Question

Conversion of carboxylic acid to hydrocarbon is carried out using

• A. \(KMnO_4\)
• B. \(LiAlH_4\) and ether
• C. NaOH and CaO
• D. \(B_2H_6\) (Diborane)

Hint:

Think of decarboxylation of the sodium salt with soda lime.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Converting a carboxylic acid into a hydrocarbon with one carbon less is called decarboxylation. The \(-COOH\) group is removed as carbon dioxide or carbonate.

Step 2: Key Formula or Approach
Heat the sodium salt of the acid with soda lime, which is a mixture of \(NaOH\) and \(CaO\). \[ RCOONa + NaOH \xrightarrow{CaO,\ \Delta} R-H + Na_2CO_3 \]

Step 3: Check option (1)
\(KMnO_4\) is an oxidising agent. It does not remove the carboxyl group. So (1) is wrong.

Step 4: Check option (2)
\(LiAlH_4\) in ether reduces the acid to a primary alcohol \(RCH_2OH\), not to a hydrocarbon. So (2) is wrong.

Step 5: Check option (3)
Soda lime (NaOH and CaO) decarboxylation gives the hydrocarbon \(R-H\). For example sodium acetate gives methane. So (3) is correct.

Step 6: Check option (4)
Diborane reduces the carboxylic group to the alcohol \(RCH_2OH\). It does not give a hydrocarbon. So (4) is wrong.

Final Answer:
A carboxylic acid is converted to a hydrocarbon by heating its sodium salt with soda lime (NaOH and CaO). This is option (3). \[ \boxed{\text{NaOH and CaO (option 3)}} \]