Atmospheric Chemistry of Isoflurane, Desflurane, and Sevoflurane: Kinetics and Mechanisms of Reactions with Chlorine Atoms and OH Radicals and Global Warming Potentials

The smog chamber/Fourier-transform infrared spectroscopy (FTIR) technique was used to measure the rate coefficients k(Cl + CF3CHClOCHF2, isoflurane) = (4.5 ( 0.8) × 10-15, k(Cl + CF3CHFOCHF2, desflurane) = (1.0 ( 0.3) × 10-15, k(Cl + (CF3)2CHOCH2F, sevoflurane) = (1.1 ( 0.1) × 10-13, and k(OH + (CF3)2CHOCH2F) = (3.5 ( 0.7) × 10-14 cm3 molecule-1 in 700 Torr of N2/air diluent at 295 ( 2 K. An upper limit of 6 × 10-17 cm3 molecule-1 was established for k(Cl + (CF3)2CHOC(O)F). The laser photolysis/laser-induced fluorescence (LP/LIF) technique was employed to determine hydroxyl radical rate coefficients as a function of temperature (241-298 K): k(OH + CF3CHFOCHF2) = (7.05 ( 1.80) × 10-13 exp[À(1551 ( 72)/T] cm3 molecule-1; k(296 ( 1 K) = (3.73 ( 0.08) × 10-15 cm3 molecule-1, and k(OH + (CF3)2CHOCH2F) = (9.98 ( 3.24) × 10-13 exp[À(969 ( 82)/T] cm3 molecule-1; k(298 ( 1 K) = (3.94 ( 0.30) × 10-14 cm3 molecule-1. The rate coefficient of k(OH + CF3CHClOCHF2, 296 ( 1 K) = (1.45 ( 0.16) × 10-14 cm3 molecule-1 was also determined. Chlorine atoms react with CF3CHFOCHF2 via H-abstraction to give CF3CFOCHF2 and CF3CHFOCF2 radicals in yields of approximately 83% and 17%. The major atmospheric fate of the CF3C(O)FOCHF2 alkoxy radical is decomposition via elimination of CF3 to give FC(O)OCHF2 and is unaffected by the method used to generate the CF3C(O)FOCHF2 radicals. CF3CHFOCF2 radicals add O2 and are converted by subsequent reactions into CF3CHFOCF2O alkoxy radicals, which decompose to give COF2 and CF3CHFO radicals. In 700 Torr of air 82% of CF3CHFO radicals undergo CÀC scission to yield HC(O)F and CF3 radicals with the remaining 18% reacting with O2 to give CF3C(O)F. Atmospheric oxidation of (CF3)2CHOCH2F gives (CF3)2CHOC(O)F in a molar yield of 93 ( 6% with CF3C(O)CF3 and HCOF as minor products. The IR spectra of (CF3)2CHOC(O)F and FC(O)OCHF2 are reported for the first time. The atmospheric lifetimes of CF3CHClOCHF2, CF3CHFOCHF2, and (CF3)2CHOCH2F (sevoflurane) are estimated at 3.2, 14, and 1.1 years, respectively. The 100 year time horizon global warming potentials of isoflurane, desflurane, and sevoflurane are 510, 2540, and 130, respectively. The atmospheric degradation products of these anesthetics are not of environmental concern.