ozonolysis

Ozonolysis is a chemical reaction in which ozone cleaves carbon–carbon double bonds (alkenes) to form carbonyl-containing fragments. The process begins with the addition of ozone across the double bond to give a molozonide that rapidly rearranges to a more stable ozonide. After the ozonide is formed, a workup step converts it into the final carbonyl products.

Two common workups determine the fate of the fragments. Reductive workup, using reagents such as zinc in acetic acid or dimethyl sulfide, reduces the ozonide to aldehydes and/or ketones corresponding to the two halves of the original double bond. Oxidative workup, typically with hydrogen peroxide in water or alcohol, oxidizes the fragments to carboxylic acids (for example, formaldehyde becomes formic acid, and other aldehydes become their corresponding acids). For terminal alkenes, reductive workup yields an aldehyde and formaldehyde; for internal alkenes, two carbonyl compounds—usually aldehydes or ketones—are formed depending on substitution.

Scope and limitations: Ozonolysis is applicable to most non-conjugated alkenes, including cyclic systems, but polyenes and molecules bearing sensitive functionalities may require protective strategies or alternative methods. The reaction is performed at very low temperatures (often −78 °C) to stabilize reactive ozonides, and ozone is a hazardous oxidant, so appropriate safety and containment measures are essential.

Applications: The reaction is used for structural elucidation, to fragment complex molecules into simpler carbonyl-containing pieces, and as a synthetic tool to introduce carbonyl functionality or to effect purposeful bond cleavage in larger substrates.