Cannizzaro reaction
Aldehydes without alpha hydrogen, treated with concentrated alkali, undergo self oxidation and reduction to give an alcohol and the sodium salt of an acid.
BenzaldehydeC₆H₅CHOAldehyde - Step 1
(i) conc. NaOH (ii) H₃O⁺
Benzoic acidC₆H₅COOHCarboxylic acid
How it works
- Hydroxide adds to the C=O of one molecule.
- A hydride transfers to a second molecule.
- One molecule becomes the carboxylate and the other the alkoxide (alcohol).
What it makes
Equal amounts of an alcohol and an acid: for example benzyl alcohol and benzoic acid from benzaldehyde.
Where it fails
Not for aldehydes with an alpha hydrogen (they undergo aldol instead). The maximum yield of each product is 50 percent.
Class 12, Chapter 8 Aldehydes, Ketones and Carboxylic Acids
Cannizzaro reaction: quick answers
Which aldehydes give the Cannizzaro reaction?
Those with no alpha hydrogen, such as methanal and benzaldehyde.
What is formed from methanal?
Methanol and sodium methanoate.
Why is this called disproportionation?
One molecule is oxidised and another is reduced.