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|Section2= |Section3= |Section8= }} 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 p''K''b 11.5 (p''K''a of the conjugated acid 2.49 at 25 °C).〔(Dissociation constants of organic acids and bases )〕 Pyrazoles are also a class of compounds that have the ring C3N2 with adjacent nitrogen atoms.〔 〕 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: : 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 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pyrazole」の詳細全文を読む スポンサード リンク
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