The Cannizzaro reaction involves self-oxidation and reduction (disproportionation) of aldehydes without an α-hydrogen atom when heated with concentrated alkali. Aldehydes lacking α-hydrogen atoms participate in this reaction.
What is the Cannizzaro reaction, and what type of aldehydes undergo this disproportionation reaction?
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The Cannizzaro reaction is a disproportionation reaction involving certain aldehydes that lack α-hydrogen atoms. In this reaction, one molecule of the aldehyde is reduced to its corresponding alcohol (usually a primary alcohol), while another molecule of the same aldehyde is oxidized to its corresponding carboxylic acid. This reaction is driven by the absence of α-hydrogen atoms, making the aldehyde unable to undergo aldol condensation. The Cannizzaro reaction is prominent for aldehydes like formaldehyde (HCHO) and benzaldehyde (C₆H₅CHO) where α-hydrogen atoms are not available, resulting in the simultaneous oxidation and reduction of the same aldehyde molecule.