Magnetic nanoparticles tris(hydrogensulfato) boron as an efficient heterogeneous acid catalyst for the synthesis of α,?-benzylidene bis(4-hydroxycoumarin) derivatives under solvent-free condition

Article abstract of DOI:10.1007/s11164-019-03881-6

Nano-ferrite supported tris(hydrogensulfato) boron [Fe₃O₄@B(HSO₄)₃] was prepared by entrapping Fe₃O₄ magnetic nanoparticles as the core and tris(hydrogensulfato) boron B(HSO₄)

Full text of DOI:10.1007/s11164-019-03881-6

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-03881-6
Magnetic nanoparticles tris(hydrogensulfato) boron
as an eꢀcient heterogeneous acid catalyst for the synthesis
of α,ά‑benzylidene bis(4‑hydroxycoumarin) derivatives
under solvent‑free condition
1
2
2
Payam Hayati · Khadijeh Eghbali · Ramin Rezaei
Received: 5 March 2019 / Accepted: 5 June 2019
©
Springer Nature B.V. 2019
Abstract
Nano-ferrite
supported
tris(hydrogensulfato)
boron
[Fe O @B(HSO ) ]
3 4 4 3
was prepared by entrapping Fe O magnetic nanoparticles as the core and
3
4
tris(hydrogensulfato) boron B(HSO ) as the outer shell. This eꢀective and magneti-
4
3
cally recoverable catalyst was employed for the synthesis of α,ά-benzylidene bis(4-
hydroxycoumarin) derivatives through the reaction of an aromatic aldehyde and
4
-hydroxycoumarin under solvent-free conditions. This acid catalyst was character-
ized by Fourier transform infrared spectroscopy, X-ray diꢀraction analysis, scanning
electron microscopy, transmission electron microscopy, thermal gravimetric analy-
sis and diꢀerential scanning calorimetry, energy-dispersive X-ray spectroscopy,
Brunauer–Emmett–Teller analysis, Barret–Joyner–Halenda analysis, vibrating sam-
ple magnetometer and titration.
Keywords Magnetic nanoparticles · Multicomponent reactions · Heterogeneous
catalysts · Biscoumarins · Tris (hydrogensulfato) boron
Introduction
One of the most common practical methods in the chemical industry is a request for
acid catalysts [1]. Homogeneous catalysts have several disadvantages over heteroge-
neous alternatives, such as equipment corrosion, manufacturing of waste, trouble in
separation and recycling, high charge and reduced eꢀectiveness [2]. Polymers [3],
*
Ramin Rezaei
rezaieramin@yahoo.com
1
2
Persian Gulf Science and Technology Park, Nano Gostaran Navabegh Fardaye Dashtestan
Company, Borazjan, Iran
Department of Chemistry, Firoozabad Branch, Islamic Azad University, Firoozabad, Iran
Vol.:(012
1
3456789)
3

P. Hayati et al.
mesoporous components [4], metal oxides [5] and nanoparticles [6] are generally
applied as support for the more simplistic heterogeneous catalytic synthesis.
Magnetite Fe O nanoparticles have now attracted wide consideration in the
3
4
ꢁ
eld of biology, medicine, electronics, and catalytic processes [7]. The high sur-
face concentrations of hydroxyl groups on the Fe O nanoparticles have led to large
3
4
increases in hydrophilic nature of these nanoparticles [8, 9]. The excellent capac-
ity and stability of the core/shell nanostructure (CSNs) could be related to both the
core and the shell framework. This composite system includes the beneꢁts of both
the core and the shell leading to improvement of physical and chemical properties.
A few synthetic methods for providing various classes of CSNs, including the Stö-
ber technique, solvothermal method and one-pot synthetic method concerning sur-
factants have already been described [10]. There were numerous eꢀorts to stabilized
Fe O nanoparticles whose surfaces have been coated with organic and inorganic
3
4
compounds. Magnetic nanoparticles that could be magnetized in the current pres-
ence of an external magnet have been properly used as catalysts in a number of dif-
ferent organic and inorganic reactions due to the high surface-to-volume ratio of
nanomaterial and imply that the large ratio of atoms is oꢀered at the surface. In
addition, the ꢁrst and most important advantages of these catalysts based on the kind
of reaction are revealed to be eꢀective, the other is to maintain their catalytic activ-
ity. Therefore, these magnetic catalysts are eꢂciently applied as catalytic systems in
lots of chemical reactions [11–16].
Boric acid is commonly used for the production of monoꢁlament ꢁberglass [17],
ꢁ
re retarding agenst of wood by impregnation [18], neutralizing active hydroꢃuo-
ric acid (HF) [19], combined with borax [20] and silicone oil [21] for industrial
applications.
Following Kiasat’s report on the planning of tris(hydrogensulfato) boron [22],
many advantages such as low price, non-toxicity and adaptation to the environment
in particular are reported for this compound. The reason for these features is dual
Lewis- Bronsted acidic sites. Because of these properties, attention has been sig-
niꢁcantly focused on catalytic applications of tris(hydrogensulfato) boron in catalyz-
ing some organic reactions [23–28]. Additionally, silica boron–sulfuric acid nano-
particles have been organized as a heterogeneous catalyst in the Ritter reaction and
the synthesis of amide derivatives [29]. Synthesis of nano-Fe O @SiO -supported
3
4
2
boron sulfonic acid and its application as heterogeneous catalyst for the synthesis of
pyrano coumarins was reported by Farahi et al. [30].
During previous decades, the synthesis of coumarin derivatives was an essential
ꢁ
eld for investigation of biological properties such as anti-HIV, antibiotic, antifun-
gal, antibacterial, antioxidant, anticancer and anticoagulants [31–33]. Furthermore,
these compounds found a number of applications such as ꢃuorescent brighten-
ers, eꢀective laser dyes, and as additives in food and cosmetics [34–36]. Amongst
numerous well-known derivatives of coumarin, biscoumarins are signiꢁcantly of
more interest. Pechmann, Perkin, Knoevenagel, Reformatsky, and Wittig reactions
are the most important synthetic methods for preparation of biscoumarins. The gen-
erally applied method which has been used for preparation of biscoumarin deriva-
tives is the Knoevenagel reaction of two equivalents of 4-hydroxycoumarin and
various aldehydes in the presence of diꢀerent catalysts like molecular iodine [37],
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
[
bmim][BF ] [38], TBAB [39], SDS [40], sulfated titania [41], SO H functionalized
4 3
ionic liquids [42], [P VPy BuSO H]HSO [43], silica-supported preyssler nanopar-
4
3
4
ticles [44], magnetite-containing sulfonated polyacrylamide [45], CuO–CeO nano-
2
0
composite [46], Montmorillonite K10·Ni -Mont [47], B(OSO H) [25], etc.
3
3
According to previous research [48, 49], a novel, active, recyclable, and mag-
netically recoverable heterogeneous catalyst is reported in this paper. The aims of
this research include obtaining the smallest particle size, reduction in the number
of catalyst preparation steps and morphological control for increasing reaction
which makes the obtained results to be comparable with other reported methods
[
[
29, 30]. Additionally, the preparation of magnetic tris (hydrogensulfato) boron
Fe O @B(HSO ) ] that has been used as an eꢀective catalyst for the synthesis of
3
4
4 3
biscoumarin derivatives is also reported in this paper
Experimental
Materials and methods
Laboratory chemicals were either prepared in our laboratory or were purchased from
Merck and Fluka. Melting points were determined in open capillaries with IA 9100
−
1
1
Series Digital Melting Point apparatus. IR spectra were obtained at 4000–400 cm
with KBr pressed powder discs using a 4300 Shimadzu FT-IR spectrometer. H
1
3
and C NMR spectra were recorded in CDCl as solvent using a Bruker Avance
3
4
00 MHz spectrometer. The crystal structure of the resulting powder was examined
by powder X-ray diꢀraction (XRD; Bruker D8 Advance TXS) using Cu Kα radi-
ation. Scanning electron microscopy (SEM) was performed on a MIRA III SEM,
Czech Republic, operated at a 15 kV accelerating voltage. We performed a trans-
mission-electron-microscopy (TEM) study on a JEOL, JEM-2100F transmission
electron microscope at an accelerating voltage of 200 kV. The Barret–Joyner–Halen-
der (BJH) speciꢁc surface areas were measured by nitrogen adsorption–desorption
at—77 K using a Belsorp mini II apparatus. The BJH method was used to deter-
mine the pore size distribution. The thermal properties of Fe O , B(HSO ) and
3
4
4 3
Fe O @B(HSO ) were further evaluated with TGA and DSC using a TG thermo-
3
4
4 3
−
1
analyser (TGA, Mettler system TA 4000) in N at a heating rate of 10 °C min .
2
EDX spectra were measured with a Bruker XFlash 6130 for analyzing phase compo-
sition and elemental distribution maps of the compounds.
Preparation of magnetic Fe O nanoparticles
3
4
Coprecipitation technique with small changes was used for preparation of mag-
netic Fe O nanoparticles. First, FeCl .4H O (2.00 g, 10.0 mmol) and FeCl .6H O
3
4
2
2
3
2
(
5.40 g, 20.0 mmol) were dissolved in 2 M hydrochloric acid solutions (25.0 mL).
Then under mechanical stirring, ammonia solution (30.0 mL, 25.0%) was added to
the FeCl /FeCl mixture. After~30 min of intense stirring, the resulting black pre-
2
3
cipitate was easily isolated by a magnetic ꢁeld and thoroughly washed with 2.0 M
1
3

P. Hayati et al.
hydrochloric acid and deionized water, respectively, and ꢁnally was ball milled
for~1 h at room temperature.
Preparation of tris(hydrogensulfato)boron B(HSO4)3
A 250 mL suction ꢃask charged with boric acid (1.55 g, 25.0 mmol) was equipped
with a gas inlet tube for conducting HCl gas over an adsorbing solution, i.e., water.
Chlorosulfonic acid (8.74 g,~5.0 mL,~75.0 mmol) was added in small portions
over a period of 30 min at 0 °C. HCl evolved from the reaction vessel immediately.
After completion of the addition, the mixture was shaken for 1 h, while the residual
HCl was eliminated by suction. Then the mixture was washed with diethyl ether to
remove the unreacted chlorosulfonic acid, giving a grayish solid material in 90%
yield (~6.8 g).
Preparation of Fe O @B(HSO ) nanoparticles
3
4
4 3
The 0.10 g (0.43 mmol) Fe O NPs and 0.10 g PVP were dispersed in a mixture
3
4
of methanol and deionized water, (10 mL 1:1), under continuous mechanical stir-
ring, and B(HSO ) nanoparticles (0.40 g, 1.32 mmol) were added to the reaction
4
3
mixture over a period of~30 min at room temperature. The mixture was stirred at
8
0 °C for~24 h. The separated powder was cooled down to room temperature, and
was washed with deionized water and absolute ethanol and dried at 60 °C overnight.
Afterward, it was calcinated in an oven furnace at 600 °C for 2 h with a heating rate
−1
of 4 °C min .
Titration of Fe O @B(HSO ) nanoparticles
3
4
4 3
Dry Fe O @B(HSO ) (0.10 g) was added to distilled water (10.0 mL) and the
3
4
4 3
resulting mixture was stirred for 24 h and then titrated with aqueous solution of
NaOH (0.10 M) as titrant and phenolphthalein as an indicator. The acidic sites load-
ing in Fe O @B(HSO ) was found to be 3.50 mmol/g.
3
4
4 3
General procedure for the preparation of biscoumarin derivatives
A mixture of 4-hydroxycoumarin (0.32 g, 2.0 mmol), aldehyde (1.0 mmol),
Fe O @B(HSO ) (0.1 g, 0.03 mol %) were mixed completely and heated in an oil
3
4
4 3
bath at 80 °C for the appropriate time as mentioned in Table 4. Following comple-
tion of the reaction as monitored by TLC, ethyl acetate (10.0 mL) was added to the
mixture, and the catalyst was separated from the reaction medium by using a magnet
−
2
(
2×10 T). The organic layer was separated, concentrated, dried over anhydrous
sodium sulfate and evaporated. A pure product was obtained through crystallization
using ethanol as solvent. The biscoumarin derivatives are characterized by compari-
son of their physical and spectral data to those reported in the literature.
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
General procedure for recycling of Fe O @B(HSO ) nanoparticles
3
4
4 3
The catalytic recyclability of Fe O @B(HSO ) was done by adding ethanol
3
4
4 3
(
2×15 mL) to remove the organic compounds and dried in an oven at 80 °C for 3 h.
The results show that the catalyst is magnetically recoverable and this process was
repeated four times without any signiꢁcant loss of activity.
Spectral analysis of compounds (3a–i)
3
2
7
,3′‑(Phenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (3a) White crystals; mp:
−
1
22–224 °C (lit.: 228–230 °C) [37].; FT-IR: υ (cm ) 3428, 3035, 1665, 1608,
1
64; H NMR: δ (ppm) 6.50 (s, 1H, CH), 7.25–8.26 (m, 13H, ArH); 11.33 (s, 1H,
1
3
OH), 11.60 (s, 1H, OH); C NMR: δ (ppm) 37.14, 103.28, 106.64, 116.40, 116.75,
1
24.35, 124.93, 126.85, 128.70, 132.58, 136.22, 153.17, 164.50, 166.02; Anal.
Calcd for C H O (411.78): C, 72.81; H, 3.91. Found: C, 72.65; H, 3.83.
2
5
16
6
3
,3′‑(2‑Hydroxyphenylmethylene)‑bis(4‑hydroxy‑2H‑chromen2‑one)
(3b) Yellow
−
1
crystals; mp: 240–242 °C (lit.: 254–256 °C) [37].; FT-IR: υ (cm ) 3353, 3045,
1
1
8
1
710, 1625, 760; H NMR: δ (ppm) 6.43 (s, 1H, CH), 7.15–8.15 (m, 12H, ArH);
1
3
.65 (s, 1H, OH), 11.60 (s, 1H, OH); C NMR: δ (ppm) 34.3, 102.89, 116.75,
24.33, 125.15, 128.22, 129.55, 131.15, 133.28, 150.85; Anal. Calcd for C H O
7
2
5
16
(
428.78): C, 70.09; H, 3.76. Found: C, 70.65; H, 3.85.
3
,3′‑(3‑Nitrophenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (3c) Yellow crys-
−
1
tals; mp: 126–128 °C (lit.: 120–124 °C) [37].; FT-IR: υ (cm ) 3424, 2928, 1658,
1
1
1
1
3
589, 1333, 765; H NMR: δ (ppm) 6.15 (s, 1H, CH), 7.23–8.18 (m, 12H, ArH);
1
3
1.58 (s, 2H, OH), C NMR: δ (ppm) 34.55, 102.88, 116.8, 124.77, 125.53, 127.9,
29.5, 131.9, 134.25, 149.86; Anal. Calcd for C H NO (456.78): C, 65.65; H,
2
5
15
8
.31; N, 3.06. Found: C, 65.70; H, 3.33, N, 3.15.
3
,3′‑(4‑Methoxyphenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one)
(3d) White
−
1
crystals, mp: 240–242 °C (lit.: 247–249 °C) [47].; FT-IR: υ (cm ): 3380, 3033,
1
1
665, 1602, 1256, 1050, 767; H NMR: δ (ppm) 3.70 (s, 3H, OCH ), 6.48 (s, 1H,
3
1
3
CH), 7.15–8.18 (m, 12H, ArH), 11.35 (s, 1H, OH), 11.50 (s, 1H, OH); C NMR:
δ (ppm) 32.12, 110.53, 116.3, 116.7, 120.92, 123.62, 124.1, 124.86, 128.12, 128.8,
1
7
34.52, 153.18, 156.52, 163.33, 165.21; Anal. Calcd for C H O (443.56): C,
26 18 7
0.58; H, 4.10. Found: C, 70.78; H, 3.93.
3
,3′‑(4‑Hydroxyphenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (3e) White crys-
−
1
tals, mp: 218–220 °C (lit.: 222–225 °C) [47].; FT-IR: υ (cm ): 3345, 3044, 1668,
1
1
1
1
610, 760, H NMR: δ (ppm) 6.46 (s, 1H, CH), 7.17–8.15 (m, 12H, ArH), 9.80 (s,
1
3
H, OH), 11.35 (s, 1H, OH), 11.67 (s, 1H, OH); C NMR: δ (ppm) 36.40, 103.15,
15.50, 116.85, 123.10, 126.59, 127.75, 151.85, 154.39, 164.52; Anal. Calcd for
C H O (429.82): C, 70.09; H, 3.76. Found: C, 70.62; H, 4.06.
2
5
16
7
1
3

P. Hayati et al.
3
,3′‑(4‑Nitrophenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (3f) Yellow crys-
−
1
tals, mp: 238–240 °C (lit.: 232–234 °C) [47].; FT-IR: υ (cm ): 3452, 3037, 1650,
1
1
615, 1346, 1085, 760; H NMR: δ (ppm) 6.60 (s, 1H, CH), 7.43–8.35 (m, 12H,
1
3
ArH); 11.45 (s, 1H, OH), 11.55 (s, 1H, OH); C NMR: δ (ppm) 35.2, 103.52,
1
05.12, 116.86, 117.13, 121.16, 122.15, 124.63, 125.87, 130.15, 132.5, 134.38,
37.44, 147.72, 151.2, 163.54, 166.32, 166.9; Anal. Calcd for C H NO (458.43):
1
2
5
15
8
C, 65.65; H, 3.31; N, 3.06. Found: C, 65.77; H, 3.30; N, 2.88.
3
,3′‑(4‑Chlorophenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one)
(3g) White
−
1
crystals, mp: 246–248 °C (lit.: 255–257 °C) [47].; FT-IR: υ (cm ): 3422, 3035,
1
2
710, 1678, 1610, 1555, 1474, 1354, 1097, 765; H NMR: δ (ppm) 6.40 (s, 1H,
1
3
CH), 7.35–8.44 (m, 12H, ArH); 11.35 (s, 1H, OH), 11.50 (s, 1H, OH); C NMR: δ
(
ppm) 34.8, 104.39, 106.28, 117.5, 124.33, 125.18, 127.0, 128.82, 133.52, 134.12,
1
3
34.8, 153.44, 164.73, 165.9; Anal. Calcd for C H ClO (445.68): C, 67.20; H,
25 15 6
.38. Found: C, 67.10; H, 3.30.
3
,3′‑(3‑phenylprop‑2‑ene‑1,1‑diyl)bis(4‑hydroxy‑2H‑chromen‑2‑one)
(3h) Yellow
−
1
crystals, mp: 235–237 °C (lit.: 230–232 °C) [37].; FT-IR: υ (cm ): 3320, 3025,
1
1
728, 1670, 1616, 760; H NMR: δ (ppm) 6.55 (s, 1H, CH), 6.68 (d, J=15.1 Hz,
H, CH=), 6.75 (d, J=15.1 Hz, 1H, CH=), 7.10–8.15 (m, 12H, ArH); 11.40 (s, 1H,
1
1
3
OH), 11.55 (s, 1H, OH); C NMR: δ (ppm) 19.52, 94.17, 118.33, 123.85, 125.39,
1
26.2, 128.0, 128.51, 129.0, 129.47, 131.76, 138.24, 154.39, 164.48, 165.83; Anal.
Calcd for C H O (437.55): C, 73.97; H, 4.14. Found: C, 73.88; H, 4.05.
2
7
18
6
3
,3′‑(furan‑2‑ylmethylene)bis(4‑hydroxy‑2H‑chromen‑2‑one) (3i) Black amorphous
−
1
solid, mp: 194–196 °C (lit.: 202 °C) [37].; FT-IR: υ (cm ): 3033, 1656, 1608, 1330,
1
7
8
1
65; H NMR: δ (ppm) 6.0 (s, 1H, CH), 6.30–6.59 (m, 3H, ArH), 7.32–8.35 (m,
1
3
H, ArH); C NMR: δ (ppm) 22.16, 102.57, 107.28, 112.41, 116.8, 124.95, 125.46,
26.9, 128.81, 144.61, 153.19, 153.73, 163.38, 165.57; Anal. Calcd for C H O
7
2
3
14
(
402.42): C, 68.66; H, 3.51. Found: C, 68.44; H, 3.46.
Results and Discussion
The magnetite nanoparticles were ꢁrst synthesized by the co-precipitation
2
+
3+
of Fe and Fe in ammonia solution according to reported procedure [50].
Tris(hydrogensulfato)boron was prepared by addition of chlorosulfonic acid to boric
acid [22].Finally, magnetic‐nanoparticle‐supported tris(hydrogensulfato)boron was
synthesized from the reaction of Fe O with tris(hydrogensulfato)boron (Scheme 1).
3
4
Characterization of Fe O @B(HSO )
4 3
3
4
Measurement of the acidic sites of Fe O @B(HSO ) was determined by the
3
4
4 3
titration method. Based on comparison of titration curves of B(HSO ) and
4
3
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
Scheme 1 Schematic representation of Fe O @B(HSO ) based on core/shell nanostructure
3
4
4 3
Fe O @B(HSO ) it was found that both curves have the same pattern and this
3
4
4 3
reꢃects that B(HSO ) is part of the catalyst structure (Figs. 1, 2).
4
3
The results of FT-IR spectra of Fe O , B(HSO ) , and Fe O @B(HSO ) demon-
3
4
4 3
3
4
4 3
strate the presence of diꢀerent chemical bonds and functional groups in the structure
of the Fe O @B(HSO ) compound (Fig. 3). The IR spectral data of Fe O display
3
4
4 3
3
4
1
1
1
4
2
0
8
6
4
2
0
Titraꢀon
First derivaꢀve
0
5
10
15
20
25
Volume of NaOH (mL)
Fig. 1 Titration and its ꢁrst derivative curves of the B(HSO ) with NaOH
4
3
1
3

P. Hayati et al.
Fig. 2 Titration and its ꢁrst
14
12
derivative curves of the
Fe O @B(HSO ) with NaOH
3
4
4 3
1
0
8
6
4
2
0
Titraꢀon
First derivaꢀve
0
5
10
15
20
25
Volume of NaOH (mL)
Fig. 3 FT-IR spectra of a Fe O , b B(HSO ) and c Fe O @B(HSO )
4 3
3
4
4 3
3
4
−1
two characteristic peaks at~452 and~875 cm , which are a result of Fe–O stretch-
−
1
ing vibrations (Fig. 3a) [51]. The peak located at~1464 cm is in agreement with
B–O bands (Fig. 3b) [51]. Furthermore, the symmetric stretching of the O=S=O
−1
fragment has been observed at~1193 cm (Fig. 3b) [52]. Also, in the IR spec-
trum of Fe O @B(HSO ) the appearance of peaks at 458 and 547, related to Fe–O
3
4
4 3
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
stretching vibrations, and shows that Fe O nanoparticles were bonded to B(HSO ) .
3
4
4 3
−
1
Eventually, the appearance of peaks at 1165, and 1632 cm can be attributed to
B–O and symmetric stretching of the O=S=O, respectively. The appearance of
−1
peaks around 3229 and 3415 cm can be assigned to the sulfonic group of the cata-
lytic surface (Fig. 3c) [31].
The crystalline phases of Fe O , B(HSO ) and Fe O @B(HSO ) were inves-
3
4
4 3
3
4
4 3
tigated by XRD. All reꢃection peaks can be readily indexed to pure cell param-
eters a=2.7992(3) Å, b=9.4097(15) Å, and c=9.4832(9) Å at 23.96 GPa and
3
+
2+
8
23 K (ICDD: 190629). Fe occupies an octahedral site and Fe is in an eight-
fold-coordinated site described as a bicapped trigonal prism. The XRD pattern
of Fe O nanoparticles (Fig. 4a) showed the peaks at 2θ=17.70°, 29.0°, 31.95°,
3
4
3
5.50°, 43.20°, 45.10°, 53.85°, 57.05°, 63.30°, and 75.30° that could be assigned
to 110, 220, 311, 222, 400, 110, 422, 511, 440, and 620 planes of Fe O , respec-
3
4
tively [53–55]. It can be seen in Fig. 4b that B(HSO ) presented the very strong
4
3
diꢀraction peak at 2θ=27.95. The characteristic diꢀraction peak of B(HSO ) is
4
3
associated with B(OH) with the pdf code (01-073-2158) [56]. The diꢀraction lines
3
of Fe O @B(HSO ) (Fig. 4c) correspond to the Fe O nanoparticles based on the
3
4
4 3
3
4
characteristic 2Ɵ peaks at about 30.5, 34.50, 43.35, 57.60, and 61.50. Additionally,
there was a peak at 2θ=27.7 due to the B(HSO ) shells of the coated Fe O .
4
3
3
4
The SEM images of Fe O , B(HSO ) , and Fe O @B(HSO ) NPs showed that
3
4
4 3
3
4
4 3
the samples have spherical-like particles. There is a tendency to form small groups
of particles due to weak forces (hydrogen bonding) between the Fe O @B(HSO )
3
4
4 3
NPs (Fig. 5) [57]. This leads to a clustering tendency and produces a monodispersed
structure of these magnetic nanoparticles.
Additionally the results of TEM imaging conꢁrmed this observation (Fig. 6a).
Based on Fig. 6b the average diameter identiꢁed from TEM images is 36 nm. It also
shows that the maximum particle size distribution was in the range of 30–48 nm.
In order to show the thermodynamic behavior of the Fe O , B(HSO ) and
3
4
4 3
Fe O @B(HSO ) , TGA and DSC have been done (Fig. 7). The uncoated Fe O
3
4
4 3
3
4
NPs exhibits a rapid weight loss about 4% from~50 to~300 °C due to elimina-
tion of adsorbed physical and chemical water. Another weight loss was seen around
8
00 °C which corresponds to decomposition of residual chemical compounds
(
Fig. 7a). TGA analysis of B(HSO ) demonstrated 40.0% weight loss between~50
4 3
and ~200 °C is due to the dehydration of B(HSO ) that is similar to boric acid
4
3
(
H BO ) [58]. In addition, a decrease in the weight percentage of B(HSO ) at
3
3
4
3
temperatures up to~875 °C is associated with the decomposition of sulfuric acid
and oxidation of boron atoms (Fig. 7b). TGA and DSC of the Fe O @B(HSO ) is
3
4
4 3
shown in Fig. 7c. The ꢁrst stage of weight loss between~25 and~100 °C is related
to removal of physically adsorbed water. There is another weight loss between~180
and~400 °C that could be attributed to the thermal crystal phase transformations of
Fe O to Fe O [45]. Based on thermal performance of the catalyst, decreases in the
3
4
2
3
weight percentage of the catalyst at temperatures up to~650 °C is related to decom-
position of sulfuric acid and oxidation of boron atoms [29].
The elemental composition of Fe O , B(HSO ) and Fe O @B(HSO ) was
3
4
4 3
3
4
4 3
obtained by using EDX analysis and the presence of Fe, O, B and S were conꢁrmed
by comparing between EDX spectra of that uncoated with Fe O , B(HSO ) and
3
4
4 3
1
3

P. Hayati et al.
Fig. 4 Powder XRD pattern of a Fe O , b B(HSO ) and c nano-Fe O @B(HSO )
4 3
3
4
4 3
3
4
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
Fig. 5 SEM photographs of a Fe O , b B(HSO ) , and c Fe O @B(HSO )
4 3
3
4
4 3
3
4
Fe O @B(HSO ) , although there were low amounts of sodium (a peak around
3
4
4 3
1
keV) and chlorine impurities (Fig. 8a, c), but the EDX analysis after four runs
showed that these impurities have been eliminated (Fig. 13). It should be noted that
the failure to detect the boron peak in Fig. 8c is due to the overlap between peaks of
boron and other elements [30].
In addition, elemental mapping has been done on Fe O @B(HSO ) to obtain the
3
4
4 3
exact information about distribution of Fe, O, S and B elements. Results and obser-
vations regarding patterns by the elemental mappings shows the uniform distribu-
tion of Fe, O, S, B and proves the homogeneity of B(HSO ) on the Fe O (Fig. 9).
4
3
3
4
Based on the N adsorption/desorption isotherm of Fe O @B(HSO ) , it is clear
2
3
4
4 3
that this isotherm could be classiꢁed as a type-IV of classical isotherms and displays
a hysteresis loop at large relatively pressures in the range of 0.64–0.98 P/Po [59],
which is belonging to the H3 type [60]. Fe O @B(HSO ) nanostructures show a
3
4
4 3
sharp peak at 9.23 nm indicating mesoporous characteristics (Fig. 10).
1
3

P. Hayati et al.
Fig. 6 TEM image of a Fe O @B(HSO ) , and b size distributions of Fe O @B(HSO )
4 3
3
4
4 3
3
4
By using BET and BJH methods, surface area, pore volume, and pore size of
Fe O @B(HSO ) were obtained and reported in Table 1.
3
4
4 3
To study the role of the B(HSO ) shell on the magnetic properties of this com-
4
3
pound, measurements were carried out in a vibrating sample magnetometer (VSM)
(
(
Fig. 11). The saturation magnetization of the Fe O @B(HSO ) (~0.47 emu/g)
3 4 4 3
Fig. 11b) was less than Fe O nanoparticles (~29.42 emu/g) (Fig. 11a) because
3
4
there is interaction between B(HSO ) and Fe O nanoparticles. This fact reveals a
4
3
3
4
small coactivity with narrow hysteresis due to the soft magnetic properties for this
nanostructure. These results are coming from the small particle size of Fe O nano-
3
4
particles and cause an inverse correlation between coercivity and particle size [61].
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
Fig. 7 TGA and DSC curves of a Fe O , b B(HSO ) and c Fe O @B(HSO )
4 3
3
4
4 3
3
4
1
3

P. Hayati et al.
Fig. 7 (continued)
These observations conꢁrm that the tris(hydrogensulfato) boron groups have func-
tionalized the surface of the magnetite nanoparticles.
Catalytic performance of Fe O @B(HSO ) in multicomponent one‑pot synthesis
3
4
4 3
of dihydropyrimidinones
After synthesis of Fe O @B(HSO ) , we investigate catalytic application of
3
4
4 3
Fe O @B(HSO ) as a magnetically heterogeneous nanocatalysts for the synthe-
3
4
4 3
sis of α,ά-benzylidene bis(4-hydroxycoumarin) by carrying out the reaction with a
1
:2 mol ratio of aldehyde and 4-hydroxycoumarin (Scheme 2).
In order to develop the reaction conditions and evaluation of catalytic perfor-
mance of Fe O @B(HSO ) , optimization reports could be carried out using the
3
4
4 3
reaction of benzaldehyde and 4-hydroxycoumarin as a reaction model and the reac-
tion conditions, including the amount of the catalyst, solvent, and reaction tempera-
ture result in quantifying the temperature and reaction time eꢀects. Highlighting the
usefulness and eꢂciency of Fe O @B(HSO ) it was examined in the absence of
3
4
4 3
catalyst. It was found that in the absence of Fe O @B(HSO ) only 15% yield of
3
4
4 3
the product was obtained even after heating at 80 °C for 120 min (Table 2, entry
1
). Optimization of the amount of catalyst was achieved by varying the amount
of catalyst (0.01, 0.03, and 0.05 wt%). The percentage of the product formation
using Fe O @B(HSO ) as the catalyst was found 55, 90 and 90%, respectively
3
4
4 3
(
Table 2, entries 2–4). It should be added that the reaction did not proceed at room
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
Fig. 8 EDX spectrum of a Fe O , b B(HSO ) and c Fe O @B(HSO )
4 3
3
4
4 3
3
4
temperature (Table 2, entry 5). The reaction temperature was also optimized. Below
8
0 °C, the reaction proceeded slowly giving a relatively low yield and no signiꢁcant
improvement was observed above 80 °C (Table 2, entries 6–7). In order to investi-
gate the eꢀect of solvent on the catalytic reaction, the reaction model in the presence
of 0.03 wt% Fe O @B(HSO ) was carried out in various solvents under reꢃux con-
3
4
4 3
ditions. The results show that in the presence of solvents, the reaction was sluggish
and H O is the best solvent in terms of both time and yield (Table 2, entries 8–11).
2
1
3

P. Hayati et al.
Fe Ka
O Ka
S Ka
B Ka
Fig. 9 Mapping analysis of Fe O @B(HSO ) nanostructures
3
4
4 3
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
Fig. 10 N adsorption–desorption isotherms (inset) with a corresponding BJH pore-size distribution
2
curve, the pore-size distribution was calculated from the desorption branch of the isotherm
Table 1 Surface data of Fe O @B(HSO )
4 3
3
4
BET surface area (m g−1)
2
Pore diameter (cm g−1)
3
Pore volume (nm)
29.143
Sample
SMF/Fe O nanospheres
1.055
0.0076
3
4
Fig. 11 Magnetization curves for a Fe O , and b Fe O @B(HSO )
4 3
3
4
3
4
Therefore, it was found that the best reaction conditions for the model reaction were
speciꢁed to be 1 mmol aldehyde, 2 mmol 4‐hydroxycoumarin, and 0.1 g (0.03 wt%)
of the Fe O @B(HSO ) catalyst under solvent-free conditions at 80 °C as revealed
3
4
4 3
in Table 2.
1
3

P. Hayati et al.
Scheme 2 Synthesis of biscoumarin derivatives catalyzed by Fe O @B(HSO )
4 3
3
4
Table 2 Eꢀect of diꢀerent
Condition/solvent Time (min) Yield (%)a
Entry Amount
of catalyst
amounts of Fe O @B(HSO )
4 3
3
4
and solvents for synthesis of
(
wt%)
biscoumarin derivativesa
1
2
3
4
5
6
7
8
9
1
1
–
80 °C/solvent-free 120
15
55
90
90
15
92
95
80
75
55
50
0.01
0.03
0.05
0.03
0.03
0.03
0.03
0.03
0.03
0.03
80 °C/solvent-free
80 °C/solvent-free
80 °C/solvent-free
r.t./solvent-free
60
15
15
180
100 °C/solvent-free 15
120 °C/solvent-free 15
Reꢃux/water
Reꢃux/ethanol
60
60
0
1
Reꢃux/chloroform 120
Reꢃux/toluene 120
Reactions carried out at 10 mmol scale with molar ratio of
benzaldehyde:4-hydroxycoumarin:1:2
a
Isolated yield
Table 3 Comparison of one-pot
synthesis of biscoumarin 3a
with Fe O @B(HSO ) , Fe O
Yield (%)a
Entry
Catalyst (0.03 wt%)
Fe O @B(HSO )
Time (min)
3
4
4 3
3
4
1
2
3
15
20
25
90
80
83
3
4
4
4 3
and B(HSO )
4
3
Fe O
3
B(HSO4)3
Reaction conditions aldehyde (1 mmol); 4-hydroxycoumarin
(
2 mmol); solvent-free; 80 °C
Isolated yield
a
Catalytic eꢂciency of the Fe O @B(HSO ) , Fe O , and B(HSO ) for the reac-
3
4
4 3
3
4
4 3
tion model was evaluated and comparative data are presented in Table 3. It can be
seen that Fe O @B(HSO ) was found to be superior in terms of yield and time of
3
4
4 3
reaction. Fe O and B(HSO ) compared to Fe O @B(HSO ) gave slightly lower
3
4
4 3
3
4
4 3
yields and reaction times were longer. Thus, we can conclude that Fe O acts not
3
4
only as a support, but also it shows good catalytic activity.
The general scope and acceptability of this method have been investigated
by the structural variations of simple and readily available aldehydes including
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
Table 4 Synthesis of
Product Time (min) Yield (%)a Mp (°C)
Entry
R
biscoumarin derivatives
catalyzed by Fe O @B(HSO )
4 3
3
4
1
2
3
4
5
6
7
8
9
C H
2-HOC H
3-NO C H
3a
3b
3c
15
15
20
10
15
15
15
30
30
60
90
80
85
90
80
85
80
80
80
–
222–224
240–242
126–128
234–236
220–222
238–240
246–248
235–237
194–196
–
6
5
6
4
2
6
4
4-CH OC H 3d
3
6
4
4-HOC H
4-NO C H
4-ClC H
3e
3f
3 g
6
4
2
6
4
6
4
Ph–CH=CH 3 h
2-Furyl
CH(CH3)3
3i
3j
1
0
Reaction conditions aldehyde (1 mmol); 4-hydroxycoumarin
(
2 mmol); Fe O @B(HSO ) ; (0.03 wt%); solvent-free; 80 °C
Isolated yields
3
4
4 3
a
aromatic, heteroaromatic and aliphatic aldehydes. It has been observed that
aldehydes containing OH lead to a faster reaction rate that could be due to the
hydrogen bonding of aldehyde with the catalyst (Table 4, entries 2 and 5). The
reaction has been performed faster with aldehyde containing OCH group and
3
required less time to give the resulting products (Table 4, entry 4). This catalyst
has worked well with aldehydes bearing sensitive functional groups like NO , Cl
2
and CH=CH to provide the related products without leading to any side products
formation (Table 4, entries 3, 6, 7 and 8). The 2-Furfural as a heteroaromatic
aldehyde has been provided as the resultant product with moderate yield (Table 4,
entry 9). However, all aromatic aldehydes and heteroaromatic aldehyde have
been prepared with the same reactivity and biscoumarin derivatives (entries 1–9,
Table 4) but in case of aliphatic aldehydes, reactions have not been done under
solvent-free conditions because of low boiling point of the aldehydes (Table 4,
entry 10).
The acceptable mechanism for the preparation of biscoumarins using
Fe O @B(HSO ) is shown in Scheme 3. As regards this, the heterogeneous cata-
3
4
4 3
lyst acts with both Lewis and Bronsted acid sites, but the main factor of acidity is
due to the presence of hydroxyl groups of HSO which is attached to the B atom.
4
In addition, acidity enhancement of catalyst is possible by the activated Lewis acid
sites due to a –I eꢀect by attaching HSO to B atoms. According to Banerji’s sug-
4
gestion [41] the acidic nature of a catalyst may simplify carbonyl group activation of
aldehyde to give complex I and thus an electron-withdrawing carbonyl group can be
increased by employing catalyst. The nucleophilic addition of 4-hydroxycoumarin to
I leads to make II. Subsequently, the removal of H O from II leads to the produc-
2
tion of (intermediate) III which can be more activated by catalyst. Then, addition
of 4-hydroxycoumarin to the activated intermediate III, leads to the production of
biscoumarin, by the Michael addition method.
Our results were compared to other results which are previously reported for the
preparation of biscoumarin derivatives (Table 5).
1
3

P. Hayati et al.
Scheme 3 Proposed mechanism for the synthesis of biscoumarins catalyzed by Fe O @B(HSO )
4 3
3
4
Furthermore, we evaluated separation and recycling of the Fe O @B(HSO )
4 3
3
4
NPs catalyst which were mentioned in the “General procedure for recycling of
Fe O @B(HSO ) nanoparticles” section. On the basis of the results of reuse of cat-
3
4
4 3
alyst it was shown that the catalyst can be used four times without signiꢁcant loss of
its catalytic activity (Fig. 12).
In order to investigate the recycling and reusability of the Fe O @B(HSO ) , the
3
4
4 3
EDX analysis after four runs showed the presence of sulfur and leaching of sulfur
has not occurred (Fig. 13).
Conclusions
In summary, a facile procedure for the synthesis of a Fe O @B(HSO ) as a het-
3
4
4 3
erogeneous powerful solid acid catalyst which is mediated by solvent-free one-pot
synthesis of biscoumarin derivatives is reported in this paper. Tris (hydrogensulfato)
boron groups are conveniently loaded on magnetic particles. Magnetic evaluation
of Fe O @B(HSO ) illustrated the paramagnetic properties of these particles. The
3
4
4 3
separation procedure of this acid magnetic catalyst is performed by the application
of an external magnetic source. This method oꢀers considerable advantages includ-
ing reusability of the catalyst for several times without signiꢁcant loss in the yield
of the reaction, short reaction time, low cost, cleaner reaction proꢁle and ease of
1
3

Magnetic nanoparticles tris(hydrogensulfato) boron as an…
Table 5 Comparison results of Fe O @B(HSO ) with some diꢀerent catalysts reported in the literature
3
4
4 3
in the synthesis of biscoumarin derivatives
Entry
Catalyst
Condition
Time (min)
Yield (%)
References
1
2
I2 (10 mol %),
H O, reꢃux
20–32
120–180
91–99
77–91
[37]
[38]
2
[bmim][BF ] (4 mmol)
Solvent-free,
4
6
0–70 °C
3
4
5
6
TBAB (10 mol %)
SDS (20 mol %)
H O, reꢃux
20–40
150–180
12–30
77–95
78–96
82–96
92–96
[39]
[40]
[41]
[42]
2
H O, 60 °C
2
−2
TiO /SO (10 mol %)
H O, 80 °C
2
4
2
[PSebim][OTf] (10 mol %)
Solvent-free,
120–180
7
0 °C
7
8
9
[P VPy-BuSO H]HSO ]
Toluene, 90 °C
36–60
20–40
10–33
8–45
90–95
82–98
94–97
89–94
[43]
[44]
[45]
[46]
4
3
4
(
0.1 mmol)
(H [NaP W O110])/
EtOH, r.t
1
4
2
5
30
SiO (0.3 mol %)
Poly(AMPS-co-AA) @Fe O
Toluene, 90 °C
3
4
(
0.04 mmol)
1
0
CuO–CeO nanocomposite
H O, reꢃux
2
2
(
0.05 g)
1
1
1
2
B(HSO ) (0.3 mmol)
EtOH/H O, 70 °C
3–6
10–30
81–98
70–90
[25]
This work
4
3
2
Fe O @B(HSO )
Solvent-free,
3
4
4 3
(
0.03 wt%);
80 °C
Run
1
2
3
4
Ti me (min)
Yields (%)
15
90
15
87
15
87
30
85
Fig. 12 Reusability of Fe O @B(HSO ) (0.03 wt%); in the reaction of benzaldehyde (1 mmol) with
3
4
4 3
4
-hydroxycoumarin (2 mmol) at 80 °C after 15 min under solvent-free conditions
1
3

P. Hayati et al.
Fig. 13 EDX of Fe O @B(HSO ) after 4th run
3
4
4 3
preparation of catalyst. The main important advantages of this catalyst compared to
similar catalysts include smaller particle size, direct connection between tris (hydro-
gensulfato) boron groups and magnetic particles and ꢁnally reduction in the number
of catalyst preparation steps.
Acknowledgements The authors acknowledge Firoozabad University Research Council for partial
ꢁ
nancial support.
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