Ethoxzolamide → 6-Hydroxy-1,3-benzothiazole-2-sulfonamide

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Reaction Steps

6-Ethoxybenzothiazole-2-sulfonamide (1.72 g, 6.7 mmol) was dissolved in dichloroethane (26 ml) and cooled to 20°. Aluminum chloride (4 g) was added portionwise such that the temperature remained 20°. After complete addition, the mixture was stirred at room temperature for 24 hours. Stirring was discontinued and after 0.5 hour, the supernatant was decanted from a tarry-like residue. This residue was cooled in an ice-water mixture and a cold solution of concentrated HCl (3 ml) in water (40 ml) was added as rapidly as possible with stirring. The resulting mixture was stirred for an hour and filtered. The solid was washed with water and suction dried to give 0.5-0.8 g. This material was combined with that from further working of the supernatant and dissolved in 20% NaOH solution, diluted to 100 ml with water and filtered. The filtrate was slowly acidified with concentrated hydrochloric acid (pH 3) and the resulting tan solid was filtered, washed with water and dried at 60°-80° C. under vacuum: total yield 1.3 g, m.p. 225°-228° C.

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