Cu-MCM-41 nanoparticles: An efficient catalyst for the synthesis of 5-substituted 1H-tetrazoles via [3+2] cycloaddition reaction of nitriles and sodium azide

Article abstract of DOI:10.1007/s12039-015-1005-9

[3 + 2] cycloaddition reaction of various types of nitriles and sodium azide (NaN ₃) were studied in the presence of nano-sized Cu-MCM-41 as an efficient recoverable heterogeneous catalyst. Nano-sized Cu-MCM-41 mesoporous molecular sieves with various Si/Cu molar ratios were synthesized by direct insertion of metal ions at room temperature. The textural properties of the materials have been studied by means of XRD, FTIR, SEM and TEM techniques. Catalytic behavior of Cu-MCM-41 was also investigated by pyridine absorption and potentiometric titration. The reactions data verified characterization results and show that Cu-MCM-41 with Si/Cu molar ratio of 20 has considerably better catalytic activity compared to the other molar ratios. To investigate reusability, the catalyst was recovered by simple filtration and reused for several cycles with consistent activity.

Full text of DOI:10.1007/s12039-015-1005-9

c
J. Chem. Sci. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-1005-9
Cu-MCM-41 nanoparticles: An efficient catalyst for the synthesis
of 5-substituted 1H-tetrazoles via [3+2] cycloaddition reaction
of nitriles and sodium azide
MOHAMMAD ABDOLLAHI-ALIBEIK∗ and ALI MOADDELI
Department of Chemistry, Yazd University, Yazd 89158-13149, Iran
e-mail: abdollahi@yazd.ac.ir; moabdollahi@gmail.com
MS received 12 August 2015; revised 20 October 2015; accepted 9 November 2015
Abstract. [3+2] cycloaddition reaction of various types of nitriles and sodium azide (NaN3) were studied
in the presence of nano-sized Cu-MCM-41 as an efficient recoverable heterogeneous catalyst. Nano-sized Cu-
MCM-41 mesoporous molecular sieves with various Si/Cu molar ratios were synthesized by direct insertion
of metal ions at room temperature. The textural properties of the materials have been studied by means of
XRD, FTIR, SEM and TEM techniques. Catalytic behavior of Cu-MCM-41 was also investigated by pyridine
absorption and potentiometric titration. The reactions data verified characterization results and show that Cu-
MCM-41 with Si/Cu molar ratio of 20 has considerably better catalytic activity compared to the other molar
ratios. To investigate reusability, the catalyst was recovered by simple filtration and reused for several cycles
with consistent activity.
Keywords. 5-substituted 1H-tetrazoles; heterogeneous catalyst; Cu-MCM-41; nanoparticles; cyclization.
1. Introduction
recovery of the catalyst. To overcome the drawbacks of
the earlier methods, attention has been paid to develop
safer and neat methods for the synthesis of 5-substituted
1H-tetrazoles.
Tetrazoles as a class of heterocycles are currently under
intensive focus because of broad spectrum of applications
in pharmaceuticals as lipophilic spacers, carboxylic acid
surrogates,1 speciality explosives,2 photography and
information recording systems.3 Tetrazoles are almost
10 times more lipophilic than the corresponding car-
boxylates, which is an important factor to bear in mind
when designing a drug molecule to pass through cell
membranes. Another advantage of tetrazolic acids over
carboxylic acids is that they are resistant to many bio-
logical metabolic degradation pathways.3
Conventionally 5-substituted 1H-tetrazoles are syn-
thesized via reaction of nitriles with hydrazoic acid,4 so-
dium azide5,6 and trimethylsilylazide (TMSN3).7 Among
them, general method is [3+2] cycloaddition of sodium
azide with various nitriles. Various catalytic systems
have been introduced for this type of reaction for mani-
pulation of this reaction through the past few years such
as Brønsted acids,8 Lewis acids including BF3.OEt2,9
AlCl3,10 metal oxides such as Cu2O,11 ZnO,12 clays
and modified clays,13 etc. Nevertheless, existing proto-
cols have some limitations such as stringent conditions,
longer reaction times, expensive and toxic metal cata-
lysts, tedious work-ups and impossible or unsatisfactory
In recent years, tendency towards heterogeneous cat-
alysts have received much attention because of recy-
clable and environmentally benign conditions. Ordered
mesoporous materials such as mesoporous silica with
narrow pore size distributions, high surface area and
controllable morphologies are interesting for a wide
range of applications in particular as heterogeneous
catalysis or catalyst support.14,15 However, due to the
low catalytic activity of MCM-41 as pure form, modi-
fied mesoporous materials based MCM-41 containing
various transition metals such as V,16 Fe,17 Cu,18 Mn,19
Co,20 Ni,21 and Mo22 have emerged as useful heteroge-
neous catalysts.
Copper is an efficient, cheap and non-toxic ingredi-
ent in many heterogeneous and homogeneous catalysts,
in particular in the synthesis of tetrazoles.23 In addi-
tion to this, copper-modified mesoporous silica show
favorable activity and recoverability in the catalyzed
transformations.24,25
We report herein, a new method for the preparation
of nano-sized Cu-MCM-41 with different Si/Cu molar
ratios through direct insertion of copper ion in sol-
gel step at room temperature without using autoclave.
We hope that copper modified MCM-41 nanoparticles
∗For correspondence

Mohammad Abdollahi-Alibeik and Ali Moaddeli
in 5 mL of deionized water) was added dropwise under
vigorous stirring. Then pH of the solution was adjusted
to 10.5 by adding 25 wt% ammonia solution. The mix-
ture was stirred for 12 h at r.t. The gel was recovered by
centrifuging and washed with ethanol (3 × 5 mL) and
deionized water (3 × 10 mL). The obtained solid was
dried at 120◦C for 2 h and calcined in air at 550◦C for
4 h. The obtained samples with Si/Cu molar ratio of 10,
20 and 30 were denoted as 10-CM, 20-CM and 30-CM,
respectively. The Cu content of the prepared cata-
lysts was measured by AAS. Cu-MCM-41 samples with
Si/Cu molar ratio of 10, 20 and 30 show CuO/SiO2
molar ratios of the 10.8, 21.7 and 33.0, respectively.
This showed that 7 to 9 percentage of copper ions was
unreacted.
Scheme 1. Synthesis of 5-shubstituted 1H-tetrazoles using
Cu-MCM-41.
efficiently catalyze the reaction of nitriles and sodium
azide for the synthesis of 5-substituted 1H-tetrazoles
(scheme 1).
2. Experimental
All chemicals were commercial products and used with-
out further purification. All reactions were monitored
by TLC and all yields refer to isolated products. Melting
points were obtained by Buchi B-540 apparatus and are
uncorrected. 1H and 13C NMR spectra were recorded in
DMSO-d6 on a Bruker DRX-400 AVANCE (400 MHz
2.2 General procedure for the synthesis of
5-substituted 1H-tetrazoles
A mixture of nitrile (1 mmol), sodium azide (1.5 mmol),
catalyst (25 mg), and DMF (3 mL) was taken in a 5 mL
round bottomed flask and heated at 120◦C. After com-
pletion of the reaction (observed on TLC) the reaction
mixture was cooled to r.t. and separated from catalyst by
centrifugation. The solvent was removed under reduced
pressure. The residue was dissolved in water (5 mL) and
acidified with HCl (37%). The precipitation was filtered
and crystallized in a mixture of water and ethanol. Fur-
ther purification with column chromatography was not
necessary.
1
for H and 100 MHz for 13C) spectrometer. Infrared
spectra of the catalysts and reaction products were
recorded on a Bruker FT-IR Equinox 55 spectropho-
tometer in KBr disks. XRD patterns were recorded on
a Bruker D8 ADVANCE X-ray diffractometer using
nickel filtered Cu Kα radiation (λ = 1.5406 Å). Scan-
ning Electron Microscopy (SEM) was performed using
KYKY-EM3200 Instrument. Potentiometric data was
collected using pH/mV meter, AZ model 86502-pH/
ORP. Atomic absorption spectroscopy analysis was per-
formed by analytic jena nova 300 model 330 Germany.
Transmittance electron microscopy was performed with
Zeiss-EM10C at 80 KV
2.3 Physical and spectroscopic data for selected
compounds
2.3a 2-(1H-Tetrazole-5-yl)pyridine (2j): White solid;
1
M.p.: 212–214◦C ; H NMR (DMSO-d6, 400 MHz): δ
2.1 Catalyst preparation
(ppm) = 7.4 (t, J = 6.4 Hz, 1H), 7.8 (t, J = 6.4 Hz,
1H), 8.0 (t, J = 8.0 Hz, 1H), 8.5 (d, J = 3.2 Hz,
1H) ppm; 13C NMR (DMSO-d6, 100 MHz): δ (ppm)
= 167.5, 159.1, 150.0, 139.4, 120.2 ppm; IR (KBr)ν:
3278, 3181, 2929, 1662, 1578, 1390, 923 cm−1.
The synthesis of nano-sized Cu-MCM-41 was carried
out by the method of direct insertion of copper ion in
sol-gel preparation step at room temperature using tetra-
ethyl orthosilicate (TEOS) as the Si source, cetyltri-
methylammonium bromide (CTAB) as the template,
ammonia as the pH control agent and Cu(OAc)2.H2O
as the copper source with the gel composition of SiO2:
Cu(OAc)2.H2O:CTAB:NH4OH:H2O = 1.00:0.050:0.127:
0.623:508 for typical preparation of Cu-MCM-41 with
Si:Cu molar ratio of 20. In a typical procedure, CTAB
(1.04 g) was dissolved in deionized water (200 mL)
under stirring, and then temperature was adjusted to
2.3b 5-(4-Chlorophenyl)-1H-tetrazole (2c): White solid;
1
M.p.: 252–253◦C; H NMR (acetone-d6, 400 MHz): δ
(ppm) = 7.65 (d, J = 8.4 Hz, 2H), 8.15 (d, J = 8.4
Hz, 2H); 13C NMR (acetone-d6, 100 MHz): δ (ppm)
= 136.5, 129.5, 129.2, 128.7, 124.0 ppm; IR (KBr) ν:
3060, 2460, 1900, 1608, 1486, 1435, 1100 cm−1.
60◦C for 15 min. To this solution, tetraethylorthosilicate 2.3c 5-(thiophen-2-yl)-1H-tetrazole (2i): White solid;
(5 mL) was added dropwise and then a solution of Cu M.p.: 205-206◦C; H NMR (DMSO-d6, 400 MHz): δ
1
(OAc)2.H2O (appropriate amount of copper precursor (ppm) = 7.87 (m, 1H), 7.79 (m, 1H), 7.28 (m, 1H); 13C

Cu-MCM-41 catalyzed synthesis of 5-sbstituted-1H tetrazoles
NMR (DMSO-d6, 100 MHz): δ (ppm) = 151.3, 130.4,
129.2, 128.6, 125.4; ; IR (KBr) ν: 3551, 3478, 3414,
3174, 3110, 3094, 2891, 2840, 2502, 1638, 1593, 1507,
1414, 1048, 970, 744, 721 cm−1.
c)
3. Results and Discussion
In this research, a new catalyst was developed for the
synthesis of 5-substituted 1H-tetrazoles by reaction of
various types of nitriles and sodium azide in the pres-
ence of Cu-MCM-41 as reusable solid acid catalyst. Cu-
MCM-41 with Si/Cu molar ratio of 10, 20 and 30 were
prepared and denoted as 10-CM, 20-CM and 30-CM,
respectively.
b)
a)
We have first characterized the prepared catalysts by
various techniques before reaction optimization. The
FT-IR absorption spectra of pure MCM-41 and Cu-
incorporated MCM-41 samples with different loading
amounts of copper are shown in figure 1. Cu-MCM-
41 samples show MCM-41 characteristic peaks but a
slight red-shift of the vibration absorption band to
the lower frequencies, corresponding to υ(Si–O–Si) at
∼1090 cm−1 and υ(Si–OH) at ∼980 cm−1, was obser-
ved in the spectra of Cu-MCM-41 samples respect to
the pure MCM-41. These results indicate the formation
of Si-O-Cu bond and incorporation of Cu in the frame-
work of MCM-41.
2.5
5.0
7.5
10.0
2 (degree)
Figure 2. Low angle XRD patterns of (a) 10-CM, (b) 20-
CM and (c) 30-CM.
changes are due to decrease in the long-range order of
the hexagonal meso-structure of MCM-41 due to the
incorporation of copper into the framework of MCM-
41 and partial substitution of the structural Si4+ by the
Cu2+ ion, resulting in the collapsing of the hexagonal
structure of MCM-41.
As shown in figure 3a, high angle XRD pattern of
10-CM shows slight presence of CuO in tenorite phase
while 20-CM (figure 3b) lacks this phase. This fact
shows high dispersion of copper ions in the MCM-41
framework and confirms the absence of segregate phase
for CuO especially for 20-CM.
The low angle XRD patterns of Cu-MCM-41 samples
with Si/Cu molar ratio of 10, 20 and 30 are shown in
figure 2. The intensity of the main peak of Cu-MCM-41
samples decreased and the width of the peak increased
with increase in copper content of the catalysts. These
The morphology of Cu-MCM-41 particles was found
spherical and nanoparticles had sizes of <100 nm
by using images from scanning electron microscopy
(figure 4).
In order to obtain a clear distinction between Lewis
and Brønsted acid sites, FT-IR analyses of pyridine ad-
sorbed on the catalyst surface were carried out and re-
(a)
(b)
10
15
20
25
30
35
40
45
50
55
60
65
70
2
(degree)
Figure 1. FT-IR spectra of (a) MCM-41, (b) 10-CM and
(c) 20-CM and (d) 30-CM.
Figure 3. High angle XRD patterns of, (a) 10-CM, (b) 20-CM.

Mohammad Abdollahi-Alibeik and Ali Moaddeli
1448 and 1599 cm−1. These results show that Lewis
acidity character of the catalyst is stronger than its
Brønsted acidity.26
The catalyst acidity character, including the acidic
strength and the total number of acidic sites were deter-
mined by potentiometric titration. According to this
method, the initial electrode potential (Ei) indicates the
maximum acid strength of the surface sites.27 There-
fore, a suspension of the catalyst in acetonitrile was
potentiometrically titrated with a solution of 0.02 M
20
0
Figure 4. SEM image of 20-CM.
sults are displayed in figure 5. The FT-IR spectrum
of pyridine adsorbed 20-CM before heat treatment
(figure 5b) shows the contribution of pyridine adducts
in the region of 1400-1650 cm−1. In this spectrum, the
peaks at 1448 and 1598 cm−1 are attributed to pyri-
dine bonded Lewis acid sites of the 20-CM. The weak
peak at 1543 cm−1 assigned to Brønsted acid sites (cor-
responds to protonation of pyridine on Brønsted acid
sites) is so hard to find in current zoom. The weak peak
at 1491 cm−1 is attributed to the combination mode. As
shown in figures 5c-g, with increasing in temperature,
characteristic peaks of Lewis acidity still remained at
-20
10-CM
20-CM
30-CM
-40
-60
-80
-100
-120
-140
-160
-180
0.00
0.10
0.20
meq/g
0.30
0.40
0.50
Figure 6. Potentiometric titration of (ꢀ) 10-CM, (•) 20-
CM and (ꢁ) 30-CM. Titrant is a a solution of 0.02 M
n-butylamine in acetonitrile.
Figure 7. TEM image of 20-CM.
Figure 5. FT-IR spectra of (a) 20-CM, (b) pyridine adsor-
bed 20-CM at ambient temperature, and pyridine adsorbed
20-CM heated at (c) 100◦C, (d) 200◦C, (e) 300◦C, (f) 400◦C Scheme 2. Model reaction for optimization of reaction
and (g) 500◦C.
conditions.

Cu-MCM-41 catalyzed synthesis of 5-sbstituted-1H tetrazoles
Table 1. Screening of reaction parameters for the synthesis of phenyltetrazolea.
Si/Cu molar
ratio
Temp. Cat. amount
Cu content
(mol%)b
Timec Yieldd
Entry
(◦C)
(mg)
Solvent (min)
(%)
1
2
3
4
5
6
7
8
9
10
20
20
20
20
20
20
20
20
10
30
120
100
110
120
120
120
reflux
120
120
120
25
25
25
10
15
35
25
25
25
25
1.8
1.8
1.8
0.7
1.1
2.5
1.8
1.8
3.6
1.2
DMF
DMF
DMF
DMF
DMF
DMF
H2O
DMSO
DMF
DMF
150
120
120
120
120
120
180
120
120
180
92
25
45
65
80
90
0
75
80
55
aReaction conditions: benzonitrile (1 mmol), NaN3 (1.5 mmol).
bCopper content of the catalyst has measured by atomic absorption instrumentation.
cReaction time is based on the consumption of benzonitrile monitored by TLC.
dIsolated yield.
n-butylamine in acetonitrile. As shown in figure 6, range of 2-3 nm. No copper oxide nanoparticles were
20-CM displays higher strength than the other observed in the TEM image, suggesting that copper
samples.
is completely dispersed in MCM-41 framework and
Mesostructure of the 20-CM sample was further also due to the incorporation of Cu into the MCM-41
studied by TEM, as shown in figure 7. Porosity of the framework, partially disordered mesoporus structure is
sample is clear and size of the pores is observed in observed.
Table 2. Synthesis of 5-substituted 1H-tetrazole derivatives.a
M.p. (◦C)
Entry
Substrate (1)
Product (2)
Timeb (min)
Yieldc (%)
Found
Reported ref
a
120
150
92
91
218-219
231-232
215-21628
231-23323
b
c
90
89
90
252-253
137-139
252-25429
138-13923
d
120
e
f
30
30
30
85
80
93
145-146
218-220
258-260
145-14630
218-22011
258-26013
g
h
i
45
75
84
89
215-216
205-206
212-214
214-2165
205-20631
21128
180
j
180
aReaction conditions: nitrile (1 mmol), NaN3 (1.5 mmol), 20-CM (25 mg), DMF (3 mL) and temperature (120◦C).
bReaction time is based on the consumption of nitrile monitored by TLC.
cIsolated yield.

Mohammad Abdollahi-Alibeik and Ali Moaddeli
To investigate the effect of Cu loading on the cat-
alytic activity of Cu-MCM-41, the model reaction was
performed in the presence of 10-CM and 30-CM sam-
ples in the optimized conditions and results show that
these catalysts have considerable lower catalytic activ-
ity relative to 20-CM (table 1, entries 9, 10).
Thereafter, the above optimized reaction conditions
were explored for the synthesis of 5-substituted 1H-
tetrazole derivatives and the results are summarized in
table 2. As exemplified in table 2, this protocol is rather
general for a wide variety of electron-rich as well as
electron-deficient aromatic nitriles (scheme 3).
Scheme 3. Synthesis of tetrazole derivatives using Cu-
MCM-41.
The most important benefit of the applied catalyst is
its reusability. Thus, the recovery and reusability of the
catalyst were investigated in the model reaction under
the optimized reaction conditions. The catalyst was sep-
arated from the reaction mixture by centrifugation and
reused three times with moderate loss of the catalytic
activity (table 3).
We perform a comparative study of the reactivity
of Cu-MCM-41 with other reported heterogeneous cat-
alytic systems. Table 4 presents other reported meth-
ods for the synthesis of 5-substituted 1H-tetrazoles via
[3+2] cycloaddition reaction of nitriles with sodium
azide. Reported results in table 4 are related to the stan-
dard reaction of benzonitrile and sodium azide at differ-
ent catalyst loadings. Results show that our method is
comparable with other catalytic systems in term of yield
and reaction time. In addition to this, moderate reaction
temperature, easy work-up and using a reusable catalyst
are other benefits of this method.
The catalytic activities of Cu-MCM-41 samples
were investigated in the synthesis of 5-substituted
1H-tetrazoles by the reaction of various nitriles and
sodium azide. To optimize the reaction conditions, ini-
tially, the reaction of benzonitrile and sodium azide was
selected as the model reaction (scheme 2).
The reaction was optimized for various parameters
such as temperature, solvent and catalyst loading. To
investigate the effect of temperature, the reaction was
performed at 100, 110 and 120◦C and the best result was
obtained at 120◦C (table 1, entries 1-3). To optimize
the catalyst amount, the model reaction was performed
in the presence of various amounts of the catalyst and
according to the obtained results 25 mg of the cata-
lyst was chosen as the best catalyst amount (table 1,
entries 4-6). The effect of solvent was also investigated
by performing the model reaction in the presence of 25
mg catalyst in various solvents (table 1, entries 7, 8).
Among them, DMF was found to be the best solvent in
terms of the time and yield of desired product.
4. Conclusion
Table 3. Reusability test of the catalyst in the model
In conclusion, we introduced an efficient catalyst
for the synthesis of 5-substituted 1H-tetrazoles from
nitriles and sodium azide with excellent to good yields
and low reaction times. Mesoporous copper modi-
fied catalyst was prepared at room temperature with-
out using hydrothermal condition with various Si/Cu
molar ratios. The catalyst was characterized by XRD,
FTIR, SEM and TEM techniques. Results show that
the Cu-MCM-1 with Si/Cu molar ratio of 20 has the
reactiona.
Entry
Fresh
Cycle 1
Cycle 2
Cycle 3
Yield (%)
Time (min)
92
120
87
120
85
120
85
120
aReaction conditions: benzonitrile (1 mmol), NaN3
(1.5 mmol), 20-CM (25 mg), DMF (3 mL) and temperature
(120◦C).
Table 4. Comparsion of our work with other heterogeneous catalysts.
Entry
Catalyst
Condition Temp.(◦C) Time (h)
yield%
1
2
3
4
5
Cu-MCM-41
Nano-ZnO
Amberlyst-15
CuFe2O4
DMF
DMF
DMSO
DMF
120
120-130
85
120
120
2
92 [this work]
7212
14
12
12
14
9232
8223
CoY zeolite
DMF
9033

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