Question

Which of the following sets of reagents are required for the conversion of ethyl bromide to propanoic acid?

• A. I,II
• B. II,III
• C. I,III
• D. I,II,III

Hint:

To add 1 Carbon and make Acid: 1. $RX \rightarrow RCN \rightarrow RCOOH$. 2. $RX \rightarrow RMgX \rightarrow RCOOH$ (using $CO_2$).

Answer 1

The Correct Option is B

Goal: Convert Ethyl Bromide ($C_2H_5Br$) to Propanoic Acid ($C_2H_5COOH$). This involves ascent of series (adding one Carbon). Method II (Nitrile Synthesis):
$C_2H_5Br \xrightarrow{KCN} C_2H_5CN \xrightarrow{H_3O^+} C_2H_5COOH$. This is a standard valid method. Method III (Grignard Synthesis):
$C_2H_5Br \xrightarrow{Mg, Ether} C_2H_5MgBr \xrightarrow{CO_2} C_2H_5COOMgBr \xrightarrow{H_3O^+} C_2H_5COOH$. This is also a standard valid method to increase carbon chain by one and form carboxylic acid. Method I (Oxidation):
$C_2H_5Br \xrightarrow{OH^-} C_2H_5OH \xrightarrow{KMnO_4} CH_3COOH$ (Ethanoic acid). This does not increase the carbon chain length. It yields a 2-carbon acid, not propanoic (3-carbon). Incorrect. Conclusion:
Methods II and III work.