Chemistry:1,2,4-Triazole

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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]

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

Portion of the structure of {[Fe(triazolate)(triazole)2](BF4)}n.[4]

1,2,4-Triazoles can be prepared using the Einhorn–Brunner reaction or the Pellizzari reaction. In 2018, it was reported that reaction of isonitriles with diazonium salts produced 2,3-disubstituted or 2,5-disubstituted 1,2,4-triazoles depending on the catalyst.[5] 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.[6]

1,2,4-Triazoles are featured in many kinds of drugs.[7][8] Notable triazoles include the antifungal drugs fluconazole and itraconazole[9] and the plant growth regulator paclobutrazol.[10] Triazolate is a common bridging ligand in coordination chemistry.[11]

The 3,5‑dihydroxy derivative, known as urazole, sees extensive industrial use as a blowing agent.[12]

References

  1. ↑ Potts K. T. (1961). "The Chemistry of 1,2,4-Triazoles.". Chemical Reviews 61 (2): 87–127. doi:10.1021/cr60210a001. 
  2. ↑ Jeffrey, G. A.; Ruble, J. R.; Yates, J. H. (1983). "Neutron diffraction at 15 and 120 K and ab initio molecular-orbital studies of the molecular structure of 1,2,4-triazole". Acta Crystallographica Section B: Structural Science 39 (3): 388–394. doi:10.1107/S010876818300258X. Bibcode: 1983AcCrB..39..388J. 
  3. ↑ Garratt, Peter J. (1996). "1,2,4-Triazoles". Comprehensive Heterocyclic Chemistry II. pp. 127–163. doi:10.1016/B978-008096518-5.00080-0. ISBN 978-0-08-096518-5. 
  4. ↑ Grosjean, Arnaud; Négrier, Philippe; Bordet, Pierre; Etrillard, Céline; Mondieig, Denise; Pechev, Stanislav; Lebraud, Eric; Létard, Jean-François et al. (2013). "Crystal Structures and Spin Crossover in the Polymeric Material [Fe(HTRZ)2(TRZ)(BF4) Including Coherent-Domain Size Reduction Effects"]. European Journal of Inorganic Chemistry 2013 (5–6): 796–802. doi:10.1002/ejic.201201121. https://hal.archives-ouvertes.fr/hal-00794417/file/GrosjeanEJIC2013_Postprint.pdf. 
  5. ↑ https://pubs.acs.org/doi/10.1021/acs.orglett.8b03069#:~:text=Isocyanides%20are%20extraordinarily%20versatile%20building,(Figure%201a).
  6. ↑ C. Ainsworth (1960). "1,2,4-Triazole". Organic Syntheses 40: 99. doi:10.15227/orgsyn.040.0099. 
  7. ↑ Keri, Rangappa S.; Patil, Siddappa A.; Budagumpi, Srinivasa; Nagaraja, Bhari Mallanna (2015). "Triazole: A Promising Antitubercular Agent". Chemical Biology & Drug Design 86 (4): 410–423. doi:10.1111/cbdd.12527. PMID 25643871. 
  8. ↑ Kaur, Ramandeep; Ranjan Dwivedi, Ashish; Kumar, Bhupinder; Kumar, Vinod (2016). "Recent Developments on 1,2,4-Triazole Nucleus in Anticancer Compounds: A Review". Anti-Cancer Agents in Medicinal Chemistry 16 (4): 465–489. doi:10.2174/1871520615666150819121106. PMID 26286663. 
  9. ↑ Kathiravan, Muthu K.; Salake, Amol B.; Chothe, Aparna S.; Dudhe, Prashik B.; Watode, Rahul P.; Mukta, Maheshwar S.; Gadhwe, Sandeep (2012). "The biology and chemistry of antifungal agents: A review". Bioorganic & Medicinal Chemistry 20 (19): 5678–5698. doi:10.1016/j.bmc.2012.04.045. PMID 22902032. 
  10. ↑ Tesfahun, Wakjira (January 1, 2018). Yildiz, Fatih. ed. "A review on: Response of crops to paclobutrazol application". Cogent Food & Agriculture 4 (1): 1–9. doi:10.1080/23311932.2018.1525169. Bibcode: 2018CogFA...425169T. 
  11. ↑ Haasnoot, Jaap G. (2000). "Mononuclear, oligonuclear and polynuclear metal coordination compounds with 1,2,4-triazole derivatives as ligands". Coordination Chemistry Reviews 200-202: 131–185. doi:10.1016/S0010-8545(00)00266-6. 
  12. ↑ Jensen, James O. (Feb 2003). "Vibrational frequencies and structural determinations of urazole". Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 59 (3): 637–650. doi:10.1016/S1386-1425(02)00210-X. 



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