molozonide

Molozonide is a short‑lived intermediate in the ozonolysis of alkenes. It refers to the primary ozonide formed by the cycloaddition of ozone to a carbon–carbon double bond, resulting in a five‑membered ring known as a 1,2,3‑trioxolane. At room temperature this species is highly unstable and decomposes rapidly via a Criegee rearrangement.

In the typical ozonolysis mechanism, the nascent molozonide fragments to give carbonyl-containing products and a reactive carbonyl oxide species, the Criegee intermediate. The carbonyl fragments are aldehydes or ketones, with the precise outcome depending on the substitution pattern of the original alkene and the workup conditions (reductive versus oxidative). The Criegee intermediate can further react with water, solvents, or other reagents to furnish the final carbonyl products.

Because of its instability, molozonide is not ordinarily isolated under standard laboratory conditions. It is generally observed only at very low temperatures or inferred spectroscopically in situ during ozonolysis. Its existence helps explain why ozonolysis proceeds through a rapid sequence of transformations rather than a single, simple addition event.

Molozonide is related to broader concepts in ozonolysis, including the Criegee intermediate and the overall oxidation pathway that converts alkenes into carbonyl compounds. It serves primarily as an mechanistic intermediate rather than a practical reagent.