4H-1,4-Benzothiazin-3-one → 3-oxo-3,4-dihydro-2H-1,4-benzothiazine-6-sulfonyl chloride

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Reaction Steps

Chlorosulfonic acid (55.93 g, 0.48 mole) was added to a 250 mL round bottom flask under nitrogen at 10° C. To this, 4H-benzo[1,4]thiazin-3-one, (20 g, 0.12 mole) was added slowly so that the reaction temperature was maintained below 20° C. during the addition. After addition, the reaction mixture was stirred at room temperature for 1.5 h and then heated to 65° C. for an additional 1 hour. The reaction was subsequently cooled and poured into ice-cold water. A solid precipitate formed and was collected via filtration. The solid was then washed with water and dried to provide 23.6 g of the title compound (75% yield). 1H NMR (CDCl3, 300 MHz): δ 9.08 (br s, NH), 7.72-7.88 (m, 3H, Ar—H), 3.68 (s, 2H, Ar—CH2); m.p.: 165-167° C.; LC-MS (M+1): 263.92

Provenance & Evidence