Pyrazolone

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Chemical compound

title: "Pyrazolone" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["pyrazolones"] description: "Chemical compound" topic_path: "general/pyrazolones" source: "https://en.wikipedia.org/wiki/Pyrazolone" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary 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.

Structure and synthesis

Pyrazolone can exist in two isomers: 3-pyrazolone and 4-pyrazolone. | 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)

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.

:[[File:Lactam-Lactim-Tautomerie Pyrazolone.svg|class=skin-invert-image|left|400px|frameless]]

The first synthesis of pyrazolones was reported in 1883 by Ludwig Knorr, via a condensation reaction between ethyl acetoacetate and phenylhydrazine. :[[File:KnorrPrep.png|class=skin-invert-image|left|420px|frameless]] Many pyrazolones are produced by functionalization of preformed pyrazolones.

Applications

Pharmaceuticals

::figure[src="https://upload.wikimedia.org/wikipedia/commons/f/f2/Phenazone2DCSD.svg" caption="[[Antipyrine]] (phenazone), the earliest pyrazolone based drug"] ::

Pyrazolones are amongst the oldest synthetic pharmaceuticals, starting with the introduction of antipyrine (phenazone) in 1880s. 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.

The basic structure has been also used in a number of newer drugs of other effects. 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.

Ligands

Pyrazolones have been studied as ligands.

References

References

  1. (2000). "Kirk-Othmer Encyclopedia of Chemical Technology".
  2. (July 1883). "Einwirkung von Acetessigester auf Phenylhydrazin". Berichte der Deutschen Chemischen Gesellschaft.
  3. (1986). "Pyrazolone Derivatives". Drugs.
  4. (December 1997). "The early history of non-opioid analgesics". Acute Pain.
  5. (2020). "Pyrazolone structural motif in medicinal chemistry: Retrospect and prospect". European Journal of Medicinal Chemistry.
  6. (2020). "Chemical reactivity and uses of 1-phenyl-3-methyl-5-pyrazolone (PMP), also known as edaravone". Bioorganic & Medicinal Chemistry.
  7. (June 2007). "Coordination modes of 5-pyrazolones: A solid-state overview". Coordination Chemistry Reviews.

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::

pyrazolones