Synthesis of tetrazoles, triazoles, and imidazolines catalyzed by magnetic silica spheres grafted acid

Article abstract of DOI:10.1080/00397911.2018.1510007

The magnetically separable catalysts are used in the synthesis of N-containing heterocycles, including tetrazoles, triazoles, and imidazolines. The magnetic silica sphere grafted sulfonic acid (MSS-SO₃H) is suitable for the synthesis of 1,2,3-triazole via the cycloaddition of nitroalkene with NaN₃, whereas the zinc-modified silica sphere catalyst (MSS-SO₃Zn) is more suitable for the synthesis of tetrazoles. The MSS-SO₃Zn catalyst also works well for the synthesis of 2-substituted imidazoline via the condensation of nitriles with ethylenediamine. Both of the MSS-SO₃H and MSS-SO₃Zn catalysts can be recovered easily by a magnet, and they can be reused without further tedious activation.

Full text of DOI:10.1080/00397911.2018.1510007

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Synthesis of tetrazoles, triazoles, and imidazolines
catalyzed by magnetic silica spheres grafted acid
Ruihang Jiang, Hong-Bin Sun, Shuang Li, Kun Zhan, Junjie Zhou, Lei Liu, Kai
Zhang, Qionglin Liang & Zhangpei Chen
To cite this article: Ruihang Jiang, Hong-Bin Sun, Shuang Li, Kun Zhan, Junjie Zhou, Lei Liu, Kai
Zhang, Qionglin Liang & Zhangpei Chen (2018) Synthesis of tetrazoles, triazoles, and imidazolines
catalyzed by magnetic silica spheres grafted acid, Synthetic Communications, 48:20, 2652-2662,
DOI: 10.1080/00397911.2018.1510007
To link to this article: https://doi.org/10.1080/00397911.2018.1510007
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2018, VOL. 48, NO. 20, 2652–2662
https://doi.org/10.1080/00397911.2018.1510007
Synthesis of tetrazoles, triazoles, and imidazolines
catalyzed by magnetic silica spheres grafted acid
Ruihang Jianga, Hong-Bin Suna, Shuang Lia, Kun Zhana, Junjie Zhoua, Lei Liua,
Kai Zhanga, Qionglin Liangb, and Zhangpei Chena
b
aDepartment of Chemistry, Northeastern University, Shenyang People’s Republic of China; Department
of Chemistry, Tsinghua University, Beijing, People’s Republic of China
ABSTRACT
ARTICLE HISTORY
Received 17 January 2018
The magnetically separable catalysts are used in the synthesis of N-
containing heterocycles, including tetrazoles, triazoles, and imidazo-
lines. The magnetic silica sphere grafted sulfonic acid (MSS-SO3H) is
suitable for the synthesis of 1,2,3-triazole via the cycloaddition of
nitroalkene with NaN3, whereas the zinc-modified silica sphere cata-
lyst (MSS-SO3Zn) is more suitable for the synthesis of tetrazoles. The
MSS-SO3Zn catalyst also works well for the synthesis of 2-substituted
imidazoline via the condensation of nitriles with ethylenediamine.
Both of the MSS-SO3H and MSS-SO3Zn catalysts can be recovered
easily by a magnet, and they can be reused without further tedious
activation.
KEYWORDS
Magnetically separable;
silica sphere; imidazolines;
triazoles; tetrazoles;
heterocycles
GRAPHICAL ABSTRACT
Introduction
With the increasing development of catalytic synthesis strategies, the reusable catalysts
have drawn much attention and resonated across numerous disciplines. In recent years,
many magnetically separable catalysts have been developed for constructing versatile
organic compounds via the C–C, C–X coupling reactions[1–4], and Fischer–Tropsch syn-
thesis reactions.[5] Besides, the magnetic nanoparticles are also widely applied to remove
phosphates from wastewater[6] and reduction of acetophenone.[7] The magnetically
CONTACT Hong-Bin Sun
sunhb@mail.neu.edu.cn; Zhangpei Chen
chenzhangpei@mail.neu.edu.cn
Department of Chemistry, Northeastern University, Shenyang 110819, People’s Republic of China.
Supplemental data (full experimental detail and 1H and 13C NMR spectra) for this article can be accessed on the
publisher’s website.
ß 2018 Taylor & Francis Group, LLC

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separable nano-catalysts also hold an important position in the synthesis of heterocycles.
For example, a graphene oxide/Fe3O4 supported Mo catalyst was reported to synthesize
dihydropyridines efficiently, and this catalyst could be reused for eight times with no
decrease in catalytic activity.[8] Similarly, the CeO2-Fe3O4 nanoparticles catalyzed syn-
thesis of benzoxazole and benzothiazole have also been presented.[9] Moreover, the
Fe3O4 supported Cu was developed for the synthesis of quinazolinones and bicyclic pyr-
imidinones,[10] and a magnetic Pd-graphene catalyst was proved to be an efficient
protocol for synthesizing 2-alkylquinolines.[11] The functionalized magnetic particles
have been used in the synthesis of indole derivatives[12] and pyrazole-fused isocoumar-
ins.[13] In this work, we applied two magnetically modified silica spheres catalysts to the
synthesis of the triazoles, tetrazoles, and imidazolines. One is Fe3O4@SiO2 grafted sul-
fonic acid catalyst (MSS-SO3H), and the other is zinc-exchanged MSS-SO3H named as
MSS-SO3Zn.
Results and discussion
The magnetic silica nanospheres were synthesized according to a typical method,[14, 15]
then 3-mercaptopropyl trimethoxysilane (MPTMS) was employed to graft the –SH
group on the silica sphere surface. The nanospheres were oxidized by H2O2, then the
catalyst MSS-SO3H was obtained. Stirring the MSS-SO3H in a concentrated Zn(NO3)2
solution for 24 h at room temperature formed the zinc-exchanged catalyst MSS-SO3Zn.
The structure of two prepared materials was characterized by HR-TEM, EDS, and VSM
analysis. From the Figure 1(a,b), we can find that the general size of the magnetic silica
sphere is about 400 nm. Figure 1(c) indicates that the magnetic Fe3O4 is in the core pos-
ition of the MSS-SO3H, and it is coated with SiO2. The edge of MSS-SO3Zn is not as
smooth as MSS-SO3H because of doping of Zn. Figure 1(d–h) further demonstrates the
structure of the nanoparticle was Fe3O4@SiO2-SO3Zn. Particularly, Figure 1(h) reveals
that Zn mainly distributes on the catalyst’s surface. Therefore, the structure presented in
Figure 1(h) was confirmed as Fe3O4@SiO2-SO3Zn.
The magnetic property of the MSS-SO3Zn and recycled MSS-SO3Zn catalyst was
investigated using a vibrating sample magnetometer at room temperature. As illustrated
in Figure 2, the magnetization curves of the prepared materials exhibited tiny hysteresis
loops, which demonstrated its paramagnetic characteristics. The magnetic intensity of
recycled MSS-SO3Zn is stronger than that of the fresh MSS-SO3Zn, this may be due to
the zinc leaching. Moreover, the catalyst can be separated by external magnetic field as
illustrated in Figure S1.
First, the as-prepared catalyst MSS-SO3H was applied to synthesize the triazoles,
whose derivatives were used widely as the agricultural chemicals.[16] Typically, the syn-
thesis of triazoles have been well developed by the Cu(I) catalyzed cycloaddition of
organic azides with terminal alkynes.[17] To avoid the possible toxicity of residual cupric
catalyst, nontoxic BiCl3,[18] and metal-free protocol were also reported.[19] A more
recent research reported an acid–base bifunctional heterogeneous catalyst.[20] In our
study, a variety of triazoles have been synthesized through the condensation between
nitroalkenes and sodium azide under the optimized reaction conditions (Table S1). As
shown in Table 1, the magnetic silica sphere based catalyst MSS-SO3H is highly effective

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Figure 1. The morphology of MSS-SO3H and MSS-SO3Zn: (a and b) HR-TEM of MSS-SO3Zn (c) TEM of
MSS-SO3H, EDS analysis of MSS-SO3Zn: (d) Fe distribution (e) O distribution; (f) Si distribution
(g) S distribution (h) Zn distribution.

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Figure 2. The VSM curses of MSS-SO3Zn (a) and recovered MSS-SO3Zn (b).
for most substrates to synthesize triazoles. The nitroalkenes bearing chloro, bromo, and
isopropyl group gave excellent yields (1a–1e). The hindrance of ortho-substituted chloro
atom led to a slightly declined yield (1c). The substrate bearing a strong electron-with-
drawing –NO2 gave 92% yield (1h), whereas the substrates bearing electron-donating
group –OH (1f, 1g) and isopropyl (1e) gave lower yields of 78%, 81%, and 83%. This
suggested that the formation of 1,2,3-triazole might proceed a pathway of a [3 þ 2]
cycloaddition, whereas the nitroalkene was the electrophiles.
With the successful application of MSS-SO3H to the synthesis of triazole, we further
investigated the cycloaddition of benzonitriles with sodium azide to synthesize tetra-
zoles, which were widely used in pharmacochemistry, coordination chemistry, photog-
raphy, and agriculture fields.[21,22] The common method of preparing 5-substituted-1H-
tetrazoles is the cycloaddition of nitriles with azide, and multitudinous catalysts have
been reported such as Lewis acid Cu2(OTf)2,[23] CdCl2,[24] Fe(OAc)2,[25] ZnCl2,[26]
AlCl3,[27] FeCl3,[28] and heterogeneous catalysts such as nanoscale ZnS[29] and Cu2O.[30]
Even Brꢀnsted acids like HCl, NH4Cl, and AcOH can be applied to synthesize tetra-
zoles via the cycloaddition of nitriles and azides.[31,32]
Considering the Brꢀnsted acidity of SO3H and its potential to catalyze the cycloadd-
ition of nitriles and azides, we applied MSS-SO3H to synthesize 5-substituted-1H-tetera-
zoles. To our delight, the MSS-SO3H showed good efficiency for this reaction after
optimizing the reaction conditions (Table S2). As listed in Table 2, some nitriles were

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Table 1. Synthesis of triazoles catalyzed by MSS-SO3H.a
Entry
1
Substrate
Product
1
Yield/%
97
1a
2
3
1b
1c
95
80
4
5
6
7
8
1d
1e
1f
83
83
78
81
92
1g
1h
aReaction conditions: 1 mmol a,b-unsaturated nitroarenes derivative and 2 mmol sodium azide, 60 ꢁC, 1 h, 2 mL DMF as
solvent, 10 wt% catalyst.
transformed into the target tetrazoles smoothly. Especially, the substrates bearing elec-
tron-withdrawing groups afforded corresponding target products in excellent yields,
such as 2a–2d. However, there were still some substrates could not offer satisfactory
yields, such as 2e–2h. In particular, more substrates bearing electron-donating groups
afforded moderate to low yields. Considering the unsatisfactory yields of the target
products, we modified the MSS-SO3H catalyst by zinc-exchanging to promote the cata-
lytic efficiency. As Table 2 shown, the zinc-exchanged MSS-SO3H presented as MSS-
SO3Zn shows better performance in this reaction, it affords higher yields than MSS-
SO3H. Similarly, the yields of electron-deficient substrates (2a–2e) were much higher
than that of electron-rich substrates (2f, 2g). Meanwhile, we screened the substrates
(2i–2l) and obtained the corresponding products in higher yields.
To explore more application of the MSS-SO3Zn catalyst, we utilized MSS-SO3Zn cata-
lyst to synthesize the imidazolines, which were applied widely with synthetic intermedi-
ates, chiral auxiliaries, chiral catalysts, and ligands for asymmetric catalysis. The
synthetic protocol is the cycloaddition of benzonitriles with ethylenediamine, which is a
typical approach. The reactions were conducted under the optimistic conditions. (The

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Table 2. Synthesis of tetrazoles using MSS-SO3H(A) & MSS-SO3Zn(B).a
Yield/%b Yield/%b
Entry
1
Substrate
Product
2
with A
with B
2a
2b
2c
2d
2e
2f
88
93
2
3
94
92
99
59
36
28
52
68
47
36
28
99
95
98
67
55
45
67
74
56
52
56
4
5
6
7
2g
2h
2i
8
9
10
11
12
2j
2k
2l
aReaction conditions, 2 mmol benzonitriles, 3.2 mmol sodium azide, 10 wt% of catalyst, 140 ꢁC for 24 h.
bIsolated yields.

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optimization is presented in Table S3). As Table 3 shown, the catalyst MSS-SO3Zn
offers moderate to good isolated yields of imidazolines in general. Both electron-donat-
ing and electron-withdrawing substrates could afford high conversions to target prod-
ucts, such as 3d and 3i. The phenylacetonitrile also gave the corresponding product in
moderate yields (3j) and some other benzonitriles (3f, 3g, and 3k) also showed moder-
ate to good conversions. The bromo atoms in 3b and 3c were substituted by –NH-
CH2CH2-NH2 because of the strong nucleophilicity of excess ethylenediamine.
Both of the MSS-SO3H and MSS-SO3Zn catalyst are magnetically recoverable. As
Figure 3 shown, MSS-SO3Zn catalyst exhibits higher catalytic activity than MSS-SO3H
for synthesizing tetrazoles but its reusability was lower than MSS-SO3H due to the
leaching of Zn. Anyway, a recovered MSS-SO3Zn catalyst can regenerate its original
catalytic activity by zinc ion exchanging. Moreover, MSS-SO3H was suitable for synthe-
sizing triazoles with high activity and reusability. However, the decreasing catalytic per-
formance of MSS-SO3H was also observed, that may due to the inevitable loss of
catalyst nanoparticles during the work up. In a word, the catalytic activity of the two
catalysts did not lose too much after six times runs. This means both of the catalyst
MSS-SO3H and MSS-SO3Zn are stable enough for the synthesis of triazoles, tetrazoles,
and imidazolines.
Experiments
Preparation of catalyst MSS-SO3H and MSS-SO3Zn
A portion of 0.2 g prepared Fe3O4 nanoparticles (method was introduced in the first
part of Supplementary Materials) was treated by ultrasonic in the 0.1 M HCl solution
for 10 min. Then, the activated Fe3O4 particles were dispersed into a mixture of 160 mL
alcohol, 40 mL deionized H2O, and 4 mL 25% NH3ꢂH2O. After that, 1 mL tetraethoxylsi-
lane (TEOS) was added into the above solution drop by drop, and the resulting mixture
was stirred for 6 h. The magnetically collected solid was put into isopropanol (200 mL),
then MPTMS (1 mL) was added into the liquid and the reaction was kept at 80 ꢁC for
3 h to functionalize the silica surface with the thiol groups. The decanted functionalized
silica sphere was put into 30 wt% H2O2 and stirred for 10 h under room temperature to
form the sulfonic acid group. Finally, the catalyst MSS-SO3H were obtained by clean-up
and drying and its structure can be described by Fe3O4@SiO2-SO3H.
The fabrication of the catalyst MSS-SO3Zn is described as below: the as-prepared
catalyst MSS-SO3H was stirred for 12 h in saturated Zn(NO3)2 alcohol solution. The
obtained particles were cleaned with alcohol for three times and dried at 80 ꢁC.
General procedure for the synthesis of triazoles (1a–1h)
A mixture of 10 wt% catalyst MSS-SO3H, (2-Nitro-vinyl)-benzene derivatives (1 mmol),
sodium azide (2 mmol) and DMF (2 mL) was added into a sealed tube, then heated for
1 h at 60 ꢁC. After the catalyst was removed by magnetic separation (Figure S1), the
solution was cooled and diluted with water, then extracted with ethyl acetate/petroleum
ether for further evaporation. After evaporation, we obtained the isolated triazoles. A
sample for characterization was purified on a flash silica column.

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Table 3. Synthesis of imidazolines catalyzed by MSS-SO3Zn.a
Entry
1
Substrate
Product
3
Yield/%
83
3a
2
3b
3c
3d
3e
3f
58
67
91
25
71
69
15
85
56
56
3
4
5
6
7
3g
3h
3i
8
9
10
3j
11
3k
aReaction conditions: benzonitrile derivatives (1 mmol), ethylenediamine (2 mL), catalyst MSS-SO3Zn (45 mg/mmol),
140 ꢁC, 24 h, isolated yield.
5 -Phenyl-1H-1,2,3-triazole (1a)
1
White solid. M.P. 140–143 ꢁC; H NMR (400 MHz, DMSO-d6) d 8.27 (s, 1H), 7.85
(d, J ¼ 7.1 Hz, 2H), 7.43 (d, J ¼ 7.8 Hz, 2H), 7.32 (s,1H). 13C NMR (101 MHz, DMSO-
d6) d 145.3, 131.2, 129.0, 128.1, 127.4, 125.9. MS (ESI) m/z for C8H7N3:
146 ([M þ H]þ).

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Figure 3. Recycling of the catalyst MSS-SO3H and MSS-SO3Zn for the synthesis of tetrazoles, tiazoles,
and imidazolines.
General procedure for the synthesis of tetrazoles (2a–2l)
The benzonitrile derivatives (2 mmol), sodium azide (3.2 mmol), and DMF (2 mL) were
mixed in a sealed tube, then 30 mg of catalyst MSS-SO3H (or catalyst MSS-SO3Zn) was
added into the tube, which was heated for 24 h under 140 ꢁC. After 24 hours’ reaction,
the catalyst was separated by magnetic force, and the solution was poured into water.
The liquid was acidified to pH 1, then ethyl acetate was added to extract the tetrazoles.
Carefully evaporating the solvent under reduced pressure, we got the isolated tetrazoles.
A sample for characterization was purified on a flash silica column.
5 -Phenyl-1H-tetrazole (2a)
1
White solid; M.P: 216–217 ꢁC; H NMR (300 MHz, DMSO-d6) d 7.64–7.65 (m, 3H), d
8.07–8.10 (m, 2H); 13C NMR (151 MHz, DMSO-d6) d 155.3, 130.3 129.9, 127.9, 126.8.
HRMS: calcd. for C7H8N4 (M þ Hþ) 147.0665; found 147.0670.
General procedure for the synthesis of imidazolines (3a–3k)
The benzonitrile derivatives (1 mmol) and ethylenediamine (2 mL) were mixed in a
sealed tube, then 45 mg of MSS-SO3Zn catalyst was added. The mixture was heated at
130 ꢁC for 24 h. After cooling, the catalyst was separated by magnetic force, and the
organic layer was detached. Deionized water and dichloromethane were added into the
organic liquid. The organic layer was evaporated to obtain the isolated imidazolines. A
sample for characterization was purified on a flash silica column.

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2 -phenyl-4,5-dihydro-1H-imidazole(3a)
1
White solid; M.P. 102ꢃ103 ꢁC; H NMR (600 MHz, Chloroform-d) d 7.39–7.78 (m,
5H), 4.61 (s, 1H), 3.77 (s, 4H); 13C NMR (151 MHz, DMSO-d6) d 163.9, 130.9, 130.6,
128.5, 127.4, 49.9. MS (ESI) m/z for C9H10N2: 147 ([M þ H]þ).
Conclusions
In conclusion, we have developed two magnetically separable and reusable catalysts to
synthesize imidazolines, tetrazoles, and triazoles. The grafted sulfuric acid based catalyst
Fe3O4@SiO2-SO3H (MSS-SO3H) showed high activity in synthesizing triazoles, whereas
the zinc-exchanged catalyst Fe3O4@SiO2-SO3Zn (MSS-SO3Zn) showed excellent per-
formance in the synthesis of tetrazoles and imidazolines. Both of them can be recovered
facilely by magnetic separation and reused for at least six runs. These heterogeneous
catalysts were consistent with the concept of environmental friendliness.
Funding
This work was financially supported by National Natural Science Foundation of China
(21235004, 21175080), the Fundamental Research Funds for the Central University
(N160503001), the Science and Technology Foundation of Liaoning Province (20170520185), and
the Ministry of Science and Technology (2013ZX09507005).
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