Synthesis of 5-nitrosalisylic acid from salicylic acid

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BACKGROUND

Principle

Nitration on salicylic acid occurs by placing a nitro group on the aromatic ring system via an electrophilic aromatic substitution reaction. Here calcium nitrate is used as the nitrating agent in presence of acetic acid. Two groups -CO₂H and -OH in salicylic acid complement each other since they both direct the entering nitro group to the 5^th position. The 5^th position and the 3^rd position are both electronically favored since the -CO₂H group is meta directing and the -OH group is ortho–para directing. The nitro group is attached at the 5^th position, and not at the 3^rd position, due to steric effects. We can also use anhydrous nitric acid or concentrated nitric acid and concentrated sulphuric acid as nitrating reagent.¹

Aim: To prepare 5-nitrosalisylic acid from salicylic acid by Nitration reaction.

Reaction:

Mechanism:
1. Generation of electrofile

2. Attack on benzene ring by acetyl nitrate

Use: Used in organic drug synthesis.

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REQUIREMENTS

Chemicals: Salicylic acid – 2 g

Acetic acid – 10 ml

Calciumnitrate tetrahydrate – 3 g

Apparatus: Conical flask

Funnel

Beaker

Filter paper

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PROCEDURE

3 g of calciumnitrate tetrahydrate is dissolved in 10 ml of acetic acid within a 100 ml conical flask by gently heating on a water bath. 2 g of salicylic acid is added and the reaction mixture is heated on a boiling water bath (below 80°C) for few minutes. A dark red solution is formed. Then the dark- red coloured reaction mixture is poured into a 100 ml beaker containing 20 ml ice cold water.
A turbid dark red coloured solution forms which is kept in a refrigerator and after 4-5 hours yellow crystals of 4-Nitrosalicylic acid separates out. The crude product is filtered at the suction pump, washed with cold water and dried. Yellow precipitate of 4-Nitrosalicylic acid is obtained with yield of 1.32 g, m.p. 234°C.

Calulation

Molecular formula of salicylic acid = C₇H₆O₃

Molecular formula of 5-nitrosalicylic acid = C₇H₅NO₅

Weight of salicylic acid = 138 g/mole

Weight of 5-nitrosalicylic acid = 198 g/mole

Theoretical yield

138 g of salicylic acid gives 198 g of 5-nitrosalicylic acid

Therefore, 2 g of salicylic acid would give…………………. ? (X) g of 5-nitrosalicylic acid

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CONCLUSION

The yield of synthesized p-bromo acetanilide was found to be 46 %

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REFERENCES

Experimental Organic Chemistry by Sonia Ratnani and Shriniwas Gurjar Published by PHI Learning Private Limited, Delhi 2012; Page No. 104
Microscale Organic Laboratory with Multistep and Multiscale Syntheses by Dana W. Mayo, Ronald M. Pike and David C. Forbes Published by John Wiley & Sons Inc.; Fifth Edition Page No. 379