The general procedure for the synthesis of 5-(oxime-based)pyrimidine-2,4,6(1H,3H,5H)-trione from barbituric acid was as follows: firstly, 352 g of sodium nitrite was weighed and dissolved in 800 ml of deionized water to prepare an aqueous sodium nitrite solution for spare. In a 10L three-necked flask, 360g of sodium hydroxide and 4L of deionized water were added, and mechanical stirring was turned on until complete dissolution. When the temperature of the solution was reduced to about 30°C, 491 g of barbituric acid was added slowly to ensure that it was completely dissolved in the sodium hydroxide solution. Subsequently, the pre-prepared aqueous sodium nitrite solution was added to the reaction system, at which time the temperature of the mixed solution should be maintained between 10-15°C. Under continuous stirring, a mixed solution consisting of 1.2 L of concentrated hydrochloric acid and 2 L of deionized water was slowly added dropwise, and the rate of dropwise acceleration was controlled to maintain the reaction temperature in the range of 10-20 °C. During the dropwise addition, the formation of yellow-red solid and the release of orange gas were observed. After the dropwise addition, the temperature of the reaction system was adjusted to room temperature (25 °C) and the reaction was continued with stirring for about 16 hours. At the end of the reaction, the orange gas produced in the reaction was first removed. Then, the reaction solution was vacuum filtered using a vacuum pump and the filter cake was collected. The filter cake was washed sequentially with deionized water and a small amount of methanol, and finally dried under vacuum to obtain 513 g of the light purple target product 5-(oxime-based)pyrimidine-2,4,6(1H,3H,5H)-trione in a molar yield of 85.2%.
