Question

How do you convert Benzoic acid to Benzene ?

Hint:

Remember: \[ RCOONa \xrightarrow[\Delta]{NaOH/CaO} RH \] This reaction is called decarboxylation. For aromatic compounds: \[ C_6H_5COOH \rightarrow C_6H_5COONa \rightarrow C_6H_6 \] Benzoic acid loses one carbon atom and gives benzene.

Answer 1

Step 1: Plan for decarboxylation.
Benzoic acid ($C_6H_5COOH$, 7 carbons) converts to benzene ($C_6H_6$, 6 carbons) by removing $-COOH$ as $CO_2$. This is achieved by soda lime decarboxylation.
Step 2: Form the sodium salt.
\[ C_6H_5COOH + NaOH \rightarrow C_6H_5COONa + H_2O \]
Step 3: Decarboxylate with soda lime.
Heat sodium benzoate with soda lime ($NaOH + CaO$): \[ C_6H_5COONa + NaOH \xrightarrow{CaO,\,\Delta} C_6H_6 + Na_2CO_3 \] \[ \boxed{C_6H_5COOH \xrightarrow{NaOH/CaO,\,\Delta} C_6H_6} \]