Question

What product is formed when a ketone reacts with hydrazine \( (\mathrm{NH_2-NH_2}) \)?

• A. Alcohol
• B. Hydrazone
• C. Amide
• D. Ester

Hint:

Reactions of aldehydes and ketones with nitrogen nucleophiles:

• \(NH_2OH\) → Oxime
• \(NH_2NH_2\) → Hydrazone
• \(NH_2NHCONH_2\) → Semicarbazone

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the product formed from the reaction between a ketone and hydrazine (\(\mathrm{NH_2-NH_2}\)). This is a characteristic reaction of carbonyl compounds.
Step 2: Key Formula or Approach:
The reaction is a nucleophilic addition-elimination, also known as a condensation reaction.
The nucleophilic nitrogen atom of hydrazine attacks the electrophilic carbonyl carbon of the ketone. This is followed by the elimination of a water molecule to form the final product. The general reaction is:
\[ \text{Ketone} + \text{Hydrazine} \rightarrow \text{Product} + \text{Water} \] Step 3: Detailed Explanation:
A ketone has the general structure \(R_2C=O\), where R is an alkyl or aryl group.
Hydrazine has the structure \(\mathrm{H_2N-NH_2}\).
In the reaction, the two hydrogen atoms from one \(\mathrm{-NH_2}\) group of hydrazine and the oxygen atom from the carbonyl group (\(C=O\)) of the ketone are eliminated as a water molecule (\(\mathrm{H_2O}\)).
A carbon-nitrogen double bond (\(C=N\)) is formed in place of the carbon-oxygen double bond.
The specific reaction is:
\[ R_2C=O + \mathrm{H_2N-NH_2} \rightarrow R_2C=N-NH_2 + \mathrm{H_2O} \] The product, with the functional group \(R_2C=N-NH_2\), is called a hydrazone.
Step 4: Final Answer:
When a ketone reacts with hydrazine, the product formed is a hydrazone. This corresponds to option (B).