The given starting material is diazoaminobenzene (C6H5−N=N−NH−C6H5).
When diazoaminobenzene is treated with an acid catalyst (HCl) and excess aniline, and warmed to 40−45∘C, it undergoes a rearrangement reaction (or dissociation followed by coupling) to form p-aminoazobenzene.
The reaction sequence is as follows:
Diazoaminobenzene reacts with HCl to form benzenediazonium chloride and aniline.
The benzenediazonium ion then couples with the excess aniline at the para position to yield p-aminoazobenzene.
Cooling and adding acetic acid helps in precipitating the free base, p-aminoazobenzene, which is a yellow dye (often called Aniline Yellow).
The structure of the yellow product (X), p-aminoazobenzene, is C6H5−N=N−C6H4−NH2.
The molecular formula of p-aminoazobenzene is C12H11N3.
Let's calculate its molar mass:
Molar mass =(12×12)+(11×1)+(3×14)
Molar mass =144+11+42=197 g mol−1
The mass of nitrogen in one mole of the compound is 3×14=42 g.
The percentage of nitrogen in the product is:
% N=19742×100≈21.32%
Rounding to the nearest integer, we get 21.
Answer: 21
