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Diazonium salts – coupling reaction
Concepts tested here
- nitrobenzene-azo-dye
All Questions
2016 Phase II 1 question
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A given nitrogen-containing aromatic compound A reacts with Sn/HCl, followed by $HNO_2$ to give an unstable compound B. B, on treatment with phenol, forms a beautiful coloured compound C with the molecular formula $C_{12}H_{10}N_2O$. The structure of compound A is:
Reduction, diazotisation and coupling with phenol give an azo dye.
$C_6H_5NO_2$ (A) $\xrightarrow{Sn + HCl\ (reduction)}$ $C_6H_5NH_2$ (aniline) $\xrightarrow{HNO_2}$ $C_6H_5N_2^+Cl^-$ (B, benzene diazonium chloride)
B + phenol → p-hydroxyazobenzene, $C_6H_5-N=N-C_6H_4-OH$ (C, coloured dye)
So A is nitrobenzene.