Nitric Acid → 3-Nitro-5-pentafluorosulfanylbenzoic Acid

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Reaction Steps

3-Pentafluorosulfanylbenzoic acid (5.0 g) was dissolved in fuming nitric acid (20 ml) and stirred at RT with exclusion of moisture. Then concentrated sulfuric acid (3 ml) was added and the mixture was stirred at 75° C. After stirring at 75° C. for 5 h, further sulfuric acid (2 ml) was added and the mixture was stirred at 75° C. for a further 2 h. After being left to stand overnight, the mixture was poured onto ice-water and stirred for 2 h. Then the precipitate was filtered off with suction and dried under high vacuum. 4.2 g of 3-pentafluorosulfanyl-5-nitrobenzoic acid were obtained. A further 900 mg were obtained from the mother liquor after extracting three times with methylene chloride, drying the combined methylene chloride phases over magnesium sulfate and concentrating the solvent. Subsequently, 4.0 g of the 3-pentafluorosulfanyl-5-nitrobenzoic acid were dissolved in thionyl chloride (25 ml) while stirring and kept under reflux with exclusion of moisture for 10 h. After standing overnight at RT, excess thionyl chloride was removed under reduced pressure, and the residue obtained was dissolved in dichloromethane (50 ml) and admixed while stirring with N,O-dimethylhydroxylamine×HCl (1.25 g) and diethylisopropylamine (1.66 g). After stirring at RT for 1 h, the mixture was concentrated under reduced pressure, and the residue was dissolved in ethyl acetate and washed five times with water. The organic phase was dried over magnesium sulfate, filtered and concentrated. The 4.2 g of crude product obtained were used directly in the next stage.

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