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) The Wolff-Kishner reduction converts a carbonyl compound (C=O) to a methylene group (CH\(_2\)). This is achieved by reacting the carbonyl compound with hydrazine (NH\(_2\)NH\(_2\)) to form a hydrazone, followed by heating with KOH and ethylene glycol, which eliminates nitrogen (N\(_2\)).

(b)Decarboxylation of sodium salts of aromatic carboxylic acids (Ar/RCOONa) occurs upon heating (\(\Delta\)) with sodium hydroxide (NaOH) and calcium oxide (CaO). The products are 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) The Cannizzaro reaction involves the disproportionation of formaldehyde (HCHO) when treated with concentrated NaOH and heat (\(\Delta\)). One formaldehyde molecule is reduced to methanol (CH\(_3\)OH), while another is oxidized to a formate anion (HCOO\(^-\)), which precipitates as sodium formate (HCOO\(^-\)Na\(^+\)).\[2\text{HCHO} \xrightarrow{\text{Conc. NaOH}, \, \Delta} \, \text{HCOO}^{-}\text{Na}^{+} + \text{CH}_3\text{OH}\]