ORDER
REPRINTS
3726
IMMING, IMHOF, AND ZENTGRAF
filtered off, washed with ice water and dried over silica gel, yielding 60 g
(93%), m.p. 95ꢀC. IR (KBr) 3093, 2919, 1686 cmÀ1. H NMR (500 MHz,
1
CDCl3): d ¼ 10.39 (s, 1H, CHO), 8.27 (d, 1H, J ¼ 1.8 Hz, 3-H ), 7.93 (ddd,
1H, J ¼ 1.1, 4.5 and 7.6 Hz, 5-H), 7.85 (d, 1H, J ¼ 8.2 Hz, 6-H). MS (70 eV)
m/z (%) 229/231 (Mþ, 8), 199/201 (100). Anal. calc. for C7H4BrNO3
(230.01): C, 36.55, H, 1.75; Br, 34.74; N, 6.09; found: C, 36.88; H,
2.01; Br, 34.90; N, 603.
6,60-Dibromoindigo (Tyrian Purple) (1): 4-Bromo-2-nitrobenzaldehyde
(50 g, 0.22 mol) was dissolved in acetone (2250 mL). 2500 mL of water were
added in small amounts. On dropwise addition of 2 N aqueous sodium
hydroxide solution, maintaining the pH at 10, the product gradually
formed and precipitated. The suspension was stirred overnight. The preci-
pitate was filtered off, washed with acetone and water and evaporated to
dryness, yielding 20 g (44%) of 6,60-dibromoindigo, m.p. >300ꢀC. IR
(KBr): n ¼ 3384, 1610, 1580, 1438, 1314, 1157 cmÀ1. MS (70 eV) m/z (%)
418/420/422 (Mþ, 100). Anal. calc. for C16H8Br2N2O2 (420.06): C, 45.75;
H, 1.92; N, 6.70; Br, 38.04; found: C, 45.60; H, 2.10; N, 6.50; Br, 37.80.
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