The CO_2 laser-induced radical-chain reactions between CH_3CF_2H and chlorine-atom donors CF_2ClCFCl_2, CF_3CCl_3 CFCl_3 or CF_2Cl_2

The CO_2 laser induced room temperature reactions of CH_3CF_2H or another protium-donorCH_3CHClCH_3 with chlorine-atom donors (Z--Cl) CFCl_2CF_2Cl, CF_3CCl_3, CFCl_3 or CF_2Cl_2, havebeen investigated. Some of these reactions can yield two important monomers (CF_2=CH_2 andCF_2=CFCl) for fluoropolymers simultaneously. The yield dependence of these two alkenes on experi-mental conditions has been studied. A laser-initiated chain process is supported by identifica-tion of Z--H intermediates in these reactions.     

Charge separation reactions of the CF2+ and CCl2+ dications

Experimental values of kinetic energy release (T) for predissociation processes of the diatomic dications CF²⁺ and CCl²⁺ have been obtained using mass-analysed ion kinetic energy spectrometry (MIKES) on a double-focusing mass spectrometer. Both unimolecular and collision-induced processes were studied. Potential energy curves for CF²⁺ and CCl²⁺ were calculated using the semi-empirical procedure due to Hurley, and applied to the interpretation of the observed T values.     

Some hydrogen abstraction reactions of the CF3CCl2 radical

The gas phase photolysis of CF₃CCl₃ in the presence of several alkanes has been used to obtain Arrhenius parameters for the abstraction of hydrogen atoms by the CF₃CCl₂ radical: Activation energies of 9.6 and 8.0 kcal/mole are found for abstraction from secondary and tertiary C–H bonds, respectively. The Arrhenius parameters are compared to those for CCl₃ and CF₃ radicals.     

Halogenation with CCl4 and CF2Cl2 vapours in arc emission spectrometry

Halocarbon vapour diluted with air or nitrogen was applied during the arc excitation of carbide forming elements in solution form, of metal samples (copper, aluminium) and powder samples (alumina, glass, RU-powder) on graphite supporting electrodes. Means were developed for the carrier vaporization of CCl₄ and for the introduction of the halocarbon vapour into the arc discharge. The gaseous agent was supplied continuously during excitation. This possibility was also subjected to some theoretical predictions. On applying CCl₄ with samples introduced in solution form, the volatilization rates of the most refractory elements (e.g. W) were found to increase at least 50 times on the basis of line intensities. Fractional distillation could be attained on constituents and matrices similar to those reported with solid agents, but the gaseous agents could be applied more easily and without contamination problems. The overall effect of halogenation on excitation processes was evaluated from line intensities integrated over the total evaporation time of a complex powder sample, with and without graphite powder dilution. A high intensification (a factor of 3–12) was obtained for the u.v. lines of the refractory constituents with halogenation, which was attributed to the increased efficiency of these elements in entering the excitation zone. Decrease in the intensities of barium atom and ion lines in the VIS range and a decrease of self-absorption were found as a consequence of halide formation in the arc fringe.     

Theoretical studies of decomposition kinetics of CF3CCl2O radical

The unimolecular decomposition reaction of CF₃CCl₂O radical has been investigated using theoretical methods. Two most important channels of decomposition occurring via C–C bond scission and Cl elimination have been considered during the present investigation. Ab initio quantum mechanical calculations are performed to get optimized structure and vibrational frequencies at DFT and MP2 levels of theory. Energetics are further refined by the application of a modified Gaussian-2 method, G2M(CC,MP2). The thermal rate constants for the decomposition reactions involved are evaluated using Canonical Transition State Theory (CTST) utilizing the ab initio data. Rate constants for C–C bond scission and Cl elimination are found to be 6.7 × 10⁶ and 1.1 × 10⁸ s^?1, respectively, at 298 K and 1 atm pressure with an energy barrier of 8.6 and 6.5 kcal/mol, respectively. These values suggest that Cl elimination is the dominant process during the decomposition of the CF₃CCl₂O radical. Transition states are searched on the potential energy surface of the decomposition reactions involved and are characterized by the existence of only one imaginary frequency (NIMAG = 1) during frequency calculation. The existence of transition states on the corresponding potential energy surface is further ascertained by performing intrinsic reaction coordinate (IRC) calculation.     

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:      

Rate coefficients and ClO radical yields in the reaction of O(1D) with CClF2CCl2F,CCl3CF3, CClF2CClF2, and CCl2FCF3

Rate coefficients, k, and ClO radical product yields, Y, for the gas‐phase reaction of O(¹D) with CClF₂CCl₂F (CFC‐113) (k₂), CCl₃CF₃ (CFC‐113a) (k₃), CClF₂CClF₂ (CFC‐114) (k₄), and CCl₂FCF₃ (CFC‐114a) (k₅) at 296 K are reported. Rate coefficients for the loss of O(¹D) were measured using a competitive reaction technique, with n‐butane (n‐C₄H₁₀) as the reference reactant, employing pulsed laser photolysis production of O(¹D) combined with laser‐induced fluorescence detection of the OH radical temporal profile. Rate coefficients were measured to be k₂ = (2.33 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₃ = (2.61 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₄ = (1.42 ± 0.25) × 10^?10 cm³ molecule^?1 s^?1, and k₅ = (1.62 ± 0.30) × 10^?10 cm³ molecule^?1 s^?1. ClO radical product yields for reactions (2)–(5) were measured using pulsed laser photolysis combined with cavity ring‐down spectroscopy to be 0.80 ± 0.10, 0.79 ± 0.10, 0.85 ± 0.12, and 0.79 ± 0.10, respectively. The quoted errors in k and Y are at the 2σ (95% confidence) level and include estimated systematic errors. © 2011 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America

Int J Chem Kinet 43: 393–401, 2011     

Kinetics of the reactions of halogenated methyl radicals (CF3, CF2Cl,CFCl2, and CCl3) with molecular chlorine

The kinetics of four gas-phase reactions involving halogenated methyl radicals (R ? CF₃, CF₂Cl, CFCI₂, and CCI₃) with molecular chlorine have been studied using a tubular reactor coupled to a photoionization mass spectrometer. The radicals were homogeneously generated by the pulsed photolysis of precursor molecules at 193 nm. The subsequent decays of the radical concentration were monitored in real-time experiments as a function of Cl₂ concentration to obtain the rate constants of these R + Cl₂ reactions. Where possible, the rate constants were measured as a function of temperature to determine Arrhenius parameters. Apparent discrepancies between these measured rate constants for CF₃ and CCl₃ with Cl₂ and ones obtained in prior indirect studies are explained. The higher activation energies for these R + Cl₂ reactions compared to that of the CH₃ + Cl₂ reaction are attributed in part to the different polarities of the transition states formed.     

Kinetics and products of chlorine atom initiated oxidation of HCF2OCF2OCF2CF2OCF2H and HCF2O(CF2O)n‐(CF2CF2O)mCF2H

Smog chamber/FTIR techniques were used to measure k(Cl + HCF₂OCF₂OCF₂‐CF₂OCF₂H) = k(Cl + HCF₂O(CF₂O)_n(CF₂CF₂O)_mCF₂H) = (5.0 ± 1.4) × 10^?17 cm³ molecule^?1 s^?1 in 700 Torr of N₂/O₂ diluent at 296 ± 1 K. The Cl‐initiated atmospheric oxidation of HCF₂OCF₂OCF₂CF₂OCF₂H and the sample of HCF₂O(CF₂O)_n(CF₂CF₂O)_mCF₂H used in this work gave COF₂ in molar yields of (476 ± 36)% and (859 ± 63)%, respectively, with no other observable carbon containing products (i.e., essentially complete conversion of both hydrofluoropolyethers into COF₂). The results are discussed with respect to the atmospheric chemistry and environmental impact of hydrofluoropolyethers of the general formula HCF₂O(CF₂O)_n(CF₂CF₂O)_mCF₂H. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 819–825, 2008     

Electron-impact ionization of CCl4 and CCl2F2

Absolute partial and total cross sections for electron-impact ionization of CCl4 and CCl2F2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of CCl3(+), CCl2(+), CCl+, C+, Cl2(+), and CCl3(2+) from CCl4; and for production of CCl(2)F+, CClF2(+), CClF(+), (CCl+ + CF2(+)), Cl+, CF+, F+, and C+ from CCl2F2. Data are also reported for formation of (CCl2(+),Cl+) and (CCl+, Cl+) ion pairs from CCl4. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly charged ions is +/- 5-7 %. The present partial cross sections for lighter fragment ions are found to be considerably greater than had been previously reported but the most recent total cross section measurements agree well with those reported here. Neither the binary-encounter-Bethe theory nor the Deutsch-Mark theory reproduces the experimental cross sections correctly for both targets.     

Some highly fluorinated acyclic,cyclic, and polycyclic derivatives of Cl2NCF2CF2NCl2 and Cl2CNCCl2CCl2NCCl2

When Cl₂NCF₂CF₂NCl₂ is heated with CF₂CFX (X = Cl, F) ClXCFCF₂N(Cl)CF₂CF₂N(Cl)CF₂CXClF (X = Cl, 2 ; F, 3 ) is formed. Mercury extracts chlorine fluoride from 2 and 3 to form new polyfluorobisazomethines, ClXCFCF₂NCFCFNCF₂CXClF (X = Cl, 4 ; F, 5 ). Photolysis of the product obtained from CCl₂NCCl₂CCl₂NCCl₂ with ClF, CF₂ClN(Cl)CF ClCFClN(Cl)CF₂Cl ( 6 ) gives another bisazomethine, CF₂ClNCFCFNCF₂Cl ( 7 ) with concomitant loss of Cl₂. At 25°C, in the presence of CsF, 4 and 5 are cyclized to give (X = Cl, 8 ; F, 9 ), and 7 forms a bicyclic derivative at 100°C, ( 1 ). Addition of chlorine fluoride to 8 and to 1 produces ( 10 ) and ( 14 ), respectively. Photolysis of 10 results in the loss of CFCl₃ to form ( 11 ), and 14 loses Cl₂ and dimerizes to the hydrazine ( 15 ). The further addition of ClF to 11 gives rise to ( 12 ) which when photolyzed at 3000 Å forms a second cyclic hydrazine, ( 13 ).     

Infrared and Raman spectra and quantum chemistry calculations for 2,2,2-trifluoroethyl trichloromethanesulfonate, CCl3SO2OCH2CF3

The infrared spectra of CCl3SO2OCH2CF3 were obtained in the gaseous, liquid and solid states and complemented with the Raman spectrum of the liquid. Quantum chemistry calculations using the density functional theory (DFT) were used to predict the most stable geometry and conformation of the studied molecule. The harmonic vibrational frequencies and force field were also calculated. Comparison with related molecules and with the predicted frequencies was used as the basis for the assignment of the observed spectral features. Subsequently, a scaling of the original force field by means of a least square procedure was made in order to reproduce as well as possible the experimental frequencies, leading to a final root mean square deviation of 10.6 cm(-1).     

Trends of Atmospheric CCl 3 F,CCl 2 F 2 and CCl 2 FCClF 2 in Shanghai (China)

Atmospheric concentrations of CCl 3 F (CFC-11), CCl 2 F 2 (CFC-12), and CCl 2 FCClF 2 (CFC-113) in troposphere in Shanghai, China (31°1N) have been routinely monitored by using gas chromatography with electron capture detector from November 1997 to December 2000. The observation shows that there is a slowly declining trend of the three compounds. On the other hand, a comparison has been drawn between the concentrations observed and the ones calculated by 2-box model on the basis of the global statistical data of CFCs production and emission. Our observation agrees with the calculations. It shows that production and emission of chlorofluorocarbons (CFCs) in China are still at a low level and gradually decreasing.     

Theoretical studies on dynamics and thermochemistry of the reactions CF(3)CHCl(2)+Cl-->CF(3)CCl(2)+HCl and CF(3)CHFCl+Cl-->CF(3)CFCl+HCl

A dual-level direct dynamics study has been carried out for the two hydrogen abstraction reactions CF(3)CHCl(2)+Cl and CF(3)CHFCl+Cl. The geometries and frequencies of the stationary points are optimized at the BHLYP/6-311G(d,p), B3LYP/6-311G(d,p), and MP2/6-31G(d) levels, respectively, with single-point calculations for energy at the BHLYP/6-311++G(3df,2p), G3(MP2), and QCISD(T)/6-311G(d,p) levels. The enthalpies of formation for the species CF(3)CHCl(2), CF(3)CHFCl, CF(3)CCl(2), and CF(3)CFCl are evaluated at higher levels. With the information of the potential energy surface at BHLYP/6-311++G(3df,2p)//6-311G(d,p) level, we employ canonical variational transition-state theory with small-curvature tunneling correction to calculate the rate constants. The agreement between theoretical and experimental rate constants is good in the measured temperature range 276-382 K. The effect of fluorine substitution on reactivity of the C-H bond is discussed.     

Kinetics of electron-induced decomposition of CF2Cl2 coadsorbed with water (ice): a comparison with CCl4

The kinetics of decomposition and subsequent chemistry of adsorbed CF(2)Cl(2), activated by low-energy electron irradiation, have been examined and compared with CCl(4). These molecules have been adsorbed alone and coadsorbed with water ice films of different thicknesses on metal surfaces (Ru; Au) at low temperatures (25 K; 100 K). The studies have been performed with temperature programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), and x-ray photoelectron spectroscopy (XPS). TPD data reveal the efficient decomposition of both halocarbon molecules under electron bombardment, which proceeds via dissociative electron attachment (DEA) of low-energy secondary electrons. The rates of CF(2)Cl(2) and CCl(4) dissociation increase in an H(2)O (D(2)O) environment (2-3x), but the increase is smaller than that reported in recent literature. The highest initial cross sections for halocarbon decomposition coadsorbed with H(2)O, using 180 eV incident electrons, are measured (using TPD) to be 1.0+/-0.2 x 10(-15) cm(2) for CF(2)Cl(2) and 2.5+/-0.2 x 10(-15) cm(2) for CCl(4). RAIRS and XPS studies confirm the decomposition of halocarbon molecules codeposited with water molecules, and provide insights into the irradiation products. Electron-induced generation of Cl(-) and F(-) anions in the halocarbon/water films and production of H(3)O(+), CO(2), and intermediate compounds COF(2) (for CF(2)Cl(2)) and COCl(2), C(2)Cl(4) (for CCl(4)) under electron irradiation have been detected using XPS, TPD, and RAIRS. The products and the decomposition kinetics are similar to those observed in our recent experiments involving x-ray photons as the source of ionizing irradiation.     

CCl和CCl2(1A1)的结构与势能函数

利用Gaussian03软件包,采用多种方法和多种基组对CCl和CCl2分子的基态结构进行优化计算,优选出B3P86/6-311+ G(3 df)方法对CCl分子进行计算得到基态为X2Ⅱ、键长RCCl=0.164 42 nm,谐振频率we=886.3062 cm-1;优选出B3P86/6-311G( 2df)方法对CC...     

CCl2(A1B1)被O2及取代甲烷类分子猝灭的动力学研究

对CCl4／Ar混合气体放电产生CCl2自由基，再用541.52nm激光将电子基态CCl2激发到激发态A^1B1（0，4，0）振动态k=0能级上，通过检测 激发态CCl2时间分辨荧光信号，测得室温下CCl2(A^1B1)被O2，CF4，CF2Cl，CH3NO2，CH2Br2等分子猝灭的实验结果，用改进的三能级模型分析处理实验数据，获得态分辨速常数KA和Ka值，并对实验结果进行了讨论。     

含CF3CF2CF2C(CF3)2基团支链型氟表面活性剂的合成及性能研究

全氟辛酸/全氟辛基磺酸(PFOA/PFOS)类氟表面活性剂因不易被生物降解且对环境有毒害作用, 被列为持久性有机污染物. 采用引入氟碳支链的策略作为PFOA/PFOS替代物的研发取向, 以六氟丙烯二聚体为原料合成了新型阳离子型、两性型、双子型和非离子型氟表面活性剂, 并对它们的表面活性和急性毒性性能进行了测试. 结果表明, 所合成的支链型表面活性剂表面活性高且毒性低. 因此, 基于六氟丙烯二聚体(HFPD)合成PFOS/PFOA替代物是一种简单、经济且环保的方法.     

Kinetic and thermochemical parameters of chlorine atom transfer reactions from CF3Cl,CF3CF2Cl,CF2ClCF2Cl,and CF2ClCFCl2 in gas phase

The following reactions: (1) were studied over the temperature ranges 533–687 K, 563–663 K, and 503–613 K for the forward reactions respectively and over 683–763 K, for the back reaction. Arrhenius parameters for chlorine atom transfer were determined relative to the combination of the attacking radicals. The ΔH_r°(1) = ?3.95 ± 0.45 kcal mol^?1 was calculated and from this value the ΔH∮(C₂F₅Cl) = ?2.66.3 ± 2.5 kcal mol^?1 and D(C₂F₅-Cl) = 82.0 ± 1.2 kcal mol^?1 were obtained. Besides, the ΔH_r°(2) was estimated leading to D(CF₂ClCF₂Cl) = 79.2 ± 5 Kcal mol^?1. The bond dissociation energies and the heat of formation are compared with those of the literature. The effect of the halogen substitutents as well as the importance of the polar effects for halogen transfer processes are discussed.     

Design and synthesis of the novel branched fluorinated surfactant intermediates with CF3CF2CF2C(CF3)2 group

Here we reported a novel and efficient method for the synthesis of the critical intermediates of branched fluorinated surfactants with CF₃CF₂CF₂C (CF₃)₂- group using HFPD as starting material. The reaction conditions were mild and easy to handle, which was promisingly applied to the industrial production.