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. [1]
Pyrazolone can exist in two isomers: 3-pyrazolone and 4-pyrazolone.
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.
The first synthesis of pyrazolones was reported in 1883 by Ludwig Knorr, via a condensation reaction between ethyl acetoacetate and phenylhydrazine. [2]
Many pyrazolones are produced by functionalization of preformed pyrazolones.
This section is missing information about safety profile of analgesics (which ones are withdrawn and whether there is a common theme in adverse effects).(August 2022) |
Pyrazolones are amongst the oldest synthetic pharmaceuticals, starting with the introduction of antipyrine (phenazone) in 1880s. [3] [4] The compounds generally act as analgesics and include dipyrone (Metamizole), aminophenazone, ampyrone, famprofazone, morazone, nifenazone, piperylon and propyphenazone. Of these dipyrone is perhaps the most widely used. [3] [5]
The basic structure has been also used in a number of newer drugs of other effects. [5] Edaravone is useful for prevention and/or therapy of arterial wall injury. [6] Eltrombopag is used to address low blood platelet count.
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. [1]
Pyrazolones have been studied as ligands. [7]