Nitric Acid → 2,3-dihydro-8-nitro-3-oxo-5H-pyrido[3,4-b][1,4]benzothiazine-4-carbonitrile 10-oxide

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Reaction Steps

To a solution of 5 parts of 2,3-dihydro-3-oxo-5H-pyrido[3,4-b][1,4]benzothiazine-4-carbonitrile in 90 parts of concentrated sulfuric acid at 0° is slowly added, with stirring, 7 parts of concentrated nitric acid. The resultant mixture is stirred at room temperature for 1 hour, whereupon 2 volumes of water is slowly stirred in. The light yellow precipitate which forms is filtered out and recrystallized from aqueous N,N-dimethylformamide to give needles of 2,3-dihydro-8-nitro-3-oxo-5H-pyrido[3,4-b][1,4]benzothiazine-4-carbonitrile 10-oxide solvated 1:1 with N,N-dimethylformamide which melts above 310°. The solvent of crystallization can be removed by prolonged heating at around 200° in vacuo.

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