Give the mechanism of the Cannizzaro reaction with an example — JEE Chemistry

The Cannizzaro reaction occurs with aldehydes having no α-hydrogen in concentrated NaOH. One molecule is oxidised and another is reduced (disproportionation).

Example: Formaldehyde

$$2HCHO \xrightarrow{conc. NaOH} HCOO^-Na^+ + CH_3OH$$

Mechanism:

1. $OH^-$ attacks one $HCHO$ → hydride donor complex
2. Hydride ($H^-$) transferred to second $HCHO$
3. Products: formate ion (oxidised) and methanol (reduced)

$$2HCHO + NaOH \rightarrow HCOONa + CH_3OH$$