Triazines are a class of

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

-containing

heterocycle A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, proper ...

s. The parent molecules'

molecular formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as paren ...

is . They exist in three

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

ic forms, 1,3,5-triazines being common.

Structure

The triazines have planar six-membered

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

-like ring but with three carbons replaced by nitrogens. The three isomers of triazine are distinguished by the positions of their nitrogen

atoms Atoms are the basic particles of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other ...

, and are referred to as 1,2,3-triazine, 1,2,4-triazine, and 1,3,5-triazine. Other

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

nitrogen

s are

pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...

s with one ring nitrogen atom,

diazine In organic chemistry, diazines are a group of organic compounds having the molecular formula . Each contains a benzene ring in which two of the C-H fragments have been replaced by isolobal nitrogen. There are three structural isomers: * pyrida ...

s with 2 nitrogen atoms in the ring,

triazole A triazole is a heterocyclic compound featuring a five-membered ring of two carbon atoms and three nitrogen atoms with molecular formula C2H3N3. Triazoles exhibit substantial Isomer, isomerism, depending on the positioning of the nitrogen atoms w ...

s with 3 nitrogens in a 5-membered ring, and tetrazines with 4 ring nitrogen atoms.

Uses

Melamine

A well known triazine is

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 ...

(2,4,6-triamino-1,3,5-triazine). With three

amino In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

substituent In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...

s, melamine is a precursor to commercial

resins A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Comm ...

Guanamine In organic chemistry, a guanamine is an organic compound with the formula (H2NC)2N3CR. They are heterocycles of the triazine class. Guanamines are closely related to melamine ((H2NC)3N3), except with one amino substituent replaced by an organic ...

s 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

melamine resin Melamine resin or melamine formaldehyde (also shortened to melamine) is a resin with melamine rings terminated with multiple hydroxyl groups derived from formaldehyde. This thermosetting plastic material is made from melamine and formaldehyde. ...

s. Some commercially important guanamines are

benzoguanamine Benzoguanamine is an organic Chemical compound, compound with the chemical formula (CNH2)2(CC6H5)N3. It is related to melamine but with one amino group replaced by phenyl. Benzoguanamine is used in the manufacturing of melamine resins. Unlike mela ...

and

acetoguanamine Acetoguanamine is an organic compound with the chemical formula (CNH2)2CCH3N3. It is related to melamine but with one amino group replaced by methyl. Acetoguanamine is used in the manufacturing of melamine resins. Unlike melamine ((CNH2)3N3), a ...

Cyanuric chloride

Another important triazine is

cyanuric chloride Cyanuric chloride is an organic compound with the formula (NCCl)3. This white solid is the chlorinated derivative of 1,3,5-triazine. It is the trimer of cyanogen chloride. Cyanuric chloride is the main precursor to the popular but controversi ...

(2,4,6-trichloro-1,3,5-triazine). Chlorine-substituted triazines are components of

reactive dye In a reactive dye, a chromophore (an atom or group whose presence is responsible for the colour of a compound) contains a substituent that reacts with the substrate. Reactive dyes have good fastness properties owing to the covalent bonding that o ...

s.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 Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

fibres in

nucleophilic substitution In chemistry, a nucleophilic substitution (SN) is a class of chemical reactions in which an electron-rich chemical species (known as a nucleophile) replaces a functional group within another electron-deficient molecule (known as the electrophile) ...

, the other triazine positions contain chromophores. Triazine compounds are often used as the basis for various

herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

s, e.g.

atrazine Atrazine ( ) is a Organochlorine compound, chlorinated herbicide of the triazine class. It is used to prevent pre-emergence broadleaf weeds in crops such as maize (corn), soybean and sugarcane and on turf, such as golf courses and residential law ...

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 Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

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 In organic chemistry, a nitrile is any organic compound that has a functional group. The name of the compound is composed of a base, which includes the carbon of the , suffixed with "nitrile", so for example is called " propionitrile" (or pr ...

and

cyanide In chemistry, cyanide () is an inorganic chemical compound that contains a functional group. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. Ionic cyanides contain the cyanide anion . This a ...

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

amidrazone Amidrazones are a class of chemical compounds formally derived from carboxylic acids. Amidrazones can exists in two tautomeric forms: hydrazide imides (RC(=NH)NHNH2) and amide hydrazones (RC(NH2)=NNH2). Uses Some amidrazones have been employed a ...

s. A classical synthesis is also the

Bamberger triazine synthesis The Bamberger triazine synthesis in organic chemistry is a classic organic synthesis of a triazine first reported by Eugen Bamberger in 1892.Hassner, A., Stumer, C., ''Organic Synthesis Based on Name Reactions'': 2nd. Ed. Tetrahedron Organic Chemist ...

Reactions

Although triazines are

compounds, their resonance energy is much lower than in

Electrophilic aromatic substitution Electrophilic aromatic substitution (SEAr) is an organic reaction in which an atom that is attached to an aromatic ring, aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitut ...

is difficult but

nucleophilic aromatic substitution A nucleophilic aromatic substitution (SNAr) is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring. Aromatic rings are usually nucleophilic, but some aromatic c ...

easier than typical chlorinated benzenes. 2,4,6-Trichloro-1,3,5-triazine is easily hydrolyzed to

cyanuric acid Cyanuric acid or 1,3,5-triazine-2,4,6-triol is a chemical compound with the chemical formula, formula (CNOH)3. Like many industrially useful chemicals, this triazine has many synonyms. This white, odorless solid finds use as a precursor or a com ...

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

s. Cyanuric chloride assists in the

amidation 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 any group, typically organyl groups or hydrogen atoms. The amide group is called a p ...

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

s. The 1,2,4-triazines can react with

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

-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

alkyne \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...

s to form pyridine rings. An alternative to using an alkyne is to use

norbornadiene Norbornadiene is an organic compound and a bicyclic hydrocarbon. Norbornadiene is of interest as a metal-binding ligand, whose complexes are useful for homogeneous catalysis. It has been intensively studied owing to its high reactivity and distin ...

which can be thought of as a masked alkyne. 1,2,3-triazines undergo Zincke-like 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 Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), ...

) 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

extractant Extraction in chemistry is a separation process consisting of the separation of a substance from a matrix. The distribution of a solute between two phases is an equilibrium condition described by partition theory. This is based on exactly ho ...

s for use in the advanced

nuclear reprocessing Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the ...

. BTPs are molecules containing a

ring bonded to two 1,2,4-triazin-3-yl groups. Triazine-based

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s have been used to bind three dinuclear

arene Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were ...

ruthenium Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is unreactive to most chem ...

(or

osmium Osmium () is a chemical element; it has Symbol (chemistry), symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a Abundance of elements in Earth's crust, trace element in a ...

) compounds to form

metallaprism Coordination cages are three-dimensional ordered structures in solution that act as hosts in host–guest chemistry. They are self-assembled in solution from organometallic precursors, and often rely solely on noncovalent interactions rather than co ...

References

* ''Heterocyclic Chemistry'' T.L. Gilchrist 1985 (1997, )