Match the LIST-I with LIST-II.
| LIST-I: Name Reaction | LIST-II: Reagent/Product | ||
| A. | Gattermann reaction | I. | Br2 / NaOH |
| B. | Coupling reaction | II. | Primary aliphatic amine |
| C. | Hofmann bromamide degradation reaction | III. | Cu/ HCl |
| D. | Gabriel phthalimide synthesis | IV. | p-Aminobenzene |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-III, B-IV, C-I, D-II
These name reactions fall into three groups: reactions of diazonium salts in which the diazo group is replaced (Sandmeyer with \( \ce{Cu2Cl2} \)/HCl, Gattermann with Cu/HCl), reactions in which it is retained (coupling with phenol or aniline), and preparations of amines (Hofmann bromamide degradation with Br2/NaOH, Gabriel phthalimide synthesis).
(A) Gattermann reaction — This matches (III) Cu/ HCl. Benzene diazonium chloride with copper powder and HCl gives chlorobenzene. The copper powder takes the place of the \( \ce{Cu2Cl2} \) used in the Sandmeyer reaction.
\( \displaystyle \ce{C6H5N2^+Cl^-} \xrightarrow{\ce{Cu/HCl}} \ce{C6H5Cl + N2} \)
(B) Coupling reaction — This matches (IV), by elimination: coupling gives p-aminoazobenzene; p-aminobenzene as printed is aniline. Benzene diazonium chloride couples with aniline at the para position to give the yellow azo dye p-aminoazobenzene.
\( \displaystyle \ce{C6H5N2^+Cl^- + C6H5NH2 -> C6H5-N=N-C6H4-NH2 + HCl} \)
(C) Hofmann bromamide degradation reaction — This matches (I) Br2 / NaOH. An amide heated with bromine and aqueous NaOH gives a primary amine with one carbon atom fewer.
\( \displaystyle \ce{RCONH2 + Br2 + 4NaOH -> RNH2 + Na2CO3 + 2NaBr + 2H2O} \)
(D) Gabriel phthalimide synthesis — This matches (II) Primary aliphatic amine. Potassium phthalimide reacts with an alkyl halide, and hydrolysis then gives a pure primary aliphatic amine. It cannot make aromatic amines, because aryl halides do not undergo nucleophilic substitution with phthalimide.
\( \displaystyle \ce{C6H4(CO)2NH + KOH} \xrightarrow{\text{ethanol}} \ce{C6H4(CO)2N^-K^+ + H2O} \)
\( \displaystyle \ce{C6H4(CO)2N^-K^+ + R-X -> C6H4(CO)2N-R + KX} \)
\( \displaystyle \ce{C6H4(CO)2N-R + 2NaOH} \xrightarrow{\text{heat}} \ce{R-NH2 + C6H4(COONa)2} \)
Shortcut: The pair (A)–(III) appears in Options (2) and (4). The pair (B)–(IV) then leaves only Option (4).
Note: It seems that there is a mistake in the original NTA paper, which prints p-Aminobenzene in item IV when it should read p-Aminoazobenzene.