G Model
CRAS2C-3857; No. of Pages 6
M. Hosseini-Sarvari, S. Najafvand-Derikvandi / C. R. Chimie xxx (2014) xxx–xxx
5
Commonly, in sulfated metallic oxides, there may be
many Lewis acid sites as well as Brønsted acid sites.
The superacidity of these materials is attributed to
the Brønsted acid sites, created or already existing,
whose acidity is increased by the presence of neighboring
strong Lewis acid sites. The strength of these Lewis acid
sites is due to an inductive effect exercised by sulfate on
the metallic cation, which becomes more deficient in
electrons [19], as seen in Scheme 2. Thus, Lewis acid sites of
ethyl acetate. The combined organic phase was washed
with water and concentrated to precipitate the crude
crystalline solid. All products were characterized by NMR,
IR, mass spectra, and CHN analysis and the data for the
known compounds were found to be identical with the
literature. The complete spectroscopic data are described
in the supporting information.
4. 5-Phenyl-1H-tetrazole (3a)
2
À
nano TiO
2
/SO
4
coordinated readily to the nitrile, and this
is the dominant factor influencing [3 + 2] cycloaddition. It
should be noted that, previously, Sharpless et al. [20]
reported that coordination of nitrile substrate to the Lewis
acidic Zn is the source of the catalytic effect in the
formation of 1H-tetrazoles, which is supported by model
calculations using density functional theory. Subsequently,
nucleophilic attack by azide followed by hydrolysis
affords tetrazole.
Yield: 97%. White solid. M.p. 215–216 8C (lit. [11] 215–
1
216 8C). H NMR (250 MHz, DMSO-d
7.55–7.61 (m, 3 H), 8.04–8.10 (m, 2 H) ppm. C NMR
6
):
d
= 3.92 (brs, 1 H),
1
3
2+
(62.9 MHz, DMSO-d
155.2 ppm. IR (KBr):
1620, 1600, 1460, 1350, 1383, 1163, 1057, 765 cm
6
):
n
d = 124.1, 127.0, 129.4, 131.2,
= 3419, 2924, 2827, 2717, 2656,
À1
.
5. 2-(1H-Tetrazol-5-yl)benzonitrile (3b)
In conclusion, we have developed a simple, ecofriendly,
and efficient method for the preparation of 5-substituted-
Yield: 90%. White solid. M.p. 208–210 8C (lit. [12] 212–
1
1
SO
H-tetrazoles via [3 + 2] cycloaddition using nano TiO
2
/
214 8C). H-NMR (250 MHz, DMSO-d
6
): d = 5.02 (brs, 1 H),
2
À
4
as a heterogeneous catalyst. Various nitriles reacted
in DMF to yield the corresponding 5-sub-
7.74 (m, 1 H), 7.92 (m, 1 H), 8.05 (d, J = 8.04 Hz, 2 H) ppm.
1
3
with NaN
3
6
C-NMR (62.9 MHz, DMSO-d ): d = 110.1, 117.2, 127.4,
stituted-1H-tetrazoles with moderate to good yields. The
catalyst can be readily recovered and reused. The
significant advantages of this methodology are high yields,
simple methodology, easy work-up, a simple work-up
procedure, and easy preparation and handling of the
catalyst. The catalyst can be recovered by filtration and
reused. This methodology may find widespread use in
organic synthesis for the preparation of 5-substituted-1H-
tetrazoles.
129.6, 131.3, 133.7, 134.8, 155.4 ppm. IR (KBr):
n
= 3096,
À1
2531, 2110, 2023, 1632, 1436, 845 cm
.
6. 3-(1H-Tetrazol-5-yl)benzonitrile (3c)
Yield: 95%. White solid. M.p. 214–216 8C (lit. [12] 214–
1
216 8C.). H-NMR (250 MHz, DMSO-d
6
):
d
= 3.93 (brs, 1 H),
):
= 117.9, 125.7, 130.2, 130.7, 131.4, 134.4, 136.7,
1
3
7.75–8.40 (m, 4 H) ppm. C-NMR (62.9 MHz, DMSO-d
6
d
1
54.8 ppm. IR (KBr):
n
= 3113, 2981, 2780, 2442, 2237,
À1
3
. Experimental
1476, 870, 780 cm
.
3.1. Catalyst preparation
7. 4-(1H-Tetrazol-5-yl) benzonitrile (3d)
2
À
powder was prepared by a sol–gel
Nano TiO
process. Titanium isobutoxide (98% Fluka) was used as the
source of TiO . An amount of 14.3 mL of Ti(OC was
2
/SO
4
Yield: 95%. White solid. M.p. 258–260 8C (lit. [12] 258–
1
260 8C). H-NMR (250 MHz, DMSO-d
6
):
d
= 4.20 (brs, 1 H),
1
3
2
4
H
9
)
4
7.93 (d, J = 8.50 Hz, 2 H), 8.16 (d, J = 8.50 Hz, 2 H) ppm. C-
NMR (62.9 MHz, DMSO-d ): = 113.3, 118.1, 127.5, 128.7,
= 3100, 2848, 2750, 2250,
hydrolyzed in 150 mL of water containing 1.25 mL of nitric
acid 65% (Merck); the aqueous solution was stirred
continuously at room temperature for 2 h to form a highly
dispersed sol, and then the sol was concentrated and dried
at 60 8C. Sulfation was done using a 0.5 M sulfuric acid
6
d
133.27, 155.2 ppm. IR (KBr):
n
À1
1480, 781 cm
.
8. 4-(1H-Tetrazole-5-yl) pyridine (3e)
À1
solution (2.0 gÁmL ). The samples, after having been dried
for 2 h at 110 8C, were calcined for 5 h at 500 8C.
Yield: 95%. White solid. M.p. 254–257 8C (lit. [12] 254–
1
2
58 8C). H-NMR (250 MHz, DMSO-d
6
):
d
= 7.27 (brs, 1 H),
1
3
3
.2. General procedure for the synthesis of tetrazoles using
7.98 (s, 2 H), 8.78 (s, 2 H) ppm. C-NMR (62.9 MHz, DMSO-
2
À
nano TiO
2
/SO
4
d
6
):
d
= 120.9, 133.2, 150.1, 155.3 ppm. IR (KBr):
n
= 3414,
À1
2
814, 2725, 1626, 1597, 1512, 1384, 1350, 1039, 833 cm
9. 2-(1H-Tetrazol-5-yl)pyridine (3f)
Yield: 90%. White solid. M.p. 208–210 8C (lit. [11] 210–
.
In a round-bottom flask, benzonitrile (1 mmol), sodium
azide (1 mmol), and nano TiO
2
À
2
/SO
4
(0.2 g) were charged.
Then the reaction mixture was stirred in distilled
dimethylformamide (1 mL) at 120 8C. The progress of
the reaction was followed by TLC (75:25 ethyl acetate:
n-hexane). After completion of the reaction, the catalyst
was separated by centrifugation, washed with doubly
distilled water and acetone, and the centrifugate was
treated with 5 N HCl (20 mL) under vigorous stirring. The
aqueous solution finally obtained was extracted twice with
1
213 8C). H-NMR (250 MHz, DMSO-d
6
): d = 3.93 (brs, 1 H),
7.64–7.58 (m, 1 H), 8.03–8.09 (m, 1 H), 8.19 (d, J = 8.76 Hz,
1
3
1H), 8.74 (d, J = 4.86 Hz, 1 H) ppm. C-NMR (62.9 MHz,
DMSO-d
IR (KBr):
1350, 1039, 833 cm
6
):
n
d
= 122.7, 126.1, 138.5, 143.3, 149.7, 154.7 ppm.
= 3417, 2818, 2724, 1623, 1599, 1512, 1384,
À1
.
2
À
Please cite this article in press as: Hosseini-Sarvari M, Najafvand-Derikvandi S. Nano TiO
2