One-pot synthesis of pyran derivatives using silica-coated magnetic nanoparticles functionalized with piperidinium benzene-1,3-disulfonate as a new efficient reusable catalyst

Article abstract of DOI:10.1007/s11164-016-2762-x

Abstract: Fe₃O₄ nanoparticles were coated with silica followed by surface modification using a silylating agent and piperidine to obtain piperidinium benzene-1,3-disulfonate salt (PBDS) silica-coated magnetic nanoparticles (SCMNPs).

Full text of DOI:10.1007/s11164-016-2762-x

Res Chem Intermed
DOI 10.1007/s11164-016-2762-x
One-pot synthesis of pyran derivatives using silica-coated
magnetic nanoparticles functionalized with piperidinium
benzene-1,3-disulfonate as a new efficient reusable catalyst
Ramin Ghorbani-Vaghei1 Vida Izadkhah1
•
•
Jafar Mahmoodi1
Received: 19 June 2016 / Accepted: 4 October 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract Fe3O4 nanoparticles were coated with silica followed by surface modification
using a silylating agent and piperidine to obtain piperidinium benzene-1,3-disulfonate
salt (PBDS) silica-coated magnetic nanoparticles (SCMNPs). The obtained catalyst was
then analyzed using various characterization techniques, including thermogravimetric
analysis (TGA), scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) imaging, and X-ray diffraction (XRD), Brunauer–Emmett–Teller
(BET), and energy-dispersive X-ray (EDX) analyses. The heterogeneous catalytic
activity was investigated in one-pot pseudo-three-component synthesis of pyran
derivatives, revealing efficient action and giving the products in high yield under green
and sustainable conditions.
Graphical Abstract A novel efficient green reusable catalyst was obtained from sil-
ica-coated magnetic nanoparticles functionalized with piperidinium benzene-1,3-disul-
fonate for synthesis of 9-aryl-9H-2,4,5,7-tetramethyl-diuracilopyrans as well as 9-aryl-
3,4,6,7-tetrahydro-2H-pyran-1,8(5H,9H)-diones.
Electronic supplementary material The online version of this article (doi:10.1007/s11164-016-2762-
x) contains supplementary material, which is available to authorized users.
&
Ramin Ghorbani-Vaghei
rgvaghei@yahoo.com
1
Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
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R. Ghorbani-Vaghei et al.
Keywords Nanomagnetic Á Piperidinium benzene-1,3-disulfonate salt Á Pyran
derivatives
Introduction
Pyran is a known structural framework found in the skeleton of many natural
products such as (-)-hennoxazole A, an antiviral agent, annularins, and elijopyrone
[1–4]. Additionally, compounds based on pyran are pharmacologically active,
showing effects such as antituberculosis [5], antitumor [6, 7], anti-human
immunodeficiency virus (HIV) [8], antifungal [9], calcium channel antagonist
[10], and antimicrobial activities [11], as well as having clinical applications
[12, 13]. Recently, a novel pyran-based phosphodiesterase 9A (PDE9A) inhibitor
showed good activity experimentally against neurodegenerative diseases such as
Down’s syndrome, Parkinson’s disease, Alzheimer’s disease, and schizophrenia
[14]. In addition to the biological activities of pyran compounds, they are good
precursors for preparation of organic compounds including polyazanaphthalenes,
chromene derivatives, lactones, pyridine-2-ones, imidoesters, and pyrimidines
[15–18].
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One-pot synthesis of pyran derivatives using silica-coated…
Considering the importance of pyran derivatives, 4H-pyrans are prepared through
several synthetic procedures, using different catalysts such as magnesium oxide
[19], silica-bonded 1,4-diazabicyclo[2.2.2]octane (DABCO) [20], and SnCl2-loaded
silica nanoparticles [21]. Green chemistry principles suggest the use of green
solvents and green catalysts to reduce waste treatment and enhance the economics
of chemical processes, associated with reduced environmental problems [22].
It is noteworthy that some methods published in literature to prepare 4H-pyrans
suffer from serious limitations such as complex synthetic pathways, long reaction
time, hard workup, and catalyst nonreusability. Therefore, according to environ-
mentally benign design, research has focused on inexpensive and efficient processes
to prepare green catalysts which can be separated easily.
Despite the remarkable efficiency of homogeneous catalysts, their separation for
reuse in subsequent reactions is extremely difficult. Thus, production and
development of new efficient heterogeneous catalysts is reasonably necessary,
based on immobilization of homogeneous as well as organocatalysts on substrates,
being of great interest to chemists. One of the most applicable such substrates is
magnetic nanoparticles (MNPs), which can be separated from a mixture using an
external magnet and reused several times [23–26]. Use of MNPs, e.g., nanoparticles
of iron oxides (IOs), as a substrate for heterogeneous catalysts has attracted the
attention of researchers [27–32]. However, hydrophobic surface and instability in
strongly acidic solutions are some of the disadvantages of MNPs, limiting their
applications [33]. Functionalization of the surface of MNPs can help to overcome
such limitations [34–36].
Correspondingly, ionic liquids (ILs), as solvents or catalysts, have gained wide
recognition due to their unique properties of reusability, environmental compati-
bility, and easy isolation from the reaction mixture [36–43]. Immobilizing
functional ILs on a surface can decrease many of their negative properties, such
as high viscosity. Hence, ILs are good candidates for functionalizing the surface of
MNPs, since MNPs and ILs complement each other, addressing the aforementioned
drawbacks [44–47].
In this work, we synthesized several new pyran derivatives using a new IL-
functionalized MNP catalyst through a pseudo-three-component condensation
reaction of aryl aldehydes and N,N-dimethylbarbituric acid and/or cyclohexane-1,3-
diones. We report herein synthesis of this important class of heterocycles from
cheap and easily available starting materials using a recyclable and efficient catalyst
under green conditions.
Experimental
Materials and methods
All commercially available chemicals were obtained from Merck and Fluka and
1
used without further purification. H and 13C nuclear magnetic resonance (NMR)
spectra were recorded on Bruker Advance 400 and 100 MHz FT NMR spectrom-
eters, respectively (undertaken at University of Mazandaran, Iran). Infrared (IR)
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R. Ghorbani-Vaghei et al.
spectroscopy was performed on a PerkinElmer GX Fourier-transform infrared (FT-
IR) spectrometer. Mass spectra were recorded on a 5973 Network mass-selective-
detector mass spectrometer (undertaken at University of Tehran, Iran). Elemental
analyses (CHN) were performed using an Elemental Combustion System 4010
(undertaken at University of Tehran, Iran). Thermogravimetric analysis (TGA) was
performed on a Pyris Diamond. Energy-dispersive X-ray analysis of the prepared
catalyst was performed on a FESEM-SIGM (Germany) instrument. Scanning
electron microscopy (SEM) was performed on an EM3200 instrument operated at
accelerating voltage of 30 kV. Transmission electron microscopy (TEM) was
performed on a ZEISS EM3200 instrument. Brunauer–Emmett–Teller (BET)
analysis was performed on a BELSORP instrument.
Preparation of magnetic nanoparticles (MNPs)
Magnetite phase was synthesized by adding FeCl3 (3 mL, 2 M dissolved in 2 M
HCl) to 10.33 mL double-distilled water, followed by dropwise addition of Na2SO3
(2 mL, 1 M) for 3 min under magnetic stirring. The solution color changed from red
to light yellow, then 80 mL NH3ÁH2O solution (0.85 M) was added under severe
stirring. After 30 min, the obtained MNPs were separated using a magnet, then
washed with distilled water to reach pH \7.5.
Preparation of silica-coated magnetic nanoparticles (SCMNPs)
¨
MNPs@SiO2 were synthesized through a modified Stober method [48]. MNPs
(4.3 mmol, 1 g) were dispersed for 30 min in a mixture of deionized water (80 mL),
ethanol (20 mL), and ammonia solution (4.0 mL, 25 % in water) using ultrasound
treatment. Then, tetraethylorthosilicate (11 mmol, 2.0 mL) was added to the
mixture and stirred for 3 h at room temperature. The resultant product was carefully
washed with deionized water and then washed twice with ethanol and dried at 60 °C
under vacuum condition (Scheme 1).
Preparation of piperidine-modified SCMNPs
SCMNPs (1.0 g) were dispersed in dry toluene (50 mL) for 30 min, then reacted
with 3-chloropropyltrimethoxysilane (CPTS, 2 mL) as silylating agent, which was
added to the mixture dropwise. The mixture was heated under reflux condition for
24 h, and the obtained SCMNPs–Pr–Cl were filtered off, washed twice with toluene,
and dried at 60 °C under vacuum condition. To prepare pi-SCMNPs, SCMNPs–Pr–
Cl (1.0 g) were added to a mixture of dry toluene (50 mL) and piperidine
(0.03 mmol, 3 mL). The reaction mixture was dispersed for about 30 min, then
heated under reflux and stirring conditions for 72 h. The solid phase was filtered,
washed with toluene and ethanol, and dried at 60 °C under reduced pressure
(Scheme 1).
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One-pot synthesis of pyran derivatives using silica-coated…
Scheme 1 Synthesis of PBDS–SCMNPs
Synthesis of piperidinium benzene-1,3-disulfonate salt (PBDS) magnetic
nanoparticles (MNPs) as catalyst
pi-SCMNPs (1.0 g) were suspended in dried acetonitrile (50 mL), and benzene-1,3-
disulfonic acid (3 mL) was added to this suspension. The mixture was stirred for
24 h at ambient temperature, then filtered, washed twice with acetonitrile, and
further washed with deionized water and dried at 60 °C under vacuum condition
(Scheme 1).
General procedure for preparation of pyranodipyrimidines
3a–f and xanthene derivatives 5a–f
A mixture of either N,N-dimethylbarbituric acid 1 (0.312 g, 2 mmol) or 1,3-
cyclohexanedione 4 (0.224 g, 2 mmol), aromatic aldehyde (1 mmol), and PBDS–
SCMNPs (20 mg) as nanocatalyst was vigorously stirred in ethanol at 70 °C under
reflux condition for appropriate times (Table 4). After reaction completion,
monitored by thin-layer chromatography (TLC), the catalyst was separated using
an external magnet. After that, the products were filtered and separated. Then, the
obtained product was recrystallized in EtOH to obtain highly purified product. The
PBDS–SCMNPs were washed for three to four times with ethanol and then dried at
50 °C for 3 h to recycle the catalyst for use in alternative reactions. In this study,
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R. Ghorbani-Vaghei et al.
PBDS–SCMNPs were used as an efficient catalyst for five times without significant
loss of catalytic activity (Fig. 1).
Results and discussion
Characterization of PBDS–SCMNPs
The synthesized PBDS–SCMNPs, as a novel and efficient catalyst, were charac-
terized using FT-IR, thermogravimetric analysis (TGA), scanning electron
microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction
(XRD) analysis, energy-dispersive X-ray spectroscopy (EDX), vibrating-sample
magnetometry (VSM), and Brunauer–Emmett–Teller (BET) specific surface area
analysis.
FT-IR spectroscopy was used to compare the produced Fe3O4 MNPs, SCMNPs,
and other core–shell surface-modified samples (Fig. 2). The FT-IR spectrum of the
magnetic Fe3O4 MNPs showed a characteristic absorption peak of Fe–O bond at
about 585 cm-1. The absorption peaks of the silica shell in the SCMNPs at around
1100 and 810 cm-1 can be ascribed to asymmetric and symmetric stretching
vibrations of Si–O–Si bond in oxygen–silicon tetrahedral, respectively. Moreover,
the absorption peaks of the SCMNPs–Pr–Cl core–shell MNPs at 2957 cm-1 are
connected to stretching vibration of C–H groups. Additionally, the absorption band
at 3408 cm-1 is related to stretching vibration of N–H on the piperidinium moiety,
and the peak appearing at 1645 cm-1 is attributed to stretching vibration of C=C
bonds of benzene-1,3-disulfonate. The two peaks observed at 1220 and 1105 cm-1
are related to vibrational modes of sulfonate groups.
TGA was applied to investigate the possible thermal stability/degradation and to
determine the content of organic groups loaded on the surface of the SCMNPs. The
first signal in both TGA and derivative thermogravimetric analysis (DTG) at around
Fig. 1 Investigating the reusability of PBDS–SCMNPs as the catalyst in the model reaction
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One-pot synthesis of pyran derivatives using silica-coated…
Fig. 2 IR spectra of MNPs (a), SCMNPs (b), SCMNPs–Pr–Cl (c), pi-SCMNPs (d), and PBDS–SCMNPs
(e)
100 °C is due to loss of water adsorbed on the surface of the compound. The DTG
result for the PBDS–SCMNPs reveals the mass loss of organic groups as they
decompose with increasing temperature (Fig. 3). Therefore, in the temperature
range between 100 and 500 °C, around 10 % weight loss is observed, confirming a
loading of 0.2 mmol/g of organic groups on the surface of the SCMNPs. Both
curves display considerable losses in four steps, and the material decomposed after
530 °C.
Furthermore, the size, shape, and morphology of the PBDS–SCMNPs were
investigated by different methods, including XRD patterns (Fig. 4) and SEM and
TEM images (Fig. 5). The XRD diagram of the MNPs displayed patterns consistent
with those of spinel ferrites as explained in literature [49, 50]. The same peaks were
identified in both of the PBDS–SCMNP XRD diagrams, indicating retention of the
crystalline spinel ferrite core structure after the reaction process. The positions and
relative intensities of all peaks confirmed the standard XRD pattern of Fe3O4 MNPs
[Joint Committee on Powder Diffraction Standards (JCPDS) card no. 85-1436],
indicating retention of the crystalline cubic spinel structure of the MNPs. The XRD
patterns of the particles showed nine characteristic peaks linked to cubic iron oxide
phase (2h = 30.10°, 35.50°, 43.10°, 53.00°, 57.00°, 62.80°) with corresponding
indices of (2 2 0), (3 1 1), (4 0 0), (3 3 1), (4 2 2), and (5 1 1). We conclude that the
resultant nanoparticles were pure Fe3O4 with spinel structure and that the grafting
process did not induce any phase change of Fe3O4. Also, reported MNPs coated
with silica showed the same XRD pattern with increased intensities in the 2h range
between 20° and 30° [50]. Considering the XRD patterns, the main peak observed at
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R. Ghorbani-Vaghei et al.
Fig. 3 The TGA and DTA curves of the PBDS–SCMNPs
Fig. 4 The XRD spectrum of MNPs (a); SCMNPs (b); SCMNPs–Pr–Cl (c); pi-SCMNPs (d); PBDS–
SCMNPs (e)
2h is equal to 35.60°; therefore, the crystalline structure of the catalyst can
obviously be identified, as presented in Table 1. The average crystallite size (D) is
also given, as determined using the Scherrer formula
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One-pot synthesis of pyran derivatives using silica-coated…
Fig. 5 SEM (a) and TEM (b) images of PBDS–SCMNPs
Table 1 XRD data for PBDS–SCMNPs
Entry
2h (°)
Peak width (FWHM) (°)
Size (nm)
Interplane distance (nm)
1
2
3
4
5
22.80
25.70
35.60
62.80
71.10
0.58
0.35
1.13
0.73
0.29
13.97
23.28
7.38
0.389564
0.346225
0.251885
0.147990
0.132436
12.75
33.67
Fig. 6 The EDX data of the PBDS–SCMNPs
123

R. Ghorbani-Vaghei et al.
D ¼ Kk=ðbcoshÞ;
where k is the X-ray wavelength, K is the Scherrer constant, b is the full-width at
half-maximum (FWHM) of the peak, and h is the Bragg diffraction angle. The
catalyst average size obtained from this equation was found to lie in the range of
7.38–33.67 nm. SEM and TEM images of PBDS–SCMNPs were further studied to
determine the particle size. Figure 5 clearly shows the dimensions and shapes of the
particles. The particle sizes obtained from SEM and TEM images (7.38–33.67 nm)
Fig. 7 The VSM analysis of the PBDS–SCMNPs in comparison with the MNPs
Fig. 8 N2 adsorption–desorption (BET) isotherms of Fe3O4 MNPs (a, c) and PBDS–SCMNPs (b, d)
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One-pot synthesis of pyran derivatives using silica-coated…
Table 2 Effect of catalyst quantity and temperature on synthesis of 9-(2-chlorophenyl)-9H-2,4,5,7-
tetramethyl-diuracilopyran (3e)
Entry
Catalyst loading (mg)
Reaction temperature (°C)
Reaction time (min)
Yielda (%)
1
–
r.t.
60
r.t.
60
r.t.
60
60
r.t.
70
70
r.t.
70
60
60
40
30
30
20
20
20
20
15
15
15
25
30
50
60
65
70
75
80
95
85
85
95
2
–
3
5
4
5
5
10
10
10
20
20
25
30
30
6
7
8
9
10
11
12
Reaction condition: N,N-dimethylbarbituric acid (2 mmol), 2-chlorobenzaldehyde (1 mmol)
a
Isolated yield
Table 3 Optimization of
reaction conditions for synthesis
Entry
Solvent
Reaction time (min)
Yielda (%)
of compound 3e at 70 °C
1
2
3
4
5
6
7
H2O
20
20
20
25
25
45
65
85
90
95
70
70
25
10
Solvent-free
EtOH
CH3CN
Acetone
CH2Cl2
Toluene
Reaction conditions: N,N-
dimethylbarbituric acid
(2 mmol),
2-chlorobenzaldehyde (1 mmol)
a
Isolated yield
support the particle size calculations presented above. Both SEM and TEM revealed
XRD patterns with characteristic peaks of the nanocatalyst. These results confirm
that our method was efficient for synthesis of PBDS–MNPs.
The EDX data for the PBDS–SCMNPs (Fig. 6) confirmed the presence of the
expected elements iron, silicon, carbon, oxygen, nitrogen, and sulfur in the catalyst.
To fully describe the catalyst, the magnetic properties of the MNPs and PBDS–
SCMNPs were characterized by VSM. The room-temperature magnetization curves
of the MNPs and PBDS–SCMNPs are shown in Fig. 7. The MNPs showed
superparamagnetic properties with saturation magnetization of about 60 emu g-1
while the saturation magnetization of the PBDS–SCMNPs was 36 emu g-1
,
.
Compared with the MNPs, the saturation magnetization of the PBDS–SCMNPs
clearly decreased since the diamagnetic influence of the organic moieties resulted in
lower mass fraction of MNPs. Even with this reduction in saturation magnetization,
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R. Ghorbani-Vaghei et al.
Table 4 Synthesis of pyranodipyrimidines and xanthene derivatives using 20 mg PBDS–SCMNPs as
catalyst
Entry Aldehyde
Product
No.
Time
(min)
Yielda
(%)
M.p.
(°C)
Reported m.p.
(°C) [51]
1
3a
3b
40
30
80
85
273–275 274–275
2
265–267 266–268
3
4
5a
5b
25
50
87
90
266–268 264–266
199–201 200–202
5
5c
70
77
268–269 265–267
6
7
3d
3e
65
50
90
80
246–248 245–246
199–201 200–203
8
3f
40
85
258–259 257–259
9
5d
5e
5f
60
60
50
85
90
85
232–233 231–233
259–261 260–262
252–254 251–253
10
11
a
Isolated yield
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One-pot synthesis of pyran derivatives using silica-coated…
Scheme 2 Synthesis of pyranodipyrimidines 3a–f and xanthene derivatives 5a–f in presence of PBDS–
SCMNPs
the solid retained sufficient magnetization to enable its separation from the reaction
mixture using a permanent magnet.
N2 adsorption–desorption measurements were carried out for Brunauer–Emmett–
Teller (BET) specific surface area analysis of the materials (Fig. 8). The BET
surface area of the PBDS–SCMNP catalyst was 79.4 m2/g (total pore vol-
ume = 0.246 cm3 g-1; mean pore diameter = 12.37 nm), and its pore size
distribution is plotted in Fig. 8. The surface area obtained for the Fe3O4 MNPs
was 10.9 m2/g (total pore volume = 0.047 cm3 g-1
; mean pore diame-
ter = 17.25 nm), and their pore size distribution is plotted in Fig. 8. The BET
surface area of the PBDS–SCMNP catalyst was higher in comparison with the
Fe3O4 MNPs. The specific surface area of the PBDS–SCMNP catalyst increased
because of the coating of the Fe3O4 MNPs by grafting organic tags. The higher
surface area of the synthesized catalyst in comparison with the Fe3O4 MNP cores
can be considered as one of the advantages of this catalyst. The pore size of both
samples mainly lay between 1 and 10 nm, revealing that the samples included both
micropores and mesopores.
Application of PBDS–SCMNPs as catalyst in synthesis
of pyranodipyrimidine 230 and xanthene derivatives
The catalytic activity of PBDS–SCMNPs was tested in the model reaction of N,N-
dimethylbarbituric acid with pyridine-2-carbaldehyde; different amounts of nano-
magnetic catalyst were investigated at room temperature to 70 °C in EtOH
(Table 2). As shown in Table 2, the best results were achieved when the reaction
was run using 20 mg nanomagnetic catalyst at 70 °C (Table 2, entry 9). On
increasing the amount of nanomagnetic catalyst or changing the temperature, the
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R. Ghorbani-Vaghei et al.
Scheme 3 Suggested mechanism for synthesis of pyran derivatives
reaction yield did not change significantly. Table 2 obviously shows that, in the
absence of nanomagnetic catalyst, the product was produced with low yield
(Table 2, entries 1 and 2).
To optimize the reaction conditions, the reaction of pyridine-2-carbaldehyde and
N,N-dimethylbarbituric acid was performed using 20 mg catalyst in numerous
solvents including H2O, EtOH, CH3CN, EtOAc, acetone, CH2Cl2, and toluene at
70 °C. The results are summarized in Table 3. As illustrated in Table 3, ethanol was
the best choice for this reaction, especially as a benign and green solvent compared
with the other organic solvents.
To investigate the generality of the optimized reaction, a wide range of
substituted aldehydes were applied to this pseudo-three-component condensation
with catalytic amount (20 mg) of PBDS–SCMNPs in EtOH at 70 °C. The results are
summarized in Table 4. The reaction time of aromatic aldehydes having electron-
withdrawing groups was shorter with higher product yields than for electron-
donating groups. Furthermore, meta- and para-substituted aromatic aldehydes
produced the products with excellent yields in shorter reaction times, while owing to
the steric effects of ortho-substituted aromatic aldehydes, rather lower yields of
their products were obtained.
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One-pot synthesis of pyran derivatives using silica-coated…
In the next test, condensation of N,N-dimethylbarbituric acid with 2-chloroben-
zaldyde was tested in the presence of recovered PBDS–SCMNP catalyst to
investigate its reusability. As shown in Fig. 1, no significant loss of catalytic activity
was observed after five cycles of the reaction (Scheme 2).
A mechanism for the synthesis of pyranodipyrimidines is proposed in Scheme 3.
Firstly, PBDS–SCMNPs activate the carbonyl group of the aldehyde (1), and
correspondingly, deprotonated PBDS–SCMNPs convert N,N-dimethylbarbituric
acid (2) to its enolic form (7). Then, through a Knoevenagel condensation,
intermediate 7 attacks the activated carbonyl group 6, and after removal of a water
molecule, compound 8 is produced. In the next step, the second molecule of
intermediate 7 attacks compound 8 via Michael addition to afford the final product 3
when a water molecule is removed.
Conclusions
Magnetically recoverable PBDS–SCMNPs were found to be a highly efficient and
economically sustainable catalyst for preparing a wide range of substituted
pyranodipyrimidines and xanthene derivatives through a pseudo-three-component
condensation reaction. The noticeable features of this methodology are short
reaction time, good to excellent product yield, use of an easily magnetically
recyclable catalyst, and green and mild reaction conditions. The PBDS–SCMNP
catalyst was completely characterized using various techniques, including FT-IR,
TGA, XRD, SEM, TEM, VSM, and BET analysis.
Acknowledgments We are grateful to Bu-Ali Sina University, Center of Excellence in Development of
Environmentally Friendly Methods for Chemical Synthesis (CEDEFMCS), for financial support.
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