14362-13-1Relevant articles and documents
Kinetics of Photochlorination of Halogen (F, Cl, Br) Substituted Methanes
Tschuikow-Roux, E.,Faraji, F.,Paddison, S.,Niedzielski, J.,Miyokawa, K.
, p. 1488 - 1495 (1988)
The reactions of photochemically generated Cl(2PJ) atoms with CH3Br, CH2Cl2, CH2Br2, CH2ClF, and CH2BrCl have been studied over the temperature range 0-95 deg C by using the competitive method with methane as a primary standard.Relative and absolute rate constants are reported.The preexponential factors for this group of compounds fall within the range (3.1-9.5)E-11 cm3s-1 and activation energies vary from 2.4 to 3.1 kcal mol-1.The results are compared with the results for other members of this series including CH3F, CH2F2, CHF3, CH3Cl, CH2Cl2, and CHCl3 from this and other laboratories and discussed in terms of the thermoch emistry involved.A sample calculation of the A factor using the thermochemical kinetics version of transition-state theory (TST) shows reasonable agreement with experiment.The sensitivity of the input parameters in the bond energy-bond order (BEBO) method prediction of activation energy and tunneling is discussed in some detail with CH2Cl2 as an example.
Absolute rate constants for the reactions of Cl atoms with CH3Br, CH2Br2, and CHBr3
Kambanis,Lazarou,Papagiannakopoulos
, p. 8496 - 8502 (1997)
The rate constants for the reactions of chlorine atoms with the complete series of the three bromomethanes CH3Br (1), CH2Br2 (2), and CHBr3 (3) were measured in a very low pressure reactor, employing a microwave discharge for the generation of Cl atoms with mass spectrometric detection of reactants and products. The experiments were performed in the temperature range 273-363 K and at total pressures approximately 1 m Torr. The reactions proceed via hydrogen atom transfer leading to HCl product and the corresponding bromomethyl radicals. Their rate constant expressions are (in cm3 molecule-1 s-1): k1 = (1.66±0.14)×10-11 exp(-1072±46/T), k2 = (0.84±0.15)×10-11 exp(-911±101/T), and k3 = (0.43±0.11)×10-11 exp(-809±142/T). The activation energy of the reaction decreases with additional bromine substitution, which is attributed to the gradual weakening of the corresponding C-H bond strength. Ab initio theoretical calculations performed at the MP2/6-31++G(2d,2p) level of theory suggest C-H bond strengths for CH3Br, CH2Br2, and CHBr3 of 416.58, 407.03, and 396.60 kJ mol-1, respectively.
Atmospheric chemistry of CH2Br2: Rate coefficients for its reaction with Cl atoms and OH and the chemistry of the CHBr2O radical
Orlando, John J.,Tyndall, Geoffrey S.,Wallington, Timothy J.,Dill, Marchoe
, p. 433 - 442 (1996)
Rate coefficients for the reaction of OH radicals and Cl atoms with dibromomethane, OH + CH2Br2 → CHBr2 + H2O (1) and Cl + CH2Br2 → CHBr2 + HCl (3), and for the reaction of Cl atoms with methyl bromide, Cl + CH3Br → HCl + CH2Br (4), have been obtained using relative rate techniques. At 298 K, the value of k1, was determined to be (1.2 ± 0.3) × 10-13 cm3 molec-1 s-1. The rate coefficients k3 and k4 were determined at a series of temperatures ranging from 228 K to 296 K and combined with the measurements of Gierczak et al., yielding the following Arrhenius expressions for k3 and k4; k3 = (6.35 ± 0.6) × 10-12 exp(-807 ± 50/T) cm3 molec-1 s-1 and k4 = ( 1.49 ± 0.2) × 10-11 exp(- 1056 ± 50/T) cm3 molec-1 s-1. In addition, the Cl atom initiated oxidation mechanism of CH2Br2 in air has been studied at 298 K. The products observed were HC(O)Br and small amounts of CO. The dominant atmospheric fate of the alkoxy radical, CHBr2O, is elimination of a Br atom, which occurs at a rate estimated to be greater than 4 × 106 s-1 in 700 torr of O2 at 298 K.
