Formaldehyde [HCHO] undergoes Cannizzaro reaction: Give reason.

Formaldehyde (HCHO) undergoes the Cannizzaro reaction due to its unique structure and the presence of an alpha hydrogen atom. The Cannizzaro reaction is a redox reaction in which an aldehyde, such as formaldehyde, acts as both an oxidizing agent and a reducing agent simultaneously. It involves the self-disproportionation of aldehydes in the presence of strong bases.

The reaction occurs in two steps:

Disproportionation of Aldehyde: The aldehyde molecule (in this case, formaldehyde) reacts with a base (e.g., NaOH or KOH) to form an anion (carbanion) and a corresponding alcohol. In the case of formaldehyde, it forms methoxide ion (CH3O-) and methanol (CH3OH).
HCHO + OH- → CH3O- + CH3OH

Redox Reaction: In this step, the carbanion (CH3O-) generated in the first step acts as a reducing agent, while another molecule of aldehyde reacts with it as an oxidizing agent. This results in the formation of a carboxylic acid and a primary alcohol. In the case of formaldehyde, the carbanion reacts with another molecule of formaldehyde to form formate ion (HCOO-) and methanol (CH3OH).
2 CH3O- + HCHO → HCOO- + CH3OH

Overall, the Cannizzaro reaction leads to the oxidation of one molecule of formaldehyde to formic acid (HCOOH) and the reduction of another molecule to methanol (CH3OH).

It is important to note that not all aldehydes undergo the Cannizzaro reaction. Aldehydes with no alpha hydrogen atoms (no hydrogen attached to the carbon adjacent to the carbonyl group) do not undergo this reaction. Formaldehyde is unique because it is the simplest aldehyde and contains an alpha hydrogen atom, making it susceptible to the Cannizzaro reaction.