Cl Atom-Initiated Oxidation of Three Homologous Methyl Perfluoroalkyl Ethers
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- 作者：Kayo Nohara ; Mitsuhiro Toma ; Shuzo Kutsuna ; Koji Takeuchi ; and Takashi Ibusuki
- 刊名：Environmental Science & Technology
- 出版年：2001
- 出版时间：January 1, 2001
- 年：2001
- 卷：35
- 期：1
- 页码：114 - 120
- 全文大小：133K
- 年卷期：v.35,no.1(January 1, 2001)
- ISSN：1520-5851
文摘
Chlorine atom-initiated photooxidations of three homologousmethyl perfluoroalkyl ethers (HFEs), n-CnF2n+1OCH3 (n =2, 3, and 5), in air in the absence of NOx were investigatedwith a long path FTIR/photochemical reaction system toelucidate the degradation mechanisms. The environmentalremoval processes of these three ethers in the tropospherewere estimated. For oxidation of the three ethers, perfluoroalkylformates (CnF2n+1OCHO; n = 2, 3 and 5) as relativelystable intermediates were produced at unity of the productionratio, which was independent of the perfluoroalkyllength. The rate constants for the reaction of Cl atomswith C2F5OCHO, C3F7OCHO, and C5F11OCHO were (1.2 ± 0.5)× 10-14, (1.2 ± 0.5) × 10-14, and (1.8 ± 0.7) × 10-14 cm3molecule-1 s-1, respectively. The rate constants of the reactionof Cl with produced perfluoroalkyl formates were largerthan these of perfluoroalkyl ethers. The formyl group of theperfluoroalkyl formates was finally converted to carbondioxide. The -CF2- of the perfluoroalkyl groups for the threeethers was mainly converted to COF2 through the C-Ccleavage; the conversion ratios from the carbons of theperfluoroalkyl group to COF2 were 48 ± 10, 76 ± 10, and 60± 10% for C2F5OCH3, n-C3F7OCH3, and n-C5F11OCH3,respectively. Sixteen percent of the perfluoroalkyl groupfor n-C3F7OCH3 was converted to C2F5COF. Similarly,the perfluoroalkyl group of n-C5F11OCH3 was converted toCnF2n+1COF (n = 2, 3, and/or 4) with the yield of15-30%, while for C2F5OCH3, the formation of CF3COF wasnot confirmed. As an oxidation product of the terminalCF3- group, 20, 22, and 16% of the CF3 group for C2F5OCH3, n-C3F7OCH3, and n-C5F11OCH3, respectively, wereconverted to CF3OOOCF3.