|Molar mass||128.09 g·mol−1|
|Melting point||245 °C (473 °F; 518 K)|
|Boiling point||260 °C (500 °F; 533 K)|
|142 g/l (20 °C)|
|S-phrases||S22, S26, S28|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Barbituric acid or malonylurea or 6-hydroxyuracil is an organic compound based on a pyrimidine heterocyclic skeleton. It is an odorless powder soluble in water. Barbituric acid is the parent compound of barbiturate drugs, although barbituric acid itself is not pharmacologically active.
The compound was discovered by the German chemist Adolf von Baeyer on December 4, 1864, the feast of Saint Barbara (who gave the compound its namesake), by combining urea and malonic acid in a condensation reaction. Malonic acid has since been replaced by diethyl malonate, as using the ester avoids the problem of having to deal with the acidity of the carboxylic acid and its unreactive carboxylate.
The α-carbon has a reactive hydrogen atom and is quite acidic (pKa = 4.01) even for a diketone species (cf. dimedone with pKa 5.23 and acetylacetone with pKa 8.95) because of the additional aromatic stabilization of the carbanion.
Using the Knoevenagel condensation reaction, barbituric acid can form a large variety of barbiturate drugs that behave as central nervous system depressants. As of 2007, more than 2550 barbiturates and related compounds have been synthesised, with 50 to 55 in clinical use around the world at present. The first to be used in medicine was barbital (Veronal) starting in 1903, and the second, phenobarbital was first marketed in 1912.
Barbituric acid is one of four ingredients used to make riboflavin (vitamin B2).
Health and safety
Overdose of barbituric acid can cause respiratory problems and death.
- Baeyer, Adolf (1864). "Untersuchungen über die Harnsäuregruppe". Annalen der Chemie und Pharmacie 131 (3): 291. doi:10.1002/jlac.18641310306.
- J. B. Dickey & A. R. Gray (1943). "Barbituric acid". Org. Synth.; Coll. Vol. 2, p. 60