Ozonolysis chemistry is receiving renewed attention as a means to break down long chain biomass molecules into more useful renewable chemical intermediates. However, ozonolysis reaction pathways and their mechanisms are not yet fully understood. Density functional theory calculations have been carried out to explore the possibility of unconventional mechanistic pathways for ozonolysis reactions. In particular, the products of ozonolysis in the presence of the excess of ozone (O3) or oxygen (O2) are investigated. The computations suggest that the reaction might be intercepted at the Criegee intermediate (CI) stage leading to a change in the final product distribution. The O3 attack on the CI results in aldehyde formation and release of O2. This previously unreported reaction is accompanied by a small activation barrier of ~10 kcal/mol. If extra O3 is present in the reaction mixture, it can further oxidize the formed aldehyde into the carboxylic acid.  The possibility of secondary ozonide (SOZ) reacting with O3 has also been explored. The calculations indicate that SOZ can be directly or indirectly decomposed into the excess acid upon exposure to O3. The indirect route here refers to the conversion of SOZ into the hydroxy anhydride, which subsequently reacts with O3 to yield an excess of acid. The mechanistic insight gained via these calculations can be used to preferentially control the outcome of the ozonolysis reaction, i.e., the aldehyde or acid can be selectively obtained by controlling the amount of O3 in the reaction mixture.

Computational modeling suggests unconventional mechanistic pathways for ozonolysis reaction

245th National Meeting (2013)

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