The Mozingo reduction, also known as thioketal reduction, is an organic reaction that converts the carbonyl group of an aldehyde or ketone into a methylene or methyl group. In simple terms, the oxygen of the carbonyl group is removed and replaced by hydrogen atoms. Thus, the Mozingo reduction is a method of carbonyl deoxygenation. ^[1–4]

The reaction is named after Ralph Mozingo, who reported the cleavage of thioethers with Raney nickel in 1942.

Mechanism

Step 1: Formation of the Dithioacetal

The aldehyde or ketone reacts with a dithiol in the presence of an acid catalyst. One sulfur atom of the dithiol first attacks the carbonyl carbon. Through an acid-catalyzed process similar to acetal formation, the second sulfur atom also attaches to the same carbon, forming a cyclic sulfur-containing compound and eliminating water from the carbonyl oxygen. ^[1–4]

Aldehydes form dithioacetals, while ketones form the corresponding dithioketals, often called thioketals.

Step 2: Desulfurization with Raney Nickel

The dithioacetal is then treated with Raney nickel. The carbon-sulfur bonds are broken on the nickel surface, and hydrogen atoms replace the sulfur-containing groups.

As a result, the original carbonyl carbon becomes a methylene group (–CH₂–) in a ketone or a methyl group (–CH₃) in an aldehyde, giving the corresponding hydrocarbon.

This second step is called hydrogenolysis, in which the carbon–sulfur bonds are broken, and hydrogen replaces the sulfur-containing groups.