aromatic); m/z (EI) 332 (M+1) for 80Br; C15H10BrNO3 calculated
m/z: 330.9.
Table 3 Recycling of deep eutectic solvent in bromination of 1-
aminoanthra-9,10-quinone at room temperature
Recycle of IL
Yield (%)a
N-(1-Amino-2-bromo-9,10-dihydro-9,10-dioxoanthracen-4-yl)
benzamide 5f. Brown colored solid. Melting point (measured)
247 ◦C (from water); lmax (MeOH)/nm 486; nmax/cm-1 3460
and 3252 br (NH), 1670,1627 and 1575 (CO) and 736 (CBr);
dH(400 MHz; CDCl3; Me4 Si) 1.5(2H, weak s, NH2),7.4-8.4
(9H, m, C–H aromatic), 9.6 (1H, s, C–H) and 13.5 (1H, s, NH);
m/z (EI) 421 (M+1) for 80Br; C21H13BrN2O3 calculated m/z:
420.0.
Fresh, Non- Recycled
First
Second
Third
Forth
Fifth
84.3%
97.5%
92.7%
93.4%
94.1%
82.0%
a Isolated by filtration.
Typical procedure for the bromination of
1-aminoanthra-9,10-quinone (5a, 5b, 5c, 5d, 5e, 5f, 5g).
1-Amino-2-bromo-4-hydroxyanthracene-9,10-dione 5g. Brown
colored solid. Melting point (measured) 198 ◦C (from water);
lmax (methanol)/nm 397; nmax/cm-1 3453 and 3306 br (NH),
1670 and 1635 (CO) and 759 (CBr); dH (400 MHz; CDCl3; Me4
Si) 3.4 (2H, s, NH), 7.5-8.4 (5H, m, C–H aromatic); m/z (EI)
318 (M+1) for 80Br; C14H8BrNO3 calculated m/z: 316.9.
1-Aminoanthra-9,10-quinone (1 g, 4.48 mmol) was added to the
deep eutectic solvent (5 ml) with stirring for 15 min, and bromine
(0.6 ml, 11.2 mmol) was slowly added to the reaction mixture. In
the case of 5c, a 4.5-molar equivalent of Br2 was used and in the
cases of 5e, 5f, 5g, 1.1 molar equivalents of Br2 were used. The
reaction mixture was stirred at 50–60 ◦C for 2 to 3 h. During the
reaction, unreacted bromine that was expelled was neutralized
in a trap containing aqueous Na2CO3 solution. The reaction
was monitored by TLC. After completion of the reaction, water
was added, the mixture filtered, and residual product dried in an
oven under vacuum.
Scale-up of bromination of 1-amino-anthra-9,10-quinone and
recycling of choline chloride: urea (deep eutectic solvent).
1-Aminoanthra-9,10-quinone 5 g (22.4 mmol) was added to
deep eutectic solvent (50 ml). The reaction mixture was stirred
for 15 min, bromine (2.9 ml, 56.0 mmol) was added slowly,
and the reaction mixture stirred at 50–60 ◦C for 2 to 3 h.
During the reaction, liberated HBr gas was neutralized using
2 N aqueous Na2CO3 solution. The reaction was monitored by
TLC. After completion of the reaction, 50 ml of water was slowly
added, the mixture was filtered to obtain the product using a
Bu¨chner funnel under vacuum and dried in an oven to afford
an orange-colored solid of 1-amino-2,4-dibromoanthra-9,10-
quinone (8.1 g, 94%). The deep eutectic solvent was recovered
from the filtrate by evaporating the water phase at 80 ◦C under
vacuum. The recycled deep eutectic solvent was used for the next
batch and recycled again.
1-Amino-2,4-dibromoanthracene-9,10-dione 5a. (1.6 g,
93.2%) An orange colored solid. Melting point (measured)
◦
◦
222 C (from water) (lit, 221 C17); lmax (methanol)/nm 381;
n
max/cm-1 3396(NH), 1670 and 1577 (CO), and 715 (CBr); dH
(400 MHz; DMSO; Me4 Si) 3.4 (2H, s, NH), 7.6-8.4(5H, m,
aromatic); m/z (EI) 380 (M-1) for 80Br. C14H7Br2NO2 calculated
m/z: 380.9
1-Amino-2,4-dibromo-5-chloroanthracene-9,10-dione
5b.
Orange colored solid. Melting point (measured) 249 ◦C from
water; lmax (methanol)/nm 415; nmax/cm-1 3452 and 3307
(NH), 167 and 1635 (CO) and 759 (CBr); dH (400 MHz; DMSO;
Me4 Si) 3.4 (1H, s, NH), 7.6-8.4(5H, m, aromatic); m/z (EI) 414
(M-1) for 80Br. C14H6Br2ClNO2 calculated m/z: 414.9.
Conclusion
1,5-Diamino-4,8-dibromoanthracene-9,10-dione 5c. Brown
colored solid. Decomposes >250 ◦C (from water); lmax
(methanol)/nm 554; nmax/cm-1 3446 and 3319(NH), 1577 and
1560 (CO) and 759 (CBr); dH (400 MHz; CDCl3; Me4 Si) 2.1
(4H, s, NH) 7.5-7.8 (2H, m, C–H); m/z (EI) 553 (M-1) for 80Br;
C14H6Br4N2O2 calculated m/z: 553.7.
The present reaction using a readily available and biodegradable
ammonium deep eutectic solvent (choline chloride : urea) pro-
vides an efficient and convenient method for the bromination of
1-aminoanthra-9,10-quinones using molecular bromine without
the use of any other catalyst or organic solvent. This method
offers marked improvements in terms of simplicity, decreased
reaction time, simple reaction conditions, general applicability,
high isolated product yields, and the use of environmentally
benign procedures and solvents. This method also eliminates the
use of hazardous organic solvents and toxic catalysts, and thus
provided a better and practical alternative to the existing proce-
dures. Most significantly, however, this procedure demonstrates
that selectivity and balance among yields are achievable. It is easy
to separate the catalyst and substrate after completion of the
reaction. The halogenated 1-aminoanthraquinones were easily
isolated with high purity. These deep eutectic solvents provide
a good alternative for industrial synthesis of mono or di-bromo
derivatives of 1-aminoanthra-9,10-quinone, as the reaction is
readily scalable.
2,4-Dibromo-1-(methylamino) anthracene-9,10-dione 5d.
Brown colored solid. Melting point (measured) 154 ◦C
(from water); lmax (Methanol)/nm 395; nmax/cm-1 3458 and
3099(NH), 1672 and 1625 (CO) and 737 (CBr); dH(400 MHz;
CDCl3; Me4 Si) 3.5 (3H, s, NHCH3), 7.4-8.0(5H, m, C–H
aromatic) and 9.9 (1H, s weak, NH); m/z (EI) 396 (M+1) for
80Br; C15H9Br2NO2 calculated m/z: 394.9.
1-Amino-2-bromo-4-methoxyanthracene-9,10-dione 5e. Brown
colored solid. Melting point (measured) 176 ◦C (from water);
lmax (methanol)/nm 411; nmax/cm-1 3434 and 3284 Br (NH),
1659 and 1625 (CO) and 798 (CBr); dH(400 MHz; CDCl3; Me4
Si) 3.9 (3H, s, OCH3), 5.3 (2H, weak s, NH), 7.4-8.4(5H, m C–H
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The Royal Society of Chemistry 2010
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