The reaction mechanisms and kinetics of CF3CHFOCH3 and CHF2CHFOCF3 with atomic chlorine: a computational study

Abstract

Due to their lack of effect on the ozone depletion, hydrofluoroethers are considered as potential candidates for third generation refrigerants. In the present work, the mechanisms and kinetics of reaction of the Cl atom with CF(3)CHFOCH(3) and CHF(2)CHFOCF(3) were investigated theoretically using quantum chemical methods and transition state theory. Four reaction pathways for the title reaction were explored. By using conventional transition state theory with Eckart tunneling correction, the rate constants of the title reaction were obtained over the temperature range 200-300 K. Kinetic calculations demonstrate that H-abstraction from the -CH(3) group in CF(3)CHFOCH(3) and H-abstraction from the -CHF2 group in CHF(2)CHFOCF(3) are major reaction pathways, with the barrier heights of the two paths calculated to be -1.04 and 4.33 kcal mol(-1), respectively. However, the contribution of H-abstraction from the -CHFO- group for the two reactions should also be taken into account with increased temperature. At 298 K, the calculated overall rate constants of the reaction of CHF(2)CHFOCF(3) with the Cl atom are 4.27 × 10(-15) cm(3) molecule(-1) s(-1), which is consistent with the experimental value of (1.2 ± 2.0) × 10(-15) cm(3) molecule(-1) s(-1).

Theoretical Study on the Reactions of (CF3)2CFOCH3 + OH/Cl and Reaction of (CF3)2CFOCHO with Cl Atom

“…It is interesting to note that the OH radical with some HFEs in rate constants are in this order: k CF 3 ­CH 2 O­CH 3 > k (CF 3 ) 2 ­CHO­CH 3 > k CF 3 ­CHFO­CH 3 > k (CF 3 ) 2 ­CFO­CH 3 . ,, From the above comparison, the results suggest that −CF 3 group substitution results in a greater decrease than F-substitution in the reactivity trend. With Cl + HFEs as criterion, k CF 3 ­CH 2 O­CH 3 > k CF 3 ­CHFO­CH 3 > k (CF 3 ) 2 ­CFO­CH 3 . , When the calculated overall rate constant of reaction (CF 3 ) 2 CFOCHO + Cl (1.12 × 10 –14 cm 3 molecule –1 s –1 ) is compared with that of reaction CF 3 CH 2 OCHO + Cl (6.43 × 10 –14 cm 3 molecule –1 s –1 ) at 298 K, a similar conclusion can be reached.…”

“…With Cl + HFEs as criterion, kCF 3 CH 2 OCH 3 > kCF 3 CHFO-CH 3 > k(CF 3 ) 2 CFOCH 3 . 50,51 When the calculated overall rate constant of reaction (CF 3 ) 2 CFOCHO + Cl (1.12 × 10 −14 cm 3 molecule −1 s −1 ) is compared with that of reaction CF 3 CH 2 OCHO + Cl (6.43 × 10 −14 cm 3 molecule −1 s −1 ) at 298 K, 23 a similar conclusion can be reached.…”

“…Hence, the H-abstraction reaction with Cl atom is a more important degradation channel for (CF 3 ) 2 CFOCH 3 than for that with OH radical. To further understand the title reactions, it is worthwhile to compare the dynamics between the title reactions and similar systems (Cl atom or OH radical with (CF 3 ) 2 CHOCH 3 , CF 3 CHFOCH 3 , CF 3 CH 2 OCH 3 , and CF 3 CH 2 OCHO). ,,,− In fact, the fluorine and −CF 3 group substitution can decrease the reactivity trend. It is interesting to note that the OH radical with some HFEs in rate constants are in this order: k CF 3 ­CH 2 O­CH 3 > k (CF 3 ) 2 ­CHO­CH 3 > k CF 3 ­CHFO­CH 3 > k (CF 3 ) 2 ­CFO­CH 3 . ,, From the above comparison, the results suggest that −CF 3 group substitution results in a greater decrease than F-substitution in the reactivity trend.…”