Animated Solution for Chemistry - Organic Compounds Containing Nitrogen: In the reaction, The product E is

The transformation of simple aromatic amines into a myriad of substituted benzenes is one of the most beautiful and powerful sequences in organic chemistry. In this problem, we are taking a journey through two classic reactions: Diazotization and the Sandmeyer reaction. Let's break down the magic step-by-step.

We start our journey with $p$-toluidine. Imagine a stable benzene ring, proudly holding an electron-donating methyl group ($-C{H}_3$) at the bottom and a primary amino group ($-N{H}_2$) at the top. They are sitting exactly opposite to each other, at the para positions. This molecule is our blank canvas.

In the first step, we treat $p$-toluidine with a mixture of sodium nitrite ($NaN{O}_2$) and hydrochloric acid ($HCl$). But there is a catch here—we must keep the reaction mixture ice-cold, strictly between $0^{\circ }C$ and $5^{\circ }C$.

Why the chill? The reaction generates the highly reactive nitrosonium ion ($N{O}^{+}$), which attacks the primary amine to form a diazonium salt. This intermediate, $p$-toluenediazonium chloride ($-N_2^{+}C{l}^{-}$), is incredibly unstable. If the temperature rises even slightly, it will violently decompose, releasing nitrogen gas and leaving behind a phenol. By keeping it cold, we trap this reactive beast, ready for our next move. This is our intermediate D.

Now that we have our diazonium salt, it's time to unleash the Sandmeyer reaction. We introduce cuprous cyanide ($CuCN$) and potassium cyanide ($KCN$), and apply a little heat ($\Delta$).

The diazonium group ($-N_2^{+}$) is arguably one of the best leaving groups in all of chemistry because it desperately wants to leave as stable, neutral nitrogen gas ($N_2$). The copper(I) catalyst facilitates a beautiful electron transfer, allowing the cyanide nucleophile ($C{N}^{-}$) to swoop in and take the place of the departing nitrogen.

As the nitrogen gas bubbles away, the $-N_2^{+}C{l}^{-}$ group is completely replaced by the $-CN$ group. Our starting $p$-toluidine has now been elegantly transformed into $p$-tolunitrile.

Looking at our options, we can clearly see that this structure—a benzene ring with a methyl group and a cyanide group at para positions—perfectly matches option (c).

This sequence is a favorite in JEE because it tests your understanding of reaction conditions and the versatility of diazonium salts. Master this, and you hold the key to synthesizing almost any substituted benzene!