and increasing the reaction
123

Fe2? supported on hydroxyapatite-core–shell-c-Fe2O3…
Table 1 Synthesis of compound 3a using different catalysts
Entry
Catalyst
Time (min)
Yield (%)e
1
2
3
4
5
6
a
Citric acida
Silicagel
Cyanuric chorideb
TBBDAc
PBBSd
c-Fe2O3–HAp-Fe2?
90
180
90
55
Not completed reaction
45
65
63
78
120
120
60
5 mol% of citric acid was used
b
c
d
e
5 mol% of cyanuric choride was used
0.25 g of N,N,N0,N0-tetrabromobenzene-1,3-disulfonamide was used
0.25 g of poly(N,N0-dibromo-N-ethyl-benzene-1,3-disulfonamide) was used
Yield of isolated products
Table 2 Optimization of reaction conditions
Entry
Amount of catalyst (mg)
Temperature (°C)
Time (min)
Yield (%)
1
2
3
4
5
6
7
5
10
15
20
20
20
25
90
90
50
35
15
15
15
20
30
51
63
75
95
93
90
85
90
90
100
120
90
temperature. In the next part, using these optimized reaction conditions, other
benzaldehydes (3b–3t) were examined in the presence of c-Fe2O3–HAp-Fe2?NPs.
It was found that all the reactions proceeded smoothly to give the corresponding
14-aryl-14H-dibenzo[a,j]xanthene derivatives in good to excellent yields and short
reaction times (Table 3). The results given in Table 3 show that, in all cases,
aromatic aldehydes containing both electron-donating and electron-withdrawing
groups reacted under solvent-free conditions with 2-naphthol and within a short
reaction time (10–35 min) to generate 14-aryl-14H-dibenzo[a,j]xanthene deriva-
tives with good to excellent yields (81–95 %). Ortho-substituted aromatic
aldehydes, however, did not react as smoothly, likely because of steric hindrance,
and longer reaction times were required to get the corresponding products in good
yields (Table 2, entries 2 and 15–16).
In order to show the merit of the present work, the advantages of c-Fe2O3–HAp-
Fe2?NPs were compared (reaction condition, time and yield) with some homoge-
neous and heterogeneous catalysts for the synthesis of 14-aryl-14H-dibenzo[a,j]xan-
thenes, and the results are presented in Table 4. Based on previous research using
123

H. S. Haeri et al.
Table 3 Synthesis of 14-aryl-14H-dibenzo[a,j]xanthene derivatives promoted by c-Fe2O3–HAp-Fe2?
NPs
Ar
O
OH
γ-Fe2O3@HAP-Fe2+
Ar
H
Solvent-free,
O
90 oC, 10-35 min
Entry
Aldehydes
Producta
Time (min)b
Yield (%)c
M.p./°C
Found
Reported
1
C6H5
3a
3b
3c
3d
3e
3f
15
30
20
10
35
15
15
10
15
15
10
25
20
30
20
20
10
30
30
20
95
81
89
87
94
86
85
92
93
90
95
90
85
95
88
85
90
88
90
86
191–193
309–311
210–212
260–262
294–295
226–228
203–205
285–287
310–312
195–197
230–231
169–171
138–139
193–195
205–206
219–220
87–89
190–191 [51]
310–331 [52]
210–211 [52]
261–263 [52]
295–296 [52]
227–228 [52]
202–203 [52]
287–288 [52]
310–311 [52]
197–198 [53]
232–234 [54]
172–173 [54]
137–138 [54]
194–195 [55]
208 [56]
2
2-NO2C6H4
3-NO2C6H4
3-OCH3C6H4
4-BrC6H4
3
4
5
6
4-CH3C6H4
4-OCH3C6H4
4-ClC6H4
7
3g
3h
3i
8
9
4-NO2C6H4
3-CH3C6H4
4Cl-3NO2C6H3
3-OHC6H4
4-OHC6H4
3-BrC6H4
10
11
12
13
14
15
16
17
18
19
20
a
3j
3k
3l
3m
3n
3o
3p
3q
3r
3s
2-CH3C6H4
2-ClC6H4
221 [56]
2,4-ClC6H3
4-[(CH3)3C]C6H4
4-C6H5C6H4
4-SCH3C6H4
89–90 [57]
303 [58]
301–302
281–283
210–212
285 [59]
3t
213 [59]
Products are characterized by spectral data (1H-NMR, 13C-NMR, and mass spectrometry)
Reactions were run till the completion as indicated by TLC
Yield of isolated products
b
c
M.p. melting point
cellulose sulfuric acid (Table 4, entry 1), Polyvinylpolypyrrolidone-bound boron
trifluoride (PVPP-BF3 ; Table 4, entry 5), zinc oxide NP (Table 4, entry 6), and p-
Toluene sulfunic acid (Table 4, entry 8) for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes derivatives, which requires long reaction time and high
temperature to complete the reaction. In the recent years, Khaksar and et al. reported
the synthesis of xanthene derivatives using Pentafluorophenyl Ammonium Triflate
(Table 4, entry 9). This method requires long reaction time and the use of hazardous
organic solvents such as toluene to complete the reaction. In the 2011, Rahmatpour
and et al. reported using Polystyrene-supported aluminium chloride (Table 4, entry
123

Fe2? supported on hydroxyapatite-core–shell-c-Fe2O3…
Table 4 Comparison of the efficiencies of various catalysts used in the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes
Entry
Catalyst/solvent/temperature
Time (h)
Yield (%)b
Refs.
1
Cellulose sulfuric acid (0.08 g)/solvent-free/110 °C
Amberlyst-15 (1 mmol)/solvent-free/125 °C
Silica sulfuric acid (0.05 g)/solvent-free/80 °C
Yb(OTf)3/[BPy]BF4 (0.01 mmol)/110 °C
PVPP-BF3/solvent-free (0.05 g)/120 °C
ZnO-NPs (0.3 mmol)/solvent-free/150 °C
p-Toluenesulfunic acid (0.1 equiv)/CH2Cl2/reflux
p-Toluenesulfunic acid (0.1 equiv)/solvent-free/125 °C
PFPAT (10 mol%)/toluene/25–30 °C
Poly(AMPS-co-AA) (0.04 g)/solvent-free/110 °C
c-Fe2O3–HAp-Fe2? NPs (20 mg)/solvent-free/90 °C
1.5–3
0.5–2
15–120a
5–7
81–97
80–94
80–96
80–95
92–98
82–92
83–95
80–96
85–97
75–92
81–95
[26]
[28]
[29]
[33]
[57]
[60]
[61]
[61]
[62]
[63]
2
3
4
5
1.5–2
40–80a
15–24
2.5–6
3–5
6
7
8
9
10
11
a
20–30
10–35
c
–
In a minute
b
c
Yield of isolated products
Our manuscript
10) and in the 2005, Khosropour and et al. using p-toluene sulfunic acid (Table 4,
entry 7) for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes derivatives.
This methods requires long reaction times, and requires harsh reaction conditions
like use of reflux conditions and also use hazardous organic solvents such as
dichloromethane. As shown in Table 4, c-Fe2O3–HAp-Fe2? NPs can act as effective
catalyst with respect to reaction times, amount of the catalyst, and yields of the
obtained products. Thus, the present protocol with c-Fe2O3–HAp-Fe2? NPs
catalysts is convincingly superior to the some reported catalytic methods.
The reusability of catalysts is of major importance in green chemistry and also is
of major importance for large scale operations and from an industrial point of view.
Thus, the recovery and reusability of c-Fe2O3–HAp-Fe2? NPs was investigated.
Catalyst reusability was also examined for the preparation of 14-(phenyl)14H-
dibenzo[a,j]xanthenes (3a) from the reaction between 2-naphthol with benzaldehyde
as a model reaction. When the reaction was completed (monitored by TLC),
ethylacetate was added until the solid crude product was dissolved. Then, c-Fe2O3–
HAp-Fe2? NPs as the catalyst were isolated from the reaction mixture by simple
filtration and reused again after washing with ethylacetate. The recovered catalyst
was reused in seven similar subsequent runs. For each of the runs, the product yield
was 95, 95, 93, 91, 91, 90 and 88 %, respectively, which verifies that the activity of
the catalyst remained unchanged throughout these seven runs (Fig. 1).
The suggested mechanism for the c-Fe2O3–HAp-Fe2? NP-catalyzed transforma-
tion is shown in Scheme 4. According to the mechanism, c-Fe2O3–HAp-Fe2? NPs
readily catalyzed the in situ formation of 14-aryl-14H-dibenzo[a,j]xanthenes 9. The
activated aromatic aldehyde 1 reacted with one molecule of 2-naphthol 2 to provide
intermediate 3, which can be regarded as a fast Knoevenagel addition. Then the
123

H. S. Haeri et al.
Fig. 1 Recyclability of the c-
Fe2O3–HAp-Fe2? NPs for the
model reaction after 10 min
H
Ar
H
OH
O
3
Cat.
HO
2
H
Ar
OH
OH
Cat.
OH
4
O
Ar
H
Cat.
1
Ar
H
OH2
Ar
H
Ar
H
Ar
OH
OH
OH
-H2O
6
OH
OH
5
7
Ar
Ar
-H2O
O
OH
OH
8
9
Scheme 4 The plausible mechanism for the condensation reaction of 2-naphthol with aldehydes
catalyzed by the c-Fe2O3–HAp-Fe2? NPs
123

Fe2? supported on hydroxyapatite-core–shell-c-Fe2O3…
active methylene of the second molecule of 2-naphthol reacted with intermediate 3
via conjugate Michael addition to produce the intermediate 7, which underwent
intramolecular cyclodehydration to give the 14-aryl-14H-dibenzo[a,j]xanthenes 9.
Conclusion
We have synthesized Fe2? supported on hydroxyapatite-core–shell-c-Fe2O3 NPs as
a green and non-toxic nanocatalyst, and successfully used the compound as a
catalyst for one-pot condensation of arylaldehydes with 2-naphthol. Some important
advantages of this work are high yield, ease of product isolation, non-use of
hazardous organic solvents, short reaction times, use of various substrates, and ease
of catalyst recovery and reuse, which make it a useful, attractive, and green strategy
for the preparation of xanthene derivatives.
Acknowledgments The authors gratefully acknowledge partial support of this study by the Payame
Noor University (PNU) of Ilam, I.R. Iran.
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