Synthesis mechanism of barbituric acid
Preparation of raw materials
To make barbituric acid, it is necessary to prepare diethyl malonate, urea and other raw materials. Diethyl malonate, with the characteristics of esters, contains active methylene in the structure; urea is a nitrogen-containing compound, with amino and carbonyl groups in the molecule. Under suitable conditions, the two can initiate a series of chemical reactions.

Initiation of reaction initiated by base
Diethyl malonate is placed in the reaction system, and an appropriate amount of strong base, such as sodium ethyl alcohol, is added. The strong base acts on the active methylene of diethyl malonate. Because methylene hydrogen has a certain acidity, under the attack of alkali, it is easy to remove protons and form carbon negative ions. The carbon anion is active and has strong nucleophilicity, which lays the foundation for subsequent reactions.

The carbon anion generated by the process of nucleophilic substitution
attacks the carbonyl carbon atom of urea with its nucleophilicity. The carbonyl group of urea has a certain electrophilicity. After the carbon anion attacks, the π bond in the carbonyl group opens, and the electron cloud transfers to the oxygen atom to form an intermediate product. This intermediate product is unstable, followed by intramolecular rearrangement and dehydration. Among them, the electron cloud on the nitrogen atom of the amino group transfers to the carbonyl carbon atom, prompting the hydroxyl group to leave, completing the dehydration process, and forming a new nitrogen-containing cyclic structure intermediate.

Further cyclization and isomerization
The intermediate continues to react, and intracellular nucleophilic addition and cyclization reactions occur. The internal chemical bonds of the molecule are rearranged to form a more stable six-membered cyclic structure. However, this structure is not the final barbituric acid, and it needs to go through the isomerization process. Through proton transfer and other means, the internal structure of the molecule is fine-tuned, and finally a stable structure of barbituric acid is formed.

The entire synthesis process requires strict control of the reaction conditions, such as temperature, reactant ratio and reaction time. The appropriate temperature and precise ratio can promote the smooth progress of the reaction in the direction of forming barbituric acid, and improve the yield and purity of the product.