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Ethyl benzothiazole-6-carboxylate (1.30 g, 6.28 mmol) prepared in the Step 36-1-2 was suspended in ethanol (10 ml) and a 1 mol/L sodium hydroxide aqueous solution (10 ml), and the mixture was heated under reflux for 40 minutes. After the mixture was allowed to cool, concentrated hydrobromic acid was added to the mixture, and the resulting mixture was adjusted to pH 4. The precipitate was separated by filtration, washed with water, and then subjected to through circulation drying to give the title compound (1.10 g, 98%) as a light-brown powder.

1. temperatureunder reflux for 40 minutes
2. temperatureto cool
3. customThe precipitate was separated by filtration
4. washwashed with water
5. customdrying