N[C:2]1[CH:3]=[C:4]([CH:8]=[C:9]([S:11]([F:16])([F:15])([F:14])([F:13])[F:12])[CH:10]=1)[C:5]([OH:7])=[O:6].N([O-])=[O:18].[Na+].N([O-])=O>S(=O)(=O)(O)O.O>[OH:18][C:2]1[CH:3]=[C:4]([CH:8]=[C:9]([S:11]([F:16])([F:15])([F:14])([F:13])[F:12])[CH:10]=1)[C:5]([OH:7])=[O:6]3-Amino-5-pentafluorosulfanylbenzoic acid (O6.007; 3.9 g) was dissolved in 35% sulfuric acid (120 ml) and cooled to −5° C., and a solution of sodium nitrite (1.1 g) in water (100 ml) was added dropwise within 10 min. After 40 min, further nitrite solution was added (2 ml), and another 2 ml and 1 ml after a further 20 min in each case. Then the cooling bath was removed and the mixture was heated to 100° C. After 5 h, the mixture was cooled and the solution was decanted. The clear, acidic solution was extracted five times with ethyl acetate. The combined extracts were dried over magnesium sulfate, filtered and concentrated. The crude product was recrystallized from ethyl acetate/heptane. 3.6 g of the desired compound were obtained.
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