Question

Explain Cannizzaro reaction with chemical equation.

Hint:

Remember: The Cannizzaro reaction takes place only with aldehydes that lack $\alpha$-hydrogen atoms (like formaldehyde and benzaldehyde). If $\alpha$-hydrogens are present, aldol condensation occurs instead.

Answer 1

The Cannizzaro reaction is a redox (disproportionation) reaction that occurs when an aldehyde without an $\alpha$-hydrogen atom (such as formaldehyde, benzaldehyde) is treated with a concentrated alkali.
In this reaction:
- One molecule of the aldehyde is oxidized to a carboxylate ion, and
- Another molecule of the same aldehyde is reduced to a primary alcohol.
General reaction:
\[ 2 \, R{-}CHO \; \xrightarrow[\text{conc. NaOH/KOH}]{} \; R{-}CH_2OH \; + \; R{-}COONa \]
Example with formaldehyde:
\[ 2 \, HCHO \; \xrightarrow[\text{conc. NaOH}]{} \; CH_3OH \; + \; HCOONa \]
Thus, the Cannizzaro reaction simultaneously produces an alcohol and a carboxylate salt.