Question Details

Which one of the following reactions does NOT give benzene as the product?

Options

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Correct Answer :

Option C

Reaction of benzenediazonium chloride with warm water to form phenol

Solution :

To determine which reaction does NOT yield benzene as the product, let us analyze each reaction shown in the images step-by-step:

1. Aromatization of n-hexane (Image 1 / Option 1):
When n-hexane is heated at 773 K and 10 - 20 atm pressure in the presence of oxides of molybdenum, vanadium, or chromium (such as ${Mo}_{2} O_{3}$ shown in the image), it undergoes dehydrogenation and cyclization (aromatization) to form benzene.
The chemical reaction is represented as:
$C_{6} H_{14} \to C_{6} H_{6} + 4 H_{2}$
Thus, this reaction produces benzene.

2. Cyclic Polymerization of Ethyne (Image 2 / Option 2):
When ethyne ( $H - C \equiv C - H$ ) is passed through a red-hot iron tube at 873 K, three molecules of ethyne undergo cyclic polymerization to yield benzene.
The chemical reaction is represented as:
$3 CH \equiv CH \to C_{6} H_{6}$
Thus, this reaction produces benzene.

3. Hydrolysis of Benzenediazonium Chloride (Image 3 / Option 3):
When benzenediazonium chloride ( $C_{6} H_{5} N_{2}^{+} {Cl}^{-}$ ) is warmed with water ( $H_{2} O$ ), it undergoes hydrolysis to form phenol ( $C_{6} H_{5} OH$ ) along with the evolution of nitrogen gas and hydrochloric acid.
The chemical reaction is represented as:
$C_{6} H_{5} N_{2}^{+} {Cl}^{-} + H_{2} O \to C_{6} H_{5} OH + N_{2} + HCl$
Since phenol is the product of this reaction rather than benzene, this reaction does NOT yield benzene.

4. Decarboxylation of Sodium Benzoate (Image 4 / Option 4):
Heating sodium benzoate ( $C_{6} H_{5} COONa$ ) with sodalime (a mixture of $NaOH$ and $CaO$ ) leads to decarboxylation, forming benzene and sodium carbonate ( ${Na}_{2} {CO}_{3}$ ).
The chemical reaction is represented as:
$C_{6} H_{5} COONa + NaOH \to C_{6} H_{6} + {Na}_{2} {CO}_{3}$
Thus, this reaction produces benzene.