Barbituric Acid

Title: Barbituric Acid
CAS Registry Number: 67-52-7
CAS Name: 2,4,6(1H,3H,5H)-pyrimidinetrione
Additional Names: malonylurea; 2,4,6-trioxohexahydropyrimidine
Molecular Formula: C4H4N2O3
Molecular Weight: 128.09
Percent Composition: C 37.51%, H 3.15%, N 21.87%, O 37.47%
Literature References: Prepn from hydurilic acid + nitric acid: Baeyer, Ann. 127, 199 (1863); ibid. 130, 129 (1864). Structure: Mulder, Ber. 6, 1233 (1873). Prepd from ethyl malonate and urea using sodium ethoxide as a condensing agent: Dickey, Gray, Org. Synth. coll. vol. II, 60 (1943). Crystal structure: Bolton, Nature 201, 987 (1964). Toxicity study: E. I. Goldenthal, Toxicol. Appl. Pharmacol. 18, 185 (1971). Unsubstituted barbituric acid has no hypnotic properties. Review: Carter, J. Chem. Educ. 28, 524 (1951).
Derivative Type: Dihydrate
Properties: Rhombs from water. mp ~248° when anhydrous, with some decompn. Strong acid. K at 25° = 9.9 ´ 10-5. uv spectrum: Hartley, J. Chem. Soc. 87, 1808 (1905). Difficultly sol in cold water; freely sol in hot water, in dil acids. Forms salts with metals. LD50 orally in male rats: >5000 mg/kg (Goldenthal).
Melting point: mp ~248° when anhydrous
Toxicity data: LD50 orally in male rats: >5000 mg/kg (Goldenthal)
Use: Manuf plastics, pharmaceuticals.
Barium Acetate Barium Benzenesulfonate Barium Bromate Barium Bromide Barium Carbonate

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
Boiling point 260 °C
Solubility in water 142 g/l (20 °C)
MSDS External MSDS
R-phrases R36/38, R43
S-phrases S22, S26, S28
NFPA 704
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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.