Question

Explain Cannizzaro's reaction with the help of benzaldehyde.

Answer 1

Two molecules of a non-enolizable aldehyde (without α-hydrogen) combine with a strong basic (conc. NaOH or KOH) in Cannizzaro's reaction, a redox reaction. An alcohol is created by reducing one molecule, while a carboxylate ion is created by oxidising the other.

Reaction Mechanism Using Benzaldehyde

• Reactants: Benzaldehyde (C₆H₅CHO)
• Reagent: Conc. NaOH/KOH
• Products: Benzyl alcohol (C₆H₅CH₂OH) and Sodium benzoate (C₆H₅COO⁻Na⁺)

Reaction:

\[\ce{2C_6H_5CHO + NaOH -> C_6H_5CH_2OH + C_6H_5COO^-Na^+}\]

• One benzaldehyde molecule is reduced to benzyl alcohol.
• The other benzaldehyde molecule is oxidized to sodium benzoate.

Importance of Reaction:

• This reaction works exclusively with aldehydes that don't include α-hydrogen, such as formaldehyde and benzaldehyde.
• It is utilised in the process of making carboxylates and alcohols. 

Benzyl alcohol and sodium benzoate are the products of Cannizzaro's reaction, which is the disproportionation of two benzaldehyde molecules in the presence of NaOH.