Pyrazole

Pyrazole
IUPAC name Pyrazole
Other names 1,2-Diazole
Identifiers
CAS number	288-13-1 Y
PubChem	1048
ChemSpider	1019 Y
DrugBank	DB02757
KEGG	C00481 Y
ChEBI	CHEBI:17241 Y
ChEMBL	CHEMBL15967 Y
Jmol-3D images	Image 1
SMILES n1cccn1
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
Properties
Molecular formula	C3H4N2
Molar mass	68.08 g mol−1
Melting point	66-70 °C
Boiling point	186-188 °C
Acidity (pKa)	14.0
Basicity (pKb)	2.5
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Pyrazole refers both to the class of simple aromatic ring organic compounds of the heterocyclic diazole series characterized by a 5-membered ring structure composed of three carbon atoms and two nitrogen atoms in adjacent positions, and to the unsubstituted parent compound. Being so composed and having pharmacological effects on humans, they are classified as alkaloids, although they are rare in nature. In 1959, the first natural pyrazole, 1-pyrazolyl-alanine, was isolated from seeds of watermelons. The term pyrazole was given to this class of compounds by Ludwig Knorr in 1883.

Reactions

• In a classical method developed by H. Pechmann in 1898, pyrazole can be synthesized from acetylene and diazomethane.

• Pyrazoles are produced synthetically through the reaction of α,β-unsaturated aldehydes with hydrazine and subsequent dehydrogenation:

• Pyrazoles react with potassium borohydride to form a class of ligands known as scorpionate. Pyrazole itself reacts with potassium borohydride to form a tridentate ligand known as Tp ligand.

Uses

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.

See also

• Imidazole, an analog with two non-adjacent nitrogen atoms
• Isoxazole, an analog with the nitrogen atom in position 1 replaced by oxygen
• Pyrrole, an analog with only one nitrogen atom, in position 1
• Pyrazolone
• Simple aromatic rings
• Triazoles, analogs with three nitrogen atoms

External links

• 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.