Sodium Hydroxide → 10-Nitro-7H-benzo[c]phenothiazine-8-carboxylic acid

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Reaction Steps

5 ml of a 2 N aqueous solution of sodium hydroxide was added to a solution of 1.7 g (9.73 mmol) of 2-amino-1-naphthalenethione in ethanol (30 ml) and the obtained mixture was heated under reflux. To this mixture was added 2.54 g(9.76 mmol) of methyl 2-chloro-3,5-dinitrobenzoate and the obtained mixture was heated under reflux for 1 hour. To this mixture were added 10 ml of a 2 N aqueous solution of sodium hydroxide and 40 ml of ethanol and the obtained mixture was heated under reflux for additional 10 hours. Then it was brought back to room temperature and concentrated. After adding water, 1 N hydrochloric acid was slowly added thereto under stirring to thereby regulate the pH value to about 1. The precipitate was recovered by filtration and washed successively with ethanol and methanol to thereby give 1.14 g of the title compound.

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