December 07, 2020
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Triazoles are a family of five-membered rings that contain three nitrogen atoms and two double bonds. The four triazole isomers (1H-1,2,3-, 2H-1,2,3-, 1H-1,2,4-, and 2H-1,2,4-) differ by the arrangement of the nitrogen atoms and the locations of their three hydrogen atoms. All of the triazoles are planar and aromatic.

1H-1,2,3-Triazole, like all triazoles, is highly soluble in water. In aqueous solution it tautomerizes to its 2H-isomer with a 1H/2H ratio of ≈1:2. Both isomers have essentially the same melting and boiling points, making them very difficult to separate from each other.

In 1910, German chemists Otto Dimroth* and Gustav Fester synthesized 1H-1,2,3-triazole by heating a solution of hydrazoic acid (HN3) and acetylene at 100 ºC for 70 h. Sodium azide can be used in place of HN3 if the solution is acidified. Dimroth is best known for his discovery of the eponymous rearrangement of amine-substituted 1,2,3-triazoles, in which the substituent nitrogen atom and its nearest ring nitrogen atom exchange places.

The 1,2,3-triazole moiety is considered to be a pharmacophore in that it can interact with specific biological targets. It is a component of such pharmaceuticals as the cephalosporin antibiotic cefatrizine; tazobactam, which broadens the spectrum of certain antibiotics; and carboxyamidotriazole, a calcium channel blocker that may be useful to combat cancer.

1H-1,2,3-Triazole hazard information

Hazard class* Hazard statement
Skin corrosion/irritation, category 2 H315—Causes skin irritation Chemical Safety Warning
Serious eye damage/eye irritation, category 2A H319—Causes serious eye irritation Chemical Safety Warning
Specific target organ toxicity, single exposure, respiratory tract irritation, category 3 H335—May cause respiratory irritation Chemical Safety Warning

*Globally Harmonized System of Classification and Labeling of Chemicals.  
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MOTW update

Baricitinib was the Molecule of the Week for March 2, 2020. It is a janus kinase inhibitor that initially showed promise against rheumatoid arthritis. This past February, researchers reported that it may limit the effects of COVID-19 by attacking a specific enzyme in the virus. On November 19, the US Food and Drug Administration issued an emergency use authorization for the combination and remdesivir (MOTW for April 6, 2020) “for the treatment of suspected or laboratory-confirmed COVID-19 in hospitalized adults and pediatric patients two years of age or older requiring supplemental oxygen, invasive mechanical ventilation, or extracorporeal membrane oxygenation.”

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1H-1,2,3-Triazole fast facts

CAS Reg. No. 288-36-8
Empirical formula C2H3N3
Molar mass 69.07 g/mol
Appearance Colorless to yellow liquid
Melting point 23–25 ºC
Boiling point 203 ºC 
Water solubility Highly soluble
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