Advanced Topic 804 of 1102 Organic Chemistry
Cannizzaro Reaction
Aldehydes lacking alpha hydrogens disproportionate in strong base to alcohol and acid.
In-depth explanation of Cannizzaro Reaction
The Cannizzaro reaction is a disproportionation in which an aldehyde with no alpha hydrogen reacts with concentrated base. Because it has no alpha hydrogen, the aldehyde cannot form an enolate, so instead one molecule accepts a hydride ion from another molecule. One aldehyde is reduced to the primary alcohol while the other is oxidized to the carboxylate salt. The reaction is therefore an example of a reaction in which the same compound is simultaneously oxidized and reduced.
Going deeper: Cannizzaro Reaction
Key ideas: Aldehydes without alpha hydrogens (HCHO, benzaldehyde) disproportionate in concentrated NaOH: one molecule is oxidised to carboxylate and another reduced to alcohol, 2 PhCHO to PhCH2OH plus PhCOONa. Mechanism: hydroxide adds to the carbonyl, then hydride transfers to a second aldehyde. In crossed Cannizzaro, formaldehyde is oxidised (the better hydride donor) and the other aldehyde is reduced.
Common mistakes and connections: Students forget the requirement of no alpha hydrogens, or expect both products from one molecule. Another error is expecting acids rather than salts in basic medium; acidification is needed. Links to aldol competition, hydride transfer and redox disproportionation.
Visualization of Cannizzaro Reaction
Two molecules of a non-enolizable aldehyde disproportionate, one being reduced to an alcohol and one oxidized to the carboxylate in a 1:1 ratio. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Two molecules of benzaldehyde in concentrated sodium hydroxide give benzyl alcohol and benzoate ion.
Frequently asked questions about Cannizzaro Reaction
What is Cannizzaro Reaction?
Aldehydes lacking alpha hydrogens disproportionate in strong base to alcohol and acid.
Is Cannizzaro Reaction a beginner, intermediate or advanced topic?
Cannizzaro Reaction is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Cannizzaro Reaction?
Study these earlier topics in Organic Chemistry first: Ketones, Nucleophilic Addition to Carbonyls, Aldol Condensation.
What comes after Cannizzaro Reaction?
The next topics in Organic Chemistry are Tollens' Test and Fehling's Test.
Can I practise Cannizzaro Reaction with quizzes?
Yes. The interactive lesson includes a self-check question on Cannizzaro Reaction, and the Organic Chemistry quiz draws on every topic in this area.
Where Cannizzaro Reaction fits in Organic Chemistry
Cannizzaro Reaction is topic 76 of 148 in Organic Chemistry.