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Concept
Ozonolysis
Summary
In organic chemistry, ozonolysis is an organic reaction where the unsaturated bonds are cleaved with ozone (). Multiple carbon–carbon bond are replaced by carbonyl () groups, such as aldehydes, ketones, and carboxylic acids. The reaction is predominantly applied to alkenes, but alkynes and azo compounds are also susceptible to cleavage. The outcome of the reaction depends on the type of multiple bond being oxidized and the work-up conditions.
Detailed procedures have been reported.
Alkenes can be oxidized with ozone to form alcohols, aldehydes or ketones, or carboxylic acids. In a typical procedure, ozone is bubbled through a solution of the alkene in methanol at −78 °C until the solution takes on a characteristic blue color, which is due to unreacted ozone. Industry however recommends temperatures near -20 °C. This color change indicates complete consumption of the alkene. Alternatively, various other reagents can be used as indicators of this endpoint by detecting the presence of ozone. If ozonolysis is performed by introducing a stream of ozone-enriched oxygen through the reaction mixture, the effluent gas can be directed through a potassium iodide solution. When the solution has stopped absorbing ozone, the excess ozone oxidizes the iodide to iodine, which can easily be observed by its violet color. For closer control of the reaction itself, an indicator such as Sudan Red III can be added to the reaction mixture. Ozone reacts with this indicator more slowly than with the intended ozonolysis target. The ozonolysis of the indicator, which causes a noticeable color change, only occurs once the desired target has been consumed. If the substrate has two alkenes that react with ozone at different rates, one can choose an indicator whose own oxidation rate is intermediate between them, and therefore stop the reaction when only the most susceptible alkene in the substrate has reacted. Otherwise, the presence of unreacted ozone in solution (seeing its blue color) or in the bubbles (via iodide detection) only indicates when all alkenes have reacted.
Official source
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