[CH3:1][O:2][C:3]([CH:5]1[CH2:10][C:9](=[O:11])[C:8]([N:12]=[N:13][C:14]2[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=2)=[C:7]([OH:20])[CH2:6]1)=[O:4].C(N)(=O)C.BrC1CC(=O)NC1=O.BrBr>C(Cl)(Cl)Cl>[CH3:1][O:2][C:3](=[O:4])[C:5]1[CH:10]=[C:9]([OH:11])[C:8]([N:12]=[N:13][C:14]2[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=2)=[C:7]([OH:20])[CH:6]=1
54.8 G. of 3-hydroxy-5-keto-4-phenylazo-3-cyclohexene-carboxylic acid methyl ester, 12.0 g. of acetamide and 2.0 g. of bromosuccinimide were stirred in 600 ml. of chloroform and treated dropwise with 32.0 g. of bromine in 400 ml. of chloroform (the reaction temperature being held below 35° C.). Soon, the separation of acetamide hydrobromide began. The mixture was stirred for an additional 30 minutes at room temperature. Then, the acetamide hydrobromide was removed by filtration and the filtrate evaporated to dryness. The residue was taken up in a small amount of ethanol, filtered under vacuum and washed with ethanol, whereby there was obtained 3,5-dihydroxy-4-phenylazo-benzoic acid methyl ester having a melting point of 216°-218° C.
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