Question

The reaction of $C{H_3}CHO$ and $N{H_2} - N{H_2}$ and the formation of $C{H_3} - CH = N - N{H_2}$ is an example of:
A) Nucleophilic substitution reaction
B) Elimination reaction
C) Condensation reaction
D) Electrophilic reaction

Answer 1

When aldehydes or ketones will react with hydrazine, it will give hydrazone. This is a name reaction known as the Wolff-Kishner reduction. This reaction is used to reduce aldehydes or ketones to alkanes with Hydrazine. We see that in this reaction the two $C - O$ bonds of aldehydes will break and will be replaced by two $C - H$ bonds.

Complete answer:
In this reaction we see that a water molecule is being removed and a carbonyl group leaves its double bonded oxygen and hydrazine leaves its double bonded nitrogen and forms a condensed product.
Let us now see how the reaction is taking place: -

            $C{H_3} - CH = O + {H_2}N - N{H_2} \to C{H_3} - CH = N - N{H_2} + {H_2}O$  

It is clear that the water molecule is being eliminated hence the reaction is called a condensation reaction. A condensation reaction is the one in which two or more molecules react to form a large molecule with the simultaneous loss of a small molecule such as water or methanol. We see that a new carbon-carbon bond is formed in the product of the reaction.

So, the correct option is (C)

Additional information: Hydrazine is very dangerous, not only it is toxic but also potentially explosive. It is also a common component of rocket fuel. It is a good reductant and a nucleophile. The formed hydrazine in the above reaction further reacts with a base to give ethane.

Note: The Wolff-Kishner reduction is used for carbon-carbon coupling. Clemmensen reduction is the same as the Wolff-Kishner reduction so you can easily get confused between the two. The difference between the two is that in Wolff kishner reduction a base is used whereas in Clemmensen reduction the conversion takes place in acidic conditions.