Cyameluric acid or 2,5,8-trihydroxy-''s''-heptazine is a chemical compound with formula , usually described as a

heptazine Heptazine, or tri-''s''-triazine or cyamelurine, is a chemical compound with formula , that consist of a planar triangular core group or three fused triazine rings, with three hydrogen atoms at the corners. It is a yellow, weakly fluorescent soli ...

molecule with the

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

atoms replaced by

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

groups A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

; or any of its

tautomer Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hydr ...

s. The substance exists as an equilibrium of 17 tautomers that easily interconvert among each other. Calculations show that the symmetric tri-oxo form (1,4,7-trihydro-2,5,8-trioxo-''s''-heptazine) is the most stable. Therefore, this compound contains

amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...

groups rather than

imidic acid In chemistry, an imidic acid is any molecule that contains the -C(=NH)-OH functional group. It is the tautomer of an amide and the isomer of an oxime. The term "imino acid" is an obsolete term for this group that should not be used in this contex ...

History

In 1834

Justus von Liebig Justus Freiherr von Liebig (12 May 1803 – 20 April 1873) was a German scientist who made major contributions to agricultural and biological chemistry, and is considered one of the principal founders of organic chemistry. As a professor at t ...

described the compounds that he named

melamine Melamine is an organic compound with the formula C3H6N6. This white solid is a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 67% nitrogen by mass, and its derivatives have fire retardant properties due t ...

melam Melam is a group of Maddalams and other similar percussion instruments' (Chenda) rhythmic performance. Those who play melam are called 'Melakaar'. In ancient Tamilakam (Tamil country) melam was used for all the occasions in temples (''Kovil Melam ...

, and

melon A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a "pepo". The ...

. In 1835

Leopold Gmelin Leopold Gmelin (2 August 1788 – 13 April 1853) was a German chemist. Gmelin was a professor at the University of Heidelberg He worked on the red prussiate and created Gmelin's test, and wrote his ''Handbook of Chemistry'', which over successiv ...

prepared novel

salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively cha ...

by heating

potassium ferrocyanide Potassium ferrocyanide is the inorganic compound with formula K4 e(CN)6�3H2O. It is the potassium salt of the coordination complex e(CN)6sup>4−. This salt forms lemon-yellow monoclinic crystals. Synthesis In 1752, the French chemist Pierr ...

with

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

); recognizing their connection to the compounds described by Liebig, he named the salts " hydromelonates" and the corresponding acid " hydromelonic". In the following years Liebig prepared the same salts by other methods, such as by fusing

potassium thiocyanate Potassium thiocyanate is the chemical compound with the molecular formula KSCN. It is an important salt of the thiocyanate anion, one of the pseudohalides. The compound has a low melting point relative to most other inorganic salts. Use in chem ...

with

antimony trichloride Antimony trichloride is the chemical compound with the formula SbCl3. It is a soft colorless solid with a pungent odor and was known to alchemists as butter of antimony. Preparation Antimony trichloride is prepared by reaction of chlorine with an ...

, and eventually determined the formula for the acid. Cyameluric acid, and salts were prepared in 1850 by W. Henneberg, by treating Gmelin's "hydromelonate" with alkali. The first person to suggest a structure for cyameluric acid was J. Loschmidt, as far back as 1861. His structure was in fact a ''meta''-

cyclophane In organic chemistry, a cyclophane is a hydrocarbon consisting of an aromatic unit (typically a benzene ring) and a chain that forms a bridge between two non-adjacent positions of the aromatic ring. More complex derivatives with multiple aromatic ...

, but it is remarkable since at that time cyclic compounds of any type were not widely recognised. The correct structure (for the trihydroxy tautomer) was published in 1937 by

Linus Pauling Linus Carl Pauling (; February 28, 1901August 19, 1994) was an American chemist, biochemist, chemical engineer, peace activist, author, and educator. He published more than 1,200 papers and books, of which about 850 dealt with scientific top ...

and J. H. Sturdivant.

Structure and properties

The various tautomeric forms differ in the position of the hydrogen atoms. Each oxygen is connected to one of the corner carbons; it may be bonded to a hydrogen, forming a hydroxy group; or may have a double bond to the carbon, in which case the hydrogen is bonded to one of several adjacent nitrogen atoms. The trihydroxy tautomer is one of several that have more than one planar

conformational isomer In chemistry, conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted just by rotations about formally single bonds (refer to figure on single bond rotation). While any two arrangements of atoms in a mo ...

. In this case, there is a symmetric one, with all three hydroxyls bent in the same direction around the ring, and an asymmetric one, with one of them bent in the opposite direction compared to the other two. Calculations show that the symmetric form 1,4,7-trihydro-2,5,8-trioxo is the most stable. The energy of the asymmetric 1,3,7-trihydro-2,5,8-trioxo form is estimated to be 5.61

kcal The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of on ...

/ mol higher, and that of the two conformations of the trihydroxy form are 19.84 (symmetric) and 20.18 (asymmetric) kcal/mol higher.

References

Johann Josef Loschmidt (1861), ''Konstitutionsformeln der Organischen Chemie in Graphischer Darstellung''. Nr. 190.

Wilhelm Engelmann Wilhelm EngelmannKarl Friedrich Pfau: Engelmann, Wilhelm. Allgemeine Deutsche Biographie 48(1904)378-9 was a German publisher and bookseller (August 1, 1808 in Lemgo – December 23, 1878 in Leipzig). Engelmann was the son of a bookseller in L ...

Leipzig Leipzig ( , ; Upper Saxon: ) is the most populous city in the German state of Saxony. Leipzig's population of 605,407 inhabitants (1.1 million in the larger urban zone) as of 2021 places the city as Germany's eighth most populous, as wel ...

. J. Liebig (1834): ''Annalen Pharmacie'', 10, 1. L. Gmelin, Ann. Pharmacie, 15, 252 (1835). J. Liebig, Ann. Chem. Pharm., 50, 337 (1844). W. Henneberg, Ibid., 73, 228 (1850). J. Liebig, Ibid., 95, 257 (1855). Linus Pauling and J. H. Sturdivant (1937): "The Structure of Cyameluric Acid, Hydromelonic Acid and Related Substances". ''Proceedings of the National Academy of Sciences'', volume 23, issue 12, page 615–620. {{doi, 10.1073/pnas.23.12.615 Henry S. Rzepa,
Joseph Loschmidt: Structural formulae, 1861
'. Accessed on 2009-06-30. Ibon Alkorta, Nadine Jagerovic, and José Elguero (2004), "Theoretical study of cyameluric acid and related compounds". ''

Arkivoc ''Arkivoc'' (''Archive for Organic Chemistry'') is a peer-reviewed open access scientific journal covering all aspects of organic chemistry. It is published by the non-profit organization Arkat USA, which was established in 2000 through a personal ...

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Article
/ref> Nitrogen heterocycles Tricyclic compounds Amides Lactims Triketones Heterocyclic compounds with 3 rings

History

Structure and properties

See also

References