Nov-Dec 2004
An Improved Procedure for the Nitration of Benzo-2,1,3-selenadiazoles
1025
Eaton's reagent was added dropwise with stirring. Once the addi-
tion of nitric acid was complete, the cooling bath was removed
and the mixture was stirred at room temperature until the reaction
was complete as judged by the disappearance of the starting
material 1 by tlc or GC/MS analysis, typically 18 to 24 h. The
reaction mixture was poured into 70 mL of ice water and stirred
until the ice had melted. The precipitate was collected by filtra-
tion, washed well with water and dried on the filter. The dried
product was recrystallized from 1,4-dioxane to afford the final
product.
4-Nitrobenzo-2,1,3-selenadiazole (2h).
This compound was obtained in 90% yield as white crystals,
1
mp 214 – 216 °C; H nmr (dimethyl sulfoxide-d ): δ 8.42 (d, J =
6
13
7.4 Hz, 1 H); 8.25 (d, J = 8.7 Hz, 1 H); 7.71 (m, 2 H); C nmr
(dimethyl sulfoxide-d ): δ 161, 151, 130, 127, 126, 120; ms: m/z
6
+
229 (M , 100%).
Anal. Calcd. for C H N O Se: C, 31.60; H, 1.33; N, 18.42.
6
3 3 2
Found: C, 31.40; H, 1.15; N, 18.24.
5-Methyl-4-nitrobenzo-2,1,3-selenadiazole (2i).
This compound was obtained in 93% yield as off-white crys-
5-Fluoro-4-nitrobenzo-2,1,3-selenadiazole (2a).
1
tals, mp 194 – 196 °C; H nmr (dimethyl sulfoxide-d ): δ 7.97 (d,
6
This compound was obtained in 94% yield as white crystals,
13
J = 9.1 Hz, 1 H); 7.58 (d, J = 9.1 Hz, 1 H); 2.41 (s, 3 H); C nmr
1
mp 237 – 239 °C; H nmr (dimethyl sulfoxide-d ): δ 8.28 (m, 1
6
(dimethyl sulfoxide-d ): δ 158, 151, 132, 131, 126, 17; ms: m/z
6
13
H); 7.88 (t, 1 H); C nmr (dimethyl sulfoxide-d ): δ 157, 155,
6
+
243 (M , 100%).
19
151, 129, 128, 120; F nmr (dimethyl sulfoxide-d ): δ -117; ms:
6
Anal. Calcd. for C H N O Se: C, 34.73; H, 2.08; N, 17.36.
7
5 3 2
+
m/z 247 (M , 100%).
Found: C, 34.82; H, 1.78; N, 17.18.
Anal. Calcd. for C H FN O Se: C, 29.29; H, 0.82; N; 17.08.
6
2
3 2
4-Fluoro-3-nitro-benzene-1,2-diamine (3).
Found: C, 29.30; H, 0.93; N, 17.14.
2,1,3-Selenadiazole 2a (12.30 g, 50 mmol) was dissolved in 50
mL of Eaton's reagent and cooled in ice while an ice - cold solu-
tion of 9.6 mL (200 mmol) of 90% nitric acid (d = 1.48) in 20 mL
of Eaton's reagent was added dropwise with stirring. Once the
addition of nitric acid was complete, the cooling bath was
removed and the mixture was stirred for 24 h at room temperature
until the reaction was complete. The reaction mixture was poured
into 500 mL of ice and stirred until the ice had melted. The pre-
cipitate was collected by filtration and washed three times with
water. The damp filter cake was transferred to a 1000 mL
Erlenmeyer flask, dissolved in 150 mL of 57% hydriodic acid,
and stirred overnight at room temperature. The mixture was then
diluted with 200 mL of water. Sulfur dioxide gas was passed in
until a negative test was obtained with potassium iodide – starch
paper. The mixture was then heated to 95 °C and held at that tem-
perature for 10 minutes with stirring. Stirring was continued
while the mixture cooled, after which it was filtered through
Celite. The filtrate was adjusted to pH = 6 with concentrated
ammonium hydroxide (about 150 mL required) and cooled in ice
to 5 °C. The precipitate was filtered, washed with ice water and
5-Fluoro-4-methyl-7-nitrobenzo-2,1,3-selenadiazole (2c).
This compound was obtained as yellow crystals, mp 209 – 210
1
3
°C; H nmr (dimethyl sulfoxide-d ): δ 8.58 (d, J
= 9.6 Hz, 1
6
F-H
13
H); 2.58 (s, 3 H); C nmr (dimethyl sulfoxide-d ): δ 159, 156,
6
19
148, 126, 120, 119, 12; F nmr (dimethyl sulfoxide-d ): δ -117;
6
+
ms: m/z 261 (M , 100%).
Anal. Calcd. for C H FN O Se: C, 32.33; H, 1.55; N, 16.16.
7
4
3 2
Found: C, 31.98; H, 1.76; N, 15.86.
5-Chloro-4-nitrobenzo-2,1,3-selenadiazole (2d).
This compound was obtained in 85% yield as white crystals,
1
mp 228 – 230 °C; H nmr (dimethyl sulfoxide-d ): δ 8.09 (d, J =
6
13
9.5 Hz, 1 H); 7.78 (d, J = 9.5 Hz, 1 H); C nmr (dimethyl sulfox-
ide-d ): δ 158, 150, 129, 127, 126; ms: m/z 263 (M , 100%).
+
6
Anal. Calcd. for C H ClN O Se: C, 27.45; H, 0.77; N, 16.01;
6
2
3 2
Cl 13.51. Found: C, 27.71; H, 0.65; N, 16.05; Cl, 13.72.
5,6-Dichloro-4-nitrobenzo-2,1,3-selenadiazole (2e).
This compound was obtained in 85% yield as off-white crys-
1
tals, mp 209 – 212 °C; H nmr (dimethyl sulfoxide-d ): δ 8.57 (s,
6
dried to afford 8.16 g (95%) of 3 as purple needles, mp 136 - 137
13
1H); C nmr (dimethyl sulfoxide-d ): δ 157, 149, 132, 126, 125;
ms: m/z 297 (M , 100%).
1
6
°C (lit. mp 137 – 139 °C [1]); H nmr (methanol-d ): δ 6.76 (d of
4
+
3
3
d, J = 8.7 Hz, J
= 5.0 Hz, 1 H), 6.32 (d of d, J = 8.7 Hz, J
= 11.2 Hz, 1 H); C nmr (dimethyl sulfoxide-d ): δ 149, 147,
134, 133, 115, 102; F nmr (dimethyl sulfoxide-d ): δ -136; ms:
F-H
13
F-H
Anal. Calcd. for C HCl N O Se: C, 24.27; H, 0.34; N, 14.15;
6
2 3 2
6
Cl 23.88. Found: C, 24.33; H, 0.34; N, 14.50; Cl, 23.94.
19
6
+
m/z 171 (M , 100%).
5-Bromo-4-nitrobenzo-2,1,3-selenadiazole (2f).
Anal. Calcd. for C H FN O : C, 42.11; H, 3.53; N, 24.55.
6
6
3 2
This compound was obtained in 86% yield as yellow crystals,
Found: C, 42.04; H, 3.43; N, 24.45.
1
mp 236 – 238 °C; H nmr (dimethyl sulfoxide-d ): δ 8.00 (d, J =
6
13
9.5 Hz, 1 H); 7.87 (d, J = 9.5 Hz, 1 H); C nmr (dimethyl sulfox-
ide-d ): δ 158, 151, 132, 127, 126, 116; ms: m/z 307 (M , 100%).
+
REFERENCES AND NOTES
6
Anal. Calcd. for C H BrN O Se: C, 23.48; H, 0.66; N, 13.69;
6
2
3 2
[1] W. Tian, S. Grivas and K. Olsson, J. Chem. Soc., Perkin
Trans. I, 257 (1993).
Br 26.03. Found: C, 23.79; H, 0.50; N, 13.76; Br, 26.30.
5-Fluoro-7-methyl-4-nitrobenzo-2,1,3-selenadiazole (2g).
[2] The original reference [2] suggested that 2b was formed dur-
ing the quenching of the reaction mixture with ice water and that the
amount of 2b formed was a function of the time and temperature of the
quenching step. We found that 2b was formed directly in the reaction
mixture in the absence of an aqueous quench. Aliquots of the nitration
mixture analyzed by GC/MS showed the presence of 2b in the nitration
This compound was obtained in 90% yield as off-white crys-
tals, mp 184 – 185 °C; H nmr (dimethyl sulfoxide-d ): δ 7.69 (d,
= 11.6 Hz, 1 H); 2.66 (s, 3 H); C nmr (dimethyl sulfoxide-
d ): δ 19; F nmr (dimethyl sulfoxide-d ): δ -116; ms: m/z 261
1
6
3
13
J
F-H
19
6
6
+
(M , 100%).
Anal. Calcd. for C H FN O Se: C, 32.33; H, 1.55; N 16.16.
mixture, in amounts that increased as a function of time. Likewise, the
13
formation of 2b could be observed directly in the reaction mixture by
C
7
4
3 2
NMR.
Found: C, 32.63; H, 1.60; N, 15.94.