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Full structural formula
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288-13-1 YesY
ChEBI CHEBI:17241 YesY
ChemSpider 1019 YesY
DrugBank DB02757 YesY
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KEGG C00481 YesY
PubChem 1048
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 is 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 atoms. Pyrazoles are also the class of compounds that have the ring C3N2 with adjacent nitrogen atoms.[1] A notable drug containing a pyrazole ring is celecoxib (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. ^ 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, p. 351 
  4. ^ H. v. Pechmann (1898). "Pyrazol aus Acetylen und Diazomethan". Berichte der deutschen chemischen Gesellschaft 31 (3): 2950–51. doi:10.1002/cber.18980310363. 
  5. ^ Fowden; Noe, Ridd and White (1959). Proc. Chem. SOC.: 131.  Missing or empty |title= (help)
  6. ^ Noe, F F; L Fowden; Richmond, P. T. (1959). "alpha-Amino-beta-(pyrazolyl-N) propionic acid: a new amino-acid from Citrullus vulgaris (water melon)". Nature 184 (4688): 69–70. Bibcode:1959Natur.184...69B. doi:10.1038/184069a0. ISSN 0028-0836. 

Further reading[edit]

A. Schmidt, A. Dreger (2011). "Recent Advances in the Chemistry of Pyrazoles. Part 2. Reactions and N-Heterocyclic Carbenes of Pyrazole". Curr. Org. Chem. 15 (16): 2897 – 2970. doi:10.2174/138527211796378497. 

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Pyrazole — Please support Wikipedia.
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Illinois State University Stories

Illinois State University Stories
Fri, 29 May 2015 09:07:30 -0700

David L. Cedeño and Christopher Hamaker, CHE, published “Synthesis and Structure of a Trigonal Planar Complex with Pyrazole Ligands, [Cu(3,5-Ph2PzH)3][Cl],” in the Journal of Chemical Crystallography. Jennifer Sharkey and Chad Kahl, Milner Library, ...
Digital Journal
Tue, 19 May 2015 09:41:15 -0700

Methyl acetoacetate is used as a starting material in the production of cyclic compounds such as coumarine and pyrazole. It is used as starting material in production of aceto- acetic esters. In perfume and cosmetic industry, it used as an solvent for ...
Mon, 20 Apr 2015 14:33:45 -0700

On Wednesday, April 22, Epizyme will present data on the identification of an aryl pyrazole as the first small molecule PRMT6 inhibitor, created from the Company's proprietary product platform. PRMT6 is a histone methyltransferase that is overexpressed ...


Fri, 14 Nov 2014 02:52:30 -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 ...


Fri, 12 Sep 2014 05:00:00 -0700

U.S. Patent No. 8809333, which is titled Imidazole, Pyrazole, and Triazole Derivatives Useful as Antibacterial Agents, protects novel hydroxamic derivatives used to treat bacterial infections by inhibiting LpxC, a catalyst enzyme necessary for lipid ...
Seeking Alpha
Tue, 28 Apr 2015 17:33:45 -0700

CARM1 is an HMT that has been implicated in a variety of solid tumors and hematologic malignancies. We also presented data on the identification of an aryl pyrazole as the first small molecule PRMT6 inhibitor created from Epizyme's proprietary product ...
Mon, 27 Apr 2015 07:24:05 -0700

Male OE-NPYDβH and WT mice (n=9–12/group) received daily i.p. injections of 3 mg kg−1 CB1-receptor inverse agonist AM251 [N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] (Tocris Bioscience, Bristol, UK) ...
Pharmaceutical Technology Magazine
Mon, 10 Nov 2014 20:37:17 -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 ...

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