Direct dynamics studies for the reactions of CF3CHFCF3 and CF3CF2CHF2 with H atoms

The rate constants of the hydrogen abstraction reactions of CF₃CHFCF₃ + H (R1) and CF₃CF₂CHF₂ + H (R2) have been calculated by means of the dual-level direct dynamics method. Optimized geometries and frequencies of stationary points and extra points along the minimum-energy path (MEP) are obtained at the MPW1K/6-311+G(d,p) level, and the classical energetic information is further corrected with the interpolated single-point energy (ISPE) approach by the G3(MP2) level of theory. Using the canonical variational transition state theory (CVT) with small-curvature tunneling corrections (SCT), the rate constants are evaluated over a wide temperature range of 200-2000 K. The calculated CVT/SCT rate constants are in good agreement with available experimental values. It is found that the variational effect is very small and almost negligible over the whole temperature region. However, the small-curvature tunneling correction plays an important role in the lower temperature range. Furthermore, the heats of formation of species CF₃CF₂CHF₂ (SC₁ or SC₂) and CF₃CF₂CF₂ are studied using isodesmic reactions to further elucidate the thermodynamic properties.     

Dual-level direct dynamics studies on the hydrogen abstraction reactions of fluorine atoms with CF<Subscript>3</Subscript>CH<Subscript>2</Subscript>X(X=F,Cl)

The kinetic properties of the hydrogen abstraction reactions of CF₃CH₂F + F → CF₃CHF + HF (R1) and CF₃CH₂Cl + F → CF₃CHCl + HF (R2) have been studied by dual-level direct dynamics method. Optimized geometries and frequencies of all the stationary points and extra points along the minimum-energy path (MEP) were obtained at the B3LYP/6-311 + G(2d,2p) level. Two complexes with energies less than that of the reactants were located in the reactant side of each reaction. The energy profiles were further refined with the interpolated single-point energies (ISPE) method at the G3(MP2) level of theory. Using canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT) method, the rate constants were evaluated over a wide temperature range of 200–2,000 K. Our calculations have shown that C–H bond activity decreases when one hydrogen atom of CF₃CH₃ is substituted by a fluorine atom, than when substituted with a chlorine atom. This is in good agreement with the experimental results.     

Theoretical study of the reaction of CF3O radicals with CO

The potential energy surface for the reaction of the CF₃O radicals with CO was investigated. The geometries and vibrational frequencies of the reactants, transition states, intermediates, and products were calculated at the UB3LYP/6-311+G(2d,p), UB3LYP/6-311+G(3df,2p) and UMP2/6-311+G(2d,p) levels of theory. The energies were improved by using the G2M(CC2) and G3B3 methods. The calculation suggests the reaction proceeds via either the fluorine abstraction of CF₃O by CO to produce FCO + CF₂O with a high energy barrier or the barrierless association of the reactants to form the trans-CF₃OCO intermediate. The trans-CF₃OCO is predicted to undergo subsequent isomerization to cis-CF₃OCO or dissociate directly to the products FCO + CF₂O and CF₃ + CO₂. The collisional stabilization of trans-CF₃OCO is dominant at room temperature, while trans-CF₃OCO isomerizing to cis-CF₃OCO followed by dissociating to CF₃ + CO₂ is accessible when temperature rises. The reason for only trans-CF₃OCO without cis-CF₃OCO observable in Ashen’s experiment [S.V. Ahsen, J. Hufen, H. Willner, J.S. Francisco, Chem. Eur. J. 8 (2002) 1189] is cis-CF₃OCO can be produced only via the isomerization of trans-CF₃OCO, and its yield is inappreciable at a low experimental temperature. The enthalpies of formation for the two conformations of CF₃OCO have been deduced: (trans-CF₃OCO) = −196.25 kcal mol⁻¹, (trans-CF₃OCO) = −197.46 kcal mol⁻¹, (cis-CF₃OCO) = −193.64 kcal mol⁻¹, and (cis-CF₃OCO) = −194.90 kcal mol⁻¹.     

Hydrogen abstraction from CF3CF2CFH2 and CF3CFHCF2H by OH radicals and Cl atoms: theoretical enthalpies and rate constants

The hydrogen abstraction reactions of CF₃CF₂CFH₂ and CF₃CFHCF₂H with OH radicals and Cl atoms have been studied theoretically by a dual-level direct dynamics method. Two stable conformers of CF₃CF₂CFH₂ with C _s and C ₁ symmetries and all possible abstraction channels for each reaction are all taken into consideration. Optimized geometries and frequencies of all the stationary points and extra points along minimum-energy path (MEP) have been computed at the BB1K/6-31+G(d, p) level of theory. To refine the energy profile of each reaction channel, single point energy calculations have been performed by the BMC-CCSD method. The rate constants are evaluated by canonical variational transition state theory (CVT) with the small-curvature tunneling correction method (SCT) over a wide temperature range of 200–1,000 K. The detailed branching ratios of four reactions are discussed. The good agreement found between our theoretical rate constants and the available experimental data suggests that the present approach could provide a reliable prediction for the CF₃CFHCF₂H + Cl reaction about which there is little experimental information. The kinetic calculations show that the SCT effect plays an important role in all channels. In addition, in order to further reveal the thermodynamic properties, the enthalpies of formation of the reactants (CF₃CF₂CFH₂ and CF₃CFHCF₂H) and the product radicals (CF₃CF₂CFH, CF₃CFCF₂H, and CF₃CFHCF₂) are evaluated by applying isodesmic reactions at both BMC-CCSD//BB1K/6-31+G(d, p) and MC-QCISD//BB1K/6-31+G(d, p) levels of theory.     

Matrix isolation study of the interaction of excited argon atoms with CF2Cl2, CF2ClBr,and CF2Br2. Infrared spectra of the CF2Cl+ and CF2Br+ molecular ions

The infrared absorptions associated with the two CF stretching fundamentals of CF₂Cl⁺ and CF₂Br⁺ have been identified in studies of the matrix-isolated products of the interaction of excited argon atoms with CF₂Cl₂, CF₂ClBr, and CF₂Br₂. The exceptionally high values of the CF stretching frequencies obtained in these experiments are consistent with the implications of previous experimental and theoretical studies.     

Vergleich der trifluormethylierungseigenschaften von(CF3)Hg,CF3I und (CF3)2te am beispiel der reaktionen mit cyclohexen,benzol und pyridin

The trifluoromethylation reactions of (CF₃)₂Hg, CF₃I and (CF₃)₂Te with cyclohexene, benzene and pyridine are compared under similar conditions. Photochemical as well as thermal reactions result in an increase of the reactivity in the series (CF₃)₂Hg < CF₃I ? (CF₃)2Te. The yields and the kind of products vary depending on the time of irradiation and the temperature. In all cases the best yields are obtained from the thermal reactions with (CF₃)₂Te. With cyclohexene only trifluoromethylated addition products are observed. The substitution reactions with pyridine yield a mixture of isomeric trifluoromethylpyridines. (CF₃)₂Hg and CF₃I react with benzene to yield only benzotrifluoride C₆H₅CF₃. The main product of the reaction of (CF₃)2Te with benzene is also benzotrifluoride; in addition to this the disubstituted bis(trifluoromethyl)benzene isomers and trifluoromethyl- cyclohexadienes are formed. ¹H, ¹⁹F n.m.r. and mass spectra are described.     

Formation of bromodifluoroacetyl fluoride, CF2BrC(O)F, in the thermal gas-phase oxidation of bromotrifluoroethene, CF2CFBr, initiated by trifluoromethylhypofluorite, CF3OF

The oxidation of CF₂CFBr by molecular O₂, initiated by CF₃OF, has been studied at 273, 253.5, 239 and 218 K. The initial pressure of CF₃OF was varied between 0.9 and 2.4 Torr, that of CF₂CFBr between 11.5 and 30.7 Torr and that of O₂ between 42.5 and 100.7 Torr. The main product was CF₂BrC(O)F (yields 81-95% based on the CF₂CFBr consumed). Minor amounts of C(O)F₂ and C(O)FBr and traces of bromotrifluoroethene epoxide were also formed. The reaction is a chain reaction with bromine atoms as chain carriers. Its basic steps are: the thermal generation of CF₃O radical by abstraction of fluorine atom from CF₃OF, chain initiation by addition of CF₃O to the double bond of alkene, leading, in presence of O₂, to the formation of bromine atom and chain propagation by the reaction of bromine atom with CF₂CFBr, originating CF₂BrCFBrO radical. The predominant fate of the latter is the bromine atom extrusion with CC bond scission playing the minor role. The full mechanism is postulated.     

Electrochemical preparation of graphite intercalation compounds containing a cyclic amide, [CF2(CF2SO2)2N]

Graphite intercalation compounds (GICs) containing the cyclo-hexafluoropropane-1,3-bis(sulfonyl)amide anion, [CF₂(CF₂SO₂)₂N]⁻, are prepared for the first time. Stages 2 and 3 GICs are obtained by electrochemical oxidation of graphite in a nitromethane electrolyte. Gallery heights of 0.85-0.86 nm are determined by powder X-ray diffraction, and the intercalate anion orientation within the intercalate galleries is modeled using an energy minimized anion structure. GIC compositions are determined by thermogravimetric, fluorine and nitrogen analyses. The chemical preparation and bifluoride displacement reactions are compared with a GIC containing the linear bis(trifluoromethanesulfonyl)amide anion, [(CF₃SO₂)₂N]⁻.     

AB initio molecular orbital studies of CF3O2H,CF3O2F and CF2(OF)2

Ab initio calculations employing an extended 4-31G basis set have been applied to the highly fluorinated molecules, CF₃O₂H, CF₃O₂F and CF₂(OF)₂. Partial geometry optimizations have also been carried out on these molecules allowing a comparison between theory and the recently completed gas-phase electron diffraction results. The O-O bond distance in CF₃O₂ H is found to be longer (by 0.02 Å) than the corresponding bond in CF₃O₂F while the CO bond is found to be shorter (by 0.02 Å) in CF₃O₂H. The OF bond in CF₃O₂F is found to be longer (by 0.03–0.04 Å) than the corresponding bond in CF₃OF or F₂O. Torsional barriers have been computed for CF₃O₂H and CF₃O₂F with the aid of Fourier analysis of the potential curves. CF₃O₂H is found to have a torsional potential about the peroxide bond rather similar to that found for H₂O₂ while in CF₃O₂F the cis and trans barriers are predicted to be much larger (14.6 and 8.4 kcal mol^?1, respectively). The threefold barrier to rotation of the CF₃ group in CF₃O₂F is predicted to be 4.4 kcal mol^?1. Various conformations of CF₂(OF)₂ have also been studied with conformations consistent with the operation of the gauche-effect being most stable. Bond separation energies and molecular properties have also been computed for these molecules.     

Novel ammonium hexafluoroarsenate salts from reaction of (CF3)2NH,CF3N(OCF3)H,CF3N[OCF(CF3)2]H,CF3NHF and SF5NHF with the strong acid HF/ASF5.

Reactions of the fluorinated amines (CF₃)₂NH, CF₃N(OCF₃)H, CF₃N[OCF(CF₃)₂]H, CF₃NHF and SF₅NHF with the strong acid HF/AsF₅ form the corresponding ammonium salts R_f¹R_f²NH₂⁺AsF₆^? and R_fNFH₂⁺ AsF₆^? in high yield. [R_f¹=CF₃, R_f²=CF₃, CF₃O, (CF₃)₂CFO; R_f=CF₃, SF₅] The colorless crystalline solids are stable for prolonged periods at 22°C in sealed FEP containers. They have dissociation pressures at 22°C ranging from ～5 torr (R_fNFH₂⁺ AsF₆^?) to ～50 torr [CF₃N(OCF₃)H₂⁺AsF₆^?]. ¹⁹F NMR and Raman spectroscopy were used to identify the compounds.     

Gas-phase reactions of CF3 and CF2 with atomic and molecular fluorine: Their significance in plasma etching

Reaction rate coefficients have been measured at 295 K for both CF₃ and CF₂ with atomic and molecular fluorine. The reaction between CF₃ and F was studied over a gas number density range of (2.4–23)×10¹⁶ cm^–3 with helium as the bath gas. The measured rate coefficient increased from (1.1–1.7)×10^–11 cm³ s^–1 as the gas number density increased over this range. In contrast to this relatively small change in rate coefficient with gas number density, the rate coefficient for CF₂+F increased from (0.4–2.3)×10^–12 cm³ s^–1 as the helium gas number density increased from (3.4–28.4)×10¹⁶ cm^–3. Even for the highest bath gas number density employed, the rate coefficient was still more than an order of magnitude lower than earlier measurements of this coefficient performed at comparable gas number densities.Both these association reactions are examined from the standpoint of the Gorin model for association of radicals and use is made of unimolecular dissociation theory to examine the expected dependence on gas number density. The calculations reveal that CF₃+F can be explained satisfactorily in these terms but CF₂+F is not well described by the simple Gorin model for association.CF₃ was found to react with molecular fluorine with a rate coefficient of (7±2)×10^–14 cm³ s^–1 whereas only an upper limit of 2×10^–15 cm³ s^–1 could be placed on the rate coefficient for the reaction between CF₂ and F₂. The values obtained for this set of reactions mean that the reaction between CF₃ and F will play an important role in plasmas containing CF₄. The high rate coefficient will mean that, under certain conditions, this particular reaction will control the amount of CF₄ consumed. On the other hand, the much lower rate coefficient for reactions between CF₂ and F means that CF₂ will attain much higher concentrations than CF₃ in plasmas where these combination reactions are dominant.     

The fluorine atom initiated oxidation of CF3CFH2 (HFC-134a) studied by FTIR spectroscopy

Experiments have been carried out on the oxidation of CF₃CFH₂ (HFC-134a). Reaction was initiated by continuous photolysis of F₂ in the near-ultraviolet. The F atoms produced abstracted a hydrogen atom from CF₃CFH₂ initiating oxidation in gas mixtures containing O₂ and made up to a total pressure of 700 torr with N₂. Product yields were measured using Fourier-transform infrared (FTIR) spectroscopy. Experiments were performed with several different partial pressures of O₂ present, and at three temperatures; 298, 323, and 357 K. The major products were HC(O)F, CF₃C(O)F, and CF₃O₃CF₃, consistent with H atom abstraction by O₂ and CC bond scission being the dominant loss processes for CF₃CFHO radicals: CF₃CFHO+0₂ → CF₃C(O)F+HO₂ (4a) CF₃CFHO+M → CF₃+HC(O)F+M (4b) The following expression was derived for the ratio of rate constants for these reactions: k_4a/k_4b=(3.8±1.6)×10⁻²⁴ exp[(2400±500)/T]cm³ molecule⁻¹ (viii) The main fate of the CF₃ radicals was formation of CF₃O₃CF₃ and small amounts of CF₃OH were detected. The results of the present experiments in which F atoms were used to initiate reaction are in good agreement with those of previous studies in which Cl atoms were employed to initiate the oxidation of HFC-134a. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 541–554, 1998     

Theoretical study on reactions of cyclic-N3 with NO, NO2 and Cl2

In this article, we report our detailed mechanistic study on the reactions of cyclic-N₃ with NO, NO₂ at the G3B3//B3LYP/6-311+G(d) and CCSD(T)/aug-cc-pVTZ//QCISD/6-311+G(d)+ZPVE levels; the reactions of cyclic-N₃ with Cl₂ was studied at the G3B3//B3LYP/6-311+G(d) and CCSD(T)/aug-cc-pVTZ//QCISD/6-31+G(d)+ZPVE levels. Both of the singlet and triplet potential-energy surfaces (PESs) of cyclic-N₃ + NO, cyclic-N₃ + NO₂ and the PES of cyclic-N₃ + Cl₂ have been depicted. The results indicate that on singlet PESs cyclic-N₃ can undergo the barrierless addition–elimination mechanism with NO and NO₂ forming the respective dominant products N₂ + ¹cyclic-NON and ¹NNO(O) + N₂. Yet the two reactions on triplet PESs are much less likely to take place under room temperature due to the high barriers. For the cyclic-N₃ + Cl₂ reaction, a Cl-abstraction mechanism was revealed that results in the product cyclic-N₃Cl + Cl with an overall barrier as high as 14.7 kcal/mol at CCSD(T)/aug-cc-pVTZ//QCISD/6-31+G(d)+ZPVE level. So the cyclic-N₃ radical could be stable against Cl₂ at low temperatures in gas phase. The present results can be useful for future experimental investigation on the title reactions.     

Ab initio quantum chemical studies on the reactions of CF3O2 with OH

The potential energy surface for the CF₃O₂ + OH reaction has been theoretically investigated using the DFT (B3LYP/6-311G(d,p)) level of theory. Both singlet and triplet potential energy surfaces are investigated. The reaction mechanism on the triplet surface is simple. However, the reaction mechanism on the singlet surface is more complicated. It is revealed that the formation of CF₃O + HO₂ is the dominant channel on the triplet surface. The potential energy surface (PES) for this reaction has been given according to the relative energies calculated at the DFT/B3LYP/6-311G(d,p) level. Because this reaction involves both triplet and singlet states, triplet–singlet intersystem crossing (ISC) crossing also have been investigated in this paper.     

DFT and ab initio theoretical study for the CF3S + CO reaction

The potential energy surface for the reaction of CF₃S with CO is calculated at the G4//B3LYP/6-311++G(d,p) level of theory. The results show that F-abstraction and addition-elimination mechanisms are involved, and the latter one is dominant thermodynamically and kinetically. The dominant channel is the reactant addition to form CF₃SCO, and then decomposes to CF₃ + OCS. While the direct F-abstraction channel and CF₃SCO isomerization channel are not significant for the title reaction due to higher barriers involved. The comparisons among four reactions of CX₃Y + CO (X = H, F; and Y = O, S) are made to imply the similar and different properties and reactivities of the same family elements and the F- and S-substituted derivatives.     

Hydrogen abstraction reactions of OH radicals with CF<Subscript>2</Subscript>ClCClXH (X = F,Cl) and CFCl<Subscript>2</Subscript>CClXH (X = F,Cl): a mechanistic and kinetic study

The reactions of OH (OD) radicals with CF₂ClCClFH (R1), CF₂ClCCl₂H (R2), CFCl₂CClFH (R3), and CFCl₂CCl₂H (R4) have been investigated theoretically by a dual-level direct dynamics method. The optimized geometries and frequencies of the stationary points are calculated at the MPW1K/6-311+G(d,p) level. To improve the reaction enthalpy and potential barrier of each reaction channel, the single-point energy calculation is made by the MC-QCISD method. The enthalpies of formation of the species CF₂ClCClFH, CF₂ClCCl₂H, CFCl₂CClFH, CFCl₂CCl₂H, CF₂ClCClF, CF₂ClCCl₂, CFCl₂CClF, and CFCl₂CCl₂ are evaluated by two sets of isodesmic reactions. Using canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT) method, the rate constants of OH and OD radicals with CF₂ClCClXH (X = F, Cl) and CFCl₂CClXH (X = F, Cl) are evaluated over a wide temperature range of 100–2,000 K at the MC-QCISD//MPW1K/6-311+G(d,p) level. The calculated CVT/SCT rate constants are consistent with available experimental data. The results show that the tunneling correction has an important contribution in the calculation of rate constants at lower temperatures. For the above-mentioned four reactions, the kinetic isotope effects are also calculated. Finally, the effect of fluorine or chlorine substitution on reactivity of the C–H bond is discussed.     

Theoretical investigation on the reaction of N2O and CO catalyzed by Fe(C6H6)

The reaction of N₂O with CO, catalyzed by Fe⁺(C₆H₆) and producing N₂ and CO₂, has been investigated at the UB3LYP/6-311+G(d) level. The computation results revealed that the reaction of Fe⁺(C₆H₆), N₂O and CO, is an O-atom abstraction mechanism. For the reaction channels, the geometries and the vibrational frequencies of all species have been calculated and the frequency modes analysis also have been given to elucidate the reaction mechanism. On the basis for geometry optimizations, the thermodynamic data of these reactions channels have been calculated using the statistical theory at 295.15 K and pressure of 0.35 Torr. Using Eyring transition state theory with Wigner correction, the activation thermodynamic data, rate constant and frequency factors for the these reaction channels also have been given. The results showed that CO and N₂O do not react without catalyst and Fe⁺(C₆H₆) can excellently mediate the reaction of N₂O and CO.     

C(CF3)2OH → OCH(CF3)2 Isomerism in some sulfur and phosphorus compounds

The insertion of (CF₃)₂CO into the PH bond of Me_nH_3?nP yields Me_nH_2?nPC(CF₃)₂OH and Me_nH_1?nP[C(CF₃)₂OH]₂ (n=O, 1), respectively [1]. MeP[C(CF₃)₂OH]₂ rearranges giving the diphosphine [MePOCH(CF₃)₂]₂ and the phosphorane MeP[OCH(CF₃)₂]₄. Me₂PH reacts with (CF₃)₂CO forming several products, e.g. MePF[OCH(CF₃)₂]₂ and Me₂PPMe₂ [1]. The phosphines tBu(R)PH(R=Me, tBu), however, add (CF₃)₂CO giving rise to the phosphinites tBu(R)POCH(CF₃)₂, which furnish stable phosphonium salts upon treating with MeI. (CF₃)₂CO inserts into the SH bond of RSH to yield RSC(CF₃)₂OH (R=H,Me,Ph), which were reacted with MeI, too. Reacting SCl₂ with LiOCH(CF₃)₂ gives S[OCH(CF₃)₂]₂ which is oxidised by chlorine to the sulfurane ClS[OCH(CF₃)₂]₃ [2]. The sulfurane is able to transfer (CF₃)₂CHO groups to phosphorus (III) compounds, e.g. P[OCH(CF₃)₂]₃ and Me₃P yielding P[OCH(CF₃)₂]₅ and [Me₃POCH(CF₃)₂]⁺Cl^?. ClS[OCH(CF₃)₂]₃ gives a stable salt upon reaction with SbCl₅, like ClP[OCH(CF₃)₂]₄. The mechanisms for these reactions are discussed.     

Darstellung und charakterisierung von CF2ClSF3 und CF2ClS(O)F

The fluorination of CF₂ClSCl with AgF₂ yields CF₂ClSF₃ together with CF₃SF₃ and CF₃SF₅. CF₂ClSF₃ is also formed when CF₂ClSCl reacts with BrF₃ which is adsorbed at HgF₂. CF₂ClS(O)F results from the mild hydrolysis reaction of CF₂ClSF₃ with glass walls. The new compounds were characterised by their NMR and mass spectra, CF₂ClS(O)F also by its IR spectrum. The volatilities of the compounds were derived from codistillation diagrams. - Furthermore, previously unreported mass spectra of CF₃SF₃ and CF₃SF₅ are given.     

Computational study on the reactions of XO (X = F, Cl and Br) with CH3SO and CH3SO2

Potential energy surface (PES) for the reactions of XO (X = F, Cl and Br) with CH₃SO and CH₃SO₂ have been calculated at MP2/6-311++G(d, p)//B3LYP/6-311++G(d, p) level. It is revealed that all the reactions take place on both singlet and triplet surfaces. The reaction mechanisms of XO (X = F, Cl and Br) with CH₃SO and CH₃SO₂ are similar: the hydrogen abstraction channel of singlet-state PES, which has the overall negative activation energy, should be the dominant channel and CH₂SO (CH₂SO₂) + HOX should be the main products. The reactions of CH₃SO (CH₃SO₂) with XO become thermodynamically favored in the sequence of FO, ClO and BrO. The topological analysis of electronic density shows that a four-member-ring structure appears in the dominant reaction pathway, it turns to three-member-ring structure via a T-shaped structure and the ring structure disappears as the reaction proceeds. Furthermore, the scope of the structure transition region, the appeared position of the four-member-ring structure and the position of T-shaped structure correlated well to the atom which linked to the four-member-ring structure.