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Full structural formula
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288-13-1 YesY
ChEBI CHEBI:17241 YesY
ChemSpider 1019 YesY
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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)
Basicity (pKb) 11.5
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Pyrazole is an 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. Pyrazole is a weak base, with pKb 11.5 (pKa of the conjugated acid 2.49 at 25 °C).[1] Pyrazoles are also a class of compounds that have the ring C3N2 with adjacent nitrogen atoms.[2] 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:[3]

Pyrazoles synthesis.png

Substituted pyrazoles are prepared by condensation of 1,3-diketones with hydrazine. For example, acetylacetone and hydrazine gives 3,5-dimethylpyrazole:[4]

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.[5]

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[6][7]

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. ^ Dissociation constants of organic acids and bases
  2. ^ Eicher, T.; Hauptmann, S. (2003). The Chemistry of Heterocycles: Structure, Reactions, Syntheses, and Applications (2nd ed.). Wiley-VCH. ISBN 3-527-30720-6. 
  3. ^ 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. 
  4. ^ William S. Johnson and Robert J. Highet (1963). "3,5-Dimethylpyrazole". Org. Synth. ; Coll. Vol. 4, p. 351 
  5. ^ H. v. Pechmann (1898). "Pyrazol aus Acetylen und Diazomethan". Berichte der deutschen chemischen Gesellschaft 31 (3): 2950–51. doi:10.1002/cber.18980310363. 
  6. ^ Fowden; Noe, Ridd and White (1959). Proc. Chem. SOC.: 131.  Missing or empty |title= (help)
  7. ^ 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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67 news items

The Biological SCENE

The Biological SCENE
Fri, 18 Sep 2015 04:15:00 -0700

To run the reaction, chemists simply mix an arene with either an aromatic nitrogen heterocycle, such as imidazole or pyrazole, or an ammonia equivalent, such as ammonium carbamate, in the presence of an acridinium catalyst and the cocatalyst 2,2,6 ...


Wed, 29 Jul 2015 02:51:12 -0700

The pyrazole salt has been found to combine good stability as a raw material and good shade intensity with a range of common couplers when formulated in hair dyeing composition. Submission I on the new hair dye was transmitted by Cosmetics Europe in ...

Toledo Blade

Toledo Blade
Sun, 06 Sep 2015 21:52:30 -0700

We have discovered that when the TRPC3 channel is closed by a drug called Pyrazole 10, fewer cells are dying. We then investigated how these cells were saved from dying. From our previous investigations and the work of others in this field, we were ...
Chemical Watch (subscription)
Fri, 24 Jul 2015 03:18:45 -0700

The hair dye ingredient 1-hexyl 4,5-diamine pyrazole sulfate is safe for use at a maximum on-head concentration of 1.0%, the European Commission's Scientific Committee on Consumer Safety (SCCS) has concluded. The committee notes in its scientific ...
Fri, 19 Jun 2015 05:01:13 -0700

Selective and direct inhibition of TRPC3 channels underlies biological activities of a pyrazole compound. Proc Natl Acad Sci USA 2009; 106: 5400–5405. | Article | PubMed |; Harguindey S, Arranz JL, Polo Orozco JD, Rauch C, Fais S, Cardone RA et al.
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) ...
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 ...
Business Wire (press release)
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 ...

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