{{Short description|Chemical compound}} '''Pyrazolone''' is 5-membered heterocycle containing two adjacent nitrogen atoms. It can be viewed as a derivative of pyrazole possessing an additional carbonyl (C=O) group. Compounds containing this functional group are useful commercially in analgesics and dyes.<ref name=KO>{{cite book |doi=10.1002/0471238961.1625180111151814.a01|chapter=Pyrazoles, Pyrazolines, and Pyrazolones|title=Kirk-Othmer Encyclopedia of Chemical Technology|year=2000|last1=Kornis|first1=Gabe I.|isbn=0-471-23896-1}}</ref>
==Structure and synthesis== Pyrazolone can exist in two isomers: 3-pyrazolone and 4-pyrazolone. <div class="skin-invert-image">{{multiple image | total_width = 300 | align = left | image1=1,2-Dihydro-3H-pyrazol-3-one Structural Formula V1.svg | image2=4H-Pyrazol-4-one Structural Formula V1.svg | footer = Chemical structures of 3-pyrazolone (left) and 4-pyrazolone (right) }}</div>{{clear-left}}
These isomers can interconvert via lactam–lactim and imine–enamine tautomerism; these conversion often display photochromism. For pyrazolone derivatives, the 3-pyrazolone isomer can be stabilized with ''N''-alkyl or ''N''-aryl substituents.
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The first synthesis of pyrazolones was reported in 1883 by Ludwig Knorr, via a condensation reaction between ethyl acetoacetate and phenylhydrazine.<ref>{{cite journal|last1=Knorr|first1=Ludwig|title=Einwirkung von Acetessigester auf Phenylhydrazin|journal=Berichte der Deutschen Chemischen Gesellschaft|date=July 1883|volume=16|issue=2|pages=2597–2599|doi=10.1002/cber.188301602194|language=German|url=https://zenodo.org/record/1425305}}</ref> :class=skin-invert-image|left|420px|frameless{{clear-left}} Many pyrazolones are produced by functionalization of preformed pyrazolones.
==Applications== ===Pharmaceuticals=== {{missing information|section|safety profile of analgesics (which ones are withdrawn and whether there is a common theme in adverse effects)|date=August 2022}} [[File:Phenazone2DCSD.svg|class=skin-invert-image|thumb|200px|right|Antipyrine (phenazone), the earliest pyrazolone based drug]]
Pyrazolones are amongst the oldest synthetic pharmaceuticals, starting with the introduction of antipyrine (phenazone) in 1880s.<ref name=pharma1>{{cite journal|last1=Brogden|first1=Rex N.|s2cid=2761563|title=Pyrazolone Derivatives|journal=Drugs|date=1986|volume=32|issue=Supplement 4|pages=60–70|doi=10.2165/00003495-198600324-00006|pmid=3552586}}</ref><ref>{{cite journal|last1=Brune|first1=Kay|title=The early history of non-opioid analgesics|journal=Acute Pain|date=December 1997|volume=1|issue=1|pages=33–40|doi=10.1016/S1366-0071(97)80033-2}}</ref> The compounds generally act as analgesics and include dipyrone (Metamizole), aminophenazone, ampyrone, famprofazone, morazone, nifenazone, piperylon and propyphenazone. Of these dipyrone (the so-called "Mexican aspirin") is perhaps the most widely used.<ref name=pharma1 /><ref name=Zhao>{{cite journal |doi=10.1016/j.ejmech.2019.111893|title=Pyrazolone structural motif in medicinal chemistry: Retrospect and prospect|year=2020|last1=Zhao|first1=Zefeng|last2=Dai|first2=Xufen|last3=Li|first3=Chenyang|last4=Wang|first4=Xiao|last5=Tian|first5=Jiale|last6=Feng|first6=Ying|last7=Xie|first7=Jing|last8=Ma|first8=Cong|last9=Nie|first9=Zhuang|last10=Fan|first10=Peinan|last11=Qian|first11=Mingcheng|last12=He|first12=Xirui|last13=Wu|first13=Shaoping|last14=Zhang|first14=Yongmin|last15=Zheng|first15=Xiaohui|journal=European Journal of Medicinal Chemistry|volume=186|article-number=111893|pmid=31761383|pmc=7115706}}</ref>
The basic structure has been also used in a number of newer drugs of other effects.<ref name=Zhao/> Edaravone is useful for prevention and/or therapy of arterial wall injury.<ref>{{cite journal |doi=10.1016/j.bmc.2020.115463|title=Chemical reactivity and uses of 1-phenyl-3-methyl-5-pyrazolone (PMP), also known as edaravone|year=2020|last1=Bailly|first1=Christian|last2=Hecquet|first2=Paul-Emile|last3=Kouach|first3=Mostafa|last4=Thuru|first4=Xavier|last5=Goossens|first5=Jean-François|journal=Bioorganic & Medicinal Chemistry|volume=28|issue=10|article-number=115463|pmid=32241621|s2cid=214766793 }}</ref> Eltrombopag is used to address low blood platelet count.
===Dyes=== Pyrazolone groups are present in several important dyes. They are commonly used in combination with azo groups to give a sub-family of azo dyes; sometimes referred to as azopyrazolones (tartrazine, orange B, mordant red 19, yellow 2G). Acid Yellow 17, Acid Yellow 23 (tartrazine), Pigment Yellow 13, and Pigment Red 38 are produced on the multi-ton scale annually.<ref name=KO/>
===Ligands=== Pyrazolones have been studied as ligands.<ref>{{cite journal|last1=CASAS|first1=J|last2=GARCIATASENDE|first2=M|last3=SANCHEZ|first3=A|last4=SORDO|first4=J|last5=TOUCEDA|first5=A|title=Coordination modes of 5-pyrazolones: A solid-state overview|journal=Coordination Chemistry Reviews|date=June 2007|volume=251|issue=11–12|pages=1561–1589|doi=10.1016/j.ccr.2007.02.010}}</ref>
==References== {{reflist}}
==External links== * {{MeshName|Pyrazolones}} * [https://pubchem.ncbi.nlm.nih.gov/compound/351317 Pubchem - 3-Pyrazolone] * [https://pubchem.ncbi.nlm.nih.gov/compound/19753145 Pubchem - 4-Pyrazolone]
{{Anti-inflammatory and antirheumatic products}}
{{Authority control}} Category:Pyrazolones