Question

How do you convert the following? Sodium benzoate to Benzene

Hint:

Soda lime decarboxylation is a standard method to remove a terminal acid group and reduce the carbon chain by one.

Answer 1

Step 1: Identify the transformation needed.
Sodium benzoate ($C_6H_5COONa$) must be converted to benzene ($C_6H_6$). This requires decarboxylation: complete removal of the $-COONa$ group from the molecule.
Step 2: Choose the reagent: soda lime.
Soda lime is a mixture of sodium hydroxide (NaOH) and calcium oxide (CaO) in a roughly 3:1 ratio. It is the classic reagent for decarboxylation of sodium salts of carboxylic acids.
Step 3: Describe the reaction.
Sodium benzoate is mixed with excess soda lime and heated strongly (dry distillation). The NaOH attacks the carboxylate, releasing sodium carbonate ($Na_2CO_3$) and generating the arene.
Step 4: Write the equation.
$C_6H_5COONa + NaOH \xrightarrow{CaO, \Delta} C_6H_6 + Na_2CO_3$. CaO keeps the mixture dry and prevents hydrolysis, allowing clean distillation of benzene vapour.