(385d) Degradation Pathways for Difluoromethanol and Implications to the Atmosphere

Several times in the last year, the U.S. EPA has announced that hydrofluorocarbons (HFCs) pose a threat to human health due to global climate change and the agency has been considering banning their use in the near future. Hydrofluoroethers (HFEs) are compounds that have been heavily patented in the last decade for use in all applications where HFCs have been used and are poised to become drop-in replacement chemicals.

Prior experimental work has shown that HFEs will react with hydroxyl radicals as their degradation processes begin. During subsequent steps, it has been found that CH_nF_3-nO radicals are often formed. The fate of these radicals is unknown although some work has been done for the perfluorinated species. In this work, computational chemistry methods are used to estimate reaction pathway branching ratios and end-point degradation species. Geometry optimizations were performed at the B3LYP/6-311g** level for all possible reaction pathways for CHF₂OH + OH, while higher level single point energy calculations at the G3(MP2) level were performed for improved energetic data. Variational transition state theory with the small curvature tunneling approximation was used to predict chemical kinetic rate constants at temperatures relevant to atmospheric conditions. To validate methodoligies, theoretically predicted values are compared to available experimental data, including that for non-fluorinated analogues where more data is available.

Results show that degradation pathways may lead to HF, a highly toxic species. Introduction of large amounts of HFEs may lead to environmental degradation through mechanisms currently not available during the use of HFCs.