Photooxidation Chemistry of Hydrofluoroolefins: Assessing the Impact of Substituents on the Greenhouse Gas Replacements

Hydrofluoroolefins (HFOs) have been evaluated in the literature as potential replacements for chlorofluorocarbons (CFCs). Herein, we investigate the photooxidation reaction mechanisms and kinetics of typical HFOs, particularly HFO-1345fz and HFO1483fzzm, using quantum chemical approaches to systematically understand their potential impact on ozone destruction and global warming. Results show that OH-addition to the C=C bond is the dominant pathway for the photooxidation reactions of HFO-1345fz and HFO-1483fzzm because of the lower energy barriers and more negative reaction energies compared to the H-abstraction pathway. In the temperature range of 216-298 K, the rate constants of the photooxidation for HFO-1483fzzm are larger than those for HFO1345fz, which is attributed to fewer F atoms at the alpha-position of the C=C bond. Assessment of global warming potential and lifetimes of HFO-1483fzzm and of HFO-1345fz shows that these HFOs exhibit short residence times and small influence on global warming. Our results provide kinetic and mechanism data for the proposal and usage of the new replacement of CFCs. Moreover, it reveals the importance of further assessing the impact of HFOs on the regional environment rather than on global warming.