Pyrazolone is 5-membered

heterocycle A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

containing two adjacent

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

atoms. It can be viewed as a derivative of

pyrazole 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, which are in ortho-substitution. Pyrazole is a weak base, with p''K''b 11.5 ( ...

possessing an additional

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containi ...

(C=O) group. Compounds containing this functional group are useful commercially in

analgesics An analgesic drug, also called simply an analgesic (American English), analgaesic (British English), pain reliever, or painkiller, is any member of the group of drugs used to achieve relief from pain (that is, analgesia or pain management). It ...

and dyes.

Structure and synthesis

Pyrazolone can exist in two isomers: 3-pyrazolone and 4-pyrazolone. These isomers can interconvert via lactam–lactim and imine–enamine

tautomerism Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hyd ...

; these conversion often display

photochromism Photochromism is the reversible transformation of a chemical species (photoswitch) between two forms by the absorption of electromagnetic radiation (photoisomerization), where the two forms have different absorption spectra. In plain language, th ...

. For pyrazolone derivatives, the 3-pyrazolone isomer can be stabilized with ''N''-alkyl or ''N''-aryl substituents. : Lactam-Lactim-Tautomerie Pyrazolone

The first synthesis of pyrazolones was reported in 1883 by

Ludwig Knorr Ludwig Knorr (2 December 1859 – 4 June 1921) was a German chemist. Together with Carl Paal, he discovered the Paal–Knorr synthesis, and the Knorr quinoline synthesis and Knorr pyrrole synthesis are also named after him. The synthesis in 18 ...

, via a condensation reaction between

ethyl acetoacetate The organic compound ethyl acetoacetate (EAA) is the ethyl ester of acetoacetic acid. It is a colorless liquid. It is widely used as a chemical intermediate in the production of a wide variety of compounds. It is used as a flavoring for food. ...

and

phenylhydrazine Phenylhydrazine is the chemical compound with the formula . It is often abbreviated as . It is also found in edible mushrooms. Properties Phenylhydrazine forms monoclinic prisms that melt to an oil around room temperature which may turn yellow ...

. :

Many pyrazolones are produced by functionalization of preformed pyrazolones.

Applications

Pharmaceuticals

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

and include dipyrone (Metamizole), aminophenazone, ampyrone, famprofazone,

morazone Morazone (Novartrina, Orsimon, Rosimon-Neu, Tarcuzate) is a nonsteroidal anti-inflammatory drug (NSAID), originally developed by the German pharmaceutical company Ravensberg in the 1950s, which is used as an analgesic. It produces phenmetrazine a ...

, nifenazone, piperylon and

propyphenazone Propyphenazone (known as isopropylantipyrine in Japan) is a derivative of phenazone with similar analgesic and antipyretic effects. Originally patented in 1931, propyphenazone is marketed as a combination formulation with paracetamol and caffe ...

. Of these dipyrone is perhaps the most widely used. The basic structure has been also used in a number of newer drugs of other effects. Edaravone is useful for prevention and/or therapy of arterial wall injury. 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 group Azo compounds are organic compounds bearing the functional group diazenyl (, in which R and R′ can be either aryl or alkyl groups). IUPAC defines azo compounds as: "Derivatives of diazene (diimide), , wherein both hydrogens are substituted ...

s to give a sub-family of azo dyes; sometimes referred to as azopyrazolones (

tartrazine Tartrazine is a synthetic lemon yellow azo dye primarily used as a food coloring. It is also known as E number E102, C.I. 19140, FD&C Yellow 5, Yellow 5 Lake, Acid Yellow 23, Food Yellow 4, and trisodium 1-(4-sulfonatophenyl)-4-(4-sulfonatop ...

, orange B,

mordant red 19 Mordant red 19 is an organic compound with the chemical formula C16H13ClN4O5S. It is classified as an azo dye.Klaus Hunger, Peter Mischke, Wolfgang Rieper, Roderich Raue, Klaus Kunde, Aloys Engel: "Azo Dyes" in ''Ullmann’s Encyclopedia of Indus ...

, yellow 2G). Acid Yellow 17, Acid Yellow 23 (tartrazine), Pigment Yellow 13, and Pigment Red 38 are produced on the multi-ton scale annually.

Structure and synthesis

Applications

Pharmaceuticals

Dyes

Ligands

References

External links