Question

Draw structure of the 2,4-dinitrophenylhydrazone derivative of benzaldehyde.

Hint:

2,4-dinitrophenylhydrazine (2,4-DNP, also called Brady's reagent) reacts with the carbonyl group of an aldehyde or ketone. The C=O oxygen is replaced by =N-NH-Ar, where Ar is the 2,4-dinitrophenyl ring.

Answer 1

Step 1: Identify the reagent.
2,4-dinitrophenylhydrazine (Brady's reagent) is \(O_2N-C_6H_3(NO_2)-NH-NH_2\), a substituted hydrazine.

Step 2: Identify the carbonyl partner.
Benzaldehyde is \(C_6H_5-CHO\).

Step 3: Know the reaction.
The \(C=O\) oxygen of benzaldehyde is replaced by \(=N-NH-Ar\), where Ar is the 2,4-dinitrophenyl ring, with loss of one water molecule.

Step 4: Build the product.
The new bond is \(C_6H_5-CH=N-NH-C_6H_3(NO_2)_2\), with the two nitro groups at the 2 and 4 positions of the second ring.

Step 5: Write it clearly.
So the derivative is the 2,4-dinitrophenylhydrazone of benzaldehyde.

Answer: The structure is \(C_6H_5-CH=N-NH-C_6H_3(NO_2)_2\), where the second benzene ring carries nitro groups at positions 2 and 4 (benzaldehyde 2,4-dinitrophenylhydrazone).