Question

A nitrogen-containing organic compound gave an oily liquid on heating with bromine and potassium hydroxide solution. On shaking the product with acetic anhydride, an antipyretic drug was obtained. The reactions indicate that the starting compound is:
A. Aniline
B. Benzamide
C. Acetamide
D. Nitrobenzene

Answer 1

Hint: All the options are nitrogen-containing organic compounds. Aniline, benzamide, acetamide, and nitrobenzene have amine, amide, amide, and nitro functional groups respectively.

Complete Step by Step Solution:
On heating with bromine and potassium hydroxide, the Hoffmann bromamide reaction takes place. In this reaction, primary amide gets degraded and forms primary amine. So first, find the compounds with amide functional groups from the given options.

Here, in the options, the first options B and C contain an amide functional group. In the question, it is mentioned that an oily compound is formed meaning it is non-volatile and aromatic compounds are non-volatile. Of the B and C options, only the B option i.e., benzamide is aromatic. And also, acetamide is solid, not an oily compound. So, the starting compound is benzamide.

Image:Hofmann bromamide reaction of benzamide and formation of antipyretic drug.

In this reaction product without a carbonyl functional group and hence benzamide forms aniline which is aromatic in nature and oily. Aniline then further reacted with acetic anhydride to give acetanilide which is an antipyretic drug.

So, the option B is correct.

Note: Antipyretic drugs are used in fever. Some examples are acetanilide, ibuprofen, and acetaminophen. Physical properties of compounds are equally important to understanding the chemistry of reactions. Here, aromatic compounds are non-volatile compounds because of the conjugation present in the system making the system stable.