Question

Write the structure of zwitter ion of sulfanilic acid. Write the reaction between benzene diazonium chloride and phenol in alkaline medium.

Hint:

Coupling with phenol happens at the para-position. If the para-position is blocked, it happens at the ortho-position.

Answer 1

Step 1: Understanding the Concept:
1. Sulfanilic acid contains both acidic (\(-SO_3H\)) and basic (\(-NH_2\)) groups, leading to internal salt formation.
2. Coupling reactions of diazonium salts occur with activated aromatic rings.
Step 2: Detailed Explanation:
Zwitter ion of Sulfanilic acid:
The proton from the sulfonic group is transferred to the amino group.
Structure: \( {}^+NH_3-C_6H_4-SO_3^- \)

Coupling with Phenol:
Benzene diazonium chloride reacts with phenol in a weakly alkaline medium (\(pH\) 9-10) at low temperature (273-278 K). The diazonium cation attacks the para-position of the phenoxide ion.
Reaction:
\[ C_6H_5N_2^+Cl^- + C_6H_5OH \xrightarrow{OH^-} C_6H_5-N=N-C_6H_4-OH + H_2O + Cl^- \]
The product is p-hydroxyazobenzene, an orange-colored dye.
Step 3: Final Answer:
The zwitter ion is \( {}^+H_3N-C_6H_4-SO_3^- \). The phenol coupling produces an orange azo dye.