Simple, Efficient, High Yield Syntheses of Substituted and Unsubstituted 5-Benzoylbarbituric Acids, and Their Corresponding Schiff Base Phenylhydrazones

Preparation procedures for biologically important benzoylbarbiturates are presented. Several procedures are optimized to cover the preparations of a wide variety of substituted 5-benzoylbarbiturates. To further explore the biological importance of these compounds, multi- gram preparation procedures for nitrophenylhydrazones of benzoylbarbiturates and their corresponding salts with organic amines are discussed. It is demonstrated that these compounds can exist in several tautomeric forms and that the equilibrium in solution can be changed by temperature as well as by the pH of the solution. X-ray structural analysis performed on one of the nitrophenylhydrazones of benzoylbarbiturates fully agrees with the presented spectroscopic studies. AM1 semi-empirical studies show that the enol form is preferred in the gas phase of benzoylbarbiturates over the keto form, which was also confirmed by NMR spectroscopic studies with chloroform as the solvent. Furthermore, AM1 computed structural and electronic properties of the dinitrophenylhydrazone of 4-hydroxybenzoylbarbiturate compared favorably with the X-ray determined structure.