Phenol → 10H-[1]Benzopyrano[3,2-b]pyridin-10-one

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Reaction Steps

According to the invention, 2-chloronicotinic acid in alkaline metal salt form is reacted with alkaline metal phenoxide without an excess of phenol at 160°-200° C. The molten mass is partly cooled, water is added until complete solubilization, the aqueous solution is acidified and the solid obtained is dried. In the cyclization step the thus obtained 2-phenoxynicotinic acid is added portionwise to 5-10 times its weight of polyphosphoric acid which has been previously heated, the temperature is raised to 160°-200° C., the reaction mixture is cooled and diluted with water. Concentrated aqueous alkali hydroxide is added to adjust the pH to 2-3, the solid is filtered, washed, dried and recrystallized, obtaining very pure 1-azaxanthone in an overall yield of 50-70%.

Provenance & Evidence