1,2,4-Triazole (as ligand in coordination compounds, Htrz abbreviation is sometimes used) is one of a pair of isomeric chemical compounds with molecular formula C2H3N3, called triazoles, 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.[1]
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| Names | |||
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| Preferred IUPAC name 1H-1,2,4-Triazole | |||
| Other names 1,2,4-Triazole pyrrodiazole | |||
| Identifiers | |||
3D model (JSmol) | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.005.476 | ||
PubChem CID | |||
| UNII | |||
CompTox Dashboard (EPA) | |||
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| Properties | |||
| C2H3N3 | |||
| Molar mass | 69.00725 | ||
| Appearance | white solid | ||
| Density | 1.439 g/cm3 | ||
| Melting point | 120 to 121 °C (248 to 250 °F; 393 to 394 K) | ||
| Boiling point | 260 °C (500 °F; 533 K) | ||
| very soluble | |||
| Acidity (pKa) | 10,3 | ||
| Basicity (pKb) | 11,8 | ||
| Hazards | |||
| Flash point | 140 °C (284 °F; 413 K) | ||
| Related compounds | |||
Related compounds | 1,2,3-triazole imidazole | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |||
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.[2] Although two tautomers can be envisioned, only one exists practically speaking.
1,2,4-Triazole is amphoteric, being susceptible to both N-protonation and deprotonation in aqueous solution. The pKa of 1,2,4-triazolium (C2N3H4+) is 2.45. The pKa of the neutral molecule is 10.26.[3]
Synthesis and occurrence
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1,2,4-Triazoles can be prepared using the Einhorn–Brunner reaction or the Pellizzari reaction. Unsubstituted 1,2,4-triazole can be prepared from thiosemicarbazide by acylation with formic acid followed by cyclization of 1-formyl-3-thiosemicarbazide into 1,2,4-triazole-3(5)-thiol; oxidation of the thiol by nitric acid or hydrogen peroxide yields 1,2,4-triazole.[5]
1,2,4-Triazoles are featured in many kinds of drugs.[6][7] Notable triazoles include the antifungal drugs fluconazole and itraconazole[8] and the plant growth regulator paclobutrazol.[9] Triazolate is a common bridging ligand in coordination chemistry.[10]