barbituric acid

Barbituric acid
IUPAC name	pyrimidine-2,4,6(1H,3H,5H)-trione
Other names	2,4,6(1H,3H,5H)-Pyrimidinetrione, 2,4,6-Trioxohexahydropyrimidine, 2,4,6-Trihydroxypyrimidine, 2,4,6-Trioxypyrimidine, 2,4,6-Pyrimidinetriol, 2,4,6-Pyrimidinetrione, Pyrimidinetriol, 2,4,6-Trihydroxy-1,3-diazine, N,N′-Malonylurea, Malonylurea, 6-Hydroxyuracil, 6-Hydroxy-Hydrouracil, N,N′-(1,3-dioxo-1,3-propanediyl)urea
Identifiers
CAS number	67-52-7 Y
PubChem	6211
EC number	200-658-0
SMILES	O=C1NC(=O)NC(=O)C1
InChI	1/C4H4N2O3/c7-2-1-3(8)6-4(9)5-2/h1H2,(H2,5,6,7,8,9)
InChI key	HNYOPLTXPVRDBG-UHFFFAOYAE
ChemSpider ID	5976
Properties
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)
Hazards
MSDS	External MSDS
R-phrases	R36/38, R43
S-phrases	S22, S26, S28
NFPA 704	1 2 0
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 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 hot 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the compound its namesake), by combining urea and malonic acid in a condensation reaction.^[1] Malonic acid has since been replaced by diethyl malonate,^[2] as using the ester avoids the problem of having to deal with the acidity of the carboxylic acid and its unreactive carboxylate.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 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.

The barbiturate enolate anion is stabilised by both the electron-withdrawing effects of the carbonyls and aromaticity.

See also

• Barbiturase
• Barbiturate

References

1. ^ Baeyer, Adolf (1864). "Untersuchungen über die Harnsäuregruppe". Annalen der Chemie und Pharmacie 131: 291. doi:10.1002/jlac.18641310306. 
2. ^ J. B. Dickey & A. R. Gray (1943), "Barbituric acid", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv2p0060 ; Coll. Vol. 2: 60