The reaction of Benzenediazonium chloride with aniline yields yellow dye. The name of the yellow dye is:

A. p-hydroxyazobenzene

B. p-aminoazebenzene

C. p-nitroazobenzene

D. o-nitroazobenzene

When Benzenediazonium chloride reacts with aniline, the product formed is a yellow dye known as p-aminoazobenzene. This reaction is a classic example of azo coupling, where a diazonium compound reacts with an aromatic amine to form an azo compound, which often has vibrant colors. So, the correct answer to your question is B. p-aminoazobenzene.

Understanding the Reaction

To grasp why p-aminoazobenzene is the product, let’s break down the components involved in this reaction:

• Benzenediazonium chloride: This is a diazonium salt, which is highly reactive due to the presence of the diazonium group (-N2+).
• Aniline: Aniline is an aromatic amine, characterized by the amino group (-NH2) attached to a benzene ring.

The Mechanism of Azo Coupling

The reaction proceeds through a mechanism known as azo coupling. Here’s how it works:

1. The diazonium ion from benzenediazonium chloride is generated, which is a positively charged species.
2. This ion then reacts with the nucleophilic aniline. The amino group on aniline donates a pair of electrons to the diazonium ion, leading to the formation of a new bond.
3. The result is the formation of an azo compound, where the azo group (-N=N-) links the two aromatic rings.

Identifying the Product

In this specific case, the reaction produces p-aminoazobenzene, where the amino group from aniline is positioned para (p-) to the azo group. This positioning is crucial as it influences the dye's properties, including its color.

Why is it Yellow?

The color of azo compounds often arises from the extended conjugation of the double bonds in the azo group and the aromatic rings. In p-aminoazobenzene, the presence of the amino group enhances the electron density, allowing for effective light absorption in the visible spectrum, which results in the characteristic yellow color.

Comparing Other Options

Let’s briefly consider the other options provided:

• A. p-hydroxyazobenzene: This compound has a hydroxyl group instead of an amino group, leading to different properties and color.
• C. p-nitroazobenzene: The nitro group is electron-withdrawing, which alters the electronic properties and color of the compound.
• D. o-nitroazobenzene: Similar to option C, the nitro group affects the color and stability of the azo compound.

None of these alternatives would yield the same yellow dye as p-aminoazobenzene when reacting with benzenediazonium chloride.

Conclusion

In summary, the reaction of Benzenediazonium chloride with aniline produces p-aminoazobenzene, a yellow dye, due to the azo coupling mechanism. This reaction is not only significant in organic chemistry but also has practical applications in dye manufacturing and the development of colorants.