Question

What is formed when benzene diazonium chloride (BDC) reacts with phenol?

• A. Azo dye (p-hydroxyazobenzene)
• B. Benzoic acid
• C. Benzene
• D. Chlorobenzene

Hint:

Remember the important azo coupling reactions: \[ \boxed{ \begin{aligned} \text{BDC + Phenol} &\rightarrow \text{p-Hydroxyazobenzene}\\ \text{BDC + Aniline} &\rightarrow \text{p-Aminoazobenzene} \end{aligned} } \] The product always contains the characteristic azo linkage \[ \boxed{-N=N-.} \]

Answer 1

The Correct Option is A

Concept: Benzene diazonium chloride undergoes an azo coupling reaction with activated aromatic compounds such as phenol and aniline. Phenol activates the benzene ring due to the electron-donating nature of the \(-OH\) group. As a result, coupling occurs mainly at the para position to form an azo compound containing the characteristic azo linkage \[ \boxed{-N=N-.} \] These coloured compounds are known as azo dyes.

Step 1: Identify the reactants.
The reactants are Benzene diazonium chloride and \[ \text{Phenol}. \] Phenol is a highly activated aromatic compound and readily undergoes electrophilic substitution.

Step 2: Understand the azo coupling reaction.
The diazonium ion acts as an electrophile. It couples with the aromatic ring of phenol at the para position to form \[ \boxed{\text{p-hydroxyazobenzene}.} \] The reaction is represented as \[ C_{6}H_{5}N_{2}^{+}Cl^{-} + C_{6}H_{5}OH \longrightarrow HO-C_{6}H_{4}-N=N-C_{6}H_{5}. \]

Step 3: Identify the product.
The product formed is \[ \boxed{\text{p-hydroxyazobenzene}} \] which is an \[ \boxed{\text{Azo dye}.} \] Hence, \[ \boxed{\textbf{Option (A)}} \] is the correct answer.