Question

The correct set of reagents for the following conversion is 

• A. (i) NaNH$_2$/liq. NH$_3$; (ii) NaNO$_2$/dil. HCl; (iii) CuCN, heat
• B. (i) HNO$_3$/H$_2$SO$_4$; (ii) Zn/HCl; (iii) NaNO$_2$/dil. HCl; (iv) CuCN, heat
• C. (i) Mg/ether, H$_3$O$^+$; (ii) (EtO)$_2$CO; (iii) NH$_2$OH; (iv) PCl$_5$
• D. (i) Mg/ether, H$_3$O$^+$; (ii) HNO$_3$/H$_2$SO$_4$; (iii) NaNO$_2$/dil. HCl; (iv) CuCN, heat

Hint:

Aryl cyanides are best prepared from diazonium salts using CuCN (Sandmeyer reaction).

Answer 1

The Correct Option is A

Step 1: Identify required transformation.
The product is p-cyano anisole, meaning CN must replace the bromine atom. The only reliable method for aryl-CN introduction is via diazonium salt (Sandmeyer reaction).
Step 2: Steps needed.
We must convert Ar–Br → Ar–NH$_2$ → Ar–N$_2^+$ → Ar–CN.
Thus the reagents must do the following:
– Nitration to form p-nitro anisole.
– Reduction of –NO$_2$ to –NH$_2$.
– Diazotization with NaNO$_2$/HCl.
– Replacement of N$_2^+$ with CN using CuCN + heat.
Step 3: Matching with options.
Option (B) exactly matches:
(i) Nitration, (ii) Reduction, (iii) Diazotization, (iv) Sandmeyer cyanation.
Step 4: Conclusion.
Thus the correct sequence is option (B).