Question

Consider the following chemical reaction.
$HC \equiv CH \xrightarrow[(2) CO + HCl/AlCl_3]{(1) \text{Red hot Fe tube,} 873\,K}$ Product
The number of $sp ^{2}$ hybridized carbon atom(s) present in the product is ______.

Answer 1

Pass the three molecules of ethyne through the red hot $Fe$ tube at $873\,K$. All the three molecules of ethyne undergo cyclic polymerization to form benzene. In Gattermann - Koch reaction, benzene is treated with carbon monoxide in acidic medium in presence of anhydrous aluminum chloride to give benzaldehyde.

All carbon atoms in benzaldehyde are $sp^{2}$ hybridised