Question

Benzonitrile can be prepared from benzaldehyde on treatment with

• A. $NH_3$
• B. $NH_3$ followed by hydrogenation with Ni
• C. $NH_2OH$
• D. $NH_2OH$ followed by dehydration with acetic anhydride

Answer 1

The Correct Option is D

Benzonitrile can be prepared from benzaldehyde on treatment with $NH _{2} OH$ followed by dehydration with acetic anhydride. This reaction occur via Beckmann rearrangement.

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For benzonitrile formation, the key step is a hydride shift followed by deprotonation of nitrogen that ultimately gives benzonitrile

Answer 2

Benzonitrile (C\(_6\)H\(_5\)CN) can be prepared from benzaldehyde (C\(_6\)H\(_5\)CHO) by first converting benzaldehyde to benzaldoxime (C\(_6\)H\(_5\)CH=NOH) and then dehydrating the benzaldoxime to benzonitrile. The overall reaction can be achieved through the following steps:

1. Formation of Benzaldoxime:
  Benzaldehyde is treated with hydroxylamine (NH\(_2\)OH) to form benzaldoxime.
  \[
  \text{C}_6\text{H}_5\text{CHO} + \text{NH}_2\text{OH} \rightarrow \text{C}_6\text{H}_5\text{CH=NOH} + \text{H}_2\text{O}
  \]

2. Dehydration of Benzaldoxime:
  Benzaldoxime is then dehydrated to form benzonitrile. This dehydration can be accomplished using a dehydrating agent such as phosphorus pentachloride (PCl\(_5\)) or thionyl chloride (SOCl\(_2\)).
  \[
  \text{C}_6\text{H}_5\text{CH=NOH} \rightarrow \text{C}_6\text{H}_5\text{CN} + \text{H}_2\text{O}
  \]

The overall process can be summarized as:
\[
\text{C}_6\text{H}_5\text{CHO} \xrightarrow{\text{NH}_2\text{OH}} \text{C}_6\text{H}_5\text{CH=NOH} \xrightarrow{\text{dehydration}} \text{C}_6\text{H}_5\text{CN}
\]

Therefore, benzonitrile can be prepared from benzaldehyde by treatment with hydroxylamine followed by dehydration of the intermediate benzaldoxime using a dehydrating agent such as phosphorus pentachloride (PCl\(_5\)) or thionyl chloride (SOCl\(_2\)).
So The correct Answer is Option (4) \(NH_2OH\) followed by dehydration with acetic anhydride