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BACKGROUND
Principle: Esters are hydrolysed either by an acid or a base. Alkaline hydrolysis of ester is irreversible which is also called saponification. Acid hydrolysis of ester is a reversible reaction. Acid hydrolysis of esters can occur by more than one type of mechanism, the common mechanism is: The alkaline hydrolysis, which occurs through a nucleophilic acyl substitution. Here Ethyl benzoate on hydrolysis with sodium hydroxide gives benzoic acid and ethyl alcohol where OH– ion of sodium hydroxide act as a nucleophile.1
Aim: To prepare benzoic acid from alkyl benzoate by Hydrolysis reaction.
Reaction:
Mechanism:
Use: It is used as a topical agent with salicylic acid to treat skin problems like irritation and inflammation which may cause by burns, insect bites, fungal infections or eczema.
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REQUIREMENTS
Chemicals: Ethyl benzoate- 2 ml
Sodium hydroxide solution 10% – 15 ml
Hdrochloric acid sufficient
Apparatus: Round bottomed flask
Reflux condenser
Funnel
Measuring cylinder
Beaker
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PROCEDURE
A mixture of ethyl benzoate (2 ml) and sodium hydroxide solution (15 ml, 10%) is refluxed in a round bottomed flask fitted with a water condenser on a water bath (temp. 90-100 oC) for about 30 minutes till the ester layer disappears. Then the solution is cooled and acidified with HCl. The resultant acidified solution is cooled in an ice bath. The separated benzoic acid precipitate is filtered and recrystallised from hot water. Yield: 1.2 g, m.p.: 122 oC.
Molecular formula of ethyl benzoate = C9H10O2
Molecular formula of benzoic acid = C7H6O2
Weight of ethyl benzoate = 150 g/mole
Weight of benzoic acid = 112 g/mole
Theoretical yield:
150 g of ethyl benzoate gives 112 g of benzoic acid
Therefore, 2 g of ethyl benzoate would give……….. ? (X) g of benzoic acid
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CONCLUSION
The yield of synthesized benzoic acid was found to be 80.53 %.
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REFERENCES
1. College Practical Chemistry by V K Ahluwalia, Sunita Dhingra and Adarsh Gulati, Published by Universities Press (India) Private Limited 2005; Page No. 255
