question_answer

Hydrolysis of an ester gives a carboxylic acid which on Kolbes electrolysis yields ethane. The ester is :

A)  methyl ethanoate

B)  methyl methanoate

C)  ethyl methanoate

D)  methyl propanoate

Correct Answer: A

Solution :

Hydrolysis of \[\text{C}{{\text{H}}_{\text{3}}}\text{COOC}{{\text{H}}_{\text{3}}}\] (methyl ethanoate) gives acetic acid and methyl alcohol. Acetic acid on electrolysis by Kolbes method gives ethane. So, the ester is methyl ethanoate. \[\underset{\text{Methyl}\,\text{ethanoate}}{\mathop{C{{H}_{3}}CO}}\,\,OH\xrightarrow{{}}\] \[\underset{\text{Acetic}\,\text{acid}}{\mathop{C{{H}_{3}}COOH+}}\,C{{H}_{3}}OH\] Kolbes electrolysis: \[\underset{\text{Acetic}\,\text{acid}}{\mathop{C{{H}_{3}}COOH}}\,\xrightarrow{{}}C{{H}_{3}}CO{{O}^{-}}+{{H}^{+}}\] At anode: or\[\underset{(Ethane)}{\mathop{C{{H}_{3}}-C{{H}_{3}}}}\,\] At cathode: \[{{H}^{+}}+{{e}^{-}}\xrightarrow{{}}H\] \[H+H\xrightarrow{{}}{{H}_{2}}\uparrow \]