Question

An aromatic compound $'A'$ having molecular formula $C_7H_6O_2$ on treating with aqueous ammonia and heating forms compound $'B'$. The compound $'B'$ on reaction with molecular bromine and potassium hydroxide provides compound $'C'$ having molecular formula $C_6H_7N$. The structure of $'A'$ is :

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

First, we find the DU of each compound.
$DU \left( C _{7} H _{6} O _{2}\right)=5$
$DU \left( C _{6} H _{7} N \right)=4$
When $C _{7} H _{6} O _{2}$ reacts with aqueous ammonia and heated it forms $C _{7} H _{7} ON$.Now, $DU \left( C _{7} H _{7} ON \right)=5$
The reagent $Br _{2} / NaOH$ is classic Hoffman Bromamide reagent and this gives a clue that B may be an Amide. This consumes one DU and by seeing remaining 6 carbon and 5 Hydrogens we can say B is Benzamide.
So Benzamide on Hoffman Degradation gives Aniline which matches with the formula of $C$.
We have to know usually $NH _{3}+$ heat gives an Amide when a carboxylic acid is used as a reagent.
So among the options, we can see option C which is a Benzoic acid matches the formula of $X$ and hence is the correct answer.