PAPER
[bmim]Br as a New Reagent for Regioselective Monobromination
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corresponding products with 56% dibromination of p- IR (KBr): 3403, 3301, 3180, 1623, 1480, 1392, 1289, 1033, 866,
–
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8
1
10 cm .
chloroaniline and 48% dibromination o-aminobenzoic
acid and 62% monobromination of p-nitroaniline, respec-
tively. But by using the present method, the same reaction
completed smoothly and gave products with high mono-
bromination, with isolated yields of 94%, 98%, 99%
H NMR (CDCl ): d = 3.94 (br s, 2 H), 6.63 (dd, J = 1.2, 8.4 Hz, 1
H), 7.19 (dd, J = 1.2, 8.4 Hz, 1 H), 7.53 (d, J = 1.2 Hz, 1 H).
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2
-Bromo-4-nitroaniline (2d)
Yellow needles; mp 104–105 °C (lit. 104.5 °C).
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1
3
respectively. In Smith’s reported method, monobromi-
nation of arylamines needed (one-pot) four steps using a
strong base (LDA), trialyklatin halide (R SnCl), Br , KF
IR (KBr): 3488, 3372, 3097, 1623, 1586, 1488, 1317, 1121, 894,
22, 745 cm .
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1
3
2
H NMR (CDCl ): d = 4.10 (br s, 2 H), 6.76 (d, J = 8.8 Hz, 1 H),
.02 (dd, J = 2.5, 8.8 Hz, 1 H), 8.36 (d, J = 2.5 Hz, 1 H).
etc. at –78 °C, and gave 76% monobromination of aniline,
0% monobromination of p-toluidine, and 40% monobro-
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8
3
mination of 1-aminonaphthalene. The same reaction com-
pleted smoothly with the present method and gave higher
yields of were 90%, 85%, 90%, respectively.
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-Bromo-2-aminobenzoic Acid (2e)
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Yellow solid; mp 231 °C (lit. 219–221 °C).
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1
IR (KBr): 3468, 3363, 1680, 1536, 1224, 881 cm .
In conclusion, we have demonstrated that the regioselec-
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H NMR (CDCl ): d = 3.26 (br s, 2 H), 6.85 (br s, 1 H), 6.95 (d, J =
3
tive monobromination of arylamines with [bmim]Br can
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8.0Hz, 1 H), 7.01 (dd, J = 2.0, 8.0 Hz, 1 H), 8.00 (d, J = 2.0Hz, 1 H).
efficiently be performed under solvent-free conditions.
This will be a highly useful method because of its ease, p-Bromo-o-toluidine (2f)
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Red solid; mp 55–57 °C (lit. 152–156 °C).
simplicity, high selectivity, and excellent yield of product.
bmim]Br plays double roles of reagent and solvent.
[
IR (KBr): 3427, 3335, 3228, 2926, 1622, 1482, 1272, 870, 813, 679
cm .
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–
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H NMR (CDCl ): d = 2.09 (s, 3 H), 3.51 (br s, 2 H), 6.53 (d, J = 8.0
Melting points were determined on digital melting point apparatus
and are not corrected. IR spectra were recorded on a VECTOR22
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Hz, 1 H), 7.08 (d, J = 8.0 Hz, 1 H), 7.14 (s, 1 H).
(
Bruker) spectrometer. NMR spectra were recorded on AVANCE
p-Bromo-N-methylaniline (2g)
Oil.
DMX 400 (Bruker) spectrometer. The ionic liquids were synthe-
sized by reaction of equimolar amount of [bmim]Br and Br at r.t.
2
The other materials are commercially available and were used with-
out further purification.
IR (film): 3423, 3050, 2983, 1600, 1504, 1317, 1261, 1178, 1075,
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14 cm .
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H NMR (CDCl ): d = 2.76 (s, 3 H), 3.27 (br s, 1 H), 6.45 (d, J = 8.0
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Synthesis of 2a–c,f,g,j–n; General Procedure
Hz, 2 H), 7.23 (d, J = 8.0 Hz, 2 H).
[
bmim]Br (1 mmol) was added very slowly (1 drop/5 s) to aryl-
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amine (1 mmol) with continuous stirring (see Table 1 for the reac-
tion conditions). After the reaction completion, the solid crude
p-Bromo-acetanilide (2h)
White solid; mp 164–165 °C (lit. 163–164 °C).
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product was extracted with Et O. The ethereal layer was concentrat-
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ed by rotary evaporator. The crude product was purified by the pre-
IR (KBr): 3439, 3305, 3262, 1670, 1604, 1536, 1489, 1393, 1315,
825, 750 cm .
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parative TLC on silica gel using a mixture of CHCl and petroleum
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ether as developer to give the corresponding pure product of mono-
bromination.
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H NMR (CDCl ): d = 2.17 (s, 3 H), 7.40 (s, 4 H).
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-Bromo-N-methanesulfonylaniline (2i)
Synthesis of 2d,e,h,i; General Procedure
Colorless solid; mp 117 °C.
[
bmim]Br (1 mmol) was added to arylamine (1 mmol) with contin-
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–
1
IR (KBr): 3414, 3299, 3073, 2924, 1616, 1455, 860 cm .
uous stirring (see Table 1 for the reaction conditions). After the re-
action completion, the reaction mixture was directly purified by
recrystallization with EtOH (95%) to give the pure p-bromoacet-
anilide.
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H NMR (DMSO): d = 3.34 (s, 3 H), 7.40 (s, 4 H).
4-Bromo-N,N-Dimethylaniline (2j)
White solid; mp 50–52 °C (lit. 51.5–53.0 °C).
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p-Bromoaniline (2a)
Brown solid; mp 63–64 °C (lit. 62–64 °C).
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IR (KBr): 3090, 1592, 1500, 1355, 1223, 1063, 805 cm .
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1
H NMR (CDCl ): d = 2.90 (s, 6 H), 6.57 (d, J = 8.8 Hz, 2 H), 7.28
d, J = 8.8 Hz, 2 H).
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IR (KBr): 3472, 3382, 1612, 1489, 1285, 817, 603, 503 cm .
(
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H NMR (CDCl ): d = 3.66(br s, 2 H), 6.57 (d, J = 8.0 Hz, 2 H), 7.22
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(
d, J = 8.0 Hz, 2 H).
1-Bromo-2-aminonaphthalene (2k)
Needles; mp 62–64 °C (lit. 63 °C).
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o-Bromo-p-toluidine (2b)
Oil.
IR (KBr): 3407, 3295, 3181, 1626, 1500, 1347, 1241, 809, 740
cm .
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IR (film): 3461, 3371, 3022, 2919, 1619, 1503, 1300, 1038, 810
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H NMR (CDCl ): d = 4.37 (br s, 2 H), 7.01 (d, J = 8.6 Hz, 1 H),
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3
cm .
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.28 (t, J = 8.0 Hz, 1 H), 7.50 (t, J = 8.4 Hz, 1 H), 7.61 (d, J = 8.6
1
H NMR (CDCl ): d = 2.22 (s, 3 H), 3.89 (br s, 2 H), 6.65 (d, J = 8.0
Hz, 1 H), 7.68 (d, J = 8.1 Hz, 1 H), 8.02 (d, J = 8.4 Hz, 1 H).
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Hz, 1 H), 6.88 (d, J = 8.0 Hz, 1 H), 7.22 (s, 1 H).
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-Bromo-1-aminonaphthalene (2l)
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,4-Dibromoaniline (2c)
Needles; mp 102–103 °C (lit. 102.5 °C).
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Colorless solid; mp 79–80 °C (lit. 78–80 °C).
Synthesis 2004, No. 17, 2809–2812 © Thieme Stuttgart · New York