3-Hydroxy-3,4-dihydroquinazoline-4-one (4-Hydroxyquinazoline 3-oxide) [1, 2]
To a solution of sodium hydroxide (16 g, 400 mmol) in water (100 ml) hydroxylamine hydrochloride (13.9 g, 200 mmol) is added in small portions with stirring. Methyl anthranilate (15.1 g = 13.0 ml, 100 mmol) is added followed by enough methanol to bring it into solution. After three days at room temperature the solution is concentrated in vacuo to about 30 ml, the material which separates, the sodium salt of 2-aminobenzhydroxamic acid, is collected on a filter and washed with ether. The aqueous filtrate is acidified to Congo with 6 N hydrochloric acid, the free hydroxamic acid which precipitates is collected, washed with water and dried in air. Extraction of the crude material with warm ether in a Soxhlet extractor yields the purified acid. It is light brown, and melts at 149 °C. The combined yield of the sodium salt and the free acid is about 70%.