Stoichiometry of Ozonation of Olefins in Organic Solvents
Stacy Wilkinson
Mentor: Sergey Nizkorodov
Ozone is known to react with organic molecules that contain unsaturated
carbon-carbon bonds (olefinic compounds), such as the double bond in trans-fatty
acids. The mechanism of ozonation of olefins dissolved in water or air is well
understood. However, room temperature ozonation of olefins in organic solvents has
received much less attention, even through it is relevant for understanding the indoor
chemistry of ozone. The goal of my project was to study the mechanism of ozonation
of environmentally relevant olefins in selected organic solvents. The Nizkorodov
group at UCI’s Chemistry Department recently observed that such reactions led to
highly unusual stoichiometry, but they were unable to explain their observations in
terms of known ozone chemistry. To better understand these observations, I conducted
a series of targeted experiments on ozonation of unsaturated fatty acids dissolved in
two very different organic solvents: CCl4, which is unreactive towards ozone, and
saturated hydrocarbons, which slowly react with ozone. Direct comparison of the
reaction stoichiometry for these two solvents provided the necessary information on
the mechanism of ozonation. Deviations from 1:1 ozone:double bond stoichiometry
were observed in both participating and non-participating solvents, and are likely due
to chain reaction mechanisms involving free radicals (OH, RO, RO2). The conclusion
is that the reaction products obtained during ozonation of olefins in organic solvents
at room temperature are likely to be more complex than expected from conventional
mechanisms.