PAPER
A One-Pot Method for the Iodination of Aryl Amines
943
under the same conditions, led to lower yields of the ex- ter were added gradually and the reaction mixture was ground for
2
0 min until gas evolution ceased. Next, KI (5 mmol, 0.83 g) was
pected iodoarenes whilst the yields of phenol by-products
were higher. It should be noted that this reaction proce-
dure requires the addition of a small amount of water to
generate wet silica sulfuric acid, and must be carried out
in a stepwise manner in order to obtain good yields. When
added to the diazonium salt and grinding was continued for 10 min.
The mixture was diluted with EtOAc (12 mL) and, after vigorous
stirring, was filtered. The residue was extracted with EtOAc (3 × 12
mL) and the combined organic layer was washed with a 10% aq
Na SO soln and then dried over anhyd Na SO The solvent was
2
3
2
4.
potassium iodide was added together with sodium nitrite, evaporated in vacuo to afford 1-iodo-4-nitrobenzene; yield: 0.438 g
we observed a mixture of products and obtained signifi- (88%).
cantly lower yields of the expected aryl iodides.
IR (KBr): 3085, 1600, 1576, 1532, 1475, 1352, 1275, 1177, 1100,
–
1
1
050, 1012, 850, 672 cm .
We found that the intermediate aryldiazonium salts sup-
ported on silica sulfuric acid (aryldiazonium silica sul-
fates, ArN2+ OSO –SiO ) were sufficiently stable to be
1
H NMR (250 MHz, CDCl ): d = 8.15 (d, J = 9 Hz, 2 H), 7.90 (d,
3
–
J = 9 Hz, 2 H).
3
2
kept at room temperature under anhydrous conditions. For
example, p-nitrophenyldiazonium silica sulfate, which
had been stored in a desiccator at room temperature for
three days, on treatment with potassium iodide and a few
drops of water provided almost the same yield of p-io-
donitrobenzene as that prepared from fresh p-nitrophenyl-
1
-Chloro-3-iodobenzene (Table 1, Entry 5)
IR (KBr): 3058, 1595, 1562, 1450, 1400, 1325, 1160, 1112, 1060,
1
–1
005, 875, 770, 745, 670 cm .
1
H NMR (250 MHz, CDCl ): d = 7.95 (s, 1 H), 7.80 (d, J = 7.9 Hz,
3
1
H), 7.52 (d, J = 7.8 Hz, 1 H), 7.18 (t, J = 7.9 Hz, 1 H).
diazonium silica sulfate (Table 1, entry 1). All the 1-Bromo-4-iodobenzene (Table 1, Entry 6)
–
1
aryldiazonium silica sulfates prepared via this procedure IR (KBr): 3055, 1598, 1475, 1450, 1070, 1000, 825, 685 cm .
1
were stable and non-explosive; the reactivity of these aryl-
H NMR (250 MHz, CDCl ): d = 7.82 (d, J = 8.4 Hz, 2 H), 7.48 (d,
3
diazonium salts decreases when they are supported on J = 8.4 Hz, 2 H).
15
silica sulfuric acid which is a bulky solid support. There-
fore, our diazotization–iodination method is safe and the
grinding of these aryldiazonium salts in a mortar is not
hazardous under laboratory conditions. In contrast to tra-
ditional methods, the diazotization–iodination reaction
rate increases using this procedure because supporting the
aryldiazonium salt on silica sulfuric acid increases the sur-
Iodobenzene (Table 1, Entry 11)
IR (KBr): 3050, 1580, 1472, 1440, 1320, 1065, 1015, 998, 730, 685,
–
1
6
50 cm .
1
H NMR (250 MHz, CDCl ): d = 7.80 (d, J = 7.9 Hz, 2 H), 7.50 (t,
3
J = 7.1 Hz, 1 H), 7.28 (t, J = 7.4 Hz, 2 H).
1
-Iodo-2-methylbenzene (Table 1, Entry 12)
1
6
face area of the reaction. Moreover, the use of solvent-
free conditions at room temperature also increases the rate 652 cm .
IR (KBr): 3056, 2930, 1590, 1472, 1465, 1380, 1275, 1032, 745,
–
1
1
7
of these reactions. Finally, after iodination was complete
and the products had been isolated, the silica gel could be
recycled by washing with acetone, 5% aqueous sodium
hydroxide solution and water, and then drying at 120 °C.
1
H NMR (250 MHz, CDCl ): d = 7.85 (d, J = 7.9 Hz, 1 H), 7.42–
3
7
.28 (m, 2 H), 7.05–6.85 (m, 1 H), 2.48 (s, 3 H).
1-Iodo-4-methoxybenzene (Table 1, Entry 14)
IR (KBr): 3045, 2940, 2905, 1588, 1570, 1480, 1450, 1286, 1242,
In summary, we have developed an efficient and experi-
mentally simple method for the diazotization–iodination
of aromatic amines in the presence of silica sulfuric acid
at room temperature under solvent-free conditions. The
resulting diazonium salts are stable and react rapidly with
–1
1
176, 1030, 1000, 830, 630 cm .
1
H NMR (250 MHz, CDCl ): d = 7.50 (d, J = 8.9 Hz, 2 H), 6.60 (d,
3
J = 8.9 Hz, 2 H), 3.80 (s, 3 H).
2
-Iodoacetophenone (Table 1, Entry 17)
potassium iodide to produce aryl iodides in moderate to IR (KBr): 3060, 2924, 1685, 1600, 1580, 1450, 1362, 1260, 1180,
–
1
good yields. Further investigations on new applications of 1100, 1075, 752, 655 cm .
1
this method are ongoing in our laboratories.
H NMR (250 MHz, CDCl ): d = 7.82 (d, J = 7.9 Hz, 1 H), 7.35–
3
7
.05 (m, 3 H), 2.50 (s, 3 H).
Melting points were measured with a Gallenkamp melting point ap-
paratus and are uncorrected. IR spectra were obtained using a
JASCO FT-IR-680 PLUS spectrometer. The H NMR spectra were
4
-Iodobenzophenone (Table 1, Entry 20)
IR (KBr): 3035, 2920, 1605, 1578, 1285, 1107, 1005, 927, 851, 817,
7
1
–1
44, 660 cm .
recorded on a Bruker 250 MHz spectrometer at 250 MHz with
1
H NMR (250 MHz, CDCl ): d = 7.90 (d, J = 8.3 Hz, 2 H), 7.78 (d,
chemical shift (d) values reported in ppm relative to an internal stan-
3
J = 7.4 Hz, 2 H), 7.70–7.55 (m, 5 H).
dard (Me Si). Silica–sulfuric acid was prepared according to the
4
1
3
literature. Spectral data are given below for representative prod-
ucts.
Acknowledgment
1
4
-Iodo-4-Nitrobenzene (Table 1, Entry 1); Typical Procedure
-Nitroaniline (2 mmol, 0.276 g), silica sulfuric acid (1.35 g) and
We gratefully acknowledge the funding support received for this
project from Islamic Azad University of Fasa and Isfahan Universi-
ty of Technology (IUT).
NaNO (4 mmol, 0.276 g) were ground with a pestle in a mortar for
a few minutes to afford a homogeneous mixture. A few drops of wa-
2
Synthesis 2009, No. 6, 941–944 © Thieme Stuttgart · New York