Question

Write the reaction involved in the following: Wolff-Kishner reduction
(b) Decarboxylation reaction
(c) Cannizzaro reaction

Hint:

- Wolff-Kishner reduction is a key method for reducing carbonyl groups to methylene groups (CH\(_2\)). - The decarboxylation reaction is widely used to remove carboxyl groups from aromatic compounds. - The Cannizzaro reaction is a redox reaction that occurs in the absence of an aldehyde with no hydrogen atom attached to the carbonyl group.

Answer 1

(a) In the Wolff-Kishner reduction, a carbonyl compound (C=O) is treated with hydrazine (NH\(_2\)NH\(_2\)) and water to form a hydrazone intermediate (C=NH\(_2\)). The reaction is then heated in the presence of KOH and ethylene glycol, which removes the nitrogen as N\(_2\), resulting in the reduction of the carbonyl group to a methylene group (CH\(_2\)).

(b) In the Decarboxylation reaction, sodium salts of aromatic carboxylic acids (Ar/RCOONa) undergo decarboxylation when treated with sodium hydroxide (NaOH) and calcium oxide (CaO) at high temperature (\(\Delta\)). This results in the formation of a hydrocarbon (Ar-H/R-H) and sodium carbonate (Na\(_2\)CO\(_3\)). \[ \text{Ar/RCOONa} + \text{NaOH} \xrightarrow{\text{CaO}, \, \Delta} \, \text{Ar-H/R-H} + \text{Na}_2\text{CO}_3 \]

(c) In the Cannizzaro reaction, formaldehyde (HCHO), in the presence of concentrated sodium hydroxide (NaOH) and heat (\(\Delta\)), undergoes disproportionation. This reaction involves two molecules of formaldehyde. One molecule is reduced to methanol (CH\(_3\)OH), while the other is oxidized to formate anion (HCOO\(^-\)), which then combines with a sodium ion (Na\(^+\)). \[ 2\text{HCHO} \xrightarrow{\text{Conc. NaOH}, \, \Delta} \, \text{HCOO}^{-}\text{Na}^{+} + \text{CH}_3\text{OH} \]