The given reaction of compound A are as follows :

IIT-JEE 2005 Mains Chemistry - Compounds Containing Nitrogen Question 16 English Explanation 1

Compound A on reaction with NaBr + MnO$$_2$$ gives brown fumes with pungent smell with the formation of compound B. Also, compound A reacts with conc. HNO$$_3$$ to produce an intermediate C which on reaction with toluene producing compound D.

The reaction of compound A with NaBr + MnO$$_2$$ is an example of redox reaction. The compound A is sulphuric acid, H$$_2$$SO$$_4$$. The products formed during the reaction are Na$$_2$$SO$$_4$$, MnSO$$_4$$, Br$$_2$$ and H$$_2$$O. The bromine gas is brown in colour and have pungent smell. The chemical reaction for the same is shown below.

IIT-JEE 2005 Mains Chemistry - Compounds Containing Nitrogen Question 16 English Explanation 2

The compound A that is sulphuric acid on reaction with conc. HNO$$_3$$ yields nitronium ion as shown below. The compound C formed is an intermediate and is nitronium ion.

$$\mathrm{\mathop {{H_2}S{O_4}}\limits_{(A)} + HN{O_3} \to HSO_4^ - + \mathop {NO_2^ \oplus }\limits_{(C)} + {H_2}O}$$

The nitronium ion on reaction with toluene, causes its nitration, producing compound D. The nitronium ion is an electrophile and causes substitution of 3 H atoms at two ortho and one para position of benzene ring by nitro group. The compound D is formed which is trinitrotoluene or TNT. The TNT is explosive in nature.

IIT-JEE 2005 Mains Chemistry - Compounds Containing Nitrogen Question 16 English Explanation 3

The complete reaction sequence is as shown below.

Final Answer :

A: H$$_2$$SO$$_4$$

B : Br$$_2$$

C: NO$$_2^+$$

IIT-JEE 2005 Mains Chemistry - Compounds Containing Nitrogen Question 16 English Explanation 4

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