JEE Challenger
More from Amines
ChemMedAdv 2008 • Paper 2

Reaction of Aniline with Sodium Nitrite and Beta Naphthol

STATEMENT-1 : Aniline on reaction with NaNO2/HCl\text{NaNO}_2/\text{HCl} at 0 ∘C0\,^\circ\text{C} followed by coupling with β\beta-naphthol gives a dark blue coloured precipitate.

and

STATEMENT-2 : The colour of the compound formed in the reaction of aniline with NaNO2/HCl\text{NaNO}_2/\text{HCl} at 0 ∘C0\,^\circ\text{C} followed by coupling with β\beta-naphthol is due to the extended conjugation.

Options

A

STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is a correct explanation for STATEMENT-1

B

STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is NOT a correct explanation for STATEMENT-1

C

STATEMENT-1 is True, STATEMENT-2 is False

D

STATEMENT-1 is False, STATEMENT-2 is True

Correct

Topics & Concepts

AminesAmines

Step-by-Step Solution

To determine the correctness of the statements, let us analyze the chemical reactions involved step-by-step:

1. Analysis of STATEMENT-1:

When aniline (C6H5NH2\text{C}_6\text{H}_5\text{NH}_2) reacts with nitrous acid (formed in situ using NaNO2\text{NaNO}_2 and HCl\text{HCl}) at 0−5 ∘C0-5\,^\circ\text{C}, it undergoes a diazotization reaction to form benzene diazonium chloride:
C6H5NH2+NaNO2+2HCl→0−5 ∘CC6H5N2+Cl−+NaCl+2H2O\text{C}_6\text{H}_5\text{NH}_2 + \text{NaNO}_2 + 2\text{HCl} \xrightarrow{0-5\,^\circ\text{C}} \text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- + \text{NaCl} + 2\text{H}_2\text{O}

When benzene diazonium chloride is coupled with β\beta-naphthol (2-naphthol) in an alkaline medium, an electrophilic aromatic substitution reaction (azo coupling) occurs at the 1-position of β\beta-naphthol, yielding 1-(phenylazo)-2-naphthol:
C6H5N2+Cl−+C10H7OH→OH−C6H5−N=N−C10H6OH+Cl−+H2O\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- + \text{C}_{10}\text{H}_7\text{OH} \xrightarrow{\text{OH}^-} \text{C}_6\text{H}_5-\text{N}=\text{N}-\text{C}_{10}\text{H}_6\text{OH} + \text{Cl}^- + \text{H}_2\text{O}

The resulting compound, 1-(phenylazo)-2-naphthol, is a scarlet-red or orange-red dye (precipitate), not a dark blue precipitate.

Therefore, STATEMENT-1 is False.

2. Analysis of STATEMENT-2:

The intense color observed in azo dyes like 1-(phenylazo)-2-naphthol is attributed to the presence of the azo chromophore (−N=N−-\text{N}=\text{N}-) linked between aromatic rings. This setup results in an extended conjugated π\pi-system across the entire molecule.

Extending the conjugation lowers the energy gap (ΔE\Delta E) between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), shifting the absorption spectrum into the visible light region.

Therefore, STATEMENT-2 is True.

Conclusion:

  • STATEMENT-1 is False.
  • STATEMENT-2 is True.

Thus, the correct option is D.

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