Sulfuric Acid → Medorinone

5-Methyl-1,6-naphthyridin-2(1H)-one also was prepared directly from the corresponding 3-cyano compound, as follows: A 650 g portion of 1,2-dihydro-5-methyl-2-oxo-1,6-naphthyridine-3-carbonitrile was added with stirring at room temperature to a solution of 2100 ml 18 M sulfuric acid in 350 ml of water. The reaction mixture was stirred mechanically and refluxed (internal temperature at 215°-220° C.) for 24 hours. The dark solution was allowed to come to ambient temperature and poured on ice. The solution was stirred and basified with 6 l of concentrated ammonium hydroxide to pH 10.5, the internal temperature being maintained at 20°-30° C. during this addition. The dark beige solid was collected by filtration, washed with a minimum of cold water and dried in an oven chamber at 65° overnight. The crude product was recrystallized twice from water with decolorizing charcoal treatment to produce 330 g of 5-methyl-1,6-naphthyridin-2(1H)-one, m.p. 245°-246° C.