Chemistry of Pyrazole PDF / PPT

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Lecture No. 31

Chemistry of Pyrazole

Session Objectives

By the end of this session, students will be able to:

➢ Discuss the chemistry, reactivity, properties and method of synthesis of pyrazole 2


Pyrazole is planar and structural isomer of imidazole

Pyrazole is much weaker base than imidazole

Pyrazole was first discovered by Buchner in 1889 during the decomposition of pyrazole
3,4,5-tricarboxylic acid

Benzo derivative of pyrazole is benzopyrazole.

Pyrazole is used as oxidants in fuels.

Orisul is an example of pyrazole sulphonamide.

Dihydropyrazoles are called pyrazolines

Pyrazolines are less stable than corresponding pyrazoles but can be converted into the latter by using mild
Oxidising agents such as lead tetra acetate.


Properties of pyrazole

It possesses a penetrating pleasant smell unlike most amines.

Introduction of alkyl groups in the ring causes an increase in the boiling point.

Pyrazoles which are unsubstituted at position 1 exhibit tautomerism. The two tautomeric forms are identical
entities and are in rapid equilibrium with each other. Two nitrogen atoms are indistinguishable.


Synthesis of pyrazole


Synthesis of pyrazole


Electrophilic substitution:

Pyrazoles are subjected to electrophilic substituion and the attack takes place at position 4.

Chlorination of SO2Cl2 of pyrazoles yields 4-chloropyrazoles.

Bromination(Br2 / dioxane) occurs at position 4.

Nitration occurs at 4 position but under more severe conditions.

Nucleophilic substitution:

Direct amination of pyrazoles with sodamide is not observed. It causes ring opening.

Metallation of n-butyl lithium takes place in position5.





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