Rate constants for the recombination of CCl₃radicals and for their reactions with Cl, Cl₂and HCl in the gas phase

Abstract

Thc gas-phase photochlorination of CHC13 has been investigated between 303.2 and 425.5"K. The reaction was followed both by a conventional and a mass spectrometric technique. Rate measurements in steady light lead to where k2, k3, k7 and k8 refer to Rate nieasurernents in intermittent light give logiok3 = -5,000/4.576T+ 8.74,which combined with eqn. (i) and (ii) and the known value of k2 yields log10k7 = 10.8 and loglok8 -9.66, independent of temperature. Using the values of k2 and k3 and thermodynamic data, onc calculates log1& = -11,3Oo/4576T+8.65 and loglok5 = --2O,000/4~576T+10~93, for thc reverse of reactions (2) and (3) respectively. All rate constants are given in mole-' 1. sec-'.The rate constant for the gas-phase recombination of trichloromethyl radicals has been measured by Tedder and Walton who found log,,k8 * = 10.9 between 350 and 446°K. This value is in line with those observed for methyl and trifhoromethyl radicals 2* but is higher than would be expected from a comparison of the values observed for C2Cl,(8-6),4 C2HC1,(9*3) and C2H5(10*5) radicals. It is also higher than a proposed value for CC13 radicals in the gas-phase (8.8) '9 and observed values in the liquid phase (7-7+8.1).* It therefore seemed important to measure li, in a chemical system different from that used by Tedder and Walton (C,H,+ CC13Br + hv). The gas-phase photochlorination of chloroform was chosen for this purpose. This reaction has been investigated using steady illumination by Chiltz, Mahieu and marten^.^ Between 360 and 430"K, the initial rate of chlorination is given by V, = -d[ClJdt = I$k3[ClJ/(k8 + k7k3[C12]/k2[CHC13]);t 6) * All rate constants are given in mole* The values S598 (CCl,) = 70.8 cal/mole deg. and AH;, 298 (CC1,) = 18 kcal/mole were chosen as mean values of existing data.

Chlorine‐photosensitized reactions in the Cl2 + O2 + 1,1,1,2‐C2H2Cl4 system

“…The preexponential factors log ( A 8/A 3' ) in mole *sec/l., ( = i) and log ( A ? / A 3) ( = ii) are very similar to those obtained for CCli (i = -7.82 and ii = 2.64) [16], CIH&li (i = -7.9) [17], CHC12CCli (i = -7.98) [18], and C2C1; (i = -7.96 and ii = 2.72) [19]. Therefore and because both eqs.…”

The UV absorption spectrum of the CCl3 radical and the kinetics of its mutual combination reaction from 253 to 623 K

“…The absorption cross section assigned to C,Cl, in order to obtain good fits, was in the range 8-12 x lo-'' cm2 molecule-' at 220 nm, which looks reasonable, as compared t o (r(CC1,) = 1.7 x lo-'' cm2 [ll] at the same wavelength. Some minor contribution to the absorption could also be expected from the formation of CCll and the consumption of CHC1, in reactions (7) and (2):…”

Theoretical study of the kinetics of chlorine atom abstraction from chloromethanes by atomic chlorine

“…The kinetics of reaction CCl 4  + Cl have been studied experimentally by Seetula [45] and DeMare and Huybrechts [48]. Their investigations were, however, performed in different temperature ranges, and the reported temperature dependencies of k (CCl 4  + Cl) expressed in the Arrhenius’ form show distinct differences in both the pre-exponential factor and the activation energy, which makes it difficult to compare the experimental and theoretical values of k (CCl 4  + Cl).…”