Question

The correct match between Item-I (starting material) and Item-II (reagent) for the preparation of benzaldehyde is :

Item-I	Item-II
(I) Benzene	(P) HCl and \(\mathrm{SnCl_2}\), \(\mathrm{H_3O^+}\)
(II) Benzonitrile	(Q) \(\mathrm{H_2}\), Pd-\(\mathrm{BaSO_4}\), S and quinoline
(III) Benzoyl Chloride	(R) CO, HCl and \(\mathrm{AlCl_3}\)

• A. (I) - (R), (II) - (P) and (III) - (Q)
• B. (I) - (P), (II) - (Q) and (III) - (R)
• C. (I) - (Q), (II) - (R) and (III) - (P)
• D. (I) - (R), (II) - (Q) and (III) - (P)

Hint:

Recall the named reactions: Gattermann-Koch (CO, HCl, AlCl3), Stephen reduction (SnCl2/HCl then H3O+) and Rosenmund reduction (H2, Pd-BaSO4).

Answer 1

The Correct Option is A

(I) Benzene \(\rightarrow\) benzaldehyde: Gattermann-Koch reaction, CO, HCl and anhydrous \(\mathrm{AlCl_3}\) (R).
(II) Benzonitrile \(\rightarrow\) benzaldehyde: Stephen reduction, \(\mathrm{SnCl_2}\)/HCl followed by hydrolysis with \(\mathrm{H_3O^+}\) (P).
(III) Benzoyl chloride \(\rightarrow\) benzaldehyde: Rosenmund reduction, \(\mathrm{H_2}\), Pd-\(\mathrm{BaSO_4}\) poisoned with S/quinoline (Q).
So (I)-(R), (II)-(P), (III)-(Q).
Answer: (1) (I) - (R), (II) - (P) and (III) - (Q)