Question

(A) Explain the following reactions and write chemical equations involved: (a) Wolff-Kishner reduction
(b) Etard reaction
(c) Cannizzaro reaction

Hint:

These reactions are important for the synthesis of various organic compounds. The Wolff-Kishner reduction is particularly useful in reducing aldehydes and ketones, while the Cannizzaro reaction is a classic example of disproportionation.

Answer 1

(a) Wolff-Kishner reduction: This reduction reaction is used to reduce carbonyl compounds (like aldehydes and ketones) to the corresponding methylene group. The reaction involves the use of hydrazine (N$_2$H$_4$) and a strong base, such as potassium hydroxide (KOH), under heat. The general equation is: \[ \text{RCHO} \xrightarrow{\text{N}_2\text{H}_4/KOH, \Delta} \text{RH} \] (b) Etard reaction: This reaction involves the oxidation of toluene (methylbenzene) to 2-formyl toluene (benzaldehyde) using chromyl chloride (CrO$_2$Cl$_2$) in the presence of nitric acid (HNO$_3$). The general equation is: \[ \text{C}_6\text{H}_5\text{CH}_3 \xrightarrow{\text{CrO}_2\text{Cl}_2, HNO_3} \text{C}_6\text{H}_4(\text{COH})\text{CH}_3 \] (c) Cannizzaro reaction: This reaction is a base-catalyzed disproportionation of non-enolizable aldehydes, where one molecule of aldehyde is reduced to alcohol, and another is oxidized to a carboxylic acid. The general equation is: \[ 2 \text{RCHO} \xrightarrow{\text{KOH}} \text{RCH}_2\text{OH} + \text{RCOOH} \]