Write Tollen’s reagent test for acetaldehyde.(ii) Write the structure of zwitter ion of sulfanilic acid. Write the reaction between benzene diazonium chloride and phenol in alkaline medium.

Answer:

(i) Tollens’ test: Tollens’ reagent is ammoniacal silver nitrate, [Ag(NH₃)₂]⁺. When acetaldehyde is warmed with it, acetaldehyde is oxidised to acetate and Ag⁺ is reduced to metallic silver, which deposits as a shining silver mirror on the inner wall of the test tube:

CH₃CHO + 2[Ag(NH₃)₂]⁺ + 3OH⁻ → CH₃COO⁻ + 2Ag↓ (silver mirror) + 4NH₃ + 2H₂O

(ii) Zwitter ion of sulfanilic acid (4-aminobenzenesulfonic acid): the acidic –SO₃H group gives its proton to the basic –NH₂ group on the same molecule:

⁺H₃N–C₆H₄–SO₃⁻ (benzene ring with –NH₃⁺ and –SO₃⁻ at para positions, 1 and 4)

Coupling reaction: benzenediazonium chloride couples with phenol in alkaline medium (NaOH, 273–278 K) at the para position of phenol to give an orange azo dye, p-hydroxyazobenzene:

C₆H₅–N₂⁺Cl⁻ + C₆H₅OH + NaOH → C₆H₅–N=N–C₆H₄–OH (p-hydroxyazobenzene, orange) + NaCl + H₂O