A. Teimouri, A. Najafi Chermahini / Polyhedron 30 (2011) 2606–2610
2609
Table 2 (continued)
Entry
Substrate
Product
Yieldsc
Zeolite
Ref.
Sulfated zirconia
H
2
O
DMF
2
H O
DMF
CN
N
N
N
NH
1l
3l
O CCH3
O CCH3
O
O
a
The products were characterized by IR, 1H NMR, 13C NMR and mass spectroscopy.
Reaction time: 24 h.
Isolated yields after recrystallization.
b
c
2
.2.1.5. 4-(1-H-Tetrazole-5-yl) pyridine (3e, Table 2, entry 5). White
2865, 2700, 2625, 1678, 1580, 1269, 843. 1H NMR (DMSO-d
400 MHz) d ppm: 7.9 (d, J = 7.4 Hz, 2H), 7.7 (d, J = 7.4 Hz, 2H),
6
,
À1
solid; M.p.: 254–258 °C. FTIR (KBr, cm ): 3080, 3060, 3028,
2
1
13
955, 2917, 2832, 2751, 2689, 1608, 1581, 1492, 1065, 784.
H
6
2.59 (s, 3H). C NMR (DMSO-d , 100 MHz) d ppm: 170, 164, 152,
NMR (DMSO-d
J = 7.8 Hz, 2H). C NMR (DMSO-d
6
, 400 MHz) d ppm: 8.0 (d, J = 7.8 Hz, 2H), 8.8 (d,
131, 128, 124, 22. MS; m/z = 204, 189, 173, 160, 145, 130, 102, 90.
1
3
6
, 100 MHz) d ppm: 165, 149,
1
34, 121. MS; m/z = 147, 119, 92, 78, 62, 50.
3
. Results and discussion
2
.2.1.6. 5-(4-Nitrophenyl)-1H-tetrazole (3f, Table 2, entry 6). White
À1
In continuation of our recent work on the applications of
solid; M.p.: 218–220 °C. FTIR (KBr, cm ): 3103, 2914, 2853,
2
d ppm: 8.1 (d, J = 8 Hz, 2H), 8.2 (d, J = 8 Hz, 2H). C NMR (DMSO-
d
1
heterogeneous reagents for the development of synthetic method-
ologies, we report a new protocol for the preparation of 5-substi-
tuted 1H-tetrazoles from a wide variety of nitriles using zeolite
and sulfated zirconia as a solid acid catalyst (Scheme 1).
In the reaction between benzonitrile 1a–l and sodium azide 2,
we investigated the effect of the benzonitrile:sodium azide ratio
and catalyst (Table 1). Attempts to carry out these reactions in
the absence of catalyst in water, DMF and MeOH did not yield
any products, indicating that the sulfated zirconia and zeolite are
acting as a catalyst (Table 1, entries 1 and 2). First, we optimized
the amount of catalyst required in the reaction between benzoni-
trile and sodium azide. Different amounts of zeolite as the catalyst
752, 2621, 1605, 1526, 1487, 861. H NMR (DMSO-d
6
, 400 MHz)
13
6
, 100 MHz) d ppm: 156, 130, 128, 124. MS; m/z = 191, 163, 149,
34, 90, 63.
1
2
7
.2.1.7. 4-(1H-Tetrazole-5-yl)benzonitrile (3g, Table 2, entry
). White solid; M.p.: 258–260 °C. FTIR (KBr, cm ): 3100, 2848,
À1
2
750, 2250, 1480, 781. 1H NMR (DMSO-d
6
, 400 MHz) d ppm: 8.0
13
(
6
d, J = 7.8 Hz, 2H), 8.2 (d, J = 7.8 Hz, 2H). C NMR (DMSO-d ,
1
1
00 MHz) d ppm: 160, 135, 132, 130, 126, 114. MS; m/z = 171,
43, 129, 103, 62.
(
20, 50 and 100 mg) were tried and it was found that 50 mg of cat-
2
8
2
.2.1.8. 3-(1H-Tetrazole-5-yl)benzonitrile (3h, Table 2, entry
alyst gave the maximum yield of the products. An increase in the
amount of catalyst did not improve the results to any great extent.
However on using 20 mg of catalyst the reaction was complete
after 76 h. In addition the amount of sulfated zirconia was opti-
mized using different amounts (10, 20 and 50 mg) of this catalyst.
It was observed that 20 mg of catalyst gave the best results. Again
an increase in the value of catalyst did not improve the yield, and
with values lower than 20 mg the reaction was only completed
after long reaction times (72 h).
One of the most important advantages of heterogeneous catal-
ysis over the homogeneous counterpart is the possibility of reusing
the catalyst by simple filtration, without loss of activity. In a typical
experiment, after the reaction was completed, the catalysts were
recovered from the reaction mixtures by simple filtration and they
were purified by washing the solid residues with deionized water
and acetone followed by drying in an oven at 100 °C for 40 min.
From each experiment, more than 98% of the catalyst was recov-
ered. The recovered catalyst was reused three times without any
loss of activity (Table 1, entries 16–18) (see Fig. 1).
À1
). White solid; M.p.: 214–216 °C. FTIR (KBr, cm ): 3113, 2981,
1
780, 2442, 2237, 1476, 870, 780. H NMR (DMSO-d
6
, 400 MHz)
, 100 MHz) d ppm:
64, 134, 133, 132, 131, 129, 115. MS; m/z = 171, 143, 102, 62.
13
d ppm: 7.7–8.1 (5H, m). C NMR (DMSO-d
1
6
2.2.1.9. 2-(1H-Tetrazole-5-yl)benzonitrile (3i, Table 2, entry 9). White
À1
solid; M.p.: 208–210 °C. FTIR (KBr, cm ): 3096, 2531, 2110, 2023,
1
1
632, 1436, 845. H NMR (DMSO-d
J = 6.8 Hz, 1H), 7.7 (t, J = 6.8 Hz, 1H), 7.8 (m, 2H).
DMSO-d , 100 MHz) d ppm: 166, 140, 136, 133, 132, 128, 126,
18. MS; m/z = 171, 143, 129, 115, 88, 76, 62, 57.
6
, 400 MHz) d ppm: 7.6 (t,
1
3
C NMR
(
1
6
2.2.1.10. 4-(1H-Tetrazole-5-yl)benzaldehyde (3j, Table 2, entry
À1
1
2
0). White solid; M.p.: 180–182 °C. FTIR (KBr, cm ): 3015, 2924,
1
854, 2713, 2612, 1667, 1440, 776. H NMR (DMSO-d
6
, 400 MHz)
d ppm: 7.9 (d, J = 7.2 Hz, 2H), 8.0 (d, J = 7.2 Hz, 2H), 9.1 (s, 1H).
1
3
6
C NMR (DMSO-d , 100 MHz) d ppm: 188, 156, 138, 131, 129,
1
28. MS; m/z = 174, 146, 130, 116, 102, 90, 57, 43.
Next we examined the effect of solvent. In the present study we
used DMF–methanol and water as the solvent. Not many organic
solvents are stable at the high temperatures necessary for cycload-
dition reactions (sometimes as high as 130 °C), and for this reason
DMF is most commonly used for this purpose [3,21,27]. However
the use of water as a clean, inexpensive, and universal solvent com-
bines features of both economic and environmental advantages. As
can be seen from Table 1, the best results were obtained from a
DMF–MeOH mixture as the solvent. Under these conditions and
using the molar ratio 1:3 benzonitrile:sodium azide, the conversion
2
1
.2.1.11. 4-(1H-Tetrazole-5-yl) benzoic acid (3k, Table 2, entry
À1
1). White solid; M.p.: 248–250 °C. FTIR (KBr, cm ): 3600–3000
1
(
br), 2500, 1760, 1500, 1480, 780. H NMR (DMSO-d
6
, 400 MHz)
, 100 MHz) d ppm: 188,
66, 138, 131, 129, 128. MS; m/z = 190, 174, 146, 130, 116, 102,
0, 75, 57.
13
d ppm: 7–8 (m, 4H). C NMR (DMSO-d
1
9
6
2.2.1.12. 4-(1H-Tetrazole-5-yl)phenyl acetate (3l, Table 2, entry
À1
1
2). White solid; M.p.: 212–214 °C. FTIR (KBr, cm ): 3097, 2925,