Emerging contaminants that are generated from pharmaceuticals, pesticides, munitions, etc. can reside in soil and water systems for years, and hence it is important to understand their environmental fates. A group of emerging contaminants such as the neonicotinoid pesticide nitenpyram and some heartburn medications contains amino and nitro groups attached to a double bond. In order to assess their environmental degradation, the kinetics and products of their oxidation reactions must be understood. The goal of the present study was to probe the impact of different functional groups on the reactivity with ozone, a common atmospheric oxidant, using compounds with selected structural motifs. Three model compounds, 1-dimethylamino-2-nitroethylene (DMNE), 2-methyl-1-nitroprop-1-ene (NTP), and 4-methyl-4-nitro-1-pentene (MNP), were selected to study the effects of amine and nitro groups on ozone-alkene reactions either singly or in combination. Preliminary results show that the ozonolysis rate constant in CCl4 solution measured using a stopped flow system for NTP, where the nitro group is attached to the vinyl carbon, is about three orders of magnitude smaller than that of 2-methyl-2-butene. In the gas phase, the rate constant is about five orders of magnitude smaller. However, for MNP where the nitro group is two carbons away from the double bond, the ozonolysis rate constants are around four and fifteen times lower than those of the corresponding alkene-ozone reaction in CCl4 solution and in the gas phase, respectively. Surprisingly, the ozonolysis rate constant for DMNE, which has the amino and nitro groups on opposite sides of the double bond has the highest value among these model compounds including 2-methyl-2-butene in CCl4 solution. The temperature dependence of the rate constants as well as the reaction products and mechanisms will be presented. Overall, this study not only provides data on rate constants and mechanisms for molecules with structures commonly found in emerging contaminants, but can also provide guidance for the design of new synthetic chemicals and materials that are more environmentally friendly.

Ozonolysis of model compounds for emerging contaminants: The synergistic effect of multi-functional groups on ozone-alkene reactions

ACS Spring 2022

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