Silica-modified magnetite Fe3O4 nanoparticles grafted with sulfamic acid functional groups: an efficient heterogeneous catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-one and tetrahydrobenzo[b]pyran derivatives

Article abstract of DOI:10.1080/17415993.2016.1177055

Silica-modified magnetite-polyoxometalates functionalized with sulfamic acid groups as hybrid nanoparticles were prepared by sulfonation of diamine-functionalized propyl group grafted on the magnetic silica-coated Fe₃O₄ nanoparticles

Full text of DOI:10.1080/17415993.2016.1177055

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Silica-modified magnetite Fe O nanoparticles
3
4
grafted with sulfamic acid functional groups:
an efficient heterogeneous catalyst for the
synthesis of 3,4-dihydropyrimidin-2(1H)-one and
tetrahydrobenzo[b]pyran derivatives
Davood Azarifar, Omolbanin Badalkhani & Younes Abbasi
To cite this article: Davood Azarifar, Omolbanin Badalkhani & Younes Abbasi (2016): Silica-
modified magnetite Fe O nanoparticles grafted with sulfamic acid functional groups:
3
4
an efficient heterogeneous catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-
one and tetrahydrobenzo[b]pyran derivatives, Journal of Sulfur Chemistry, DOI:
10.1080/17415993.2016.1177055
To link to this article: http://dx.doi.org/10.1080/17415993.2016.1177055
Published online: 02 Jun 2016.
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Date: 04 June 2016, At: 12:32

JOURNAL OF SULFUR CHEMISTRY, 2016
http://dx.doi.org/10.1080/17415993.2016.1177055
Silica-modified magnetite Fe O nanoparticles grafted with
3
4
sulfamic acid functional groups: an efficient heterogeneous
catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-one
and tetrahydrobenzo[b]pyran derivatives
Davood Azarifar , Omolbanin Badalkhani and Younes Abbasi
Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran
ABSTRACT
ARTICLE HISTORY
Silica-modified magnetite-polyoxometalates functionalized with sul-
famic acid groups as hybrid nanoparticles were prepared by sulfona-
tion of diamine-functionalized propyl group grafted on the magnetic
silica-coated Fe3O4 nanoparticles. This heterogeneous nanocatalyst
was explored to present high catalytic performance for the syn-
thesis of 3,4-dihydropyrimidinones and tetrahydrobenzo[b]pyrans
under mild reaction conditions. The properties of this nanocatalyst
were characterized by FT- infrared, energy-dispersive X-ray spec-
trum, scanning electron microscope, X-ray diffraction, X-ray fluores-
cence and elemental analysis. Easy separation of the nanocatalyst by
using an external magnet, recyclability, non-toxicity, versatility and
high stability of the catalyst combined with low reaction times and
excellent yields make the present protocol very useful and attractive
for the synthesis of the titled products.
Received 29 November 2015
Accepted 27 March 2016
KEYWORDS
Heterogeneous nanocatalyst;
magnetic nanoparticles;
sulfonation; 3; 4-dihydro
pyrimidin-2(1H)-one;
tetrahydrobenzo[b]pyran
1. Introduction
In the past decade, many reports on the synthesis and applications of magnetic nanopar-
ticles (MNPs) on different industrial and biological fields such as magnetic resonance
CONTACT Davood Azarifar
azarifar@basu.ac.ir
Faculty of Chemistry, Bu-Ali Sina University, Zip Code 65178,
Hamedan, Iran
Supplemental data for this article can be accessed here. http://dx.doi.org/10.1080/17415993.2016.1177055
©
2016 Informa UK Limited, trading as Taylor & Francis Group

2
D. AZARIFAR ET AL.
imaging, drug delivery, bioseparation, hyperthermia and catalytic processes have been
published. Also, magnetic NPs have attracted much research interests as excellent sup-
ports for various catalysts which can be easily separated from the products simply by using
an external magnetic field and recycled.[1–4] Moreover, the surface of magnetic metal
oxide NPs such as magnetic Fe O nanoparticles could be functionalized and modified
3
4
by various organic and inorganic materials such as silica, polymers, biomolecules, metals,
etc. which have been used as selective and efficient catalysts in a wide range of catalytic
reactions.[5,6] Among these nanocatalytic systems, nano-oxide-supported functionalized
polyoxometalates have emerged as useful catalysts in organic reactions.[7] These heteroge-
neous catalysts contain reactive sites with high mobility similar to those in homogeneous
catalysts and can be easily recycled. Based on these preferences, different types of acids such
as phosphotungstic acid (H PW O ) and sulfonic acid have been grafted on the func-
3
12 40
tionalized silica-coated Fe O MNPs and are successfully used for selectively catalyzing
3
4
chemical transformations.[7–11]
Among the important heterocyclic compounds, 3,4-dihydropyrimidin-2(1H)-ones and
their derivatives are well-documented compounds which have attracted enormous syn-
thetic interest due to their therapeutic, pharmacological and biological properties.[12]
Many of these compounds exhibit vital medicinal properties such as antiviral, antibacterial,
antitumor, antihypertensive, neuropeptide Y (NPY) antagonism and anti-inflammatory
activities.[13] Amongst the most important drugs used, monastrol is a well-known
medicine which acts as a specific inhibitor of mitotic kinesin Eg5 and is considered as a
lead compound for the development of new anticancer drugs.[14] The most used methods
for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones are based on the three-component
Biginelli condensation reaction between an aldehyde, urea or thiourea, and an easily eno-
lizable carbonyl compound.[15,16] So far, many efficient and versatile catalytic approaches
in the synthesis of 3,4-dihydropyrimidin-2(1H)-ones have been developed and scope for
further developments toward milder reaction conditions and better selection of the catalyst
and reaction components still exists.[17]
Another well-documented class of heterocyclic compounds of important pharmacolog-
ical and therapeutic properties belongs to 4H-chromene derivatives which have received
great attention in synthetic organic chemistry. Similarly, a large number of chromene
derivatives perform different biological and pharmacological activities as spasmolytic,
diuretic, anticoagulant, anticancer and anti-anaphylactic agents.[18] With respect to the
importance of 4H-chromenes, different methods have been developed for the synthe-
sis of these compounds employing various catalysts such as ionic liquids,[19] hexadecyl
trimethyl ammonium bromide,[20] Mg/La-mixed metal oxides,[21] and nanosilica.[22] In
addition, several other methods have been developed based on different conditions using
reactants in solid or molten states,[23] and electrolysis condition.[24]
Following our previous reports on the synthesis of different heterocyclic compounds
including 4H-chromenes and 3,4-dihydropyrimidinones using various catalysts such
as nano-magnetic mixed lanthanum strontium magnesium oxide nanoparticles,[25]
nano-titania-supported Preyssler-type heteropoly acid,[26] and under ultrasonic irra-
diation condition,[27] herein, we wish to report the one-pot three-component syn-
thesis of the titled products employing sulfamic acid-functionalized magnetic Fe O4
3
nanoparticles as an efficient and magnetically recoverable heterogeneous catalyst
(
Scheme 1).

JOURNAL OF SULFUR CHEMISTRY
3
Scheme 1. Synthesisof3,4-dihydropyrimidin-2(1H)-ones2a–2land4H-chromenes3a–3kcatalyzedby
Fe3O4@SiO2@N(SO3H)NH(SO3H) MNPs.
2. Results and discussion
Our concept of supported amino sulfuric acid catalysis involves the surface of a nano-
magnetic support material which is modified with a monolayer of covalently bonded
organo amine sulfonic acid moieties. For our purpose, we have chosen, for the first time,
to immobilize the sulfanilic acid groups on silica-modified magnetic Fe O nanoparti-
3
4
cles, Fe O @SiO @N(SO H)-NH(SO H). Following the previously reported method,[28]
3
4
2
3
3
as illustrated in Scheme 2, in the first step, FeCl ·6H O and FeCl ·4H O were reacted
3
2
2
2
+
2
+3
in basic solution under ultrasonication to co-precipitate the Fe and Fe ions that
resulted in the formation of Fe O MNPs. In the second step, in order to protect the Fe O
3
4
3
4
NPs from possible oxidation or aggregation, a layer of SiO was coated on the external
2
surface of the Fe O NPs by using the previously reported method.[29] Subsequently,
3
4
Scheme 2. Steps of the synthesis of the catalyst Fe3O4@SiO2@N(SO3H)-NH(SO3H) NPs.

4
D. AZARIFAR ET AL.
the silanol groups on the surface of Fe O @SiO nanoparticles were treated with 3-
3
4
2
chloropropyltrimethoxysilane to obtain Fe O @SiO -Cl. Then, the resulted chloropropyl-
3
4
2
grafted Fe O @SiO was reacted with ethylenediamine to obtain Fe O @SiO @NH-NH
2
3
4
2
3
4
2
MNPs. In the final step, the sulfonation of the both amine groups in Fe O @SiO @NH-
3
4
2
NH was implemented by reaction with chlorosulfonic acid under ultrasonication to yield
2
ꢀ
the N,N -disulfonated MNPs Fe O @SiO @N(SO H)-NH(SO H).
3
4
2
3
3
The characterization of the catalyst was performed by elemental, Fourier transform
infrared (FT-IR), energy-dispersive X-ray spectrum (EDX), scanning electron micro-
scope (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses. The ele-
mental analysis showed that the carbon, hydrogen, nitrogen and sulfur contents of the
prepared catalyst were 6.04, 1.04, 2.40 and 9.36 (wt%), respectively. This analysis con-
firms a loading of 2.92 mmol of sulfonic acid groups per gram of the support, and
indicative of the successful sulfonization of the both amino groups in the prepared
Fe O @SiO -NH-NH NPs.
3
4
2
2
The FT–IR spectra of the Fe O NPs, chloropropyl-grafted Fe O @SiO and the cata-
3
4
3
4
2
lyst Fe O @SiO @N(SO H)-NH(SO H) are shown in Figure 1. In these spectra, the peaks
3
4
2
3
3
−
1
exhibited, respectively, at 570, 583 and 597 cm are ascribed to Fe–O stretching vibration.
In addition, the sharp bands appearing at 1083 and 1079 cm are attributed to Si–O–Si
asymmetric stretching vibration confirmatory to the survival of a SiO layer around Fe O
nanoparticles. The bands centered at 1615–1630 and 1509 cm were attributed to the
bending vibrations of O–H and N–H bonds, respectively. Also, the asymmetric stretch-
ing vibrations of O–H and N–H groups appeared at 3467 and 3191 cm , respectively.
−
1
2
3
4
−
1
−
1
−
1
The appearance of the bands at 2958 and 2851 cm assigned for the asymmetric and
symmetric C–H stretching vibrations, respectively, combined with the appearance of the
−
1
S=O stretching vibration band at 1207 and 1127 cm , and also the increase in the inten-
−
1
sities of the band at 3422 cm as shown in Figure 1(c) confirms that the sulfonated
amine-functionalized propyl moieties are successfully anchored on the surface of the
silica-coated Fe O NPs.
3
4
As shown in Figure 2, the SEM image indicates that the prepared Fe O @SiO @N
3
4
2
(
SO H)-NH(SO H) nanoparticles possess an average diameter of about 41 nm and the cat-
3 3
alyst is made up of core-shell structure with spherical morphology. Also, the SEM image
shows that the size and morphology of the Fe O @SiO @N(SO H)-NH(SO H) NPs were
3
4
2
3
3
not noticeably changed in comparison with the ungrafted Fe O nanoparticles.[30]
3
4
The components of the Fe O @SiO -Cl nanoparticles were characterized by using
3
4
2
XRF analysis. The XRF spectrum of the Fe O @SiO -Cl shown in Figure 3 exhibits the
3
4
2
elemental composition (Si, Cl and Fe).
Moreover, as shown in Figure 4, the EDX was obtained from the synthesized catalyst
Fe O @SiO @N(SO H)-NH(SO H) in which the expected elemental composition (C, N,
3
4
2
3
3
O, Si, S, Fe) is shown clearly.
Figure 5 presents the crystalline structure of Fe O @SiO @N(SO H)-NH(SO H)
3
4
2
3
3
nanoparticles identified with the XRD technique. The diffraction peaks are appeared
with 2θ = 30.0°, 35.7°, 43.7°, 53.6°, 57.4° and 62.6°. As shown in this figure, the posi-
tions and relative intensities of the peaks match well with those of the unfunctionalized
Fe O nanoparticles.[31] In this XRD pattern of Fe O @SiO @N(SO H)-NH(SO H),
3
4
3
4
2
3
3
the characteristic peaks of Fe O did not show any significant change except that the
3
4

JOURNAL OF SULFUR CHEMISTRY
5
(a)
(b)
(c)
Figure 1. FT-IR spectra of synthesized Fe3O4 NPs (a), Fe3O4@SiO2-Cl (b) and Fe3O4@SiO2@N(SO3H)-
NH(SO3H) NPs (c).
Figure 2. SEM images of Fe3O4@SiO2@N(SO3H)-NH(SO3H) NPs.

6
D. AZARIFAR ET AL.
Figure 3. The XRF spectrum of the prepared Fe3O4@SiO2-Cl NPs.
Figure 4. The EDX spectrum of Fe3O4@SiO2@N(SO3H)-NH(SO3H) NPs.
intensities and width of the peaks were slightly decreased after being modified with SO H
3
groups.
To evaluate the catalytic activity of Fe O @SiO @N(SO H)-NH(SO H) in the synthe-
3
4
2
3
3
sis of 4H-chromenes, we initially studied the one-pot three-component reaction between
benzaldehyde, malononitrile and 5,5-dimethyl-1,3- cyclohexanedione (dimedone) as sim-
ple model reaction. To establish the reaction conditions, the effects of the catalyst loading,
solvent and temperature on the rate and yield of this model reaction were investigated. The
results summarized in Table 1 clearly indicate that the best results in terms of the reaction
rates and yields are obtained when the reaction was carried out using the mixture of equal
volumes of EtOH and H O as the solvent of choice under reflux conditions with a catalyst
2
loading of 0.01 g (entry 8). In addition, the important role of the catalyst in the reaction
was approved by repeating the reaction in the absence of the catalyst with optimal condi-
tions and noting that a trace amount of the expected product was formed and only slight

JOURNAL OF SULFUR CHEMISTRY
7
(
a)
b)
(
(c)
Figure 5. XRD pattern of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2@N(SO3H)-NH(SO3H) NPs.
Table 1. Screening the reaction parameters for the model synthesis of 2-amino-7,7-dimethyl-5-oxo-4-
phenyl-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile.a
Entry
Catalyst (g)
Solventb
Temperature (°C)
Time (min)
Yield (%)c
1
2
3
4
5
6
7
8
9
0
1
2
3
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
No solvent
H2O
EtOH
r.t.
r.t.
r.t.
r.t.
120
120
120
60
60
60
30
10
5
10
10
10
90
25
48
54
67
75
96
98
98
95
96
95
trace
15
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
50
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
1
1
1
1
0.02
0.03
No catalyst
No catalyst
aConditions: benzaldehyde (1 mmol), 5,5-dimethyl-1,3- cyclohexanedione (1 mmol), malononitrile (1.2 mmol) and solvent
(
5 mL).
b
c
The solvent ratio used for EtOH/H2O is 2.5 mL:2.5 mL.
Isolated pure yield.
improvement of the yield was observed after a prolonged reaction time of 90 min (entries
1
2, 13).
Moreover, versatility and the catalytic potential of the catalyst were similarly explored
in the synthesis 3,4-dihydropyrimidin-2(1H)-ones using the one-pot three-component

8
D. AZARIFAR ET AL.
Table 2. Screening the reaction parameters for the model synthesis of 5-methoxycarbonyl-6-methyl-4-
a
phenyl-3,4-dihydropyrimidin-2(1H)-one.
Entry
Catalyst (g)
Solvent
Temperature (°C)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
0
1
2
3
0.01
0.01
0.01
0.02
0.02
0.02
0.03
0.01
0.01
No solvent
H2O
EtOH
No solvent
H2O
EtOH
No solvent
No solvent
No solvent
No solvent
No solvent
No solvent
No solvent
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
50
80
100
100
100
100
8
8
8
8
8
8
8
4
4
4
1
0.5
5
46
12
30
45
15
28
45
70
80
94
96
96
trace
1
1
1
1
a
0.01
0.01
0.01
No catalyst
Conditions: benzaldehyde (1 mmol), methyl acetoacetate (1 mmol), urea (1.5 mmol), solvent (5 mL).
Isolated pure yield.
b
condensation reaction of benzaldehyde, methyl acetoacetate and urea as the model reac-
tion. To establish the reaction conditions, we studied the effects of the same green solvents
H O and EtOH, catalyst loading and reaction temperature on the reaction. According to
2
the results summarized in Table 2, the optimal results for the reaction are obtained in the
absence of solvent using a catalyst loading of 0.01 g at 100°C (entry 12). The value of the
catalyst in the reaction was substantiated by conducting the reaction in the absence of the
catalyst that resulted in no detectable amount of the expected product with almost full
recovery of the starting materials even after a prolonged reaction time (entry 13).
To develop the scope of the reactions, we conducted these reactions with a series of alde-
hydes under the optimized conditions (a catalyst loading of 0.01 g, solvent-free, reaction
temperature of 100°C for the synthesis of 3,4-dihydropyrimidinones, and the catalyst load-
ing of 0.01 g, and H O/EtOH mixture as the solvent under reflux condition for the synthesis
2
of 4H-chromenes); the results are summarized in Tables 3 and 4, respectively. As shown in
these tables, the aldehydes carrying electron-donating and electron-withdrawing groups
all undergo these reactions to afford the respective products in excellent yields irrespective
of the nature of the substituent groups. All the products were characterized by their physi-
1
13
cal properties and spectral (FT-IR, H NMR and C NMR) analysis which were in accord
with those reported in the literature. The characteristic data for some selected products are
presented in the Experimental section.
2
.1. Proposed catalytic reaction mechanisms
A possible mechanism to explain the formation of 4H-chromenes is depicted in Scheme 3.
It is likely that the initial step involves the Fe O @SiO @N(SO H)-NH(SO H)-catalyzed
3
4
2
3
3
condensation of the aldehyde with malononitrile followed by dehydration to produce

JOURNAL OF SULFUR CHEMISTRY
9
Table 3. Synthesis of 3,4-dihydropyrimidin-2(1H)-ones 2a–2l catalyzed by nonmagnetic catalyst
Fe3O4@SiO2@ N (SO3H)NH(SO3H) under solvent-free conditions.a
M.p. (°C)
Entry
Ar
Product
Time (min)
Yield (%)b
Found
Reported
1
2
3
4
5
6
7
8
C6H5
2-ClC6H4
4-ClC6H4
2a
2b
2c
2d
2e
2f
2g
2h
2i
30
35
30
35
20
40
30
30
35
35
40
40
85
79
87
83
95
87
81
85
91
89
87
89
213–215
248–251
206–208
197–200
207–211
238–240
285–287
210–213
236–240
138–140
200–203
189–191
208–211[33]
252–253[34]
204–206[34]
192–194[35]
206–209[33]
235–237[33]
284–286[33]
208–211[33]
–
4-FC6H4
4-MeC6H4
4-HOC6H4
2-MeOC6H4
3-ClC6H4
2,5-(MeO)2C6H3
C6H5(CH2)2
3-C5H4N
new
9
new
1
1
1
a
0
1
2
2j
2k
2l
–
–
–
new
2-C4H4S
Conditions: aldehyde (1 mmol), methyl acetoacetate(1 mmol), urea(1.5 mmol), catalyst (0.01 g).
Isolated pure yield.
b
Table 4. Synthesis of 4H-chromenes 3a–3k catalyzed by nonmagnetic catalyst Fe3O4@SiO2@N
SO3H)NH(SO3H) in EtOH/H2O at the reflux temperature.a
(
M.p. (°C)
Reported
Entry
Ar
Product
Time (min)
Yield (%)b
Found
1
2
3
4
5
6
7
8
9
C6H5
3a
3b
3c
3d
3e
3f
3g
3h
3i
10
35
20
25
10
30
15
35
20
20
30
96
90
91
89
98
88
95
86
91
95
94
231–233
196–198
211–214
211–213
216–218
194–196
211–213
209–211
182–185
216–218
200–202
227–229[36]
199–200[37]
217–218[38]
224–225[36]
212–214[36]
192–194[37]
212–215[36]
212–215[37]
178–180[38]
210–212[36]
–
4-BrC6H4
2-ClC6H4
3-ClC6H4
4-ClC6H4
4-FC6H4
4-MeC6H4
4-HOC6H4
4- NO2C6H4
3-NO2C6H4
2-C4H4S
1
1
0
1
3j
3k
aConditions: aldehyde (1 mmol), 5,5-dimethyl-1,3- cyclohexanedione (1 mmol), malononitrile (1.2 mmol), EtOH/H2O
2.5 mL/2.5 mL), catalyst (0.01 g).
(
b
Isolated pure yield.

10
D. AZARIFAR ET AL.
Scheme 3. A possible reaction path way for the synthesis of tetrahydrobenzo[b]pyran derivatives
catalyzed by Fe3O4@SiO2@N(SO3H)-NH(SO3H) MNPs.
the arylidenemalononitrile intermediate I. Subsequently, the catalyst-induced nucleophilic
addition of the enolizable dimedone to the intermediate I followed by consecutive
intramolecular cyclization occurs to provide the intermediate II which rearranges to afford
the expected product 4H-chromene.
Similarly, a plausible reaction mechanism suggested for the synthesis of dihydropy-
rimidinones in the presence of the same catalyst is illustrated in Scheme 4. Initially, the
aldehyde is activated by the catalyst and undergoes the electrophilic addition with urea
followed by dehydration to provide the intermediate I. On the other hand, the methyl ace-
toacetate is enolized in the presence of the catalyst to yield the intermediate II which reacts
with the intermediate I in an Aldol-type reaction to produce the intermediate III. Sequen-
tially, the intermediate III undergoes annulation and dehydration to produce the expected
products.

JOURNAL OF SULFUR CHEMISTRY
11
Scheme 4. A possible reaction path way for the catalytic synthesis of dihydropyrimidinones catalyzed
by Fe3O4@SiO2@N(SO3H)-NH(SO3H).
2.2. Catalyst recyclability
The catalytic recyclability of the catalyst Fe O @SiO @N(SO H)-NH(SO H) was exam-
3
4
2
3
3
ined for the model reaction of benzaldehyde, dimedone and malononitrile. The recycling
process involved the isolation of the catalyst from the reaction mixture simply by using a
magnet bar. The recovered catalyst was purified by washing with ethyl acetate followed by
drying in an oven. The results summarized in Figure 6 indicate that the catalyst can be used
Figure 6. Catalytic reusability of Fe3O4@SiO2@N(SO3H)-NH(SO3H) NPs for the synthesis of
4H-chromenes.

12
D. AZARIFAR ET AL.
for five consecutive times without the noticeable loss of catalytic activity. The integrity of
the recovered catalyst was examined and proved to be as active as the originally used cat-
alyst. Moreover, the XRD analysis of the recovered catalyst indicated that its structural
integrity remains intact after separation from the reaction mixture.
3. Conclusion
In this research, Fe O @SiO @N(SO H)-NH(SO H) magnetic nanocomposite was
3
4
2
3
3
successfully prepared and characterized by FT-IR, SEM, XRF, EDX and XRD analyses.
The catalytic activity of this solid acid nanocomposite was probed through the one-
pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones and tetrahydrobenzo[b]pyran deriva-
tives by three-component reactions of aldehydes with acetoacetate, urea or malononitrile
and dimedone, respectively. The attractive features of this method are simple proce-
dure, cleaner reaction, easy recyclability and reusability of the catalyst, easy workup
and performing multicomponent reactions under solvent-free conditions for the syn-
thesis of dihydropyrimidin-2(1H)-ones or the use of green solvents for the synthesis of
4
H-chromenes.
4. Experimental
4
.1. General remarks
FT-IR spectra were recorded on a Shimadzu 435-U-04 FT spectrometer (KB pellets). NMR
spectra were recorded on 300 MHz BRUKER and 90 MHz JEOL FX 90Q spectrometers in
CDCl (or DMSO-d ). Melting points were determined in open capillary tubes using a
3
6
BUCHI 510 apparatus. SEM was performed on a KYKY-EM3200 instrument operated at
6 kV accelerating voltage. The XRD was recorded on a ITAL APD 2000 powder diffrac-
tometer equipped with Cu K radiation (λ = 1.54056 Å) operated at 40 kV and 30 mA,
2
α
at a scanning speed of 2 s from 10° to 90° (2θ). Qualitative analysis of the Fe O @SiO -Cl
3
4
2
sample was performed by using energy-dispersive X-ray fluorescence spectroscopy (Brand:
Link analytical XR300). EDX analysis of the prepared catalyst was performed on a SEM-
TESCAN MIRA3-FEG instrument. The elemental analyses (C, H, N, S) were obtained
from a Vario El Series II elemental analyzer flowchart. Ultrasonication was performed in
a 2200 ETH-SONICA ultrasound cleaner with a frequency of 45 kHz.
4.2. Synthesis of the catalyst
4
.2.1. Synthesis of magnetic Fe O nanoparticles
3
4
+
2
+3
First, Fe O nanoparticles were prepared by co-precipitation of Fe and Fe ions with a
3
4
molar ratio of 1:2 following the reported method.[28] FeCl ·4H O (1.790 g, 9.0 mmol) and
2
2
FeCl ·6H O (4.865 g, 18 mmol) were dissolved in 100 mL deionized water and ultrasoni-
3
2
cated twice for 15 min each time under N atmosphere. Then, an aqueous 25% NH OH
2
4
solution (10 mL) was immediately added to the mixture under nitrogen gas and vigor-
ously stirred for a further 30 min at room temperature. The resulting black precipitate
was isolated and washed twice with distilled water and twice with 0.02 M NaCl aqueous
solution. Magnetic Fe O nanoparticles were separated in an external magnetic field and
3
4

JOURNAL OF SULFUR CHEMISTRY
13
dried under vacuum. The FT–IR spectra of the prepared Fe O nanoparticles are shown
3
4
in Figure 1(a).
4
.2.2. Synthesis of silica-coated magnetite Fe O nanoparticles (Fe O @SiO )
3
4
3
4
2
According to the previously reported method,[29] 30 mL of 0.2 M citric acid solution was
added to 1 g of the prepared magnetic Fe O nanoparticles and the mixture was ultra-
3
4
sonicated for 30 min. Then, the pH value of the mixture was adjusted to 5.2 by adding
.4 mL of aqueous ammonia solution. The reaction mixture was stirred under reflux condi-
0
tion for 90 min. The resulting reaction mixture was cooled to room temperature and 2 mL
of ammonia solution was added until the pH value was reached to 11. Then, a solution
of 1.2 mL tetraethyl orthosilicate in 12 mL ethanol was added dropwise and the resulted
mixture was sonicated for 30 min at room temperature followed by refluxing for 24 h.
The resulting solid Fe O @SiO nanoparticles were successively washed with ethanol and
3
4
2
deionized water. Finally, the dark brown precipitate was separated in a magnetic field and
dried in vacuum.
4.2.3. Synthesis of chloropropyl-modified silica-coated magnetite nanoparticles
(
Fe O @SiO -Cl)
3
4
2
Chloropropyl modification of the magnetite Fe O nanoparticles (Fe O @SiO ) was car-
3
4
3
4
2
ried out according to the reported method.[32] The Fe O @SiO (1 g) was dispersed in
3
4
2
5
(
0 mL of dry xylene and ultrasonicated for 60 min. Then, 3-chloropropyltrimethoxysilan
1.8 mL, 10 mmol) was added dropwise to the dispersion and ultrasonicated for 30 min.
The resulted mixture was subsequently refluxed at 140°C under vigorous stirring for
4 h. The resulted bright brown nanoparticles were magnetically separated, consecutively
washed twice with dry xylene and twice with ethanol, and then dried at 60°C. The FT–IR
spectrum obtained from the prepared Fe O @SiO -Cl nanoparticles is given in Figure
2
3
4
2
1
(b). Also, the XRF of the Fe O @SiO -Cl shown in Figure 3 exhibits the elemental
3 4 2
composition (Si, Cl, Fe).
4.2.4. Synthesis of diamine-functionalized silica-coated magnetite nanoparticles
(
Fe O @SiO @NH-NH )
3
4
2
2
A dispersion of 1 g of Fe O @SiO -Cl in 50 mL of CH CN was ultrasonicated for 30 min.
3
4
2
3
Subsequently, 1 mL ethylene diamine (15 mmol) and 0.1 mL of triethyl amine were added
dropwise to the reaction mixture and refluxed for 24 h. The resulted solid product was
separated from the solution using a magnet bar, washed with water/ethanol, and finally
dried at 60°C.
4
.2.5. Conversion of the Fe O @SiO @NHNH MNPs into the disulfonated derivative
3 4 2 2
Fe O @SiO @N(SO H)NH(SO H) MNPs
3
4
2
3
3
A dispersion of 1 g of the prepared magnetite Fe O @SiO @NH-NH nanoparticles
3
4
2
2
in 50 mL chloroform was ultrasonicated for 15 min. Then, chlorosulfonic acid (0.8 mL,
2 mmol) was added dropwise and the resulting reaction mixture was stirred for 4 h. The
1
resulted brick-red powder was successively separated by using a magnet bar, washed with
ethanol (3 × 30 mL) to remove the remaining acid, and dried overnight at room tempera-
ture. The successful synthesis of this sample was confirmed based on the FT–IR, EDX and
elemental analyses.

14
D. AZARIFAR ET AL.
4
.3. General procedure for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones 2a-l
using the nanocatalyst Fe O @SiO @N(SO H) NH(SO H)
3
4
2
3
3
To a mixture of methyl acetoacetate (1 mmol), aromatic aldehyde 1 (1 mmol) and urea
1.5 mmol) in a 100 mL round-bottomed flask, the synthesized catalyst (0.01 g) was added
(
and the mixture was mechanically stirred at 100°C for an appropriate time (Table 3). After
completion of the reaction as monitored by TLC, 10 mL of ethanol was added to the reac-
tion mixture and stirring was continued at room temperature for 10 min. The catalyst was
easily isolated by using a magnet bar and the product was obtained after removal of the
solvent under reduced pressure. Then, the product was treated with water followed by crys-
tallization from EtOH. The products were characterized by their physical and spectral (IR,
1
13
H and CNMR) analysis and compared with the reported data. The spectral data of the
new products are presented below.
4.3.1. 5-Methoxycarbonyl-6-methyl-4-(2,5-dimethoxyphenyl)-3,4-dihydropyrimidin-
2(1H)-one (2i)
Chartreuse yellow solid, m.p. 236–240°C; IR (KBr, cm−1): 3243 and 3107 (N–H str.), 2946
1
(
(
C-H str.) 1710, 1686 (C=O str.), 1643 (C=C str.). H NMR (90 MHz, DMSO-d ) δ: 2.28
6
s, 3H, CH ), 3.48, 3.65 (s, 3H, –COOCH ), 3.74 (s, 6H, –OCH ), 5.41 (s, 1H, CH), 7.24,
3 3 3
1
3
6
.85 and 6.55 (m, 4H, Ar–H), 7.70 (s, 1H, NH), 9.14 (s, 1H, NH) ppm. CNMR (300 MHz,
DMSO-d ) δ: 18.2, 49.4, 51.2, 55.7, 56.4, 97.7, 112.3, 112.7, 114.2, 132.9, 149.7, 151.1, 152.7,
6
1
53.4, 166.2 ppm. Anal. Calcd. for C H N O : C, 58.82; H, 5.92; N, 9.15; Found: C, 58.86;
15 18 2 5
H, 5.94; N, 9.18.
4.3.2. 5-Methoxycarbonyl-6-methyl-4-(2-phenylethyl)-3,4-dihydropyrimidin-2(1H)-
one (2j)
Cream solid, m.p. 138–140°C; IR (KBr, cm−1): 3252, 3114 (N–H str.), 2949 (C–H str.),
1
1
724, 1686 (C=O str.); 1658 (C=C str.). H NMR (90 MHz, DMSO-d ) δ: 2.16 (s, 3H,
6
CH ), 1.27 and 2.97 (m, 4H, CH CH ), 3.55 (s, 3H, –OCH ), 5.17 (s, 1H, CH), 7.20, 7.45
3
2
2
3
1
3
(
m, 5H, Ar–H), 7.73 (s, 1H, NH), 9.04 (s, 1H, NH) ppm. CNMR (300 MHz, DMSO-d6)
δ: 18.2, 30.4, 50.4, 51.1, 99.3, 126.1, 128.7, 142.0, 149.2, 153.2, 166.3 ppm. Anal. Calcd. for
C H N O : C, 65.68; H, 6.61; N, 10.21; Found: C, 65.72; H, 6.65; N, 10.26.
1
5
18
2
3
4.3.3. 5-Methoxycarbonyl-6-methyl-4-(pyridin-3-yl)-3,4-dihydropyrimidin-2(1H)-one
(2k)
Slime green solid, m.p. 200–203°C; IR (KBr, cm−1): 3212 and 3092 (N–H str.), 2949 (C–H
1
str.), 1707, 1677 (C=O str.), 1648 (C=C str.). H NMR (90 MHz, DMSO-d ) δ: 2.28 (s, 3H,
6
CH ), 3.53 (s, 3H, –OCH ), 5.20 (s, 1H, CH), 7.38, 7.58, 7.80 (m, 4H, Ar–H), 8.44 (s, 1H,
NH), 9.33 (s, 1H, NH) ppm. CNMR (22.5 MHz, DMSO-d ) δ: 17.8, 50.8, 51.9, 57.6, 98.1,
3
3
1
3
6
1
23.8, 133.8, 139.8, 147.8, 151.9, 157.7, 165.5 ppm. Anal. Calcd. for C H N O : C, 58.29;
12 13 3 3
H, 5.30; N, 16.99; Found: C, 58.34; H, 5.37; N, 17.05.
4.3.4. 5-Methoxycarbonyl-6-methyl-4-(thiophen-2-yl)-3,4-dihydropyrimidin-2(1H)-
one (2l)
Cream solid, m.p. 189–191°C; IR (KBr, cm−1): 3440–3115 (N–H str.), 2948 (C–H str.),
1
1
690, 1642 (C=O str.); 1607 (C=C str.). H NMR (400 MHz, DMSO-d ) δ: 2.2 (s, 3H,
6

JOURNAL OF SULFUR CHEMISTRY
15
CH ), 3.6 (s, 3H, –OCH ), 5.4 (s, 1H, CH), 6.91, 6.95 (m, 2H, Ar–H), 7.3 (s, H, H-CS),
3
3
1
3
7
1
.9 (s, 1H, NH), 9.4 (s, 1H, NH) ppm. CNMR (400 MHz, DMSO-d ) δ: 18.2, 49.7, 51.4,
6
00.0, 124.0, 125.1, 127.2, 149.1, 152.8, 160.3, 165.9 ppm. Anal. Calcd. for C H N O S:
1
1
12
2
3
C, 52.37; H, 4.79; N, 11.10; S, 12.71; Found: C, 52.45; H, 4.85; N, 11.16; S, 12.42.
4
.4. General procedure for the synthesis of 4H-chromenes 3a–3k using the
nanocatalyst Fe O @SiO @N(SO H)NH(SO H)
3
4
2
3
3
To a mixture of aromatic aldehyde 1 (1 mmol), malononitrile (1.2 mmol) and dimedone
(
1 mmol) in the mixed solvent EtOH (2.5 mL)/H O (2.5 mL) was added the nanocatalyst
2
(0.01 g) and the resulting mixture was stirred at the reflux temperature for an appropriate
time (Table 4). After completion of the reaction as monitored by TLC, 10 mL hot ethanol
was added to the reaction mixture and stirring was continued for further 10 min. Then,
the catalyst was separated from the reaction mixture simply by using an external magnet
bar. The remaining solution was diluted with 50 mL of water and filtered to collect the
solid products which were dried under vacuum. Crystallization in 96% ethanol provided
the pure products. The structures of the products were established on the basis of their
1
13
physical and spectral (IR, H NMR and CNMR) data which were in accord with those
reported in the literature. A number of selected data are presented below.
4.4.1. 2-Amino-4-(3-chlorophenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-
chromene-3-carbonitrile (3d)
White solid, m.p. 211–213°C, IR (KBr, cm−1): 3394, 3329, 3198, 2960, 2199, 1682, 1654,
1
1
2
604, 1370, 1214. H NMR (90 MHz, DMSO-d ) δ: 1.07 (s, 6H, CH ), 2.21 (s, 2H, CH ),
6
3
2
1
3
.44 (s, 2H, CH ), 4.65 (s, 2H, NH ), 4.84 (s, 1H, CH), 7.192 (s, 4H, H–Ar) ppm. C NMR
2
2
(
1
22.5 MHz DMSO-d ) δ: 196.3, 163.4, 159.0, 147.6, 133.3, 130.8, 127.5, 127.1, 126.4, 120.0,
12.5, 58.0, 50.3, 35.7, 32.3, 28.7, 27.2 ppm.
6
4.4.2. 2-Amino-4-(4-hydroxyphenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-
chromene-3-carbonitrile (3h)
White solid, m.p. 209–211°C, IR (KBr, cm−1): 3362, 3331, 3193, 2964, 2894, 2193, 1682,
1
1
2
9
1
651, 1605, 1371, 1215. H NMR (90 MHz, DMSO) δ: 0.90 (s, 3H, CH ), 0.97 (s, 3H, CH ),
3
3
.13 (s, 2H, CH ), 2.44 (s, 2H, CH ), 4.00 (s, 1H, CH), 6.63 (s, 2H, NH ), 6.84 (s, 4H, H–Ar),
2
2
2
1
3
.19 (s, 1H, OH) ppm. C NMR (22.5 MHz DMSO-d ) δ: 196.4, 163.4, 159.2, 156.0, 135.4,
6
28.5, 122.2, 115.5, 114.6, 59.9, 50.6, 41.4, 34.3, 33.2, 29.2, 27.4 ppm.
4.4.3. 2-Amino-7,7-dimethyl-4-(4-nitrophenyl)-5-oxo-5,6,7,8-tetrahydro-4H-
chromene-3-carbonitrile (3i)
Cream solid, m.p. 182–185°C, IR (KBr, cm−1): 3451, 3374, 3333, 3257, 3216, 2960, 2876,
1
2
196, 1688, 1671, 1594, 1520, 1362, 1218. H NMR (90 MHz, DMSO-d ) δ: 0.96 (s, 3H,
6
CH ), 1.04 (s, 3H, CH ), 2.17 (s, 2H, CH ), 2.53 (s, 2H, CH ), 4.37 (s, 1H, CH), 7.18 (m,
3
3
2
2
1
3
4
H, H–Ar), 8.12 (s, 2H, NH ) ppm. C NMR (22.5 MHz, DMSO-d ) δ: 195.8, 162.9, 158.7,
2
6
1
52.3, 146.3, 128.5, 124.1, 119.3, 112.1, 57.1, 49.9, 35.7, 34.5, 28.3, 27.1 ppm.

16
D. AZARIFAR ET AL.
4.4.4. 2-Amino-7,7-dimethyl-5-oxo-4-(thiophen-2-yl)-5,6,7,8-tetrahydro-4H-
chromene-3-carbonitrile (3k)
White solid, m.p. 200–202°C, IR (KBr, cm−1): 3382, 3321, 3208, 2963, 2878, 2198, 1678,
1
1
660, 1602,1466, 1374,1214. H NMR (400 MHz, DMSO-d ) δ: 0.98 (s, 3H, CH ), 1.05
6
3
(
s, 3H, CH ), 2.1–2.2 (s, 2H, CH ), 2.4–2.5 (s, 2H, CH ), 4.5 (s, 1H, CH), 6.6–6.9 (m,
3 2 2
1
3
2
1
3
H, H-Ar), 7.1–7.3 (s, H, H-CS, s, 2H, NH ) ppm. C NMR (400 MHz DMSO-d ) δ:
2
6
95.51, 162.47, 158.87, 149.25, 126.78, 124.39, 123.97, 119.58, 112.88, 57.99, 49.83, 31.71,
0.37, 28.61, 26.42 ppm. Anal. Calcd. for C H N O S: C, 63.98; H, 5.37; N, 9.33; S, 10.67;
1
6
16
2
2
Found: C, 64.08.72; H, 5.42; N, 9.38; S, 10.62.
Funding information
The authors wish to thank the Research Council of the Bu-Ali Sina University (Iran) for the financial
support to carry out this research.
ORCID details
Davood Azarifar http://orcid.org/0000-0002-7331-2748
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