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 first synthesised by Adolf von Baeyer.
Naming
It remains unclear why Baeyer chose to name the compound that he discovered "barbituric acid". In his textbook
Organic Chemistry, the American organic chemist
Louis Fieser (1899–1977) initially speculated that the name stemmed from the German word
Schlüsselbart (literally, the beard (
Bart, Latin:
barba) of a key (
Schlüssel), that is, the bit of a key), because Baeyer had regarded barbituric acid as central (or "key") to understanding
uric acid and its derivatives. However, Fieser subsequently decided that Baeyer had named the compound after a young lady whom he had met and who was called "Barbara"' hence the name "barbituric acid" was a combination of the name "Barbara" and "uric acid".
[Levi, Leo (1957) "The barbituric acids, their chemical structure, synthesis and nomenclature," United Nations: Office on Drugs and Crime.][Fiesler, L. F., Organic Chemistry (Boston, Massachusetts: D.C. Heath and Company, 1944), p. 247.][See also:
]
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Willstätter, Richard Martin, Aus meinen Leben: von Arbeit, Musse und Freunden From (Weinheim, Germany: Arthur Stoll, 1949). English translation: Willstätter, R. with L. S. Hornig, trans., From My Life: The Memoirs of Richard Willstätter (New York, New York: W. A. Benjamin, 1965), "Memories of Adolf von Baeyer," p. 119.
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Cohen, W. A. T. (1943) "Chemisch-Historische Aanteekenigen: De nomenclatur van enkele organische zuren" (Chemical-historical notes: the nomenclature of some organic acids), Chemisch Weekblad, 40: 176.
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Kauffman, George B. (1980) "Adolf von Baeyer and the naming of barbituric acid," Journal of Chemical Education, 57: 222–223.
Other sources claim that Baeyer named the compound after
Saint Barbara, either because he discovered it on the feast day of St. Barbara (December 4) or because he sometimes lunched with artillery officers and St. Barbara is their patron saint.
[Jie Jack Li, Laughing Gas, Viagra, and Lipitor: The Human Stories Behind the Drugs We Use (Oxford, England: Oxford University Press, 2006), p. 204.][Alex Nickon, Ernest F. Silversmith, Organic Chemistry: The Name Game: Modern Coined Terms and Their Origins (New York, New York: Pergamon Press, 1987), pp. 133–134.]
Synthesis
Barbituric acid was first prepared and named in 1864 by the German chemist Adolf von Baeyer, by reducing what Baeyer called
Alloxanbromid (
alloxan dibromide, now: 5,5-dibromobarbituric acid) with
hydrocyanic acid,
[Baeyer, Adolf (1863) "Untersuchungen über die Harnsäuregruppe" (Investigations of the uric acid group), Annalen der Chemie, 127: 1–27' 199–236' see especially pages 231–235. Baeyer names barbituric acid on page 3: "Man wird sehen, wie sich diese Materialien in einfachster Weise um die Substanz N2C4O3H4, die ich Barbitursäure nennen will, gruppieren lassen und wie also die Frage nach der Konstitution der Harnsäure und ihrer Derivate auf die Untersuchung dieser Substanz zurückgekehrt ist." (One will see how these materials can be grouped most simply around the substance N2C4O3H4, which I will call "barbituric acid", and thus how the question of the constitution of uric acid and its derivatives is traced back to the investigation of this substance.)] and later by reducing dibromobarbituric acid with a combination of
sodium amalgam and
hydrogen iodide.
[Baeyer, Adolf (1864) "Untersuchungen über die Harnsäuregruppe" (Investigations of the uric acid group), Annalen der Chemie, 130: 129–175; p. 136.] In 1879, the French chemist Édouard Grimaux synthesized barbituric acid from
malonic acid,
urea, and phosphorus oxychloride (POCl
3).
[Grimaux, Edouard (1879) "Synthèse des dérivés uriques de la série de l'alloxane" (Synthesis of uric derivatives of the alloxan series), Bulletin de la Société chimique de Paris, 2nd series, 31: 146–149.] Malonic acid has since been replaced by
diethyl malonate,
[Arthur Michael (1887) "Ueber neue Reactionen mit Natriumacetessig- und Natriummalonsäureäthern" (On new reactions with sodium acetoacetic- and sodium malonic acid esters), Journal für Praktische Chemie, 2nd series, 35: 449-459; p. 456.] because using the ester avoids the problem of having to deal with the acidity of the
carboxylic acid and its unreactive
carboxylate.
Properties
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.
Uses
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 a chemical building block in the laboratory synthesis of riboflavin (vitamin B2) and in a method of producing the pharmaceutical drug minoxidil.
Health and safety
See also
External links
