The Cannizzaro reaction is a distinctive chemical process involving the self-redox (reduction-oxidation) of an aldehyde that lacks an α-hydrogen. Named after its discoverer, Stanislao Cannizzaro, this reaction stands out among aldehyde reactions because, unlike most others, it does not require the presence of α-hydrogens.

In the Cannizzaro reaction, two molecules of an aldehyde react in the presence of a strong base. One molecule is reduced to form a primary alcohol, while the other is oxidized to produce a carboxylic acid. This simultaneous oxidation and reduction of the same compound is what characterizes the Cannizzaro reaction as a self-redox process.

The mechanism of the reaction begins with the strong base deprotonating the hydrate form of the aldehyde, leading to the formation of a di-anion. This di-anion then acts as a nucleophile, attacking another molecule of the aldehyde. The resulting intermediate undergoes a series of proton transfers, ultimately yielding the final products.

A key aspect of the Cannizzaro reaction is the necessity for the aldehyde to lack an α-hydrogen. Most other aldehyde reactions, such as the Aldol condensation, require the presence of α-hydrogens for the reaction to occur. In contrast, the absence of α-hydrogens in the Cannizzaro reaction prevents the aldehyde from undergoing enolate formation, which would otherwise compete with the Cannizzaro mechanism.

In summary, the Cannizzaro reaction is unique among aldehyde reactions due to its self-redox nature and the stipulation that the aldehyde must lack an α-hydrogen. This reaction offers a valuable method for the simultaneous synthesis of alcohols and carboxylic acids from aldehydes.