The Cannizzaro reaction named after Stanislao Cannizzaro is a chemical reaction that involves disproportionation of any aldehyde lacking a hydrogen atom in the alpha position, in the presence of a strong base. The oxidation product is a carboxylic acid and the reduction product is an alcohol. In the presence of a alpha hydrogen atom, the aldol condensation is the preferred reaction

The first reaction step is nucleophilic addition of the base (for instance the hydroxy anion) to the aldehyde. The di-anion exists in a very stong basic environment.

Both intermediates can react further. A intramolecular hydride migration is made possible by the electron donating character of the alpha oxygen anion. This reaction creates a hydroxyl anion and a carboxylic acid

A special condition is the crossed cannizaro reaction. This variation is more common these days because the original Cannizzaro reaction yields a mixture of alcohol and carboxylix acid. For example any aldehyde can be reduced when in the presence of Formaldehyde. Formaldehyde is oxidized to acetic acid and the corresponding alcohol is obtained in a high yield although the atom economy is still low.

Industrial example:

• butyraldehyde reacts with an excess of formaldehyde in presence of sodium hydroxide to form trimethylolpropane (TMP, (CH₂OH)₃CCH₂CH₃) and sodium formiate ¹.

References

• Translated in part from German Wiki original
• ¹ www.basf.com [1]