Question

What is the end product (B) in the following reaction sequence?

(A) $ n - butylamine $
(B) $ n - propyl cyanide $
(C) $ propyl\;isocyanide $
(D) $ n - propylamine $

Answer 1

Hint: Above reactions suggest that butanamide $ C{H_3}C{H_2}C{H_2}CON{H_2} $ reacts with Phosphorus pentoxide $ {{\text{P}}_2}{{\text{O}}_5} $ to give product A and when Product A is treated with Lithium Aluminium hydride $ LiAl{H_4} $ it gives a product B. Phosphorus pentoxide is used for dehydration reaction to convert amides into nitriles. Lithium Aluminum hydride is a reducing agent used to convert cyanides into amines.

Complete answer:
Phosphorus pentoxide is a dehydrating agent, it is used for the conversion of nitriles from primary amides. Since butanamide is a primary amide, it will undergo dehydration to form cyanide and water the reaction taking place will be:

From the reaction we can see the product formed is $ {\text{n}} - propyl cyanide $ . According to the question the $ {\text{n}} - propyl cyanide $ is the product A.
Now, product A or $ {\text{n}} - propyl cyanide $ is treated with Lithium Aluminum hydride which is a reducing agent used to convert cyanides or nitriles into amines to get product B, the reaction taking place will be:

From the reaction we can see the product formed is $ {\text{n}} - butylamine $ . According to the question the $ {\text{n}} - butylamine $ must be the product B.
So, option (A) is the correct answer.

Note:
Phosphorus pentoxide is a very good dehydrating agent it is used in different areas as a part of Onodera reagent which is used for the oxidation of alcohols, used for converting some mineral acids into anhydrides. Lithium Aluminum hydride is a good reducing agent it is used to reduce polar bonds. It has many uses: it is used to convert aldehyde and ketone to primary and secondary alcohols respectively, carboxylic acids to primary alcohols, amides and nitrile to amines.