1-methylquinazoline-2,4(1H,3H)-dione

119-68-6

917-61-3

604-50-2

An aqueous solution (25 mL) of sodium cyanate (28 mmol) was added dropwise to an aqueous solution (50 mL) of N-methyl-phthalaminobenzoic acid (20 mmol) and acetic acid (0.2 mL) under stirring conditions. When the temperature of the reaction mixture rose to 40 °C, sodium hydroxide was added in batches until the reaction temperature reached 75 °C. The reaction temperature was maintained at this temperature with continuous stirring for 4 hours. This temperature was maintained and the reaction was stirred continuously for 4 hours without cooling. Upon completion of the reaction, the precipitated crystals were collected by filtration and dissolved in boiling water (50 mL). Subsequently, the above solution was acidified with 50% sulfuric acid solution to pH 1-2. The precipitated crystals were filtered, washed with water and finally recrystallized from 50% acetic acid solution to afford the target product 1-methyl-2,4(1H,3H)-quinazolinedione (2.92 g, 84% yield); the melting point was 278 °C. The reaction was carried out at a temperature of 75 °C for 4 hours.