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Full structural formula Skeletal formula with numbers
Ball-and-stick model Space-filling model
CAS number 288-13-1 YesY
PubChem 1048
ChemSpider 1019 YesY
DrugBank DB02757
KEGG C00481 YesY
ChEBI CHEBI:17241 YesY
Jmol-3D images Image 1
Molecular formula C3H4N2
Molar mass 68.08 g mol−1
Melting point 66 to 70 °C (151 to 158 °F; 339 to 343 K)
Boiling point 186 to 188 °C (367 to 370 °F; 459 to 461 K)
Acidity (pKa) 14.0
Basicity (pKb) 2.5
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Pyrazole is the organic compound with the formula C3H3N2H. It is a heterocycle characterized by a 5-membered ring of three carbon atoms and two adjacent nitrogen centres. Pyrazoles are also the class of compounds that have the ring C3N2 with adjacent nitrogen centres.[1] A notable drug containing a pyrazole ring is Celebrex.

Preparation and reactions[edit]

Pyrazoles are synthesized by the reaction of α,β-unsaturated aldehydes with hydrazine and subsequent dehydrogenation:[2]

Pyrazoles synthesis.png

Substituted pyrazoles are prepared by condensation of 1,3-diketones with hydrazine. For example, acetylacetone and hydrazine gives 3,5-dimethylpyrazole:[3]

CH3C(O)CH2C(O)CH3 + N2H4 → (CH3)2C3HN2H + 2 H2O


The term pyrazole was given to this class of compounds by German Chemist Ludwig Knorr in 1883.[citation needed] In a classical method developed by German chemist Hans von Pechmann in 1898, pyrazole was synthesized from acetylene and diazomethane.[4]

Conversion to scorpionates[edit]

Pyrazoles react with potassium borohydride to form a class of ligands known as scorpionate. Pyrazole itself reacts with potassium borohydride at high temperatures (~200 °C) to form a tridentate ligand known as Tp ligand:

KBH4 + 3 C3H3N2H → KBH(C3H3N2)3 + 3 H2

Occurrence and uses[edit]

Celecoxib, a pyrazole derivative used as an analgesic

In medicine, derivatives of pyrazoles are used for their analgesic, anti-inflammatory, antipyretic, antiarrhythmic, tranquilizing, muscle relaxing, psychoanaleptic, anticonvulsant, monoamineoxidase inhibiting, antidiabetic and antibacterial activities.

In 1959, the first natural pyrazole, 1-pyrazolyl-alanine, was isolated from seeds of watermelons[5][6]

Related heterocycles[edit]

Imidazole is an analog of pyrazole with two non-adjacent nitrogen atoms. In isoxazole, another analog, the nitrogen atom in position 1 replaced by oxygen.


  1. ^ Eicher, T.; Hauptmann, S. (2003). The Chemistry of Heterocycles: Structure, Reactions, Syntheses, and Applications (2nd ed.). Wiley-VCH. ISBN 3-527-30720-6. 
  2. ^ Review article (properties, biological activities, syntheses of pyrazoles): A. Schmidt, A. Dreger (2011). "Recent Advances in the Chemistry of Pyrazoles. Properties, Biological Activities, and Syntheses". Curr. Org. Chem 15 (9): 1423–1463. doi:10.2174/138527211795378263. 
  3. ^ William S. Johnson and Robert J. Highet (1963), "3,5-Dimethylpyrazole", Org. Synth. ; Coll. Vol. 4: 351 
  4. ^ Pyrazol aus Acetylen und Diazomethan H. v. Pechmann Berichte der deutschen chemischen Gesellschaft Volume 31 Issue 3, Pages 2950–51, 1898 doi:10.1002/cber.18980310363
  5. ^ Fowden; Noe, Ridd and White, (1959). Proc. Chem. SOC.,: 131. 
  6. ^ Noe, F F; L Fowden (1959). "alpha-Amino-beta-(pyrazolyl-N) propionic acid: a new amino-acid from Citrullus vulgaris (water melon)". Nature 184: 69–70. doi:10.1038/184069a0. ISSN 0028-0836. 

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Pyrazole — Please support Wikipedia.
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71 news items

Business Wire (press release)
Wed, 05 Nov 2014 10:56:15 -0800

The report provides key statistics on the market status of the 5-Amino-1-(2-Hydroxyethyl) Pyrazole manufacturers and is a valuable source of guidance and direction for companies and individuals interested in the industry. Firstly, the report provides a ...
Nashville Post (subscription)
Wed, 03 Dec 2014 10:19:05 -0800

US 8,901,125 entitled SUBSTITUTED BICYCLIC ALKOXY PYRAZOLE ANALOGS AS ALLOSTERIC MODULATORS OF MGLUR5 RECEPTORS invented by P. Jeffrey Conn, Brentwood, TN; Craig W. Lindsley, Brentwood, TN; Shaun R. Stauffer, Brentwood, TN ...
Futura Sciences
Thu, 27 Nov 2014 08:33:16 -0800

Des amides de pyrazole pourraient fournir de nouveaux traitements antipaludéens. Ces composés dérèglent les concentrations de sodium dans les cellules du parasite, ce qui provoque une entrée massive d'eau, puis le gonflement et l'explosion des cellules ...
Mon, 10 Nov 2014 08:00:25 -0800

The team demonstrated the effectiveness of the technique by using it to modify a wide variety of heterocyclic structures that are frequently present in drug molecules, including furans, benzofurans and benzothiophenes; indole, pyrrole, thiazole ...
Pharmaceutical Technology Magazine
Mon, 10 Nov 2014 19:27:30 -0800

The main structural feature of Taselisib is a seven-membered benzoxazepine core that is substituted with a functionalized pyrazole at one end and an N-isopropyl-3-methyl-1,2,4-triazole heterocycle at the other end. The discovery route to prepare the ...


Fri, 12 Sep 2014 05:08:05 -0700

Pfizer, Inc., is a major American developer of pharmaceutical medications and vaccines for a wide spectrum of medical disciplines. The majority of Pfizer's business is operated in the northeastern United States, where the company has its corporate ...


Fri, 14 Nov 2014 02:53:09 -0800

This structure is held together by a combination of [N–H···N] hydrogen bonds between the terminal ​pyrazole rings and [π···π] stacking between the electron-rich pyrazoles and electron-poor ​tetrafluorobenzenes. Such a synergistic arrangement makes this ...
Chemical Watch (subscription)
Thu, 18 Sep 2014 09:07:30 -0700

ipconazole (ISO), expected by 14 November. It will cover the endpoints of reproductive 2; STOT RE 2; acute toxicity 4; aquatic acute 1; and aquatic chronic 1;; 5-fluoro-1,3-dimethyl-N-[2-(4-methylpentan-2-yl)phenyl]-1H-pyrazole-4-carboxamide. Expected ...

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