Theoretical Study of the Reactions of CF₃OCHF₂ with the Hydroxyl Radical and the Chlorine Atom

Abstract

Theoretical investigations are carried out on the reaction mechanism of the reactions of CF3OCHF2 (HFOC-125) with the OH radials and Cl atoms, as well as the heats of formation of CF3OCHF2 and CF3OCF2. The electronic structure information on the potential energy surface for each reaction is obtained at the B3LYP/6-311G(d,p) level, and energetic information is further refined by G3(MP2) theory. The direct dynamics calculation of the hydrogen abstraction reactions are also performed at the G3(MP2)//B3LYP/ 6-311G(d,p) level. The classical energy profile is corrected by interpolated single-point energies (ISPE) approach, incorporating the small-curvature tunnelling effect (SCT) calculated by the variational transition-state theory (VTST). The rate constants are in good agreement with the experimental data and are found to be k1 = 4.95 x 10(-30)T(5.40)exp(-347/T) and k2 = 1.86 x 10(-23)T(3.43)exp(-1579/T) cm3 molecule(-1)s(-1) over the temperature range 200-2000 K. The rate constants at 298 K for these two reactions are 3.38 x 10(-16) and 2.80 x 10(-17) cm3 molecule(-1)s(-1), respectively. Using group-balanced isodesmic reactions as working chemical reactions, the standard enthalpies of formation for CF3OCHF2 and CF3OCF2 are -312.3 +/- 1.0 and -257.3 +/- 1.0 kcalmol(-1), respectively, evaluated by G3(MP2) theory based on the B3LYP/6-311G(d,p) geometries. The theoretical studies provide rate constants of the title reactions and the enthalpies of the species, which are important parameters in determining the atmospheric lifetime and the feasible pathways for the loss of HFOC-125.

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

“…Therefore, the variational effect is small for the dynamic computation of the channel R1b. In a paper studying the reaction of CF 3 OCH 3 with the OH radical by Wu et al, 22 the V a G and V MEP curves are also similar in shape and the maximum values of the two curves are located at the same position (s = 0), which further supports the credibility of our results. As can be seen from Figure 3b, the ZPE is practically constant as s varies, with only a gentle drop near the saddle point.…”

Atmospheric Oxidation Mechanism and Kinetics of Hydrofluoroethers, CH3OCF3, CH3OCHF2, and CHF2OCH2CF3, by OH Radical: A Theoretical Study

“…As shown in Scheme , the H-atom abstraction from CH 3 and CHF 2 groups of CH 3 OCHF 2 leads to the formation of alkyl radical intermediates, I8 and I9 with H 2 O through the corresponding reactant complexes, RC4 and RC5, transition states, TS8 and TS9 and intermediate complexes, IC5 and IC6. The energy barrier for TS8 and TS9 is 7.6 and 8.2 kcal/mol, and are comparable with the energy barrier of 8 kcal/mol reported for the H-atom abstraction reaction of CF 3 OCHF 2 by OH radical . The presence of F atom in CHF 2 group slightly increase the energy barrier corresponding to H-atom abstraction from CHF 2 group.…”

“…In this two-step process, CHF 2 O • and CH 3 O • are formed along with the CH 3 OH and CHF 2 OH through the transition states, TS10 and TS11, with energy barriers of 29.8 and 26.1 kcal/mol, respectively. The relative enthalpies corresponding to the formation of I10 + CH 3 OH and I2 + CHF 2 OH are −5.1 and −8.7 kcal/mol and are comparable with the enthalpies of −5.4 and −8.9 kcal/mol reported for the C–O bond breaking reaction of CF 3 OCHF 2 with OH radical . As shown in Scheme , the alkyl radical intermediate, I8 dissociates into COF 2 and CH 3 radical (I11) through the transition state, TS12, and intermediate complex, IC9.…”

A Theoretical Investigation of the Decomposition and Reactivity of the CHF2CF2CF2OCH2O• Radical from HFE-356pcc3 between 200 and 400 K

“…The rate constants of decomposition and reactivity of CHF 2 CF 2 CF 2 OCH 2 O• were calculated using CTST as given by the following [25] (6) and for the bimolecular reactions by (7) where k B is Boltzmann's constant and h is Planck's constant, T is the temperature in kelvin, and Q R are partition functions of the transition states and reactants respectively, ∆E is the barrier height (including the zero-point energy) and R is the universal gas constant. The value www.prkm.co.uk of the tunnelling correction factor Γ (T) was calculated using Wigner's method and is given by the following [26] (8)…”

“…HFEs are a class of compounds which have been improved to replace CFCs in applications such as carrier fluids for lubricant deposition, heat transfer agents for semiconductor and electronic manufacture and for cleaning of electronic devices. In recent years, as regards the effect of HFEs on environmental destruction, several experimental and theoretical studies have been conducted [7][8][9][10][11][12][13][14]. Therefore, it is vital to evaluate the atmospheric, chemical and environmental hazards of CHF 2 CF 2 CF 2 OCH 3 (HFE-356pcc3) before large-scale industrial application.…”