Gas-Phase Reaction between CF2O and CF3C(O)OH: Characterization of CF3C(O)OC(O)F

The thermal decomposition of trifluoroacetic acid and carbonyl fluoride (CF₂O) has been extensively studied because of their importance in the oxidation of hydrochlorofluorocarbons in the atmosphere. We hitherto present the study of the thermal reaction between these two molecules. The reaction mechanism was studied using Fourier transform infrared spectroscopy in the temperature range of 513-573 K. The reaction proceeds homogeneously in the gas phase through the formation of a reaction intermediate, here characterized as CF₃C(O)OC(O)F (detected for the first time in this work), the major final products being CF₃C(O)F, HF, and CO₂. We demonstrate that the reaction is first-order with respect to each reagent, second-order global and the mechanism consists of two steps, the first being the rate-determining one. The E_a = 110.1 ± 6.1 kJ mol^-1 and A = (1.2 ± 0.2) × 10^-12 cm³ molec^-1 s^-1 values were obtained from the experimental data. The low activation energy is explained by the hydrogen-bond interactions between the -OH group of the acid and the F atom of the CF₂O. First-principles calculations at the G4MP2 level of theory were carried out to understand the dynamics of the decomposition. Thermodynamic activation values found for this reaction are as follows: Δ H^⧧ = 105.6 ± 6.4 kJ mol^-1, Δ S^⧧ = -88.6 ± 9.7 J mol^-1 K^-1, and Δ G^⧧ = 153.7 ± 13.5 kJ mol^-1. The comparison between theory and experimental results showed excellent similarities, thus strengthening the proposed mechanism.

Structural and conformational properties of fluoroformic acid anhydride, FC(O)OC(O)F

The conformational properties and geometric structures of fluoroformic acid anhydride, FC(O)OC(O)F, have been studied by vibrational spectroscopy, gas electron diffraction (GED), single-crystal X-ray diffraction, and quantum chemical calculations (HF, MP2, and B3LYP methods with 6-31G* and B3LYP/6-311+G* basis sets). Satellite bands in the IR matrix spectra, which increase in intensity when the matrix gas mixture is heated prior to deposition as a matrix, indicate the presence of two conformers at room temperature. According to the electron diffraction analysis, the prevailing conformer is of C(2) symmetry with both C=O bonds synperiplanar with respect to the opposite C-O bond ([sp, sp] conformer). The minor conformer [15(5)% from IR matrix and 6(11)% from GED] is predicted by quantum chemical calculations to possess an [sp, ac] structure. FC(O)OC(O)F crystallizes in the orthorhombic system in the space group P2(1)2(1)2(1) with a = 6.527(1) angstroms, b = 7.027(1) angstroms, and c = 16.191(1) angstroms and four formula units per unit cell. In the crystal, only the [sp, sp] conformer is present, and the structural parameters are very similar to those determined by GED.

Synthesis and characterization of trifluoromethyl fluoroformyl peroxycarbonate, CF3OC(O)OOC(O)F

The synthesis of CF(3)OC(O)OOC(O)F is accomplished by the photolysis of a mixture of (CF(3)CO)(2)O, FC(O)C(O)F, CO, and O(2) at -15 degrees C using a low-pressure mercury lamp. The new peroxide is obtained in pure form in low yield after repeated trap-to-trap condensation and is characterized by NMR, IR, Raman, and UV spectroscopy. Geometrical parameters were studied by ab initio methods [B3LYP/6-311+G(d)]. At room temperature, CF(3)OC(O)OOC(O)F is stable for many days in the liquid or gaseous state. The melting point is -87 degrees C, and the boiling point is extrapolated to 45 degrees C from the vapor pressure curve log p = 8.384 - 1715/T (p/mbar, T/K). A possible mechanism for the formation of CF(3)OC(O)OOC(O)F is discussed, and its properties are compared with those of related compounds.

Atmospheric chemistry of HFE-7500 [n-C3F7CF(OC2H5)CF(CF3)2]: reaction with OH radicals and Cl atoms and atmospheric fate of n-C3F7CF(OCHO*)CF(CF3)2 and n-C3F7CF(OCH2CH2O*)CF(CF3)2 radicals

Relative rate techniques were used to measure k(OH + HFE-7500) = (2.6+/-0.6) x 10(-14), k(Cl + HFE-7500) = (2.3+/-0.7) x 10(-12), k[Cl + n-C3F7CF(OC(O)H)CF(CF3)2] = (9.7+/-1.4) x 10(-15), and k[Cl + n-C3F7CF(OC(O)CH3)CF(CF3)2] < 6 x 10(-17) cm3 molecule(-1) s(-1) at 295 K [HFE-7500 = n-C3F7-CF(OC2H5)CF(CF3)2]. From the value of k(OH + HFE-7500) an estimate of 2.2 years for the atmospheric lifetime of HFE-7500 is obtained. Two competing loss mechanisms for n-C3F7-CF(OCHO.CH3)CF(CF3)2 radicals were identified in 700 Torr of N2/O2 diluent at 295 K; reaction with O2 and decomposition via C-C bond scission with kO2/k(decomp) = 0.013+/-0.006 Torr(-1). The Cl atom initiated oxidation of HFE-7500 in N2/O2 diluent gives n-C3F7CF(OC(O)CH3)CF(CF3)2 as the major product and n-C3F7CF(OC(O)H)CF(CF3)2 as a minor product. The atmospheric oxidation of HFE-7500 gives n-C3F7-CF(OC(O)CH3)CF(CF3)2 and n-C3F7CF(OC(O)H)CF(CF3)2 as oxidation products. The results are discussed with respect to the atmospheric chemistry and environmental impact of HFE-7500.