Which of the following reagents will bring out the following transformation ? (A) \(\text{NaNO}_2\)/HCl and Cu/HCl (B) \(\text{NaNO}_2\)/NaOH and Cu/HCl (C) \(\text{NaNO}_2\)/HCl and \(\text{Cu}_2\text{Cl}_2\)/HCl (D) \(\text{NaNO}_2\)/NaOH and \(\text{Cu}_2\text{Cl}_2\)/HCl Choose the correct answer from the options given below:
Show Hint
Diazotisation needs acid, not NaOH. Then Sandmeyer (Cu2Cl2/HCl) or Gattermann (Cu/HCl) gives chlorobenzene.
Step 1: Plan the route.
To swap NH2 for Cl on a benzene ring, we first turn NH2 into a good leaving group, N2+, and then let a copper salt supply chloride.
Step 2: The acid test for the first reagent.
Diazotisation needs HNO2 generated in situ: $\text{NaNO}_2 + \text{HCl} \rightarrow \text{HNO}_2 + \text{NaCl}$. In NaOH there is no free HNO2, so NaNO2/NaOH cannot be the first reagent. This removes (B) and (D) at once.
Step 3: Second reagent.
For the diazonium chloride $\text{ArN}_2^+\text{Cl}^-$ both Cu2Cl2/HCl (Sandmeyer) and Cu/HCl (Gattermann) give $\text{ArCl} + \text{N}_2$.
Step 4: Combine.
Valid pairs are NaNO2/HCl with Cu/HCl, which is (A), and NaNO2/HCl with Cu2Cl2/HCl, which is (C). The correct set is (A) and (C) only.
Final Answer:
The correct choice is (A) and (C) only, which is option 1.
\[ \boxed{\text{Option 1}} \]
