Cl atom-initiated oxidation of three homologous methyl perfluoroalkyl ethers

Chlorine atom-initiated photooxidations of three homologous methyl perfluor oalkyl ethers (HFEs), n-CnF2n+1OCH3 (n = 2, 3, and 5), in air in the absenc e of NOx were investigated with a-long path FTIR/photochemical reaction sys tem to elucidate the degradation mechanisms. The environmental removal proc esses of these three ethers in the troposphere were estimated. For oxidatio n of the three ethers, perfluoroalkyl formates (CnF2n+1OCHO; n = 2, 3 and 5 ) as relatively stable intermediates were produced at unity of the producti on ratio, which was independent of the perfluoroalkyl length. The rate cons tants for the reaction of CI atoms with C2F5OCHO, C3F7OCHO, and C5F11OCHO w ere (1.2 +/- 0.5) x 10(-14), (1.2 +/- 0.5) x 10(-14), and (1.8 +/- 0.7) x 1 0(-14) cm(3) molecule(-1) s(-1), respectively. The rate constants of the re action of Cl with produced perfluoroalkyl formates were larger than these o f perfluoroalkyl ethers. The formyl group of the perfluoroalkyl formates wa s finally converted to carbon dioxide. The -CF2- of the perfluoroalkyl grou ps for the three ethers Was mainly converted to COF2 through the C-C cleava ge; the conversion ratios from the carbons of the perfluoroalkyl group to C OF2 were 48 +/- 10, 76 +/- 10 and 60 +/- 10% for C2F5OCH3, n-C3F7OCH3, and n-C5F11OCH3, respectively. Sixteen percent of the perfluoroalkyl group for n-C3F7OCH3 Was converted to C2F5COF. Similarly, the perfluoroalkyl group of n-C5F11OCH3 was converted to CnF2n+1COF (n = 2, 3, and/or 4) with the yiel d of 15-30%, while for C2F5OCH3, the formation of CF3COF was not confirmed. As an oxidation product of the terminal CF3- group, 20, 22, and 16% of the CF3 group for C2F5- OCH3, n-C3F7OCH3, and n-C5F11OCH3, respectively, were converted to CF3OOOCF3.