Animated Solution for Chemistry - Organic Compounds Containing Nitrogen: Consider the above reaction, compound $B$ is

Diazotization

Let's embark on this fascinating two-step organic synthesis journey. We begin with our starting material, sulphanilic acid, which features both a primary amine group ($-N{H}_2$) and a sulfonic acid group ($-S{O}_{3}H$) on a benzene ring.

When we treat this molecule with a mixture of sodium nitrite ($NaN{O}_2$) and hydrochloric acid ($HCl$) at a chilly temperature of $273-278$ K, a classic reaction takes place.

This is the renowned diazotization process. The primary amine group is highly susceptible to these conditions and is swiftly converted into a diazonium salt ($-N_2^{+}C{l}^{-}$).

Interestingly, the sulfonic acid group at the para position is completely inert under these conditions and remains untouched. This selective transformation yields our intermediate compound, Intermediate A.

Azo Coupling

With our reactive diazonium salt in hand, we move to the second phase of the reaction. We introduce a new player: N,N-dimethylaniline.

The diazonium ion is electron-deficient, making it an excellent electrophile. It eagerly seeks out an electron-rich aromatic ring to attack. This type of reaction is known as an electrophilic aromatic substitution, specifically an azo coupling.

To predict where the diazonium ion will attack, we must analyze the directing effects of the $-N(C{H}_3{)}_2$ group on the N,N-dimethylaniline ring.

This group is a powerful electron-donating group, making the ring highly activated. It directs incoming electrophiles to the ortho and para positions.

However, there is a catch! The diazonium ion is a very bulky electrophile. If it tries to attack the ortho position, it faces severe steric hindrance from the bulky dimethylamino group.

Because of this spatial crowding, the electrophile takes the path of least resistance and exclusively attacks the para position.

Methyl Orange

As the coupling concludes, the two benzene rings become permanently linked by a vibrant nitrogen-nitrogen double bond, known as an azo linkage ($-N=N-$).

Because the attack happened at the para position, both the sulfonic acid group and the dimethylamino group end up exactly opposite to the azo linkage on their respective rings.

This beautifully symmetric, highly conjugated molecule is our final product B. You might even recognize it by its common name: Methyl Orange, a famous pH indicator used in laboratories worldwide!

Comparing our derived structure with the given options, it is crystal clear that Option (c) perfectly matches our result.