Experimental and theoretical investigation of the kinetics of the reaction of atomic chlorine with 1,4-dioxane

A kinetic study of the reactions of atomic bromine with the trimethylbenzenes

This work presents the results of kinetic measurements for the reactions of atomic bromine with the three isomers of trimethylbenzene at temperatures from 295 K to 354 K and at pressures close to atmospheric. The atomic bromine was produced by photolysis of Br2 in a thermostated Pyrex chamber as described in our previous work. The reactants were present as dilute mixtures in argon with Br2 in sufficient excess to scavenge the free radical products of the initiation step. Chemical analysis was by gas chromatography and the rate coefficients were calculated from the chromatographic results using the relative rate method. The experimentally measured temperature dependence of the rate coefficients for the reactions of Br with the trimethylbenzenes is given in the units cm3 molec.-1 s-1 by: 1,2,3-trimethylbenzene + Br, log10(k) = -9.57 ± 0.43 - (996 ± 134)/T; 1,2,4-trimethylbenzene + Br, log10(k) = -9.74 ± 0.29 - (968 ± 91)/T; 1,3,5-trimethylbenzene + Br, log10(k) = -9.87 ± 0.26 - (1079 ± 85)/T. The enthalpies and entropies of activation for these reactions are compared to those for the reactions of Br with toluene and the xylenes.

Photo-oxidation reaction of tert-butyl chloride with OH radicals and Cl atoms in the troposphere and its implications

In the present work, the temperature-dependent kinetics for the reaction of tert-butyl chloride (TBC) with OH radicals and Cl atoms were determined experimentally between 268 and 363 K, and theoretically between 200 and 400 K. Pulsed laser photolysis-laser induced fluorescence (PLP-LIF) and relative rate (RR) methods were used to obtain the rate coefficients for the reaction of TBC with OH radicals and Cl atoms, respectively. The Arrhenius equations and were obtained for both reactions based on the experimentally measured rate coefficients. The theoretical rate coefficients were determined at the CCSD(T)/aug-cc-pVTZ//M06-2X/6-31+G(d,p) level for the reaction of TBC with OH radicals and at the CCSD(T)/cc-pVDZ//MP2/6-311+G(d,p) level for the reaction with Cl atoms with incorporated tunnelling corrections. The product analysis of both reactions in the presence of oxygen (O₂) was carried out, and a degradation pathway for TBC was proposed. The potential implications of these reactions in the atmosphere were discussed using the obtained kinetic parameters.

The kinetics of the reactions of Br atoms with the xylenes: an experimental and theoretical study

This work reports the temperature dependence of the rate coefficients for the reactions of atomic bromine with the xylenes that are determined experimentally and theoretically. The experiments were carried out in a Pyrex chamber equipped with fluorescent lamps to measure the rate coefficients at temperatures from 295 K to 346 K. Experiments were made at several concentrations of oxygen to assess its potential kinetic role under atmospheric conditions and to validate comparison of our rate coefficients with those obtained by others using air as the diluent. Br₂ was used to generate Br atoms photolytically. The relative rate method was used to obtain the rate coefficients for the reactions of Br atoms with the xylenes. The reactions of Br with both toluene and diethyl ether (DEE) were used as reference reactions where the loss of the organic reactants was measured by gas chromatography. The rate coefficient for the reaction of Br with diethyl ether was also measured in the same way over the same temperature range with toluene as the reference reactant. The rate coefficients were independent of the concentration of O₂. The experimentally determined temperature dependence of the rate coefficients of these reactions can be given in the units cm³ molecule^-1 s^-1 by: o-xylene + Br, log₁₀(k) = (-10.03 ± 0.35) - (921 ± 110)/T; m-xylene + Br, log₁₀(k) = (-10.78 ± 0.09) - (787 ± 92/T); p-xylene + Br, log₁₀(k) = (-9.98 ± 0.39) - (956 ± 121)/T; diethyl ether + Br, log₁₀(k) = (-7.69 ± 0.55) - (1700 ± 180)/T). This leads to the following rate coefficients, in the units of cm³ molecule^-1 s^-1, based on our experimental measurements: o-xylene + Br, k(298 K) = 7.53 × 10^-14; m-xylene + Br, k(298 K) = 3.77 × 10^-14; p-xylene + Br, k(298 K) = 6.43 × 10^-14; diethyl ether + Br, k(298 K) = 4.02 × 10^-14. Various ab initio methods including G3, G4, CCSD(T)/cc-pV(D,T)Z//MP2/aug-cc-pVDZ and CCSD(T)/cc-pV(D,T)Z//B3LYP/cc-pVTZ levels of theory were employed to gain detailed information about the kinetics as well as the thermochemical quantities. Among the ab initio methods, the G4 method performed remarkably well in describing the kinetics and thermochemistry of the xylenes + Br reaction system. Our theoretical calculations revealed that the reaction of Br atoms with the xylenes proceeds via a complex forming mechanism in an overall endothermic reaction. The rate determining step is the intramolecular rearrangement of the pre-reactive complex leading to the post-reactive complex. After lowering the relative energy of the corresponding transition state by less than 1.5 kJ mol^-1 for this step in the reaction of each of the xylenes with Br, the calculated rate coefficients are in very good agreement with the experimental data.

Reaction of chlorine radical with tetrahydrofuran: a theoretical investigation on mechanism and reactivity in gas phase

Reaction of chlorine (Cl) radical with heterocyclic saturated ether, tetrahydrofuran has been studied. The detailed reactivity and mechanism of this reaction is analyzed using hybrid density functional theory (DFT), B3LYP and BB1K methods, and aug-cc-pVTZ basis set. To explore the mechanism of the reaction of tetrahydrofuran with Cl radical, four possible sites of hydrogen atom (H) abstraction pathways in tetrahydrofuran were analyzed. The barrier height and rate constants are calculated for the four H-abstraction channels. The BB1K calculated rate constant for α-axial H-abstraction is comparable with the experimentally determined rate constant. It reflects that α-axial H-abstraction is the main degradation pathway of tetrahydrofuran with Cl radical. DFT-based reactivity descriptors are also calculated and these values describe α-axial H-abstraction as the main reaction channel.