Question

A carbon compound ‘A’ is widely used as a preservative in pickles and has a molecular formula of C₂H₄O₂. This compound reacts with ethanol to form a sweet smelling compound ‘B’.

1. Identify the compound ‘A’ and write its structure.
2. Write the chemical equation for the reaction of ‘A’ with ethanol to form compound ‘B’. State the role of the presence of an acid in the reaction.
3. How can we get compound ‘A’ back from ‘B’?
4. How can ‘A’ be obtained from ethanol?
5. Name the gas produced when compound ‘A’ reacts with washing soda.

Answer 1

i. Compound A: Acetic acid

\[\begin{array}{cc}
\ce{H}\phantom{.......}\\
|\phantom{.......}\\
\ce{H - C - C = O}\\
|\phantom{......}|\\
\phantom{...}\ce{H}\phantom{....}\ce{OH}\\
\end{array}\]

ii. 

\[\begin{array}{cc}
\phantom{........................}\ce{{O}}\\
\phantom{........................}||\phantom{}\\
\ce{CH3COOH + \underset{(A)}{C2H5OH} ->[acid] \underset{(B)}{CH3 - C - O - C2H5} + H2O}\\
\end{array}\]

Acid acts as a catalyst in this reaction.

iii. By treating it with sodium hydroxide and then reacting with hydrochloric acid, compound ‘B’ is changed into compound ‘A’:

\[\ce{\underset{(B)}{CH3COOC2H5} ->[NaOH] C2H5OH + CH3COONa}\]

\[\ce{CH3COONa + \underset{(dil)}{HCl} ->\underset{(A)}{CH3COOH} + NaCl}\]

iv. Oxidation of ethanol can lead to the formation of acid.

\[\ce{C2H5OH ->[KMnO4] CH3COOH}\]

v. Acid reacts with washing soda, releasing CO₂ gas.

\[\ce{2CH3COOH + Na2CO3 -> 2CH3COONa + CO2 + H2O}\]