Table of Contents
Introduction of pyrazole
Introduction of pyrazole, it is a 5-membered heterocyclic compound which contains 2 nitrogen molecules. It is an important organic compound in pharmaceutical & agrochemical industries. It is an important building block in organic synthesis and has numerous applications in medicinal chemistry, agrochemicals, and materials science. Pyrazole derivatives exhibit a wide range of biological activities such as anti-inflammatory, analgesic, antipyretic, antitumor, antimicrobial, and insecticidal properties.
Chemistry of pyrazole
Pyrazole molecules are aromatic in nature because their planar conjugated ring structure have 6 delocalized π electron. Pyrazole, just like other nitrogen containing heterocyclic have different tautomeric structures. Three tautomeric forms can be written for unsubstituted pyrazole.
Pyrazole derivatives in which the two neighbour carbon atoms of the nitrogen atoms on the ring carry different substituents have five tautomeric structures.
Physical properties of pyrazole
1. It is a crystalline solid having pyridine like odour & bitter taste.
2. It is melting point is 70°C.
3. Its boiling point is 187°C.
4. It is soluble in water & organic solvents.
Chemical reaction of pyrazole
1. Ring opening reaction
When pyrazolium salts are treated with caustic alkalis, disubstituted hydrazine’s are formed.
Pyrazole can be chlorinated by chlorinating reagent such as chlorine water, chlorine in carbon tetrachloride hypochlorous acid. Chlorine in acetic acid & sulfuryl chloride in chloroform. Pyrazole is brominated by bromine in chloroform bromine in acetic acid.
Pyrazole ring is generally stable to oxidation, however with peroxide transformed into its 2-oxide.
The reduction of pyrazole with sodium & alcohol or by catalytic hydrogenation over palladium results in 2-pyrazolines.
Synthesis of pyrazole
1. From pyrimidine
Pyrimidine reacts with hydrazine solution to give pyrazole.
2. Knorr pyrazole synthesis
In this reaction, hydrazine & 1,3-dicarbonyl compound are converted into a pyrazole using an acid catalyst.
3. From nitrile imines
Pyrazole is produced by the dipolar cycloaddition between alkynes with nitrile imines.
4. From diazo compound
Diazo compounds add to an acetyl eric derivatives gives pyrazole.
Medicinal uses of pyrazole
1. Many pyrazole compounds are used as dyes & medicines
2. Antipyrine is used as anti-pyretic, analgesic.
3. Tartrazine is used as a yellow dye for food.
4. Phenylbutazone is used as anti-inflammatory drug.
5. Borazole is a H2 receptor agonist.
6. It is used clinically to test gastric secretory function.
7. Lonazole is a non-steroidal anti-inflammatory drug.