Nitric Acid → 3-Nitro-5-pentafluorosulfanylbenzoic Acid

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Reaction Steps

3-Pentafluorosulfanylbenzoic acid (3.0 g) was dissolved in fuming nitric acid (20 ml) and stirred at RT with exclusion of moisture. Then concentrated sulfuric acid (1.5 ml) was added and the mixture was stirred at 75° C. After stirring at 75° C. for 6 h, the mixture was left to stand overnight, then further sulfuric acid (1.5 ml) was added and the mixture was heated to 75° C. for 8 h while stirring. After being left to stand overnight, the mixture was added to ice-water and stirred for 2 h. The crystallization which set in was completed in a refrigerator overnight. Then the precipitate was filtered off with suction and dried under high vacuum. 2.7 g of 3-pentafluorosulfanyl-5-nitrobenzoic acid were obtained. A further 530 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, the 3-pentafluorosulfanyl-5-nitrobenzoic acid (2.7 g) was dissolved in methanol (70 ml), Raney nickel (about 500 mg) was added and hydrogenation was effected under a hydrogen atmosphere (hydrogen balloon). After 2 h, the catalyst was filtered off and the filter residue was washed thoroughly with methanol. The filtrate was concentrated and dried under high vacuum. 2.3 g of crude product were obtained, which were converted directly in the next stage.

Provenance & Evidence