# Pyrazole

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Pyrazole Names Preferred IUPAC name 1H-Pyrazole[1] Systematic IUPAC name 1,2-Diazacyclopenta-2,4-diene Other names 1,2-Diazole Identifiers CAS Number 288-13-1 Y 3D model (JSmol) Interactive image Beilstein Reference 103775 ChEBI CHEBI:17241 Y ChEMBL ChEMBL15967 Y ChemSpider 1019 Y DrugBank DB02757 Y ECHA InfoCard 100.005.471 EC Number 206-017-1 Gmelin Reference 1360 KEGG C00481 Y PubChem CID 1048 UNII 3QD5KJZ7ZJ Y CompTox Dashboard (EPA) DTXSID2059774 InChI InChI=1S/C3H4N2/c1-2-4-5-3-1/h1-3H,(H,4,5) Y Key: WTKZEGDFNFYCGP-UHFFFAOYSA-N Y InChI=1/C3H4N2/c1-2-4-5-3-1/h1-3H,(H,4,5) Key: WTKZEGDFNFYCGP-UHFFFAOYAW SMILES c1cn[nH]c1 Properties Chemical formula C3H4N2 Molar mass 68.079 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 Hazards GHS labelling:[2] Pictograms Signal word Danger Hazard statements H302, H311, H315, H318, H319, H335, H372, H412 Precautionary statements P260, P262, P264, P264+P265, P270, P271, P273, P280, P301+P317, P302+P352, P304+P340, P305+P351+P338, P305+P354+P338, P316, P317, P319, P321, P330, P332+P317, P337+P317, P361+P364, P362+P364, P403+P233, P405, P501 Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Chemical compound

**Pyrazole** is an [organic compound](/source/Organic_compound) with the [formula](/source/Chemical_formula) (CH)3N2H. It is a [heterocycle](/source/Heterocycle) characterized as an [azole](/source/Azole) with a 5-membered ring of three [carbon](/source/Carbon) atoms and two adjacent nitrogen atoms, which are in [ortho-substitution](/source/Arene_substitution_pattern). Pyrazoles are also a class of compounds that have the ring C3N2 with adjacent nitrogen atoms. Pyrazole itself has few applications but many substituted pyrazoles are of commercial interest. Notable drugs containing a pyrazole ring are [celecoxib](/source/Celecoxib) (celebrex) and the anabolic steroid [stanozolol](/source/Stanozolol).

## Properties

Pyrazole is a weak base, with p*K*b 11.5 (p*K*a of the conjugate acid 2.49 at 25 °C).[3] According to [X-ray crystallography](/source/X-ray_crystallography), the compound is planar. The two C-N distances are similar, both near 1.33 Å[4]

## History

The term pyrazole was given to this class of compounds by German Chemist [Ludwig Knorr](/source/Ludwig_Knorr) in 1883.[5] In a classical method developed by German chemist [Hans von Pechmann](/source/Hans_von_Pechmann) in 1898, pyrazole was synthesized from [acetylene](/source/Acetylene) and [diazomethane](/source/Diazomethane).[6]

## Preparation

Pyrazoles are synthesized by the reaction of α,β-unsaturated [aldehydes](/source/Aldehyde) with [hydrazine](/source/Hydrazine) and subsequent [dehydrogenation](/source/Dehydrogenation):[7]

Substituted pyrazoles are prepared by condensation of 1,3-[diketones](/source/Diketone) with hydrazine ([Knorr](/source/Knorr_pyrrole_synthesis)-type reactions).[8][9] For example, [acetylacetone](/source/Acetylacetone) and [hydrazine](/source/Hydrazine) gives 3,5-dimethylpyrazole:[10]

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

A wide variety of pyrazoles can be made so:[8]

## Occurrence and uses

[Celecoxib](/source/Celecoxib), a pyrazole-derived analgesic

In 1959, the first natural pyrazole, [1-pyrazolyl-alanine](https://en.wikipedia.org/w/index.php?title=1-pyrazolyl-alanine&action=edit&redlink=1), was isolated from seeds of [watermelons](/source/Watermelons).[11][12]

In medicine, derivatives of pyrazole are widely used,[13] including [celecoxib](/source/Celecoxib) and similar [COX-2 inhibitors](/source/COX-2_inhibitors), [zaleplon](/source/Zaleplon), [betazole](/source/Betazole), and [CDPPB](/source/CDPPB).[14] The pyrazole ring is found within a variety of pesticides as fungicides, insecticides and herbicides,[13] including [fluoxapiprolin](https://en.wikipedia.org/w/index.php?title=Fluoxapiprolin&action=edit&redlink=1),[15] [fenpyroximate](https://en.wikipedia.org/w/index.php?title=Fenpyroximate&action=edit&redlink=1), [fipronil](/source/Fipronil), [tebufenpyrad](/source/Tebufenpyrad) and [tolfenpyrad](https://en.wikipedia.org/w/index.php?title=Tolfenpyrad&action=edit&redlink=1).[16] Pyrazole moieties are listed among the highly used ring systems for small molecule drugs by the US FDA[17]

[3-(Difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic acid](/source/3-(Difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic_acid) is used in the manufacture of six commercial fungicides which are inhibitors of [succinate dehydrogenase](/source/Succinate_dehydrogenase).[18][19]

Pyrazole is an inhibitor of the [alcohol dehydrogenase](/source/Alcohol_dehydrogenase) enzyme, and, as such, is used as an adjuvant with ethanol, to induce alcohol dependency in experimental laboratory mice.[20]

### Conversion to scorpionates

Pyrazoles react with [potassium borohydride](/source/Potassium_borohydride) to form a class of ligands known as [scorpionate](/source/Scorpionate_ligand). Pyrazole itself reacts with [potassium borohydride](/source/Potassium_borohydride) at high temperatures (~200 °C) to form a [tridentate ligand](/source/Tridentate_ligand) known as [Tp ligand](/source/Trispyrazolylborate):

## See also

- [3,5-dimethylpyrazole](/source/3%2C5-Dimethylpyrazole)

- [Pyrazolidine](/source/Pyrazolidine), fully saturated analogue

- [imidazole](/source/Imidazole), structural analogue of pyrazole with two *non*-adjacent nitrogen atoms.

- [isoxazole](/source/Isoxazole), another analogue, the nitrogen atom in position 1 replaced by oxygen.

## References

1. **[^](#cite_ref-iupac2013_1-0)** "Front Matter". *Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book)*. Cambridge: [The Royal Society of Chemistry](/source/Royal_Society_of_Chemistry). 2014. p. 141. [doi](/source/Doi_(identifier)):[10.1039/9781849733069-FP001](https://doi.org/10.1039%2F9781849733069-FP001). [ISBN](/source/ISBN_(identifier)) [978-0-85404-182-4](https://en.wikipedia.org/wiki/Special:BookSources/978-0-85404-182-4).

1. **[^](#cite_ref-2)** ["Pyrazole"](https://pubchem.ncbi.nlm.nih.gov/compound/1048#section=Safety-and-Hazards). *pubchem.ncbi.nlm.nih.gov*. Retrieved 17 February 2024.

1. **[^](#cite_ref-3)** ["Dissociation constants of organic acids and bases"](http://sites.chem.colostate.edu/diverdi/all_courses/CRC%20reference%20data/dissociation%20constants%20of%20organic%20acids%20and%20bases.pdf) (PDF). [Archived](https://web.archive.org/web/20170712202558/http://sites.chem.colostate.edu/diverdi/all_courses/CRC%20reference%20data/dissociation%20constants%20of%20organic%20acids%20and%20bases.pdf) (PDF) from the original on 12 July 2017.

1. **[^](#cite_ref-4)** La Cour, Troels; Rasmussen, Svend Erik; Hopf, Henning; Waisvisz, Jacques M.; Van Der Hoeven, Marcel G.; Swahn, Carl-Gunnar (1973). "The Structure of Pyrazole, C3H4N2, at 295 K and 108 K as determined by X-Ray Diffraction". *Acta Chemica Scandinavica*. **27**: 1845–1854. [doi](/source/Doi_(identifier)):[10.3891/acta.chem.scand.27-1845](https://doi.org/10.3891%2Facta.chem.scand.27-1845).

1. **[^](#cite_ref-5)** [Knorr, L.](/source/Ludwig_Knorr) (1883). ["Action of ethyl acetoacetate on phenylhydrazine. I"](https://zenodo.org/record/1425305). *Chemische Berichte*. **16**: 2597–2599. [doi](/source/Doi_(identifier)):[10.1002/cber.188301602194](https://doi.org/10.1002%2Fcber.188301602194).

1. **[^](#cite_ref-6)** [von Pechmann, Hans](/source/Hans_von_Pechmann) (1898). ["Pyrazol aus Acetylen und Diazomethan"](https://zenodo.org/record/1425922). *[Berichte der deutschen chemischen Gesellschaft](/source/Berichte_der_deutschen_chemischen_Gesellschaft)* (in German). **31** (3): 2950–2951. [doi](/source/Doi_(identifier)):[10.1002/cber.18980310363](https://doi.org/10.1002%2Fcber.18980310363).

1. **[^](#cite_ref-7)** Schmidt, Andreas; Dreger, Andrij (2011). "Recent Advances in the Chemistry of Pyrazoles. Properties, Biological Activities, and Syntheses". *[Curr. Org. Chem.](/source/Curr._Org._Chem.)* **15** (9): 1423–1463. [doi](/source/Doi_(identifier)):[10.2174/138527211795378263](https://doi.org/10.2174%2F138527211795378263).

1. ^ [***a***](#cite_ref-KnorrEx_8-0) [***b***](#cite_ref-KnorrEx_8-1) Nozari, Mohammad; Addison, Anthony W.; Reeves, Gordan T.; Zeller, Matthias; Jasinski, Jerry P.; Kaur, Manpreet; Gilbert, Jayakumar G.; Hamilton, Clifton R.; Popovitch, Jonathan M.; Wolf, Lawrence M.; Crist, Lindsay E.; Bastida, Natalia (2018). ["New Pyrazole- and Benzimidazole-derived Ligand Systems"](https://doi.org/10.1002/jhet.3155). *Journal of Heterocyclic Chemistry*. **55** (6): 1291–1307. [doi](/source/Doi_(identifier)):[10.1002/jhet.3155](https://doi.org/10.1002%2Fjhet.3155).

1. **[^](#cite_ref-Eicher_9-0)** Eicher, T.; Hauptmann, S. (2003). *The Chemistry of Heterocycles: Structure, Reactions, Syntheses, and Applications* (2nd ed.). Wiley-VCH. [ISBN](/source/ISBN_(identifier)) [3-527-30720-6](https://en.wikipedia.org/wiki/Special:BookSources/3-527-30720-6).

1. **[^](#cite_ref-10)** Johnson, William S.; Highet, Robert J. (1951). "3,5-Dimethylpyrazole". *Organic Syntheses*. **31**: 43. [doi](/source/Doi_(identifier)):[10.15227/orgsyn.031.0043](https://doi.org/10.15227%2Forgsyn.031.0043).

1. **[^](#cite_ref-11)** Fowden; Noe; Ridd; White (1959). *[Proc. Chem. Soc.](/source/Proc._Chem._Soc.)*: 131. {{[cite journal](https://en.wikipedia.org/wiki/Template:Cite_journal)}}: Missing or empty |title= ([help](https://en.wikipedia.org/wiki/Help:CS1_errors#citation_missing_title))

1. **[^](#cite_ref-12)** Noe, F. F.; Fowden, L.; Richmond, P. T. (1959). ["alpha-Amino-beta-(pyrazolyl-N) propionic acid: a new amino-acid from *Citrullus vulgaris* (water melon)"](https://doi.org/10.1038%2F184069a0). *[Nature](/source/Nature_(journal))*. **184** (4688): 69–70. [Bibcode](/source/Bibcode_(identifier)):[1959Natur.184...69B](https://ui.adsabs.harvard.edu/abs/1959Natur.184...69B). [doi](/source/Doi_(identifier)):[10.1038/184069a0](https://doi.org/10.1038%2F184069a0). [PMID](/source/PMID_(identifier)) [13804343](https://pubmed.ncbi.nlm.nih.gov/13804343). [S2CID](/source/S2CID_(identifier)) [37499048](https://api.semanticscholar.org/CorpusID:37499048).

1. ^ [***a***](#cite_ref-Kabi_13-0) [***b***](#cite_ref-Kabi_13-1) Kabi, Arup K.; Sravani, Sattu; Gujjarappa, Raghuram; et al. (2022). "Overview on Biological Activities of Pyrazole Derivatives". *Nanostructured Biomaterials*. Materials Horizons: From Nature to Nanomaterials. pp. 229–306. [doi](/source/Doi_(identifier)):[10.1007/978-981-16-8399-2_7](https://doi.org/10.1007%2F978-981-16-8399-2_7). [ISBN](/source/ISBN_(identifier)) [978-981-16-8398-5](https://en.wikipedia.org/wiki/Special:BookSources/978-981-16-8398-5).

1. **[^](#cite_ref-:0_14-0)** Faria, Jéssica Venância; Vegi, Percilene Fazolin; Miguita, Ana Gabriella Carvalho; dos Santos, Maurício Silva; Boechat, Nubia; Bernardino, Alice Maria Rolim (1 November 2017). "Recently reported biological activities of pyrazole compounds". *Bioorganic & Medicinal Chemistry*. **25** (21): 5891–5903. [doi](/source/Doi_(identifier)):[10.1016/j.bmc.2017.09.035](https://doi.org/10.1016%2Fj.bmc.2017.09.035). [ISSN](/source/ISSN_(identifier)) [0968-0896](https://search.worldcat.org/issn/0968-0896). [PMID](/source/PMID_(identifier)) [28988624](https://pubmed.ncbi.nlm.nih.gov/28988624).

1. **[^](#cite_ref-15)** ["Public Release Summary on the evaluation of the new active constituent fluoxapiprolin in the product Xivana Prime 20 SC Fungicide"](https://www.apvma.gov.au/sites/default/files/publication/98651-public_release_summary_on_the_evaluation_of_the_new_active_constituent_fluoxapiprolin_in_the_product_xivana_prime_20_sc_fungicide.pdf) (PDF). Australian Pesticides and Veterinary Medicines Authority. Retrieved 14 August 2025.

1. **[^](#cite_ref-16)** [FAO](http://www.fao.org/docrep/019/i3518e/i3518e.pdf)

1. **[^](#cite_ref-17)** Taylor, R. D.; MacCoss, M.; Lawson, A. D. G. J Med Chem 2014, 57, 5845.

1. **[^](#cite_ref-Walter_18-0)** Walter, Harald (2016). "Fungicidal Succinate-Dehydrogenase-Inhibiting Carboxamides". In Lamberth, Clemens; Dinges, Jürgen (eds.). *Bioactive Carboxylic Compound Classes: Pharmaceuticals and Agrochemicals*. Wiley. pp. 405–425. [doi](/source/Doi_(identifier)):[10.1002/9783527693931.ch31](https://doi.org/10.1002%2F9783527693931.ch31). [ISBN](/source/ISBN_(identifier)) [9783527339471](https://en.wikipedia.org/wiki/Special:BookSources/9783527339471).

1. **[^](#cite_ref-19)** Jeschke, Peter (2021). "Current Trends in the Design of Fluorine-Containing Agrochemicals". In Szabó, Kálmán; Selander, Nicklas (eds.). *Organofluorine Chemistry*. Wiley. pp. 363–395. [doi](/source/Doi_(identifier)):[10.1002/9783527825158.ch11](https://doi.org/10.1002%2F9783527825158.ch11). [ISBN](/source/ISBN_(identifier)) [9783527347117](https://en.wikipedia.org/wiki/Special:BookSources/9783527347117). [S2CID](/source/S2CID_(identifier)) [234149806](https://api.semanticscholar.org/CorpusID:234149806).

1. **[^](#cite_ref-20)** Xiao, T.; Chen, Y.; Boisvert, A.; Cole, M.; Kimbrough, A. (2023). ["Chronic Intermittent Ethanol Vapor Exposure Paired with Two-Bottle Choice to Model Alcohol Use Disorder"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11164185). *Journal of Visualized Experiments* (196). [doi](/source/Doi_(identifier)):[10.3791/65320](https://doi.org/10.3791%2F65320). [PMC](/source/PMC_(identifier)) [11164185](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11164185). [PMID](/source/PMID_(identifier)) [37427930](https://pubmed.ncbi.nlm.nih.gov/37427930).

## Further reading

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](/source/Doi_(identifier)):[10.2174/138527211796378497](https://doi.org/10.2174%2F138527211796378497).

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Adapted from the Wikipedia article [Pyrazole](https://en.wikipedia.org/wiki/Pyrazole) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Pyrazole?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.