Synthesis of 1,3-substituted pyrazole from diarylhydrazone and vicinal diol

BACKGROUND

Principle: 1,3-substituted pyrazole is prepared by cyclization of diarylhydrazone and vicinaldiol in presence of ferric chloride and tert-butylhydroperoxide (TBHP) which is also called regio selective synthesis of substituted pyrazole.

Aim: To prepare 1,3-diphenyl pyrazole from diphenyl hydrazone and a vicinal diol.

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Use: Can be used as an antibacterial and antiviral agent.

REQUIREMENTS

Chemicals:

1-benzyledene-2-phenyl hydrazine,

Ethane-1,2-diol(ethylene glycol),

Ferric chloride,

Tert-butyl hydroperoxide,

Acetyl acetone,

Sodium chloride,

Ethyl acetate,

Sodium sulphate.

Apparatus:

Water-bath,

Beaker,

Measuring cylinder,

Thermometer,

Stirrer,

Separatory funnel

Buchner funnel, etc

PROCEDURE

1,3-substituted pyrazole

About 4.55 g of 1-benzyledene-2-phenyl hydrazine is dissolved in the solution of 25 ml of vicinal diol and ferric chloride (5 mol %). Then another solution of tert-butyl hydroperoxide (5.3 g) in 25 ml of acetyl-acetone is added to it. Mix solution is maintained at a temperature range of 90 to 100^o C.

The mixed solution is left to reach room temperature and stirred for 6 hours. Content is poured into water and extracted with ethyl-acetate three times. The combined organic solution is washed with water, then with a saturated solution of sodium chloride, passed through sodium sulphate, and evaporated under a vacuum. About 3.15 g of the final product is found with m.p: 185^oC.

Calculation of yield:

– Molecular Formula (MF) of 1-benzyledene-2-phenyl hydrazine = C₁₃H₁₂N₂

– MF of 1,3-diphenyl pyrazole = C₁₅H₁₂N₂

– Molecular weight (MW) of 1-benzyledene-2-phenyl hydrazine = 196 g/ mol

– MW of 1,3-diphenyl pyrazole = 220 g/ mol

196 g of 1-benzyledene-2-phenyl hydrazine yields 1,3-diphenyl pyrazole = 220 g

4.55 g of 1-benzyledene-2-phenyl hydrazine shall yield 1,3-diphenyl pyrazole = (220 / 196) × 4.55 = 5.1 g

Therefore, Theoretical yield of 1,3-diphenyl pyrazole = 5.1 g

If reported Practical yield = 3.15 g

Then, Percentage Practical yield = (Practical yield / Theoretical yield) × 100

                                                     = (3.15 / 5.1) × 100 = 61.76 %

CONCLUSION

The percent yield of 1,3-diphenyl pyrazole is 61.75 % with m.p. 185 °C.

REFERENCES

1. N. Panda, A. K. Jena, J. Org. Chem., 2012, 77, 9401-9406.
2. Practical Heterocyclic Chemistry by A. O. Fitton and R. K. Smalley Academic Press London and New York, Page. 25.

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