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Pyrazole

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Pyrazole

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IUPAC name
Pyrazole
Other names
1,2-Diazole
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288-13-1 7pxY ChEBI CHEBI:17241 7pxY ChEMBL ChEMBL15967 7pxY ChemSpider 1019 7pxY DrugBank DB02757 7pxY Jmol-3D images Image KEGG C00481 7pxY PubChem Template:Chembox PubChem/format colspan=2 style="background:#f8eaba; border-top:2px solid transparent; border-bottom:2px solid transparent; text-align:center;" #REDIRECTmw:Help:Magic words#Other
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C3H4N2 Molar mass Lua error in Module:Math at line 495: attempt to index field 'ParserFunctions' (a nil value). g·mol−1 Melting point Script error: No such module "convert". Boiling point Script error: No such module "convert". Acidity (pKa) 14.0 Basicity (pKb) 2.5
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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

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

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

History

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

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

File:Celecoxib structure.png
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

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.

References

  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. ISSN 0028-0836. doi:10.1038/184069a0. 

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:10.2174/138527211796378497.