Introduction
Ozonolysis is an organic reaction where ozone (O3) is used to cleave unsaturated bonds, such as those found in alkenes or alkynes. This process results in the replacement of multiple carbon-carbon bonds with carbonyl (C=O) groups, leading to the formation of compounds such as aldehydes, ketones, and carboxylic acids. While alkenes are the primary targets of this reaction, alkynes can also undergo ozonolysis.
In the process, ozone is passed through a solution of the alkene in methanol at a temperature of -78 °C until the solution turns blue, indicating the presence of unreacted ozone. Once the addition is complete, a reagent is added to transform the intermediate ozonide into a carbonyl derivative. Reductive conditions are typically preferred over oxidative conditions for this step. Triphenylphosphine, thiourea, zinc dust, or dimethyl sulfide can be used to yield aldehydes or ketones, while sodium borohydride can be used to produce alcohols.
The mechanism of the reaction involves the formation of an intermediate molozonide through a 1,3-dipolar cycloaddition between the alkene and ozone. This molozonide then undergoes a retro-1,3-dipolar cycloaddition to yield a carbonyl oxide and an aldehyde or ketone. These products can then react again in a 1,3-dipolar cycloaddition to produce a stable ozonide intermediate.
Reaction
Mechanism
