chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with formula or , whose molecule would consist of 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 three cyanamido groups or substituted for 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.
The compound had not been properly isolated as of 2010, due to its tendency to
polymer
A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
ize. However, removal of three protons yields the melonate (formerly hydromelonate) anion , whose salts are stable and have been known since the 19th century. Removal of only two protons yields the divalent hydrogenmelonate anion .
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 ...
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 salt "hydromelonate" and the corresponding acid "hydromelonic". In the following years Liebig prepared the same salt 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
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 a ...
, and eventually determined the formula for the acid.
The correct structure for the cation 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.
Starting in the 1970s, melonates have attracted new interest, motivated by research in
cubic
Cubic may refer to:
Science and mathematics
* Cube (algebra), "cubic" measurement
* Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex
** Cubic crystal system, a crystal system w ...
carbon nitride
Carbon nitrides are organic compounds consisting only of carbon and nitrogen atoms.
Covalent network compounds
These materials are organic semiconductors. Due to its hydrogen-bonding motifs and electron-rich properties, this carbon material is ...
c-. Salts of many cations have been synthesized and studied, including mixed-cation salts and calcium hydrogenmelonate . The structure of potassium melonate pentahydrate was elucidated only in 2005.
Preparation
Sodium and potassium melonates are still routinely prepared by variations of one of Liebig's methods, namely by reacting
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 ...
with molten
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 ...
,
potassium cyanate
Potassium cyanate is an inorganic compound with the chemical formula, formula KOCN (sometimes denoted KCNO). It is a colourless solid. It is used to prepare many other compounds including useful herbicide. Worldwide production of the potassium an ...
, or
sodium thiocyanate
Sodium thiocyanate (sometimes called sodium sulphocyanide) is the chemical compound with the formula NaSCN. This colorless deliquescent salt is one of the main sources of the thiocyanate anion. As such, it is used as a precursor for the synth ...
. Other salts can be prepared by
double displacement reaction
A salt metathesis reaction (also called a double displacement reaction, double replacement reaction, or double decomposition) is a type of chemical reaction in which two ionic compounds in aqueous solution exchange their component ions to form two ...
s.
Melonates
Alkali melonates are soluble in water without decomposition. Treatment of melonates with alkali gives salts of
cyameluric acid
Cyameluric acid or 2,5,8-trihydroxy-''s''-heptazine is a chemical compound with formula , usually described as a heptazine molecule with the hydrogen atoms replaced by hydroxyl groups ; or any of its tautomers.
The substance exists as an equilibri ...
.
Potassium melonate pentahydrate has planar sheets of melonate anions with potassium cations between the layers. The same generals structure is seen in the anhydrous salt (except that the melonate ions are asymmetric due to an group being turned by 180°) and in the salts and .
Melonate salts decompose when melted with
cyanate
The cyanate ion is an anion with the chemical formula . It is a resonance of three forms: (61%) ↔ (30%) ↔ (4%).
Cyanate is the derived anion of isocyanic acid, H−N=C=O, and its lesser tautomer cyanic acid (a.k.a. cyanol), H−O−C� ...
s to form tricyanomelaminates, the first selective decomposition reaction leading from heptazines to
triazine
Triazines are a class of nitrogen-containing heterocycles. The parent molecules' molecular formula is . They exist in three isomeric forms, 1,3,5-triazines being common.
Structure
The triazines have planar six-membered benzene-like ring but ...
carbon
Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
in the form of
nanotubes
A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized:
* ''Single-walled carbon nanotubes'' (''SWC ...
.
See also
*
Melem
In chemistry, melem is a chemical compound, compound with formula ; specifically, 2,5,8-triamino-heptazine or 2,5,8-triamino-tri-''s''-triazine, whose molecule can be described as that of heptazine with the three hydrogen atoms replaced by amino gr ...
,
*
Cyameluric acid
Cyameluric acid or 2,5,8-trihydroxy-''s''-heptazine is a chemical compound with formula , usually described as a heptazine molecule with the hydrogen atoms replaced by hydroxyl groups ; or any of its tautomers.
The substance exists as an equilibri ...
,
References
J. Liebig, Ibid., 10, 1 (1834).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. Fabian Karl Keßler (2019), Structure and Reactivity of s-Triazine-Based Compounds in C/N/H Chemistry '. Doctoral thesis, Fakultät für Chemie und Pharmazie,
Ludwig-Maximilians-Universität München
The Ludwig Maximilian University of Munich (simply University of Munich, LMU or LMU Munich; ) is a public university, public research university in Munich, Bavaria, Germany. Originally established as the University of Ingolstadt in 1472 by Duke ...
Sophia J. Makowski, Daniel Gunzelmann, Jürgen Senker, Wolfgang Schnick (2009): "Protonated Melonate Ca C6N7(NCN)3�7H2O – Synthesis, Crystal Structure, and Thermal Properties". ''Zeitschrift für anorganische und allgemeine Chemie'' (''ZAAC''), volume 635, issue 15, pages 2434-2439. Andreas Sattler and Wolfgang Schnick (2009): "On the Formation and Decomposition of the Melonate Ion in Cyanate and Thiocyanate Melts and the Crystal Structure of Potassium Melonate,". ''European Journal of Inorganic Chemistry'', volume 2009, issue 33, pages 4972-4981. Corinna Clauss, Jörg Wagler, Marcus Schwarz, Anke Schwarzer, and Edwin Kroke (2010): "Lithium Melonate, – Synthesis, Crystal Structure and Thermal Properties of a Novel Precursor for Graphitic Carbon Nitrides". 'Zeitschrift für anorganische und allgemeine Chemie'' (''ZAAC''), vlume 636, issue 1, pages 196-200. Corinna Clauss, Marcus Schwarz, and Edwin Kroke (2010): "Microwave-induced decomposition of nitrogen-rich iron salts and CNT formation from iron(III)–melonate ". ''Carbon'', volume 48, issue 4, pages 1137-1145. Wolfgang Schnick and Sophia Makowski (2010): and – Synthesis, Crystal Structure and Thermal Behavior of two Novel Alkali Melonates . ''CSSD HAL'', article hal-00511998 version 1 {{doi, 10.1002/zaac.200900232Nitrogen heterocyclesHeterocyclic compounds with 3 ringsNitriles