p-Aminoazobenzene is produced from:

Benzene diazonium chloride and aniline

The correct answer is option 2. Benzene diazonium chloride and aniline.

The production of p-aminoazobenzene involves a couple of key reactions: the diazotization of aniline and the azo coupling reaction. Here is a step-by-step explanation:

Diazotization

Part 1: Formation of nitrosonium ion from \(HNO_2\)

Now let us dig into how some of these reactions work.

First, let’s go through formation of the diazonium salt, a process called “diazotization”.

The first key reagent for this process is either sodium nitrite \((NaNO_2)\) or nitrous acid \((HNO_2)\).   Sodium nitrite has the advantage of being an easily handled salt, while \(HNO_2\) is a somewhat unstable liquid.

The second key reagent is a strong mineral acid like \(HCl\); if \(NaNO_2\) is used, \(HCl\) converts it into \(HNO_2\).

The key purpose of HCl is to further convert HNO2 into the powerful electrophile \(NO^+\), the “nitrosonium ion”, which is the key electrophile in the reaction that forms the diazonium salt. The nitrosonium ion is formed through protonation of OH and resultant loss of water:

Part 2: Formation of the diazonium ion

The next step is formation of the diazonium ion from the reaction between the amine and the nitrosonium ion, which also requires acid. The first step is formation of a new N–N bond, which occurs through attack of the nitrosonium ion by the aromatic amine (Step 1). This is followed by two proton transfers from nitrogen to oxygen (Steps 2 and 3) accompanied by reorganization of the pi bonding framework [forming N–N (pi), breaking N–O (pi) ]. The final step is formation of the nitrogen-nitrogen triple bond accompanied by expulsion of water (Step 4).

Azo Coupling Reaction

The diazonium ion reacts with the aniline molecule. In the presence of an alkaline medium, the aniline acts as a nucleophile and attacks the diazonium ion. This results in the formation of p-aminoazobenzene:

Here, p-aminoazobenzene  is formed along with a proton \((H^+)\).

Summary

Diazotization converts aniline into benzene diazonium chloride.

Azo Coupling of benzene diazonium chloride with aniline forms p-aminoazobenzene.

This sequence is widely used in dye chemistry and organic synthesis to introduce azo groups into aromatic compounds.