Question

: The reagent used in Wolff-Kishner reduction is:
A. $N{{H}_{2}}-N{{H}_{2}}$and KOH in ethylene glycol
B. Zn-Hg/conc. HCl
C. $NaB{{H}_{4}}$
D. Na-Hg/${{H}_{2}}O$

Answer 1

Hint:Wolff-Kishner reduction is a reduction reaction which involves formation of saturated hydrocarbons from carbonyl compounds/ This reaction is similar to Clemmenson’s reduction reaction except for the reagents and catalysts used and pH conditions.

Complete step-by-step answer:The Wolf-Kishner reduction got its name after a Danish chemist, Wolf-Kishner. This reduction reaction is a reaction that is performed to reduce carbonyl compounds such as aldehydes or ketones to hydrocarbons that is alkanes using basic solution of hydrazine and a strong base (KOH).
We should remember that in this method aldehyde or ketone is heated with a mixture of hydrazine and a strong base (KOH) to $453-473K$in ethylene glycol as solvent.
Let us understand the complete process of reaction in brief. During this reduction, aldehyde or ketone is first converted to hydrazone with hydrazine and then on treatment with a strong base it gets converted to hydrocarbon (alkane)
The reaction is illustrated below
$C{{H}_{3}}CHO+N{{H}_{2}}-N{{H}_{2}}\to C{{H}_{3}}CH=NN{{H}_{2}}\xrightarrow[Glycol]{KOH,453-473K}C{{H}_{3}}-C{{H}_{3}}+{{N}_{2}}$
In the above reaction we have used the following reagents
1. Hydrazine $\left( N{{H}_{2}}-N{{H}_{2}} \right)$
2. KOH in ethylene glycol.
The Wolff-Kishner reduction has been modified into several techniques, each with their own advantages and disadvantages.

Hence, the correct option is A.

Note:We should note that, Because the Wolff-Kishner reduction requires highly basic conditions, it is unsuitable for base sensitive substrates. In some cases, formation of the required hydrazone will not occur at sterically hindered carbonyl groups, thus preventing the reaction. However, this method can be superior to the related clemenson's reduction for compounds containing acid-sensitive functional groups such as pyrroles and for high molecular weight compounds.