1-Disulfo-[2,2-bipyridine]-1,1-diium chloride ionic liquid as an efficient catalyst for the green synthesis of 5-substituted 1H-tetrazoles

Article abstract of DOI:10.1016/j.molstruc.2021.131289

A simple, green and efficient method has been developed for the synthesis of 5-substituted 1H-tetrazole derivatives through [2+3] cycloaddition reaction in good to excellent yields between various benzonitriles and sodium azide. For this purpose, 1-disulfo-[2,2-bipyridine]-1,1-diium chloride ([BiPy](HSO₃)₂Cl₂) system as an ionic liquid catalyst have been extended for the construction of these valuable products. This procedure has significant advantages, including using ethylene glycol as a green solvent. The other advantages of this method are inexpensive and ease the preparation of the catalyst, mild reaction conditions, green reaction medium, easy workup, short reaction time, and simple experimental process.

Full text of DOI:10.1016/j.molstruc.2021.131289

Journal of Molecular Structure 1247 (2022) 131289
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
1-Disulfo-[2,2-bipyridine]-1,1-diium chloride ionic liquid as an
efficient catalyst for the green synthesis of 5-substituted 1H-tetrazoles
Elaheh Aali, Mostafa Gholizadeh∗, Nazanin Noroozi-Shad
Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple, green and efficient method has been developed for the synthesis of 5-substituted 1H-tetrazole
derivatives through [2+3] cycloaddition reaction in good to excellent yields between various benzonitriles
and sodium azide. For this purpose, 1-disulfo-[2,2-bipyridine]-1,1-diium chloride ([BiPy](HSO3)2Cl2) sys-
tem as an ionic liquid catalyst have been extended for the construction of these valuable products. This
procedure has significant advantages, including using ethylene glycol as a green solvent. The other advan-
tages of this method are inexpensive and ease the preparation of the catalyst, mild reaction conditions,
green reaction medium, easy workup, short reaction time, and simple experimental process.
© 2021 Elsevier B.V. All rights reserved.
Received 5 May 2021
Revised 25 July 2021
Accepted 10 August 2021
Available online 20 August 2021
Keywords:
Cycloaddition reaction
1-Disulfo-[2,2-bipyridine]-1,1-diium chloride
Ionic liquid
Tetrazoles
1. Introduction
amount of catalyst, long reaction times, high reaction temperatures
and low yields of the desired product. Moreover, in most of these
Tetrazoles and their derivatives are very important heterocyclic
scaffolds that exhibit a wide range of applications in organic syn-
thesis, coordination chemistry, agriculture, material science and es-
pecially in the field of medicinal chemistry [1–3]. Tetrazoles are
found in various biologically and pharmacologically active moi-
eties such as anti-inflammatory, antibiotic, antiallergic, antiviral,
antifungal, antitubercular, antihypertensive, -anti-HIV and antineo-
plastic agents [4–8]. Among tetrazole derivatives, 5-substituted-1H-
tetrazoles can widely employ as isosteric replacements of the car-
boxylic acid group in medicinal chemistry [8–11].
reports, conventional volatile organic solvents are often applied as
the reaction solvent, which after the reaction they would produce
a large amount of wastes.
Nowadays, organic reactions using ionic liquids (ILs) as cata-
lysts have been attracted a great deal of attention not only ow-
ing to their easily available and environmentally friendly proper-
ties but also their excellent catalysts and a medium having weakly
coordinating ions, i.e. organic cation and inorganic/organic anion in
synthetic organic compounds [26–29]. The non-volatility and non-
flammability properties of ILs such as high thermal and chemi-
cal stability and capability of solving many organic and inorganic
materials make them eco-friendly reaction solvents, catalysts, and
reagents [30–33]. Among these applications, acidic ionic liquids are
one of the most important compounds which have been used suc-
cessfully in various organic reactions [34,35].
Various synthetic approaches have been developed for the syn-
thesis of tetrazoles, including nitriles, amides, thioamides, amines,
ketones, alkenes, imidoyl chlorides, heterocumulenes, and iso-
cyanides [12,13]. Among these methods, one of the most direct
and convenient pathways for the synthesis of 5-substituted-(1H)-
tetrazoles is [2+3] cycloaddition between nitriles and azides group
[14,15].
Encouraged by our ongoing studies in the field of ILs and our
continuous interest in the development of efficient green synthetic
methodologies, herein, we would like to report a facile, green,
and efficient protocol for the synthesis of 5-substituted-(1H)-
tetrazoles employing IL 1-disulfo-[2,2-bipyridine]-1,1-diium chlo-
ride ([BiPy](HSO3)2Cl2) as an ionic liquid catalyst (Scheme 1). Fur-
thermore, the reaction parameters including the amount of the cat-
alyst, molar ratio of the reactants and temperature were also opti-
mized.
Since then, numerous catalysts have been employed in synthe-
sis of tetrazoles, such as, CdCl2 [16], Fe(OAc)2, ZnCl2 [17], ZnBr2
[18], CuFe2O4 nanoparticles [19], Zn/Al hydrotalcite [20], AlCl3 [21],
BF3·OEt2 [22], Ln(OTf)3-SiO2 [23], CAN supported HY-zeolite [24],
TBAF [25] and etc. Although each of the above conventional meth-
ods has its merit, however, most of these catalysts normally suf-
fer from the use of expensive reagents and toxic metals, the large
∗
Corresponding author.
E-mail address: m_gholizadeh@um.ac.ir (M. Gholizadeh).
https://doi.org/10.1016/j.molstruc.2021.131289
0022-2860/© 2021 Elsevier B.V. All rights reserved.

E. Aali, M. Gholizadeh and N. Noroozi-Shad
Journal of Molecular Structure 1247 (2022) 131289
Scheme 1. Synthesis of 5-substituted-(1H)-tetrazoles.
2. Experimental
5-Phenyl-1H-tetrazole (Table 3, entry 1) White solid. mp 214–
216 °C (Lit 214-216 °C); FT-IR (KBr) υmax/cm−1 3125, 3043, 2982,
2913, 2692, 2606, 2557, 1613, 1563, 1485, 1465, 1163, 1056, 726,
703. 1H NMR (400 MHz, DMSO-d6, ppm) δ 7.60-7.64 (m, 3H, Ph),
8.02-8.07(m, 2H, Ph).
2.1. Reagents and materials
All chemical reagents and solvents were purchased from Merck
and Sigma-Aldrich chemical companies and were used as re-
ceived without further purification. The purity determinations of
the products and the progress of the reactions were accomplished
by TLC on silica gel polygram STL G/UV 254 plates. The melt-
ing points of the products were determined with an Electrother-
mal Type 9100 melting point apparatus. The FT-IR spectra were
recorded on pressed KBr pellets using an AVATAR 370 FT-IR spec-
trometer (Therma Nicolet spectrometer, USA) at room temperature
in the range between 4000 and 400 cm−1 with a resolution of 4
cm−1. NMR spectra were recorded on an NMR Bruker Avance spec-
trometer at 300 MHz in CDCl3 or DMSO-d6 as a solvent in the
presence of tetramethylsilane as internal standard and the coupling
constants (J values) are given in Hz. Elemental analysis was per-
formed using a Thermo Finnigan Flash EA 1112 Series instrument
(furnace: 900 °C, oven: 65 °C, flow carrier: 140 mL min−1, flow
reference 100 mL min-1). Thermogravimetric analysis (TGA) was
performed with a Shimadzu Thermogravimetric Analyzer (TG-50)
in the temperature range of 25–800 °C at a heating rate of 10 °C
min−1 under air atmosphere. Elemental compositions were carried
out using an SC7620 energy dispersive spectrum (EDS) presenting
a 133 eV resolution at 20 kV. All yields refer to the isolated prod-
ucts after purification by recrystallization.
5-(3,5-Dimethoxyphenyl)-1H-tetrazole (Table 3, entry 3)
White solid.mp 204-205 °C (Lit 204-205 °C); FT-IR (KBr) υmax/cm−1
3129, 3064, 3011, 2975, 2941, 2843, 2757, 2712, 2634, 1605, 1562,
1480, 1430, 1287, 1208, 1167, 1162, 1054, 827, 747. 1H NMR (400
MHz, DMSO-d6, ppm) δ 3.84 (s, 6H, OMe), 6.72 (t, J=2Hz, 1H,
Ph),7.21 (d, J=2Hz,2H,Ph), 16.91 (br, s, 1H, NH).
5-(4-Boromophenyl)-1H-tetrazole (Table 3, entry 4) White
solid. mp 264-265 °C (Lit 265 °C); FT-IR (KBr)) υmax/cm−1 3329,
3089, 3063, 2996, 2900, 2781, 2633, 1652, 1604, 1482, 1431, 1157,
1078, 1054, 829, 744. 1H NMR (400 MHz, DMSO-d6, ppm) δ 7.83
(d, J=12 HZ, 2H, Ph), 8.01 (d, J=12, 2h, Ph).
5-(4-Chlorophenyl)-1H-tetrazole (Table 3, entry 5) White
solid.mp 261-262 °C (Lit 261-263 °C); FT-IR (KBr) υmax/cm−1 3092,
3060, 3007, 2978, 2851, 2725, 2622, 2537, 2471, 1609, 1564, 1486,
1435, 1160, 1096, 1053, 1020, 990, 833, 745, 508. 1H NMR (400
MHz, DMSO-d6, ppm) δ 7.68 (d, J=8.42HZ, 2H, Ph), 8.05 (d, J=8.8
HZ, 2H, Ph).
5-butyl-1H-tetrazole (Table 3, entry 8) White solid. mp 40-
42 °C (Lit 40-42 °C); FT-IR (KBr) υmax/cm−1 3364, 3080, 3051, 2873,
1578, 1556, 1454, 1415, 1249, 1210, 1086, 1038, 992, 951, 891, 758,
651, 618.
5-(Thiophen-2-yl)-1H-tetrazole (Table 3, entry 9) White solid.
mp 206-207 °C (Lit 206-207 °C); FT-IR (KBr) υmax/cm−1 3109, 3074,
2974, 2891, 2780, 2722, 2628, 2659, 2500, 2456, 1830, 1595, 1503,
1411, 1233, 1139, 1046, 962, 853, 740, 719. 1H NMR (400 MHz,
DMSO-d6, ppm) δ 7.29-7.32 (m, 1H, Thiophen), 7.82 (dd, J=6.1Hz,
1H, Thiophen) 7.90 (dd, 1Hz, J=1H, Thiophen).
2.2. Preparation of catalyst
1-disulfo-[2,2-bipyridine]-1,1-diium chloride ([BiPy](HSO3)2Cl2)
Ionic liquid as the catalyst was synthesized according to the re-
ported method in the literature procedure [36]. Generally, over 5
min in an ice bath, Chlorosulfonic acid (1.75 g, 15 mmol) was
added dropwise to a round-bottomed flask (100 mL) containing
2,2ˊ-bipyridine (1.17 g, 7.5 mmol) in dry CH2Cl2 (50 mL). Subse-
quently, the reaction mixture was stirred for 2 h at room temper-
ature, then stood for 5 min, and the solvent was decanted. The
residue was washed with dry diethyl ether (3 × 50 mL) and dried
under vacuum to give [BiPy](HSO3)2Cl2 as a white solid in 98%
yield.
5-(3,4,5-trimethoxyphenyl)-1H-tetrazole (Table 3, entry 11)
White solid. mp 202-203 °C (Lit 202-203 ◦C); FT-IR (KBr)
υ
max/cm−1 3441, 2974, 2949, 2842, 1646, 1599, 1469, 1235, 1179,
1125, 999, 870, 759, 661, 535, 470.
4-(1H-Tetrazol-5-yl)pyridine (Table 3, entry 13) White solid.mp
255-258 °C (Lit 255-258 °C); FT-IR (KBr)) υmax/cm−1 3338, 2924,
2872, 2855, 1666, 1598, 1570, 1460, 1421, 1380, 1151, 1095, 803,
752, 735, 717, 465.
4-nitro-2-(1H-tetrazol-5-yl)aniline (Table 3, entry 14) White
solid. mp 268-270 °C (Lit 268-270 °C); FT-IR (KBr) υmax/cm−1 3566,
3423, 3322, 3203, 2926, 2851, 1628, 1575, 1492, 1468, 1316, 1258,
1139, 1106, 914, 822, 750, 717, 563, 471.
2.3. General procedure for the synthesis of 5-substituted
1H-tetrazoles
4-chloro-2-(1H-tetrazol-5-yl)aniline (Table 3, entry 15) White
solid. 192-194 °C (Lit 192-194 °C); FT-IR (KBr) υmax/cm−1 3404,
2925, 2855, 1687, 1621, 1507, 1468, 1409, 1100, 931, 808, 722, 649,
471.
A
mixture of nitriles (1 mmol), NaN3 (1.5 mmol),
[BiPy](HSO3)2Cl2 as catalyst (4 mol %) in EG (3 mL) as green
solvent was heated at 80 °C for 1-2 h. the reaction was monitored
using TLC. After completion of the reaction, the reaction mixture
was cooled to room temperature. Then H2O (5 mL) was added
(the catalyst was separated from the reaction mixture with solving
in water), and extraction with ethyl acetate was performed. The
corresponding tetrazole was extracted with ethyl acetate (2 × 15
ml). The resultant organic layer was washed with distilled water,
dried over anhydrous sodium sulfate and concentrated by distil-
lation to afford the crude solid product. The crude material was
purified enough but for more purification, column chromatography
on silica gel (hexane/AcOEt 1:1) was afforded.
3. Results and discussion
3.1. Characterization of the catalyst
Characterizations of the catalyst ([BiPy](HSO3)2Cl2) was carried
out using various techniques, such as fourier transform infrared
spectroscopy (FT-IR), elemental analysis (CHNS), thermogravimet-
ric analysis (TGA), and energy-dispersive spectrum (EDS).
2

E. Aali, M. Gholizadeh and N. Noroozi-Shad
Journal of Molecular Structure 1247 (2022) 131289
Table 1
Optimization of different reaction parameters for the preparation of 5-phenyl-1H-tetrazole.
Entry
Molar ratio (benzonitrile/NaN3)
Catalyst(g)
Solvent
Temperature (°C)
Time (h)
Isolated yield (%)
1
1:3
1:3
1:3
1:3
1:3
1:3
1:2
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
-
Solvent-free
DMF
100
r.t
24
24
24
3.5
3.5
3
-
2
-
-
3
-
DMF
80
-
4
0.01
0.02
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
EG
80
75
80
85
85
99
-
5
EG
80
6
EG
80
7
EG
80
2.5
1.5
24
24
24
24
24
24
24
24
5
8
EG
80
9
H2O
r.t
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
H2O
Reflux
r.t
5
EtOH
EtOH
CHCl3
CHCl3
CH2Cl2
CH2Cl2
CH3CN
CH3CN
DMF
-
Reflux
r.t
5
5
30
10
5
r.t
30
10
70
80
80
40
55
65
85
70
80
95
95
r.t
40
4.5
3
r.t
Solvent-free
Solvent-free
PEG 400
PEG 400
EG
r.t
4
80
3.75
2.5
2
r.t
100
r.t
1
EG
50
2.75
1.5
1.5
EG
100
140
EG
Bold indicates the optimized reaction conditions.
The successful synthesis of the [BiPy](HSO3)2Cl2 was confirmed
by FT-IR spectra (Fig. S1). In Fig. S1(a), broad peaks at 2193–3500
cm−1 are indicated the OH stretching of the SO3H groups [13].
Moreover, adsorption bands at 1515 and 1602 cm−1 can be at-
tributed to C=C and C=N vibrations, respectively [37]. Besides, the
infrared spectra of recovered [BiPy](HSO3)2Cl2, Fig. S1(b), indicates
the stability of the catalyst after recovery which can be reused
without noticeable changes in its structure. Also, the energy dis-
persive spectrum (EDS) analysis of [BiPy](HSO3)2Cl2 revealed the
presence of C, O, S and Cl elements in this catalyst (Fig. S2). The
results of this analysis confirm the successful functionalization of
[BiPy](HSO3)2Cl2. TGA was performed to determine the thermal
stability of [BiPy](HSO3)2Cl2 (Fig. S3). The TGA curves of the cata-
lyst exhibited three steps of weight loss. The first small weight loss
of about 3.1% at temperatures below 200 °C is relating to the des-
orption of physically adsorbed water. The second large weight loss
of about 77% around 220-450 °C resulted from the decomposition
of SO3H groups. The further weight losses above 450 °C of about
11.6% resulted from the decomposition of the ligand. These results
indicate that sulfonic acid groups have been grafted to bipyridine.
These observations were also in good agreement with the results
obtained from the elemental analysis analysis (CHNS) (C = 30.48,
H = 3.77, N = 7.04% and S = 16.09%) (Fig. S4).
Initially, in order to confirm the catalyst efficiency, the reaction
was performed without the catalyst. The results showed that no
reaction occurred in the absence of the catalyst after 24h (Table 1,
entries 1-3), which indicates the role of the catalyst in this reac-
tion. Then, we optimized the amounts of catalyst for the model
reaction (Table 1, entries 4-6). As can be seen in this table, with
increasing the amount of catalyst from 0.02 g to 0.04 g, the yield
of the desired product and the reaction time was increased and
decreased, respectively. The best result was afforded using 0.04
g of catalyst. Therefore 0.04 g of the catalyst, was chosen as the
most effective quantity. Furthermore, increasing the amounts of
the catalyst did not improve the reaction condition and the de-
creasing yields of the desired product and increasing the reaction
time were observed. The amount of sodium azide was next stud-
ied. The quantity of NaN3 was optimized to 1 Equiv. The results
showed that the employment of an excess of NaN3 to 3 Equiv did
not significantly improve the yield (Table 1, entries 6-8). In order
to gain the most suitable solvent, the model reaction was tried in
different solvents. The results indicate that the use of protic polar
solvents, such as H2O and EtOH were not effective in the reaction,
which led to no product (Table 1, entry 9-12). When the reaction
was carried out under solvent-free condition, even at the higher
temperature, the yield of the product was not improved any fur-
ther (Table 1, entry 21, 22). Due to the optimization results and
the basic purpose of green chemistry, EG provided the best result
that was selected as the best green solvent (Table 1, entry 8). Vary-
ing the reaction temperature was also investigated. The reaction
yield decreased to 70% at room temperature (Table 1, entry 24)
and even when the reaction was carried out at a higher tempera-
ture (more than 80 to 140 °C) the yield was not improved (Table 1,
entry 26, 27). The results demonstrated that 80 °C was the opti-
mum reaction temperature. Consequently, treating benzonitrile (1
mmol) with sodium azide (1 mmol) using 0.04 g of catalyst in EG
as a green solvent at 80 °C was the most suitable condition for this
reaction (Table 1, entry 8).
3.2. Catalytic performance of the [BiPy](HSO3)2Cl2 in the synthesis of
5-Substituted-1H-tetrazole
We examined the performance of [BiPy](HSO3)2Cl2 as an effi-
cient, stable and commercially available catalyst for the synthe-
sis of 5-Substituted-1H-tetrazole derivatives. To discover the opti-
mized reaction condition and application of the catalyst, the re-
action between benzonitrile and sodium azide (NaN3) is carried
out as a model reaction for the synthesis of 5-phenyl-1H-tetrazole.
For this purpose, the effects of various factors including solvent,
amount of the catalyst, amount of sodium azide and temperature
were considered in the model reaction. The obtained results are
summarized in Table 1.
In addition, to show the efficiency of this methodology for
the synthesis of 5-Substituted-1H-tetrazoles via the reaction be-
3

E. Aali, M. Gholizadeh and N. Noroozi-Shad
Journal of Molecular Structure 1247 (2022) 131289
Fig. 1. Synthesis of 5-Phenyl-1H-tetrazole in the presence of the reused [BiPy](HSO3)2Cl2.
Table 2
Comparison of the efficiency catalytic activity of [BiPy](SO3H)2-Cl2 with those of certain literature
precedents for the synthesis of 5-phenyl-1H-tetrazole.
Entry
Catalysts
Solvent
Temperature(°C)
Time(h)
Yeild(%)
Ref
1
2
3
4
5
Mesoporous-ZnS
Cu–Zn alloy
ZnBr2
DMF
DMF
H2O
DMSO
EG
120
120
Reflux
85
36
10
24
12
1.5
96
95
76
92
99
[38]
[39]
[40]
Amberlyst-15
[BiPy](SO3H)2-Cl2
[41]
80
This work
tween benzonitrile and sodium azide, the results afforded with
[BiPy](HSO3)2Cl2 were compared with some of those reported in
the literature (Table 2). It can be seen that our catalyst works well
and the present procedure was found to be the most effective and
the desired products can be achieved in excellent yields (92-99%)
in a shorter reaction time.
withdrawing groups are found to be more reactive in comparison
to those with electron-donating groups and alkyl nitriles. The re-
sults demonstrated that a wide range of activated and inactivated
aryl/heteroaryl and alkyl nitriles can react well in good to excellent
yields. The results are presented in Table 3.
The reusability and recovery of the [BiPy](HSO3)2Cl2 catalyst
were studied in the 5-Phenyl-1H-tetrazole synthesis (Fig. 1). After
the completion of the reaction, the catalyst was recycled by simple
extraction and dried in an oven at 45 °C for 24 hours to the solid
residue obtained. Then, the next run of the reaction with fresh
substrates and the recycled catalyst was performed. As shown in
Fig. 1, the [BiPy](HSO3)2Cl2 could be recycled over 4 cycles with-
out significant loss of its activity.
Encouraged by these results and recognized the generality and
applicability of the catalyst for this reaction, we next examined the
substrate effect under the optimal reaction conditions.
Therefore, to expand the scope of this methodology, the ef-
fect of the substrates was examined. For this purpose, the reac-
tions between NaN3 and a range of aryl and alkyl nitriles were
examined under the same reaction conditions to form the corre-
sponding tetrazole. A wide variety of nitriles containing electron-
donating and electron-withdrawing substituents showed great re-
activity with sodium azide in air atmosphere. The experimental
results show that the electronic properties of the substituents on
the aromatic rings of the nitriles substrate have no remarkable
effect on the reaction. However, aryl nitriles containing electron-
The postulated mechanism for the synthesis of 5-Substituted-
1H-tetrazoles has been summarized in Fig. 2. Initially, the first step
is progressed via the coordination of nitrogen atoms of nitrile (1)
with H of sulfonated catalyst. The [3+2] cycloaddition via nucle-
≡
ophilic attack of the azide ion (2) on the C N bond of nitrile (1)
takes place readily to form the Int(II). Finally, protonation of tetra-
4

E. Aali, M. Gholizadeh and N. Noroozi-Shad
Journal of Molecular Structure 1247 (2022) 131289
Table 3
Synthesis of different structurally 5-substituted-1H-tetrazoles in the presence of [BiPy](SO3H)2-Cl2 in Ethyleneg-
lycol.
Entry
Substrate
Product
Time(h)
Isolated yield (%)
M.p (°C) [ref.]
1
2
1.5
99
210-213 [42]
2.5
1.5
95
80
148-150 [43]
207-210 [19]
3
4
5
1.5
1.5
85
85
264-265 [44]
266-269 [45]
6
7
2
2
80
90
264-266 [46]
248-251 [47]
8
1.5
1.5
1.5
96
90
98
43-47 [48]
210-214 [49]
38-41 [50]
9
10
11
2.5
90
207-210 [48]
12
13
0.75
1.5
98
97
117-120 [51]
253-257 [42]
14
1.5
95
268-271 [44]
15
16
1.5
1.5
90
95
193-196 [52]
130-132 [53]
(continued on next page)
5

E. Aali, M. Gholizadeh and N. Noroozi-Shad
Journal of Molecular Structure 1247 (2022) 131289
Table 3 (continued)
Entry
Substrate
Product
Time(h)
Isolated yield (%)
M.p (°C) [ref.]
17
1
85
140-143 [54]
Fig. 2. Proposed mechanism for the synthesis of 5-Substituted-1H-tetrazoles.
zole salt with H2O leads to the formation of the 5-substituted-1H-
tetrazole product (3) as a more stable tautomer.
Acknowledgments
The author is grateful for the partial support of this work (grant
number 3/51085) by the Ferdowsi University of Mashhad Research
Council.
4. Conclusions
In conclusion, we have illustrated that [BiPy](HSO3)2Cl2 is po-
tentially a good candidate as the efficient catalyst for the prepara-
tion of 5-Substituted-1H-tetrazoles under air atmosphere. In this
work, the catalyst has been successfully synthesized and char-
acterized by various methods such as fourier transform infrared
spectroscopy (FT-IR), elemental analysis (CHNS), thermogravimet-
ric analysis (TGA), and energy-dispersive spectrum (EDS). The syn-
thesized catalyst has shown excellent activities for the synthe-
sis of Substituted tetrazoles from aryl/heteroaryl/alkyl nitriles and
sodium azide reaction. Besides, the easy extractive of the catalyst
and desired product, and the use of ethylene glycol as green sol-
vent, can be considered as a strong practical superiority of this
methodology. This catalytic operation has a wide scope of all aryl,
heteroaryl and alkyl nitriles and products could be easily pre-
pared in good to excellent yields under mild and green conditions
and the use of non-toxic reagents. Notably, this methodology as a
valuable route will provide a facile, effective, and environmentally
friendly route for the preparation of 5-Substituted-1H-tetrazoles.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.131289.
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Declaration of Competing Interest
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