Barbituric acid

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Barbituric acid
Barbituric acid.png Barbituric-acid-3D-balls.png
CAS number 67-52-7 YesY
PubChem 6211
ChemSpider 5976 YesY
UNII WQ92Y2793G YesY
EC number 200-658-0
KEGG C00813 YesY
ChEBI CHEBI:16294 YesY
Jmol-3D images Image 1
Molecular formula C4H4N2O3
Molar mass 128.09 g mol−1
Appearance White crystals
Melting point 245 °C (473 °F; 518 K)
Boiling point 260 °C (500 °F; 533 K)
Solubility in water 142 g/l (20 °C)
MSDS External MSDS
R-phrases R36/38, R43
S-phrases S22, S26, S28
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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the compound its namesake), by combining urea and malonic acid in a condensation reaction.[1] Malonic acid has since been replaced by diethyl malonate,[2] as using the ester avoids the problem of having to deal with the acidity of the carboxylic acid and its unreactive carboxylate.

The synthesis of barbituric acid from malonic acid and urea

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 stabilisation 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.

Barbituric acid is used in synthesis of riboflavin[citation needed].

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, phenobarbitone a.k.a. phenobarbital was first marketed in 1912.

See also[edit]


  1. ^ Baeyer, Adolf (1864). "Untersuchungen über die Harnsäuregruppe". Annalen der Chemie und Pharmacie 131 (3): 291. doi:10.1002/jlac.18641310306. 
  2. ^ J. B. Dickey & A. R. Gray (1943), "Barbituric acid", Org. Synth. ; Coll. Vol. 2: 60