Aniline Yellow (Azo Dye Coupling)

Formula / Core Reaction:

$$\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- + \text{C}_6\text{H}_5\text{NH}_2 \xrightarrow{\text{pH } 4-5} \text{C}_6\text{H}_5\text{-N=N-C}_6\text{H}_4\text{-NH}_2 + \text{HCl}$$

Concept: Electrophilic aromatic substitution reaction (azo coupling) where benzene diazonium chloride attacks aniline in weakly acidic conditions ($$\text{pH } 4-5$$) to form p-aminoazobenzene.

Notation / Key Observation:

• $$\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^-$$: Benzene diazonium chloride;
• $$\text{C}_6\text{H}_5\text{-N=N-C}_6\text{H}_4\text{-NH}_2$$: p-Aminoazobenzene (Aniline Yellow dye).