Cl-atom transfer from CFCl3 to the c-C6H11 radical. An indirect estimation of the CFCl2?Cl bond dissociation energy

The Cl-transfer reaction between CFCl₃ and c-C₆H₁₁ radicals (R) was studied in liquid cyclohexane (RH). The Arrhenius parameters for Cl abstraction were determined in the RH-CFCl₃ system versus the termination reaction between cyclohexyl radicals and competitively versus addition to C₂Cl₄ in the RH-CFCl₃-C₂Cl₄ system. The two sets of results are in very good agreement and give the following Arrhenius expression for the reaction R + CFCL₃ → RCl + CFCl₂ (2): where θ = 2.303RT in kcal/mol. Comparison with Cl-transfer data of other chloromethanes and chloroethanes shows that an increase in the C? Cl bond dissociation energy is the main cause of the reduced reactivity of CFCl₃. Based on a previously developed correlation, D(CFCl₂ ? Cl) is estimated to be equal to 74.4 kcal/mol.     

Studies by the electron cyclotron resonance (ECR) technique: VIII. Interaction of low-energy electrons with the chlorine-containing molecules CCl4, CHCl3, CH2Cl2, CnH2n+1 Cl(n = 1 to 4). C2H3Cl,COCl2, NOCl,CNCl and Cl2

Rate constants, in some cases also activation energies and energy dependences, were measured for the capture of low-energy electrons by the molecules CCl₄, CHCl₃, CH₂Cl₂, C_nH_2n+1 Cl(n = 1 to 4), C₂H₃Cl, COCl₂, NOCl, CNCl and Cl₂ Potential energy curves were calculated for a number of negative ions.For ineffective scavengers the possibility of contributing scattering effects on the observed changes in signal intensity upon electron energy variation is indicated. In CCl₄ the observed energy dependence suggests the existence of intermediate negative ions. For Cl₂ good agreement was obtained between the calculated curves based on experimental data for electron capture and a recent self-consistent field analysis.     

Investigation of radical reactions in C2Cl4 and C2Cl4/O2 discharges by EPR,mass, and emission spectroscopy

The reaction of tetrachloroethylene, C₂Cl₄, with O(³P) atoms as well as the plasma decomposition of C₂Cl₄ and C₂Cl₄/O₂ mixtures have been investigated by combined application of electron paramagnetic resonance (EPR) and emission and mass spectroscopies. C₂Cl₄ plasma decomposition is shown to proceed primarily to the formation of CCl₃ radicals and chlorine-deficient products, which are ultimately involved in the formation of carbonaceous layers. A simple reaction model accounts for all the detected stable and radical species, encountered during the plasma decomposition. The model also enables order-of-magnitude estimates of decomposition rate constants to be made. The suppression of the formation of both carbonaceous layers and products C_mCl_n (m3) in C₂Cl₄/O₂ discharges is explained using results of an investigation of elementary reactions in the system C₂Cl₄/O(³P)/O₂. The stable products of C₂Cl₄/O₂ discharges, i.e., COCl₂, CCl₄, and C₂Cl₆, respectively, are shown to originate from recombination of the peroxy radicals CCl₃OO and C₂Cl₅OO.     

Rates of reaction of atomic oxygen with C2H3F,C2H3Cl,C2H3Br, 1,1-C2H2F2, and 1,2-C2H2F2

Rate constants for the reactions of atomic oxygen (O³P) with C₂H₃F, C₂H₃Cl, C₂H₃Br, 1,1-C₂H₂F₂, and 1,2-C₂H₂F₂ have been measured at 307°K using a discharge-flow system coupled to a mass spectrometer. The rate constants for these reactions are (in units of 10¹¹ cm³ mole^?1 s^?1) 2.63 ± 0.38, 5.22 ± 0.24, 4.90 ± 0.34, 2.19 ± 0.18, and 2.70 ± 0.34, respectively. For some of these reactions, the product carbonyl halides were identified.     

Radiation-induced dechlorination of carbon tetrachloride in cyclohexane and n-hexane mixtures. III. The kinetics of liquid-phase reactions of trichloromethyl radicals

The kinetics of gamma-radiation-induced free-radical chain reactions in solutions of carbon tetrachloride in mixtures of varying composition of cyclohexane and n-hexane was investigated in the temperature range of 296°–413°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated alkyl radicals with the solute. The kinetics of the following reactions were studied: The following rate expression was obtained: The error limits are the standard deviation from the least mean-square Arrhenius plots. The present results, combined with previously measured activation parameters for hydrogen-atom abstraction from c-C₆H₁₂ and n-C₆H₁₄ by CCl₃ radicals relative to CCl₃ combination, afford experimental evidence that the decay of trichloromethyl species in alkane solutions is a diffusion-limited process. The thesis that activation energies of reactions (4) and (5) in the liquid phase are equal to their respective values in the gas phase is confirmed.     

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.     

Reactivity of radicals CCl3(CH2CHR)n (R=H,CH3, Cl; n=1, 2) in addition reactions with unsaturated compounds

Using EPR spectroscopy, the rate constants for the addition of radicals CC1₃(CH₂· CH₂)_n, (R¹ for n=1 and R² for n=2), CCl₃CH₂CHCH₃ (R³), and CCl₃CH₂CHCl (R⁴) to unsaturated compounds CH₂=CHX (X=C₆H₅, COOCH₃, CN) and CH₂=C(CH₃)Y (Y=C₆H₅, COOCH₃) at 22C have been determined. The radicals R¹ and R² exhibit ambiphilic, and R⁴ electrophilic character towards the selected unsaturated compounds. It has been shown that the presence of the CCl₃ group in the -position of the radical center has little effect on the reactivity of the radical. Replacement of a hydrogen on the -carbon in radical R¹ by a CH₃ group or chlorine atom leads to a considerable reduction in the rate of addition of the radicals to the unsaturated compounds examined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 548–554, March, 1991.     

Chlorine-photosensitized oxidations of chloroethanes and chloroethylenes in the gas phase

Long-chain chlorine-photosensitized oxidation has been observed in the gas phase at about 355°K for 1,1,2,2- and 1,1,1,2-C₂H₂Cl₄, C₂HCl₅, and C₂Cl₄ but not for C₂H₆, 1,2-C₂H₄Cl₂, 1,1,1-C₂H₃Cl₃, C₂H₄, and 1,2-C₂H₂Cl₂. This is shown to depend on the exothermicity of the dissociation of the chloroethoxy radicals which must be involved in each reaction system.     

Abstraction of chlorine atoms from chloroalkanes. V. The liquid-phase reaction between Et3SiH radicals and CH2Cl2, CHCl3, CCl4, and CCl3CN

The kinetics of chlorine transfer from CH₂Cl₂, CHCl₃, CCl₄, and CCl₃CN to the triethylsilyl radical was studied in the liquid phase by a competitive method. Br abstraction from 1-bromopentane was used as a reference. The following Arrhenius parameters were determined: where the error limits are two standard deviations (2σ). Based on these results, the observed reactivity trends in the chlorine transfer reactions of Et₃Si radicals appear to primarily reflect the variation in entropy of activation rather than in activation energies.     

Temperature-dependent kinetics studies of the reactions of C2H5O2 and n-C3H7O2 radicals with NO

The rate coefficients for the gas-phase reactions of C₂H₅O₂ and n-C₃H₇O₂ radicals with NO have been measured over the temperature range of (201–403) K using chemical ionization mass spectrometric detection of the peroxy radical. The alkyl peroxy radicals were generated by reacting alkyl radicals with O₂, where the alkyl radicals were produced through the pyrolysis of a larger alkyl nitrite. In some cases C₂H₅ radicals were generated through the dissociation of iodoethane in a low-power radio frequency discharge. The discharge source was also tested for the i-C₃H₇O₂ + NO reaction, yielding k_{298 K} = (9.1 ± 1.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, in excellent agreement with our previous determination. The temperature dependent rate coefficients were found to be k(T) = (2.6 ± 0.4) × 10⁻¹² exp{(380 ± 70)/T} cm³ molecule⁻¹ s⁻¹ and k(T) = (2.9 ± 0.5) × 10⁻¹² exp{(350 ± 60)/T} cm³ molecule⁻¹ s⁻¹ for the reactions of C₂H₅O₂ and n-C₃H₇O₂ radicals with NO, respectively. The rate coefficients at 298 K derived from these Arrhenius expressions are k = (9.3 ± 1.6) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ for C₂H₅O₂ radicals and k = (9.4 ± 1.6) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ for n-C₃H₇O₂ radicals. © 1996 John Wiley & Sons, Inc.     

Activation of C2H6, C3H8, HC(CH3)3, and c-C3H6 by gas-phase Ru+ and the thermochemistry of Ru-ligand complexes

The reactions of Ru⁺ with C₂H₆, C₃H₈, HC(CH₃)₃, and c-C₃H₆ at hyperthermal energies have been studied using guided ion beam mass spectrometry. It is found that dehydrogenation is efficient and the dominant process at low energies in all four reaction systems. At high energies, C-H cleavage processes dominate the product spectrum for the reactions of Ru⁺ with ethane, propane, and isobutane. C-C bond cleavage is a dominant process in the cyclopropane system. The reactions of Ru⁺ are compared with those of the first-row transition metal congener Fe⁺ and the differences in behavior and mechanism are discussed in some detail. Modeling of the endothermic reaction cross sections yields the 0-K bond dissociation energies (in eV) of D ₀(Ru-H)=2.27±0.15, D ₀(Ru⁺-C)=4.70±0.11, D ₀(Ru⁺-CH)=5.20±0.12, D ₀(Ru⁺-CH₂)=3.57±0.05, D ₀(Ru⁺-CH₃)=1.66±0.06, D ₀(Ru-CH₃)=1.68±0.12, D ₀(Ru⁺-C₂H₂)=1.98±0.18, D ₀(Ru⁺-C₂H₃)=3.03±0.07, and D ₀(Ru⁺-C₃H₄)=2.24±0.12. Speculative bond energies for Ru⁺=CCH₂ of 3.39±0.19 eV and Ru⁺=CHCH₃ of 3.19±0.15 eV are also obtained. The observation of exothermic processes sets lower limits for the bond energies of Ru⁺ to ethene, propene, and isobutene of 1.34, 1.22, and 1.14 eV, respectively.     

Some hydrogen atom abstraction reactions of CF2H and CFH2 radicals,and the C?H bond dissociation energy in CF2H2

By photolyzing (CF₂H)₂CO and (CFH₂)₂CO the hydrogen atom abstraction reactions of CF₂H radicals with (CF₂H)₂CO, H₂, D₂, CH₄, C₂H₆, n? C₄H₁₀ and iso? C₄H₁₀, and the reactions of CFH₂ radicals with (CFH₂)₂CO and n? C₄H₁₀, have been studied. Arrhenius parameters for these reactions are compared with related systems. From a knowledge of the activation energies for the forward and reverse reactions a value of the bond dissociation energy, D(CF₂H? H) = 97.4 ± 1.3 kcal mole^?1 at a mean temperature of 543°K is obtained. This value is subject to much uncertainty due to possible compensation effects in the Arrhenius parameters. These effects are discussed for this and the other reactions, and the data suggest that D(CF₂H? H) is approximately 100 kcal mole^?1, and that D(CFH₂? H) is very similar. Other literature data tend to confirm these approximate values.     

Bildung siliciumorganischer Verbindungen. 110. Reaktionen von (Cl3Si)2CCl2, seiner Si-methylierten Derivate,von (Cl3Si)2CHCl, (Cl3Si)2C(Cl)Me und Me2CCl2 mit Silicium (Cu-Kat.)

Formation of Organosilicon Compounds. 110. Reactions of (Cl₃Si)₂CCl₂ and its Si-methylated Derivatives as well as of (Cl₃Si)₂CHCl, (Cl₃Si)₂C(Cl)Me and Me₂CCl₂ with Silicon (Cu cat.) The reactions of (Cl₃Si)₂CCl₂ 1 , its Si-methylated derivatives (Me₃Si)₂CCl₂ 8 , Me₃Si? CCl₂? SiMe₂Cl 9 , (ClMe₂Si)₂CCl₂ 10 , Me₃Si? CCl₂? SiMeCl₂ 11 , Cl₂MeSi? CCl₂? SiCl₃ 12 as well as of (Cl₃Si)₂CHCl 38 , (Cl₃Si)₂CClMe 39 and of Me₂CCl₂ with Si (Cu cat.) in a fluid bed reactor ( 38 and 39 also in a stirred solid bedreactor) arc presented. While (Cl₃Si)₂CCl₂ 1 yields C(SiCl₃)₄ 2 the 1,1,3,3-tetrachloro-2,2,4,4-tetrakis(trichlorsilyl)-1,3-disilacyclobutane Si₆C₂Cl₁₆ 3 and the related C-spiro linked disilacyclobutanes Si₈C₃Cl₂₀ 4 , Si₁₀C₄Cl₂₄ 5 , Si₁₂C₅Cl₂₈ 6 , Si₁₄C₆Cl₃₂ 7 this type of compounds is not obtained starting from the Si-methylated derivatives 8, 9, 10, 11 They Produce a number of variously Si-chlorinated and -methylated tetrasila- and trisilamethanes. However, Cl₂MeSi? CCl₂? SiCl₃ 12 forms besides of Si-chlorinated trisilamethanes also the disilacyclobutanes Si₆C₂Cl₁₅Me 34 and cis- and trans Si₆C₂Cl₁₄Me₂ 35 as well as the spiro-linked disilacyclobutanes Si₈C₃Cl₁₉Me 36 , Si₈C₃Cl₁₈Me₂ 37 . (Cl₃Si)₂CHCl 38 mainly yields HC(SiCl₃)₃ 31 and also the disilacyclobutanes cis- and trans-(Cl₃Si)HC(SiCl₂)₂CH(SiCl₃) 41 and (Cl₃Si)₂C(SiCl₂)₂CH(SiCl₃) 45 the 1,3,5-trisilacyclohexane [Cl₃Si(H)C? SiCl₂]₃ 44 as well as [(Cl₃Si)₂CH]₂SiCl₂, and (Cl₃Si)₂CClMe 39 mainly yields (Cl₃Si)₂C?CH₂and (Cl₃Si)₂besides of HC(SiCl₃)₃, MeC(SiCl₃)₃and (Cl₃Si)₃C? SiCl₂Me.,. Me₂CCl₂ 59 mainly yields Me(Cl)C?CH₂, Me₂CHCl and HCl₂Si? CMe₂? SiCl₃, besides of Me₂C(SiCl₃)₂ and Me₂C(SiCl₂H)₂ Compound 3 crystallizes triclinically in the space group P1 (Nr. 2) mit a = 900,3, b = 914,0, c = 855,3 pm, α = 116,45°, β = 101,44°, γ = 95,86° and one molecule per unit cell. Compound 4 crystallizes monoclinically in thc space group C2/c (no. 15) with a = 3158.3,b = I 103.7, c = 2037.4 pm, β = 1 16.62° and 8 molecules pcr unit cell. The disilacyclobutane ring of compound 3 is plane, showing a mean distance of d (Si-C) =19 1.8 pm and the usual deformations of endocyclic angles: α_Si = 94,2°> 85,8° = α_C.The spiro-linked disilacyclobutane rings of compound 4 are slightly folded by a mean angle of (19.0°). Their mean distances were found to be d (Si? C) = 190.4 pm relating to the central carbon atom and 192.0 pm to the outer ones, respectively. The deformations of endocyclic angles: α_Si = 93,9°> 84,4° = α_C are comparable to those of compound 3.     

Kinetics of the reactions of C2H5, n‐C3H7, and n‐C4H9 radicals with Cl2 at the temperature range 190–360 K

The kinetics of the C₂H₅ + Cl₂, n‐C₃H₇ + Cl₂, and n‐C₄H₉ + Cl₂ reactions has been studied at temperatures between 190 and 360 K using laser photolysis/photoionization mass spectrometry. Decays of radical concentrations have been monitored in time‐resolved measurements to obtain reaction rate coefficients under pseudo‐first‐order conditions. The bimolecular rate coefficients of all three reactions are independent of the helium bath gas pressure within the experimental range (0.5–5 Torr) and are found to depend on the temperature as follows (ranges are given in parenthesis): k(C₂H₅ + Cl₂) = (1.45 ± 0.04) × 10^?11 (T/300 K)^{?1.73 ± 0.09} cm³ molecule^?1 s^?1 (190–359 K), k(n‐C₃H₇ + Cl₂) = (1.88 ± 0.06) × 10^?11 (T/300 K)^{?1.57 ± 0.14} cm³ molecule^?1 s^?1 (204–363 K), and k(n‐C₄H₉ + Cl₂) = (2.21 ± 0.07) × 10^?11 (T/300 K)^{?2.38 ± 0.14} cm³ molecule^?1 s^?1 (202–359 K), with the uncertainties given as one‐standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±20%. Current results are generally in good agreement with previous experiments. However, one former measurement for the bimolecular rate coefficient of C₂H₅ + Cl₂ reaction, derived at 298 K using the very low pressure reactor method, is significantly lower than obtained in this work and in previous determinations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 614–619, 2007     

Free-radical chain dechlorination of chloroethanes in liquid triethylsilane

The kinetics and mechanism of the free-radical chain dechlorination of C₂Cl₆, C₂Cl₅H, and sym-C₂Cl₄H₂ in Et₃SiH wereinvestigated over a wide temperature range. The propagation step of the dechlorination of chloroethanes (C₂Cl_x H_6?x) proceeds by the following reactions: Analysis of the temperature dependence of product formation gave the Arrhenius expressions for k₄/k₃ which in turn were utilized for the estimation of the absolute Arrhenius parameters for hydrogen abstraction from Et₃SiH. Our results show that the values of E_abs are lower in Et₃SiH than in c-C₆H₁₂ by about 2–3 kcal/mol, while the A factors are almost equal. In competitive studies k₂ was determined versus Br abstraction from n-C₅H₁₁Br. The relative Arrhenius parameters determined by this method show that variations in both A factors and activationenergies are responsible for the reactivity trends observed in the Cl transfer reactions of Et₃Si radicals.     

The reactions of some interstellar ions with benzene,cyclopropane and cyclohexane

The reactions of the cyclic molecules C₆H₆ (benzene), c-C₃H₆ (cyclopropane) and c-C₆H₁₂ (cyclohexane) with ArH⁺ (ArD⁺), H₃⁺, N₂H⁺, CH₅⁺, HCO⁺, OCSH⁺, C₂H₃⁺, CS₂H⁺ and H₃O⁺ have been studied at 300 K using a SIFT apparatus. All the reactions except those of C₂H₃⁺ proceed via proton transfer and all are fast except the H₃O⁺ and CS₂H⁺ reactions with c-C₆H₁₂ which are endothermic and which establish that the proton affinity of c-C₆H₁₂ is 160 ± 1 kcal mol⁻¹, which is considerably lower than the published value. In the c-C₃H₆ and the c-C₆H₁₂ reactions multiple products are observed and hence “breakdown curves” for the protonated molecules are constructed and the appearance energies of the various ion products are consistent with available thermochemical data. The reactions of C₂H₃⁺ with these cyclic molecules are atypical within this series of reactions in that they appear to proceed largely via hydride ion transfer. The implications of the results of this study to interstellar chemistry are alluded to.     

Excess enthalpies and molecular interactions in solutions of 1-fluoroalkanes in alkanes,benzene or tetrachloromethane. A group contribution (DISQUAC) study

Molar excess enthalpies H ^E at 298.15 K and atmospheric pressure were determined for 12 binary liquid mixtures, 1-fluoropentane, 1-fluorohexane, or 1-fluorononane + a non-polar solvent (hexane, cyclohexane, benzene, or tetrachloromethane) and were interpreted by the DISQUAC group contribution model. 1-Fluoroalkane + n-alkane mixtures are characterized by two types of groups or contact surfaces, fluorine (F) and alkane (CH₃, CH₂), the remaining mixtures by the additional contact surfaces of the solvents (C₆H₁₂ C₆H₆, or CCl₄). The interchange energies, entirely dispersive, of the alkane-solvent contacts were determined independently from the study of solvent-alkane mixtures. The dispersive F-alkane parameters were assumed to equal the parameters of perfluoroalkanes + n-alkanes. The shape of the H ^E curves of 1-fluorolkane + polarizable solvent (C₆H₆, CCl₄) mixtures are best reproduced by the model when the quasi-chemical F-solvent parameters are assumed to equal zero. The quasi-chemical F-alkane (the same for n-alkanes and cyclohexane) and the dispersive F-solvent parameters were estimated in this work. The 1-fluoroalkane solutions in C₆H₆ or CCl₄ exhibit the characteristic features of polar solute + polarizable solvent mixtures, viz., the deviations from the ideality are less positive than in alkanes and the experimental H ^E curves are strongly asymmetrical.     

New 1,1′-Ring-substituted Vanadocene Dichlorides. Crystal structures of [V(η5-C5H4SiMe3)2Cl2] and [V(η5-C5H5)2Cl2]

The 1,1′-ring-substituted vanadocene dichlorides [V(η⁵-C₅H₄R)₂Cl₂] (R = CMe₃, SiMe₃, SiEt₃) have been prepared from VCl₄ and the appropriate lithiated cyclopentadiene, C₅H₄RLi, in 1 : 2 ratios. All complexes were characterized by elemental microanalysis and IR spectroscopy. The crystal structures of [V(η⁵-C₅H₄SiMe₃)₂Cl₂] 3 and the parent compound [V(η⁵-C₅H₅)₂Cl₂] 1 have been determined by X-ray diffraction and are in accordance with expectations. Compound 1 crystallizes with two crystallographically independent molecules in its monoclinic unit cell. These two molecules are quite similar in their essential structural features. Compound 3 crystallizes in the triclinic space group P1 . The trimethylsilylcyclopentadienyl rings are bound in a staggered relative orientation.     

The pyrolysis of CCl4 and C2Cl6 in the gas phase. Mechanistic modeling by thermodynamic and kinetic parameter estimation

A detailed radical reaction mechanism is proposed to describe the thermal reactions of CCl₄ and C₂Cl₆ in the gas phase quantitatively. A consistent set of activation energies and preexponential factors for all elementary reactions, in combination with enthalpies of formation and entropies for all species involved, is computer optimized to fit experimental pressure-rise curves and concentration profiles. For this purpose new experimental results on the pyrolysis of CCl₄ are used, together with published kinetic data on the pyrolysis of C₂Cl₆ (in the absence and in the presence of Cl₂). © 1996 John Wiley & Sons, Inc.     

Inclusion Compounds of Cyclotriveratrylene (2,3,7,8,12,13-hexamethoxy-5,10-dihydro-15H-tribenzo[a,d,g]cyclononene) with Chlorinated Guests

Inclusion compounds were formed between the host cyclotriveratrylene, H, (2,3,7,8,12,13-hexamethoxy-5,10-dihydro-15H-tribenzo[a,d,g]cyclononene) and the guests carbon tetrachloride, 1,1,1-trichloroethane, 1,1,1-trichloropropane and 1,1,2-trichloroethane. 1 (H·CCl₄) has guest molecules in channels alternating with channels of host molecules. 2 (H·C₂H₃Cl₃·C₃H₅Cl₃) and 3 (H·2C₂H₃Cl₃) exhibit a slightly different packing arrangement with one guest molecule in the host cavity and the rest of the guest molecules in channels. The stability and reactivity of these inclusion compounds were investigated.