Reaction Of CCl2 Research Articles

Quantum chemical and kinetic study of the CCl2 self-recombination reaction

The temperature and pressure dependencies of the rate constant of the recombination reaction CCl2 + CCl2 + M → C2Cl4 + M have been theoretically studied between 300 and 2000 K. Quantum-chemical calculations were employed to characterize relevant parts of the potential energy surface of this process. The limiting rate constants were analyzed using the unimolecular reaction theory. The resulting low pressure rate constant can be represented as k0 = [Ar] 3.5 × 10−23 (T/300 K)−8.7 exp(−1560 K/T) cm3 molecule−1 s−1.The high pressure rate constants derived from a simplified statistical adiabatic channel model (SSACM) and from a SACM combined with classical trajectory calculations (SACM/CT) are k∞ = (1.7 ± 1.0) × 10−12 (T/300)0.8±0.1 cm3 molecule−1 s−1 and k∞ = (5.4 ± 3.0) × 10−13 (T/300)0.7±0.1 cm3 molecule−1 s−1. The falloff curves were represented in terms of these limiting rate constants. Reported experimental results are satisfactorily described with the present model. The calculations indicate that the CCl2 + CCl2 reaction proceeds via the stabilization of C2Cl4, with a contribution of the C2Cl3 + Cl → C2Cl4 reaction, and at sufficiently high temperatures the channel CCl2 + CCl2 → C2Cl2 + 2Cl becomes relevant.

Theoretical study on the methyl radical with chlorinated methyl radicals CH3−nCln (n = 1, 2, 3) and CCl2

Radical-radical reactions involving chlorinated methyl radicals are particularly important in the mechanism of combustion of chlorinated hydrocarbons. Yet, they are usually difficult to study experimentally. In this paper, four chloride-related radical-radical reactions, i.e., CH3+CH(3-n)Cln (n = 1, 2, 3) and CH3+CCl2, are theoretically studied for the first time by means of the Gaussian-3//B3LYP potential energy surface survey combined with the master equation study over a wide range of temperatures and pressures. Our calculated results show that the three CH3+CH(3-n)Cln reactions can barrierlessly generate the former two kinetically allowed products P1 H(2)C=C(H)(3-n)Cl(n-1)+HCl and P2 CH3CH(3-n)Cl(n-1)+Cl with the very high predominance of P1 over P2. For the CH3 reaction with the biradical CCl2, which inevitably takes place during the CH3+CCl3 reaction and yet has never been studied experimentally or theoretically, H(2)C=CCl2+H and H(2)C=C(H)Cl+Cl are predicted to be the respective major and minor products. The results are compared with the recent laser photolysis/photoionization mass spectroscopy study on the CH3+CH(3-n)Cln (n = 1, 2, 3) reactions. The predicted rate constants and product branching ratios of the CH3+CCl2 reaction await future experimental verification.

Reaction kinetic studies of CCl2 (X̃(0,0,0)) with C2H2 and H2O molecules

Abstract Absolute reaction rate constants for the ground state dichlorocarbene CCl2 with C2H2 and H2O have been measured (T=293 K). The CCl2 radicals were produced by laser photolysis of CCl4 molecules at 213 nm and then electronically excited to the CCl2 ( A ) state at 541.0 nm with Nd:YAG laser pumped dye laser. The technique of laser-induced fluorescence was employed to measure the relative concentrations at different reaction time and, then, obtain their rate constants. They are (3.3 ± 0.5) × 10−13 cm3 molecule−1 s−1 for the reaction of CCl2 + C2H2 and (4.8 ± 2.0) × 10−14 cm3 molecule−1 s−1 for the reaction of CCl2 + H2O (total pressure=12 Torr, T=293 K), respectively. It is found that the rate constant for reaction CCl2 + C2H2 slightly increases with the total pressure (P=10–50 Torr). But for the reaction CCl2 + H2O, it is independent on the total pressure. The mechanisms for these two reactions have been theoretically studied using a high-level ab initio calculation. For the reaction of CCl2 + H2O, it is found that there are two reaction mechanisms: insertion and addition-elimination. Three primary product channels, HCl + HClCO, HCl + trans-ClCOH and HCl + cis-ClCOH, are studied in detail. For the reaction of CCl2 + C2H2, there are also two reaction mechanisms: insertion and three-cyclo-addition. The addition of C atom in CCl2 radical to C–C triple bond in C2H2 molecule may be the dominant reaction channel giving a three-member-ring structure, CCl2 CHCH radical, as the primary intermediate.

Kinetics of the Reaction of the CCl2 Biradical with Molecular Chlorine

The kinetics of the reaction of CCl2 with molecular chlorine has been studied using the laser photolysis/photoionization mass spectrometry technique. Dichloromethylene biradicals were produced by the pulsed laser photolysis of carbon tetrachloride, and the kinetics of their decay due to reaction with Cl2 were monitored in direct time-resolved experiments. Rate constants were determined as a function of temperature (300−750 K) and can be described by the Arrhenius expression k1 = (1.3 ± 0.3) × 10-11 exp(−(281 ± 96) K/T) cm3 molecule-1 s-1. Rate constants of reaction 1 are independent of the bath gas density within the experimental range [He] = (3−12) × 1016 atoms cm-3. CCl3 was observed as a primary product of the reaction.

Kinetics of the CCl3 + CH3 Radical−Radical Reaction

The CCl3 + CH3 (1) cross-radical reaction was studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 306−800 K and bath gas (helium) density region (3−12) × 1016 atoms cm-3. The observed rate constant of reaction 1 is independent of temperature and equal to (2.05 ± 0.30) × 10-11 cm3 molecule-1 s-1. Formation of C2H2Cl2 and C2H3Cl2 was detected; however, only the C2H3Cl2 radical can be identified as a product of reaction 1 on the basis of the experimental information since the contribution of reaction 1 to the signal of C2H2Cl2 could not be separated from that of the reaction of CCl2 with CH3 (CCl2 being a minor product of photolysis of all precursors of CCl3 used). The experimental values of the rate constant are in reasonable agreement with the prediction based on the “geometric mean rule”. A separate experimental attempt to determine the rate constant of the high-temperature CCl3 + O2 (10) reaction res...

A New Mechanism for the Reaction of Carbenes with OH Groups

The reaction pathway for the 2H2O + CCl2 reaction through a cyclic five-atom transition structure was studied using ab initio molecular orbital theory. The MP2 method in conjunction with the DZP basis set was used for geometry optimizations, and single point energy calculations were performed at MP2 and MP4 levels with the cc-pVDZ and cc-pVTZ basis sets. The solvent effect on the activation free energy was evaluated by Monte Carlo statistical mechanics calculations. The new mechanism has a high rate constant, and we predict a lifetime of seven nanoseconds for dichlorocarbene in aqueous solution. We have proposed that this mechanism occurs for the reaction of dichlorocarbene with water, and possibly may be involved in many reactions of carbenes with alcohols. We have also shown that it can explain the following experimental facts: (a) alteration of the product isotopic effect on addition of a second alcohol, (b) difference between product and kinetic isotopic effects, and (c) no linear dependence of the observed rate constant for carbene decay on alcohol concentration.

A theoretical ab initio and Monte Carlo simulation study of the pyridine+CCl2 reaction kinetics in the gas phase and in carbon tetrachloride solution using canonical flexible transition state theory

The potential energy surface for the pyridine+CCl2 reaction was studied at the abinitio MP4/6-311G(2df,p)//MP2/6-31G(*) level of theory. The MP4/6-311G(2df,p) energies were evaluated by the additivity approximation E[MP4/6-311G(2df,p)]≈E[MP4/6-31G(*)]+E[MP2/6-311G(2df,p)]-E[MP2/6-31G(*)]. The first step proceeds by the addition of CCl2 to pyridine forming a dipolar ylide structure without an activation barrier. Then this species rearranges to a more stable biradical like ylide on a picosecond time scale. The generalized transition state for dipolar ylide formation occurs at a large center of mass distance between the species, and to calculate the reaction rate constant we have used canonical flexible transition state theory. The configurational integral was solved by Monte Carlo simulation and statistical perturbation theory, and the potential of mean force in the gas phase was obtained. This procedure was extended to the liquid phase by including the solvent coordinates in the configurational integral. The activation free energy in the gas phase and in carbon tetrachloride solution was calculated as 1.44 and 2.62 kcal mol-1, respectively. The corresponding rate constants are 5.5×1011 and 7.5×1010 l mol-1 s-1. The last value is in reasonable agreement with the experimental result of 7×109 l mol-1 s-1 determined in isooctane solution.

Reaction of CCl2 with CH2NH and the formation of dipolar and biradical ylide structures

The potential energy surface for the reaction between CH2NH and CCl2 has been investigated using ab initio methods. We have performed geometry optimizations at the MP2/6-31G* level of theory and single point calculations at the MP4(SDQ)/6-311++G** level. The reaction step for ylide formation has a free energy of activation predicted to be 5.0 kcal mol–1. The parallel 1,2-cycloaddition reaction has a calculated free energy barrier of 16.5 kcal mol–1, indicating that this second pathway is not competitive with ylide formation. The structure of the azomethine ylide formed in the first reaction step is similar to that found for the ylide resulting from the reaction of methylene with ammonia and corresponds to a dipolar species. This is highly unstable and rearranges to its more stable isomer, the biradical azomethine ylide, which has a structure similar to the corresponding carbonyl ylide. This species has a free energy barrier to ring closure calculated to be 21.2 kcal mol–1, so it has reasonable kinetic stability. The resulting aziridine has a free energy of 24.1 kcal mol–1 lower than the biradical azomethine ylide, and the activation free energy of ring opening is calculated to be 45.3 kcal mol–1.

Reaction Paths for Aqueous Decomposition of CCl2

The potential energy surface (PES) for the H2O + CCl2 reaction was investigated at the ab initio SCF and MP2 levels of theory, employing the DZP basis set, in order to determine the mechanism of basic aqueous decomposition of CCl2. Several possible pathways were considered, including reactions with other H2O molecules and OH-. We have found that the first step corresponds to insertion of CCl2 into the O−H bond of water, resulting in the CHCl2OH species. This molecule loses HCl in one elimination reaction catalyzed by OH-, forming ClCHO. Again, OH- catalyzes the elimination of other HCl, resulting in CO, the decomposition product. The first step is the slow one, and we have used transition-state theory to estimate the rate constant for the aqueous decomposition of CCl2. The obtained rate constant was used for building a general picture of CHCl3 decomposition in basic aqueous solution. The results of the present study are in agreement with experimental observations.

Synthese, IR-Spektrum und Kristallstruktur von 1.3.5-Trichlortriazinium-hexachloroantimonat, [HC3N3Cl3]SbCl6 / Synthesis, IR Spectrum and Crystal Structure of 1.3.5-Trichlortriazinium Hexachloroantimonate, [HC3N3Cl3]SbCl6

Abstract 1,3,5-Trichlortriazinium hexachloroantimonate has been prepared by the reaction of CCl2 = N-COCl with antimony pentachloride in boiling dichloromethane. The compound was characterized by IR spectroscopy and by a crystal structure determination. [HC3N3Cl3]SbCl6 crystallizes in the monoclinic space group P21/n with four formula units per unit cell. 2503 observed unique reflections, R = 0.029. Lattice dimensions at 19 °C: a = 1314.1(1), b = 958.2(1), c = 1329.1(1) pm, β = 117.113(5)°). The compound forms ion pairs via a linear N-H ··· Cl bridge, thus distorting the SbCl6 - ion from octahedral geometry. The C3N3 skeleton of the [HC3N3Cl3]+ ion is nearly planar, but the hydrogen atom lies about 30 pm out of this plane.

Multiphoton absorption and decomposition studies of chloroform-d induced by a pulsed 13CO2 laser

The multiphoton absorption (MPA) and decomposition (MPD) of chloroform-d induced by various 13CO2 [00°1 → 0°0] lines were studied for pressures from 0.133 to 13.3 kPa. MPA results show a cross-section increasing with pressure up to a plateau value which is likely due to rotational hole-filling. A MPA "spectrum" of the average number of photons absorbed versus wavenumber for different 13CO2 laser lines is shifted to lower wavenumbers compared to the small signal absorption spectrum by at least 5 cm−1 suggesting that a small amount of anharmonicity bottle-necking is occurring in CDCl3. A comparison of the MPD probability versus fluence for CDCl3 with that measured by other workers for fluoroform indicates that the CDCl3 is decomposed at a slightly lower fluence by an appropriate line of a pulsed CO2 laser.For the pressure range (0.2 to 4.0 kPa) and laser pulse-width used, the MPD is second order in CDCl3. The primary decomposition channel is elimination of DCl followed by reaction of CCl2 to give C2Cl2, C2Cl4, and Cl2. The DCl produced exchanges with a source of H2O in the reaction cell to give significant quantities of HCl. A post-pulse reaction between (HCl + DCl) and C2Cl2. produces (C2DCl3 + C2HCl3). Significant quantities of CCl4 are also produced by undetermined reactions.