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Question
What are esters? How are esters prepared? Write the chemical equation for the reaction involved. What happens when an ester reacts with sodium hydroxide? Write the chemical equation for the reaction and also state the name and use of this reaction.
Solution
Esters
They are sweet-smelling organic compounds, with the general formula RCOOR' (R and R' are similar or dissimilar alkyl groups).
Preparation of ester
Esters are prepared by esterification which is a reaction between carboxylic acids and alcohols in the presence of an acid.
For example, when ethanoic acid reacts with ethanol in the presence of an acid, ethyl ethanoate is formed. Ethyl ethanoate is an ester, and has a sweet smell.
\[{{CH}_3 {CH}_2 OH}_{\text{Ethanol}} + {{CH}_3 COOH}_{\text{Ethanoic acid}} \to^{\text{Acid}} {{CH}_3 {COOCH}_2 {CH}_3}_{\text{Ethyl ethanoate }(\text{Ester})} + {H_2 O}_{\text{Water}}\]
Reaction with sodium hydroxide
Ethyl acetate (an ester) reacts with sodium hydroxide (base) to form ethanol (alcohol) and ethanoic acid (carboxylic acid).
\[{{CH}_3 {COOCH}_2 {CH}_3}_{\text{Ethyl ethanoate }(\text{Ester})} \to^{NaOH} {{CH}_3 {CH}_2 OH}_{\text{Ethanol}} + {{CH}_3 COOH}_{\text{Ethanoic acid}}\]
Thus, alcohol and carboxylic acid can be reclaimed from an ester by reacting it with an acid or a base. This reaction is used in the preparation of soaps and it is known as saponification reaction.
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