Process for the preparation of sodium thiobarbiturate

The method of preparing sodium thiobarbiturate with a yield of more than 99% of theory and a purity of at least 99.8%, which comprises reacting dimethyl malonate, thiourea and sodium methylate in methanol at the reflux temperature of methanol at atmospheric pressure, at a mol ratio of 1 mol of one of the three reactants thiourea, dimethyl malonate and sodium methylate per 1 to 1.25 mols of the other two reactants, separating the sodium thiobarbiturate from the methanol by a conventional solid/liquid separation procedure, and recycling all or some of the methanol recovered in the solid/liquid separation procedure for use as a reaction medium in a subsequent reaction of thiourea, dimethyl malonate and sodium methylate to form sodium thiobarbiturate.