Kinetics and mechanism for the thermal chlorination of chloroform in the gas phase: Inclusion of HCl elimination from CHCl3

HCl elimination from chloroform is shown to be the lowest energy channel for initiation in the thermal conversion of chloroform to CCl₄, with chlorine gas in the temperature range of 573–635 K. Literature data on this reaction is surveyed and we further estimate its kinetic parameters using ab initio and density functional calculations at the G3//B3LYP/6‐311G(d,p) level. Rate constants are estimated and reported as functions of pressure and temperature using quantum RRK theory for k( E ) and master equation analysis for fall‐off. The high‐pressure limit rate constant of this channel is k(CHCl₃ → ¹CCl₂ + HCl) = 5.84 × 10⁴⁰ × T ^?8.7 exp(?63.9 kcal/mol/ RT ) s^?1, which is in good agreement with literature values. The reactions of ¹CCl₂ with itself, with CCl₃, and with CHCl₃ are incorporated in a detailed mechanistic analysis for the CHCl₃ + Cl₂ reaction system. Inclusion of these reactions does not significantly change the mechanism predictions of Cl₂ concentration profiles in previous studies (Huybrechts, Hubin, and Van Mele, Int J Chem Kinet 2000, 32, 466) over the temperature range of 573–635 K; but Cl₂, CHCl₃, C₂Cl₆ species profiles are significantly different at elevated temperatures. Inclusion of the ¹CCl₂ + Cl₂ → CCl₃ + Cl reaction (abstraction and chain branching), which is found to have dramatic effects on the ability of the model to match to the experimental data, is discussed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 647–660, 2003     

Determination of the Rate Constant of the Reaction of CCl2 with HCl

The rate constant of the reaction between CCl₂ radicals and HCl was experimentally determined. The CCl₂ radicals were obtained by infrared multiphoton dissociation of CDCl₃. The time dependence of the CCl₂ radicals' concentration in the presence of HCl was determined by laser‐induced fluorescence. The experimental conditions allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C₂Cl₄ and to the reaction with HCl to form CHCl₃. The rate constant for the self‐recombination reaction was determined to be in the high‐pressure regime. The value obtained at 300 K was (5.7 ± 0.1) × 10^?13 cm³ molecule^?1 s^?1, whereas the value of the rate constant measured for the reaction with HCl was (2.7 ± 0.1) × 10^?14 cm³ molecule^?1 s^?1.     

Photocatalysis of Chloroform Decomposition by the Hexachlororuthenate(IV) Ion

Dissolved hexachlororuthenate(IV) effectively catalyzes the photodecomposition of chloroform to hydrogen chloride and phosgene under near‐UV (λ > 345 nm) irradiation, whereby RuCl₆^2? is not itself photocatalytically active, but is photochemically transformed into a species that is active, possibly RuCl₅(CHCl₃)^?. Conversion to a photoactive species during irradiation is consistent with the acceleration of the decomposition rate during the early stages and with the apparent inverse dependence of the decomposition rate on the initial concentration of RuCl₆^2?. The displacement of Cl^? by CHCl₃ in the coordination sphere to create the photoactive species is consistent with the retardation of photodecomposition by both Cl^? and H₂O. The much smaller photodecomposition rate in CDCl₃ suggests that C–H bond dissociation occurs during the primary photochemical event, which is also consistent with the presence of a CHCl₃ molecule in the first coordination sphere.     

Plasma-catalytic Reactor for Decomposition of Chlorinated Hydrocarbons

The conversion of trichloromethane in mixtures with air was investigated under normal pressure in a gliding discharge (GD) reactor operated in both a homogeneous gas system and with a solid catalyst. The Pt catalyst supported by a honey-comb cordierite structure was placed in the reactor below the ends of the electrodes. Cl₂ and HCl were the main products of the CHCl₃ conversion. The presence of CCl₄ was also noted. The influence of the electrode length and the distance between the electrodes in the narrowest section on CHCl₃ conversion was examined. The Pt catalyst revealed some activity in the trichloromethane processing. This resulted in an increased overall CHCl₃ conversion with the portion of CHCl₃ converted to CCl₄ smaller than that in the homogeneous system. The effect of temperature on CHCl₃ conversion was found to be significant.     

Dissociation of Physisorbed Halomethane Molecules by KrF Excimer Laser Radiation

The competitive processes of photolysis and desorption of CF₂Cl₂, CCl₄, CHF₂Cl, CHCl₃, CH₂Cl₂, CH₂I₂, and CH₃I halomethane molecules physisorbed on fused silica were experimentally studied. These processes were induced by the absorption of high-intensity UV radiation from a KrF excimer laser by these molecules. It was shown that a common feature in the behavior of all of these compounds is nonlinear dependence of desorption on radiation intensity, typical nonlinearity indices being very high: n = 5–7. One-photon dissociation was carried out in the adsorbed state of CCl₄, CH₂I₂, and CH₃I molecules absorbing radiation with a wavelength of 248 nm and in a gas phase. The photofragments are characterized by kinetic energies lower than 0.2 eV. The multiphoton fragmentation of the adsorbed molecules was observed and discussed.     

Influence of Water Vapor on CCl4 and CHCl3 Conversion in Gliding Discharge

The effect of initial concentration of tetrachloromethane and trichloromethane on their conversion in gliding discharge was determined. The conversion of CCl₄ and CHCl₃ was carried out in air containing 20 or 8000 ppm of water vapor. The flow rate of the air containing 1.2, 2.5, or 6.0 vol% of CCl₄ or CHCl₃ was 200 Nl/h. The amount of tetrachloromethane and trichloromethane reacted was determined for a constant value of specific energy which was varied with 2.0 and 4.0 VAh/Nl. The amounts of CCl₄ and CHCl₃ reacted were a linear function of the initial concentration of these compounds in the inlet gas. The results obtained have shown that water vapor present in the air has a favorable effect on the conversion of tetrachloromethane and trichloromethane in gliding discharge.     

Determination of halogenated hydrocarbons by flow injection ozone chemiluminescence

A flow injection gas phase chemiluminometer has been constructed for monitoring halogenated compounds which upon UV radiation consume ozone. The ozone concentration is followed by the ethylene-ozone chemiluminescent reaction and by UV absorption. The sensitivity depends on the ability of each compound to consume ozone and the limits of quantification vary from 9.6 and 25 nmol for CFCl₃ and CF₂Cl₂ to 22.5 and 17.2 μmol for CHCl₃ and CH₃CCl₃, respectively.     

Encapsulation of Halocarbons in a Tetrahedral Anion Cage

Caged supramolecular systems are promising hosts for guest inclusion, separation, and stabilization. Well‐studied examples are mainly metal‐coordination‐based or covalent architectures. An anion‐coordination‐based cage that is capable of encapsulating halocarbon guests is reported for the first time. This A₄L₄‐type (A=anion) tetrahedral cage, [(PO₄)₄ L ₄]^12?, assembled from a C₃‐symmetric tris(bisurea) ligand ( L ) and phosphate ion (PO₄^3?), readily accommodates a series of quasi‐tetrahedral halocarbons, such as the Freon components CFCl₃, CF₂Cl₂, CHFCl₂, and C(CH₃)F₃, and chlorocarbons CH₂Cl₂, CHCl₃, CCl₄, C(CH₃)Cl₃, C(CH₃)₂Cl₂, and C(CH₃)₃Cl. The guest encapsulation in the solid state is confirmed by crystal structures, while the host–guest interactions in solution were demonstrated by NMR techniques.     

Angle-resolved photoelectron spectroscopy of the chloro-substituted methanes

The angular distribution parameter, β, was determined for the valence orbitals (IP ′ 21.2 eV) of CCl₄, CHCl₃, CH₂Cl₂, and CH₃Cl in the 10–30 eV photon energy range using dispersed polarized synchrotron radiation. The energy dependence of β in the photoelectron energy range of 2 to 10 eV for the non-bonding chlorine n(Cl) orbitals of these molecules was found to be similar for all n(Cl) orbitals investigated. The energy dependence of β for the σ orbitals in these molecules was similar to that observed previously for other σ orbitals. The experimental CCl₄ results were compared with theoretical CCl₄ results obtained using the Xα multiple scattering formalism. Theory predicts the existence of two strong shape resonances in each of the valence orbitals of CCl₄. The overall agreement between experiment and theory is evaluated along with the experimental evidence concerning the verification of the predicted shape resonances.     

Solvent Effect on the Ligand Exchange between Bis(diethyldithiocarbamato)copper(II) and Bis(diethyldiselenocarbamato)copper(II)

EPR and spectrophotometric study on the products of ligand‐exchange taking place on mixing bis(diethyldiselenocarbamato)copper(II), [Cu(Et₂dsc)₂], and bis(diethyldithiocarbamato)copper(II), [Cu(Et₂dtc)₂], solutions is reported. EPR spectra monitored at room temperature for one month period reveal a stable equilibrium among the parents (chromophores CuS₄ and CuSe₄) and the obtained mixed‐chelate [Cu(Et₂dtc)(Et₂dsc)] complex (chromophore CuS₂Se₂) in heptane, hexane, benzene, toluene, acetone, DMFA, DMSO and dichloromethane. In CCl₄ and CHCl₃ two new additional EPR spectra appear attributed to the mixed‐chelate complexes with the chromophores CuSSe₃ and CuS₃Se which are not observed with electronic spectroscopy. The intensities of all five EPR spectra decrease with the time. It is assumed that the new mixed‐chelates observed in CCl₄ and CHCl₃ are obtained in a reaction of [Cu(Et₂dtc)(Et₂dsc)] or [Cu(Et₂dtc)₂] with the ester of diselenocarbamic acid which is formed in a parallel reaction of [Cu(dsc)₂]with CCl₄ or CHCl₃.     

Si-C coupling reaction of polychloromethanes with HSiCl3 in the presence of Bu4PCl: Convenient synthetic method for bis(chlorosilyl)methanes

Coupling reaction of polychloromethanes CH_4−nCl_n (n = 2-4) with HSiCl₃ in the presence of tetrabutylphosphonium chloride (Bu₄PCl) as a catalyst occurred at temperatures ranging from 30 °C to 150 °C. The reactivity of polychloromethanes increases as the number of chlorine-substituents on the carbon increases. In the reactions of CCl₄ with HSiCl₃, a variety of coupling products such as bis(chlorosilyl)methanes CH₂(SiCl₃)(SiXCl₂) [X = Cl (1a), H (1b)], (chlorosilyl)trichloromthanes Cl₃CSiXCl₂ [X = Cl (2a), H (2b)], and (chlorosilyl)dichloromthanes Cl₂HCSiXCl₂ [X = Cl (3a), H (3b)] were obtained along with reductive dechlorination products such as CHCl₃ and CH₂Cl₂ depending on the reaction temperature. In the reaction of CCl₄, 2a is formed at the initial stage of the coupling reaction and converted to give CHCl₃ at low temperature of 30 °C, to give 1a, 3a, and CHCl₃ at 60 °C, and to afford 1a as major product and CH₂Cl₂ in competition above 100 °C. Si-H bond containing silylmethanes can be formed by the H-Cl exchange reaction with HSiCl₃. Reaction of CHCl₃ with HSiCl₃ took placed at 80 °C to give three compounds 1a, 3a, and CH₂Cl₂, and finally 3a was converted to give 1a and CH₂Cl₂ at longer reaction time. While the condition for the reaction of CH₂Cl₂ with HSiCl₃ required a much higher temperature of 150 °C. Under the optimized conditions for synthesizing bis(chlorosilyl)methanes 1a,b, a mixture of 1a and 1b were obtained as major products in 65% (1a:1b = 64:1) and 47% (42:5) yields from the reaction of CCl₄ and CHCl₃ at 100 °C for 8 h, respectively, and in 41% (34:7) yield from that of CH₂Cl₂ at 170 °C for 12 h. In the Si-C coupling reaction of polychloromethanes with HSiCl₃, it seems likely that a trichlorosilyl anion generated from the reaction of HSiCl₃ with Bu₄PCl is an important key intermediate.     

The effect of polymer side chains on vapor sorption in polyacrylate and polymethacrylate solutions

The segment fraction Ψ₁ activity coefficients, a₁/Ψ₁, of solvents have been determined by the piezoelectric sorption method for 0.1 ≤ Ψ₁ ≤ 0.5 in binary solutions of chlorinated methanes [carbon tetrachloride (CCl₄), chloroform (CHCl₃), and dichloromethane (CH₂Cl₂)] with aromatic hydrocarbons (benzene and toluene) in poly(methyl methacrylate), poly(methyl acrylate), poly(ethyl methacrylate), and poly(n-butyl acrylate) at 23.5°C. The present results for toluene in PMMA agree with previously published values obtained by gas-liquid chromatography. For CCl₄ and the aromatic hydrocarbons, the polymer–solvent interaction parameter χ is positive and constant, while for the polar solvents (CHCl₃ and CH₂Cl₂), χ is negative and increases with increasing Ψ₁. The effect of the polymer side chains on vapor sorption in nonpolar and polar solvent systems is discussed in terms of the χ parameter.     

A New Set of Gas/Water Partition Coefficients for the Chloromethanes

In the literature, there is a considerable number of articles and reviews providing data and information on the solubility of chloromethanes in water. However, the substantial difference between the numerical values given by various authors hinders their practical application. In the current work we present the harmonized results of experimentally determined gas/water partition coefficients of CH₂Cl₂, CHCl₃, and CCl₄, in the temperature range from 278 to 343 K, and with on uncertainty limit of less than 10%.     

A New Set of Gas/Water Partition Coefficients for the Chloromethanes

Summary. In the literature, there is a considerable number of articles and reviews providing data and information on the solubility of chloromethanes in water. However, the substantial difference between the numerical values given by various authors hinders their practical application. In the current work we present the harmonized results of experimentally determined gas/water partition coefficients of CH₂Cl₂, CHCl₃, and CCl₄, in the temperature range from 278 to 343 K, and with on uncertainty limit of less than 10%.     

Radio-high performance liquid chromatographic study on radioactive38Cl compounds

Reaction of recoild³⁸Cl atoms with o-dichlorobenzene in the presence of carbon tetrachloride or iodine has been studied by using radio-high performance liquid chromatography. The major products were detected by a 4-channel-wavelengths spectrophotometric detector. The radioactivity of³⁸Cl compounds including minor products was measured with a NaI(T1) scintillation detector. The main products found were³⁸Cl labeled HCl/Cl₂, CHCl₃, CCl₄, o-, p-, m-C₆H₆Cl₂ and polymer, whereas only minor products such as HCl/Cl₂, CHCl₃, C₂Cl₆, C₆H₃Cl₃, and polymer were found in the radio-chromatogram. The reaction mechanisms of recoil³⁸Cl atom are briefly described.     

Photoprocesses induced by short-wavelength excimer laser radiation in adsorbed halomethane molecules

Photolysis and desorption induced by ArF and KrCl laser irradiation of CH₂I₂, CH₃I, CCl₄, CHCl₃, CH₂Cl₂, CF₂Cl₂, and CHF₂Cl molecules adsorbed on fused silica were studied. One-photon fragmentation, as well as nonlinear dissociation and desorption processes, were observed. It was found that three-step fragmentation is a widespread phenomenon for molecules that experience resonant absorption of laser radiation. To explain the phenomenon, a mechanism based on stimulated emission was proposed. The nonlinear character of desorption is associated with redistribution of absorbed energy in adsorbed molecules and its transfer to the substrate.     

Photocatalytic degradation of chloroform by bis (bipyridine)dichlororuthenium(III/II)

Broadband (λ > 320 nm) irradiation of chloroform solutions of either [Ru(bpy)₂Cl₂] or [Ru(bpy)₂Cl₂]Cl exposed to air led to a photostationary state, in which [Ru(bpy)₂Cl₂]⁺ predominated, and to the continuous decomposition of CHCl₃, as evidenced by the accumulation of HCl, hydroperoxides (CCl₃OOH and CHCl₂OOH), and tetra-, penta-, and hexachloroethane. The addition of Cl^? increased the rate of photodecomposition, while the replacement of Cl^? by F^? greatly decreased the rate. The observations are consistent with a photocatalytic cycle in which [Ru(bpy)₂Cl₂]⁺ is photochemically reduced to [Ru(bpy)₂Cl₂], which is thermally reoxidized by CCl₃OO or CCl₃OOH. In the absence of air a much slower photodecomposition reaction takes place leading to continuously increasing concentrations of chloroethanes. The data are consistent with a catalytic cycle in which [Ru(bpy)₂Cl₂]⁺ is photoreduced, as in aerated solutions, while [Ru(bpy)₂Cl₂] is photooxidized with chloroform as the substrate.     

Kinetic Study of the CCl2 Radical Recombination Reaction by Laser‐Induced Fluorescence Technique

An experimental setup that coupled IR multiple‐photon dissociation (IRMPD) and laser‐induced fluorescence (LIF) techniques was implemented to study the kinetics of the recombination reaction of dichlorocarbene radicals, CCl₂, in an Ar bath. The CCl₂ radicals were generated by IRMPD of CDCl₃. The time dependence of the CCl₂ radicals’ concentration in the presence of Ar was determined by LIF. The experimental conditions achieved allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C₂Cl₄. The rate constant for this reaction was determined in both the falloff and the high‐pressure regimes at room temperature. The values obtained were k₀ = (2.23 ± 0.89) × 10^?29 cm⁶ molecules^?2 s^?1 and k_∞ = (6.73 ± 0.23) × 10^?13 cm³ molecules^?1 s^?1, respectively.     

Synthesis of Dendritic Phenol Ether Derivatives with a Naphthalene Core

A series of dendritic phenol ether derivatives with a naphthalene core were synthesized by the Williamson reaction as a coupling reaction between 1‐hydroxymethylnaphthalene and polyether‐based dendritic fragments in the presence of phase‐transfer catalyst and alkali. The modified method for chlorination of dendritic benzyl alcohol was also developed using PPh₃ and CCl₄ as reagents and CH₂Cl₂/CCl₄ as solvent.     

Determination of Rate Constants for Aqueous Reactions of HCFC‐123 and HCFC‐225ca with OH− Along with Henry's Law Constants of Several HCFCs

Henry's law constants of six kinds of hydrochlorofluorocarbons (HCFCs) were determined at 313–353 K by means of a phase‐ratio variation headspace method: and (K_H³⁵³ in M atm^?1, ΔH_sol in kJ mol^?1) = (0.0070 ± 0.0006, –23 ± 2), (0.0038 ± 0.0011, –22 ± 10), (0.0065 ± 0.0007, –21 ± 3), (0.0026 ± 0.0007, –23 ± 8), (0.0016 ± 0.0003, –30 ± 4), and (0.0022 ± 0.0003, –25 ± 4), respectively, for HCFC‐141b (CH₃CCl₂F), HCFC‐142b (CH₃CClF₂), HCFC‐123 (CF₃CHCl₂), HCFC‐124 (CF₃CHClF), HCFC‐225ca (CF₃CF₂CHCl₂), and HCFC‐225cb (CClF₂CF₂CHClF). Errors represent two standard deviations only for the fitting. The decay of headspace partial pressures of these HCFCs via hydrolysis was discerned only for CF₃CHCl₂ and CF₃CF₂CHCl₂ under the experimental conditions examined. Rate constants (k_OH– in M^?1 s^?1) for aqueous reactions of CF₃CF₂CHCl₂ and CF₃CHCl₂ with OH^? at 313–353 K were determined to be and , respectively, from monitoring changes in headspace partial pressure over prescribed concentrations of aqueous NaOH as a function of the headspace time duration and concentration of aqueous NaOH. The calculations performed included consideration of gas–water equilibrium and hydrolysis at both headspace and room temperatures. The calculation for CF₃CHCl₂ also included consideration of salting‐out effects: The salting coefficient of NaCl on a natural log basis was determined to be 0.36 ± 0.06 M^?1, and this value was used for consideration of the salting‐out effect of NaOH. Whereas the activation energy for CF₃CF₂CHCl₂ was greater than that for CF₃CHCl₂, the k_OH– value at 353 K of CF₃CF₂CHCl₂ was 10³ times larger than that of CF₃CHCl₂, indicating that reaction mechanisms for these two HCFCs differed from each other. The aqueous reaction of CF₃CF₂CHCl₂ with OH^? was found to proceed through dehydrofluorination on the basis of detection of CF₃CF?CCl₂ as a primary degradation product of the reaction and proportionality of the rate constants to both concentrations of CF₃CF₂CHCl₂ and OH^?.