Synthesis of Salicylic Acid from Alkyl Salicylate

BACKGROUND

Salicylic Acid

Principle:

Alkaline hydrolysis of esters is called saponification and is an irreversible process. Here one mole of methyl salicylate (oil of wintergreen) reacts with two moles of sodium hydroxide to form sodium-salicylate with methanol and water, each of one mole.

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Sodium salicylate is reacted with sulfuric acid or hydrochloric acid to remove the sodium ion and forms salicylic acid with sodium sulphate as a byproduct.¹

Aim: To prepare salicylic acid from methyl-salicylate by hydrolysis reaction.

Reaction:

Use:

It is used to synthesize aspirin, with benzoic acid it is used as a topical product to treat skin irritation and inflammation caused by burns, insect bites, fungal infections, or eczema as a topical agent.

REQUIREMENTS

Chemicals:   

• Methyl- salicylate
• Sulfuric acid (6M)
• Sodium hydroxide (6M)

Apparatus:   

• 200 ml beaker
• 125 ml Erlenmeyer flask
• Filtration apparatus
• 200 ml reflux apparatus

PROCEDURE

3 ml methyl-salicylate (density – 1.184) is taken in to a 200 ml RBF. 50 ml of 6M NaOH solution is added to it with a couple of boiling chips. The solution is refluxed for 30-45 minutes from the point the mixture starts to boil. If the reaction mixture still has oil or is cloudy, continued to reflux.

Once the mixture is clear and homogeneous, then the solution is checked whether it no longer having smell of oil of wintergreen. If the smell still exists, then continued to reflux for some more minutes. Boiling chips are removed and the solution is transferred to a 250 ml beaker.

A 6M H₂SO₄ or hydrochloric acid is added slowly with stirring until the pH is 2.0. The mix solution is cooled in an ice-bath for 10 minutes, vacuum filtered and rinsed with ice cold water. The product is recrystalised from hot water; yield 1.2 g m.p.158-159^o.

Calculation

Molecular formula of methyl-salicylate = C₈H₈O₃

Molecular formula of salicylic acid = C₇H₆O₃

Weight of methyl salicylate = 152 g/mole

Weight of salicylic acid = 138 g/mole

Theoretical yield:

152 g of methyl salicylate gives 138 g of salicylic acid

Therefore, 3.5 g of methyl salicylate would give……….. ? (X) g of salicylic acid

CONCLUSION

The yield of synthesized salicylic acid was found to be 80.64 %.

REFERENCES

1. Green Chemistry Environmentally Benign Reaction by V.K. Ahluwalia; Published by Ane Books Pvt. Ltd. First Edition; Page No. 155.

Also Read:

• Synthesis of Benzil from Benzoin
• Synthesis of p-bromoacetanilide from Acetanilide
• Synthesis of p-bromoacetanilide from acetanilide
• To Prepare and Submit Acetanilide from Aniline
• Determination of saponification value of the given oil/fat
• Hydrolysis of Ethyl Acetate
• Synthesis of Dibenzal Acetone from Benzaldehyde by Claison Schmidt Reaction

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