1,2,4-Triazole (as ligand in coordination compounds, Htrz abbreviation is sometimes used) is one of a pair of

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

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 ...

s with

molecular formula In chemistry, 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, ...

CHN, called

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 isomerism, depending on the positioning of the nitrogen atoms within t ...

s, which have a five-membered ring of two carbon atoms and three nitrogen atoms. 1,2,4-Triazole and its derivatives find use in a wide variety of applications.

Structure and properties

1,2,4-Triazole is a planar molecule. The C-N and N-N distances fall into a narrow range 136 - 132 picometers, consistent with the aromaticity. Although two tautomers can be envisioned, only one exists practically speaking. 1,2,4-Triazole is

amphoteric In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used. One type of amphoteric species are amphiproti ...

, being susceptible to both N-protonation and deprotonation in aqueous solution. The pK_a of 1,2,4-triazolium (C₂N₃H₄⁺) is 2.45. The pK_a of the neutral molecule is 10.26.

Synthesis and occurrence

1,2,4-Triazoles can be prepared using the

Einhorn–Brunner reaction The Einhorn–Brunner reaction is the designation for the chemical reaction of imides with alkyl hydrazines to form an isomeric mixture of 1,2,4-triazoles. It was initially described by the German chemist Alfred Einhorn in a paper, published in ...

or the

Pellizzari reaction The Pellizzari reaction was discovered in 1911 by Guido Pellizzari, and is the organic reaction of an amide and a hydrazide to form a 1,2,4-triazole. The product is similar to that of the Einhorn-Brunner reaction, but the mechanism itself is not ...

. Unsubstituted 1,2,4-triazole can be prepared from

thiosemicarbazide Thiosemicarbazide is the chemical compound with the formula H2NC(S)NHNH2. A white, odorless solid, it is related to thiourea (H2NC(S)NH2) by the insertion of an NH center. They are commonly used as ligands for transition metals. Many thiosemicar ...

by acylation with

formic acid Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure . It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Es ...

followed by cyclization of 1-formyl-3-thiosemicarbazide into 1,2,4-triazole-3(5)-thiol; oxidation of the thiol by

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

yields 1,2,4-triazole. 1,2,4-Triazoles are featured in many kinds of drugs. Notable triazoles include the

antifungal drug An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as cryp ...

fluconazole Fluconazole is an antifungal medication used for a number of fungal infections. This includes candidiasis, blastomycosis, coccidiodomycosis, cryptococcosis, histoplasmosis, dermatophytosis, and pityriasis versicolor. It is also used to prevent ...

and

itraconazole Itraconazole, sometimes abbreviated ITZ, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. It may be given by mouth ...

and the

plant growth regulator Plant hormone (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pat ...

paclobutrazol Paclobutrazol (PBZ) is the ISO common name for an organic compound that is used as a plant growth retardant and triazole fungicide. It is a known antagonist of the plant hormone gibberellin, acting by inhibiting gibberellin biosynthesis, reduc ...

. Triazolate is a common

bridging ligand In coordination chemistry, a bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually r ...

in coordination chemistry.

References

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