Question

Complete the equation : \[ CH_3CHO + H_2NNH_2 \longrightarrow ? \]

Hint:

Important reactions of aldehydes and ketones: \[ RCHO + H_2NNH_2 \rightarrow RCH=NNH_2 + H_2O \] \[ R_2CO + H_2NNH_2 \rightarrow R_2C=NNH_2 + H_2O \] The products formed are called hydrazones.

Answer 1

Step 1: Reaction type.
Aldehydes react with hydrazine ($H_2NNH_2$) by nucleophilic addition followed by elimination (condensation) to form hydrazones.
Step 2: Nucleophilic addition.
The $-NH_2$ nitrogen of hydrazine attacks the electrophilic carbonyl carbon of $CH_3CHO$, forming the unstable tetrahedral intermediate $CH_3CH(OH)NHNH_2$.
Step 3: Elimination gives the hydrazone.
Water is eliminated, forming a $C=N$ double bond. The product is acetaldehyde hydrazone: \[ CH_3CHO + H_2NNH_2 \rightarrow CH_3CH=NNH_2 + H_2O \] \[ \boxed{CH_3CHO + H_2NNH_2 \rightarrow CH_3CH=NNH_2 + H_2O} \]