Kinetics and the mechanism of the thermal reaction between trifluoromethylhypofluorite and hexafluoropropene

The kinetics of the thermal reaction between CF₃OF and C₃F₆ have been investigated between 20 and 75°C. It is a homogeneous chain reaction of moderate length where the main product is a mixture of the two isomers 1-C₃F₇OCF₃ (68%) and 2-C₃F₇OCF₃ (32%). Equimolecular amounts of CF₃OOF₃ and C₆F₁₄ are formed in much smaller quantities. Inert gases and the reaction products have no influence on the reaction, whereas only small amounts of oxygen change the course of reaction and larger amounts produce explosions. The rate of reaction can be represented by eq. (I): The following mechanism explains the experimental results: Reaction (5) can be replaced by reactions (5a) and (5b), without changing the result: Reaction (4) is possibly a two-step reaction: For ∣CF₃ = ∣C₃F₆∣, ν_20°C = 36.8, ν_50°C = 24.0, and ν_70°C = 14.2.     

The kinetics and the mechanism of the thermal decomposition of bis(trifluoromethyl) trioxide. The influence of carbonmonoxide on its decomposition

The kinetics of the thermal decomposition of CF₃O₃CF₃ has been investigated in the pressure range of 15–599 torr at temperatures between 59.8 and 90.3°C and also in the presence of CO between 42 and 7°C. The reaction is homogeneous. In the absence of CO the only reaction products are CF₃O₂CF₃ and O₂. The rate of reaction is strictly proportional to the trioxide pressure, and is not affected by the total pressure, the presence of inert gases, and oxygen. The following mechanism explains the experimental results: In the presence of CO there appear CO₂, (CF₃OCO)₂, and CF₃O₂C(O)OCF₃ as products. With increasing temperature the amount of peroxicarbonate decreases, while the amounts of oxalate and CO₂ increase. The rate of decomposition of the trioxide above a limiting pressure of about 10 torr CO is strictly first order and independent of CO pressure, total pressure, and the pressure of the products. The addition of larger amounts of O₂ to the CO containing system chaqnges the course of the reaction.     

The kinetics of the gas-phase thermal isomerization and decomposition of Trans- and Cis-1,2-Bis(trifluoromethyl)-1,2,3,3-tetrafluorocyclopropane

The kinetics of the gas-phase thermal isomerization between trans- and cis-1,2-bis(trifluoromethyl)-1,2,3,3-tetrafluorocyclopropane as well as their decomposition to trans- and cis-perfluoro-2-butene, respectively, and CF₂, was studied in the temperature range of 473–533°K, with an initial pressure of reactant of 1.5 to 7.0 Torr. Some runs were also made with the addition of SF₆ as an inert gas up to a total pressure of 100 Torr. The reactions are first order and homogeneous. The rate constants for the geometrical isomerization fit the following Arrhenius relations: and the corresponding equations for the decomposition of the trans and cis-cyclopropane are .     

Kinetics and mechanism of the gas-phase thermal reaction between bis(fluoroxy) difluoromethane CF2(OF)2 and carbon monoxide

The kinetics of the gas-phase thermal reaction between CF₂(OF)₂ and CO has been studied in a static system at temperatures ranging between 110 and 140°C. The only reaction products were CF₂O and CO₂, giving the following stoichiometry: The reaction is homogeneous. The rate is strictly second order in CF₂(OF)₂ and CO, and is not affected by the total pressure or by the presence of reaction products. Oxygen promotes a sensitized oxidation of CO and inhibits the formation of CF₂O. The experimental results in the absence of oxygen can be explained by a chain mechanism similar to that proposed for the reaction between F₂O and CO with an overall rate constant of From the experimental data obtained on the oxygen-inhibited reaction, the rate constant for the primary process can be calculated: The chain length v = 2.5 is independent of the temperature. Taking for collision diameters σ = 6 Å and σ_CO = 3.74 Å, a value α = 5.3 × 10^?3 for the steric factor is obtained.     

The kinetics of the thermal bromination of CF3I. Determination of the bond dissociation energy D(CF3−I)

The kinetics of the thermal bromination reaction have been studied in the range of 173–321°C. For the step we obtain where θ=2.303RT cal/mole. From the activation energy for reaction (11), we calculate that This is compared with previously published values of D(CF₃?I). The relevance of the result to published work on k_c for a combination of CF₃ radicals is discussed.     

The Competitive dehydrohalogenation of 1,1,1-trifluoro-2-chloroethane in reflected shock waves

The thermal decomposition of 1,1,1-trifluoro-2-chloroethane has been investigated in the single-pulse shock tube between 1120° and 1300deg;K at total reflected shock pressures from ～2610 to 3350 torr. Under these conditions, the major reaction is the α,α-elimination of hydrogen chloride, with The decomposition also involves the slower α,β-elimination of hydrogen fluoride, with the first-order rate constant given by At temperatures above 1270°K, two additional minor products were observed. These were identified as CF₂CFCl and CF₃CHCl₂ and suggest C? Cl rupture as a third reaction channel leading to complicated kinetics.     

The kinetics of the reactions of i-C3F7 radicals with BR2 and HBr

The reactions have been studied competitively in the vapor phase over the range of 52–204°C. The i-C₃F₇ radicals were generated by means of the reaction It was found that where θ = 2.303RT J/mol. Absolute Arrhenius parameters are derived for the reactions where R = CF₃, C₂F₅, and i-C₃F₇.     

Time-resolved vibrational chemiluminescence: Rate constants for the reactions of F atoms with H2O and HCN,and for the relaxation of HF (v = 1) by H2O and HCN

Rate constants have been determined at (298 ± 4) K for the reactions: and the relaxation processes: Time-resolved HF(1,0) emission was observed following the photolysis of F₂ with pulses from an excimer laser operating on XeCl (λ = 308 nm). Analysis of the emission traces gave first-order constants for reaction and relaxation, and their dependence on [H₂O] and [HCN] yielded:      

Kinetics of the thermal decomposition of bis-pentafluorosulfur trioxide(SF5O3SF5) in the presence of carbon monoxide

The thermal decomposition of SF₅O₃SF₅ in the presence of CO has been investigated between -9.8°C and + 9.9°C. Besides traces of S₂F₁₀, equimolecular amounts of SF₅O₂SF₅ and CO₂ are formed. The reaction is homogeneous. Its rate is proportional to the pressure of the trioxide and in dependent of the total pressure, the pressure of inert gases and of carbon monoxide: where k = k_1∞ = 10^16.32±0.40 exp(?25,300 ± 500 cal)/RT sec^?1. Consequently, In the presence of oxygen a sensitized CO₂ formation is observed. A mechanism is given which explains the experimental results.     

The kinetics of free radical chain reactions in solutions of trichlorofluorethylene in cyclohexane

The kinetics of the gamma-radiation-induced free radical chain reaction in solutions of C₂Cl₃F in cyclohexane (RH) was investigated over a temperature range of 87.5–200°C. The following rate constants and rate constant ratios were determined for the reactions: In competitive experiments in ternary solutions of C₂Cl₄ and C₂Cl₃F in cyclohexane the rate constant ratio k_2c/k_2a was determined By comparing with previous data for the addition of cyclohexyl radicals to other chloroethylenes it is shown that in certain cases the trends in activation energies for cyclohexyl radical addition can be correlated with the C? Cl bond dissociation energies in the adduct radicals.     

Unexpectedly rapid vapor-phase reaction between bromine and methyl iodide

The overall reaction (1) occurs readily in the gas phase, even at room temperature in the dark. The reaction is much faster than the corresponding process and does not involve the normal bromination mechanism for gas phase reactions. Reaction (1) is probably heterogeneous although other mechanisms cannot be excluded. The overall reactions (1) (2) proceed, for all practical purposes, completely to the right-hand side in the vapor phase. The expected mechanism is (3) (4) (5) (6) (7) where reaction (3) is initiated thermally or photochemically. Reaction (4) is of interest because little kinetic data are available on reactions involving abstraction of halogen by halogen and also because an accurate determination of the activation energy E₄ would prmit us to calculate an acccurate value of the bond dissociation energy D(CH₃? I).     

The kinetics and the mechanism of the thermal gas-phase reaction between bis(trifluoromethyl)trioxide,CF3O3CF3 and 1,1-dichlorodifluoroethylene,CF2CCI2

The thermal addition of CF₃O₃CF₃(T) to CF₂CCl₂(E) has been investigated between 49.6 and 69.5°C. The initial pressure of CF₃O₃CF₃ was varied between 7 and 240 torr and that of CF₂CCl₂ between 4 and 600 torr. Four products of formula CF₃O(E)_j OOCF₃, where j = 1 → 4 are formed. The sum of the products Σ CF₃O(E)_jOOCF₃ is equal to the amount of trioxide decomposed. The reaction is homogeneous. Its rate is not affected by the total pressure and the presence of inert gas. It is a free radical telomerization with four basic steps: thermal decomposition of CF₃O₃CF₃ into CF₃O^. and CF₃O₂^., chain initiation by addition of CF₃O^. to olefin incorporated in, and telomeric radicals termination. The consumption of alkene is well represented by the equation: where (d[E]/d[T]) = is the mean chain length of telomerization. varies from 1.45 at 1.5 torr of E to 3.3 at 400 torr of E. Above this pressure E has no influence on . The estimated value of the constant for the addition of telomeric radicals to alkene is:      

The kinetics and the mechanism of the thermal gas-phase reaction between NO2 and 1,1-dichlorodifluoroethylene,CF2CCl2

The kinetics of the gas phase reaction between NO₂ and CF₂CCl₂ has been investigated in the temperature range from 50 to 80°C. The reaction is homogeneous. Three products are formed: O₂NCF₂CCl₂NO₂ and equimolecular amounts of CINO and of O₂NCF₂C(O)Cl. The rate of consumption of the reactants is independent of the total pressure, the reaction products, and added inert gases and can be represented by a second-order reaction: However, the distribution of the products is influenced by the pressure of the present gases, which favor the formation of the dinitro-compound in a specific way. The effect of CF₂CCl₂ is the greatest. In the absence of added gases, the ratio of O₂NCF₂CCl₂NO₂ to that of O₂NCF₂C(O)Cl is proportional to (CF₂CCl₂ + γ_P products). The experimental results can be explaned by the following mechanism: P and X represent the products and the added gases:      

Thermal stability of alcohols

3,3-Dimethylbutanol-2 (3,3-DMB-ol-2) and 2,3-dimethylbutanol-2 (2,3-DMB-ol-2) have been decomposed in comparative-rate single-pulse shock-tube experiments. The mechanisms of the decompositions are The rate expressions are They lead to D(iC₃H₇? H) – D((CH₃)₂(OH) C? H) = 8.3 kJ and D(C₂H₅? H) – D(CH₃(OH) CH? H) = 24.2 kJ. These data, in conjunction with reasonable assumptions, give and The rate expressions for the decomposition of 2,3-DMB-1 and 3,3-DMB-1 are and      

Kinetic study of gas-phase reactions with CF2Cl2 and CFCl3. Analysis using the transition state theory (TST) of the chlorine atom transfer reactions by CF3 and CH3 radicals from halomethanes

The following gas-phase reactions: were studied by the competitive method with CF₃I as the source of radicals. The kinetic parameters obtained in the temperature range 533–613 K and 503–613 K respectively for chlorine atom transfer reactions are given by: where θ = 2.303 RT (cal mol^?1). The Arrhenius A values were calculated for seven chlorine atom transfer reactions (CF₂Cl₂, CFCl₃, CCl₄ with CF₃ radicals; CF₃Cl, CF₂Cl₂, CFCl₃ and CCl₄ with CH₃ radicals) by using the thermochemical kinetic version of the Transition State Theory (TST).     

The gas-phase kinetics of the reaction of 1,1,1-trifluoroethyl iodine with HI: The C?I bond dissocation energy in 2,2,2-trifluoroethyl iodide

The kinetics of the gas-phase reaction of 2,2,2-trifluoroethyl iodide with hydrogen iodide has been studied over the temperature range of 525°K to 602°K and a tenfold variation in the ratio of CF₃CH₂I/HI. The experimental results are in good agreement with the expected free radical-mechanism: An analysis of the kinetic data yield: where θ =2.303RT in kcal/mol. If these results are combined with the assumption that E₂ = 0 ± 1 kcal/mol, then one obtains DH (CF₃CH₂? I) = 56.3 kcal/mol. This result may be compared with DH(CH₃CH₂? I) = 52.9 kcal/mol and suggests that substitution of three fluorines for hydrogen in the beta position strengthens the C? I bond slightly.     

The kinetics and the mechanism of the thermal decomposition of bis-pentafluorosulfurtrioxide (SF5OOOSF5)

The thermal decomposition of SF₅O₃SF₅ has been investigated between 5 and 25°C. In the presence of sufficient high pressures of O₂ the only products formed are SF₅O₂SF₅ and O₂: The reaction is homogeneous. Its rate is strictly first order with respect to the trioxide pressure and independent of the total pressure of the reaction products and of oxygen above a certain limiting pressure: The experimental results can be explained with the following mechanism: In the presence of O₂ > 100 Torr the concentration of SF₅ is insignificantly small. Therefore reactions (5) and (6) do not have to be considered any more, and steps (2) and (2′) will be of no importance. From reactions (1)–(4) it follows: The numerical value of the factor [1 + (k′₁²/2k₃k₄)^1/2] is small. It can be estimated that E₃ ? 2 ± 1 kcal; therefore, E – E₁ ≤ 1 kcal, and D = (26 – 1) ± 1.0 kcal.     

Kinetics of the thermal decomposition of CF3CHCL2 in a single-pulse shock tube

The pyrolysis of 2,2-dichloro-1,1,1-trifluoroethane was studied over the temperature range of 1120–1260°K at total reflected shock pressures from ～2800 to 3100 torr. Below 1260°K, the decomposition leads to three reaction products which were identified as CF₂CFCl, CF₂CFH, and CF₃CCl₃. The results are interpreted in terms of a parallel C? Cl bond rupture process which becomes competitive with the molecular HCI elimination. The rate constant for the α,α-elimination process has been deduced to be It was also possible to obtain the overall rate constant for the formation of CF₂CFH, which is given by Some evidence for hydrogen fluoride elimination was found at temperatures above 1260°K. However, at these higher temperatures C? C bond scission also occurs and the kinetics of the system become untractable.     

Reaction of CF3 radicals with group IV tetramethyls

Arrhenius parameters have been measured for the abstraction of hydrogen from the C Si, Ge, and Sn tetramethyls: The rate constants correlate with the proton chemical shift, which is related to a polar effect. In all cases except carbon, a hot-molecule β-fluorine rearrangement-elimination reaction occurs following radical combination: We suggest the occurrence of a radical exchange reaction for the Si, Sn, and Ge systems, with k_exchange (CF₃ + Sn(Me)₄) ～ 10⁷ ml m^?1 s^?1.     

H2S-promoted thermal isomerization of butene-2 CIS to butene-1 or butene-2 trans around 500°C

H₂S increases the thermal isomerization of butene-2 cis (B_c) to butene-1 (B₁) and butene-2 trans (B_t) around 500°C. This effect is interpreted on the basis of a free radical mechanism in which buten-2-yl and thiyl free radicals are the main chain carriers. B₁ formation is essentially explainedby the metathetical steps: whereas the free radical part of B_t formation results from the addition–elimination processes: . It is shown that the initiation step of pure B_c thermal reaction is essentially unimolecular: and that a new initiation step occurs in the presence of H₂S: . The rate constant ratio has been evaluated: and the best values of k₁ and k_1', consistent with this work and with thermochemical data, are . From thermochemical data of the literature and an “intrinsic value” of E_?3 ? 2 kcal/mol given by Benson, further values of rate constants may be proposed: is shown to be E₄ ? 3.5 ± 2 kcal/mol, of the same order as the activation energy of the corresponding metathetical step.