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 centres. Pyrazoles are also the class of compounds that have the ring C3N2 with adjacent nitrogen centres. A notable drug containing a pyrazole ring is Celebrex.
Preparation and reactions
Pyrazoles are synthesized by the reaction of α,β-unsaturated aldehydes with hydrazine and subsequent dehydrogenation:
Substituted pyrazoles are prepared by condensation of 1,3-diketones with hydrazine. For example, acetylacetone and hydrazine gives 3,5-dimethylpyrazole:
- 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. In a classical method developed by German chemist Hans von Pechmann in 1898, pyrazole was synthesized from acetylene and diazomethane.
Conversion to scorpionates
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:
- KBH4 + 3 C3H3N2H → KBH(C3H3N2)3 + 3 H2
Occurrence and uses
, 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
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.
- ^ Eicher, T.; Hauptmann, S. (2003). The Chemistry of Heterocycles: Structure, Reactions, Syntheses, and Applications (2nd ed.). Wiley-VCH. ISBN 3-527-30720-6.
- ^ 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.
- ^ William S. Johnson and Robert J. Highet (1963), "3,5-Dimethylpyrazole", Org. Synth.; Coll. Vol. 4: 351
- ^ Pyrazol aus Acetylen und Diazomethan H. v. Pechmann Berichte der deutschen chemischen Gesellschaft Volume 31 Issue 3, Pages 2950–51, 1898 doi:10.1002/cber.18980310363
- ^ Fowden; Noe, Ridd and White, (1959). Proc. Chem. SOC.,: 131.
- ^ Noe, F F; L Fowden (1959). "alpha-Amino-beta-(pyrazolyl-N) propionic acid: a new amino-acid from Citrullus vulgaris (water melon)". Nature 184: 69–70. ISSN 0028-0836.
3D model of Pyrazole.
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Chemical Watch (subscription)
Thu, 18 Sep 2014 09:07:30 -0700
ipconazole (ISO), expected by 14 November. It will cover the endpoints of reproductive 2; STOT RE 2; acute toxicity 4; aquatic acute 1; and aquatic chronic 1;; 5-fluoro-1,3-dimethyl-N-[2-(4-methylpentan-2-yl)phenyl]-1H-pyrazole-4-carboxamide. Expected ...
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 ...
International Environmental Technology
Wed, 20 Aug 2014 02:17:24 -0700
The chemical formula for Cyantraniliprole is C19H14BrClN6O2 , and the International Union of Pure and Applied Chemistry name is 3-bromo-1-(3-chloro-2-pyridyl)-4′-cyano-2′-methyl-6′-(methylcarbamoyl)pyrazole-5-carboxanilide. It is similar ...
Targeted News Service (subscription)
Mon, 25 Aug 2014 11:33:45 -0700
ALEXANDRIA, Va., Aug. 25 -- Pfizer, New York, has been assigned a patent (8,809,333) developed by five co-inventors for "imidazole, pyrazole, and triazole derivatives useful as antibacterial agents." The co-inventors are Matthew Frank Brown, Stonington ...
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