Sulfonic acid-functionalized silica-coated magnetic nanoparticles as an efficient reusable catalyst for the synthesis of 1-substituted 1H-tetrazoles under solvent-free conditions

Article abstract of DOI:10.1039/c4dt01664e

Regarding green chemistry goals, silica-coated magnetite nanoparticles open up a new avenue to introduce a very useful and efficient system for facilitating catalyst recovery in different organic reactions. Therefore, in this paper the preparation of sulf

Full text of DOI:10.1039/c4dt01664e

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Sulfonic acid-functionalized silica-coated
magnetic nanoparticles as an efficient reusable
catalyst for the synthesis of 1-substituted
Cite this: Dalton Trans., 2014, 43,
12967
1
H-tetrazoles under solvent-free conditions†
Hossein Naeimi* and Samaneh Mohamadabadi
Regarding green chemistry goals, silica-coated magnetite nanoparticles open up a new avenue to intro-
duce a very useful and efficient system for facilitating catalyst recovery in different organic reactions.
Therefore, in this paper the preparation of sulfonic acid-functionalized silica-coated magnetic nanoparti-
3 4 3 4
cles with core–shell structure (Fe O @silica sulfonic acid) is presented by using Fe O spheres as the core
Received 5th June 2014,
Accepted 1st July 2014
and silica sulfonic acid nanoparticles as the shell. The catalyst was characterized by infrared spectroscopy,
scanning electron microscopy, X-ray diffraction analysis, dynamic light scattering, thermogravimetric ana-
lysis and vibrating sample magnetometry. Nanocatalyst can be recovered using an external magnet and
reused for subsequent reactions 6 times without noticeable deterioration in catalytic activity.
DOI: 10.1039/c4dt01664e
www.rsc.org/dalton
an amine, triethyl orthoformate, using AcOH, PCl
5 3
, In(OTf) ,
Introduction
Yb(OTf) , SSA, [HBIm]BF , natrolite zeolite, chitosan-sup-
3
4
Magnetic iron oxide nanoparticles have attracted much ported magnetic ionic liquid (CSMIL) and Fe O @SiO /salen
3
4
2
1
7–25
research interest over recent years because of their unique complex of Cu(II) as catalysts.
physicochemical properties and great potential for various bio- In this work, silica-coated magnetite nanoparticles are syn-
medical applications. In several pioneering works magnetic thesized through two steps. The magnetite nanoparticles are
nanoparticles were claimed as an effective tool for magneti- firstly prepared by a co-precipitation method. Then the magne-
1
2
cally assisted biomolecule separation, biochemical sensing,
tite nanoparticles are used to synthesize Fe O @SiO compo-
3 4 2
3
,4
5,6
26
NMR imaging,
targeted drug delivery
and cancer treat- site nanoparticles through the modified Stöber method. The
7
,8
ment through hyperthermia. The requirements for any bio- ability of this nano-magnetic solid acid to catalyze the one-pot,
medical application of magnetic nanoparticles include the three-component reaction between triethyl orthoformate, an
chemical stability, biocompatibility, strong magnetization and amine and sodium azide is also described. Mild reaction con-
low coercivity of the dispersed magnetic nanoparticles.
ditions, catalyst with high catalytic activity and good reusabil-
9
Tetrazoles have a wide range of applications. For example, ity, and simple magnetic work-up make this methodology an
they have roles in material science including explosives and interesting option for the economic synthesis of 1-substituted
1
0,11
rocket propellants.
In addition, they can also function as 1H-tetrazoles under solvent-free conditions.
1
2
ligands in coordination chemistry and information recording
1
3
systems.
Tetrazoles can be prepared by several methods including
acid-catalyzed cycloaddition between hydrazoic acid and iso-
Results and discussion
Preparation and characterization of the catalyst
1
4
cyanides, acid-catalyzed cycloaddition between isocyanides
1
5
and trimethyl azide, cyclization between primary amines, or Fe O @silica sulfonic acid core–shell composite, with Fe O
3
4
3 4
their salts, with an orthocarboxylic acid ester in acetic acid or spheres as the core and silica sulfuric acid nanoparticles as
1
6
trifluoroacetic acid and sodium azide, and cyclizations from the shell, was prepared by a simple, low-cost and convenient
method. Magnetite nanoparticles were synthesized by the co-
precipitation route. To improve the chemical stability of the
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan,
magnetite nanoparticles, their surfaces were successfully
Kashan, 87317, IR Iran. E-mail: naeimi@kashanu.ac.ir; Fax: +98-361-5912397;
modified by the suitable deposition of silica onto the nanopar-
Tel: +98-361-5912388
ticle surface by the ammonia-catalyzed hydrolysis of tetraethyl-
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4dt01664e
1
orthosilicate (TEOS). Next, the SiO spheres served as support for
2
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 12967–12973 | 12967

View Article Online
Paper
Dalton Transactions
Scheme 1 Preparation steps for fabricating sulfonic acid-functionalized
3 4
magnetic Fe O nanoparticles.
3 4 3 4 2 3 4
Fig. 2 XRD patterns of (a) Fe O , (b) Fe O @SiO and (c) Fe O @silica
sulfonic acid.
the immobilization of SO H groups by simple mixing of core–
3
shell composite and chlorosulfonic acid in CH
2 2
Cl (Scheme 1).
of (220), (311), (400), (422), (511) and (440) are indexed to the
crystalline cubic inverse spinel structure of Fe nanoparti-
cles. The sizes of the nanoparticles were evaluated from the
XRD data using the Debye–Scherrer equation, which gives a
relationship between particle size and peak broadening:
Fe @silica sulfonic acid nanocomposite was character-
3 4
O
3 4
O
ized by Fourier transform infrared (FT-IR) spectroscopy, X-ray
diffraction (XRD), thermogravimetric analysis (TGA), scanning
electron microscopy (SEM), dynamic light scattering (DLS) and
vibrating sample magnetometry (VSM).
Fig. 1 shows the FT-IR spectra of pure Fe
3 4 3 4 2
O , Fe O @SiO
d ¼ kλ=ðβ cos θÞ
core–shell, and Fe @silica sulfonic acid nanoparticles. The
3 4
O
−
1
absorption peak at approximately 570 cm corresponds to the
stretching vibration of the Fe–O bond and the adsorption of
the silica coating on the magnetite surface was indicated by
where d is the particle size of the crystal, k is the Scherrer con-
stant (0.94), λ is the X-ray wavelength (0.15406 nm), β is the
line broadening in radians obtained from the full width at half
maximum (FWHM), and θ is the Bragg diffraction angle of the
XRD diffraction peaks. The average MNPs core diameter was
calculated to be 21 nm from the XRD results using the above
equation.
−
1
the band near 1100 cm assigned to the Si–O stretching
vibration. Also, successful sulfonic acid functionalization of
the silica layer on Fe
tion bands at 1040 and 1130 cm related to the stretching of
3 4
O surface was evidenced by the absorp-
−1
−1
the S–O bonds. A peak appeared at about 3400 cm due to the
stretching of OH groups in the SO H moiety (Fig. 1c). These
FT-IR spectra provided evidence of the formation of a silica
TGA was used to study the thermal stability of the acid cata-
lyst (Fig. 3). It is clear that, for the Fe O @silica sulfonic acid
3
3
4
MNPs, there are three steps of weight loss. (1) Below 150 °C,
there was a mass loss that was attributable to the loss of
adsorbed solvent or trapped water from the catalyst. (2)
Around 150–500 °C, a large weight reduction occurred, which
can be mainly ascribed to the decomposition of SO H groups
Fig. 3b). (3) Above 500 °C, the occurrence of further mass
shell onto the surface of Fe
of the silica shell.
3 4
O and the acid functionalization
Fig. 2 shows the XRD patterns of magnetic nanoparticles.
The observed diffraction peaks appearing at 2θ = 30.3°, 35.6°,
3.3°, 53.8°, 57.4° and 62.9° corresponding to the diffractions
3
4
(
losses at higher temperature resulted from the decomposition
2
7
of the silica shell.
Fig. 1 Comparison of FT-IR spectra for (a) Fe
c) Fe @silica sulfonic acid.
3 4 3 4 2
O , (b) Fe O @SiO and
(
3
O
4
3 4 2 3 4
Fig. 3 TGA curves of (a) Fe O @SiO and (b) Fe O @silica sulfonic acid.
12968 | Dalton Trans., 2014, 43, 12967–12973
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
The morphology and structure of prepared samples were
characterized by SEM. Fig. 4a shows that the Fe O nanoparti-
3
4
cles are spherical in shape with an average size of 20 ± 2 nm.
Fig. 4b shows that most of the Fe @SiO nanoparticles are
spherical with larger particle size and smoother surface. The
SEM image shown in Fig. 4c demonstrates that Fe @silica
sulfonic acid nanoparticles are approximately spherical.
The DLS measurements of Fe O @silica sulfonic acid nano-
3
O
4
2
3 4
O
3
4
particles are shown in Fig. 5. In order to determine the fraction
of the particle population that aggregates, comparisons
between the intensity-averaged DLS data and number-averaged
DLS data were made. From this slurry, an aqueous stock dis-
persion (100 ml acetone with 5 g Fe
3 4
O @silica sulfonic acid)
was prepared using an ultrasonic bath for 30 min.
3 4
Fig. 5 DLS of Fe O @silica sulfonic acid.
The magnetic property of the catalyst was studied by VSM.
On the basis of Fig. 6, the saturation magnetization value was
measured to be 50.86 emu g− for Fe
1
O
@SiO
−1
3
4
2
and 14 emu g
for Fe O @silica sulfonic acid. The results show that the
3 4
surface modification reaction has little impact on the magnet-
ism of nano-adsorbent before and after modification, and also
the saturation magnetization of sulfonic acid-functionalized
silica-coated magnetic nanoparticles is lower than that of
+
Fe
3 4 2
O @SiO nanoparticles. Furthermore, the number of H
−
1
sites (0.33 mmol g ) for Fe
titatively determined by acid–base titration.
3 4
O @silica sulfonic acid was quan-
2
7
Optimization of the reaction conditions
In further studies regarding the effect of catalyst amount on
formation of 1-substituted 1H-tetrazoles, we found that the
yields were obviously affected by the amount of catalyst. It was
3 4
found that 0.02 g Fe O @silica sulfonic acid was sufficient to
catalyze the reaction of 4-chloroaniline, triethyl orthoformate
and sodium azide at 100 °C (Table 1, entry 4). The usage of
higher amounts of catalyst did not increase the yields signifi-
cantly, while decreasing the amount of catalyst reduced the
yields (Table 1). Also, when the reaction was attempted
without the addition of catalyst, no desired product was
obtained (Table 1, entry 1).
After optimization of the reaction conditions, the reaction
of triethyl orthoformate and sodium azide with various amines
Fig. 4 SEM images of (a) Fe
3
O
4
, (b) Fe
3
O
4
@SiO
2
and (c) Fe
3
O
4
@silica
3 4 2
Fig. 6 Magnetization curves for the prepared (a) Fe O @SiO and (b)
sulfonic acid.
3 4
Fe O @silica sulfonic acid.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 12967–12973 | 12969

View Article Online
Paper
Dalton Transactions
Table 1 Effect of catalyst amount on formation of 1-substituted 1H- the desired product within 50 min in 97% yield in shorter reac-
a
tetrazoles
tion time and lower temperature than SSA and natrolite
zeolite. Also this catalyst is comparable with In(OTf)
BF , CSMIL and Fe @SiO /salen Cu(II).
3
, [HBIm]-
b
Entry
Cat. amount (g)
Time (min)
Yield (%)
4
3
O
4
2
1
2
3
4
5
6
No catalyst
0.005
0.01
0.02
0.03
300
150
120
80
50
50
0
65
82
95
80
63
Experimental section
Chemicals
0.05
a
Iron(II) chloride tetrahydrate (99%), iron(III) chloride hexa-
hydrate (98%), tetraethoxysilane (TEOS), chlorosulfonic acid
and other chemical materials were purchased from Fluka and
Merck and used without further purification.
Reaction conditions: 4-chloroaniline (1 mmol), triethyl orthoformate
b
(1.2 mmol), and sodium azide (1 mmol). Isolated yield.
was carried out according to the general experimental pro-
cedure shown in Scheme 2.
Apparatus
In all cases, the corresponding 1-substituted 1H-tetrazoles
were obtained in high to excellent yields and in short reaction
times. Therefore, we carried out the reaction of several anilines
with triethyl orthoformate and sodium azide in the presence
of 0.02 g Fe O @silica sulfonic acid. The results are summar-
Products were characterized by comparison of their physical
1
13
data, and IR, H NMR and C NMR spectra with known
samples. NMR spectra were recorded with a Bruker Advance
DPX 400 MHz spectrometer at 400 and 100 MHz in CDCl as
3
3
4
solvent in the presence of TMS as internal standard. IR spectra
were recorded as KBr pellets using a Perkin-Elmer 781 spectro-
photometer. The purity determination of the products and
reaction monitoring were accomplished by thin-layer chrom-
atography (TLC) on silica gel PolyGram SILG/UV 254 nm
plates. XRD patterns of samples were obtained with a Philips
ized in Table 2.
A wide range of anilines containing electron-withdrawing
groups and electron-donating groups such as bromo, chloro,
methyl and acetyl underwent condensation in short reaction
times with excellent isolated yields. The para-position anilines
(Table 2, entries 3 and 4) gave good results in comparison to the
Xpert X-ray powder diffractometer (CuK radiation,
.154056 nm). The particle morphology was examined by SEM
Hitachi S4160 scanning electron microscope). TGA patterns
k =
ortho-position anilines (Table 2, entries 6 and 10). There is more
steric hindrance for the ortho-position anilines (o-Cl, -Me) on
product formation than the para-position (p-Cl, -Me) anilines.
All known compounds were characterized by comparing their
physical and spectral data with those reported in the literature.
0
(
were obtained for characterization of the heterogeneous cata-
lyst with a Rheometric Scientific Inc. 1998 thermal analysis
apparatus under a N atmosphere. DLS was performed with a
2
Malvern ZEN 3600. Melting points were measured using a
Yanagimoto micro melting point apparatus. A Bandelin ultra-
sonic HD 3200 with probe model KE of 76.6 mm in diameter
was used to produce ultrasonic irradiation.
Reusability of the catalyst
The reusability is one of the important properties of this cata-
lyst. The possibility of recovery of the catalyst was investigated
for the reaction of aniline, triethyl orthoformate, and sodium
azide under optimized conditions. After completion of the
model reaction, the catalyst was recovered from the reaction
mixture simply by an external magnet. Then the recovered
catalyst was washed with ethyl acetate, and reused for sub-
sequent reactions 6 times without noticeable deterioration in
catalytic activity (Fig. 7).
Preparation of Fe O (MNPs)
3
4
Magnetic nanoparticles were synthesized by co-precipitation of
FeCl ·6H O and FeCl ·4H O in ammonia solution, according
3
2
2
2
7,28
2
to a reported procedure.
3 2
Typically, FeCl ·6H O (15.136 g)
and FeCl ·4H O (6.346 g) were dissolved in 0.64 L deionized
2
2
water under nitrogen at 90 °C and added to a 25% ammonium
hydroxide solution (0.08 L) with vigorous mechanical stirring.
After the color of the bulk solution turned to black the reaction
Comparison of the Fe O @silica sulfonic acid catalyst with
other catalysts
3
4
was carried out for 60 min in N atmosphere. The resulting
2
In subsequent experiments, the activity of the prepared catalyst
was measured in the model reaction. From Table 3, it is clear
that Fe O @silica sulfonic acid worked remarkably well to give
black MNPs were isolated by applying an external magnet,
washed 3 times with deionized water and then dried under
vacuum at 60 °C for 12 h.
3
4
Preparation of Fe O @SiO
2
3
4
3 4 2
The Fe O @SiO nanospheres were prepared by a modified
Stöber method. Briefly, Fe O (0.50 g) was dispersed in a
3
4
mixture of ethanol (50 mL), deionized water (5 mL) and TEOS
0.20 mL), followed by the addition of 5.0 mL of NaOH
(10 wt%). This solution was stirred mechanically for 30 min
(
Scheme 2 Synthesis of 1-substituted 1H-tetrazoles catalyzed by
Fe @silica sulfonic acid.
3
O
4
12970 | Dalton Trans., 2014, 43, 12967–12973
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
a
3 4
Table 2 Preparation of 1-substituted 1H-tetrazoles in the presence of Fe O @silica sulfonic acid
b
Entry
1
Substrate
Product
Time (min)
50
Yield (%)
TON
97
95
95
92
87
146.96
2
3
4
5
80
80
60
70
143.94
143.94
139.39
131.81
6
7
100
90
82
90
124.24
136.36
8
9
180
100
78
96
118.18
151.51
1
1
0
1
135
150
83
84
125.75
127.27
12
170
81
122.72
a
b
Reaction conditions: amines (1 mmol), triethyl orthoformate (1.2 mmol), and sodium azide (1 mmol). Isolated yield.
3 4 2
at room temperature. Then the product, Fe O @SiO , was (0.5 g) was added into the flask and dispersed ultrasonically
separated by an external magnet and was washed with for 10 min in dry CH Cl (10 mL). Chlorosulfonic acid (0.4 mL)
2
2
deionized water and ethanol three times and dried at 80 °C for was added dropwise to a cooled ice-bath over a period of
1
0 h.
30 min at room temperature. After completion of the addition,
the mixture was shaken for 90 min, while the residual HCl was
eliminated by suction. Then the Fe O @silica sulfonic acid
Preparation of Fe
3 4
O @silica sulfonic acid
3
4
A suction flask was equipped with a constant pressure drop- was separated from the reaction mixture by a magnetic field
ping funnel. The gas outlet was connected to a vacuum system and washed several times with dried CH Cl . Finally, Fe
through an adsorbing solution of alkali trap. Fe O @silica silica sulfonic acid was dried under vacuum at 60 °C.
O @
3 4
2
2
3
4
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 12967–12973 | 12971

View Article Online
Paper
Dalton Transactions
1
(
7
1
CvC); H NMR (CDCl
3
, 400 MHz) δ (ppm): 6.98–7.00 (d, 2H),
1
3
.27–7.29 (d, 2H), 8.09 (s, 1H tetrazole); C NMR (CDCl3,
00 MHz) δ (ppm): 120.35, 128.85, 129.47, 143.52, 149.50.
1
-(4-Methylphenyl)-1H-tetrazole (3d). Light yellow solid
−1
2
(
87% yield); m.p. = 92–99 °C; IR (KBr)/ν (cm ): 3022 (C–H, sp
stretch, Ar), 2918 (C–H, sp stretch), 1664 (CvN), 1607, 1506
CvC); H NMR (CDCl
3
1
(
3
, 400 MHz) δ (ppm): 2.34 (s, 3H),
6
.94–6.96 (d, 2H), 7.11–7.13 (d, 2H), 8.17 (s, 1H tetrazole);
C NMR (CDCl , 100 MHz) δ (ppm): 20.79, 119.08, 129.63,
3
1
3
130.17, 142.95, 149.77.
Fig. 7 Reusability of Fe
triethyl orthoformate, and sodium azide under solvent-free conditions.
3
O
4
@silica sulfonic acid for the reaction of aniline,
1-(3-Methylphenyl)-1H-tetrazole (3e). White solid (85%
−1
2
yield); m.p. = 53–55 °C; IR (KBr)/ν (cm ): 3167 (C–H, sp
3
stretch, Ar), 2923 (C–H, sp stretch), 1690 (CvN), 1594, 1483
1
(
(
CvC); H NMR (CDCl , 400 MHz) δ (ppm): 2.33 (s, 3H), 6.86
3
Table 3 Comparison of different catalysts in the formation of 1-substi-
a
s, 1H), 6.89–6.91 (d, 2H), 7.18–7.22 (t, 1H), 8.21 (s, 1H tetra-
tuted 1H-tetrazoles
1
3
zole); C NMR (CDCl
19.97, 124.06, 129.19, 139.26, 145.28, 149.23.
-(2-Methylphenyl)-1H-tetrazole (3f). White solid (82%
3
, 100 MHz) δ (ppm): 21.43, 115.93,
b
Temp. Time Yield
1
Entry Catalyst
Solvent (°C)
(min) (%)
Ref.
1
−
1
2
1
2
3
4
5
6
7
SSA
Neat
Neat
Neat
Neat
Neat
120
120
100
100
70
100
100
300
240
90
30
60
60
50
95
82
89
91
92
96
97
20
22
18
21
23
24
—
yield); m.p. = 152–155 °C; IR (KBr)/ν (cm ): 3015 (C–H, sp
stretch, Ar), 2870 (C–H, sp stretch), 1664 (CvN), 1488, 1590
CvC); H NMR (CDCl
Natrolite zeolite
In(OTf)
[HBIm]BF
CSMIL
3
3
1
(
3
, 400 MHz) δ (ppm): 2.33 (s, 3H),
4
7.02–7.03 (d, 1H), 7.05–7.07 (d, 1H), 7.18–7.22 (t, 2H), 8.08 (s,
Fe
Fe
3
O
O
4
@SiO
@silica sulfonic
2
/salen Cu(II) Neat
13
1
1
H-Tetrazole); C NMR (CDCl , 100 MHz) δ (ppm): 17.94,
3
3
4
Neat
17.68, 123.43, 127, 128.71, 130.72, 144.10, 147.78.
acid
1
-(2,4-Dimethylphenyl)-1H-tetrazole (3g). White solid (90%
a
Reaction conditions: aniline (1 mmol), triethyl orthoformate
−1
2
yield); m.p. = 133–135 °C; IR (KBr)/ν (cm ): 3069 (C–H, sp
stretch, Ar), 2914 (C–H, sp stretch), 1663 (CvN), 1495, 1607
CvC); H NMR (CDCl , 400 MHz) δ (ppm): 2.29 (s, 3H), 2.30
3
s, 3H), 6.94–6.96 (d, 1H), 6.98–7.00 (d, 1H), 7.02 (s, 1H), 8.00
(
(
3 4
1.2 mmol), and sodium azide (1 mmol), Fe O @silica sulfonic acid
b
3
0.02 g), solvent free at 100 °C. Isolated yield.
1
(
(
(
General synthesis for the preparation of 1-substituted
H-tetrazoles
s, 1H tetrazole).
1
1-(4-Acetylphenyl)-1H-tetrazole (3h). Yellow solid (78%
−
1
2
A mixture of amine (1 mmol), sodium azide (1 mmol), triethyl yield); m.p. = 175–176 °C; IR (KBr)/ν (cm ): 3075 (C–H, sp
orthoformate (1.2 mmol) and Fe O @silica sulfonic acid (0.02 g) stretch, Ar), 2995 (C–H, sp stretch), 1669 (CvN), 1499, 1585
3 4
was placed in a round-bottomed flask and stirred at 100 °C. The (CvC); H NMR (CDCl , 400 MHz) δ (ppm): 2.60 (S, 3H),
3
1
3
progress of the reaction was monitored by TLC. After completion 7.13–7.15 (d, 2H), 7.95–7.97 (d, 2H), 8.30 (s, 1H tetrazole).
of the reaction, the reaction mixture was cooled to room temp-
1-(3-Chlorophenyl)-1H-tetrazole (3i). White solid (81%
erature and diluted with ethyl acetate (3 × 20 mL). The catalyst yield); m.p. = 137–139 °C; IR (KBr)/ν (cm− ): 3065 (C–H, sp
1
2
1
was removed by an external magnet, and then the resulting solu- stretch, Ar), 1669 (CvN), 1473, 1586 (CvC); H NMR (CDCl ,
3
tion was washed with water and dried over anhydrous Na
After concentration, a crystallization step was performed using 7.26–7.27 (t, 1H), 8.14 (s, 1H tetrazole); C NMR (CDCl3,
2
SO
4
.
400 MHz) δ (ppm): 6.92–6.94 (d, 1H) 7.07–7.09 (d, 2H)
1
3
1
EtOAc–hexane (1 : 9). The products were characterized by
H
100 MHz) δ (ppm): 117.45, 119.23, 123.73, 130.34, 135.12,
NMR, C NMR, FT-IR and melting points. We report the spec- 146.14, 149.72.
tral data of the synthesized compounds.
1-(2-Chlorophenyl)-1H-tetrazole (3j). White solid (79%
-(Phenyl)-1H-tetrazole (3a). Yellow solid (97% yield); m.p. = yield); m.p. = 129–131 °C; IR (KBr)/ν (cm− ): 3023 (C–H, sp
13
1
2
1
−1
2
1
6
3–65 °C; M.P.Lit: 65–67 °C; IR (KBr)/ν (cm ): 3126 (C–H, sp
stretch Ar), 1694 (CvN), 1597, 1498 (CvC); H NMR (CDCl , 400 MHz) δ (ppm): 7.03–7.50 (m, 4H), 8.10 (s, 1H tetrazole).
3
stretch, Ar), 1670 (CvN), 1481, 1598 (CvC); H NMR (CDCl ,
1
3
4
00 MHz) δ (ppm): 7.07–7.34 (m, 5H, Ar), 8.20 (s, 1H tetrazole).
1-(Naphthalen-1-yl)-1H-tetrazole (3k). White solid (84%
-(4-Bromophenyl)-1H-tetrazole (3b). White solid (95% yield); m.p. = 132–135 °C; IR (KBr)/ν (cm− ): 3048 (C–H, sp
1
2
1
−
1
2
1
yield); m.p. = 169–170 °C; IR (KBr)/ν (cm ): 3060 (C–H, sp
stretch, Ar), 1659 (CvN), 1576, 1482 (CvC); H NMR (CDCl
stretch, Ar), 1658 (CvN), 1574, 1432 (CvC); H NMR (CDCl ,
3
1
3
,
400 MHz) δ (ppm): 7.23–8.27 (m, 7H), 8.36 (s, 1H tetrazole).
4
1
1
00 MHz) δ (ppm): 6.92–6.94 (d, 2H), 7.40–7.42 (d, 2H), 8.09 (s,
1-[2-(1H-Tetrazol-1-yl)phenyl]-1H-tetrazole (3l). White solid
1
3
−1
H tetrazole); C NMR (CDCl , 100 MHz) δ (ppm): 116.43, (83% yield); m.p. = 167–169 °C; IR (KBr)/ν (cm ): 3062 (C–H,
3
2
1
20.76, 132.03, 143.99, 149.29.
sp stretch, Ar), 1619 (CvN) 1458, 1588 (CvC); H NMR
1
-(4-Chlorophenyl)-1H-tetrazole (3c). White solid (95% (CDCl , 400 MHz) δ (ppm): 7.30–7.70 (m, 4H), 8.11 (s, 1H tetra-
3
1
3
yield); m.p. = 153–155 °C; M.P.Lit: 155–156 °C; IR (KBr)/ν zole); C NMR (CDCl , 100 MHz) δ (ppm): 115.76, 122.37,
cm ): 3057 (C–H, sp stretch, Ar), 1661 (CvN), 1485, 1581 138.50, 142.40.
3
−
1
2
(
12972 | Dalton Trans., 2014, 43, 12967–12973
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
9
R. N. Butler and A. R. Katritzky, in Comprehensive Hetero-
cyclic Chemistry, ed. C. W. Rees and E. F. V. Scriven, Perga-
mon, Oxford, UK, 1996, vol. 4.
Conclusion
3 4
In conclusion, we have firstly reported that Fe O @silica sulfo-
nic acid can be an efficient and reusable catalyst for one-pot 10 (a) V. A. Ostrovskii, M. S. Pevzner, T. P. Kofmna,
synthesis of 1-substituted 1H-tetrazoles from an amine, triethyl
orthoformate and sodium azide. The catalytic research on
novel approaches toward magnetic nanoparticles should be
improved to enhance organic synthesis. For that purpose, the
M. B. Shcherbinin and I. V. Tselinskii, Targets Heterocycl.
Syst., 1999, 3, 467; (b) M. Hiskey, D. E. Chavez, D. L. Naud,
S. F. Son, H. L. Berghout and C. A. Bome, Proc. Int. Pyrotech.
Semin., 2000, 27, 3.
magnetic nanocatalyst provides a high surface area for inter- 11 M. U. S. Brown, Patent 3,338,915, 1967; Chem. Abstr., 1968,
action with compounds. This catalyst can provide a new way 87299.
for continuous processes, because of its simple recyclability. 12 (a) V. V. Nilulin, T. V. Artamonova and G. I. Koldobskii,
Good yields, short reaction times, solvent-free conditions, non-
toxicity and recyclability with a very easy operation are the
most important advantages of the synthesized catalyst. The
Russ. J. Org. Chem., 2003, 39, 1525–1529; (b) V. V. Nilulin,
T. V. Artamonova and G. I. Koldobskii, Russ. J. Org. Chem.,
2005, 41, 444–445.
catalyst can be easily recovered from the reaction system by an 13 G. I. Koldobskii and V. A. Ostrovskii, Usp. Khim., 1994, 63,
external magnet and reused 6 times without noticeable
deterioration in catalytic activity.
847.
14 (a) D. M. Zimmerman and R. A. Olofson, Tetrahedron Lett.,
1969, 58, 5081; (b) F. G. Fallon and R. M. Herbst, J. Org.
Chem., 1957, 22, 933.
1
5 T. Jin, S. Kamijo and Y. Yamamoto, Tetrahedron Lett., 2004,
Acknowledgements
45, 9435.
The authors are grateful to University of Kashan for supporting 16 Y. Satoh and N. Marcopulos, Tetrahedron Lett., 1995, 36,
this work by grant no. 159148/43.
1759–1762.
1
1
7 A. K. Gupta and C. H. Oh, Tetrahedron Lett., 2004, 45,
4113–4116.
8 K. Dhiman, M. Adinath and H. Alakananda, Tetrahedron
Lett., 2009, 50, 2668–2670.
Notes and references
1
2
3
O. Olsvik, T. Popovic, E. Skjerve, K. S. Cudjoe, E. Hornes, 19 W. Su, Z. Hong, W. Shan and X. Zhang, Eur. J. Org. Chem.,
J. Ugelstad and M. Uhlen, Clin. Microbiol. Rev., 1994, 7, 43–54.
2006, 2723–2726.
M. N. Widjojoatmodjo, A. C. Fluit, R. Torensma and 20 D. Habibi, H. Nabavi and M. Nasrollahzadeh, J. Chem.,
J. Verhoef, J. Immunol. Methods, 1993, 165, 11–19.
2012, 1–4.
R. Weissleder, G. Elizondo, J. Wittenberg, C. A. Rabito, 21 T. M. Potewar, S. A. Siddiqui, R. J. Lahoti and
H. H. Bengele and L. Josephson, Radiology, 1990, 175, 489–
93.
J. W. M. Bulte, L. D. Ma, R. L. Magin, R. L. Kamman,
K. V. Srinivasan, Tetrahedron Lett., 2007, 48, 1721–1724.
22 D. Habibi, M. Nasrollahzadeh and T. A. Kamali, Green
Chem., 2011, 13, 3499–3504.
4
4
C. E. Hulstaert, K. G. Go, T. H. The and L. de Leij, Magn. 23 A. khalafi-Nezhad and S. mohammadi, RSC Adv., 2013, 3,
Reson. Med., 1993, 29, 32–37.
4362–4371.
P. K. Gupta, C. T. Hung, F. C. Lam and D. G. Perrier, 24 F. Dehghani, A. R. Sardarian and M. Esmaeilpour, J. Orga-
Int. J. Pharm., 1988, 43, 167–177.
nomet. Chem., 2013, 743, 87–96.
T. Neuberger, B. Schöpf, H. Hofmann, M. Hofmann and 25 N. T. Pokhodylo, V. S. Matiychuk and M. D. Obushak, Tetra-
5
6
B. von Rechenberg, J. Magn. Magn. Mater., 2005, 293, 483–
96.
A. Jordan, P. Wust, H. Fahling and R. Scholz,
Int. J. Hyperthermia, 1993, 9, 51–58.
hedron, 2008, 64, 1430.
26 W. Stöber, A. Fink and E. Bohn, J. Colloid Interface Sci.,
1968, 26, 62–69.
27 F. Nemati, M. M. Heravi and R. Saeedirad, Chin. J. Catal.,
2012, 33, 1825–1831.
4
7
8
U. Hafeli, W. Schutt, J. Teller and M. Zborowski, Scientific
and Clinical Applications of Magnetic Carriers, Plenum Press, 28 K. D. Kim, S. S. Kim, Y. H. Choa and H. T. Kim, J. Ind. Eng.
New York and London, 1997, pp. 527–534.
Chem., 2007, 13, 1137–1141.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 12967–12973 | 12973