Triazines are a class of nitrogen-containing . The parent molecules' molecular formula is . They exist in three forms, 1,3,5-triazines being common.
Structure
The triazines have planar six-membered
benzene-like ring but with three carbons replaced by nitrogens. The three isomers of triazine are distinguished by the positions of their nitrogen
atoms, and are referred to as 1,2,3-triazine, 1,2,4-triazine, and 1,3,5-triazine.
Other aromatic nitrogen are with one ring nitrogen atom, with 2 nitrogen atoms in the ring, with 3 nitrogens in a 5-membered ring, and with 4 ring nitrogen atoms.
Uses
Melamine
A well known triazine is
melamine (2,4,6-triamino-1,3,5-triazine). With three
amino , melamine is a precursor to commercial
resins.
are closely related to melamine, except with one amino substituent replaced by an organic group. This difference is exploited in the use of guanamines to modify the crosslinking density in
. Some commercially important guanamines are
benzoguanamine and
acetoguanamine.
Cyanuric chloride
Another important triazine is cyanuric chloride (2,4,6-trichloro-1,3,5-triazine). Chlorine-substituted triazines are components of
.
[Horst Tappe, Walter Helmling, Peter Mischke, Karl Rebsamen, Uwe Reiher, Werner Russ, Ludwig Schläfer and Petra Vermehren "Reactive Dyes"in Ullmann's Encyclopedia of Industrial Chemistry 2000, Wiley-VCH, Weinheim. ] These compounds react through a chlorine group with hydroxyl groups present in
cellulose fibres in nucleophilic substitution, the other triazine positions contain chromophores. Triazine compounds are often used as the basis for various
, e.g.
atrazine.
Other
Triazines also have wide use in the oil and gas and petroleum processing industries as a non-regenerating sulfide removal agent: they are applied to fluid streams to remove
hydrogen sulfide gas and mercaptan species, which can decrease the quality of the processed hydrocarbon and be harmful to pipeline and facility infrastructure if not removed.
Synthesis
The more common 1,3,5-isomers are prepared by trimerization of
nitrile and
cyanide compounds, although more specialized methods are known.
The 1,2,3- and 1,2,4-triazines are more specialized methods. The former family of triazines can be synthesized by thermal rearrangement of 2-azidocyclopropenes. Also mainly of specialized interest, the 1,2,4-isomer is prepared from condensation of 1,2-dicarbonyl compounds with . A classical synthesis is also the Bamberger triazine synthesis.
Reactions
Although triazines are
aromatic compounds, their
resonance energy is much lower than in
benzene. Electrophilic aromatic substitution is difficult but nucleophilic aromatic substitution easier than typical chlorinated benzenes. 2,4,6-Trichloro-1,3,5-triazine is easily hydrolyzed to
cyanuric acid by heating with water. 2,4,6-Tris(phenoxy)-1,3,5-triazine results when the trichloride is treated with phenol. With amines, one or more chloride is displaced. The remaining chlorides are reactive, and this theme is the basis of the large field of
.
Cyanuric chloride assists in the amidation of .[ Triazine-Promoted Amidation of Various Carboxylic Acids Jeremy Schlarb 1999 Article ]
The 1,2,4-triazines can react with electron-rich dienophiles in an inverse electron demand Diels-Alder reaction. This forms a bicyclic intermediate which normally then extrudes a molecule of nitrogen gas to form an aromatic ring again. In this way the 1,2,4-triazines can be reacted with to form pyridine rings. An alternative to using an alkyne is to use norbornadiene which can be thought of as a masked alkyne.[Shi, B.; Lewis, W.; Campbell, I. B.; Moody, C. J. Org. Lett., 2009, 3686-3688 ]
1,2,3-triazines undergo Zincke reaction nucleophilic substitution with secondary amines to give β-amino aldehydes.
In 2007, a method for synthesizing highly porous triazine-based polymers was discovered, and found to be useful (in conjunction with palladium) for the selective reduction of phenols.
Ligands
A series of 1,2,4-triazine derivatives known as bis-triazinyl bipyridines (BTPs) have been considered as possible
for use in the advanced nuclear reprocessing.
[ Development Of Electrochemical Separations Of Uranium And Re Elements From Fluoride Melts] BTPs are molecules containing a
pyridine ring bonded to two 1,2,4-triazin-3-yl groups.
Triazine-based have been used to bind three dinuclear arene ruthenium (or osmium) compounds to form .
-
Heterocyclic Chemistry T.L. Gilchrist 1985 (1997, )
See also
-
Hexahydro-1,3,5-triazine
-
6-membered rings with one nitrogen atom: pyridine
-
6-membered rings with two nitrogen atoms:
-
6-membered rings with four nitrogen atoms:
-
6-membered rings with five nitrogen atoms: pentazine
-
6-membered rings with six nitrogen atoms: hexazine
