Solvent-free synthesis of 1-aryl-1H-1,2,3,4-tetrazoles using FeCl 3-SiO2 catalysis under conventional and ultrasound irradiation conditions

Article abstract of DOI:10.3184/174751913X13729393880865

1-Aryl-1H-1,2,3,4-tetrazoles were synthesised by the solvent-free reactions of aryl amines, sodium azide and triethyl orthoformate using FeCl ₃-SiO₂ as an effective heterogeneous catalyst under conventional and ultrasound irradiation

Full text of DOI:10.3184/174751913X13729393880865

4
64 RESEARCH PAPER
AUGUST, 464–466
JOURNAL OF CHEMICAL RESEARCH 2013
Solvent-free synthesis of 1-aryl-1H-1,2,3,4-tetrazoles using FeCl –SiO
3
2
catalysis under conventional and ultrasound irradiation conditions
Davood Habibi*, Samaneh Mostafaee and Leila Mehrabi
Department of Organic Chemistry, Bu-Ali Sina University, Hamedan, Iran
1
-Aryl-1H-1,2,3,4-tetrazoles were synthesised by the solvent-free reactions of aryl amines, sodium azide and triethyl
orthoformate using FeCl –SiO as an effective heterogeneous catalyst under conventional and ultrasound irradiation
3
2
conditions. This method has the advantages of high yields, simple methodology and easy work-up. The catalyst can
be recovered by simple filtration and reused delivering good yields.
Keywords: 1-aryl-1H-1,2,3,4-tetrazoles, triethyl orthoformate, aryl amine, sodium azide, FeCl –SiO , heterogeneous catalyst
3
2
The preparation of substituted tetrazoles has been the subject
of thorough investigation, over the last few decades. Tetrazoles
removed from the reaction mixtures by simple filtration. The
recovered catalyst was reused three times without any loss of
activity (Table 2, entry 1). No deterioration of the catalyst was
observed, confirming the high stability of the applied catalytic
system under the reaction conditions.
1
have a wide range of applications in pharmaceutical, material
2
–4
and coordination chemistry. However, the use of these
compounds is limited by their availability.
5
–7
The common methods of preparing tetrazoles suffer from
disadvantages such as low yield, long reaction times, harsh
reaction conditions, tedious work-up and from the presence
of hydrazoic acid which is highly toxic and explosive.
To show the advantages of the present work in comparison
with the results reported in the literature, we compared FeCl –
3
6
19
7
SiO with AcOH, ionic liquid andYb(OTf) in the synthesis
2 3
3
of the 1-substituted tetrazoles (Table 3). As shown, FeCl –SiO2
is a better catalyst with respect to the reaction times and yields
In recent years heterogeneous catalysts have become
important in organic syntheses because of economic and
environmental considerations. Among various silica-based
heterogeneous catalysts, FeCl –SiO has advantages of low
of the products. In comparison with Yb(OTf) and AcOH,
3
it uses only 20 mol % of the catalyst with a shorter reaction
time and improved yield and in contrast with the ionic
liquids, this method does not require purification by column
chromatography.
3
2
8
–10
cost, ease of preparation and recyclability.
A large number of organic reactions can be carried out in a
higher yield, shorter reaction time and milder conditions under
ultrasonication. Compared with traditional methods, this
To determine the specific effect of ultrasonic irradiation, all
reactions were carried out under the new condition and the
results showed that the new procedure gave better yields with
shorter reaction times (Table 2). This observation is probably
1
1,12
method is more convenient and can be easily controlled.
In continuation of our work on the synthesis of heterocycles
20
1
3–18
consistent with the basic concept of the green chemistry.
and application of the heterogeneous reagents,
we report
To the best of our knowledge, this new procedure provides the
first example of an efficient ultrasound promoted one-pot
three-component approach to the synthesis of 1-substituted
aryl tetrazoles.
a new protocol for preparation of 1-aryl tetrazoles from the
reaction of wide variety of primary amines, sodium azide and
triethyl orthoformate using FeCl –SiO as a solid acid catalyst
3
2
under conventional conditions and ultrasound irradiation
Scheme 1).
(
Conclusions
In conclusion, we have developed a novel and highly efficient
method for the solvent-free synthesis of 1-aryl tetrazoles by
the treatment of primary aryl amines with ethyl orthoformate
and sodium azide in the presence of FeCl –SiO as catalyst
under conventional conditions and ultrasound irradiation.
The significant advantages of this method are high yields,
elimination of dangerous and harmful hydrazoic acid, a simple
work-up procedure and easy preparation and handling of the
catalyst. The catalyst can be recovered by filtration and reused.
Results and discussion
First, we optimised the required amount of the catalyst in the
reaction between aniline, sodium azide and triethyl orthofor-
mate (Table 1). The optimum amount of FeCl –SiO was found
3
2
3
2
to be 0.02 g in the presence of amine (2 mM), sodium azide
(
2 mM) and triethyl orthoformate (2.4 mM).
Next we examined a variety of amines possessing a wide
range of functional groups to establish the scope of the FeCl3–
SiO promoted reaction to form the 1-substituted tetrazoles.
2
The results are summarised in Table 2.
Table 1 Preparation of 1-phenyl-1H-1,2,3,4-tetrazole (2a) using
Recovery and catalyst reusability are important issues in the
cyclisation reactions. Easy catalyst separation and recycling
in successive batch operations can greatly increase the
efficiency of the reaction. FeCl –SiO as an inexpensive and
various amounts of FeCl
3
–SiO
2
under solvent-free conditions at
1
30 °Ca
Entry
FeCl
3
–SiO
2
/g
Temperature/°C
Yield/%b
3
2
non-hazardous solid acid catalyst can easily be handled and
1
2
3
4
5
6
7
8
9
0.008
0.01
0.015
0.02
0.02
0.02
0.02
0.02
0.00
130
130
130
130
120
110
100
90
72
85
91
95
80
63
45
34
0.0c
130
a
Reaction conditions: amine (2 mmol), NaN
formate (2.4 mmol), reaction time (2.30 h).
3
(2 mmol), ortho-
Scheme 1 Synthesis of the 1-aryl-1H-1,2,3,4-tetrazoles under
b
conventional and ultrasound irradiation.
Isolated yield.
c
In the absence of catalyst at 130 °C, no reaction was observed
even after 2.30 h.
*
Correspondent. E-mail: davood.habibi@gmail.com

JOURNAL OF CHEMICAL RESEARCH 2013 465
Table 2 Preparation of the 1-substituted tetrazoles (2a–k) by reaction of different amines (1a–k) with sodium azide and triethyl
b
c
3 2
orthoformate in the presence of FeCl –SiO under conventional conditions or ultrasound irradiation
Entry
1
R in R–NH
2
R in 1-substituted 1H-1,2,3,4-tetrazoles
-2a
Time/h
Yield/%a
Ref.
2.30b
95 , 92
b
d
7, 19
C
6
H
5
-1a
6 5
C H
c
c
2.0
96
b
c
b
2
3
4
5
6
7
8
9
3-H
4-H
2-H
4-ClC
2-ClC
4-BrC
3-F CC
4-H CCOC
2,4-(H
3
CC
CC
CC
6
H
4
-1b
3-H
4-H
2-H
4-ClC
2-ClC
4-BrC
3-F CC
4-H CCOC
2,4-(H C)
3
CC
CC
CC
6
H
4
-2b
2.45
.45
90
7
7, 19
19
c
1
92
b
c
b
3
6
H
4
-1c
-1d
-1e
3
6
H
4
-2c
-2d
-2e
2.15
.45
85
c
1
92
b
b
3
6
H
4
3
6
H
4
3.0
75
c
b
c
c
2.30
79
b
6
H
4
6
H
4
2.45
93
7, 19
7
c
1
.30
95
b
b
6
H
4
-1f
6
H
4
-2f
3.0
79
c
c
2.15
83
b
c
b
6
H
4
-1g
6
H
4
-2g
2.45
85
23
c
2.00
89
b
c
b
3
6
H
4
-1h
-1i
-1j
3
6
H
4
-2h
-2i
-2j
2.30
.45
84
23
c
1
89
b
c
b
3
6
H
4
3
6
H
4
2.45
.45
87
19
c
1
2.30
89
b
c
b
1
1
0
1
3
C)
2
C
6
H
3
3
2
C
6
H
3
76
23
c
2
.00
.30
82
b
c
b
3
71
c
2-H
2
NC
6
H
4
-1k
3.00
74
23
2k
a
Yield refers to the pure isolated product.
Under thermal conditions at 130 °C.
Under ultrasound irradiation conditions at 45 °C.
Yield after the third cycle.
b
c
d
3 2 3
Table 3 Comparison of FeCl –SiO with AcOH, ionic liquid and Yb(OTf) in synthesis of 1-phenyl-1H-1,2,3,4-tetrazole (2a)
Entry
Catalyst
Amine:orthoformate:sodium azide:catalyst mol %, reaction conditions
Time
Yield/%
1
2
3
4
AcOH
1:3:1.1:70 %, AcOH, reflux, recrystallisation
2.5 h
6 h
25 min
90 min
85
85
89
95
Yb(OTf)
3
3 2 4
1:1.2:1:20 %, CH OC H OH, 100 °C, recrystallisation
Ionic liquid
FeCl –SiO
3 2
1:1.2:1:30 %, Ionic liquid, 100 °C, column chromatography
2:2.4:2:20 %, Solvent-free, 130 °C, recrystallisation
Experimental
combined organic layers were washed with brine and dried over
anhydrous Na SO . After concentration, the product was crystallised
from EtOAc–hexane to afford the pure product.
All reagents were purchased from the Merck and Aldrich chemical
companies and used without further purification. Products were
characterised by spectroscopy data (FT-IR, H NMR and C NMR
spectra), elemental analysis (CHN) and melting points. The NMR
spectra were recorded in DMSO and CDCl . H NMR spectra were
2
4
1
13
The products were characterised by spectroscopic methods,
elemental analysis (CHN) and melting points and the physical data
of known compounds were found to be identical with those reported
1
3
7
13
in the literature. C NMR spectra displayed signals about δ = 147–
recorded on a Bruker Avance DRX 90 MHz instrument. The chemical
shifts (δ) are reported in ppm relative to the TMS as internal standard
1
9
1
57 ppm for C5 of tetrazole ring.
1-Phenyl-1H-1,2,3,4-tetrazole (2a, Table 2, entry 1): M.p. 65–
13
and J values are given in Hz. C NMR spectra were recorded at
2.5 Hz. FT-IR (KBr) spectra were recorded on a Perkin-Elmer 781
spectrophotometer. Ultrasonication was performed in a PARSONIC
600s ultrasound cleaner with a frequency of 28 kHz and an output
7
1
6
6 °C (lit: 64–65 °C) ; H NMR (90 MHz, CDCl ): δ = 7.39–6.99 (m,
3
2
4
H), 8.21 (s, 1H).
1
-(3-Methylphenyl)-1H-1,2,3,4-tetrazole (2b, Table 2, entry 2):
2
7 1
M.p. 53–55 °C (lit: 53–54 °C) ; H NMR (90 MHz, CDCl ): δ = 2.30
3
power of 50 W (Builtin heating, 20–70 °C thermostatically adjust-
able). Melting points were taken in open capillary tubes with a BUCHI
(
s, 3H), 6.82–7.19 (m, 4H), 8.19 (s, 1H).
-(4-Methylphenyl)-1H-1,2,3,4-tetrazole (2c, Table 2, entry 3):
1
5
10 melting point apparatus and were uncorrected. The elemental
7
1
M.p. 94–95 °C (lit: 93–94 °C) ; H NMR (90 MHz, CDCl ): δ = 2.30
3
analysis was performed using Heraeus CHN–O-Rapid analyser. TLC
was performed on silica gel polygram SIL G/UV 254 plates.
(
s, 3H), 6.92–7.27 (m, 4H), 8.16 (s, 1H).
-(2-Methylphenyl)-1H-1,2,3,4-tetrazole (2d, Table 2, entry 4):
1
22
1
21
M.p. 153–155 °C (lit: 153–155 °C) ; H NMR (90 MHz, CDCl ):
Preparation of FeCl –SiO catalyst
3
3
2
δ = 3.38 (s, 3H), 6.88–7.17 (m, 4H), 7.87 (s, 1H).
Silica gel (10 g, 70–230 mesh) was added to a solution of ferric
chloride hexahydrate (1.2 g) in acetone (16 mL), at room temperature.
The solvent was evaporated under reduced pressure and the resulting
yellow powder was kept under nitrogen at room temperature for
further reactions.
1
-(4-Chlorophenyl)-1H-1,2,3,4-tetrazole (2e, Table 2, entry 5):
7
1
M.p. 156–158 °C (lit: 157–158 °C) ; H NMR (90 MHz, CDCl ):
3
δ = 6.96 (d, J = 6.8 Hz, 2H), 7.28 (d, J = 6.7 Hz, 2H), 8.09 (s, 1H).
1
-(2-Chlorophenyl)-1H-1,2,3,4-tetrazole (2f, Table 2, entry 6):
22
1
M.p. 127–131 °C (lit: 127–131 °C) ; H NMR (90 MHz, CDCl ):
3
Synthesis of the 1-aryl-1H-1,2,3,4-tetrazoles; typical procedure
δ = 7.10–7.44 (m, 4H), 8.07 (s, 1H).
FeCl –SiO (0.02 g) was added to a mixture of amine (2 mM), NaN
1-(4-Bromophenyl)-1H-1,2,3,4-tetrazole (2g, Table 2, entry 7):
3
2
3
22
1
(2 mM), triethyl orthoformate (2.4 mM) and stirred at 130 °C or soni-
M.p. 183–185 °C (lit: 183–185 °C) ; H NMR (90 MHz, CDCl ):
3
cated in an ultrasonic cleaner water bath at 45 °C for the appropriate
time (Table 2). After completion (as monitored by TLC), the reaction
mixture was diluted with cold water (5 mL) and extracted with ethyl
acetate (3×10 mL). The catalyst was removed by filtration and the
δ = 6.90 (d, J = 8.7 Hz, 2H), 7.40 (d, J = 7.7 Hz, 2H), 8.07 (s, 1H).
1-(3-Trifluoromethylphenyl)-1H-1,2,3,4-tetrazole (2h, Table 2,
22
1
entry 8): M.p. 125–127 °C (lit: 125–127 °C) ; H NMR (90 MHz,
DMSO–d ): δ = 7.60–7.20 (m, 4H), 8.19 (s, 1H).
6

4
66 JOURNAL OF CHEMICAL RESEARCH 2013
1
-(4-Acetylphenyl)-1H-1,2,3,4-tetrazole (2i, Table 2, entry 9):
4
5
6
7
8
9
0
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22
1
M.p. 147–154 °C (lit: 147–154 °C) ; H NMR (90 MHz, CDCl ):
δ = 2.59 (s, 3H), 7.09–8.00 (m, 4H), 8.29 (s, 1H).
3
1-(2,4-Dimethylphenyl)-1H-1,2,3,4-tetrazole (2j, Table 2, entry 10):
22 1
M.p. 133–135 °C (lit: 133–135 °C) ; H NMR (90 MHz, DMSO-d ):
δ = 3.33 (s, 1H), 6.95 (s, 3H), 7.81 (s, 1H).
6
1
1,1′-(1,2-Phenylene)bis(1H-1,2,3,4-tetrazole) (2k, Table 2, entry 11):
11 M. Ashokkumar and T. Mason, Sonochemistry, Kirk Othmer Encyclopedia
of Chemical Technology, John Wiley and Sons, New York, 2007.
12 K.S. Suslick and G.J. Price, Ann. Rev. Mater. Sci., 1999, 29, 295.
22 1
M.p. 167–169 °C (lit: 167–169 °C) ; H NMR (90 MHz, DMSO–d ):
δ = 7.12–7.69 (m, 4H), 8.30 (s, 1H).
6
1
3
D. Habibi, M. Nasrollahzadeh, A.R. Faraji and Y. Bayat, Tetrahedron,
010, 66, 3866.
2
We gratefully acknowledge the Bu-Ali Sina University, for the
support of this work.
1
4
T.A. Kamali, M. Bakherad, M. Nasrollahzadeh, S. Farhangi and D. Habibi,
Tetrahedron Lett., 2009, 50, 5459.
T.A. Kamali, D. Habibi and M. Nasrollahzadeh, Synlett, 2009, 16, 2601.
M. Nasrollahzadeh, D. Habibi, Z. Shahkarami and Y. Bayat, Tetrahedron,
1
1
5
6
Received 23 April 2013; accepted 20 May 2013
Paper 1301909 doi: 10.3184/174751913X13729393880865
Published online: 9 August 2013
2
009, 65, 10715.
17 D. Habibi, M. Nasrollahzadeh and Y. Bayat, Synth. Commun., 2011, 41,
2135.
1
1
8
9
D. Habibi and M. Nasrollahzadeh, Monatsh. Chem., 2012, 143, 925.
T.M. Potewar, S.A. Siddiqui, R.J. Lahoti and K.V. Srinivasan, Tetrahedron
Lett., 2007, 48, 1721.
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