[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]=154.8 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 dissolved in 400 ml. of chloroform. The reaction temperature was kept below 35° C. Separation of acetamide hydrobromide soon began. The mixture was stirred at room temperature for an additional 30 minutes and the acetamide hydrobromide was removed by filtration. The filtrate was evaporated to dryness and the residue taken up in a small amount of ethanol, removed by filtration under vacuum and washed with ethanol, whereby there was obtained 3,5-dihydroxy-4-phenylazo-benzoic acid methyl ester of melting point 216°-218° C.
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