Melem
Encyclopedia
A heptazine, or tri-s-triazine or cyamelurine, is a type of chemical compound
that consist of a planar triangular core group, C6N7, or three fused triazine
rings, with three substituent
s at the corners of the triangle.
The general form is 1,3,4,6,7,9,9b-heptaazaphenalene. The parent compound C6N7H3, where the three substituents are hydrogens, is called 1,3,4,6,7,9-hexaazacyc1[3.3.3]azine or tri-s-triazine proper.
Heptazines were discovered in the 19th century but their study has long been hampered by their general insolubility. They are used as flame retardants and have been the object of interest recently for potential applications in electronics materials, explosives, and more.
first mentioned the heptazines in the 1830s when he discovered a polymeric substance after mercury thiocyanate ignition. Justus von Liebig
named the polymer melon. Much later in 1937 Linus Pauling
showed by x-ray crystallography
that heptazines are in fact fused triazines. The unsubstituted heptazine C6N7H3 was synthesized by Ramachandra S. Hosmane
and others from the group of N. Leonard in the early 1980s. The structure of Berzelius's melon was confirmed only in 2001.
solid with melting point over 300 °C. The compound is generally stable and soluble in organic solvents such as acetonitrile
, but is decomposed by water. It has a peculiar crystal structure, whose cell spans 16 molecules in asymmetric positions and orientations.
homologue, but not a heptazine, is the dimer melam
, the fused product of 2,4-diamino-6-chloro-s-triazine with melamine
. Melem, melon, and melam are effective flame retardant
compounds. The compounds have in common that they melt or decompose at very high temperatures and that they are insoluble in any solvent. This makes characterisation difficult.
The heptazine derivate with three hydroxyl
substituents is called cyameluric acid and has many possible tautomer
ic structures. Of the seventeen tautomeric forms, calculations showed that of the tri-oxo forms was found to be the most stable. Therefore this compound is not a hydroxide
but an amide
. 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
, but it is remarkable since at that time cyclic compounds of any type were not widely recognised.
The heptazine derivate with an azide
substituent and two hydroxyl groups is called Linus Pauling's mystery molecule. It is the last molecule he drew on his chalkboard (preserved for posterity) before he died in 1994. Two theories attempt to lift the mystery. It is suggested that Pauling failed to solve the double helix structure of DNA
before Watson
and Crick
because he viewed uracil
as an amide and not as the tautomer
ic hydroxy compound. The other theory suggests that Pauling intended to use the compound as a potential spectroscopic label for binding to DNA. Nelson Leonard observed that Pauling "must have returned to the source of his original structural inspiration for a new application."
The tri-azido derivatives are investigated for their use as high-energy-density materials (explosives).
It is believed that the graphite form of the carbon nitride
C3N4 is built up of linked heptazines. Heptazines could be a precursor molecule to the diamond
-like beta carbon nitride
.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
that consist of a planar triangular core group, C6N7, or three fused triazine
Triazine
A triazine is one of three organic chemicals, isomeric with each other, whose molecular formula is 333 and whose empirical formula is CHN.- Structure :...
rings, with three substituent
Substituent
In organic chemistry and biochemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon...
s at the corners of the triangle.
The general form is 1,3,4,6,7,9,9b-heptaazaphenalene. The parent compound C6N7H3, where the three substituents are hydrogens, is called 1,3,4,6,7,9-hexaazacyc1[3.3.3]azine or tri-s-triazine proper.
Heptazines were discovered in the 19th century but their study has long been hampered by their general insolubility. They are used as flame retardants and have been the object of interest recently for potential applications in electronics materials, explosives, and more.
History
Jöns Jakob BerzeliusJöns Jakob Berzelius
Jöns Jacob Berzelius was a Swedish chemist. He worked out the modern technique of chemical formula notation, and is together with John Dalton, Antoine Lavoisier, and Robert Boyle considered a father of modern chemistry...
first mentioned the heptazines in the 1830s when he discovered a polymeric substance after mercury thiocyanate ignition. Justus von Liebig
Justus von Liebig
Justus von Liebig was a German chemist who made major contributions to agricultural and biological chemistry, and worked on the organization of organic chemistry. As a professor, he devised the modern laboratory-oriented teaching method, and for such innovations, he is regarded as one of the...
named the polymer melon. Much later in 1937 Linus Pauling
Linus Pauling
Linus Carl Pauling was an American chemist, biochemist, peace activist, author, and educator. He was one of the most influential chemists in history and ranks among the most important scientists of the 20th century...
showed by x-ray crystallography
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
that heptazines are in fact fused triazines. The unsubstituted heptazine C6N7H3 was synthesized by Ramachandra S. Hosmane
Ramachandra S. Hosmane
Ramachandra "" S. Hosmane is a retired Senior Professor of Organic Chemistry at University of Maryland, Baltimore County. Dr. Hosmane has over 150 peer-reviewed research publications in reputed international journals. He holds four U.S. patents, three of which have been licensed to industries...
and others from the group of N. Leonard in the early 1980s. The structure of Berzelius's melon was confirmed only in 2001.
Parent molecule
The parent substance C6N7H3 is a yellow, weakly fluorescentFluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
solid with melting point over 300 °C. The compound is generally stable and soluble in organic solvents such as acetonitrile
Acetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...
, but is decomposed by water. It has a peculiar crystal structure, whose cell spans 16 molecules in asymmetric positions and orientations.
Derivatives and uses
The specific compound with three amino substituents is called melem. When heptazine is polymerized with the tri-s-triazine units linked through an amine (NH) link, it is called melon. Another melamineMelamine
Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....
homologue, but not a heptazine, is the dimer melam
Melam (chemistry)
Melam is a condensation product of melamine.-Synthesis:Melam was discovered by Liebig in 1834 from the residue of heating ammonium thiocyanate.-Chemical property:...
, the fused product of 2,4-diamino-6-chloro-s-triazine with melamine
Melamine
Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....
. Melem, melon, and melam are effective flame retardant
Flame retardant
Flame retardants are chemicals used in thermoplastics, thermosets, textiles and coatings that inhibit or resist the spread of fire. These can be separated into several different classes of chemicals:...
compounds. The compounds have in common that they melt or decompose at very high temperatures and that they are insoluble in any solvent. This makes characterisation difficult.
The heptazine derivate with three hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
substituents is called cyameluric acid and has many possible tautomer
Tautomer
Tautomers are isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization. This reaction commonly results in the formal migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond...
ic structures. Of the seventeen tautomeric forms, calculations showed that of the tri-oxo forms was found to be the most stable. Therefore this compound is not a hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
but an amide
Amide
In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...
. The first person to suggest a structure for cyameluric acid was J. Loschmidt
Johann Josef Loschmidt
Jan or Johann Josef Loschmidt , who referred to himself mostly as 'Josef' , was a notable Austrian scientist who performed groundbreaking work in chemistry, physics , and crystal forms.Born in Carlsbad, a town located in the Austrian Empire , Loschmidt...
, as far back as 1861. His structure was in fact a meta-cyclophane
Cyclophane
A cyclophane is a hydrocarbon consisting of an aromatic unit and an aliphatic chain that forms a bridge between two non-adjacent positions of the aromatic ring. More complex derivatives with multiple aromatic units and bridges forming cagelike structures are also known...
, but it is remarkable since at that time cyclic compounds of any type were not widely recognised.
The heptazine derivate with an azide
Azide
Azide is the anion with the formula N3−. It is the conjugate base of hydrazoic acid. N3− is a linear anion that is isoelectronic with CO2 and N2O. Per valence bond theory, azide can be described by several resonance structures, an important one being N−=N+=N−...
substituent and two hydroxyl groups is called Linus Pauling's mystery molecule. It is the last molecule he drew on his chalkboard (preserved for posterity) before he died in 1994. Two theories attempt to lift the mystery. It is suggested that Pauling failed to solve the double helix structure of DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
before Watson
James D. Watson
James Dewey Watson is an American molecular biologist, geneticist, and zoologist, best known as one of the co-discoverers of the structure of DNA in 1953 with Francis Crick...
and Crick
Francis Crick
Francis Harry Compton Crick OM FRS was an English molecular biologist, biophysicist, and neuroscientist, and most noted for being one of two co-discoverers of the structure of the DNA molecule in 1953, together with James D. Watson...
because he viewed uracil
Uracil
Uracil is one of the four nucleobases in the nucleic acid of RNA that are represented by the letters A, G, C and U. The others are adenine, cytosine, and guanine. In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine.Uracil is a common and...
as an amide and not as the tautomer
Tautomer
Tautomers are isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization. This reaction commonly results in the formal migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond...
ic hydroxy compound. The other theory suggests that Pauling intended to use the compound as a potential spectroscopic label for binding to DNA. Nelson Leonard observed that Pauling "must have returned to the source of his original structural inspiration for a new application."
The tri-azido derivatives are investigated for their use as high-energy-density materials (explosives).
It is believed that the graphite form of the carbon nitride
Graphitic carbon nitride
Graphitic carbon nitride is a family of compounds with a general formula near to C3N4 and structures based on triazine units which, depending on reaction conditions, exhibit different degrees of condensation, properties and reactivities.-Preparation:...
C3N4 is built up of linked heptazines. Heptazines could be a precursor molecule to the diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
-like beta carbon nitride
Beta carbon nitride
Beta carbon nitride is a material predicted to be harder than diamond.The material was first proposed in 1985 by Marvin Cohen and Amy Liu. Examining the nature of crystalline bonds they theorised that carbon and nitrogen atoms could form a particularly short and strong bond in a stable crystal...
.
External links
- Flame retardants supplier http://www.specialchem4polymers.com/tc/Melamine-Flame-Retardants/index.aspx?id=4013