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 a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

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 In chemistry, 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 reloca ...

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

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

groups rather than

imidic acid In organic chemistry, imidic acids are organic compounds with the structure . They are tautomeric to non- tertiary amides () and isomeric to oximes (). The term " imino acid" is an obsolete term for this group that should not be used in this c ...

History

In 1834

Justus von Liebig Justus ''Freiherr'' von Liebig (12 May 1803 – 18 April 1873) was a Germans, German scientist who made major contributions to the theory, practice, and pedagogy of chemistry, as well as to agricultural and biology, biological chemistry; he is ...

described the compounds that he named

melamine Melamine is an organic compound with the formula C3H6N6. This white solid is a trimer (chemistry), trimer of cyanamide, with a 1,3,5-Triazine, 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass, and its derivatives ha ...

melam The term "melam" means "ensemble," as in a "musical ensemble." In Kerala, "melam" refers to a group of Maddalam (drums) and similar percussion instruments (such as a Chenda) in a rhythmic performance. Those who play in melams are called 'Melakaa ...

, and

melon A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. It can also specifically refer to ''Cucumis melo'', commonly known as the "true melon" or simply "melon". The term "melon" can apply to both the p ...

. 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 Potassium ferricyanide, red prussiate and created Gmelin's test, and wrote his ''Handbook of Chemistry ...

prepared novel

salts In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...

by heating

potassium ferrocyanide Potassium hexacyanidoferrate(II) 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 chemi ...

with

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

); 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. Uses Ch ...

with antimony trichloride, 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 Catenation, chain that forms a bridge (chemical), bridge between two non-adjacent positions of the aromatic ring. More complex der ...

, 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 and peace activist. He published more than 1,200 papers and books, of which about 850 dealt with scientific topics. ''New Scientist'' called him one of the 20 gre ...

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, rotamers are chemical species that differ from one another primarily due to rotations about one or more single bonds. Various arrangements of atoms in a molecule that differ by rotation about single bonds can also be referred to as ...

. 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 KCAL may refer to: * KCAL (AM), a radio station (1410 AM) licensed to Redlands, California, United States * KCAL-FM, a radio station (96.7 FM) licensed to Redlands, California, United States *KCAL-TV KCAL-TV (channel 9) is an independent tel ...

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

References

Henry S. Rzepa,
Joseph Loschmidt: Structural formulae, 1861
'. Accessed on 2009-06-30. {{Cite journal , last1=Alkorta , first1=Ibon , last2=Jagerovic , first2=Nadine , last3=Elguero , first3=José , date=2004-03-06 , editor-last=Muthyala , editor-first=Ramaiah , title=Theoretical study of cyameluric acid and related compounds , url=https://www.arkat-usa.org/arkivoc-journal/browse-arkivoc/ark.5550190.0005.415 , journal=Arkivoc , language=en , volume=2004 , issue=4 , pages=130–136 , doi=10.3998/ark.5550190.0005.415 , issn=1551-7012, doi-access=free , hdl=2027/spo.5550190.0005.415 , hdl-access=free Nitrogen heterocycles Tricyclic compounds Amides Lactims Triketones Heterocyclic compounds with 3 rings

History

Structure and properties

See also

References