A theoretical insight into atmospheric chemistry of HFE-7100 and perfluoro-butyl formate: reactions with OH radicals and Cl atoms and the fate of alkoxy radicals

• Published in: New journal of chemistry 2016, Vol.4 (7), p.6148-6155
• Main Authors: Mishra, Bhupesh Kumar, Lily, Makroni, Deka, Ramesh Chandra, Chandra, Asit K
• Format: Article
• Language: English
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/c5nj02752g

A mechanistic study on the hydrogen abstraction reaction of HFE-7100 (n-C 4 F 9 OCH 3 ) with atmospheric oxidants has been carried out in the gas-phase by performing DFT-based M06-2X/6-31+G(d,p) calculations. We observe a complex mechanism due to the presence of the pre-reactive and post-reactive complexes at the entrance and exit channels, respectively. The standard enthalpies of formation for species and bond dissociation energy for C-H bonds are also reported. The rate expressions were determined for reaction channels in the broad temperature range of 250-1000 K. The rate coefficients over the studied temperature range yield the following Arrhenius expressions (cm 3 molecule −1 s −1 ): k OH = 2.87 × 10 −24 · T 3.66 exp(527/ T ) and k Cl = 1.68 × 10 −19 · T 2.71  exp(207/ T ). At 298 K, the results were found to agree comparatively well with modest differences in rates for reactions. Finally, the atmospheric lifetime and global warming potential of HFE-7100 are computed to be 2.12 years and 155.3, respectively. We also investigated the reactivity of the alkoxy radical (C 4 F 9 OCH 2 O&z.rad;), considering three decomposition channels including oxidative pathways. Based on thermochemical data, we can speculate that oxidative pathways are dominant for the decomposition of C 4 F 9 OCH 2 O&z.rad; radicals, which is in concurrence with experimental observations. The radiative efficiency and global warming potential of fluoroesters (C 4 F 9 OC(O)H) are also calculated and compared with parent species. The calculated rate constants for C 4 F 9 OCH 3 + OH/Cl reactions are found to be 1.94 × 10 −14 and 1.74 × 10 −12 cm 3 molecule −1 s −1 , respectively, at 298 K. The atmospheric lifetime and global warming potential for HFE-7100 are computed to be 2.12 years and 155.3, respectively.